Showing papers by "Raymond Viskanta published in 1990"
Journal Article•
TL;DR: In this paper, the effects of a nonuniform velocity profile on the local convection coefficient for a uniform heat flux surface were investigated on a planar, free surface jet of water.
Abstract: Experiments have been conducted on a planar, free surface jet of water to investigate the effects of a nonuniform velocity profile on the local convection coefficient for a uniform heat flux surface. Heat transfer coefficient distributions were measured for heat fluxes ranging from 0.24 to 1.47 MW/m 2 and for Reynolds numbers (based on the average nozzle velocity and nozzle width) from 15,000 to 54,000
44 citations
TL;DR: In this article, the effects of a non-uniform velocity profile on the local convection coefficient for a uniform heat flux surface were investigated on a planer, free surface jet of water.
Abstract: Experiments have been conducted on a planer, free surface jet of water to investigate the effects of a nonuniform velocity profile on the local convection coefficient for a uniform heat flux surface. Heat transfer coefficient distributions were measured for heat fluxes ranging from 0.24 to 1.47 MW/m{sup 2}and for Reynolds numbers (based on the average nozzle velocity and nozzle width) from 15,000 to 54,000. This range of flow conditions yielded turbulent velocity profiles similar to those of channel flow. Results have been obtained for both single-phase convection and nucleate boiling. Relative to results for a uniform velocity profile, the nonuniform profile was found to enhance heat transfer significantly. However, enhancement is attributed primarily to increased levels of turbulence and only secondarily to changes in the velocity profile.
42 citations
TL;DR: In this article, an experimental measurement of the dynamic internal temperature distribution in soda-lime glass plates using thermocouples fused in the glass has been carried out and the results showed that a 20% increase in phonon conductivity significantly improved the agreement between measured and predicted centerline to surface temperature differences.
Abstract: Experimental measurement of the dynamic internal temperature distribution in soda-lime glass plates using thermocouples fused in the glass has been carried out. Experimentally measured temperatures are compared to predictions obtained from the solution of the transient energy equation where the internal radiative transfer has been accounted for using rigorous radiative transfer theory. A discussion of the experimental method, the process used to fuse the thermocouples in the test plates and the rigorous formulation of the energy equation, for semitransparent materials is given. Predicted and measured instantaneous surface temperatures are compared and very good agreement is obtained. It is also concluded that the empriical equation for the phonon conductivity used in the analysis underpredicts the conductivity. A 20% increase in phonon conductivity is shown to significantly improve the agreement between measured and predicted centerline to surface temperature differences.
34 citations
TL;DR: An active thermal insulation system consisting of a semitransparent porous medium with gas injection is considered for protecting a structure from intense radiation flux (≈5 MWm −2 ).
6 citations
TL;DR: In this paper, the effect of augmenting or opposing thermal and solutal body forces on the flow, temperature and concentration distributions of a single-component fluid was analyzed and shown to be very similar to that for a single component fluid.
Abstract: Results are presented that illustrate the effect of augmenting or opposing thermal and solutal body forces on the flow, temperature and concentration distributions. For augmenting buoyancy forces, the flow field is very similar to that for a single-component fluid. Multicellular flow patterns are observed for opposing buoyancy forces that depend on the buoyancy parameter. The solutal buoyancy force does not dominate the flow field for all values of opposing body forces, because the solutal gradient is vertical. The concentration gradient affects the natural convection through both the additional buoyancy force and the thermophysical properties of the gas mixture.