1. Heat Exchangers
Heat Exchangers

2. Heat Exchangers
A heat exchanger is used to exchange heat between two fluids of different temperatures, which are separated by a solid wall.
Heat exchangers are used to carry out energy conversion and utilization. They utlize a wide range of flow configurations.
Applications in heating and air conditioning, power production, waste heat recovery, chemical processing, food processing, sterilization in bio-processes.
Heat exchangers are classified according to flow arrangement and type of construction.
Heat Exchangers

3. . Flow in a double-pipe heat exchanger.

4. Heat Exchangers
Chee 318

5. •Heat Exchanger (HEX) Rating
Checkingthe existing design for compatibility with the user requirements (outlet temperature, heat load etc.)
given: flow rates, inlet temperatures, allowable pressure drop; thus HT area and passage dimensions
find: heat transfer rate, fluid outlet temperatures, actual pressure drop
•HEX Sizing
Thermal and pressure drop considerations, maintenance scheduling with fouling consideration.
given: inlet and outlet temperatures, flow rates, pressure drop
find: dimensions -type and size of HEX
Heat Exchangers

6. steady-state, steady flow• no heat generation in the HEX
Assumptions for Basic Design Equations for Sizing
steady-state, steady flow•
no heat generation in the HEX
• negligible ΔPE, ΔKE
• adiabatic processes
• no phase change (later)
• constant specific heats and other physical properties.
Heat Exchangers

7. Heat Exchanger Analysis
LMTD Method
Expression for convection heat transfer for flow of a fluid inside a tube:
For case 3 involving constant surrounding fluid temperature:
Heat Exchangers

8. Concentric Tube Construction• • - : :
Heat Exchangers

9. Heat Exchangers

10. Heat Exchangers

11. Heat Exchangers

12. Heat Exchangers

13. Heat Exchangers

14. Heat Exchangers

17. Overall Heat Transfer Coefficient
For tubular heat exchangers we must take into account the conduction resistance in the wall and convection resistances of the fluids at the inner and outer tube surfaces.
(11.3a)
Note that:
where inner tube surface
outer tube surface
Heat Exchangers

18. Example 1
Heat Exchangers

19. Heat Exchangers

20. Heat Exchangers