Brazil nut effect
Encyclopedia
Granular material
A granular material is a conglomeration of discrete solid, macroscopic particles characterized by a loss of energy whenever the particles interact . The constituents that compose granular material must be large enough such that they are not subject to thermal motion fluctuations...
subjected to shaking or vibration will exhibit circulation patterns similar to types of fluid convection
Convection
Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
. It is sometimes described as the Brazil nut effect when the largest particles end up on the surface of a granular material containing a mixture of variously sized objects; this derives from the example of a typical container of mixed nuts, where the largest will be Brazil nut
Brazil Nut
The Brazil nut is a South American tree in the family Lecythidaceae, and also the name of the tree's commercially harvested edible seed.- Order :...
s. The phenomenon is also known as the muesli effect since it is seen in packets of breakfast cereal
Breakfast cereal
A breakfast cereal is a food made from processed grains that is often, but not always, eaten with the first meal of the day. It is often eaten cold, usually mixed with milk , water, or yogurt, and sometimes fruit but sometimes eaten dry. Some cereals, such as oatmeal, may be served hot as porridge...
containing particles of different sizes
Volume
Volume is the quantity of three-dimensional space enclosed by some closed boundary, for example, the space that a substance or shape occupies or contains....
but similar density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
, such as muesli
Muesli
Muesli is a popular breakfast cereal based on uncooked rolled oats, fruit and nuts. It was developed around 1900 by Swiss physician Maximilian Bircher-Benner for patients in his hospital...
mix.
Under experimental conditions, granular convection of variously sized particles has been observed forming convection cells similar to fluid motion. The convection of granular flows is becoming a well-understood phenomenon.
Explanation
It may be counter-intuitive to find that the largest and (presumably) heaviest particles rise to the top, but there are several possible explanations:- The center of mass of the whole system (containing the mixed nuts) in an arbitrary state is not optimal (because of the space close to the Brazil nuts); it has the tendency to be higher due to gravity. When the nuts are shaken, gravity will make sure the center of mass of the system moves down and this can only be done by moving the Brazil nuts up. Gravity will also make sure they stay up.
- Including the effects of air in spaces between particles, larger particles may become buoyantBuoyancyIn physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...
or sink. Smaller particles can fall into the spaces underneath a larger particle after each shake. Over time, the larger particle rises in the mixture.
(According to Heinrich Jaeger, "[this] explanation for size separation might work in situations in which there is no granular convection, for example for containers with completely frictionless side walls or deep below the surface of tall containers (where convection is strongly suppressed). On the other hand, when friction with the side walls or other mechanisms set up a convection roll pattern inside the vibrated container, we found that the convective motion immediately takes over as the dominant mechanism for size separation.")
- When shaken, the particles move in vibration-induced convectionConvectionConvection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
flow: individual particles move up through the middle, across the surface, and down the sides. If a large particle is involved, it will be moved up to the top by convection flow. Once at the top, the large particle will stay there because the convection currents are too narrow to sweep it down along the wall. - The phenomenon is related to Parrondo's paradox inasmuch as the Brazil nuts move to the top of the mixed nuts against the gravitational gradient when subjected to random shaking.
Granular convection has been probed by the use of MRI imaging where convection rolls similar to those in fluids (Bénard cells) can be visualized.
Manufacturing
The effect is of serious interest for some manufacturing operations; once a heterogeneous mixture of granular materials has been produced, it is usually undesirable for the different particle types to segregate. Several factors determine the severity of the Brazil nut effect, including the sizes and densitiesDensity
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
of the particles, the pressure
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
of any gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
between the particles, and the shape of the container. A rectangular box (such as a box of breakfast cereal) or cylinder
Cylinder (geometry)
A cylinder is one of the most basic curvilinear geometric shapes, the surface formed by the points at a fixed distance from a given line segment, the axis of the cylinder. The solid enclosed by this surface and by two planes perpendicular to the axis is also called a cylinder...
(such as a can of nuts) works well to counter the effect, while a cone
Cone (geometry)
A cone is an n-dimensional geometric shape that tapers smoothly from a base to a point called the apex or vertex. Formally, it is the solid figure formed by the locus of all straight line segments that join the apex to the base...
-shaped container results in what is known as the reverse Brazil nut effect.
Astronomy
In astronomyAstronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...
, it is also seen in some low density, or rubble pile
Rubble pile
In astronomy, rubble pile is the informal name for an object that is not a monolith, consisting instead of numerous pieces of rock that have coalesced under the influence of gravity...
asteroid
Asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
s, for example the asteroid 25143 Itokawa
25143 Itokawa
25143 Itokawa is an Apollo and Mars-crosser asteroid. It was the first asteroid to be the target of a sample return mission, the Japanese space probe Hayabusa.-Discovery and naming:...
.
Geology
In geologyGeology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
, this phenomenon is one of the causes of inverse grading
Graded bedding
In geology, a graded bed is one characterized by a systematic change in grain or clast size from the base of the bed to the top. Most commonly this takes the form of normal grading, with coarser sediments at the base, which grade upward into progressively finer ones...
which can be observed in many situations including soil liquefaction
Soil liquefaction
Soil liquefaction describes a phenomenon whereby a saturated soil substantially loses strength and stiffness in response to an applied stress, usually earthquake shaking or other sudden change in stress condition, causing it to behave like a liquid....
during earthquake
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
s or mudslides.
External links
- Convection rolls in almost densely filled rotating containers, University of Magdeburg
- PhysicsWeb: The Brazil Nut Effect
Granular material
A granular material is a conglomeration of discrete solid, macroscopic particles characterized by a loss of energy whenever the particles interact . The constituents that compose granular material must be large enough such that they are not subject to thermal motion fluctuations...
subjected to shaking or vibration will exhibit circulation patterns similar to types of fluid convection
Convection
Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
. It is sometimes described as the Brazil nut effect when the largest particles end up on the surface of a granular material containing a mixture of variously sized objects; this derives from the example of a typical container of mixed nuts, where the largest will be Brazil nut
Brazil Nut
The Brazil nut is a South American tree in the family Lecythidaceae, and also the name of the tree's commercially harvested edible seed.- Order :...
s. The phenomenon is also known as the muesli effect since it is seen in packets of breakfast cereal
Breakfast cereal
A breakfast cereal is a food made from processed grains that is often, but not always, eaten with the first meal of the day. It is often eaten cold, usually mixed with milk , water, or yogurt, and sometimes fruit but sometimes eaten dry. Some cereals, such as oatmeal, may be served hot as porridge...
containing particles of different sizes
Volume
Volume is the quantity of three-dimensional space enclosed by some closed boundary, for example, the space that a substance or shape occupies or contains....
but similar density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
, such as muesli
Muesli
Muesli is a popular breakfast cereal based on uncooked rolled oats, fruit and nuts. It was developed around 1900 by Swiss physician Maximilian Bircher-Benner for patients in his hospital...
mix.
