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RESEARCH PAPERS: Evaporation, Boiling, and Condensation

An Experimental Study on the Effect of Gravitational Orientation on Flow Boiling of Water in 1054×197μm Parallel Minichannels

[+] Author and Article Information
Satish G. Kandlikar

Thermal Analysis and Microfluidics Laboratory, Mechanical Engineering Department, Rochester Institute of Technology, Rochester, New York 14623, USAsgkeme@rit.edu

Prabhu Balasubramanian

Thermal Analysis and Microfluidics Laboratory, Mechanical Engineering Department, Rochester Institute of Technology, Rochester, New York 14623, USAprabhu@mechtech.com

J. Heat Transfer 127(8), 820-829 (Feb 08, 2005) (10 pages) doi:10.1115/1.1928911 History: Received April 19, 2004; Revised February 08, 2005

Microchannels and minichannels are being considered for high heat flux applications under microgravity environment in space missions. An experimental study is undertaken to determine the effect of gravitational orientation on flow boiling characteristics of water in a set of six parallel minichannels, each 1054μm wide by 197μm deep and 63.5mm long with a hydraulic diameter of 333μm. Three orientations—horizontal, vertical downflow, and vertical upflow—are investigated under identical operating conditions of heat and mass fluxes. High-speed images are obtained to reveal the detailed two-phase flow structure and liquid-vapor interactions. The experimental data and high speed flow visualization indicate that compared to the horizontal case, the flow becomes less chaotic for the vertical upflow case, while the reversed flow becomes more pronounced in the vertical downflow case. The resulting increase in the backflow is responsible for channel-to-channel flow maldistribution and heat transfer degradation. From the heat transfer data it is concluded that the performance of the tested channels in a microgravity environment will be similar to the horizontal flow case.

Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 4

Plug flow. Successive frames from (a) to (f) taken at 0.16ms time interval indicating plug flow in a single channel from a set of six parallel horizontal minichannels. G=120kg∕m2s, q″=317kW∕m2, Ts=110.9°C, x=0.361, flow from left to right. Scale: channel width—1054μm.

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Figure 3

Churn flow. Successive frames from (a) to (g) taken at 0.16ms time interval indicating churn flow in a single channel from a set of six parallel horizontal minichannels. G=120kg∕m2s, q″=317kW∕m2, Ts=110.9°C, x=0.361, flow from left to right. Scale: channel width—1054μm.

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Figure 2

Cross section of the test section

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Figure 6

Wavy flow. Successive frames from (a) to (g) taken at 0.16ms time interval indicating wavy flow in a single channel from a set of six parallel horizontal minichannels. G=120kg∕m2s, q″=317kW∕m2, Ts=110.9°C, x=0.361, flow from left to right. Scale: channel width—1054μm.

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Figure 19

Quality versus. heat transfer coefficient. G=120kg∕m2s, q″=317kW∕m2, and Ts=110.6°C.

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Figure 18

Time-averaged pressure drop fluctuations after correcting for the gravitation term. G=120kg∕m2s, q″=317kW∕m2, and Ts=110.6°C.

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Figure 17

Merger of vapor plugs during backflow. Successive frames from (a) to (f) taken at 0.33ms time interval indicating plug to annular flow in a single channel from a set of six parallel vertical minichannels with upward flow. G=120kg∕m2s, q″=317kW∕m2, Ts=110.6°C, and x=0.179. Scale: channel width—1054μm.

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Figure 16

Bubble growth fluctuation. Successive frames from (a) to (f) taken at 0.83ms time interval indicating bubble becoming smaller as a result of back flow of the upstream interface in a single channel from a set of six parallel vertical minichannels with upward flow. G=120kg∕m2s, q″=317kW∕m2, Ts=110.6°C, and x=0.179. Scale: channel width—1054μm.

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Figure 15

Backflow or flow reversal extending into the inlet manifold. Successive frames from (a) to (f) taken at 0.33ms time interval indicating back flow in a single channel from a set of six parallel vertical minichannels with downflow. G=120kg∕m2s, q″=317kW∕m2, Ts=114.5°C, and x=0.181. Scale: channel width—1054μm.

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Figure 14

Wavy annular flow with strong thin film nucleation. Successive frames from (a) to (f) taken at 0.33ms time interval indicating wavy flow with strong thin film nucleation in a single channel from a set of six parallel vertical minichannels with downward flow. G=120kg∕m2s, q″=317kW∕m2, Ts=114.5°C, and x=0.362. Scale: channel width—1054μm.

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Figure 13

Plug to annular flow. Successive frames from (a) to (f) taken at 0.16ms time interval indicating plug to annular flow in a single channel from a set of six parallel vertical minichannels with downward flow. G=120kg∕m2s, q=317kW∕m2, Ts=114.5°C, and x=0.362. Scale: channel width—1054μm.

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Figure 12

Dry out and rewetting. Successive frames from (a) to (f) taken at 0.33ms time interval indicating dry out and rewetting in a single channel from a set of six parallel vertical minichannels with downward flow. G=120kg∕m2s, q″=317kW∕m2, Ts=114.5°C, and x=0.362. Scale: channel width—1054μm.

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Figure 11

Churn flow with presence of bubble, slug, and annular flow. Successive frames from (a) to (f) taken at 0.33ms time interval indicating churn flow with the presence of bubbly and plug flow in a single channel from a set of six parallel vertical minichannels with downward flow. G=120kg∕m2s, q″=317kW∕m2, Ts=114.5°C, and x=0.362. Scale: channel width—1054μm.

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Figure 9

Bubble and vapor plug merger. Successive frames from (a) to (f) taken at 0.16ms time interval indicating bubble, plug merger in a single channel from a set of six parallel vertical minichannels with downflow. G=120kg∕m2s, q″=317kW∕m2, Ts=114.5°C, and x=0.362. Scale: channel width—1054μm.

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Figure 7

Breakup of liquid slug. Successive frames from (a) to (e) taken at 0.16ms time interval indicating breakup of a liquid slug, with a brief churn flow section in a single channel from a set of six parallel vertical minichannels with downward flow. G=120kg∕m2s, q″=317kW∕m2, Ts=114.5°C, and x=0.181. Scale: channel width—1054μm.

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Figure 5

Vapor plug disappearance due to pressure wave. Successive frames from (a) to (g) taken at 0.16ms time interval indicating plug flow in a single channel from a set of six parallel horizontal minichannels. G=120kg∕m2s, q″=317kW∕m2, Ts=110.9°C, x=0.180, flow from left to right. Scale: channel width—1054μm.

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Figure 10

Bubbly flow in liquid slug. Successive frames from (a) to (f) taken at 0.16ms time interval indicating bubbly flow in a single channel from a set of six parallel vertical minichannels with downward flow. G=120kg∕m2s, q″=317kW∕m2, Ts=114.5°C, and x=0.362. Scale: channel width—1054μm.

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Figure 8

Bubble merger. Successive frames from (a) to (f) taken at 0.33ms time interval indicating bubble merger in a single channel from a set of six parallel vertical minichannels with downward flow. G=120kg∕m2s, q″=317kW∕m2, Ts=114.5°C, and x=0.362. Scale: channel width—1054μm.

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