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RESEARCH PAPERS: Heat Exchangers

Stability Behavior of a Natural Circulation Loop with End Heat Exchangers

[+] Author and Article Information
N. M. Rao1

Department of Mechanical Engineering,  Dr. Babasaheb Ambedkar Technological University, “Vidyavihar,” Lonere-402 103 Maharashtra State, Indianmuralidhararao@yahoo.com

B. Maiti

 Indian Institute of Technology, Kharagpur, Kharagpur-721 302, West Bengal, Indiabmaiti@mech.iitkgp.ernet.in

P. K. Das

 Indian Institute of Technology, Kharagpur, Kharagpur-721 302, West Bengal, Indiapkd@mech.iitkgp.ernet.in

1

Corresponding author.

J. Heat Transfer 127(7), 749-759 (Jan 10, 2005) (11 pages) doi:10.1115/1.1924569 History: Received April 30, 2004; Revised January 10, 2005

The present investigation describes the stability behavior of NCL with end heat exchangers. The one-dimensional transient conservation equations of the loop fluid and the two fluid streams of cold end and hot end heat exchangers are solved simultaneously using the finite element program. For the stability analysis the loop response is found for an imposed finite perturbation to the loop circulation rate. Though the stability may depend on the number of parameters, variation of two nondimensional parameters, namely Ch* and GrL, is studied. Selecting the specific combinations of the above two parameters three different cases of stability, namely, stable, neutrally stable, and unstable, are demonstrated. The stability behavior is scanned over a wide range of Ch* and GrL values and the stability envelope is also constructed.

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Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic diagram of a NCL with end heat exchangers

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Figure 2

Schematic diagrams of end heat exchanger of NCL: (a) hot end heat exchanger (HEHE), (b) cold end heat exchanger (CEHE)

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Figure 3

Comparison between numerical and analytical results at steady state: (a) Hot and cold stream temperature profile, (b) coupling fluid temperature profile (Ntuh∗=5.0, Ntuc∗=2.0, Ch∗=100000, Cc∗=1000, GrL=100000000, Rh=5000, Rc=1000, K1=2.0 and K2=20.0)

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Figure 4

Variation of cold stream outlet temperature and coupling fluid flow rate at stable equilibrium (a) 15% perturbation, (b) 25% perturbation, (c) 35% perturbation

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Figure 5

State space plot of hot and cold stream outlet temperatures for stable condition

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Figure 6

Typical characteristics of the loop for neutral stability

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Figure 7

Time series plot of hot and cold stream outlet temperatures for neutral stability

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Figure 8

State space plot of hot and cold stream outlet temperatures for neutral stability

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Figure 9

Typical characteristics of the loop for unstable condition

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Figure 10

Typical characteristics of the loop for unstable condition variation of coupling fluid temperature. (a) At the inlet of heat exchangers, (b) at the exit of heat exchangers, (c) at the midpoint of heat exchangers

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Figure 11

State space plot of hot and cold stream outlet temperatures for unstable condition

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Figure 13

Change of stability behavior with the increase of GrL, (a) for Ch*=1×104GrL=1.0×108, (b) for Ch*=1×104GrL=1.2×109, (c) for Ch*=1×104GrL=1.24×109, (d) for Ch*=1×104GrL=2.0×109, (e) for Ch*=1×104GrL=1.0×1011

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