Under experimental conditions, granular convection of variously sized particles has been observed forming convection cells similar to fluid motion. The convection of granular flows is becoming a well-understood phenomenon.
Explanation
It may be counter-intuitive to find that the largest and (presumably) heaviest particles rise to the top, but there are several possible explanations:- The center of mass of the whole system (containing the mixed nuts) in an arbitrary state is not optimal (because of the space close to the Brazil nuts); it has the tendency to be higher due to gravity. When the nuts are shaken, gravity will make sure the center of mass of the system moves down and this can only be done by moving the Brazil nuts up. Gravity will also make sure they stay up.
- Including the effects of air in spaces between particles, larger particles may become buoyantBuoyancyIn physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...
or sink. Smaller particles can fall into the spaces underneath a larger particle after each shake. Over time, the larger particle rises in the mixture.
(According to Heinrich Jaeger, "[this] explanation for size separation might work in situations in which there is no granular convection, for example for containers with completely frictionless side walls or deep below the surface of tall containers (where convection is strongly suppressed). On the other hand, when friction with the side walls or other mechanisms set up a convection roll pattern inside the vibrated container, we found that the convective motion immediately takes over as the dominant mechanism for size separation.")
- When shaken, the particles move in vibration-induced convectionConvectionConvection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
flow: individual particles move up through the middle, across the surface, and down the sides. If a large particle is involved, it will be moved up to the top by convection flow. Once at the top, the large particle will stay there because the convection currents are too narrow to sweep it down along the wall. - The phenomenon is related to Parrondo's paradox inasmuch as the Brazil nuts move to the top of the mixed nuts against the gravitational gradient when subjected to random shaking.
Granular convection has been probed by the use of MRI imaging where convection rolls similar to those in fluids (Bénard cells) can be visualized.
Manufacturing
The effect is of serious interest for some manufacturing operations; once a heterogeneous mixture of granular materials has been produced, it is usually undesirable for the different particle types to segregate. Several factors determine the severity of the Brazil nut effect, including the sizes and densitiesDensity
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
of the particles, the pressure
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
of any gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
between the particles, and the shape of the container. A rectangular box (such as a box of breakfast cereal) or cylinder
Cylinder (geometry)
A cylinder is one of the most basic curvilinear geometric shapes, the surface formed by the points at a fixed distance from a given line segment, the axis of the cylinder. The solid enclosed by this surface and by two planes perpendicular to the axis is also called a cylinder...
(such as a can of nuts) works well to counter the effect, while a cone
Cone (geometry)
A cone is an n-dimensional geometric shape that tapers smoothly from a base to a point called the apex or vertex. Formally, it is the solid figure formed by the locus of all straight line segments that join the apex to the base...
-shaped container results in what is known as the reverse Brazil nut effect.
Astronomy
In astronomyAstronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...
, it is also seen in some low density, or rubble pile
Rubble pile
In astronomy, rubble pile is the informal name for an object that is not a monolith, consisting instead of numerous pieces of rock that have coalesced under the influence of gravity...
asteroid
Asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
s, for example the asteroid 25143 Itokawa
25143 Itokawa
25143 Itokawa is an Apollo and Mars-crosser asteroid. It was the first asteroid to be the target of a sample return mission, the Japanese space probe Hayabusa.-Discovery and naming:...
.
Geology
In geologyGeology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
, this phenomenon is one of the causes of inverse grading
Graded bedding
In geology, a graded bed is one characterized by a systematic change in grain or clast size from the base of the bed to the top. Most commonly this takes the form of normal grading, with coarser sediments at the base, which grade upward into progressively finer ones...
which can be observed in many situations including soil liquefaction
Soil liquefaction
Soil liquefaction describes a phenomenon whereby a saturated soil substantially loses strength and stiffness in response to an applied stress, usually earthquake shaking or other sudden change in stress condition, causing it to behave like a liquid....
during earthquake
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
s or mudslides.
External links
}- Convection rolls in almost densely filled rotating containers, University of Magdeburg
- PhysicsWeb: The Brazil Nut Effect
Granular material
A granular material is a conglomeration of discrete solid, macroscopic particles characterized by a loss of energy whenever the particles interact . The constituents that compose granular material must be large enough such that they are not subject to thermal motion fluctuations...
subjected to shaking or vibration will exhibit circulation patterns similar to types of fluid convection
Convection
Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
. It is sometimes described as the Brazil nut effect when the largest particles end up on the surface of a granular material containing a mixture of variously sized objects; this derives from the example of a typical container of mixed nuts, where the largest will be Brazil nut
Brazil Nut
The Brazil nut is a South American tree in the family Lecythidaceae, and also the name of the tree's commercially harvested edible seed.- Order :...
s. The phenomenon is also known as the muesli effect since it is seen in packets of breakfast cereal
Breakfast cereal
A breakfast cereal is a food made from processed grains that is often, but not always, eaten with the first meal of the day. It is often eaten cold, usually mixed with milk , water, or yogurt, and sometimes fruit but sometimes eaten dry. Some cereals, such as oatmeal, may be served hot as porridge...
containing particles of different sizes
Volume
Volume is the quantity of three-dimensional space enclosed by some closed boundary, for example, the space that a substance or shape occupies or contains....
but similar density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
, such as muesli
Muesli
Muesli is a popular breakfast cereal based on uncooked rolled oats, fruit and nuts. It was developed around 1900 by Swiss physician Maximilian Bircher-Benner for patients in his hospital...
mix.
Under experimental conditions, granular convection of variously sized particles has been observed forming convection cells similar to fluid motion. The convection of granular flows is becoming a well-understood phenomenon.
