Experiments were performed to investigate spray cooling on microstructured surfaces. Surface modification techniques were utilized to obtain microscale indentations and protrusions on the heater surfaces. A smooth surface was also tested to have baseline data for comparison. Tests were conducted in a closed loop system with ammonia using RTI’s vapor atomized spray nozzles. Thick film resistors, simulating heat source, were mounted onto 1×2cm2 heaters, and heat fluxes up to 500W/cm2 (well below critical heat flux limit) were removed. Two nozzles each spraying 1cm2 of the heater area used 96ml/cm2min(9.7gal/in.2h) liquid and 13.8ml/cm2s(11.3ft3/in.2h) vapor flow rate with only 48 kPa (7 psi) pressure drop. Comparison of cooling curves in the form of surface superheat (ΔTsat=TsurfTsat) versus heat flux in the heating-up and cooling-down modes (for increasing and decreasing heat flux conditions) demonstrated substantial performance enhancement for both microstructured surfaces over smooth surface. At 500W/cm2, the increases in the heat transfer coefficient for microstructured surfaces with protrusions and indentations were 112% and 49% over smooth surface, respectively. Moreover, results showed that smooth surface gives nearly identical cooling curves in the heating-up and cooling-down modes, while microstructured surfaces experience a hysteresis phenomenon depending on the surface roughness level and yields lower surface superheat in the cooling-down mode, compared with the heating-up mode, at a given heat flux. Microstructured surface with protrusions was further tested using two approaches to gain better understanding on hysteresis. Data indicated that microstructured surface helps retain the established three-phase contact lines, the regions where solid, liquid, and vapor phases meet, resulting in consistent cooling curve and hysteresis effect at varying heat flux conditions (as low as 25W/cm2 for the present work). Data also confirmed a direct connection between hysteresis and thermal history of the heater.

1.
Pais
,
M. R.
,
Chow
,
L. C.
, and
Mahefkey
,
E. T.
, 1992, “
Surface Roughness and Its Effects on the Heat Transfer Mechanism in Spray Cooling
,”
ASME J. Heat Transfer
0022-1481,
114
, pp.
211
219
.
2.
Sehmbey
,
M. S.
,
Pais
,
M. R.
, and
Chow
,
L. C.
, 1992, “
Effect of Surface Material Properties and Surface Characteristics in Evaporative Spray Cooling
,”
J. Thermophys. Heat Transfer
0887-8722,
6
(
3
), pp.
505
511
.
3.
Kim
,
J. H.
,
You
,
S. M.
, and
Choi
,
U. S.
, 2004, “
Evaporative Spray Cooling of Plain and Microporous Coated Surfaces
,”
Int. J. Heat Mass Transfer
0017-9310,
47
, pp.
3307
3315
.
4.
Stodke
,
C.
, and
Stephan
,
P.
, 2005, “
Spray Cooling Heat Transfer on Microstructured Surfaces
,”
Sixth World Conference on Experimental Heat Transfer, Fluid Mechanics, and Thermodynamics
, Matsushima, Miyagi, Japan.
5.
Amon
,
C.
,
Yao
,
S. C.
,
Wu
,
C. F.
, and
Hsieh
,
C. C.
, 2005, “
Microelectromechanical System-Based Evaporative Thermal Management of High Heat Flux Electronics
,”
ASME J. Heat Transfer
0022-1481,
127
, pp.
66
75
.
6.
Hsieh
,
C. C.
, and
Yao
,
S. C.
, 2006, “
Evaporative Heat Transfer Characteristics of a Water Spray on Micro-Structured Silicon Surfaces
,”
Int. J. Heat Mass Transfer
,
49
, pp.
962
974
. 0017-9310
7.
Silk
,
E.
,
Kim
,
J.
, and
Kiger
,
K. T.
, 2006,
Enhanced Surface Spray Cooling With Embedded and Compound Extended Surface Structures
,”
Proceedings of the ITHERM 2006
, San Diego, CA.
8.
Coursey
,
J.
,
Kim
,
J.
, and
Kiger
,
K. T.
, 2006, “
Spray Cooling of High Aspect Ratio Open Microchannels
,”
Proceedings of the ITHERM 2006
, San Diego, CA.
9.
Bergles
,
A. E.
, and
Chyu
,
M. C.
, 1982, “
Characteristics of Nucleate Pool Boiling From Porous Metallic Coatings
,”
ASME J. Heat Transfer
,
104
, pp.
279
285
. 0022-1481
10.
Marto
,
P. J.
, and
Lepere
,
V. J.
, 1982, “
Pool Boiling Heat Transfer From Enhanced Surfaces to Dielectric Fluids
,”
ASME J. Heat Transfer
,
104
, pp.
292
299
. 0022-1481
11.
Shi
,
M. -H.
,
Ma
,
J.
, and
Wang
,
B. -X.
, 1993, “
Analysis on Hysteresis in Nucleate Pool Boiling Heat Transfer
,”
Int. J. Heat Mass Transfer
0017-9310,
36
(
18
), pp.
4461
4466
.
12.
Hwang
,
G. -S.
, and
Kaviany
,
M.
, 2006, “
Critical Heat Flux in Thin, Uniform Porous Coatings
,”
Int. J. Heat Mass Transfer
0017-9310,
49
, pp.
844
849
.
13.
Pais
,
M. R.
,
Tilton
,
D.
,
Chow
,
L. C.
, and
Mahefkey
,
E. T.
, 1989, “
High Heat Flux, Low Superheat Evaporative Spray Cooling
,”
Proceedings of the 27th AIAA Aerospace Sciences Meeting
, Reno, NV.
14.
Yang
,
J.
,
Chow
,
L. C.
, and
Pais
,
M. R.
, 1996, “
Nucleate Boiling Heat Transfer in Spray Cooling
,”
ASME J. Heat Transfer
0022-1481,
118
, pp.
668
671
.
15.
Rini
,
D. P.
,
Chen
,
R. H.
, and
Chow
,
L. C.
, 2002, “
Bubble Behavior and Nucleate Boiling Heat Transfer in Saturated FC-72 Spray Cooling
,”
ASME J. Heat Transfer
0022-1481,
124
, pp.
63
72
.
16.
Horacek
,
B.
,
Kiger
,
K.
, and
Kim
,
J.
, 2005, “
Single Nozzle Spray Cooling Heat Transfer Mechanisms
,”
Int. J. Heat Mass Transfer
0017-9310,
48
(
8
), pp.
1425
1438
.
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