Enhancement of Natural Convection Heat Transfer and Development of High-Performance Heat Transfer Plate Using Grid Fins

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This research project consists of two parts. The one part is to investigate the heat transfer and fluid flow of natural convection over a horizontal, heated plate. The another part is to develop the enhancement technique for the natural convection heat transfer from a horizontal plate. In the first part, the special concern was directed to the local heat transfer characteristics over the heated plate. The following four regions were found to appear over the plate with the distance from the plate edge. These are (1)the laminar boundary layr region at the very vicinity of the plate edge, (2)the separation region, where the above boundary layr flow separates three-dimensionally, (3)the turbulent flow region and (4)the impinging flow region, where the main stream from the both edges impinge with each other and turn to the vertical direction. The heat transfer coefficients show minimum in the turbulent flow region which covers considerable portion of the plate. Thus, the key for the heat transfer enhancement exists in this region. In the second part, a technique was developed to increase the heat transfer coefficients of the turbulent region. For this purpose, rectangular grid fins were installed on the heated plate. The grids inhibit the mainstream from the edges to the center of the plate and promote the cellular motion within the grid. The apparent heat transfer coefficients of thus treated plate reached double and triple as much as those of the smooth plate, respectively, when the grids with height 10mm and 3mm were used.