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Research Papers: Heat Exchangers

Effect of Plate Characteristics on Axial Dispersion and Heat Transfer in Plate Heat Exchangers

[+] Author and Article Information
K. Shaji

Department of Mechanical Engineering,
Indian Institute of Technology Madras,
Chennai 600036, India

Sarit K. Das

Heat Transfer and Thermal Power Laboratory,
Department of Mechanical Engineering,
Indian Institute of Technology Madras,
Chennai 600036, India
e-mail: skdas@iitm.ac.in

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the Journal of Heat Transfer. Manuscript received August 2, 2010; final manuscript received October 20, 2012; published online March 20, 2013. Assoc. Editor: Phillip M. Ligrani.

J. Heat Transfer 135(4), 041801 (Mar 20, 2013) (10 pages) Paper No: HT-10-1339; doi: 10.1115/1.4022993 History: Received August 02, 2010; Revised October 20, 2012

A new mathematical model of single-blow transient testing technique is proposed for the determination of heat transfer and dispersion coefficients in plate heat exchangers (PHEs) in which the flow maldisrtibution effects are separated from the fluid back-mixing. The fluid axial dispersion is used to characterize the back-mixing and other deviations from plug flow. Single-blow experiments are carried out with different number of plates for various flow rates with three different plate geometries of 30 deg, 60 deg, and mixed (30 deg/60 deg) chevron angles. The outlet temperature response to an exponential inlet temperature variation is solved numerically using finite difference method. In the present work, the whole curve matching technique is used to determine the values of Nusselt number and dispersive Peclet number. Since the maldistribution effects are separated, these data are independent of test conditions and hence using a regression analysis, general correlations are developed for Nusselt number and Peclet number of the present plate heat exchangers. The applicability of the single-blow test data is validated using a two-fluid experiment. Two-fluid experiments are conducted on the same plate heat exchanger with smaller and larger number of plates and the results have been compared with its simulation which used the Nusselt number and Peclet number correlations developed by the new model of single-blow test as the inputs.

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Figures

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Fig. 1

Photographic view of the corrugated plates

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Fig. 2

Schematic view of single-blow experimental setup

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Fig. 3

Schematic view of two-fluid experimental setup

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Fig. 4

Flow friction characteristics of the chevron plates

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Fig. 5

Channel and flow configuration for single-pass PHE

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Fig. 6

The outlet temperature response within the channels of a plate heat exchanger: (a) 81 plates of 30 deg chevron angle (m2 = 2.35) and (b) 57 plates of 60 deg chevron angle (m2 = 0.49)

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Fig. 7

Curve matching between experimental values and the model for different types of plates: (a) 81 plates (m2 = 2.35) at Re = 2053 (30 deg plates), and (b) 57 plate (m2 = 0.49) at Re = 2555 (60 deg plates)

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Fig. 8

Variation of Nusselt number with Reynolds number for different chevron angle plates

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Fig. 9

Variation of Peclet number with Reynolds number for different chevron angle plates

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Fig. 10

Comparison of the experimental temperature responses with theoretical model at: (a) Re = 1470, N = 20, NTU = 0.741, Rg2 = 1.0 under uniform flow distribution (m2 = 0.15, 30 deg plates), and (b) Re = 920, N = 80, NTU = 1.023, Rg2 = 1.12 under nonuniform flow distribution (m2= 2.1, 30 deg plates)

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