社団法人日本機械学会 Acta Medica Okayama 0387-5016 62 594 1996 比較的浅い底面加熱を受ける上部開放矩形くぼみに球状粒子を一段充填した場合の共存対流熱伝達 : 第2報, くぼみ長さの効果 330 337 EN Koichi Ozaki Hideo Inaba Forced-natural-mixed convection heat transfer characteristics of a one-stage spherical particle layer in an air flow are investigated experimentally. The one-stage spherical particle layer is provided in a rectangular cavity having a heating bottom surface and is installed at the lower part of a rectangular air channel. Three types of spherical particles, which have almost the same diameter (about 10 mm) but different thermal conductivities, are tested. The cavity length is varied from 19.6 mm to 90 mm, and the cavity depth is varied between 0 mm and 10 mm. The variation of the heat transfer coefficient with the length of the heating surface can be explained by the flow behavior around the particle layer ; that is, the case of the zero cavity depth, the flow is suppressed by the particles within about three rows from the leading edge. Therefore, the heat transfer coefficient increases with a derease in the length of the heating surface. In the case with a shorter heating surface (about twice the diameter of the particle), a considerable increase in the heat transfer coefficient is achieved because the flow from the upstream runs through the particle layer. In the case of the cavity depth having almost the same value as the diameter of the particles, air flows over the particle layer and air near the cavity bottom is almost still. In this case, a decrease of the length of the heat transfer surface decreases the extent of the flow in the depth direction, and the heat transfer coefficient is also decreased. The heat transfer coefficient can be expressed as a nondimensional heat transfer correlation, where the effects of the cavity length, the cavity depth, the air velocity and the temperature difference between the air and the bottom surface of the cavity are taken into consideration. No potential conflict of interest relevant to this article was reported.