Natural Convection From a Tube Bundle in a Thin Inclined Enclosure

2004 ◽  
Vol 126 (2) ◽  
pp. 702-709 ◽  
Author(s):  
W. Liu ◽  
J. H. Davidson ◽  
F. A. Kulacki
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Tube Bundle ◽  
Convection Heat Transfer ◽  
Constant Heat Flux ◽  
Working Fluid ◽  
Measured Temperature ◽  
Transfer Coefficients ◽  
Rectangular Array ◽  
Operating Modes

Natural convection heat transfer coefficients for a rectangular array of eight tubes contained in a thin enclosure of aspect ratio 9.3:1 and inclined at 30 deg to the horizontal are measured for a range of transient operating modes typical of a load side heat exchanger in unpressurized integral collector-storage systems. Water is the working fluid, and thermal charging is accomplished via a constant heat flux on the upper boundary. All other boundaries are well insulated. Results for isothermal and stratified enclosures yield the following correlation for the overall Nusselt number: NuD=0.728±0.002RaD0.25,4.0×105⩽RaD⩽1.4×107. The flow field in the enclosure is inferred from measured temperature distributions. The temperature difference that drives natural convection is also determined. The results extend earlier work for the case of a single tube and provide limiting case heat transfer data for a tube bundle that occupies the upper portion of the collector storage.

Natural Convection From a Tube Bundle in a Thin Inclined Enclosure

2003 ◽  
Author(s):  
Wei Liu ◽  
Jane H. Davidson ◽  
F. A. Kulacki
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Tube Bundle ◽  
Storage System ◽  
Convection Heat Transfer ◽  
Constant Heat Flux ◽  
Working Fluid ◽  
Measured Temperature ◽  
Transfer Coefficients ◽  
Rectangular Array

Natural convection heat transfer coefficients for a rectangular array of eight tubes contained in a thin enclosure of aspect ratio 9.3:1 and inclined at 30 degrees to the horizontal are measured for a range of transient operating modes typical of a load side heat exchanger in unpressurized integral collector-storage systems. Water is the working fluid, and thermal charging is accomplished via a constant heat flux on the upper boundary. All other boundaries are well insulated. Results for isothermal and stratified enclosures yield the following correlation for the overall Nusselt number: NuD=(0.728±0.002)RaD0.25,4.0×105≤RaD≤1.4×107. The flow field in the enclosure is inferred from measured temperature distributions. The temperature difference that drives natural convection is also determined. The results extend earlier work for the case of a single tube and provide limiting case heat transfer data for a tube bundle that occupies the upper portion of the collector storage system.

Natural Convection Heat Transfer Characteristics of Flat Plate Enclosures

1979 ◽  
Vol 101 (1) ◽  
pp. 120-125 ◽  
Author(s):  
K. R. Randall ◽  
J. W. Mitchell ◽  
M. M. El-Wakil
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Aspect Ratio ◽  
Tilt Angle ◽  
Convection Heat Transfer ◽  
Transfer Coefficients ◽  
Number Range ◽  
Grashof Number ◽  
Average Heat ◽  
Plate Spacing

Heat transfer by natural convection in rectangular enclosures has been experimentally studied using interferometric techniques. The effects of Grashof number, tilt angle, and aspect ratio on both the local and average heat transfer coefficients have been determined. The Grashof number range tested was 4 × 103 to 3.1 × 105, and the aspect ratio (ratio of enclosure length to plate spacing) varied between 9 and 36. The angles of tilt of the enclosure with respect to the horizontal were 45, 60, 75 and 90 deg. Correlations are developed for both local and average Nusselt number over the range of test variables. The effect of tilt angle is found to reduce the average heat transfer by about 18 percent from the value of 45 deg to that at 90 deg. No significant effect of aspect ratio over the range tested was found. A method for characterizing the flow regimes that is based on heat transfer mechanisms is proposed.

