Simultaneous Retrieval of Total Hemispherical Emissivity and Specific Heat From Transient Multimode Heat Transfer Experiments

2008 ◽  
Vol 130 (6) ◽  
Author(s):  
G. Venugopal ◽  
M. Deiveegan ◽  
C. Balaji ◽  
S. P. Venkateshan
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Specific Heat ◽  
Transient Response ◽  
Convection Heat Transfer ◽  
Simultaneous Estimation ◽  
Transfer Coefficients ◽  
Transient Heating ◽  
Number Range ◽  
Total Hemispherical Emissivity

Transient cooling experiments of a heated vertical aluminum plate with an embedded heater, in quiescent air, were conducted for the simultaneous estimation of total hemispherical emissivity and specific heat of the plate material. During cooling, the heat loss from the hot plate by natural convection and radiation was taken into account. During the experiments, plate temperatures were recorded at several locations using a data acquisition system. A numerically computed transient response of the plate is then compared with the experimentally known transient response to estimate the residual, the minimization of which using Levenberg–Marquardt’s iterative procedure retrieves the parameters pertinent to the problem. The experiments were conducted for three different surface emissivities of the plate obtained by using suitable surface treatment. A consistency test for the present approach was also done by conducting transient heating experiments using the retrieved values of parameters and a comparison of simulated and calculated natural convection heat transfer coefficients as a function of temperature. The experiments have been performed over a temperature range of 320–430K and a Rayleigh number range of 2×106–2×107. The emissivity values are in good agreement with previous reported results.

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.

Natural Convection Heat Transfer From a Plate in a Semicircular Enclosure

1992 ◽  
Vol 114 (1) ◽  
pp. 121-126 ◽  
Author(s):  
G. A. Moore ◽  
K. G. T. Hollands
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Rayleigh Number ◽  
Plate Thickness ◽  
Fluid Motion ◽  
Convection Heat Transfer ◽  
Bulk Fluid ◽  
Number Range ◽  
Balance Technique ◽  
Conductive Component

In the subject geometry, a long thin plate at uniform temperature is contained coaxially and symmetrically in a long semicircular trough closed at the top and having a uniform but different temperature. Heat flows across the air-filled region between the two by both natural convection and gaseous conduction. The problem of characterizing the free convective component of this heat transfer—that is, the component caused by bulk fluid motion—is treated experimentally by using a heat balance technique, with the measurements being repeated at different pressures, in order to cover a wide Rayleigh number range, from Ra ≈ 10 to Ra ≈ 108. Nusselt number versus Rayleigh number plots are presented for each of several combinations of plate-to-trough spacing and tilt angle, and the plots are correlated by equations. The problem of characterizing the conductive component is treated by numerically solving the steady diffusion equation in the air-filled region, and the results are correlated as a function of the spacing and the plate thickness.

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.

Natural Convection Heat Transfer From an Array of Rectangular Protrusions in an Enclosure Filled With Dielectric Liquid

1994 ◽  
Vol 116 (2) ◽  
pp. 138-147 ◽  
Author(s):  
Y. Joshi ◽  
M. D. Kelleher ◽  
M. Powell ◽  
E. I. Torres
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Vertical Wall ◽  
Convection Heat Transfer ◽  
Dielectric Liquid ◽  
Bottom Surface ◽  
Surface Boundary ◽  
Electronic Packages ◽  
Number Range ◽  
Surface Boundary Conditions

An experimental investigation of natural convection liquid immersion cooling of a three by three array of rectangular protrusions in an enclosure is presented. The heated elements geometrically simulated 20 pin dual-inline electronic packages and were mounted on a plexiglass substrate, which formed one vertical wall of a dielectric liquid filled rectangular enclosure. The remaining vertical boundaries of the enclosure were insulated, while the top and bottom were maintained at prescribed temperatures using individual heat exchanger plates. Protrusion surface temperatures in steady state are reported for a range of power dissipation levels for three fluorinert liquids spanning a Prandtl number range from about 20 to 1400. The influence of enclosure top and bottom surface boundary conditions and its width on element temperatures is investigated. Non-dimensional heat transfer results are empirically correlated. Changes in component temperatures due to partial powering of the array are also measured.

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 From Horizontal Rectangular Fin Arrays

1967 ◽  
Vol 89 (1) ◽  
pp. 32-38 ◽  
Author(s):  
F. Harahap ◽  
H. N. McManus
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Flow Field ◽  
Convection Heat Transfer ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Transfer Coefficients ◽  
Average Heat ◽  
Heat Transfer Coefficients

Average heat-transfer coefficients are presented for fin arrays positioned with the base oriented horizontally. The flow field associated with the natural convection from the fin arrays was investigated and used as a model to find parameters to generalize the data. The proposed correlation overcomes the inadequacy of parameters available previously for horizontal rectangular fins.

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