Design And Experimental Research On Two-stage Compressive Refrigerating System

In recent years, with the rapid development of the science and economy, the demand for low temperature is getting strict in both living and production. The evaporation temperature can not achieve a lower value because of limits of the volumetric coefficient and the delivery temperature in a single-stage compressive refrigerating system. Therefore, the multi-stage compression is gradually raising people’s attention and getting favored by scientists and engineering. In this paper, the experimental installation of two-stage compression with a single stage throttling and incomplete inter cooling is designed and set up. In the two-stage compression system, a contraction is divided into two stages where the compression ratio is small in single stage, which ensures two compressors can run stably. Firstly, according to the designed conditions and parameters, the related theoretical values are calculated preliminary, which decide the design calculations and selections of main equipment in the system, such as compressors, condenser, etc. Given required control of the system, the control units is designed and selected. In the next stage, self-assembled experimental working device is set up. The calorimeter used in the device is a new tube-in-tube type, in which a copper tube is sheathed on the electric heating rod and rolled up. The refrigerant is heated when it flows through the calorimeter, and the power of the electric heating rod is the cooling capacity of system. The measured results are accurate and the speed is fast, which greatly reduce the measurement time.The experimental stability of two-stage compressive refrigerating system is verified before the influence of the amount of refrigerant charge, the cooling water flow, the evaporation temperature, the degrees of opening of throttle on the performance of two-stage compressive refrigerating system is investigated. By analyzing the experimental data, the reasons of changing of the date are analyzed and the two-stage compression system is reasonably improved. In the experiment, the precision manual modulation valve is used to adjust the middle pressure, the rotor flowmeter is to control the cooling water flow, and the contacting voltage regulator is to change the evaporating temperature.The improved two-stage compressive refrigerating system is stable and easy to operate. The data shows that the system’s COP is relatively large when the amount of refrigerant charge is 1.8kg. When the evaporation temperature is-30℃,the cooling water flow is 7kg / min, the degree of opening of manual throttle is 0.1, the value of COP reaches maximum, that is 1.06. At this time, the intermediate pressure corresponding to the degree of opening of throttle is about 0.63 MPa, the compression ratios of high and low temperature compressors are 2.48 and 3.45 respectively, the values of delivery temperature are 102 ℃ and 78.6 ℃ respectively, and all of conditions can effectively solve the problems of large compression ratio and high delivery temperature when the evaporation temperature of single-stage compression is low. At the same time, the refrigeration system can be used as a training installation platform, which can test the thermodynamic state parameters of the inlet and outlet of each equipment in the two-stage compression system at any time, and can provide reference of data and theoretical analysis for studying the two-stage compression system used in the refrigeration and heat pump circulation system.