Experimental Investigation of Natural Convection Heat Transfer in Volumetrically Heated Spherical Segments

1996 ◽  
Vol 118 (1) ◽  
pp. 31-37 ◽  
Author(s):  
F. J. Asfia ◽  
B. Frantz ◽  
V. K. Dhir
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Convection Heat Transfer ◽  
Reactor Vessel ◽  
Core Material ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
External Cooling

External cooling of a light water reactor vessel by flooding of the concrete cavity with subcooled water is one of several management strategies currently being considered for accidents in which significant relocation of core material is predicted to occur. At present, uncertainty exists with respect to natural convection heat transfer coefficients between the pool of molten core material and the reactor vessel wall. In the present work, experiments were conducted to examine natural convection heat transfer in internally heated partially filled spherical pools with external cooling. In the experiments, Freon-113 was contained in a Pyrex bell jar, which was cooled externally with subcooled water. The pool was heated using a 750 W magnetron taken from a conventional microwave. The pool had a nearly adiabatic free surface. The vessel wall temperature was not uniform and varied from the stagnation point to the free surface. A series of chromel–alumel thermocouples was used to measure temperatures in both steady-state and transient conditions. Each thermocouple was placed in a specific vertical and radial location in order to determine the temperature distribution throughout the pool and along the inner and outer walls of the vessel. In the experiments, pool depth and radius were varied parametrically. Both local and averages heat transfer coefficients based on pool maximum temperature were obtained. Rayleigh numbers based on pool height were varied from 2 × 1010 to 1.1 × 1014. Correlations for the local heat transfer coefficient dependence on pool angle and for the dependence of average Nusselt number on Rayleigh number and pool depth have been developed.

An Experimental Investigation of Natural Convection With Vertical Cylinders in Mercury

1974 ◽  
Vol 96 (4) ◽  
pp. 455-458 ◽  
Author(s):  
L. E. Wiles ◽  
J. R. Welty
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Natural Convection ◽  
Flat Plate ◽  
Convection Heat Transfer ◽  
Vertical Cylinder ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Flat Plates

An experimental investigation of laminar natural convection heat transfer from a uniformly heated vertical cylinder immersed in an effectively infinite pool of mercury is described. A correlation was developed for the local Nusselt number as a function of local modified Grashof number for each cylinder. A single equation incorporating the diameter-to-length ratio was formulated that satisfied the data for all three cylinders. An expression derived by extrapolation of the results to zero curvature (the flat plate condition) was found to agree favorably with others’ work, both analytical and experimental. The influence of curvature upon the heat transfer was found to be small but significant. It was established that the effective thermal resistance through the boundary layer is less for a cylinder of finite curvature than for a flat plate. Consequently, local heat transfer coefficients for cylinders are larger than those for flat plates operating under identical conditions.

Numerical Study on Fluid Flow and Heat Transfer of Mixed Convection to a Stagnation Region From an Upward-Facing Horizontal Plate

2011 ◽  
Author(s):  
Akihiko Mitsuishi ◽  
Kenzo Kitamura
Keyword(s):  
Heat Transfer ◽  
Mixed Convection ◽  
Numerical Study ◽  
Infinite Plate ◽  
Convection Heat Transfer ◽  
Constant Heat Flux ◽  
Working Fluid ◽  
Stagnation Region ◽  
Typical Structure ◽  
Recent Experimental Study

Mixed convection heat transfer from an upward-facing horizontal semi-infinite plate to a stagnation region is studied by means of direct numerical simulation. All the cases studied are simulated under constant heat flux condition on the plate. Assuming that the working fluid is air at room temperature and pressure, the Prandtl number is kept at 0.71. The Reynolds and the modified Grashof numbers are in the ranges of 102−103 and 107−108, respectively. Longitudinal vortical structure, which was discovered in the recent experimental study, is successfully simulated. The typical structure appears as a pair of counter-rotating vortices being elongated over the plate. The relationship between this structure and the heat transfer rate is clarified. Characteristics of the vortices are investigated in detail.

Boundary Condition Dependent Natural Convection in a Rectangular Pool With Internal Heat Sources

2006 ◽  
Vol 129 (5) ◽  
pp. 679-682 ◽  
Author(s):  
Seung Dong Lee ◽  
Jong Kuk Lee ◽  
Kune Y. Suh
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Natural Convection ◽  
Convection Heat Transfer ◽  
Internal Heat ◽  
Working Fluid ◽  
Natural Convection Heat Transfer ◽  
Heat Sources ◽  
Internal Heat Sources ◽  
Volumetric Heat Generation

This paper presents results of steady-state experiments concerned with natural convection heat transfer of air in a rectangular pool in terms of the Nusselt number (Nu) versus the modified Rayleigh number (Ra′) varying from 109 to 1012. Cartridge heaters were immersed in the working fluid to simulate uniform volumetric heat generation. Two types of boundary conditions were adopted in the test: (I) top cooled, and (II) top and bottom cooled. The other sides were kept insulated. In the case of boundary condition II, the upward heat transfer ratio, Nuup∕(Nuup+Nudn), turned out to be 0.7–0.8 in the range of Ra′ between 1.05×1010 and 3.68×1011.

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