This is a theoretical, numerical, and experimental study of natural convection heat transfer from an immersed surface with intermittent uniform heat flux. Scale analysis predicts that the “on” time interval can be optimized such that the overall Nusselt number is maximized. Furthermore, Nu increases monotonically as the “off” time interval decreases. These features are verified and determined more accurately by complete numerical simulations for a vertical flat surface in the range 103 ≤ Ra ≤ 105 and Pr = 7, where Ra is based on heat flux and wall height. They are further verified by means of water experiments in the range 1010 ≤ Ra ≤ 1011. The pulsating heater configurations tested experimentally are the vertical cylinder, which approximates boundary layer flow on a plane surface, and the horizontal cylinder. The optimal square-wave heat pulse for a natural convection immersion heater is reported in general (scaling correct) terms.

1.
Bejan, A., 1984, Convection Heat Transfer, Wiley, New York.
2.
Chung
P. M.
, and
Anderson
A. D.
,
1961
, “
Unsteady Laminar Free Convection
,”
ASME JOURNAL OF HEAT TRANSFER
, Vol.
83
, pp.
473
478
.
3.
FIDAP Theoretical Manual, 1991, Fluid Dynamics International, Evanston, IL, Vol. 6.03.
4.
Gebhart
B.
,
1961
, “
Transient Natural Convection From Vertical Elements
,”
ASME JOURNAL OF HEAT TRANSFER
, Vol.
83
, pp.
61
70
.
5.
Gebhart
B.
, and
Adams
D. E.
,
1961
, “
Measurements of Transient Natural Convection on Flat Vertical Surfaces
,”
ASME JOURNAL OF HEAT TRANSFER
, Vol.
83
, pp.
1
4
.
6.
Gebhart
B.
, and
Dring
R. P.
,
1967
, “
The Leading Edge Effect in Transient Natural Convection Flow From a Vertical Plate
,”
ASME JOURNAL OF HEAT TRANSFER
, Vol.
89
, p.
274
275
.
7.
Goldstein
R. J.
, and
Eckert
E. R. G.
,
1960
, “
The Steady and Transient Free Convection Boundary Layer on a Uniformly Heated Vertical Plate
,”
Int. J. Heat Mass Transfer
, Vol.
1
, pp.
208
218
.
8.
Goldstein
R. J.
, and
Briggs
D. G.
,
1964
, “
Transient Free Convection About Vertical Plate and Cylinders
,”
ASME JOURNAL OF HEAT TRANSFER
, Vol.
86
, p.
490
490
.
9.
Hassani
A. V.
, and
Hollands
K. G. T.
,
1989
, “
On Natural Convection Heat Transfer From Three-Dimensional Bodies of Arbitrary Shape
,”
ASME JOURNAL OF HEAT TRANSFER
, Vol.
111
, pp.
363
371
.
10.
Hellums, J. D., and Churchill, S. W., 1961, “Transient and Steady State, Free and Natural Convection, Numerical Solutions,” Paper No. 118, Int. Heat Transfer Conf., Boulder, CO.
11.
Ingham
D. B.
,
1978
, “
Transient Free Convection on an Isothermal Vertical Flat Plate
,”
Int. J. Heat Mass Transfer
, Vol.
21
, pp.
67
69
.
12.
Kelleher
M. D.
, and
Yang
K. T.
,
1968
, “
Heat Transfer Response of Laminar Free-Convection Boundary Layers Along a Vertical Heated Plate to Surface-Temperature Oscillations
,”
ZAMP
, Vol.
19
, pp.
31
44
.
13.
Mollendorf
J. C.
, and
Gebhart
B.
,
1970
, “
An Experimental Study of Vigorous Transient Natural Convection
,”
ASME JOURNAL OF HEAT TRANSFER
, Vol.
92
, pp.
628
634
.
14.
Monold
E. R.
, and
Yang
K. T.
,
1962
, “
Asymptotic Solutions for Unsteady Laminar Free Convection on a Vertical Plate
,”
ASME Journal of Applied Mechanics
, Vol.
29
, pp.
124
126
.
15.
Nanda
R. J.
, and
Sharma
V. P.
,
1963
a, “
Free Convection Laminar Boundary Layers in Oscillatory Flow
,”
J. Fluid Mechanics
, Vol.
15
, pp.
419
428
.
16.
Nanda, R. J., and Sharma, V. P., 1963b, “Free Convection Laminar Boundary Layers in Oscillatory Flow,” AIAA J., Vol. pp. 937–938.
17.
Sammakia
B.
, and
Gebhart
B.
,
1978
, “
Transient and Steady-State Numerical Solutions in Natural Convection
,”
Numerical Heat Transfer
, Vol.
1
, pp.
529
545
.
18.
Schetz
J. A.
, and
Eichhorn
R.
,
1962
, “
Unsteady Natural Convection in the Vicinity of a Double Infinite Vertical Plate
,”
ASME JOURNAL OF HEAT TRANSFER
, Vol.
84
, pp.
334
338
.
19.
Siegel
R.
,
1958
, “
Transient Free Convection From a Vertical Flat Plate
,”
Trans. ASME
, Vol.
80
, pp.
347
359
.
20.
Sparrow
E. M.
, and
Gregg
J. L.
,
1958
, “
Similar Solutions for Free Convection From a Nonisothermal Vertical Plate
,”
Trans. ASME
, Vol.
80
, pp.
379
386
.
21.
Sparrow
E. M.
, and
Gregg
J. L.
,
1960
, “
Nearly Quasi-Steady Free Convection Heat Transfer in Gases
,”
ASME JOURNAL OF HEAT TRANSFER
, Vol.
82
, pp.
258
260
.
22.
Vargas, J. V. C, 1994, “Combined Heat Transfer and Thermodynamics Problems With Applications in Refrigeration,” Ph.D. Thesis, Duke University, Durham, NC.
23.
Yang
J. W.
,
Scaccia
C
, and
Goodman
J.
,
1974
, “
Laminar Natural Convection About Vertical Plates With Oscillatory Surface Temperature
,”
ASME JOURNAL OF HEAT TRANSFER
, Vol.
96
, pp.
9
14
.
24.
Yovanovich, M. M., 1987, “On the Effect of Shape, Aspect Ratio and Orientation Upon Natural Convection From Isothermal Bodies of Complex Shape,” ASME HTD-Vol. 82, pp. 121–129.
This content is only available via PDF.
You do not currently have access to this content.