FLUID FLOW AND HEAT TRANSFER OF NATURAL CONVECTION AROUND MULTIPLE HEAT SOURCES PLACED IN THE SAME HORIZONTAL PLANE

本文对同一水平面内多个热源的自然对流羽流相互作用进行了实验研究。重点研究了水平排列的垂直板、水平圆柱体和水平向上的水平排板周围的流体流动和换热，这些排板以固定的间隔放置，并在恒定的热流密度下加热。在室温下，测试流体是水。用染料显示了这些热源周围的流场。结果表明，离开热源的羽流相互作用，聚集在热源之间的对称面上。即使当热源之间的间隔比热源的尺寸大十倍时，这些相互作用也会发生。研究了羽流相互作用对热源换热特性的影响。结果表明，竖板的局部换热系数变化不大，而水平圆柱体和水平板的局部换热系数受羽流干扰的影响较大。可视化研究发现，当相互作用发生时，上述两个热源上的分离点向热源中心移动，这可能导致局部系数的变化。在此基础上，研究了上向水平平板的换热特性。结果表明，板间距较小时，局部换热系数受影响较大。然而，羽流相互作用对换热系数的影响随间距的增加而减小，当间距超过50 mm时，各平板的总换热系数与单板的换热系数相同。

Interactions of natural convection plumes issued from multiple heat sources placed in the same horizontal plane have been investigated experimentaly in the present study. The special concerns were focused on the fluid flow and the heat transfer around the horizontal rows of vertical plates, horizontal cylinders and upward-facing horizontal plates, which were placed at the constant intervals and were heated with the constant heat fluxes. The test fluid is water at room temperature. The flow field around these heat sources were visualized with dye. The results demonstrate that the plumes departed from the heat sources interact with each other and gather to the symmetrical plane between the heat sources. These interactions occur even when the intervals between the heat sources are ten times larger than the dimensions of the heat sources. The influences of the plume interactions on the heat transfer characteristics of the heat sources were also investigated. The results for the vertical plates show no substantial change in the local heat transfer coefficients, while the local coefficients of the horizontal cylinders and of the horizontal plates are changed by the plume interaction. It is found from the visualization study that the separation points over the above two heat sources move toward the center of the heat sources when the interactions occur and this could cause the variations in the local coefficients. On the basis of the above discussions, the heat transfer characteristics of the upward-facing horizontal plates were investigated. It was revealed that the local heat transfer coefficients are affected seriously when the plates are placed at small intervals. However, the effect of the plume interaction on the heat transfer coefficients becomes smaller with increasing the intervals, and the over-all coefficients of the plates become the same as those of the single plate when the plate intervals exceed 50mm.