Effect of Vibration on Heat Transfer From Spheres

1969 ◽  
Vol 91 (3) ◽  
pp. 337-343 ◽  
Author(s):  
C. B. Baxi ◽  
A. Ramachandran
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Free Convection ◽  
Flow Velocity ◽  
Forced Convection ◽  
Vertical Plane ◽  
Convection Heat Transfer ◽  
Transfer Coefficients ◽  
Sinusoidal Vibration ◽  
Vibrational Velocity

The effect of vibration on free and forced convection heat transfer from spheres was investigated. Test spheres made of copper were subjected to sinusoidal vibration in the vertical plane, this being perpendicular to the direction of airstream in the case of forced convection studies. In free convection studies the amplitude of vibration was varied from 4 mm to 25.5 mm and the frequency of vibration from 150 cpm to 930 cpm. It was found that the effect of vibration on Nusselt number was negligible for values of vibrational Reynolds number less than 200. For values of vibrational Reynolds number greater than 200, the vibration increased the heat transfer coefficient considerably and values of heat transfer coefficients as high as seven times the free convection values without vibration were obtained. The following correlations were obtained for heat transfer from spheres to air: freeconvectionwithoutvibration,NNu=2+0.401(NGr)0.25for4×103<NGr<6×104 and free convection with vibration: hvho=0.83(NRe)v0.5(a/D)0.1(NGr)0.251.28 In the case of forced convection studies with vibration, the amplitude of vibrations varied between 4 mm and 12.4 mm, and the frequency of vibration from 200 cpm to 1600 cpm. The flow velocity was varied from 24.5 ft/sec to 84 ft/sec. The results in the absence of vibration could be represented by: NNu = 0.304 (NRe)0.56 or NNu = 2 + 0.222 (NRe)0.587 in the range 6 × 103 < NRe < 3.3 × 104. Nusselt numbers were not found to be affected by the imposition of vibrational velocity even as high as 19.6 percent of the flow velocity.

Effects of Free Convection and Axial Conduction on Forced-Convection Heat Transfer Inside a Vertical Channel at Low Peclet Numbers

1984 ◽  
Vol 106 (2) ◽  
pp. 297-303 ◽  
Author(s):  
L. C. Chow ◽  
S. R. Husain ◽  
A. Campo
Keyword(s):  
Heat Transfer ◽  
Free Convection ◽  
Forced Convection ◽  
Convection Heat Transfer ◽  
Vertical Channel ◽  
Reynolds Numbers ◽  
Convection Heat ◽  
Constant Property ◽  
Axial Conduction ◽  
Forced Convection Heat Transfer

A numerical investigation was conducted to study the simultaneous effects of free convection and axial conduction on forced-convection heat transfer inside a vertical channel at low Peclet numbers. Insulated entry and exit lengths were provided in order to assess the effect of upstream and downstream energy penetration due to axial conduction. The fluid enters the channel with a parabolic velocity and uniform temperature profiles. A constant-property (except for the buoyancy term), steady-state case was assumed for the analysis. Results were categorized into two main groups, the first being the case where the channel walls were hotter than the entering fluid (heating), and the second being the reverse of the first (cooling). For each group, heat transfer between the fluid and the walls were given as functions of the Grashof, Peclet, and Reynolds numbers.

A Study of Forced Convection Direct Air Cooling in the Downstream Vicinity of Heat Sinks

1990 ◽  
Vol 112 (3) ◽  
pp. 234-240 ◽  
Author(s):  
G. L. Lehmann ◽  
S. J. Kosteva
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Heat Sink ◽  
Convection Heat Transfer ◽  
Heat Sinks ◽  
Air Cooling ◽  
Transfer Coefficients ◽  
Packaging System ◽  
Transfer Rates ◽  
Heat Transfer Coefficients

An experimental study of forced convection heat transfer is reported. Direct air cooling of an electronics packaging system is modeled by a channel flow, with an array of uniformly sized and spaced elements attached to one channel wall. The presence of a single or complete row of longitudinally finned heat sinks creates a modified flow pattern. Convective heat transfer rates at downstream positions are measured and compared to that of a plain array (no heat sinks). Heat transfer rates are described in terms of adiabatic heat transfer coefficients and thermal wake functions. Empirical correlations are presented for both variations in Reynolds number (5000 < Re < 20,000) and heat sink geometry. It is found that the presence of a heat sink can both enhance and degrade the heat transfer coefficient at downstream locations, depending on the relative position.

