| Because of the double pressures of energy saving and environmental protection,refrigerant R32 becomes the focus of alternative refrigerants research again for its good thermal performance,however high discharge temperature of compressor becomes the biggest obstacle to applicat.The rolling rotary compressor of high back pressure type is widely used in room air conditioner,which can adapt the condition of wet compression,so the method of suction vapor-liquid maxture refrigerant becomes an excellent choice that can reduce the compressor discharge temperature basing on the cost not increased.In this paper,the experimental study on suction vapor-liquid mixture refrigerant for R32 refrigeration system by the variable refrigerant volume chiller.First of all,we compared R32,R410 A,R290 with R22 in theory,and analized these popular alternative refrigerants currently.Secondly,based on the characteristic of high discharge temperature,we compared four kinds of methods to reduce the compressor discharge temperature.Finally,through a large amount of experiments verified the reliability and operability of the method that suction liquid refrigerant.The main contents: Comparison of thermal performances and the influences of different suction refrigerant state on system performance under air conditioning and refrigeration conditions;The difference of two types of method to reduce the compressor discharge temperature,and the effect on system performance.Combined with the practical application,we discussed why suction liquid refrigerant method was the best choice;The impact on variable frequency scroll rotary compressor performance with different R32 suction status;The optimal of suction refrigerant quality for R32 wet compression refrigeration system;The effect of hunting of superheated temperature onthe performanceof a variable refrigerant flow refrigeration system.Theoretical analysis: Under the standard air conditioning condition,the refrigerant suction state from overheat to the two-phase,the cooling capacity,compressor power consumption and the compressor discharge temperature per unit mass flow of R32,R22,R410 A and R290 are decline like a broken line.The COPs of former three kinds of refrigerant are increase firstly and then decrease overall.However,R290 decreases all the time.The COP exist a maximum with suction liquid refrigerant,and the compressor discharge temperature is greatly reduced.Compressor as the key component of refrigeration system,the primary consideration is the impact of system conditions changing on the compressor,and then find the running state that matches it.through the experiment under conditions of variable frequency under constant pressure ratio and variable pressure ratio under constant frequency,test the effects with different suction state on efficiency of rolling rotary compressor.The experimental results show that: when suction refrigerant superheated,compressor can maintain a high isentropic compression efficiency and volume efficiency,the superheat degree has a little effect on compressor efficiency.However the change trend of the efficiency of the compressor with vapor-liquid mixture suction has difference with the suction superheated;Compared to x = 1,when x = 0.9,the isentropic compression efficiency and volumetric efficiency decreased by about 6.0% and 8.5% respectively,the decrease amplitude was very small.Under constant frequency,the greater the pressure ratio is,the larger of reduce amplitude of compressor efficiency is.Under constant pressure ratio,the higher the frequency is,the smaller of decrease amplitude is;the change trend of the isentropic compression efficiency and the comprehensive efficiency coefficient is same,but considering the comprehensive efficiency coefficient,the compressor works best at the rated frequency.In order to eliminate the interference caused by mass flow changes in refrigeration system,study on the heat transfer characteristics of the plate heat exchanger by changing the heat power of chilled water on the evapor side under stable electronic expansion valve opening and frequency.Research the heat transfer and pressure drop characteristics with different suction refrigerant state and different mass flow density(different valve opening).The experimental results show that: the refrigerant outlet state from overheat to the two-phase state,the heat transfer coefficient on Refrigerant side increases rapidly initially and then decreased slowly,the temperature difference of heat transfer decreases quickly and then decreases slowly,the pressure drop only has a small decline: The effectiveness of plate heat exchanger increase gradually.But after balancing the effectiveness of plate heat exchanger and the system performance,when the evaporator outlet refrigerant quality is close to 1,the heat transfer performance reaches the best.The "0 superheated degree" hunting study showed: The hunting of superheated degree of evaporator outlet was affected not only by the opening degree of elcetronic expansion valve,but also the cooling capacity.The hunting of superheated degree hunting ranged from 0°C to 4°C.After considering the standard condition,and simulating the actual operating conditions,we evaluated the effect on the cooling capacity,power,COP,discharge temperature,pressure ratio and others system performance parameters comprehensively.The conclusion were that the system performance reached optimal when suction refrigerant quality in the range of 0.96 ~ 1.In the case of the compressor efficiency requirements are not very high,small and medium sized R32 air conditioner can satisfied the requirements by sacrificing a small amount of compressor efficiency.Using the method that suction liquid refrigerant not only can reduce the compressor discharge temperature,but also improve system performance. |
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