Explanation
It may be counter-intuitive to find that the largest and (presumably) heaviest particles rise to the top, but there are several possible explanations:- The center of mass of the whole system (containing the mixed nuts) in an arbitrary state is not optimal (because of the space close to the Brazil nuts); it has the tendency to be higher due to gravity. When the nuts are shaken, gravity will make sure the center of mass of the system moves down and this can only be done by moving the Brazil nuts up. Gravity will also make sure they stay up.
- Including the effects of air in spaces between particles, larger particles may become buoyantBuoyancyIn physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...
or sink. Smaller particles can fall into the spaces underneath a larger particle after each shake. Over time, the larger particle rises in the mixture.
(According to Heinrich Jaeger, "[this] explanation for size separation might work in situations in which there is no granular convection, for example for containers with completely frictionless side walls or deep below the surface of tall containers (where convection is strongly suppressed). On the other hand, when friction with the side walls or other mechanisms set up a convection roll pattern inside the vibrated container, we found that the convective motion immediately takes over as the dominant mechanism for size separation.")
- When shaken, the particles move in vibration-induced convectionConvectionConvection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
flow: individual particles move up through the middle, across the surface, and down the sides. If a large particle is involved, it will be moved up to the top by convection flow. Once at the top, the large particle will stay there because the convection currents are too narrow to sweep it down along the wall. - The phenomenon is related to Parrondo's paradox inasmuch as the Brazil nuts move to the top of the mixed nuts against the gravitational gradient when subjected to random shaking.
Granular convection has been probed by the use of MRI imaging where convection rolls similar to those in fluids (Bénard cells) can be visualized.
Manufacturing
The effect is of serious interest for some manufacturing operations; once a heterogeneous mixture of granular materials has been produced, it is usually undesirable for the different particle types to segregate. Several factors determine the severity of the Brazil nut effect, including the sizes and densitiesDensity
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
of the particles, the pressure
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
of any gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
between the particles, and the shape of the container. A rectangular box (such as a box of breakfast cereal) or cylinder
Cylinder (geometry)
A cylinder is one of the most basic curvilinear geometric shapes, the surface formed by the points at a fixed distance from a given line segment, the axis of the cylinder. The solid enclosed by this surface and by two planes perpendicular to the axis is also called a cylinder...
(such as a can of nuts) works well to counter the effect, while a cone
Cone (geometry)
A cone is an n-dimensional geometric shape that tapers smoothly from a base to a point called the apex or vertex. Formally, it is the solid figure formed by the locus of all straight line segments that join the apex to the base...
-shaped container results in what is known as the reverse Brazil nut effect.
Astronomy
In astronomyAstronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...
, it is also seen in some low density, or rubble pile
Rubble pile
In astronomy, rubble pile is the informal name for an object that is not a monolith, consisting instead of numerous pieces of rock that have coalesced under the influence of gravity...
asteroid
Asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
s, for example the asteroid 25143 Itokawa
25143 Itokawa
25143 Itokawa is an Apollo and Mars-crosser asteroid. It was the first asteroid to be the target of a sample return mission, the Japanese space probe Hayabusa.-Discovery and naming:...
.
Geology
In geologyGeology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
, this phenomenon is one of the causes of inverse grading
Graded bedding
In geology, a graded bed is one characterized by a systematic change in grain or clast size from the base of the bed to the top. Most commonly this takes the form of normal grading, with coarser sediments at the base, which grade upward into progressively finer ones...
which can be observed in many situations including soil liquefaction
Soil liquefaction
Soil liquefaction describes a phenomenon whereby a saturated soil substantially loses strength and stiffness in response to an applied stress, usually earthquake shaking or other sudden change in stress condition, causing it to behave like a liquid....
during earthquake
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
s or mudslides.
External links
}- Convection rolls in almost densely filled rotating containers, University of Magdeburg
- PhysicsWeb: The Brazil Nut Effect
Granular material
A granular material is a conglomeration of discrete solid, macroscopic particles characterized by a loss of energy whenever the particles interact . The constituents that compose granular material must be large enough such that they are not subject to thermal motion fluctuations...
subjected to shaking or vibration will exhibit circulation patterns similar to types of fluid convection
Convection
Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
. It is sometimes described as the Brazil nut effect when the largest particles end up on the surface of a granular material containing a mixture of variously sized objects; this derives from the example of a typical container of mixed nuts, where the largest will be Brazil nut
Brazil Nut
The Brazil nut is a South American tree in the family Lecythidaceae, and also the name of the tree's commercially harvested edible seed.- Order :...
s. The phenomenon is also known as the muesli effect since it is seen in packets of breakfast cereal
Breakfast cereal
A breakfast cereal is a food made from processed grains that is often, but not always, eaten with the first meal of the day. It is often eaten cold, usually mixed with milk , water, or yogurt, and sometimes fruit but sometimes eaten dry. Some cereals, such as oatmeal, may be served hot as porridge...
containing particles of different sizes
Volume
Volume is the quantity of three-dimensional space enclosed by some closed boundary, for example, the space that a substance or shape occupies or contains....
but similar density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
, such as muesli
Muesli
Muesli is a popular breakfast cereal based on uncooked rolled oats, fruit and nuts. It was developed around 1900 by Swiss physician Maximilian Bircher-Benner for patients in his hospital...
mix.
Under experimental conditions, granular convection of variously sized particles has been observed forming convection cells similar to fluid motion. The convection of granular flows is becoming a well-understood phenomenon.
Explanation
It may be counter-intuitive to find that the largest and (presumably) heaviest particles rise to the top, but there are several possible explanations:- The center of mass of the whole system (containing the mixed nuts) in an arbitrary state is not optimal (because of the space close to the Brazil nuts); it has the tendency to be higher due to gravity. When the nuts are shaken, gravity will make sure the center of mass of the system moves down and this can only be done by moving the Brazil nuts up. Gravity will also make sure they stay up.
- Including the effects of air in spaces between particles, larger particles may become buoyantBuoyancyIn physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...
or sink. Smaller particles can fall into the spaces underneath a larger particle after each shake. Over time, the larger particle rises in the mixture.
(According to Heinrich Jaeger, "[this] explanation for size separation might work in situations in which there is no granular convection, for example for containers with completely frictionless side walls or deep below the surface of tall containers (where convection is strongly suppressed). On the other hand, when friction with the side walls or other mechanisms set up a convection roll pattern inside the vibrated container, we found that the convective motion immediately takes over as the dominant mechanism for size separation.")