Optimum Arrangement of Rectangular Fins on Horizontal Surfaces for Free-Convection Heat Transfer

1970 ◽  
Vol 92 (1) ◽  
pp. 6-10 ◽  
Author(s):  
Charles D. Jones ◽  
Lester F. Smith
Keyword(s):  
Heat Transfer ◽  
Free Convection ◽  
Design Method ◽  
Convection Heat Transfer ◽  
Transfer Coefficients ◽  
Maximum Heat ◽  
Heat Transfer Coefficients ◽  
Maximum Heat Transfer ◽  
Optimum Arrangement ◽  
Free Convection Heat

Experimental average heat-transfer coefficients for free-convection cooling of arrays of isothermal fins on horizontal surfaces over a wider range of spacings than previously available are reported. A simplified correlation is presented and a previously available correlation is questioned. An optimum arrangement for maximum heat transfer and a preliminary design method are suggested, including weight considerations.

Heat Transfer to Supercritical Water in Smooth-Bore Tubes

1965 ◽  
Vol 87 (4) ◽  
pp. 477-483 ◽  
Author(s):  
H. S. Swenson ◽  
J. R. Carver ◽  
C. R. Kakarala
Keyword(s):  
Heat Transfer ◽  
Forced Convection ◽  
Supercritical Water ◽  
Convection Heat Transfer ◽  
Physical Property ◽  
Transfer Coefficients ◽  
Property Variation ◽  
Wide Range ◽  
Fully Developed Turbulent Flow ◽  
Data Points

Local forced convection heat-transfer coefficients for supercritical water flowing inside smooth-bore tubes were obtained experimentally over a range of pressures (3300 to 6000 psia) and bulk temperatures (167 to 1068 F). Because the thermophysical properties of supercritical fluids change rapidly with temperature in the pseudocritical range, conventional forced convection correlations were unable to fit the data. However, a satisfactory correlation for fully developed turbulent flow was obtained by properly modifying the conventional nondimensional model to account for the physical property variation across the boundary layer. Out of 2951 data points, 95 percent lie within ±15 percent of the correlation. It was also found that the same equation correlated supercritical pressure heat-transfer data of carbon dioxide over a wide range of conditions with good accuracy.

Transient Forced Convection Heat Transfer to Helium During a Step in Heat Flux

1983 ◽  
Vol 105 (2) ◽  
pp. 350-357 ◽  
Author(s):  
P. J. Giarratano ◽  
W. G. Steward
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Forced Convection ◽  
Carbon Film ◽  
Convection Heat Transfer ◽  
Fast Response ◽  
Operating Conditions ◽  
Convection Heat ◽  
Transfer Coefficients ◽  
Forced Convection Heat Transfer

Transient forced convection heat transfer coefficients for both subcritical and supercritical helium in a rectangular flow channel heated on one side were measured during the application of a step in heat flux. Zero flow data were also obtained. The heater surface which served simultaneously as a thermometer was a fast response carbon film. Operating conditions covered the following range: Pressure, 1.0 × 105 Pa (1 bar) to 1.0 × 106 Pa (10 bar); Temperature, 4 K–10 K; Heat Flux, 0.1 W/cm2−10 W/cm2; Reynolds number, 0–8 × 105. The experimental data and a predictive correlation are presented.

Experimental Study of Forced Convection From Isothermal Circular and Square Cylinders and Toroids

1997 ◽  
Vol 119 (1) ◽  
pp. 70-79 ◽  
Author(s):  
G. Refai Ahmed ◽  
M. M. Yovanovich
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Forced Convection ◽  
Convection Heat Transfer ◽  
Reynolds Numbers ◽  
Empirical Models ◽  
Experimental Program ◽  
Convection Heat ◽  
Forced Convection Heat Transfer ◽  
Wide Range

Experimental studies of forced convection heat transfer from different body shapes were conducted to determine the effects of Reynolds number and different characteristic body lengths on the area-averaged Nusselt number. Although the bodies differed significantly in their shapes, they had approximately the same total surface area, A = 11,304 mm2 ± 5%. This ensured that for a given free stream velocity and total heat transfer rate all bodies had similar trends for the relationship of Nusselt and Reynolds numbers. The experimental program range was conducted in the Reynolds number range 104≤ReA≤105 and Prandtl number 0.71. Finally, the empirical models for forced convection heat transfer were developed. These empirical models were valid for a wide range of Reynolds numbers 0≤ReA≤105. The present experimental correlations were compared with available correlation equations and experimental data. These comparisons show very good agreement.

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