HEAT TRANSFER

Heat is a form of energy and can be defined as energy that transmits from one body to another as the result of a temperature difference between the two bodies. All the other energy that is transferred occur as work.

Heat transfer takes place from a highes temperature to a lower temperature (from a warm body to a cold body) and never in the opposite direction. Since heat is energy, it is not destroyed or used up in any process. The rate of heat transfer is always proportional to the difference in temperature that is causing the transfer. The transfer of energy as heat occurs in three ways :
i. By conduction
ii. By convection
iii. By radiation

LATENT HEAT

Latent heat is the process whereby heat is added but there is no rise in temperature. An example is when heat is added to water while it is boiling in an open container. Once water has reached the boiling point, adding more heat only makes it boil faster, it does not raise the temperature.

SENSIBLE HEAT

When a change of temperature can be measured by thermometer and the level of heat or heat intensity has changed, it is called sensible heat.

SPECIFIC HEAT

The specific heat (c) is the amount of heat necessary to raise the temperature of 1lb of a substance to 1˚F. Every substance has a different specific heat. For example, the specific heat of water is 1Btu/lb ˚F , where as the specific heat of ice is 0.5 Btu/lb ˚F.

CALCULATING HEAT QUANTITY OF HEAT

From the definition of specific heat, it is evident that the quantity of heat energy supplied to, or given up by any given mass of material to bring about a specified temperature change can be determined from the following relationship :

Q = (m) (c) (T2 – T1)

Where Q = The quantity of heat energy in British
Thermal Units (Btu)
m = The mass in pounds
c = The specific heat in Btu per pound per degree Fahrenheit
T1 = The initial temperature in degrees Fahrenheit
T2 = The final temperature in degrees Fahrenheit, consistent with T1