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Research Papers

Film Thickness and Heat Transfer Measurements in a Spray Cooling System With R134a

[+] Author and Article Information
Eduardo Martínez-Galván

TECNUN, University of Navarra, Paseo de Manuel Lardizábal, 13 San Sebastián, Guipúzcoa 20018, Spainemartinez@tecnun.es

Juan Carlos Ramos

TECNUN, University of Navarra, Paseo de Manuel Lardizábal, 13 San Sebastián, Guipúzcoa 20018, Spainjcramos@tecnun.es

Raúl Antón

TECNUN, University of Navarra, Paseo de Manuel Lardizábal, 13 San Sebastián, Guipúzcoa 20018, Spainranton@tecnun.es

Rahmatollah Khodabandeh

Department of Energy Technology, Royal Institute of Technology (KTH), Brinellvägen 68, Stockholm 10044, Swedenrahmatollah.khodabandeh@energy.kth.se

J. Electron. Packag 133(1), 011002 (Mar 03, 2011) (11 pages) doi:10.1115/1.4001857 History: Received November 30, 2009; Revised April 09, 2010; Published March 03, 2011; Online March 03, 2011

Experimental measurements in a spray cooling test rig have been carried out for several heat fluxes in the heater and different spray volumetric fluxes with the dielectric refrigerant R134a. Results of the heat transfer and the sprayed refrigerant film thickness measurements are presented. The film thickness measurements have been made with a high speed camera equipped with a long distance microscope. It has been found that there is a relation between the variation in the average Nusselt number and the film thickness along the spray cooling boiling curve. The heat transfer regimes along that curve are related not only with a variation in the average Nusselt number but also with changes in the film thickness. The qualitative analysis of those variations has served to understand better the heat transfer mechanisms occurring during the spray cooling.

Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Diagram of the test rig

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Figure 2

Test rig installation

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Figure 3

Spray cooling boiling curves at different volumetric fluxes

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Figure 4

Dimensionless spray cooling boiling curves

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Figure 5

CHF versus ideal critical heat flux as a function of the mass flow rate at different spray Weber numbers

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Figure 6

Spray efficiency at the CHF point as a function of the modified Weber number.

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Figure 7

Average Nusselt number as a function of the heat flux at different Weber numbers

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Figure 8

Measurement zone of film thickness: (a) sketch of heater base and spray cone impact area; (b) picture of the spray cone impinging over the heater.

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Figure 9

Original image taken with the high speed camera and a close-up of the film edge loaded with MATLAB ®

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Figure 10

Example of a rescaled image with the “imadjust” MATLAB ® function and a close-up of the film edge

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Figure 11

Example of the calculated film edge position (yellow line), with the uncertainty limits (upper red line and lower blue line).

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Figure 12

One example of the film thickness measurement as a result of the implemented algorithm

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Figure 13

Local average film thickness at We=12,648 for different heat fluxes

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Figure 14

Dimensionless total average film thickness as a function of the dimensionless heat flux for four Weber numbers

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Figure 15

Dimensionless total average film thickness τ and average Nusselt number Nu as functions of the dimensionless heat flux for a Weber number of 50,541

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Figure 16

Dimensionless total average film thickness τ and average Nusselt number Nu as functions of the dimensionless heat flux for three different Weber numbers: 38,666, 25,692, and 12,648

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