上方是高温的工件表面,下方是温度约为介质沸点的液面。因此,水平向下表面蒸汽膜内气体温度分布的特点是:上方高,而下方低。这样的温度分布使气体之间不可能发生自发的对流。但是,在冷却初期,当与上方侧面蒸汽膜相通时,靠上方蒸汽膜内的层流层带动,紧挨高温表面,因此温度最高的一层热气体仍然可能绕过边角进入侧面的层流层中,由此带动底平面以下气体水平的放射状流动。随后,为弥补顶层气体流失造成的空 Above the workpiece surface is high temperature, below the temperature is about the boiling point of the liquid medium. Therefore, the characteristics of gas temperature distribution in the vapor film on the horizontal downward surface are that the upper part is high and the lower part is lower. Such a temperature distribution makes it impossible for spontaneous convection between the gases. However, in the early stages of cooling, the laminar flow in the upper vapor film, when in contact with the vapor film above the side, is brought close to the hot surface so that the warmest layer of hot gas may still bypass the laminar flow entering the side surface Layer, thereby driving the radial level below the bottom plane of the radial flow. Subsequently, to make up for the top air loss caused by the empty