This PPT contains modes of heat transfer and related laws you can check video: https://youtu.be/3B3bFvK12Ao

1. Heat Transfer
Prof. S A Dahake

2. Basics of Heat Transfer
 Heat transfer is a discipline of thermal engineering that concerns the generation, use,
conversion, and exchange of thermal energy
 Heat is the energy which can transfer from one place to another due to temperature
difference
 Heat transfer is the study of rate of transfer of heat energy

3. Modes of Heat Transfer

4. Conduction
 It is the transfer of heat from one part to another part
of substance without transfer of molecules
 Conduction occurs in solid, liquid and gases
 Example is: when heat provide to metal rod from one
end it feels to other end

5. Fouriers Law
 The rate of heat flow through a simple homogeneous solid is directly
proportional to the area measured normal to the direction of heat flow
and the temperature gradient in the direction of heat flow.
 𝑄 ∝ A
𝑑𝑇
𝑑𝑥
 Q – heat transfer rate
 A – Area of heat flow normal to heat flow direction
 dT – Temperature difference between two faces of block thickness dx
 dx thickness of solid body

𝑑𝑇
𝑑𝑥
- Temperature gradient in the direction of heat flow

6. Cont…
 Thus, Q = -k A
𝑑𝑇
𝑑𝑥
 Heat flux q =
𝑄
𝐴
= −𝑘
𝑑𝑇
𝑑𝑥
 Where, k is sign of proportionality called coefficient of thermal
conductivity of material
 Negative sign indicate heat flow from higher to lower temperature body

7. Convection
 It is the process of heat transfer between a solid
surface to fluid in motion
 Heat energy is transfer by means of moving
matter
 Convection takes place in liquid and gases
 There are two types of convection
 Natural &
 Forced

8.  Natural convection or free convection
 It occurs due to temperature differences which affect the density
 Example of natural convection is the rise of smoke from a fire
 Forced convection
 It is a special type of heat transfer in which fluids are forced to move, in order to
the heat transfer
 This forcing can be done with a ceiling fan, a pump, suction device, or other
Cont…

9. Newtons law of cooling
 The rate of convective heat transfer between a surface and the fluid was first
suggested by Newtons law of cooling
 It states that the rate of heat transfer is proportional to heat flow direction and
temperature difference between watt surface temperature Tw in direction
perpendicular to heat flow direction
 Q ∝ A (Tw-T∞)
 Q = h A (𝑇𝑤 − 𝑇∞)
 Where, h is constant of proportionality called coefficient of convective heat
transfer
 Q =
(Tw−T∞)
1
ℎ𝐴
 Convective thermal resistance, R = 1
ℎ𝐴 =
(𝑇𝑤−𝑇∞)
𝑄

10. Radiation
 Radiation heat transfer is the energy that is emitted by matter in the form
of photons or electromagnetic waves.

11. Wiens law
 It states that wavelength λ corresponding to maximum energy is inversely
proportional to the absolute temperature of hot body
 λ =
1
𝑇
 λT = const = 0.0029 mK

12. Kirchoffs law
 It states that emmisivity of body at a particular temperature is equal to its
absorptivity from the body at same temperature

13. Stefan- Boltzman law
 This law states that emissive power of black body is directly proportional
to fourth power of its absolute temperature
 q ∝ T^4
 For area A, Q ∝ A. T^4
 Q = σ. A. T^4
 q – emissive power or heat flux
 A – radiating area
 Q – rate of heat energy radiated
 σ – Stefan boltzman constant = 5.67*10^-8 W/m^2k^4

14. THANK YOU
 Prof S A Dahake