- When shaken, the particles move in vibration-induced convectionConvectionConvection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
flow: individual particles move up through the middle, across the surface, and down the sides. If a large particle is involved, it will be moved up to the top by convection flow. Once at the top, the large particle will stay there because the convection currents are too narrow to sweep it down along the wall. - The phenomenon is related to Parrondo's paradox inasmuch as the Brazil nuts move to the top of the mixed nuts against the gravitational gradient when subjected to random shaking.
Granular convection has been probed by the use of MRI imaging where convection rolls similar to those in fluids (Bénard cells) can be visualized.
Manufacturing
The effect is of serious interest for some manufacturing operations; once a heterogeneous mixture of granular materials has been produced, it is usually undesirable for the different particle types to segregate. Several factors determine the severity of the Brazil nut effect, including the sizes and densitiesDensity
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
of the particles, the pressure
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
of any gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
between the particles, and the shape of the container. A rectangular box (such as a box of breakfast cereal) or cylinder
Cylinder (geometry)
A cylinder is one of the most basic curvilinear geometric shapes, the surface formed by the points at a fixed distance from a given line segment, the axis of the cylinder. The solid enclosed by this surface and by two planes perpendicular to the axis is also called a cylinder...
(such as a can of nuts) works well to counter the effect, while a cone
Cone (geometry)
A cone is an n-dimensional geometric shape that tapers smoothly from a base to a point called the apex or vertex. Formally, it is the solid figure formed by the locus of all straight line segments that join the apex to the base...
-shaped container results in what is known as the reverse Brazil nut effect.
Astronomy
In astronomyAstronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...
, it is also seen in some low density, or rubble pile
Rubble pile
In astronomy, rubble pile is the informal name for an object that is not a monolith, consisting instead of numerous pieces of rock that have coalesced under the influence of gravity...
asteroid
Asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
s, for example the asteroid 25143 Itokawa
25143 Itokawa
25143 Itokawa is an Apollo and Mars-crosser asteroid. It was the first asteroid to be the target of a sample return mission, the Japanese space probe Hayabusa.-Discovery and naming:...
.
Geology
In geologyGeology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
, this phenomenon is one of the causes of inverse grading
Graded bedding
In geology, a graded bed is one characterized by a systematic change in grain or clast size from the base of the bed to the top. Most commonly this takes the form of normal grading, with coarser sediments at the base, which grade upward into progressively finer ones...
which can be observed in many situations including soil liquefaction
Soil liquefaction
Soil liquefaction describes a phenomenon whereby a saturated soil substantially loses strength and stiffness in response to an applied stress, usually earthquake shaking or other sudden change in stress condition, causing it to behave like a liquid....
during earthquake
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
s or mudslides.
External links
- Convection rolls in almost densely filled rotating containers, University of Magdeburg
- PhysicsWeb: The Brazil Nut Effect
Granular material
A granular material is a conglomeration of discrete solid, macroscopic particles characterized by a loss of energy whenever the particles interact . The constituents that compose granular material must be large enough such that they are not subject to thermal motion fluctuations...
subjected to shaking or vibration will exhibit circulation patterns similar to types of fluid convection
Convection
Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
. It is sometimes described as the Brazil nut effect when the largest particles end up on the surface of a granular material containing a mixture of variously sized objects; this derives from the example of a typical container of mixed nuts, where the largest will be Brazil nut
Brazil Nut
The Brazil nut is a South American tree in the family Lecythidaceae, and also the name of the tree's commercially harvested edible seed.- Order :...
s. The phenomenon is also known as the muesli effect since it is seen in packets of breakfast cereal
Breakfast cereal
A breakfast cereal is a food made from processed grains that is often, but not always, eaten with the first meal of the day. It is often eaten cold, usually mixed with milk , water, or yogurt, and sometimes fruit but sometimes eaten dry. Some cereals, such as oatmeal, may be served hot as porridge...
containing particles of different sizes
Volume
Volume is the quantity of three-dimensional space enclosed by some closed boundary, for example, the space that a substance or shape occupies or contains....
but similar density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
, such as muesli
Muesli
Muesli is a popular breakfast cereal based on uncooked rolled oats, fruit and nuts. It was developed around 1900 by Swiss physician Maximilian Bircher-Benner for patients in his hospital...
mix.
Under experimental conditions, granular convection of variously sized particles has been observed forming convection cells similar to fluid motion. The convection of granular flows is becoming a well-understood phenomenon.
Explanation
It may be counter-intuitive to find that the largest and (presumably) heaviest particles rise to the top, but there are several possible explanations:- The center of mass of the whole system (containing the mixed nuts) in an arbitrary state is not optimal (because of the space close to the Brazil nuts); it has the tendency to be higher due to gravity. When the nuts are shaken, gravity will make sure the center of mass of the system moves down and this can only be done by moving the Brazil nuts up. Gravity will also make sure they stay up.
- Including the effects of air in spaces between particles, larger particles may become buoyantBuoyancyIn physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...
or sink. Smaller particles can fall into the spaces underneath a larger particle after each shake. Over time, the larger particle rises in the mixture.
(According to Heinrich Jaeger, "[this] explanation for size separation might work in situations in which there is no granular convection, for example for containers with completely frictionless side walls or deep below the surface of tall containers (where convection is strongly suppressed). On the other hand, when friction with the side walls or other mechanisms set up a convection roll pattern inside the vibrated container, we found that the convective motion immediately takes over as the dominant mechanism for size separation.")
- When shaken, the particles move in vibration-induced convectionConvectionConvection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
flow: individual particles move up through the middle, across the surface, and down the sides. If a large particle is involved, it will be moved up to the top by convection flow. Once at the top, the large particle will stay there because the convection currents are too narrow to sweep it down along the wall. - The phenomenon is related to Parrondo's paradox inasmuch as the Brazil nuts move to the top of the mixed nuts against the gravitational gradient when subjected to random shaking.
Granular convection has been probed by the use of MRI imaging where convection rolls similar to those in fluids (Bénard cells) can be visualized.
