Experimental Study On Inverter Compression System Under Variable Conditions

Although inverter compression system is more energy efficient than fixed speed compression system,its performance is more complicated because of the united controlling method for inverter compressor and electronic expansion valve.Due to the changefulness of the applicated condition for inverter compression system,the research for the performance of inverter compression system under variable conditions has practical significance.The inverter rotary compression experiment system is studied,and the following projects are researched: when the state of the refrigerant at compressor suction is superheated,the hunting of superheated temperature,the system performance with compressor frequency and superheated temperature and the controlling characteristic of electronic expansion valve under variable compressor frequency;when that is two-phase,the volumetric efficiency and electrical efficiency of compressor with suction vapor quality and the steady state modeling of inverter compressor.The hunting of superheated temperature is investigated.With the increase of the electronic expansion valve opening,the amplitude of superheated temperature changes from 1K to 3K,then back to 1K,while the flow pattern at the outlet of evaporator changes from superheated flow to the alternating flow of superheated flow and mist flow,then changes to the alternating flow of mist flow and gas-liquid flow,finally changes to the gas-liquid flow.The results show that the change of the mechanism of heat transfer is the basic reason for the hunting.The heat transfer mechanism changed from single phase forced convection to liquid film boiling convection leads to the decrease of the mass flow rate,which results in the heat transfer mechanism backs to single phase forced convection.To accurately predict the hunting characteristic,both of the heat load and the mass flow should be considered.The system performance under variable compressor frequency is investigated.The maximum COP is at the condition that the superheated temperature is 2K and the low frequency(25Hz~35Hz).For different frequency and same superheated temperature,compared with high frequency(40Hz~60Hz),the electrical efficiency is higher and the volumetric efficiency is lower at low frequency.For same frequency and different superheated temperature,both of the electrical efficiency and the volumetric efficiency has maximum value when the superheated temperature at the range from 4K to 6K.Moreover,there are some remarkable results at low compression frequency condition that the thimbleful liquid refrigerant at compressor suction will leads to rapidly drop of the volumetric efficiency,and controlled proportional band of electrical expansion valve will be narrow.Increasing the heat transfer temperature difference of evaporator could improve the performance at low compression frequency condition.In addition,the discharge temperature has linear relationship with suction superheated temperature at each frequency,and the slopes are same.The inverter rotary compressor is modeled in this paper.For fixed pressure ratio,the electrical efficiency is related to superheated temperature,but the volumetric efficiency is not.Both of them linear decrease with decreasing vapor quality.According to the regulation,the inverter rotary compressor model is published.Its maximum relative error is 1.83%,and minimum relative error is 0.05%,which demonstrates the precision of the model.The noteworthy phenomenon is that the performance of compressor more worsen operating at lower frequency and suction vapor quality,which means the model is suitable for the operating condition with the frequency higher than the rated frequency and the suction vapor quality greater than 0.90.Study for the inverter compression refrigerant system in this paper provides the reference for system controlling and performance improvement in practice,and the modelling method for the dynamic performance of inverter compressor.