Vapor compression heat pump

Because of air compression type heat pump is difficult to achieve two isothermal processes, and because of the air cooling ability is poor, so now the vast majority of practical application for vapor compression heat pump. Its circulation principle diagram and working principle of the heat source diagram as shown in figure 6-6-1 and figure 6-6-2, only the freezer into evaporator, cooler into condenser. Now common circulatory system as shown in figure 6-6-4.

System within the working medium (such as ammonia and freon, etc.) in the system through four processes, namely, evaporation process, compression process, the cooling process and expansion process. 1 in the evaporator, working medium liquid evaporated into low pressure steam, heat absorption into the compressor (after the compression to the condensing pressure, consumes mechanical work W, then into the condenser 3, make the working medium steam condenses into liquid, when the condensation pressure constant, gives off heat and Q1. From the condenser of the liquid working medium, the expansion valve pressure P2 (or throttle) 4, temperature also dropped to the corresponding saturation temperature 72. With the pressure as working medium has become a vapor liquid two phase mixture, and then into the evaporator, in Q2 heat absorption and evaporation, on this auspicious beginning Zhou Erxia cycle,

The utility of the heat pump cycle with two isothermal, such as there is a difference between office process. First of all, because of the liquid to avoid compression, so the working substance before into the enlistment shrink machine to have a certain degree of superheat; Second, compression and expansion process is not bean process. So, the actual work coefficient of heat pump cycle is far lower than the reverse carnot cycle work coefficient, the irreversible loss available effective coefficient to estimate. Recognize and heat transfer temperature difference of heat exchange equipment, properties of the thermodynamic cycle way, compressor and so on many factors, according to the current technical level, around the o. o. 75, 45 a concave corpse of a compression type heat pump at about 2, 7.

In order to improve the performance of heat pump, make full use of the sensible heat of the cooled working medium, should make the compressor inlet steam in the overheated state, for the condensate supercooling, as shown in figure 6-6-6. Figure 5-6-7 said with Rll 4 and ll as a working medium into steam superheat and condensate supercooling degree and concave strict work coefficient increase rate curve.