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Showing papers in "Journal of Heat Transfer-transactions of The Asme in 1969"


Journal ArticleDOI
TL;DR: In this article, the spectral absorption coefficient and the total emissivities of soot suspensions were calculated for the room temperature optiaI.1 and 2.5-1O.
Abstract: Data on the room temperature optiaI.1 constants of soot are presentedfor the 'Wavelength regions 0.4-().8j.1 and 2.5-1O.0j.l. Dispersion formulas are developedfor interpolating the data between0.8 and 2.5j.1. The results are used to calculate the spectral absorption coefficient and the total emissivities of soot suspensions. It is shown that the correct values of the optiaI.l constants are neededin the use of light-scattering techniques for the measurement of the soot concentration but that uncertainties introduced in flux

746 citations




Journal ArticleDOI
TL;DR: Heat finite propagation velocity effects on temperature distribution and heat flux for step temperature change at semi-infinite body surface were studied in this article, where the authors considered a semi-inverse body surface.
Abstract: Heat finite propagation velocity effects on temperature distribution and heat flux for step temperature change at semiinfinite body surface

210 citations


Journal ArticleDOI
TL;DR: In this article, the authors developed an analysis based on the integration of the transport equations to predict the deterioration in heat transfer at high heat fluxes, and the results have been compared with the previously available experimental results for steam.
Abstract: At slightly supercritical pressure and in the neighborhood of the pseudo-critical temperature (defined as the temperature corresponding to the peak in specific heat at the operating pressure), the heat transfer coefficient between fluid and tube wall is strongly dependent on the heat flux. For large heat fluxes, a marked deterioration takes place in the heat transfer coefficient in the region where the bulk fluid temperature is below and the wall temperature above the pseudo-critical temperature. An analysis has been developed, based on the integration of the transport equations, to predict the deterioration in heat transfer at high heat fluxes, and the results have been compared with the previously available experimental results for steam. Experiments have been performed with carbon dioxide for additional comparison. Limits of safe operation in terms of the allowable heat flux for a particular flow rate have been determined both theoretically and experimentally. Experiments with twisted tape inserted in the test section to generate swirl have shown that the heat transfer rates can be improved by this method. Qualitative visual observations have been made of the flow under varying conditions of heat flux and flow rate.

172 citations



Journal ArticleDOI
TL;DR: In this article, an experimental investigation on turbulent natural convection boundary layers has been conducted with water on a vertical plate of constant heat flux, with the emphasis on the turbulent regime.
Abstract: An experimental investigation on turbulent natural convection boundary layers has been conducted with water on a vertical plate of constant heat flux. Local heat transfer data are presented for laminar, transition, and turbulent natural convection, with the emphasis on the turbulent regime. The data extend to a modified Rayleigh number of 1016 for a threefold range in Prandtl number. The results indicate that natural transition occurs in the range 1012 < Ra* < 1014 ; i.e., fully developed turbulent flow occurs by Ra* = 104 . This latter value can be as low as 2 × 1013 with the use of a trip rod. The physical structure of the turbulent boundary-layer flow was studied using the combined time-streak marker hydrogen bubble method. Temperature data and temperature corrected velocity data obtained by hot-film sensors are presented for Ra* values between 8.7 × 1013 and 7.1 × 1014 . For the range of variables investigated, the major conclusions are (a) the local heat transfer coefficient exhibits a slight decrease with length, (b) confirmation that the vortex street layer in the transition region decays into a longitudinal-vortex-type structure, and (c) the outer portion of the thermal and velocity fields can be approximated by power profiles that fit almost all the data available to date.

169 citations











Journal ArticleDOI
TL;DR: In this article, a general method of analysis is presented for determining the developing velocity field and pressure drop for laminar flow in the entrance region of ducts having arbitrary cross sections.
Abstract: A general method of analysis is presented for determining the developing velocity field and pressure drop for laminar flow in the entrance region of ducts having arbitrary cross sections. Application of the solution method is made to rectangular ducts and to triangular ducts. Available experimental data are compared with the analytical results and good agreement is found to prevail. Development characteristics for six ducts are brought together and compared, and various trends are identified.





Journal ArticleDOI
TL;DR: In this article, columnar, counterrotating, vertical vortices were produced on a heated, vertical, flat plate under free-convection conditions in air using a high-voltage d-c electric field.
Abstract: Experimental results are presented to show that columnar, counterrotating, vertical vortices can be produced on a heated, vertical, flat plate under free-convection conditions in air using a high-voltage d-c electric field. The vortices result from the corona discharge on 0.002-in.-dia parallel wires of alternate high voltage and ground potential placed vertically on the surface of a phenolic laminate plate. Heat-transfer rates are measured using an energy-balance method, and the thermal boundary layer is made visible using a Mach-Zehnder interferometer. Experimental curves are presented to illustrate the increase in the heat-transfer rate with increase in the electric-field power. Interference photographs and frames from a motion picture show the effects of the vortices on the thermal boundary layer. The convective part of the heat transfer from the 10 × 10 in. plate is more than doubled before the electric-field power becomes as large as 5 percent of the increase in the heat-transfer rate. Local heat-transfer rates are highest at the high-voltage wires and lowest at the grounded wires.



Journal ArticleDOI
TL;DR: In this paper, heat transfer by combined free and forced convection from a heated tube to a transverse air stream has been experimentally studied over a wide range of Grashof and Reynolds numbers.
Abstract: Heat transfer by combined free and forced convection from a heated tube to a transverse air stream has been experimentally studied over a wide range of Grashof and Reynolds numbers. The data obtained have been correlated with Gr/Re2.5 as the correlating parameter. Criteria for transition from free convection to combined convection and from combined convection to forced convection have also been obtained.