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Theory of Heat Exchanging P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Understanding of Qualities of An Ideal Heat Exchangers…..

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Presentation on theme: "Theory of Heat Exchanging P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Understanding of Qualities of An Ideal Heat Exchangers….."— Presentation transcript:

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2 Theory of Heat Exchanging P M V Subbarao Professor Mechanical Engineering Department I I T Delhi Understanding of Qualities of An Ideal Heat Exchangers…..

3 Theoretical Base for Working of Heat Exchangers A Simple adiabatic Heat Exchanger model. Hot fluid Cold fluid

4 Electrical Analogy of A Finite Heat Exchanger Hot fluid Cold fluid

5 Basic Information for Overall Resistance/Conductance

6 Heat Transfer between two fluids separated by finite thick surface wall

7 First Level Engineering Compromise: Area Energy Balance:

8 Second Level Engineering Compromise:  T effective Mean Temperature Difference A Simple adiabatic Heat Exchanger model.

9 Second Level Engineering Compromise:  T

10 Simple Counter Flow Heat Exchangers

11 Simple Counter Flow Heat Exchangers: C < 1

12 Simple Parallel Flow Heat Exchangers

13 Theoretical Base for Working of Heat Exchangers For an Infinitesimal Heat communication between cold and hot. A Simple adiabatic Heat Exchanger model.

14 Third Level Engineering Compromise: variation of U U

15 How many "zones" are involved in A HX?

16 Various Simple Zones (HX)

17 How many "zones" are involved in A HX? "Zones" can best be defined as regimes of phase changes where the overall heat transfer coefficient (U) will vary. Using T-Q (Temperature-Heat) diagrams are the best way to pinpoint zones. The system is defined as co-current or countercurrent and the diagram is constructed. The diagram on the left illustrates the use of T-Q diagrams. These diagrams should accompany your basic (input- output) diagram of the heat exchanger. Defining zones is one of the most important aspects of heat exchanger design.

18 Role of SG in Rankine Cycle

19 Gas to Phase Changing Fluid Heat Exchange Liquid Heating

20 DPNL Platen SHTR RHTRRHTR LTSH Economiser APH ESP ID Fan drum Furnace BCW pump Bottom ash stack screen tubes Thermal Structure of A Boiler Furnace

21 didi dodo DiDi Tubular Flow Annular Flow Overall heat transfer coefficient of a used HX, based on outside area: A Simple Heat Exchanger

22 Overall heat transfer coefficient of a new/cleaned HX, based on outside area: Thermal resistance of any annular solid structure:


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