Rolling piston compressor two-stage compression intermediate air supply refrigeration / heat pump system. The compressor consists of a high-pressure chamber and a low-pressure chamber driven by a single motor. The throttling process is divided into a cascade throttling and a secondary throttling, with the flasher as the boundary. The working process is as follows: the liquid working fluid of the outlet condenser is throttled by the first expansion valve and then enters into the flasher. In the flasher, the refrigerant is separated into a liquid state and a gaseous state, and the gaseous refrigerant is replenished into the intermediate cavity through the gas supply line. Inside, the liquid refrigerant exits the flasher and enters the secondary expansion valve for secondary throttling, and then enters the evaporator to complete a working process.
Relative air volume; mass flow rate (kg/s) of working fluid at 6 points.
The isentropic efficiency of the low-pressure compression work 1 compression process per unit mass of working medium; nm is the mechanical efficiency; nmo is the isentropic efficiency of the 2' compression process of the electric high-voltage compression work.
The cooling coefficient of performance coefficient of heating performance is derived from the mass ratio of the high and low pressure working chamber according to the mass conservation. 2 Calculate the gaseous working volume (m3/kg) of the model unit mass refrigerant temperature state point 2'.
~(8), taking the R410A working fluid as an example, the calculation of the cooling and heating performance of the system with the high and low pressure volume ratio is calculated. It can be seen from the figure that the cooling EER and the heating COP increase first and then decrease with the increase of the volume ratio, and reach their respective maximum values ​​at a certain volume ratio. For example, the maximum EER value of the refrigeration corresponds to a pressure-to-volume ratio of about 0.7, and the heating condition is about 0.6. The determination of this value provides the most important basis for the compressor structural design.
3 Based on the calculation results of the construction of the experimental bench, a volume ratio and a cold environment were processed. The manual expansion valve on the king circuit controls the evaporation temperature, and the intermediate pressure is adjusted by the opening degree of the secondary expansion valve. Instruments such as temperature, pressure, flow and electric power have met the relevant accuracy requirements. Wang wants to obtain the performance index as follows: the inlet temperature of the water in the evaporator (°C); t2 is the outlet temperature of the water in the evaporator (°C).
; t3 is the outlet temperature of the water in the condenser (°C); t4 is the inlet temperature (°C) of the water in the condenser.
The input power of the compressor is directly measured by a high-precision electrical parameter integrated measuring instrument.
4 Test results and analysis 4.1 Refrigeration performance When the temperature t is 2, C, the cooling EER ratio changes with the relative qi volume. EERd and EERS respectively represent the two-stage, single-stage compression refrigeration EER. It can be seen from the figure that as the relative qi volume increases, the ratio increases first and then decreases, and the relative qi volume is 15%~20%. maximum. After checking the saturated state property table of R410A, it can be seen that when the condensation temperature is 45 ° C and the liquid refrigerant with a subcooling degree of 5 C is throttled to 1.1 to 1.5 MPa, the saturated gas content is also 15% to 20%, indicating that the gas is supplied. All are gases, and the separation of the flasher is ideal.
Fig. 4Variationofcoolingperformance shows the relationship between the performance ratio of the refrigeration performance coefficient and the evaporation temperature. The ordinate is the ratio of the performance ratio. Pd/Ps, Q0d/Q0s, and EERd/EERs represent the ratio of the power, cooling capacity, and cooling EER of the two-stage system to the single-stage compressor at the same evaporation and condensation temperature, respectively. As can be seen from the figure, as the evaporation temperature increases, the power ratio Pd/Ps gradually decreases, because the decrease in the amount of gas at the high evaporation temperature causes the compressor power to increase in the same rate. The cooling capacity ratio Qd /Qs shows the same trend as the power, that is, the cooling capacity increases from 5% to 15% compared with the no-compensation gas, but as the evaporation temperature increases, the cooling capacity increases. The reason is also that the degree of subcooling of the liquid before the main expansion valve is lowered due to an increase in the evaporation temperature and a decrease in the amount of replenishment. The EERd/EERs change with the increase of evaporation temperature is not obvious, basically maintained at the level of 1.10~1.12, and the air supply can increase the refrigeration EER of the system by about 10%. 4.2 The heating performance indicates the variation of the performance ratio of the heating condition with the evaporation temperature. . Taking the performance of the single-stage compression system at the rated working condition evaporation temperature of 7.0 °C as a comparison standard, the heating performance change of the evaporation temperature of 0.5~3.0 °C was investigated, P(7.0C), Qk(7.0C), COP(7.0C ) indicates the compressor power, heating capacity, and heating COP of the single-stage compression system at the evaporation temperature of 7.0 ° C. The ordinate indicates the magnitude of the ratio. It can be seen from the figure that the compressor power continues to increase with the increase of the evaporation temperature, and the heating capacity first increases and then stabilizes as the evaporation temperature increases. The main reason is that the evaporation temperature is increased, the suction amount of the compressor is increased, the power is increased, and the high pressure stage is responsible for the compression of the supplemental gas. The increase in heat is determined by the amount of exhaust gas. However, as the evaporating temperature increases, the amount of air is reduced, so the amount of heat increase is also reduced, but the amount of heat is always controlled at the rated condition. 92% ~ 95%. Because of the different trends of heating and compressor power, the trend of the ratio COP increases first, then decreases, and reaches the maximum at =1.2~1.3C.
4.3 Under the condition of ultra-low temperature heating and ultra-low temperature, the heating performance at the evaporation temperature of -26C is mainly investigated, and the results are seen. As can be seen from the figure, compared with the evaporation temperature of 7C, the compressor power is reduced to less than 90%, and the heating COP is reduced to about 60%. The key parameter heat can reach about 58% of the rated heating capacity. The effect of qi is: by adding low-value gas refrigerant, reducing the exhaust temperature of the compressor and improving the stability of the system under severe conditions; on the other hand, improving the quality of the secondary compressed gas and the entire system The amount of gas forces a reduction in compressor power and heat production at low evaporation temperatures.
5 Conclusions The experimental research on the refrigeration, heating and ultra-low temperature heating performance of the system is carried out, and the best refrigeration performance and heating performance are obtained. The volume ratio of high and low pressure chambers is 0.6~0.7, and the relative air supply range is 15%~20%. Compared with the single-stage compression system, the cooling capacity of the two-stage compression intermediate air supply system can be increased by 5% and 15%, and the system of cooling EER with 10% double-stage compression intermediate air supply forces the reduction of heat generation at low evaporation temperature. Under the condition of evaporation temperature 0.53.0C, the heating capacity is 92% 95% under the rated working condition of 7.0C; under the ultra-low temperature condition of 27.6-26.1T, the heating capacity can reach 55% of the rated heating capacity.
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