Heat transfer

Definition: it is the study of mechanism and rate of transferred of energy (heat) from the region of high temperature to the region of low temperature.

Heat transfer occurs in 3 processes:

1. Conduction: main method of transfer of heat through solids

Mechanism: flow of heat due to the transfer of vibration energy from one molecular to another.

2. Convection:

Mechanism: transfer heat from one region to another by the motion of the fluid caused by differences in density arising from temperature gradient in the system.

3. Radiation:

Mechanism: radiate heat in the form of electromagnetic waves which travel in straight lines at the speed of light e.g. IR & sun light.

Heat transfer by conduction: the quantity of heat is given by Furrier's equation:

Where Q = quantity of heat

A = Area

T1-T2 = Temperature difference

 Time = Ө

X = …………………………

K =…………………………..

q =……………………………

Unit of heat transfer:

Q = ……………………..

A = …………………….

T =……………………..

 …………………….= Ө

X = meter or centimeter

K =…………………………..

q = watts = Joules\sec

Example

Calculate the amount of heat that will flow through a sheet of steel, 10mm in thickness, 0.6mm wide and 1m long in 30min. with 70  temperature in one side and 30
in the other side       where K= 43W\

Solution …………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………….