In a heat pipe, operating fluid saturates wick structures system and establishes a capillary-driven circulation loop for heat transfer. Thus, the thermophysical properties of the operating fluid inevitably impact the transitions of phase-change mode and the capability of heat transfer, which determine both the design and development of the associated heat pipe systems. This article investigates the effect of liquid properties on phase-change heat transfer. Two different copper wick structures, cubic and cylindrical in cross section, 340 μm in height and 150 μm in diameter or width, are fabricated using an electroplating technique. The phase-change phenomena inside these wick structures are observed at various heat fluxes. The corresponding heat transfer characteristics are measured for three different working liquids: water, ethanol, and Novec 7200. Three distinct modes of the phase-change process are identified: (1) evaporation on liquid–vapor interface, (2) nucleate boiling with interfacial evaporation, and (3) boiling enhanced interface evaporation. Transitions between the three modes depend on heat flux and liquid properties. In addition to the mode transition, liquid properties also dictate the maximum heat flux and the heat transfer coefficient. A quantitative characterization shows that the maximum heat flux scales with Merit number, a dimensionless number connecting liquid density, surface tension, latent heat of vaporization, and viscosity. The heat transfer coefficient, on the other hand, is dictated by the thermal conductivity of the liquid. A complex interaction between the mode transition and liquid properties is reflected in Novec 7200. In spite of having the lowest thermal conductivity among the three liquids, an early transition to the mode of the boiling enhanced interface evaporation leads to a higher heat transfer coefficient at low heat flux.

References

References
1.
Ranjan
,
R.
,
Murthy
,
J. Y.
, and
Garimella
,
S. V.
,
2011
, “
A Microscale Model for Thin-Film Evaporation in Capillary Wick Structures
,”
Int. J. Heat Mass Transfer
,
54
, pp.
169
179
.
2.
Faghri
,
A.
,
1995
,
Heat Pipe Science and Technology
,
Taylor & Francis
,
New York
.
3.
Liao
,
Q.
, and
Zhao
,
T. S.
,
2000
, “
A Visual Study of Phase-Change Heat Transfer in a Two-Dimensional Porous Structure With a Partial Heating Boundary
,”
Int. J. Heat Mass Transfer
,
43
(
7
), pp.
1089
1102
.
4.
Weibel
,
J. A.
, and
Garimella
,
S. V.
,
2012
, “
Visualization of Vapor Formation Regimes During Capillary-Fed Boiling in Sintered-Powder Heat Pipe Wicks
,”
Int. J. Heat Mass Transfer
,
55
, pp.
3498
3510
.
5.
Vityaz
,
P. A.
,
Konev
,
S. K.
,
Medvedev
,
V. B.
, and
Sheleg
,
V. K.
,
1984
, “
Heat Pipes With Bidispersed Capillary Structures
,”
5th International Heat Pipe Conference
, Vol.
1
, pp.
127
135
.
6.
Semenic
,
T.
, and
Catton
,
I.
,
2009
, “
Experimental Study of Biporous Wicks for High Heat Flux Applications
,”
Int. J. Heat Mass Transfer
,
52
, pp.
5113
5121
.
7.
Reilly
,
S. W.
, and
Catton
,
I.
,
2009
, “
Improving Biporous Heat Transfer by Addition of Monoporous Interface Layer
,”
ASME
Paper No. HT2009-88257.
8.
Cao
,
X. L.
,
Cheng
,
P.
, and
Zhao
,
T. S.
,
2002
, “
Experimental Study of Evaporative Heat Transfer in Sintered Copper Bidispersed Wick Structures
,”
J. Thermophys. Heat Transfer
,
16
(
4
), pp.
547
552
.
9.
Wang
,
J.
, and
Catton
,
I.
,
2004
, “
Vaporization Heat Transfer in Biporous Wicks of Heat Pipe Evaporators
,”
13th International Heat Pipe Conference
, Vol.
2
, pp.
76
86
.
10.
Weibel
,
J. A.
,
Garimella
,
S. V.
, and
North
,
M. T.
,
2010
, “
Characterization of Evaporation and Boiling From Sintered Powder Wicks Fed by Capillary Action
,”
Int. J. Heat Mass Transfer
,
53
, pp.
4204
4215
.
11.
Peterson
,
G. P.
,
Duncan
,
A. B.
, and
Weichold
,
M. H.
,
1993
, “
Experimental Investigation of Micro Heat Pipes Fabricated in Silicon Wafers
,”
ASME J. Heat Transfer
,
115
(
3
), pp.
751
756
.
12.
Gillot
,
C.
,
Avenas
,
Y.
,
Cézac
,
N.
,
Poupon
,
G.
,
Schaeffer
,
C.
, and
Fournier
,
E.
,
2003
, “
Silicon Heat Pipes Used as Thermal Spreaders
,”
IEEE Trans. Compon. Packag. Technol.
,
26
(
2
), pp.
332
339
.
13.
Ivanova
,
M.
,
Laï
,
A.
,
Gillot
,
C.
,
Sillon
,
N.
,
Schaeffer
,
C.
,
Lefevre
,
F.
,
Lallemand
,
M.
, and
Fournier
,
E.
,
2006
, “
Design, Fabrication and Test of Silicon Heat Pipes With Radial Microcapillary Grooves
,”
The Tenth Intersociety Conference on Thermal and Thermomechanical Phenomena in Electronics Systems
, San Diego, CA, May 30–June 2, pp.
545
551
.
14.
Berre
,
M. L.
,
Launay
,
S.
,
Sartre
,
V.
, and
Lallemand
,
M.
,
2003
, “
Fabrication and Experimental Investigation of Silicon Micro Heat Pipes for Cooling Electronics
,”
J. Micromech. Microeng.
,
13
(
3
), pp.
436
441
.
15.
Dunn
,
P. D.
, and
Reay
,
D. A.
,
1982
,
Heat Pipes
,
Pergamon Press
,
Oxford, UK
, p.
24
.
16.
Ramm
,
P.
,
Klumpp
,
A.
,
Merkel
,
R.
,
Weber
,
J.
,
Wieland
,
R.
,
Ostmann
,
A.
, and
Wolf
,
J.
,
2003
, “
3D System Integration Technologies
,”
Mater. Res. Soc. Symp. Proc.
,
766
, p.
E5.6
.
17.
Nam
,
Y.
,
Sharratt
,
S.
,
Byon
,
C.
,
Kim
,
S. J.
, and
Ju
,
Y. S.
,
2010
, “
Fabrication and Characterization of the Capillary Performance of Superhydrophilic Cu Micropost Arrays
,”
J. Microelectromech. Syst.
,
19
(
3
), pp.
581
588
.
18.
Cai
,
S. Q.
, and
Bhunia
,
A.
,
2014
, “
Geometrical Effects of Porous Wick Structures on Capability of Liquid-to-Vapor Phase Change
,”
Int. J. Heat Mass Transfer
,
79
, pp.
981
988
.
You do not currently have access to this content.