0
TECHNICAL BRIEFS

# Entropy Generation in Counter Flow Gas to Gas Heat Exchangers

[+] Author and Article Information
Hany Ahmed Mohamed

Mechanical Engineering Department, Faculty of Engineering, Assiut University, Assiut, Egypthah@aun.eun.eg

J. Heat Transfer 128(1), 87-92 (Apr 13, 2005) (6 pages) doi:10.1115/1.2130407 History: Received October 02, 2004; Revised April 13, 2005

## Abstract

Analysis of heat transfer and fluid flow thermodynamic irreversibilities is realized on an example of a counter flow double pipe heat exchanger utilizing turbulent air flow as a working fluid. During the process of mathematical model creation and for different working and constructing limitations, total thermodynamic irreversibility is studied. The present work proves that the irreversibility occurred due to unequal capacity flow rates (flow imbalance irreversibility). It is concluded that the heat exchanger should be operated at effectiveness, $ε$, greater than 0.5 and the well operating conditions will be achieved when $ε$ approaches one where low irreversibility is expected. A new equation is adopted to express the entropy generation numbers for imbalanced heat exchangers of similar design with smallest deviation from the exact value. The results obtained from the new equation are compared with the exact values and with those obtained by Bejan (Bejan, A., 1997, Advanced Engineering Thermodynamics, Wiley, New York).

###### FIGURES IN THIS ARTICLE
<>
Copyright © 2006 by American Society of Mechanical Engineers
Your Session has timed out. Please sign back in to continue.

## Figures

Figure 1

Schematic drawing for the double pipe heat exchanger model

Figure 2

Effect of the heat exchanger effectiveness on the entropy generation number at various temperature ratios for balanced heat exchangers

Figure 3

Effect of the heat exchanger effectiveness on the entropy generation number at various values of hot stream Reynolds number for balanced heat exchangers

Figure 4

Effect of the heat exchanger effectiveness on the entropy generation number at various rd, rP and SL for balanced heat exchangers at constant Re2=5×104

Figure 5

Entropy generation number in a balanced counter flow heat exchanger at zero pressure drops

Figure 6

The entropy generation number for imbalanced counter flow heat exchangers as dependent on Ω and Tr at zero pressure drop

Figure 7

Comparisons between Ns values obtained from the new equation with the corresponding exact one at SL=20, Re2=5×104, rP=1, rd=0.5, Ω=1 and different Tr

Figure 8

Comparisons between the new and Bejan (4) equations with the corresponding exact values at SL=20, Re2=5×104, rP=1, rd=0.5, Ω=1, Tr=0.7–0.9 and ε=0.6–0.9

Figure 9

Entropy generation number due to temperature difference, NsT, and pressure drops, NsP, against ε at Ω=1 for different Tr

Figure 10

Entropy generation number, Ns, against 1∕Ω at ε=0.5 for different Tr

Figure 11

Entropy generation number, Ns, against ε at 1∕Ω=0.5 for different Tr

Figure 12

Entropy generation number, Ns, against ε at Tr=0.2,0.6 for different 1∕Ω

Figure 13

Entropy generation number, Ns, against ε at Tr=0.4,0.8 for different 1∕Ω

Figure 14

Entropy generation number, Ns, against ε at Tr=0.5,0.9 for different 1∕Ω

## Errata

Some tools below are only available to our subscribers or users with an online account.

### Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related Proceedings Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

• TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
• EMAIL: asmedigitalcollection@asme.org
Sign In