向蒸发器循环过量液体的制冷系统在实践中已经使用了40多年。最常见的用途是在具有多个蒸发器的大吨位应用中。其主要优点是降低了运营费用，这得益于更高的系统效率。ASHRAE手册和产品目录1973年的系统卷中介绍了液体过量供给系统的原理和设计指南。常用的制冷剂有R-12、R-22、R-502和R-50- 717（氨）。对于R-12和R-502，建议的最小再循环率（即总制冷剂流量与蒸发率之比）为2:1，对于大直径下料管中的氨，建议的最小再循环率为Gor 7:1。液体溢流系统采用低压接收器；用于分离离开蒸发器的蒸汽和液体的累积器。连接管道被称为湿式回流管，以并流方式输送液体和气体的混合物。本次调查的目的是改进根据给定压降确定这些管线尺寸的方法。 在研究的第一阶段，对管道中的气液流动进行了详细的文献研究，重点是水平流动。通过对文献的研究，选择了六种两相压降计算方法。这些方法是由以下研究人员使用的:洛克哈特·马丁内利、马丁内利·纳尔逊、休马克、杜克勒和巴罗西。引文:ASHRAE交易，第82卷，第2部分，华盛顿州西雅图

Refrigeration systems that circulate an oversupply of liquid to the evaporator have been used in practice for more than 40 years. The most common usage is in large tonnage applications having multiple evaporators. The main advantage is reduced operating expenses, which result from higher system efficiency. Principles and design guidelines for liquid overfeed syste~s are presented in the 1973 Systems Volume of ASHRAE Handbook & Product Directoryl. The refrigerants commonly used are R-12, R-22,R-502, and R-717 (ammonia). Recommended minimum rates of recirculation, i.e., ratio of total refrigerant flow rate to evaporation rate, are from 2 to 1 for R-12 and R-502 and to Gor 7to 1 for ammonia in large diameter downfeed tubes.Liquid overfeed systems employ a low pressure receiverorl;iccumulator to separate the vapor and liquid leaving the evaporator. The inte~connecting piping is referred to as a wet return and carries a mixture of· liquid and gas in cocurrent flow. An improved method of sizing these lines for a given pressure drop was the objective of this investigation. In the first phase of the study a detailed literaturestirvey on gasliquid flow in pipes was conducted, with an emphasis- on horizontal flow. A study of the literature resulted in the seiection of six methods of two-phase pressure drop calculation. These methods were due to the following investigators: Lockhart-Martinelli, Martinelli-Nelson, Hughmark, Dukler, and Baroczy.