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Research Papers

Dynamic Numerical Microchannel Evaporator Model to Investigate Parallel Channel Instabilities

[+] Author and Article Information
Tom Saenen

Laboratoire de Transfert de Chaleur et de Masse,
École Polytechnique Fédérale De Lausanne,
Lausanne CH-1015, Switzerland
e-mail: tom.saenen@epfl.ch

John R. Thome

Laboratoire de Transfert de Chaleur et de Masse,
École Polytechnique Fédérale De Lausanne,
Lausanne CH-1015, Switzerland
e-mail: john.thome@epfl.ch

1Corresponding author.

Contributed by the Electronic and Photonic Packaging Division of ASME for publication in the JOURNAL OF ELECTRONIC PACKAGING. Manuscript received September 25, 2015; final manuscript received December 31, 2015; published online March 10, 2016. Assoc. Editor: Mehdi Asheghi.

J. Electron. Packag 138(1), 010901 (Mar 10, 2016) (13 pages) Paper No: EP-15-1091; doi: 10.1115/1.4032490 History: Received September 25, 2015; Revised December 31, 2015

A fully dynamic model of a microchannel evaporator is presented. The aim of the model is to study the highly dynamic parallel channel instabilities that occur in these evaporators in more detail. The numerical solver for the model is custom-built and the majority of the paper is focused on detailing the various aspects of this solver. The one-dimensional homogeneous two-phase flow conservation equations are solved to simulate the flow. The full three-dimensional (3D) conduction domain of the evaporator is also dynamically resolved. This allows for the correct simulation of the complex hydraulic and thermal interactions between the microchannels that give rise to the parallel channel instabilities. The model uses state-of-the-art correlations to calculate the frictional pressure losses and heat transfer in the microchannels. In addition, a model for inlet restrictions is also included to simulate the stabilizing effect of these components. In the final part of the paper, validation results of the model are presented, in which the stability results of the model are compared with the existing experimental data from the literature. Next, a parametric study is performed focusing on the stabilizing effects of the solid substrate properties. It is found that increasing the thermal conductivity and thickness of the solid substrate has a strong stabilizing effect, while increasing the number of microchannels has a small destabilizing effect. Finally, representative dynamic results are also given to demonstrate some of the unique capabilities of the model.

Copyright © 2016 by ASME
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References

Figures

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Fig. 1

Typical microchannel evaporator configuration and modeled evaporator

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Fig. 2

Microchannel evaporator cross section

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Fig. 3

Microchannel evaporator longitudinal section, with ● the central nodes and ○ the staggered nodes

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Fig. 4

Maximum solid temperature for different grid sizes

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Fig. 5

Steady-state pressure drop curve as a function of the channel mass flux

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Fig. 6

Validation of the dynamic evaporator model with 50 μm wide inlet restrictions, using R236fa as refrigerant

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Fig. 7

Validation of the dynamic evaporator model with 25 μm wide inlet restrictions, using R236fa as refrigerant

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Fig. 8

Validation of the dynamic evaporator model with 75 μm wide inlet restrictions, using R236fa as refrigerant

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Fig. 9

Validation of the dynamic evaporator model with 50 μm wide inlet restrictions, using R245fa as refrigerant

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Fig. 10

Validation of the dynamic evaporator model with 50 μm wide inlet restrictions, using R1234ze as refrigerant

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Fig. 11

Onset of instability channel mass flux for a varying thermal conductivity of the solid substrate

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Fig. 12

Onset of instability channel mass flux for a varying solid substrate thickness below the microchannels

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Fig. 13

Onset of instability channel mass flux for a varying number of microchannels

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Fig. 14

Inlet velocity of the perturbed and unperturbed microchannels, input heat flux of 25 W/cm2

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Fig. 15

Outlet velocity of the perturbed and unperturbed microchannels, input heat flux of 25 W/cm2

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Fig. 16

Maximum wall temperature difference, input heat flux of 25 W/cm2

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