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RESEARCH PAPERS: Heat Exchangers

Exchanger Performance Behavior Through Irreversibility Analysis for 1-2 TEMA G Heat Exchangers

[+] Author and Article Information
Ramesh K. Shah

 Subros Limited, Noida, UP, India 201304shahrk@asme.org

Teodor Skiepko

Department of Mechanical Engineering, Bialystok Technical University, Wiejska 45C, 15-351 Bialystok, Polandtskiepko@pb.bialystok.pl

J. Heat Transfer 127(12), 1296-1304 (Jun 22, 2005) (9 pages) doi:10.1115/1.2098827 History: Received February 27, 2004; Revised June 22, 2005

The objective of this paper is to illustrate, discuss, and explain the interrelationship between the temperature difference irreversibility and heat exchanger effectiveness to clarify the performance trends of exchangers with some complex flow arrangements. This is because there is no physical explanation provided for the following results presented by Shah and Skiepko (ASME J. Heat Transfer, 126, pp. 994–1002, 2004): the heat exchanger effectiveness can be maximum, having an intermediate value or minimum at the maximum irreversibility operating point depending upon the flow arrangement of two fluids; similarly, the heat exchanger effectiveness can be minimum or maximum at the minimum irreversibility operating point. The analysis of such complex performance behavior is presented in this paper with an example of overall parallelflow and counterflow 1-2 TEMA G exchangers. This is accomplished by the decomposition of complex flow arrangements into simple subexchangers, and then the overall irreversibility trends for the exchangers are explained by irreversibilities produced due to temperature difference and fluid mixing in component subexchangers. It is shown for 1-2 TEMA G exchangers that the temperature difference irreversibility for a pure parallelflow subexchanger passes through a maximum at finite value of NTU1, and then approaches 0 when NTU1. On the contrary, the irreversibility for a pure counterflow subexchanger attains a minimum value at finite NTU1 and then increases with NTU1 and approaches maximum at NTU1 for 1–2 TEMA G exchangers. This is because the temperatures at the inlet of the subexchangers are variable and dependent on the exit temperatures from the preceding subexchangers. Detailed exchanger effectivenesses and temperature ratios are presented as a function of NTU1 for the explanation.

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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

Normalized temperature difference irreversibility S*∕Smax*, temperature effectiveness P1 and ratio of the outlet fluid temperatures T1,o∕T2,o versus NTU1 for pure counterflow and parallelflow arrangements, determined for ϑ=2 at R1=2

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Figure 2

Flow configuration for 1–2 TEMA G exchanger with overall parallelflow; two subexchangers have parallelflow (Aa and Ab) and the other two (Bc and Bd) have counterflow passes

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Figure 3

Flow configuration for 1–2 TEMA G exchanger with overall counterflow; two subexchangers have parallelflow and the other two have counterflow passes

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Figure 4

Ssubex* and Stot*, as a function of NTU1 for a 1–2 TEMA G with overall parallelflow exchanger determined for ϑ=2.0 at R1=2

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Figure 5

Temperature effectiveness P1 and contribution of particular subexchangers Xε,j in overall effectiveness ε as a function of NTU1 for a 1–2 TEMA G with overall parallelflow for ϑ=2.0 at R1=2

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Figure 6

Hot-to-cold fluid temperature ratios at the inlet and outlet of subexchangers as a function of NTU1 for a 1–2 TEMA G with overall parallelflow determined for ϑ=2.0 at R1=2

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Figure 7

S*=Sirr∕Cmin, as a function of NTU1 for a 1–2 TEMA G with overall counterflow exchanger determined for ϑ=2.0 at R1=2

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Figure 8

Temperature effectiveness P1 and contribution of particular subexchangers Xε,j in overall effectiveness ε as a function of NTU1 for a 1–2 TEMA G with overall counterflow determined for ϑ=2.0 at R1=2

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Figure 9

Hot-to-cold fluid temperature ratios at the inlet and outlet of subexchangers as a function of NTU1 for a 1–2 TEMA G with overall counterflow determined for ϑ=2.0 at R1=2

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Figure 10

Comparisons of irreversibility S*=Sirr∕Cmin peculiar behavior as a function of NTU1,subex for subexchangers operating as elements of complex flow arrangements and operating standalone for a 1–2 TEMA G with overall parallelflow and counterflow determined at ϑ=2.0 at R1=2

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