Narain Amitabh, Kulkarni Shantanu, Mitra Soumya, Kurita Jorge H, Kivisalu Michael T
Department of Mechanical Engineering-Engineering Mechanics, Michigan Technological University, Houghton, Michigan 49931, USA.
Ann N Y Acad Sci. 2009 Apr;1161:321-60. doi: 10.1111/j.1749-6632.2008.04324.x.
Reported experimental and computational results confirm that both the flow features and heat transfer rates inside a condenser depend on the specification of inlet, wall, and exit conditions. The theoretical and experimental results presented in this paper allow us to propose important exit condition based categorization of these flows. Of these, category II flows are defined to be cases for which exit pressures are left unspecified. However it is shown here that steady flows under specified exit pressure conditions (category I flows) are more stable and can be more easily achieved under all conditions (normal or zero-gravity). Existence of self-selected exit pressure conditions for unspecified exit condition cases (category II flows) are more difficult to achieve and are often limited to gravity driven flows. In practice, however, special hardware arrangements are required for repeatable realization of both these categories of flow. If this is not so, one often has an inadvertent category I flow (flows with specified exit pressure) without the explicit knowledge of the exit pressure value. For microgravity situations, the remedy is to run condensers under suitably specified inlet and exit pressures (category I conditions) as well as a proper cooling strategy (i.e., proper wall temperature variations).
已报道的实验和计算结果证实，冷凝器内部的流动特性和传热速率均取决于入口、壁面和出口条件的设定。本文给出的理论和实验结果使我们能够基于出口条件对这些流动进行重要的分类。其中，II类流动被定义为出口压力未作规定的情况。然而，本文表明，在规定出口压力条件下的稳定流动（I类流动）更稳定，并且在所有条件下（正常或零重力）都更容易实现。对于未规定出口条件的情况（II类流动），自选择出口压力条件的存在更难实现，并且通常限于重力驱动的流动。然而，在实际中，要可重复地实现这两类流动都需要特殊的硬件配置。如果不是这样，人们常常会在没有明确知晓出口压力值的情况下，不经意间得到I类流动（具有规定出口压力的流动）。对于微重力情况，补救方法是在适当规定的入口和出口压力（I类条件）以及适当的冷却策略（即适当的壁面温度变化）下运行冷凝器。
