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Research Papers: Evaporation, Boiling, and Condensation

Transient Two-Phase Flow Patterns by Application of a High Voltage Pulse Width Modulated Signal and the Effect on Condensation Heat Transfer

[+] Author and Article Information
Kevin Ng, James S. Cotton

Department of Mechanical Engineering,  McMaster University, 1280 Main Street West, McMaster University, Hamilton, ON, L8S 4L7, Canadangkk2@mcmaster.ca

Chan Y. Ching1

Department of Mechanical Engineering,  McMaster University, 1280 Main Street West, McMaster University, Hamilton, ON, L8S 4L7, Canadangkk2@mcmaster.ca

1

Corresponding author.

J. Heat Transfer 133(9), 091501 (Jul 27, 2011) (10 pages) doi:10.1115/1.4003901 History: Received June 03, 2010; Revised March 30, 2011; Accepted April 01, 2011; Published July 27, 2011; Online July 27, 2011

The objectives of this study are (i) to determine the transient phase redistributions of a two-phase flow in a smooth horizontal annular channel by applying high voltage pulses to induce electric fields and (ii) to quantify the resultant changes in the condensation heat transfer. The experiments were performed using refrigerant R-134a flowing in the annular channel that was cooled on the outside by a counter-current flow of water. The electric fields are established by applying high voltage to a concentric rod electrode inside a grounded tube. The effect of the electrohydrodynamic (EHD) forces on the changes to the initial stratified/stratified wavy flow pattern was visualized using a high speed camera. The EHD effect results in the redistribution of the liquid–vapor phase within the channel and unique flow structures, such as twisted liquid cones and entrained droplets, are observed. These structures only appear during the initial application of EHD and are absent in the steady state. Experiments were performed using a 8 kV pulse width modulated (PWM) signal with duty cycles ranging from 0% to 100% to evaluate the heat transfer and pressure drop characteristics of the transient EHD flow patterns. The resultant heat transfer increased with the duty cycle to approximately 2.7-fold at a mass flux of 45–55 kg/m2 s and 1.2-fold at a mass flux of 110 kg/m2 s. The enhancement was higher as the pulse width was increased.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of experimental test facility

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Figure 2

Detail of heat exchanger and flow visualization test section

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Figure 3

Detail of heat exchange channel and electrode

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Figure 4

Side profile images of (a) the flow pattern in the absence of EHD, of the twisted liquid cones after applying a 8 kV pulse for (b) 29 ms, (c) 58 ms, (d) 115 ms, and (e) top–down view of the twisted liquid cones after 58 ms for a mass flux of 55 kg/m2 s

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Figure 5

Side profile images of flow patterns for a pulse width of 58 ms, average quality of 50%, duty cycle of (i) 10%, (ii) 50%, (iii) 90%, and (iv) 100% (DC) for a mass flux of 55 kg/m2 s

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Figure 6

Side profile images of the flow pattern for an average quality of 50%, duty cycle of 10%, mass flux of 55 kg/m2 s and a pulse width of (i ) 29 ms and (ii) 115 ms

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Figure 7

Side profile images of the flow pattern for a pulse width of 58 ms, average quality of 50%, duty cycle of 50% and a mass flux of 110 kg/m2 s

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Figure 8

Effect of duty cycle on the (i) heat transfer enhancement ratio and (ii) heat transfer coefficient for a mass flux of 55 kg/m2 s, average quality of 50% and pulse width of ○ 29, Δ58, and □ 115 ms

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Figure 9

Effect of duty cycle on the (i) pressure drop ratio and (ii) pressure drop for a mass flux of 55 kg/m2 s, average quality of 50% and pulse width of ○ 29, Δ58, and □ 115 ms

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Figure 10

Effect of duty cycle on the (i) heat transfer enhancement ratio and (ii) heat transfer coefficient for a pulse width of 58 ms, average quality of 50% and mass flux of Δ 45, □ 55, and ○ 110 kg/m2 s

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Figure 11

Effect of duty cycle on the (i) pressure drop ratio and (ii) pressure drop for a pulse width of 58 ms, average quality of 50% and mass flux of Δ 45, □ 55, and ○ 110 kg/m2 s

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Figure 12

Heat transfer enhancement per applied effective voltage for different duty cycles for the case of a mass flux of 55 kg/m2 s, average quality of 50% and pulse width of ○ 29, Δ 58, and □ 115 ms

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