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RESEARCH PAPERS

J. Heat Transfer. 1962;84(3):193-204. doi:10.1115/1.3684336.

The influence of surface heat loss is treated analytically for unidimensional thermoelectric energy converters. Also, conditions are formulated whereby a gain in thermoelectric generator system efficiency can result from the transfer of heat from the thermoelectric conductors to a convecting fluid. While the general problem of the temperature distribution along the unidimensional conductor is described by a nonlinear differential equation, practical utility is demonstrated for linearization by assuring constant Thomson coefficient and mean-temperature properties within the range of most contemporary thermoelectric materials and applications. Influences of surface heat loss are discussed and demonstrated upon the longitudinal temperature distribution and the source and sink heat conduction rates.

Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1962;84(3):207-213. doi:10.1115/1.3684339.

The importance of surfare condition on nucleate boiling has long been recognized. It has also been known that only cavities of a narrow size range can be active nucleation sites. In order to define the size range of active cavities as a function of wall temperature or heat flux, a model is proposed. The model pictures a bubble nucleus at a site enveloped by a warm liquid. The nucleus will begin to grow into a bubble only when the surrounding liquid is sufficiently superheated. The time required for the liquid to attain this superheat is called the waiting period. The transfer of heat from the superheated liquid into the bubble is considered to be a transient conduction process. A cavity is considered effective only if the waiting period is finite. This criterion gives the limiting sizes of effective cavities. The equations show that maximum and minimum sizes of effective cavities are functions of subcooling, pressure of the system, physical properties, and the thickness of the superheated liquid layer. Comparison of theoretical prediction with experimental data from several sources was made. The fluids considered were ether, pentane, and water, with water under various degrees of subcooling. The theory did predict the incipience of boiling and size range of cavities successfully.

Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1962;84(3):217-224. doi:10.1115/1.3684344.

This paper is based on the PhD thesis investigation by H. Lurie [1] on the transient heat transfer from a vertical submerged metallic ribbon undergoing a step in Joule heating leading to boiling on its surface. The tests were made in deaerated distilled water at atmospheric pressure with pool temperatures at saturation and 112 deg F subcooled, and with heat generation rates per unit of ribbon surface area from nonboiling to 1.6 × 106 Btu/ft2 hr. Although the heat capacity of the ribbon is low, the surface temperature overshoot compared to the steady-state temperature is minor with values of less than 10 deg F. The time required to reach this overshoot, or the time required to reach steady state, is very short and decreases with increasing heat flux. These values are short compared to Goldstein and Eckert [2] and Siegel’s [3] estimates of the time required to develop the hydro-dynamic and thermal boundary layers in natural convection, and indicate that nucleate boiling heat transfer is probably a weak function of the fluid circulation. Some further support for this is evidenced by calculated transient temperatures based on steady nucleate boiling heat transfer which are in reasonable agreement with the measured performance.

Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1962;84(3):225-233. doi:10.1115/1.3684345.

A perturbation technique is used to obtain analytically the velocity and temperature oscillations in a laminar free convection boundary layer on a plane wall vibrating transversely. The problem is divided into high and low values of ω4x where ω and x are, respectively, the dimensionless frequency and distance from the leading edge. Solutions are compared by plotting the oscillating components of the wall shear stress and temperature gradient. Results in the intermediate region of ω4x are estimated by extrapolation of the solutions obtained for each limiting region.

Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1962;84(3):235-242. doi:10.1115/1.3684348.

The effectiveness and the heat transfer have been measured in a system involving the tangential injection of air from a single spanwise slot into the turbulent boundary layer of an external air stream, with the velocity of the external stream increasing in a way that concentrated the acceleration in a region downstream of the initial mixing zone. The effectiveness was changed but little from the value that would have existed had the free-stream velocity remained at its initial value and both temperature profiles and analytical considerations show that this invariability of the effectiveness is associated with thermal boundary-layer thicknesses that are much larger than the hydrodynamic thicknesses. Heat-transfer coefficients are shown to be predictable from existing information provided that the momentum thickness Reynolds number is large enough.

Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1962;84(3):245-250. doi:10.1115/1.3684351.

