This paper aims to show how confocal microscopy can be useful for characterizing menisci in a flat plate heat pipe made of silicon. The capillary structure is made of radial microgrooves whose width decreases from the periphery to the center of the system. A transparent plate is used to close the system and allow visualizations. The confocal method allows measuring both the liquid film shape inside the grooves and the condensate films on the fins. The film thickness is lower than $10 μm$. The measurements show that the condensate film forms a drop connected to the meniscus in the grooves but their curvatures are reversed. As a result, a very thin region shall exist where the liquid formed by condensation is drained to the grooves. The drop curvature radius decreases from the condenser to the evaporator like the meniscus radius in the grooves. Therefore, a small part of the liquid is drained by the fins from the evaporator to the condenser. Furthermore, the condensate film covers a large part of the system and can also be in contact with the evaporator at high heat fluxes.

1.
Lallemand
,
M.
, and
Lefèvre
,
F.
, 2004, “
Micro/Mini Heat Pipes for the Cooling of Electronic Devices
,”
13th International Heat Pipe Conference
, Shanghai, China, pp.
12
22
.
2.
Rullière
,
R.
,
Lefèvre
,
F.
, and
Lallemand
,
M.
, 2007, “
Prediction of the Maximum Heat Transfer Capability of Two-Phase Heat Spreaders—Experimental Validation
,”
Int. J. Heat Mass Transfer
0017-9310,
50
, pp.
1255
1262
.
3.
Hopkins
,
R.
,
Faghri
,
A.
, and
Khrustalev
,
D.
, 1999, “
Flat Miniature Heat Pipes With Micro Capillary Grooves
,”
ASME J. Heat Transfer
0022-1481,
121
, pp.
102
109
.
4.
Lips
,
S.
,
Lefèvre
,
F.
, and
Bonjour
,
J.
, 2008, “
Nucleate Boiling in a Flat Grooved Heat Pipe
,”
Int. J. Therm. Sci.
1290-0729,
48
, pp.
1273
1278
.
5.
,
B.
,
Gerner
,
F. M.
,
,
P.
,
Henderson
,
T.
, and
Baker
,
K. W.
, 1997, “
Experimental Results for Low-Temperature Silicon Micromachined Micro Heat Pipe Arrays Using Water and Methanol as Working Fluids
,”
Exp. Heat Transfer
0891-6152,
10
, pp.
253
272
.
6.
Le Berre
,
M.
,
Launay
,
S.
,
Sartre
,
V.
, and
Lallemand
,
M.
, 2003, “
Fabrication and Experimental Investigation of Silicon Heat Pipes for Cooling Electronics
,”
J. Micromech. Microeng.
0960-1317,
13
, pp.
436
441
.
7.
Das Gupta
,
S.
,
Schonberg
,
J. A.
, and
Wayner
,
P. C.
, 1993, “
Investigation of an Evaporating Extended Meniscus Based on the Augmented Young–Laplace Equation
,”
ASME J. Heat Transfer
0022-1481,
115
, pp.
201
208
.
8.
Stephan
,
P. C.
, and
Busse
,
C. A.
, 1992, “
Analysis of the Heat Transfer Coefficient of Grooved Heat Pipe Evaporator Walls
,”
Int. J. Heat Mass Transfer
0017-9310,
35
, pp.
383
391
.
9.
Ichikawa
,
N.
,
Hosokawa
,
K.
, and
Maeda
,
R.
, 2004, “
Interface Motion of Capillary-Driven Flow in Rectangular Microchannel
,”
J. Colloid Interface Sci.
0021-9797,
280
, pp.
155
164
.
10.
Gokhale
,
S. J.
,
Plawsky
,
J. L.
, and
Wayner
,
P. C.
, 2003, “
Experimental Investigation of Contact Angle, Curvature, and Contact Line Motion in Dropwise Condensation and Evaporation
,”
J. Colloid Interface Sci.
0021-9797,
259
, pp.
354
366
.
11.
Mederic
,
B.
,
Miscevic
,
M.
,
Platel
,
V.
,
Lavieille
,
P.
, and
Joly
,
J. -L.
, 2004, “
Experimental Study of Flow Characteristics During Condensation in Narrow Channels: The Influence of the Diameter Channel on Structure Patterns
,”
Superlattices Microstruct.
0749-6036,
35
, pp.
573
586
.
12.
Jones
,
B. J.
,
Lee
,
P. -S.
, and
Garimella
,
S. V.
, 2008, “
Infrared Micro-Particle Image Velocimetry Measurements and Predictions of Flow Distribution in a Microchannel Heat Sink
,”
Int. J. Heat Mass Transfer
0017-9310,
51
, pp.
1877
1887
.