在制冷工程中，冷却设备通常有两种方式:一种是利用制冷剂直接蒸发被冷却物体，另一种是利用制冷剂间接冷却被冷却物体。采用二种方法的优点是:可以将制冷剂系统集中在机房内或很小的范围内，使制冷系统的连接管道和接头大大减少，便于密封和系统检漏，对于一些易燃有毒的制冷剂，可以提高制冷设备的性和可靠性；同时，制冷剂的充注量也大大减少；特别是在大容量、集中冷却的设备中，利用冷却剂可以方便地解决制冷量的控制和分配问题。便于机器的操作和管理。冷水机组空调领域采用水作为冷媒，在低温冷冻制冷领域，更常用乙二醇、甘油等盐溶液或有机制冷剂。

In refrigeration engineering, there are usually two ways for cooling equipment: one is to use refrigerant to directly evaporate the cooled object, and the other is to use refrigerant to indirectly cool the cooled object. The advantage of using two methods is that the refrigerant system can be concentrated in the computer room or within a small range, greatly reducing the connection pipes and joints of the refrigeration system, facilitating sealing and system leakage detection. For some flammable and toxic refrigerants, it can improve the safety and reliability of refrigeration equipment; At the same time, the amount of refrigerant charged is greatly reduced; Especially in high-capacity, centralized cooling equipment, the use of coolant can easily solve the problem of controlling and distributing refrigeration capacity. Easy to operate and manage the machine. In the field of chiller air conditioning, water is used as the refrigerant. In the field of low-temperature refrigeration, salt solutions such as ethylene glycol and glycerol or organic refrigerants are more commonly used.

水的冰点是0℃，只适用于冷却温度在0℃以上的场合。无机盐水溶液具有较低的凝固温度，适合在中低温制冷设备中载冷。盐水溶液的比重和比热比较大，所以盐水溶液的体积循环量小。但盐水溶液具有腐蚀性，尤其是微酸性的稀盐溶液，与空气接触，对金属材料的腐蚀性很强。

The freezing point of water is 0 ℃ and is only suitable for cooling temperatures above 0 ℃. Inorganic saline solutions have a lower solidification temperature and are suitable for cooling in medium to low temperature refrigeration equipment. The specific gravity and specific heat of saline solution are relatively high, so the volume circulation of saline solution is small. However, saline solutions are corrosive, especially slightly acidic dilute salt solutions that come into contact with air and have a strong corrosive effect on metal materials.

在有机制冷剂中，乙二醇、丙二醇和甘油水溶液被广泛使用。乙二醇和丙二醇的水溶液特性相似，共晶温度可达-60℃左右，比重和比热容大。丙二醇比乙二醇更具腐蚀性。乙二醇比丙二醇低，微毒，浓度不一样温度也不一样。甘油(丙三醇)是一种非常稳定的化合物，其水溶液对金属无腐蚀性、性，可与食物直接接触，因此是一种很好的冷却剂。而甘油的导热系数相对较低，换热稍差，需要大面积的换热器，增加了成本。其中乙二醇应用广泛，如大型冷库、低温热泵、冷热源集中的制冷空调试验装置等，但乙二醇对金属也有微弱的腐蚀作用。

In organic refrigerants, aqueous solutions of ethylene glycol, propylene glycol, and glycerol are widely used. The aqueous solutions of ethylene glycol and propylene glycol have similar characteristics, with a eutectic temperature of around -60 ℃ and a high specific gravity and heat capacity. Propylene glycol is more corrosive than ethylene glycol. Ethylene glycol is cheaper than propylene glycol, slightly toxic, and has different concentrations and temperatures. Glycerol (glycerol) is a very stable compound, and its aqueous solution is non corrosive and non-toxic to metals. It can come into direct contact with food, making it a good coolant. However, the thermal conductivity of glycerol is relatively low, and the heat transfer is slightly poor, requiring a large-area heat exchanger, which increases the cost. Ethylene glycol is widely used, such as in large-scale cold storage, low-temperature heat pumps, refrigeration and air conditioning testing devices with concentrated cold and heat sources, but ethylene glycol also has a weak corrosive effect on metals.