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Research Papers: Evaporation, Boiling, and Condensation

Heater Size and Gravity Based Pool Boiling Regime Map: Transition Criteria Between Buoyancy and Surface Tension Dominated Boiling

[+] Author and Article Information
Rishi Raj

Department of Mechanical Engineering, University of Maryland, College Park, MD 20742rraj@umd.edu

Jungho Kim1

Department of Mechanical Engineering, University of Maryland, College Park, MD 20742kimjh@umd.edu

1

Corresponding author.

J. Heat Transfer 132(9), 091503 (Jul 06, 2010) (10 pages) doi:10.1115/1.4001635 History: Received December 03, 2009; Revised March 19, 2010; Published July 06, 2010; Online July 06, 2010

A pool boiling regime map demarcating the boundary between the surface tension and buoyancy dominated boiling regimes is developed based on heater size and gravity. For large heaters and/or high gravity conditions, boiling is dominated by buoyancy, and the ebullition cycle dominates the contribution to heat transfer. As the gravity level and/or heater size is decreased, surface tension forces become increasingly dominant, and a decrease in heat transfer is observed. The ratio of the heater size Lh (length of a side for a square heater) to the capillary length Lc is found to be a suitable parameter to define the transition criterion between these regimes. Based on the data obtained using FC-72 and pentane, the threshold value of Lh/Lc above which pool boiling is buoyancy dominated was found to be about 2.1. This transition criterion was found to be the same for gravity levels between 0g1.7g and liquid subcoolings between 6.6°C and 26.6°C.

Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Boiling curves using FC-72 at 1.7g for selected heaters on (a) 2.7 mm microheater array (12), ΔTsub=31°C, and (b) 7 mm microheater array (13), ΔTsub=6.6°C, and P=1 atm

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Figure 2

Boiling curve using n-perfluorohexane at three heater sizes and (a) 1.7g, (b) 1.0g, (c) 0.3g, and (d) 0.05g(14), ΔTsub=26°C, and P=1 atm (7 mm microheater array)

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Figure 3

7 mm (left) and 2.7 mm (right) microheater arrays

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Figure 4

CAD model of the experimental package

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Figure 5

The schematic of the dominant heat transfer paths for the (a) natural convection and (b) forced convection cases

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Figure 6

Boiling curve for different heater sizes using FC-72 at ΔTsub=26.6°C, P=1 atm, and 7 mm microheater array

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Figure 7

Bottom view images for 36, 9, and 4 heaters at three superheats, FC-72, ΔTsub=26.6°C, P=1 atm, and 7 mm microheater array

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Figure 8

Departure frequency versus superheat for FC-72, ΔTsub=26.6°C, P=1 atm, and 7 mm microheater array

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Figure 9

Boiling curve for different heater sizes using FC-72, ΔTsub=16.6°C, P=1 atm, and 2.7 mm microheater array

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Figure 10

Boiling curve using FC-72 for different heater sizes for normal and delayed nucleations, ΔTsub=26.6°C, P=1 atm, and 7 mm microheater array

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Figure 11

Boiling curve for different heater sizes using FC-72, ΔTsub=8.6°C, P=1 atm, and 7 mm microheater array

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Figure 12

Departure frequency versus superheat for the (a) buoyancy dominated regime and (b) the surface tension dominated regime at two subcoolings using 7 mm microheater array and FC-72

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Figure 13

Boiling curves at different heater sizes for pentane, ΔTsub=8°C, P=1 atm, and 7 mm microheater array

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Figure 14

Bottom view image for 25 heaters: (a) FC-72, ΔTsub=8.6°C; (b) pentane, ΔTsub=8°C, P=1 atm, ΔTw∼40°C, and 7 mm microheater array

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Figure 15

Pool boiling regime map for flat surfaces

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