In order to achieve a better understanding of the physical mechanism of interaction between free convection and sound, an experimental investigation of the local heat-transfer coefficient around the circumference of a heated horizontal cylinder, both in the presence and absence of a strong stationary sound field, has been carried out. The results show that superposition of intense sound upon the free-convection temperature-velocity field about a heated horizontal cylinder increases the heat-transfer coefficient both on the under and upper portions of the cylinder’s surface. In the presence of a sound field for which SPL = 146 db (re 0.0002 microbar) and f = 1500 cps, the maximum measured increases in the local heat-transfer coefficient on the under and upper portions of a 3/4 -in-diam cylinder—relative to the free convection case at the same temperature potential—were found to be approximately 250 and 1200 per cent, respectively. A comparison of these results with earlier flow-visualization studies indicates that the relatively large percentage increase in the heat-transfer coefficient on the upper portion of the cylinder is caused by the oscillating vortex flow which is characteristic of thermoacoustic streaming. The reasons for the increase in the heat-transfer coefficient on the lower portion of the cylinder appear to be: (a) An increase in laminar boundary-layer velocities (steady components) in this region; and (b) modification of the boundary-layer temperature profile due to acoustically induced oscillations (unsteady components) within the laminar boundary layer. The experimental data presented can be used to check the validity of future analytical investigations of thermoacoustic phenomena.

Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1962;84(3):251-254. doi:10.1115/1.3684354.

An investigation has been made to determine the effect of low frequency oscillations of relatively large amplitude on the rate of heat transfer from a small horizontal wire to water. Frequencies from 0 to 4.25 cps and amplitudes to 2.76 in. were employed. Temperature differences up to 140 deg F provided heat flux from 2000 to 300,000 Btu/hr ft2 . A Reynolds number was defined based on the mean velocity of the wire, and it was shown that heat-transfer rates may be predicted by either forced, free, or mixed convection correlations depending on the relative magnitudes of Reynolds and Grashof numbers.

Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1962;84(3):257-261. doi:10.1115/1.3684359.

Forced convection heat transfer from a cylindrical heating element with crossflow occurs in many situations of practical interest, but heat-transfer coefficients for liquids have been reported in the literature only for Reynolds numbers below 200. This paper correlates new data taken with water and ethylene glycol at Reynolds numbers from 40 to 100,000 and Prandtl numbers from 1 to 300. The effects of temperature differences large enough to produce significant changes in viscosity across the boundary layer have also been investigated and are correlated in terms of a viscosity ratio.

Commentary by Dr. Valentin Fuster

DISCUSSIONS

TECHNICAL BRIEFS

Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1962;84(3):264-265. doi:10.1115/1.3684363.
Abstract
Topics: Flow (Dynamics)
Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1962;84(3):265-266. doi:10.1115/1.3684364.
Abstract
Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1962;84(3):266-267. doi:10.1115/1.3684365.

A method is developed for estimating the transient temperature on the surface of a slab initially at some uniform temperature and radiating to a sink at 0 deg R. Results of the calculations using finite difference techniques on an IBM 7090 computer are presented graphically in terms of dimensionless parameters.

Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1962;84(3):268. doi:10.1115/1.3684366.

This technical brief reports the results of an experimental investigation of the influence of horizontal transverse mechanical vibrations (frequency order of magnitude: 100 cps) upon the rate of convective heat transfer from a horizontal cylinder. The results of the experiments are compared with earlier findings. It is shown that, in spite of a tenfold difference in frequency (and amplitude), the heat-transfer correlations previously obtained for the case of horizontal acoustical vibrations [1] are also valid for horizontal mechanical vibrations, and that the character of the boundary-layer flow is the same (thermoacoustic streaming [2]) for these two cases.

Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1962;84(3):270-271. doi:10.1115/1.3684368.
Abstract
Topics: Emissions
Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1962;84(3):271-272. doi:10.1115/1.3684369.

Real surfaces involved in thermal radiation exchange processes do not emit or reflect radiation with equal intensity in all directions, i.e., the surfaces are not diffuse. Shape factors for two geometrical cases for surfaces which are electrical conductors are presented as well as an estimate of the error resulting from assumed Lambertonian radiation emission for one case.

Commentary by Dr. Valentin Fuster

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