Combined Natural Convection–Conduction and Radiation Heat Transfer in a Discretely Heated Open Cavity

1996 ◽  
Vol 118 (1) ◽  
pp. 56-64 ◽  
Author(s):  
A. A. Dehghan ◽  
M. Behnia
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Source ◽  
Radiation Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Radiation Heat ◽  
Transfer Coefficients ◽  
Thermal Fields ◽  
Discrete Heat Source

Combined natural convection, conduction, and radiation heat transfer in an open-top upright cavity containing a discrete heat source has been modeled numerically. The surface emissivity has been varied and its effects on the flow and thermal fields have been determined for different values of Rayleigh number. The complex interaction of the three modes of heat transfer mechanisms is explored by solving the coupled convection, conduction, and radiation equations. It is noted that the inclusion of radiation has a significant effect on the flow, resulting in the formation of a recirculation zone within the cavity. Comparison of the local heat transfer coefficients for the conjugate analysis and no radiation case reveals that the inclusion of radiation has a negligible effect on the heat transfer performance of the heat source. However, comparison of the numerical results with experimental observations shows that accurate prediction of the flow and thermal fields is strongly dependent on the consideration of radiation heat transfer in the numerical case.

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.

scholarly journals Effect of Heat Source Placement on Natural Convection from Cylindrical Surfaces

Energies ◽  
2020 ◽  
Vol 13 (17) ◽  
pp. 4334
Author(s):  
Andrej Kapjor ◽  
Peter Durcansky ◽  
Martin Vantuch
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Source ◽  
Theoretical Models ◽  
Heat Transfer Process ◽  
Heat Output ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Thermal Fields ◽  
Horizontal Cylinders

Placement of heat source can play a significant role in final heat output, or heat source effectivity. Because of this, there is a need to analyze thermal fields of the heat exchange system by natural convection, where the description by criterion equations is desired, as the net heat output from tubes can be quantified. Based on known theoretical models, numerical methods were adapted to calculate the heat output with natural air flow around tubes, where mathematical models were used to describe the heat transfer more precisely. After validation of heat transfer coefficients, the effect of wall and heat source placement was studied, and the Coanda effect was also observed. The heat source placement also has an effect at the boundary layer, which can change and therefore affect the overall heat transfer process. The optimal wall-to-cylinder distance for an array of horizontal cylinders near a wall was also expressed as a function of the Rayleigh number and number of cylinders in the array.

scholarly journals Turbulent Natural Convection from a Vertical Plane Surface

1968 ◽  
Vol 90 (1) ◽  
pp. 1-6 ◽  
Author(s):  
R. Cheesewright
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Natural Convection ◽  
Vertical Plane ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Convection Boundary Layer ◽  
Transfer Coefficients ◽  
Turbulent Natural Convection ◽  
Heat Transfer Coefficients

The paper reports the results of an experimental investigation which was intended to clarify the present uncertain position with regard to the distributions of mean temperature and mean velocity in a turbulent natural-convection boundary layer. Data reported for the turbulent boundary layer for Grashof numbers between 1010 and 1011 include local heat transfer coefficients as well as temperatures and velocities. Local heat transfer coefficients and temperature distributions are also reported for the laminar and transitional boundary-layer regions. Results are compared with other experimental data and with theoretical predictions.

Natural Convection Heat Transfer From a Staggered Vertical Plate Array

1993 ◽  
Vol 115 (4) ◽  
pp. 938-945 ◽  
Author(s):  
G. Tanda
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Vertical Plate ◽  
Convection Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

An experimental study was performed to evaluate the natural convection heat transfer characteristics of an array of four staggered vertical plates. The thermal input at each plate was the same or differed from plate to plate depending on various heating modes. The effects of the interplate spacing and the plate-to-ambient temperature difference were investigated. The experiments were performed in air. Convective interactions among the plates were identified by examining the per-plate heat transfer coefficients and the local heat transfer coefficients along the vertical sides of plates. Local heat transfer results were obtained by means of the schlieren quantitative technique. Comparison of local heat transfer coefficients along the plate assembly with those of a continuous vertical plate (having the same height) showed enhancements up to a factor of two. Comparison of average heat transfer results with those for a parallel plate channel having the same exchanger size showed only little reductions in heat transfer rate, despite a 28 percent reduction in heat transfer area, with enhancements, in terms of specific heat flux, up to 30 percent.

