Showing papers by "Ephraim M Sparrow published in 1977"

Analysis of melting in the presence of natural convection in the melt region

Abstract: An analysis of multidimensional melting is performed which takes account of natural convection induced by temperature differences in the liquid melt. Consideration is given to the melt region created by a heated vertical tube embedded in a solid which is at its fusion temperature. Solutions were obtained by an implicit finite-difference scheme tailored to take account of the movement of the liquid-solid interface as melting progresses. The results differed decisively from those corresponding to a conventional pure-conduction model of the melting problem. The calculated heat transfer rate at the tube wall decreased at early times and attained a minimum, then increased and achieved a maximum, and subsequently decreased. This is in contrast to the pure conduction solution whereby the heat transfer rate decreases monotonically with time. The thickness of the melt region was found to vary along the length of the tube, with the greatest thickness near the top. This contrasts with the uniform thickness predicted by the conduction solution. These findings indicate that natural convection effects, although unaccounted for in most phase change analyses, are of importance and have to be considered.

Heat transfer and fluid flow analysis of interrupted-wall channels with application to heat exchangers

Abstract: An analysis has been made of laminar flow and heat transfer in channels whose walls are interrupted periodically along the streamwise direction. Such channels are frequently employed in high-performance compact heat exchangers. Numerical solutions of the mass, momentum, and energy conservation equations yielded local heat transfer and pressure drop results. These results were obtained for a range of Reynolds numbers and for several values of a dimensionless geometrical parameter characterizing the streamwise length L of the individual plate segments which make up the interrupted walls. The Prandtl number was fixed at 0.7 for all the calculations. The basic heat transfer and pressure drop results were employed to investigate whether an interrupted-wall channel experiences an augmented heat transfer rate compared with that for a parallel plate channel. For conditions of equal heat transfer surface area and equal pumping power, appreciably higher heat transfer rates prevailed in the interrupted-wall channel for a wide range of operating conditions. The augmentation was especially marked for relatively short channels and high Reynolds numbers. The results also demonstrated the existence of a new type of fully developed regime, one that is periodic. At sufficiently large downstream distances, the velocity and temperature profiles repeat their values at successive axial stations separated by a distance 2L and, in addition, the average heat transfer coefficient for a plate segment takes on a constant value.