PHT PPT

2. Outlines
 Introduction
 Conduction
 Convection
 Radiation
 Heat transfer equipment
 Applications

3. Introduction
• Heat is a form of energy
• Passes from higher temp. body to lower temp. body
• Heat can travel through a medium and also through a vacuum
Hot Body
( 100 °C)
Cold Body
( 20 °C)
Heat flow
Body
( 50 °C)
Body
( 50 °C)
No Heat flow
Thermal Equilibrium

4. Introduction
 Modes of heat transfer
1) Conduction (Solids)
2) Convection (Fluids)
3) Radiation (Air, Vacuum)

5. Conduction
• Heat is transfer from one body to another without appreciable motion of
particles
• Needs medium
• Molecular phenomenon
• Without bulk motion of particles

6. Conduction
• Fourier’s law for conduction
Q = - k A
𝑑𝑇
𝑑𝑋
Where, Q = Rate of heat flow, W or J/s
k = Thermal conductivity, W/m K
A = Cross sectional area, 𝑚2
T = Temperature, K and x = Thickness, m
(Note : Negative sign denotes heat transfer in the direction of decreasing temperature)
Thermal Conductivity
(k)
Solids
↑
Liquids
↑
Gases

7. Convection
• Heat is transfer by diffusion + bulk motion of fluid
• Needs medium
Free / Natural
Convection
Forced
Convection
Convection
Mixing of fluid by
external devices
Change in density
of fluid with temp.

8. Convection
• Newton’s law of cooling for convection
𝑄
𝐴
= h (𝑇𝑤 - 𝑇∞)
Q = h A (𝑇𝑤 - 𝑇∞)
• Film heat transfer coefficient value h (W/ 𝑚2
K) depends on nature of flow and
thermodynamics property
For Free or Natural convection :
Gases : 2 – 25
Liquid : 50 – 100
For Forced convection :
Gases : 25 – 250
Liquid : 50 – 20,000

9. Radiation
• Heat is transfer by electro-magnetic waves or photons
• Does not need medium
• Example : Heat is transferred from sun to earth

10. Radiation
• Steafan – Boltzmann Law (For black body):
Eb ∝ T4
Eb = σ T4
Where, 𝐸𝑏 = Total emissive power of black body, W/ m2
T = Temperature, K and 𝜎 = Steafan – Boltzmann constant = 5.67 × 10−8 W/(m2 K4)
• For non-black body
Eb = e σ T4
Where, e = emissivity of non-black body

11. Heat Transfer Equipment
 What is heat transfer equipment ? ... known as heat exchanger
• U-tube heat exchanger
• Shell & tube heat exchanger
• Plate & frame heat exchanger
• Finned tube heat exchanger
• Cooling tower
• Condenser

12. Heat Transfer Equipment
 U-tube heat exchanger

13. Heat Transfer Equipment
 Shell & tube heat exchanger

14. Heat Transfer Equipment
 Plate & frame heat exchanger

15. Heat Transfer Equipment
 Finned tube heat exchanger

16. Heat Transfer Equipment
 Cooling tower (Natural draft)

17. Heat Transfer Equipment
 Cooling tower (Forced draft)

18. Heat Transfer Equipment

19. Heat Transfer Equipment
 Condenser

20. Applications
• Chemical and petrochemical plants
• Air Conditioning Systems
• Power production
• Waste Heat recovery
• Automobile Radiator
• Central Heating System
• Electronic Parts

21. Thank you
Satish Movaliya
Contact no. : +91 94096 32035
E-mail : satishmovaliya@gmail.com