Manufacturing
The effect is of serious interest for some manufacturing operations; once a heterogeneous mixture of granular materials has been produced, it is usually undesirable for the different particle types to segregate. Several factors determine the severity of the Brazil nut effect, including the sizes and densitiesDensity
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
of the particles, the pressure
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
of any gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
between the particles, and the shape of the container. A rectangular box (such as a box of breakfast cereal) or cylinder
Cylinder (geometry)
A cylinder is one of the most basic curvilinear geometric shapes, the surface formed by the points at a fixed distance from a given line segment, the axis of the cylinder. The solid enclosed by this surface and by two planes perpendicular to the axis is also called a cylinder...
(such as a can of nuts) works well to counter the effect, while a cone
Cone (geometry)
A cone is an n-dimensional geometric shape that tapers smoothly from a base to a point called the apex or vertex. Formally, it is the solid figure formed by the locus of all straight line segments that join the apex to the base...
-shaped container results in what is known as the reverse Brazil nut effect.
Astronomy
In astronomyAstronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...
, it is also seen in some low density, or rubble pile
Rubble pile
In astronomy, rubble pile is the informal name for an object that is not a monolith, consisting instead of numerous pieces of rock that have coalesced under the influence of gravity...
asteroid
Asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
s, for example the asteroid 25143 Itokawa
25143 Itokawa
25143 Itokawa is an Apollo and Mars-crosser asteroid. It was the first asteroid to be the target of a sample return mission, the Japanese space probe Hayabusa.-Discovery and naming:...
.
Geology
In geologyGeology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
, this phenomenon is one of the causes of inverse grading
Graded bedding
In geology, a graded bed is one characterized by a systematic change in grain or clast size from the base of the bed to the top. Most commonly this takes the form of normal grading, with coarser sediments at the base, which grade upward into progressively finer ones...
which can be observed in many situations including soil liquefaction
Soil liquefaction
Soil liquefaction describes a phenomenon whereby a saturated soil substantially loses strength and stiffness in response to an applied stress, usually earthquake shaking or other sudden change in stress condition, causing it to behave like a liquid....
during earthquake
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
s or mudslides.
External links
- Convection rolls in almost densely filled rotating containers, University of Magdeburg
- PhysicsWeb: The Brazil Nut Effect
Granular material
A granular material is a conglomeration of discrete solid, macroscopic particles characterized by a loss of energy whenever the particles interact . The constituents that compose granular material must be large enough such that they are not subject to thermal motion fluctuations...
subjected to shaking or vibration will exhibit circulation patterns similar to types of fluid convection
Convection
Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
. It is sometimes described as the Brazil nut effect when the largest particles end up on the surface of a granular material containing a mixture of variously sized objects; this derives from the example of a typical container of mixed nuts, where the largest will be Brazil nut
Brazil Nut
The Brazil nut is a South American tree in the family Lecythidaceae, and also the name of the tree's commercially harvested edible seed.- Order :...
s. The phenomenon is also known as the muesli effect since it is seen in packets of breakfast cereal
Breakfast cereal
A breakfast cereal is a food made from processed grains that is often, but not always, eaten with the first meal of the day. It is often eaten cold, usually mixed with milk , water, or yogurt, and sometimes fruit but sometimes eaten dry. Some cereals, such as oatmeal, may be served hot as porridge...
containing particles of different sizes
Volume
Volume is the quantity of three-dimensional space enclosed by some closed boundary, for example, the space that a substance or shape occupies or contains....
but similar density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
, such as muesli
Muesli
Muesli is a popular breakfast cereal based on uncooked rolled oats, fruit and nuts. It was developed around 1900 by Swiss physician Maximilian Bircher-Benner for patients in his hospital...
mix.
Under experimental conditions, granular convection of variously sized particles has been observed forming convection cells similar to fluid motion. The convection of granular flows is becoming a well-understood phenomenon.
Explanation
It may be counter-intuitive to find that the largest and (presumably) heaviest particles rise to the top, but there are several possible explanations:- The center of mass of the whole system (containing the mixed nuts) in an arbitrary state is not optimal (because of the space close to the Brazil nuts); it has the tendency to be higher due to gravity. When the nuts are shaken, gravity will make sure the center of mass of the system moves down and this can only be done by moving the Brazil nuts up. Gravity will also make sure they stay up.
- Including the effects of air in spaces between particles, larger particles may become buoyantBuoyancyIn physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...
or sink. Smaller particles can fall into the spaces underneath a larger particle after each shake. Over time, the larger particle rises in the mixture.
(According to Heinrich Jaeger, "[this] explanation for size separation might work in situations in which there is no granular convection, for example for containers with completely frictionless side walls or deep below the surface of tall containers (where convection is strongly suppressed). On the other hand, when friction with the side walls or other mechanisms set up a convection roll pattern inside the vibrated container, we found that the convective motion immediately takes over as the dominant mechanism for size separation.")
- When shaken, the particles move in vibration-induced convectionConvectionConvection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
flow: individual particles move up through the middle, across the surface, and down the sides. If a large particle is involved, it will be moved up to the top by convection flow. Once at the top, the large particle will stay there because the convection currents are too narrow to sweep it down along the wall. - The phenomenon is related to Parrondo's paradox inasmuch as the Brazil nuts move to the top of the mixed nuts against the gravitational gradient when subjected to random shaking.
Granular convection has been probed by the use of MRI imaging where convection rolls similar to those in fluids (Bénard cells) can be visualized.
Manufacturing
The effect is of serious interest for some manufacturing operations; once a heterogeneous mixture of granular materials has been produced, it is usually undesirable for the different particle types to segregate. Several factors determine the severity of the Brazil nut effect, including the sizes and densitiesDensity
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
of the particles, the pressure
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
of any gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
between the particles, and the shape of the container. A rectangular box (such as a box of breakfast cereal) or cylinder
Cylinder (geometry)
A cylinder is one of the most basic curvilinear geometric shapes, the surface formed by the points at a fixed distance from a given line segment, the axis of the cylinder. The solid enclosed by this surface and by two planes perpendicular to the axis is also called a cylinder...
(such as a can of nuts) works well to counter the effect, while a cone
Cone (geometry)
A cone is an n-dimensional geometric shape that tapers smoothly from a base to a point called the apex or vertex. Formally, it is the solid figure formed by the locus of all straight line segments that join the apex to the base...
-shaped container results in what is known as the reverse Brazil nut effect.
Astronomy
In astronomyAstronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...
