Modes of Heat Transfer
There are three Modes of Heat Transfer from one place to another-
- Conduction
- Convection
- Radiation
Read More- Heat and Mass Transfer: Objective Questions with Answers
CONDUCTION
What do you understand by Conduction?
- In this mode of heat transfer, heat is transferred from one place to another without the net motion of the molecules of the medium.
- Conduction generally takes place in solids.
- It is a slow process compared to convection and radiation.
- It is experimentally observed that at a steady state.
The rate of heat flow (∆Q/∆t) is proportional to (T1-T2)
T1, T2 are temp. at hot and cold ends at steady states
Also (∆Q/∆t) is proportional to Area
and inversely proportional to the length
Thus, (∆Q/∆t) = KA (T1-T2)/L
K= thermal conductivity of a material
SI Unit of K is watt/mK or watt/mC
- K depends only on the type of materials.
NOTE-
- Length is always taken along the Flow of Heat
- Cross-Sectional area (A) is taken perpendicular to the flow of heat.
Read More- Radiation: What is Shape Factor?
Important Basic Formulas
Series Combination of Rods
- If the rate of heat flow is the same in each rod then the combination is called series combination.
Let R1 = L1/K1A & R2 = L2/K2A
Then, Req = R1 + R2
- Rate of Heat Flow (Heat Current)
∆Q/∆T = (T1-T2)/ Req
- Equivalent Thermal Conductivity (Keq)
Req = R1 + R2
Then, (L1 + L2)/KeqA = (L1/K1A1) + (L2/K2A2)
(L1 + L2)/Keq = (L1/K1) + (L2/K2)
Since A=A1=A2
- For n rods combination
(L1 + L2 +L3 +….Ln)/Keq = (L1/K1) + (L2/K2) + (L3/K3) +…….. (Ln/Kn)
Read More- Convection Heat Transfer Process
Read More- Radiation Heat Transfer Process
Conceptual Knowledge
At 4 degrees Celsius density of water is maximum. So as water is heated from 0 to 4, the density of water increases and there is no motion of water molecules. So during heating from 0 to 4 degrees Celsius, heat transfer takes place only due to conduction.
If water is further heated from 4 degree then the transfer of heat takes place due to convection.