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Research Papers: Two-Phase Flow and Heat Transfer

Steady-State Behavior of a Two-Phase Natural Circulation Loop With Thermodynamic Nonequilibrium

[+] Author and Article Information
Dipankar N. Basu

Department of Mechanical Engineering, IIT, Kharagpur 721302, Indiadipankar@mech.iitkgp.ernet.in

Souvik Bhattacharyya

Department of Mechanical Engineering, IIT, Kharagpur 721302, Indiasouvik@mech.iitkgp.ernet.in

P. K. Das

Department of Mechanical Engineering, IIT, Kharagpur 721302, Indiapkd@mech.iitkgp.ernet.in

J. Heat Transfer 131(2), 022901 (Jan 05, 2009) (12 pages) doi:10.1115/1.2994721 History: Received January 28, 2008; Revised July 17, 2008; Published January 05, 2009

A model to predict the steady-state behavior of a rectangular two-phase natural circulation loop has been proposed. The analysis employs a one-dimensional two-fluid model to identify various system parameters, with particular emphasis on the subcooled boiling region. The onset of two-phase region and point of net vapor generation and associated liquid temperatures and vapor qualities have been estimated using a few widely recognized correlations. Predicted results demonstrate that the consideration of subcooled boiling may have significant effect on system behavior, particularly around the transition regions. The interaction of saturated bubbles and subcooled liquid and associated change in heat transfer and frictional forces has been discussed in detail. Fluid stream has been observed to have different combinations of flow stream conditions at boiler exit and condenser inlet. Five probable combinations have been identified and a generalized working-regime map has been proposed on NsubNZu plane. Attempts have been made to identify the influence of various control parameters. A favorable sink condition (higher coolant flow rate or lower coolant entry temperature) has been found to be of particular importance to attain a wider operating range of wall heat flux and better heat transfer characteristics. A design map has been proposed to identify favorable operating condition in terms of control parameters to ensure complete condensation.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 5

Effect of wall heat flux on vapor quality

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Figure 6

Longitudinal variation of temperature and quality in and downstream of the boiler for three different cases

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Figure 7

Longitudinal variation of temperature and quality in and downstream of the boiler for 400 kW/m2 heat flux

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Figure 8

Generalized flow-regime map to identify fluid stream condition at boiler exit

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Figure 9

Effect of coolant mass flow rate on loop mass flux and condenser entry quality

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Figure 10

Design graph for optimum coolant flow rate and inlet temperature to avoid two-phase condition at downcomer

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Figure 11

Comparison of present model prediction with experimental data (29)

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Figure 4

Effect of wall heat flux on boiler entry and exit temperatures and condenser entry temperature

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Figure 3

Effect of wall heat flux on loop mass flux for rectangular two-phase NCL

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Figure 2

Geometry of rectangular two-phase natural circulation loop

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Figure 1

Appearance of subcooled boiling zone

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