Experiments were performed to measure the heat transfer coefficient on the surface of a square flush heat source mounted at the center of an FR-4 plate in a small horizontal enclosure. The plate area was six times larger than the heat source area. Four cases were considered: the plate facing upwards and downwards, and the backside either insulated or convecting. The heat transfer coefficients exhibited distinct behavior at high aspect ratio in which the dominant length scales were related to the source. At intermediate aspect ratios, the length scales of both the source and the enclosure were relevant, and at small aspect ratios a conduction limit was observed. The heat transfer coefficients at high aspect ratios exceeded the prior correlations by 14 percent for upward facing isolated plates when the ratio of heat source area to perimeter was used as the significant length scale, but the dependence on Ra1/4 was consistent. For the downward facing case, the data exceeded the values for a uniformly heated isolated plate by 68 percent. Classical correlations for shallow differentially heated horizontal enclosures were not satisfactory in describing the dependence on enclosure height.

Issue Section:
Technical Papers
Topics:
Cooling, Heat, Natural convection, Heat transfer coefficients, Heat conduction, Plates (structures)
1.
Al-Arabi
M.
, and
El-Riedy
M. K.
,
1976
, “
Natural Convection Heat Transfer From Isothermal Plates of Different Shapes
,”
Intl. J. Heat and Mass Transfer
, Vol.
19
, pp.
1399
–
1404
.
2.
Buller, M. L., and Duclos, T. G., 1982, “Thermal Characteristics of Horizontally Oriented Electronic Components in an Enclosed Environment,” Proc. Electronic Components Conference, pp. 153–157.
3.
Ellison, G. N., 1989, Thermal Computations for Electronic Equipment, Robert E. Krieger Publishing Co., Malabar, Fl.
4.
Fishenden, M., and Saunders, O. A., 1957, An Introduction to Heat Transfer, Clarendon Press, London, p. 89.
5.
Gebhart, B., Jaluria, Y., Mahajan, R. L., and Sammakia, B., 1988, Buoyancy Induced Flows and Transport, Hemisphere Pub. Corp., Washington, DC.
6.
Globe
S.
, and
Dropkin
D.
,
1959
, “
Natural Convection Heat Transfer in Liquids Confined Between Two Horizontal Plates
,”
ASME JOURNAL OF HEAT TRANSFER
, Vol.
81C
, pp.
24
–
28
.
7.
Goldstein
R. J.
, and
Chu
T. Y.
,
1969
, “
Thermal Convection in a Horizontal Layer of Air
,”
Prog. Heat Mass Transfer
, Vol.
2
, pp.
55
–
75
.
8.
Goldstein
R. J.
,
Sparrow
E. M.
, and
Jones
D. C.
,
1973
, “
Natural Convection Mass Transfer Adjacent to Horizontal Plates
,”
Int. J. Heat Mass Transfer
, Vol.
116
, p.
1025
1025
.
9.
Goldstein
R. J.
,
Chiang
H. D.
, and
See
D. L.
,
1990
, “
High Rayleigh Number Convection in a Horizontal Enclosure
,”
J. Fluid Mech.
, Vol.
213
, pp.
111
–
126
.
10.
Hanneman, R. E., 1994, “Thermal Management in Electronics: The Next Ten Years,” invited lecture, IEEE Semiconductor Thermal Measurement and Management Symposium, SEMITHERM X, February 1994.
11.
Hollands
K. G. T.
,
Raithby
G. D.
, and
Konicek
L.
,
1975
, “
Correlation Equations for Free Convection Heat Transfer in Horizontal Layers of Air and Water
,”
Int. J. Heat Mass Transfer
, Vol.
18
, pp.
879
–
884
.
12.
Husar
R. J.
, and
Sparrow
E. M.
,
1968
, “
Patterns of Free Convection Adjacent to Horizontal Heated Surfaces
,”
Int. J. Heat Mass Transfer
, Vol.
11
, pp.
1206
–
1208
.
13.
Hybrid Thermal Modeller, 1996, Pacific Numerix Corporation, Scottsdale, AZ.
14.
Incropera, F. P., and DeWitt, D. P., 1990, Introduction to Heat Transfer, John Wiley & Sons, pp. 517–525.
15.
Kitamura
K.
, and
Kimura
F.
,
1995
, “
Heat Transfer and Fluid Flow of Natural Convection Adjacent to Upward-Facing Horizontal Plates
,”
Int. J. Heat Mass Transfer
, Vol.
38
, No.
17
, pp.
3149
–
3159
.
16.
Krane, R. J., and Phillips, T. J., 1986, “Natural Convection Cooling of a Horizontally-Oriented Component Board in a Low-Aspect Ratio Enclosure,” Heat Transfer in Electronic Equipment, 1986, ASME HTD-Vol. 57, pp. 113–122.
17.
Lall, B. S., Ortega, A. and Kabir, H., 1994, “Thermal Design Rules for Electronic Components on Conducting Boards in Passively Cooled Enclosures,” Proc. IEEE Intersociety Conference on Thermal Phenomena in Electronic Systems, ITHERM 94, Piscataway, NJ.
18.
Lall, B. S., 1998, “Natural Convection Heat Transfer from Discrete Heat Sources on a Conducting Board in a Shallow Enclosure,” Ph.D. thesis, Dept. of Aero. and Mech. Eng., University of Arizona, Tucson, AZ.
19.
Lasance, C. J. M., 1994, “Accurate Temperature Prediction in Consumer Electronics: A Must but Still a Myth,” in Cooling of Electronic Systems, S. Kakac, and H. Yuncu, eds., Kluwer Academic Publishers Group, Boston, MA, pp. 859–898.
20.
Lloyd, J. R., and Moran, W. R., 1974, “Natural Convection Adjacent to Horizontal Surfaces of Various Planforms,” ASME Paper 74WA/HT-66.
21.
McAdams, W. H., 1954, Heat Transmission, 3rd ed., chpt. 7, McGraw-Hill, NY.
22.
Moffat
R. J.
,
1988
, “
Describing the Uncertainties in Experimental Results
,”
Exptl. Thermal Fluid Sci.
, Vol.
1
, pp.
3
–
17
.
23.
Myrum
T. A.
,
1990
, “
Natural Convection from a Heat Source in a Top-Vented Enclosure
,”
ASME JOURNAL OF HEAT TRANSFER
, Vol.
112
, pp.
632
–
639
.
24.
Torrance
K. E.
,
Orleff
L.
, and
Rockett
J. A.
,
1969
a, “
Experiments on Natural Convection in Enclosures With Localized Heating from Below
,”
J. Fluid Mech.
, Vol.
36
, Part 1, pp.
21
–
31
.
25.
Torrance
K. E.
, and
Rockett
J. A.
,
1969
b, “
Numerical Study of Natural Convection in an Enclosure with Localized Heating From Below—Creeping Flow to the Onset of Laminar Stability
,”
J. Fluid Mech
, Vol.
36
, Part 1, pp.
33
–
54
.
This content is only available via PDF.
Copyright © 1998
 by The American Society of Mechanical Engineers
You do not currently have access to this content.