Peltier
 
Heat Transfer Equations

 

See also Material Properties and Unit Conversions


 

Thermal Resistance

image of thermal resistance equation   image of diagram of thermal resistance in material

Where;

R is thermal resistance in C/watt
L is the length in meters (m)
K is the Thermal Conductivity of the material in watts/meter C
A is the cross sectional area in meters squared (m2).

Example


Time Required to Cool (or heat) an Object [or, Q required to cool or heat an object within a specific time]

image of equation for Newtons law of cooling or the time required to change the temp of an object   image of generic objects being heated or cooled showing heat gain or heat loss

Where;

Q is the heat added (or being removed) from the object in watts
m is the mass (weight) of the object in Kg
Cp is the Specific heat of the object material in J/Kg C
t is the time required to cool down (or heat up) the object in seconds
Ts is the starting temperature in C
Tf is the final temperature in C

Example


Heat Gain (or loss) - through the walls of an insulated container

image of equation to calculate the heat flow into an insulated container   cut away view of insulated container for cooling

Where;

Q is the heat lost or gained in watts
L is the thickness of insulation in meters (m)
K is the Thermal Conductivity of the insulation material in watts/meter K (or C)
A is the outside surface area of the container in meters squared (m2).
h is the Heat Transfer Coefficient of the surface material in watts/meter2 C
Ta is the Outside ambient air temperature in C
TI is the Inside temperature in C

Natural or Free Convection is essentially still to slightly stirred air with h values ranging from 1 to 25.
Forced Convection is air moved by a fan or other active method. h values range from 25 to 100.

Excel fileExcel Calculator Worksheet


Heat Loss (or gain) - by Convection

image of equation to calculate the heat flow into an insulated container    

Where;

Q is the heat lost (or gained) in watts
h is the Heat Transfer Coefficient of the surface material in watts/meter2 C
A is the exposed surface area in meters squared (m2).
Ts is the surface temperature in C
Ta is the ambient air temperature in C

Natural or Free Convection is essentially still to slightly stirred air with h values ranging from 1 to 25.
Forced Convection is air moved by a fan or other active method. h values range from 10 to 100.

Heat is "gained" or added to a surface when the ambient air (Ta) is higher than the surface temperature (Ts).

Example


Peltier

 
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