, it is also seen in some low density, or rubble pile
Rubble pile
In astronomy, rubble pile is the informal name for an object that is not a monolith, consisting instead of numerous pieces of rock that have coalesced under the influence of gravity...
asteroid
Asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
s, for example the asteroid 25143 Itokawa
25143 Itokawa
25143 Itokawa is an Apollo and Mars-crosser asteroid. It was the first asteroid to be the target of a sample return mission, the Japanese space probe Hayabusa.-Discovery and naming:...
.
Geology
In geologyGeology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
, this phenomenon is one of the causes of inverse grading
Graded bedding
In geology, a graded bed is one characterized by a systematic change in grain or clast size from the base of the bed to the top. Most commonly this takes the form of normal grading, with coarser sediments at the base, which grade upward into progressively finer ones...
which can be observed in many situations including soil liquefaction
Soil liquefaction
Soil liquefaction describes a phenomenon whereby a saturated soil substantially loses strength and stiffness in response to an applied stress, usually earthquake shaking or other sudden change in stress condition, causing it to behave like a liquid....
during earthquake
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
s or mudslides.
External links
- Convection rolls in almost densely filled rotating containers, University of Magdeburg
- PhysicsWeb: The Brazil Nut Effect
Granular material
A granular material is a conglomeration of discrete solid, macroscopic particles characterized by a loss of energy whenever the particles interact . The constituents that compose granular material must be large enough such that they are not subject to thermal motion fluctuations...
subjected to shaking or vibration will exhibit circulation patterns similar to types of fluid convection
Convection
Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
. It is sometimes described as the Brazil nut effect when the largest particles end up on the surface of a granular material containing a mixture of variously sized objects; this derives from the example of a typical container of mixed nuts, where the largest will be Brazil nut
Brazil Nut
The Brazil nut is a South American tree in the family Lecythidaceae, and also the name of the tree's commercially harvested edible seed.- Order :...
s. The phenomenon is also known as the muesli effect since it is seen in packets of breakfast cereal
Breakfast cereal
A breakfast cereal is a food made from processed grains that is often, but not always, eaten with the first meal of the day. It is often eaten cold, usually mixed with milk , water, or yogurt, and sometimes fruit but sometimes eaten dry. Some cereals, such as oatmeal, may be served hot as porridge...
containing particles of different sizes
Volume
Volume is the quantity of three-dimensional space enclosed by some closed boundary, for example, the space that a substance or shape occupies or contains....
but similar density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
, such as muesli
Muesli
Muesli is a popular breakfast cereal based on uncooked rolled oats, fruit and nuts. It was developed around 1900 by Swiss physician Maximilian Bircher-Benner for patients in his hospital...
mix.
Under experimental conditions, granular convection of variously sized particles has been observed forming convection cells similar to fluid motion. The convection of granular flows is becoming a well-understood phenomenon.
Explanation
It may be counter-intuitive to find that the largest and (presumably) heaviest particles rise to the top, but there are several possible explanations:- The center of mass of the whole system (containing the mixed nuts) in an arbitrary state is not optimal (because of the space close to the Brazil nuts); it has the tendency to be higher due to gravity. When the nuts are shaken, gravity will make sure the center of mass of the system moves down and this can only be done by moving the Brazil nuts up. Gravity will also make sure they stay up.
- Including the effects of air in spaces between particles, larger particles may become buoyantBuoyancyIn physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...
or sink. Smaller particles can fall into the spaces underneath a larger particle after each shake. Over time, the larger particle rises in the mixture.
(According to Heinrich Jaeger, "[this] explanation for size separation might work in situations in which there is no granular convection, for example for containers with completely frictionless side walls or deep below the surface of tall containers (where convection is strongly suppressed). On the other hand, when friction with the side walls or other mechanisms set up a convection roll pattern inside the vibrated container, we found that the convective motion immediately takes over as the dominant mechanism for size separation.")
- When shaken, the particles move in vibration-induced convectionConvectionConvection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
flow: individual particles move up through the middle, across the surface, and down the sides. If a large particle is involved, it will be moved up to the top by convection flow. Once at the top, the large particle will stay there because the convection currents are too narrow to sweep it down along the wall. - The phenomenon is related to Parrondo's paradox inasmuch as the Brazil nuts move to the top of the mixed nuts against the gravitational gradient when subjected to random shaking.
Granular convection has been probed by the use of MRI imaging where convection rolls similar to those in fluids (Bénard cells) can be visualized.
Manufacturing
The effect is of serious interest for some manufacturing operations; once a heterogeneous mixture of granular materials has been produced, it is usually undesirable for the different particle types to segregate. Several factors determine the severity of the Brazil nut effect, including the sizes and densitiesDensity
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
of the particles, the pressure
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
of any gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
between the particles, and the shape of the container. A rectangular box (such as a box of breakfast cereal) or cylinder
Cylinder (geometry)
A cylinder is one of the most basic curvilinear geometric shapes, the surface formed by the points at a fixed distance from a given line segment, the axis of the cylinder. The solid enclosed by this surface and by two planes perpendicular to the axis is also called a cylinder...
(such as a can of nuts) works well to counter the effect, while a cone
Cone (geometry)
A cone is an n-dimensional geometric shape that tapers smoothly from a base to a point called the apex or vertex. Formally, it is the solid figure formed by the locus of all straight line segments that join the apex to the base...
-shaped container results in what is known as the reverse Brazil nut effect.
Astronomy
In astronomyAstronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...
, it is also seen in some low density, or rubble pile
Rubble pile
In astronomy, rubble pile is the informal name for an object that is not a monolith, consisting instead of numerous pieces of rock that have coalesced under the influence of gravity...
asteroid
Asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
s, for example the asteroid 25143 Itokawa
25143 Itokawa
25143 Itokawa is an Apollo and Mars-crosser asteroid. It was the first asteroid to be the target of a sample return mission, the Japanese space probe Hayabusa.-Discovery and naming:...
.
Geology
In geologyGeology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
, this phenomenon is one of the causes of inverse grading
Graded bedding
In geology, a graded bed is one characterized by a systematic change in grain or clast size from the base of the bed to the top. Most commonly this takes the form of normal grading, with coarser sediments at the base, which grade upward into progressively finer ones...
which can be observed in many situations including soil liquefaction
Soil liquefaction
Soil liquefaction describes a phenomenon whereby a saturated soil substantially loses strength and stiffness in response to an applied stress, usually earthquake shaking or other sudden change in stress condition, causing it to behave like a liquid....
during earthquake
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
s or mudslides.
