HEAT TRANSFER - 1

Heat Transfer helps us to understand various aspects for the transfer of heat through various materials(solids, liquid and gasses) through various known process such as conduction, convection, radiation etc.
So, it finds a great use in engineering applications.


Heat is transferred from higher temperature to lower temperature. [secondary information]
There are three different ways in which heat can be transferred:

1. Conduction:- it is process by which heat can be transferred in solids.

2. Convection:- it is aprocess by which heat is transferred in fluides (gaseous &liquid)

3. Radiation:- it is a process in which the heat is transferred in the form of electromagnetic waves without yhe aid of any material medium.


Thermal conductivity:

In solids, heat is transferred through conduction. We will study conduction of heat through a solid bar in the following sector.


Consider a solid bar of thickness d and area of cross-section A. The left side of bar is maintained at Q_A temperature and right side at Q_B

Let us suppose Q_AQ_B

Heat flows from higher temperature to lower temperature after some time, the temp of each section becomes constant with time. This is known as steady state.
In steady state, if Q Amount of heat crosses through any cross section in time T, then
  and  
or,
K: coefficient of thermal conductivity.

For a small thickness Dx along the direction of heat and whose thickness dx is small and temperature difference is Q

[Secondary information]
Quantity called the temperature gradient and minus sign indicates that is negative along the direction of heat flow.

[Secondary Information]
We can compose the equation with the Ohm's Law
V₁ - V₂ = I.R
I =
Similarly  
hence is called thermal resistance rth.
R_th =


Accretion of Ice [Secondary Information]:

Consider a layer of ice of thickness x has air temp - Q⁰c and is 0⁰c.