Jack Waldvogel - Academia.edu (original) (raw)
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Papers by Jack Waldvogel
International Journal of Heat and Mass Transfer, 1989
Abstract An experimental investigation of the heat transfer by combined convection from a smooth,... more Abstract An experimental investigation of the heat transfer by combined convection from a smooth, isothermal cubic cavity with a variety of side-facing apertures is described. The study was motivated by the desire to predict the convective loss from large solar thermal-electric receivers and to understand the mechanisms which control this loss. Hence, emphasis is placed on the large Rayleigh number, Ra, and large Reynolds number. Re, regimes; on Richardson numbers, Ri, of the order of unity; and on large ratios of the cavity wall temperature, Tw, to the ambient temperature, T∞. The data which are presented cover the ranges: 1
A combined theoretical and experimental study is reported which investigates remelting phenomena ... more A combined theoretical and experimental study is reported which investigates remelting phenomena during the splat cooling of two liquid-metal droplets impacting sequentially on a substrate. Under conditions of sufficiently high superheat it was proposed theoretically and demonstrated experimentally that an initial deposit is remelted by the subsequent impact of molten material. It is shown that the amount of superheat as well as the variation of thermophysical properties, particularly the latent heat and the melting temperature, influence the degree of remelting. Experimental findings supported to a certain extent the theoretical model assumptions that the splats could be represented by thin discs and that the heat transfer and solidification within the splat propagates in the axial direction only. However, the experiments showed that these assumptions are better suited for the central region of the splat. The occurrence of remelting often depended on the radial location for a given amount of superheat. For most part, the splat exhibited globular microstructure. Lamellar structures were observed near the top and the periphery of the splat, indicating slower cooling rates at these locations. The theoretical model constituted a good compromise between accuracy and simplicity and predicted the correct trends of the remelting phenomenon. Nomenclature V c Specific heat (J kg-1 K-1) z d Diameter of a spherical droplet (ram) Az D Diameter of the splat (ram) h, Convective heat-transfer coefficient 9 (W m-2 K-1) hc Contact heat-transfer coefficient (Win-2 K-s)
International Journal of Heat and Mass Transfer, 1989
Abstract An experimental investigation of the heat transfer by combined convection from a smooth,... more Abstract An experimental investigation of the heat transfer by combined convection from a smooth, isothermal cubic cavity with a variety of side-facing apertures is described. The study was motivated by the desire to predict the convective loss from large solar thermal-electric receivers and to understand the mechanisms which control this loss. Hence, emphasis is placed on the large Rayleigh number, Ra, and large Reynolds number. Re, regimes; on Richardson numbers, Ri, of the order of unity; and on large ratios of the cavity wall temperature, Tw, to the ambient temperature, T∞. The data which are presented cover the ranges: 1
A combined theoretical and experimental study is reported which investigates remelting phenomena ... more A combined theoretical and experimental study is reported which investigates remelting phenomena during the splat cooling of two liquid-metal droplets impacting sequentially on a substrate. Under conditions of sufficiently high superheat it was proposed theoretically and demonstrated experimentally that an initial deposit is remelted by the subsequent impact of molten material. It is shown that the amount of superheat as well as the variation of thermophysical properties, particularly the latent heat and the melting temperature, influence the degree of remelting. Experimental findings supported to a certain extent the theoretical model assumptions that the splats could be represented by thin discs and that the heat transfer and solidification within the splat propagates in the axial direction only. However, the experiments showed that these assumptions are better suited for the central region of the splat. The occurrence of remelting often depended on the radial location for a given amount of superheat. For most part, the splat exhibited globular microstructure. Lamellar structures were observed near the top and the periphery of the splat, indicating slower cooling rates at these locations. The theoretical model constituted a good compromise between accuracy and simplicity and predicted the correct trends of the remelting phenomenon. Nomenclature V c Specific heat (J kg-1 K-1) z d Diameter of a spherical droplet (ram) Az D Diameter of the splat (ram) h, Convective heat-transfer coefficient 9 (W m-2 K-1) hc Contact heat-transfer coefficient (Win-2 K-s)