External links
- Convection rolls in almost densely filled rotating containers, University of Magdeburg
- PhysicsWeb: The Brazil Nut Effect
Granular material
A granular material is a conglomeration of discrete solid, macroscopic particles characterized by a loss of energy whenever the particles interact . The constituents that compose granular material must be large enough such that they are not subject to thermal motion fluctuations...
subjected to shaking or vibration will exhibit circulation patterns similar to types of fluid convection
Convection
Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
. It is sometimes described as the Brazil nut effect when the largest particles end up on the surface of a granular material containing a mixture of variously sized objects; this derives from the example of a typical container of mixed nuts, where the largest will be Brazil nut
Brazil Nut
The Brazil nut is a South American tree in the family Lecythidaceae, and also the name of the tree's commercially harvested edible seed.- Order :...
s. The phenomenon is also known as the muesli effect since it is seen in packets of breakfast cereal
Breakfast cereal
A breakfast cereal is a food made from processed grains that is often, but not always, eaten with the first meal of the day. It is often eaten cold, usually mixed with milk , water, or yogurt, and sometimes fruit but sometimes eaten dry. Some cereals, such as oatmeal, may be served hot as porridge...
containing particles of different sizes
Volume
Volume is the quantity of three-dimensional space enclosed by some closed boundary, for example, the space that a substance or shape occupies or contains....
but similar density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
, such as muesli
Muesli
Muesli is a popular breakfast cereal based on uncooked rolled oats, fruit and nuts. It was developed around 1900 by Swiss physician Maximilian Bircher-Benner for patients in his hospital...
mix.
Under experimental conditions, granular convection of variously sized particles has been observed forming convection cells similar to fluid motion. The convection of granular flows is becoming a well-understood phenomenon.
Explanation
It may be counter-intuitive to find that the largest and (presumably) heaviest particles rise to the top, but there are several possible explanations:- The center of mass of the whole system (containing the mixed nuts) in an arbitrary state is not optimal (because of the space close to the Brazil nuts); it has the tendency to be higher due to gravity. When the nuts are shaken, gravity will make sure the center of mass of the system moves down and this can only be done by moving the Brazil nuts up. Gravity will also make sure they stay up.
- Including the effects of air in spaces between particles, larger particles may become buoyantBuoyancyIn physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...
or sink. Smaller particles can fall into the spaces underneath a larger particle after each shake. Over time, the larger particle rises in the mixture.
(According to Heinrich Jaeger, "[this] explanation for size separation might work in situations in which there is no granular convection, for example for containers with completely frictionless side walls or deep below the surface of tall containers (where convection is strongly suppressed). On the other hand, when friction with the side walls or other mechanisms set up a convection roll pattern inside the vibrated container, we found that the convective motion immediately takes over as the dominant mechanism for size separation.")
- When shaken, the particles move in vibration-induced convectionConvectionConvection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
flow: individual particles move up through the middle, across the surface, and down the sides. If a large particle is involved, it will be moved up to the top by convection flow. Once at the top, the large particle will stay there because the convection currents are too narrow to sweep it down along the wall. - The phenomenon is related to Parrondo's paradox inasmuch as the Brazil nuts move to the top of the mixed nuts against the gravitational gradient when subjected to random shaking.
Granular convection has been probed by the use of MRI imaging where convection rolls similar to those in fluids (Bénard cells) can be visualized.
Manufacturing
The effect is of serious interest for some manufacturing operations; once a heterogeneous mixture of granular materials has been produced, it is usually undesirable for the different particle types to segregate. Several factors determine the severity of the Brazil nut effect, including the sizes and densitiesDensity
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
of the particles, the pressure
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
of any gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
between the particles, and the shape of the container. A rectangular box (such as a box of breakfast cereal) or cylinder
Cylinder (geometry)
A cylinder is one of the most basic curvilinear geometric shapes, the surface formed by the points at a fixed distance from a given line segment, the axis of the cylinder. The solid enclosed by this surface and by two planes perpendicular to the axis is also called a cylinder...
(such as a can of nuts) works well to counter the effect, while a cone
Cone (geometry)
A cone is an n-dimensional geometric shape that tapers smoothly from a base to a point called the apex or vertex. Formally, it is the solid figure formed by the locus of all straight line segments that join the apex to the base...
-shaped container results in what is known as the reverse Brazil nut effect.
Astronomy
In astronomyAstronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...
, it is also seen in some low density, or rubble pile
Rubble pile
In astronomy, rubble pile is the informal name for an object that is not a monolith, consisting instead of numerous pieces of rock that have coalesced under the influence of gravity...
asteroid
Asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
s, for example the asteroid 25143 Itokawa
25143 Itokawa
25143 Itokawa is an Apollo and Mars-crosser asteroid. It was the first asteroid to be the target of a sample return mission, the Japanese space probe Hayabusa.-Discovery and naming:...
.
Geology
In geologyGeology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
, this phenomenon is one of the causes of inverse grading
Graded bedding
In geology, a graded bed is one characterized by a systematic change in grain or clast size from the base of the bed to the top. Most commonly this takes the form of normal grading, with coarser sediments at the base, which grade upward into progressively finer ones...
which can be observed in many situations including soil liquefaction
Soil liquefaction
Soil liquefaction describes a phenomenon whereby a saturated soil substantially loses strength and stiffness in response to an applied stress, usually earthquake shaking or other sudden change in stress condition, causing it to behave like a liquid....
during earthquake
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
s or mudslides.
