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Research Papers: Jets, Wakes, and Impingment Cooling

High Heat Flux With Small Scale Monodisperse Sprays

[+] Author and Article Information
Sergio Escobar-Vargas

Department of Mechanical Engineering,
Santa Clara University,
Santa Clara, CA 95053
e-mail: sescobarvargas@scu.edu

Jorge E. Gonzalez

Mechanical Engineering Department,
City College of New York,
New York, NY 10031
e-mail: gonzalez@me.ccny.cuny.edu

Drazen Fabris

Department of Mechanical Engineering,
Santa Clara University,
Santa Clara, CA 95053
e-mail: dfabris@scu.edu

Ratnesh Sharma

NEC Laboratories America,
Cupertino, CA 95014
e-mail: ratnesh@sv.nec-labs.com

Cullen Bash

Hewlett Packard Laboratories,
Palo Alto, CA 94304
e-mail: cullen.bash@hp.com

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF Heat TRANSFER. Manuscript received June 27, 2011; final manuscript received February 23, 2012; published online October 5, 2012. Assoc. Editor: Bruce L. Drolen.

J. Heat Transfer 134(12), 122202 (Oct 05, 2012) (9 pages) doi:10.1115/1.4006486 History: Received June 27, 2011; Revised February 23, 2012

This work is aimed at cooling small surfaces (1.3 mm × 2 mm and 3 mm × 5 mm) using spray from thermal ink jet (TIJ) atomizers. Particular interests in this work include obtaining heat fluxes near the critical heat flux (CHF), understanding the correlation between the heat dissipation efficiency (η) and the liquid film thickness (δ) through experimental data, and understanding the primary mode of heat transfer on spray cooling at different liquid film thickness. Current experimental results indicate that high heat fluxes (∼4 × 107 W/m2) are obtained for controlled conditions of cooling mass flow rate, higher efficiencies are achieved at smaller liquid film thickness (δ ≈ 5 μm → η ≈ 0.9), and the heat transfer by conduction through the film becomes dominant as δ decreases.

Copyright © 2012 by ASME
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References

Figures

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Fig. 1

Nozzles distribution in the thermal atomizer. (a) Separation between nozzles row. Each nozzle row is 5 mm long approximately. (b) Nozzle diameter and distance between adjacent nozzles.

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Fig. 2

Cross section schematic of the copper block insulation

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Fig. 3

Schematic of thermocouple locations with dimensions in mm. (a) Copper finger extending from the block base has an upper surface of 3 × 5 mm, depth of thermocouple holes is 2 mm. (b) Copper finger extending from the block base has an upper surface of 1.3 × 2 mm, thermocouples were attached to the side of the fin since no drills were perforated. Drawing not to scale.

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Fig. 4

Spray cooling experimental setup with enhanced section on the atomizer-substrate system

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Fig. 5

Experimental setup to measure drop diameter and drop velocity

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Fig. 6

Experimental and modeled drop velocity decay with distance from the TIJ nozzle

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Fig. 7

Copper fin leading to the cooled surface with the labeling of thermocouples and heat flows defined on the fin

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Fig. 8

Time history of the experiments: (a) temperature response and (b) dissipated heat transfer rate

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Fig. 9

Wetted area evolution. Temperatures near the surface are (a) 104.2 °C, (b) 117.7 °C, (c) 122.4 °C, (d) 122.9 °C, (e) 128.9 °C, and (f) 130.9 °C.

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Fig. 10

Wetted area determination near CHF. Experiment conditions: active nozzles 48, frequency 2.5 kHz, temperature near the surface 130 °C.

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Fig. 11

Wetted area evolution with changes of temperature for different experiments. Heater area (Ah) is 3 × 5 mm.

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Fig. 12

Experimental high heat flux dissipation compared to other works. Forty-eight active nozzles, and frequencies varying from 1 kHz to 5 kHZ, heater substrate 3 × 5 mm. References: Current Work, CW; Pais et al. [11]; Mudawar and Valentine [34]; Sawyer et al. [40]; Cabrera and Gonzalez [35]; Halvorson et al. [41]; Sharma et al. [14]. Current work heat fluxes are near CHF, references heat fluxes are CHF.

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Fig. 13

Heat transfer efficiency trend and comparison to different works. Forty-eight active nozzles, and frequencies varying from 1 kHz to 5 kHZ, heater substrate 3 × 5 mm. References: Current Work, CW; Pais et al. [11]; Mudawar and Valentine [34]; Estes and Mudawar [15]; Horacek et al. [19]; Sawyer et al. [40]; Cabrera and Gonzalez [35]; Halvorson et al. [41]; Sharma et al. [14]. Current heat fluxes are near CHF, references heat fluxes are CHF.

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Fig. 14

Boiling phenomena over a hot substrate. (a) Thin liquid film, (b) bubble, (c) bubble break up, and (d) thick liquid film.

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Fig. 15

Heat transfer efficiency relation to the liquid film thickness. Frequencies varying from 1 kHz to 5 kHZ, heater substrate 1.3 × 2 mm.

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Fig. 16

Schematic of a control volume on top of a hot body

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Fig. 17

Convective heat transfer coefficient correlation to liquid film thickness using pure conduction through the film (dashed line) and experimentally calculated heat transfer rates (red open points). Experiment conditions of frequencies varying from 1 kHz to 5 kHZ, heater substrate 1.3 × 2 mm.

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