An Experimental Study of Natural Convection Heat Transfer in Concentric and Eccentric Horizontal Cylindrical Annuli

1978 ◽  
Vol 100 (4) ◽  
pp. 635-640 ◽  
Author(s):  
T. H. Kuehn ◽  
R. J. Goldstein
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Natural Convection ◽  
Convection Heat Transfer ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Transfer Coefficients ◽  
Laminar Convection

An experimental study has been conducted to determine the influence of eccentricity and Rayleigh number on natural convection heat transfer through a fluid bounded by two horizontal isothermal cylinders. Eccentricity of the inner cylinder substantially alters the local heat transfer on both cylinders, but the overall heat transfer coefficients change by less than 10 percent over the range of eccentricities investigated. Heat transfer results using the concentric geometry are given for Rayleigh numbers from 2.2 × 102 to 7.7 × 107 which includes regions of conduction, laminar convection, and partially turbulent convection.

Heat Transfer of Melting Nonadecane Spheres in Natural Convection of Water

2005 ◽  
Author(s):  
Yuta Tanaka ◽  
Makoto Hishida ◽  
Gaku Tanaka
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Shape Transformation ◽  
Heat Transfer Coefficients ◽  
Lower Hemisphere ◽  
Transfer Study ◽  
Good Agreement

This paper deals with experimental and analytical heat transfer study of nonadecane spheres melting in natural convection of water. Experimental local and average heat transfer coefficients were obtained by analyzing photo images of the shape transformation of the nonadecane spheres. The relevant dimensionless parameters were varied in the ranges of 1.8×107 ≤ Grn·Prn ≤ 1.8×108 and 0.04 ≤ CnΔT/Ln ≤ 0.16. We found that (1) the melting nonadecane sphere was covered with thin nonadecane liquid film flowing upwards along the sphere to make a liquid cap on the top. The cap regularly repeated formation and splitting off, (2) on the lower hemisphere the experimental local heat transfer coefficients were slightly higher than the analytical ones and on the upper hemisphere the experimental local heat transfer coefficients were slightly lower than the analytical ones, and (3) the experimental average Nusselt number was correlated by Nu = 0.151 (Grn·Prn)0.257(CnΔT/Ln)0.117 that was in good agreement with the theoretical one.

The Effect of Regulating Elements on Convective Heat Transfer along Shaped Heat Exchange Surfaces

2013 ◽  
Vol 34 (1) ◽  
pp. 5-16 ◽  
Author(s):  
Jozef Cernecky ◽  
Jan Koniar ◽  
Zuzana Brodnianska
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Cfd Simulation ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Temperature Fields ◽  
Transfer Coefficients ◽  
Heat Transfer Intensification ◽  
Heat Transfer Coefficients ◽  
Forced Air

Abstract The paper deals with a study of the effect of regulating elements on local values of heat transfer coefficients along shaped heat exchange surfaces with forced air convection. The use of combined methods of heat transfer intensification, i.e. a combination of regulating elements with appropriately shaped heat exchange areas seems to be highly effective. The study focused on the analysis of local values of heat transfer coefficients in indicated cuts, in distances expressed as a ratio x/s for 0; 0.33; 0.66 and 1. As can be seen from our findings, in given conditions the regulating elements can increase the values of local heat transfer coefficients along shaped heat exchange surfaces. An optical method of holographic interferometry was used for the experimental research into temperature fields in the vicinity of heat exchange surfaces. The obtained values correspond very well with those of local heat transfer coefficients αx, recorded in a CFD simulation.

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