Rate of heat flow
Encyclopedia
The rate of heat flow between two systems is measured in watt
s (joules per second).
The formula for rate of heat flow is ∆Q/∆t = -K×A×∆T/x ,
where ∆Q/∆t is the rate of heat flow; -K is the thermal conductivity factor; A is the surface area; ∆T is the change in temperature and x is the thickness of the material (∆T/x is called the temperature gradient and is always negative because of the heat of flow always goes from more thermal energy to less).
and specific heat. System A has an average temperature of 500 kelvin
s and system B has an average temperature of 400 kelvins. If thirty seconds after the systems are put in contact they both reach 450 K, then the average rate of heat flow is:
50 J/30 s, or rather 1.66 W.
(note: specific heat and masses = 1)
Watt
The watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...
s (joules per second).
The formula for rate of heat flow is ∆Q/∆t = -K×A×∆T/x ,
where ∆Q/∆t is the rate of heat flow; -K is the thermal conductivity factor; A is the surface area; ∆T is the change in temperature and x is the thickness of the material (∆T/x is called the temperature gradient and is always negative because of the heat of flow always goes from more thermal energy to less).
Example
Assume there are two systems with the same massMass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...
and specific heat. System A has an average temperature of 500 kelvin
Kelvin
The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...
s and system B has an average temperature of 400 kelvins. If thirty seconds after the systems are put in contact they both reach 450 K, then the average rate of heat flow is:
50 J/30 s, or rather 1.66 W.
(note: specific heat and masses = 1)
See also
- Heat transferHeat transferHeat transfer is a discipline of thermal engineering that concerns the exchange of thermal energy from one physical system to another. Heat transfer is classified into various mechanisms, such as heat conduction, convection, thermal radiation, and phase-change transfer...
- Heat conductionHeat conductionIn heat transfer, conduction is a mode of transfer of energy within and between bodies of matter, due to a temperature gradient. Conduction means collisional and diffusive transfer of kinetic energy of particles of ponderable matter . Conduction takes place in all forms of ponderable matter, viz....
- Heat fluxHeat fluxHeat flux or thermal flux is the rate of heat energy transfer through a given surface. The SI derived unit of heat rate is joule per second, or watt. Heat flux is the heat rate per unit area. In SI units, heat flux is measured in W/m2]. Heat rate is a scalar quantity, while heat flux is a vectorial...
- WattWattThe watt is a derived unit of power in the International System of Units , named after the Scottish engineer James Watt . The unit, defined as one joule per second, measures the rate of energy conversion.-Definition:...
- FluxFluxIn the various subfields of physics, there exist two common usages of the term flux, both with rigorous mathematical frameworks.* In the study of transport phenomena , flux is defined as flow per unit area, where flow is the movement of some quantity per time...