| The problem of greenhouse effect and ozone layer destruction is becoming more and more serious.Traditional refrigerants destroy the ozone layer,so it is an inevitable trend to seek new environmental protection alternative refrigerants.R32,as one of the most suitable medium-term alternative refrigerants,is widely applied in domestic HVAC.R32 is good for environment,and has good heat transfer performance and small filling capacity,which is also suitable for small diameter heat exchanger.However,R32 has the characteristics of low viscosity and poor miscibility with lubricating oil.In order to ensure R32 refrigeration system operating safely and efficiently,it is necessary to study the characteristics of R32 refrigerant,analyze its performance in air conditioning products,and discuss the impact of lubricating oil on R32 heat exchanger.In this paper,the R32 microchannel parallel flow evaporator is studied by the method of experiment and theory.The main contents are as follow:(1)The rapid calculation model of R32’s thermal physical properties and transmission characteristics is established.The accuracy of the model is0.064% as a whole.It can become the basis of system simulation.The p-V-T state equation is established based on Martin-Hou form.Compared with the formula and tested data in printed publication,the calculated deviation is less than 8.7%(2)Based on tested data,a physical property model of R32 adaptive lubricating oil was established.The overall accuracy of the model was 1.95%.Based on the ideal mixing principle and the classical enhanced model,calculation models of R32/lubricating oil mixture’s physical properties are calculated.According to features of R32 vapor pressure,a new solubility calculation model is proposed,which accuracy can reach 0.29%.According to stratification experiment of R32/lubricating oil mixture,the mutual solubility curve model is established,which overall accuracy is 1.03%.(3)Research on evaporation and condensation heat transfer of R32 refrigerant in recent years are summarized in this paper,and experimental database of R32 boiling heat interchange coefficient is established.Based on it,commonly used correlations are tested,and a new correlation of R32 boiling heat interchange coefficient is proposed.The mean error of new correlation is 16.29%,and more than 85% of calculation deviation is within ±30%.(4)Using the distributed parameter method,a steady-state simulation model of R32 evaporator is established.Using pure R32 evaporator calculated model,modify physical parameters of R32/lubricating oil mixture,adjust correlations of heat interchange and pressure loss,and correct thermal resistance of oil film on pipe wall.After that,the micro-channel evaporator simulation model suitable for R32/lubricating oil mixture is established.(5)Design and build the experimental station of R32 air conditioning system.And the accuracy of simulation models are verified according to it.Use experimental station to analyze the performance of evaporator in various operating conditions.Combined with the experimental working conditions,analyze variable structure of the evaporator.Change oil circulation rate by using lubricating oil filling system,test performance of evaporator in different oil content,and find out the influence of lubricating oil on the heat exchanger.When the oil content of mixture attains 7.5%,heat exchange attenuation of the evaporator is 93.4% and pressure drop is 1.61 times of original. |
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