External links
- Convection rolls in almost densely filled rotating containers, University of Magdeburg
- PhysicsWeb: The Brazil Nut Effect
Granular material
A granular material is a conglomeration of discrete solid, macroscopic particles characterized by a loss of energy whenever the particles interact . The constituents that compose granular material must be large enough such that they are not subject to thermal motion fluctuations...
subjected to shaking or vibration will exhibit circulation patterns similar to types of fluid convection
Convection
Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
. It is sometimes described as the Brazil nut effect when the largest particles end up on the surface of a granular material containing a mixture of variously sized objects; this derives from the example of a typical container of mixed nuts, where the largest will be Brazil nut
Brazil Nut
The Brazil nut is a South American tree in the family Lecythidaceae, and also the name of the tree's commercially harvested edible seed.- Order :...
s. The phenomenon is also known as the muesli effect since it is seen in packets of breakfast cereal
Breakfast cereal
A breakfast cereal is a food made from processed grains that is often, but not always, eaten with the first meal of the day. It is often eaten cold, usually mixed with milk , water, or yogurt, and sometimes fruit but sometimes eaten dry. Some cereals, such as oatmeal, may be served hot as porridge...
containing particles of different sizes
Volume
Volume is the quantity of three-dimensional space enclosed by some closed boundary, for example, the space that a substance or shape occupies or contains....
but similar density
Density
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
, such as muesli
Muesli
Muesli is a popular breakfast cereal based on uncooked rolled oats, fruit and nuts. It was developed around 1900 by Swiss physician Maximilian Bircher-Benner for patients in his hospital...
mix.
Under experimental conditions, granular convection of variously sized particles has been observed forming convection cells similar to fluid motion. The convection of granular flows is becoming a well-understood phenomenon.
Explanation
It may be counter-intuitive to find that the largest and (presumably) heaviest particles rise to the top, but there are several possible explanations:- The center of mass of the whole system (containing the mixed nuts) in an arbitrary state is not optimal (because of the space close to the Brazil nuts); it has the tendency to be higher due to gravity. When the nuts are shaken, gravity will make sure the center of mass of the system moves down and this can only be done by moving the Brazil nuts up. Gravity will also make sure they stay up.
- Including the effects of air in spaces between particles, larger particles may become buoyantBuoyancyIn physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...
or sink. Smaller particles can fall into the spaces underneath a larger particle after each shake. Over time, the larger particle rises in the mixture.
(According to Heinrich Jaeger, "[this] explanation for size separation might work in situations in which there is no granular convection, for example for containers with completely frictionless side walls or deep below the surface of tall containers (where convection is strongly suppressed). On the other hand, when friction with the side walls or other mechanisms set up a convection roll pattern inside the vibrated container, we found that the convective motion immediately takes over as the dominant mechanism for size separation.")
- When shaken, the particles move in vibration-induced convectionConvectionConvection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
flow: individual particles move up through the middle, across the surface, and down the sides. If a large particle is involved, it will be moved up to the top by convection flow. Once at the top, the large particle will stay there because the convection currents are too narrow to sweep it down along the wall. - The phenomenon is related to Parrondo's paradox inasmuch as the Brazil nuts move to the top of the mixed nuts against the gravitational gradient when subjected to random shaking.
Granular convection has been probed by the use of MRI imaging where convection rolls similar to those in fluids (Bénard cells) can be visualized.
Manufacturing
The effect is of serious interest for some manufacturing operations; once a heterogeneous mixture of granular materials has been produced, it is usually undesirable for the different particle types to segregate. Several factors determine the severity of the Brazil nut effect, including the sizes and densitiesDensity
The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...
of the particles, the pressure
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
of any gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
between the particles, and the shape of the container. A rectangular box (such as a box of breakfast cereal) or cylinder
Cylinder (geometry)
A cylinder is one of the most basic curvilinear geometric shapes, the surface formed by the points at a fixed distance from a given line segment, the axis of the cylinder. The solid enclosed by this surface and by two planes perpendicular to the axis is also called a cylinder...
(such as a can of nuts) works well to counter the effect, while a cone
Cone (geometry)
A cone is an n-dimensional geometric shape that tapers smoothly from a base to a point called the apex or vertex. Formally, it is the solid figure formed by the locus of all straight line segments that join the apex to the base...
-shaped container results in what is known as the reverse Brazil nut effect.
Astronomy
In astronomyAstronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...
, it is also seen in some low density, or rubble pile
Rubble pile
In astronomy, rubble pile is the informal name for an object that is not a monolith, consisting instead of numerous pieces of rock that have coalesced under the influence of gravity...
asteroid
Asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
s, for example the asteroid 25143 Itokawa
25143 Itokawa
25143 Itokawa is an Apollo and Mars-crosser asteroid. It was the first asteroid to be the target of a sample return mission, the Japanese space probe Hayabusa.-Discovery and naming:...
.
Geology
In geologyGeology
Geology is the science comprising the study of solid Earth, the rocks of which it is composed, and the processes by which it evolves. Geology gives insight into the history of the Earth, as it provides the primary evidence for plate tectonics, the evolutionary history of life, and past climates...
, this phenomenon is one of the causes of inverse grading
Graded bedding
In geology, a graded bed is one characterized by a systematic change in grain or clast size from the base of the bed to the top. Most commonly this takes the form of normal grading, with coarser sediments at the base, which grade upward into progressively finer ones...
which can be observed in many situations including soil liquefaction
Soil liquefaction
Soil liquefaction describes a phenomenon whereby a saturated soil substantially loses strength and stiffness in response to an applied stress, usually earthquake shaking or other sudden change in stress condition, causing it to behave like a liquid....
during earthquake
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
s or mudslides.
External links
- Convection rolls in almost densely filled rotating containers, University of Magdeburg
- PhysicsWeb: The Brazil Nut Effect
-
- The Brazil Nut Effect: Numerical Simulation Example of the numerical simulation of the Brazil Nut Effect.
- "Why brazils always end up on top", BBC NewsBBC NewsBBC News is the department of the British Broadcasting Corporation responsible for the gathering and broadcasting of news and current affairs. The department is the world's largest broadcast news organisation and generates about 120 hours of radio and television output each day, as well as online...
, 15 November 2001 - "Why does shaking a can of coffee cause the larger grains to move to the surface?", Scientific AmericanScientific AmericanScientific American is a popular science magazine. It is notable for its long history of presenting science monthly to an educated but not necessarily scientific public, through its careful attention to the clarity of its text as well as the quality of its specially commissioned color graphics...
, 9 May 2005 - "Of airbags, Avalungs and avalanche safety", Toronto StarToronto StarThe Toronto Star is Canada's highest-circulation newspaper, based in Toronto, Ontario, Canada. Its print edition is distributed almost entirely within the province of Ontario...
, 13 January 2008 - Sixty Symbols: Brazil Nut Effect, The University of Nottingham