Research Papers

An Appraisal of System Mean Void Fraction and Its Application for the Moving Boundary Simulation of Phase-Change Heat Exchangers

[+] Author and Article Information
S. P. Datta

Department of Mechanical Engineering,
Indian Institute of Technology Kharagpur,
Kharagpur 721302, India
e-mail: santanu@mech.iitkgp.ernet.in

R. K. Chandra

HXE, RPD, HEEP, BHEL, Haridwar,
Uttarakhand 249403, India
e-mail: rahul.mechlife@gmail.com

P. K. Das

Professor and Head
Department of Mechanical Engineering,
Indian Institute of Technology Kharagpur,
Kharagpur 721302, India
e-mail: pkd@mech.iitkgp.ernet.in

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received June 1, 2014; final manuscript received May 18, 2015; published online August 11, 2015. Assoc. Editor: Sumanta Acharya.

J. Heat Transfer 137(12), 121015 (Aug 11, 2015) (9 pages) Paper No: HT-14-1380; doi: 10.1115/1.4030964 History: Received June 01, 2014

In gas–liquid two-phase flow, void fraction is the most unique parameter which influences all the transport processes. In the most general case, though the void fraction varies nonlinearly with the channel length, many practical simulations make use of the “system mean void fraction.” The present investigation makes a critical assessment of different system mean void fraction models for a wide range of slip velocity and density difference between the phases. To this end, different correlations for slip ratio have been considered and, for all the cases, closed form expression for the system mean void fraction has been presented. The local as well as the system mean void fractions have also been estimated numerically from a heat transfer based model. Predictions from the heat transfer based model and the slip ratio based model have been compared. As an application, the slip ratio based system mean void fraction is used in to build the moving boundary model for phase-change heat exchangers. The prediction of startup transients for both an evaporator and a condenser of an automotive air conditioning system (AACS) agrees well with the experimental results.

Copyright © 2015 by ASME
Topics: Porosity , Density
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Fig. 1

Control volume of a channel segment containing a two-phase flow

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Fig. 4

Combined effect of slip and density ratios on system mean void fraction (simulated)

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Fig. 2

Variation of simulated local void fraction with the nondimensional length at different slip ratios

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Fig. 3

Variation of simulated local void fraction with the nondimensional length at different density ratios (xin=0,xout=1)

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Fig. 5

System mean void fraction (simulated) using different slip models as a function of inlet quality and density ratio (xout=1)

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Fig. 6

System mean void fraction (simulated) using different slip models and heat transfer based model as a function of outlet quality and density ratio (xin=0)

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Fig. 7

Schematic diagram of the heat exchangers: (a) evaporator and (b) condenser

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Fig. 9

Comparison with simulated mean evaporator zone temperature and measured outlet

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Fig. 8

Simulated mean evaporator pressure and comparison with experiment

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Fig. 10

Simulated mean condenser pressure and comparison with experiment

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Fig. 11

Comparison with simulated mean condenser zone temperature and measured outlet



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