In a refrigeration cycle,the compressor has two main functions within the refrigeration cycle.One function is to pump the refrigerant vapor from the evaporator so that the desired temperature and pressure can be maintained in the evaporator.The second function is to increase the pressure of the refrigerant vapor through the process of compression,and simultaneously increase the temperature of the refrigerant vapor.By this change in pressure the superheated refrigerant flows through the system.（在制冷循环中,压缩机有两个主要功能｡一个功能是从蒸发器吸入制冷剂蒸气,以维持蒸发器需要的温度和压力｡第二个功能是通过压缩过程提高制冷剂蒸气的压力,同时提高制冷剂蒸气的温度,通过压力的这种变化,过热的制冷剂蒸气在系统中流动｡）
Refrigerant compressors,which are known as the heart of the vapor-compression refrigeration systems,can be divided into two main categories:displacement compressors, and dynamic compressors.（制冷压缩机,被认为是蒸气压缩式制冷系统的心脏,可以分成两大类:•
容积型压缩机•
速度型压缩机）
Note that both displacement and dynamic compressors can be hermetic,semihermetic,or open types.The compressor both pumps refrigerant round the circuit and produces the required substantial increase in the pressure of the refrigerant.The refrigerant chosen and the operating temperature range needed for heat pumping generally lead to a need for a compressor to provide a high pressure difference for moderate flow rates,and this is most often met by a positive displacement compress or using a reciprocating piston.Other types of positive displacement compressor use rotating vanes or cylinders or intermeshing screws to move the refrigerant.In some large rapplications,centrifugal or turbine compress or sare used,which are not positive displacement machines but accelerate the refrigerant vapor as it passes through the compressor housing.（注意:容积型压缩机和速度型压缩机,都可以是全封闭式,半封闭式或开启式｡压缩机不仅泵送制冷剂绕回路循环,而且产生制冷剂所需提高的压力｡选择的制冷剂和热传送所需要的工作温度范围需要压缩机在适当的制冷剂流速下提供一个高的压差,通常采用往复式活塞式容积型压缩机可以满足这些要求｡其它的容积型压缩机使用旋转的叶片或汽缸或相互啮合的螺杆使制冷剂流动｡在许多较大型应用中,离心式或涡旋式压缩机得到使用,它们不是属于容积型压缩机,但能使制冷剂蒸气通过压缩腔时得到加速｡）
In the market,there are many different types of compressor available,in terms of both enclosure type and compression system.Here are some options for evaluating the most common types(DETR,1999):（就封闭型和压缩系统而言,在市场上有许多不同类型的可选用的压缩机｡以下是一些评测最普通类型的选项(DETR,1999):）
Reciprocating compressors are positive displacement machines, available for every application.The efficiency of the valve systems has been improved significantly on many larger models.Capacity control is usually by cylinder unloading(a method which reduces the power consumption almost in line with the capacity).（活塞式压缩机属于容积型压缩机,适用于一切应用场合｡在一些大型压缩机中,阀系统的效率得到了很大的改善｡通常通过汽缸卸载来实现容量调节(这是减少动力消耗,与容量相符合的一种方法)｡）
Scroll compressors are rotary positive displacement machines with a constant volume ratio.They have good efficiencies for air conditioning and high temperature refrigeration applications.They are only available for commercial applications and do not usually have in-built capacity control.（涡旋式压缩机属于旋转式容积型压缩机,其具有恒定的容积比｡它们在空调和高温制冷系统中有很高的效率｡它们仅适合于商用,且通常不具备内置容量调节装置｡）
Screw compressors are available in large commercial and industrial sizes and are generally fixed volume ratio machines.Selection of a compressor with the incorrect volume ratio can result in a significant reduction in efficiency.Part load operation is achieved by a slide valve or lift valve unloading.Both types give a greater reduction in efficiency on part load than the reciprocating capacity control systems.（螺杆式压缩机用于大型工业和商业系统,且通常具有固定的容积比｡选择不恰当容积比的压缩机能导致效率明显的降低｡部分负荷工作是通过滑阀或提升阀卸载完成的｡与往复式压缩机的容量调节系统相比,以上两类压缩机在部分负荷下的工作效率更低｡）
