Performance Study Of R404A Direct Contact Condensation Refrigeration System

For traditional vapor compression refrigeration cycle,the high temperature and high pressure refrigerant gas discharged by the compressor release its heat in the condenser and exchange heat with the cooling medium.The refrigerant and the cooling medium exchange heat through the convective heat transfer of both side fluid and through the conduction heat transfer on the condenser wall.The condenser heat transfer characteristics of the wall material,the surface features of the wall will accumulate oil or dirt by which led to an increase of the thermal resistance,a decrease of the heat transfer efficiency.And then the heat transfer temperature difference between refrigerant and cooling medium will increase,the refrigeration compressor exhaust temperature,pressure ratio and volumetric efficiency will reduce.So the compressor power consumption increases and the performance of the refrigeration system decreases.Compared with the traditional surface type condensation heat transfer,direct contact condensation heat transfer has higher heat transfer efficiency,avoids and reduces the corrosion on the heat transfer surface,saves materials,reduces investment cost and operation cost,and could realize high efficiency heat transfer with small temperature difference.So Ning Jinghong et al,put forward a new idea to make the high temperature and high pressure refrigerant vapor of compressor direct contact with a cold liquid refrigerant in a traditional vapor compression refrigeration system,in order to improve the condensation efficiency,reduce the compressor exhaust pressure,improve the performance of refrigeration cycle system.Such the direct contact with the cooling refrigeration cycle system has an important theoretical and practical application value.In the early stage,the research group designed an additional cold source type direct contact refrigeration system.And compared with the conventional R717/R744 cascade refrigeration cycle,the optimal COP of the R717/ R744-dcc direct contact refrigeration cycle can be improved by 5.2%.Compared with conventional R290 single-stage compression refrigeration cycle,the COP of the additional cooling source R290 direct contact condensation refrigeration cycle can be improved by 7.5%.In this paper,an improved direct contact condensation refrigeration cycle is designed and use R404 A as refrigerant working substance which is commonly used in the refrigeration field.Theoretical analysis the performance of R404 A and two kinds of its alternative refrigerants R454 C and R455 A single-stage direct contact condensation refrigeration cycle,R404 A two-stage direct contact condensation refrigeration cycle and R404 A cascade direct contact condensation refrigeration cycle.And then the performance of R404 A single-stage direct contact condensation refrigeration cycle were studied experimentally.The following conclusions were made:(1)According to the theoretical analysis,compared with R404 A single-stage conventional vapor compression refrigeration cycle,the average power consumption of the compressor can be reduced by 1.5% and the average COP of the cycle can be increased by1.5% under the condition of medium temperature in the direct contact condensation refrigeration cycle.Under the condition of low temperature,the average power consumption of the compressor can be reduced by 2.1%,and the average COP of the cycle can be increased by 13.5%.(2)According to the theoretical analysis,under the condition of medium temperature,the single-stage cycle performances of two kinds of R404 A substitute refrigerants: R455 A and R454 C are inferior to that of R404 A single-stage cycle.But when using the direct contact condensation cycle,the performance of the two new refrigerants cycles' COP value can be increased by 0.7% ~ 2.5%,the discharge temperature of compressor can reduce0.2 ? ~ 2 ?.(3)According to theoretical analysis,compared with R404 A conventional two-stage vapor compression refrigeration cycle,the average power consumption of the compressor can be reduced by 1.2%,and the maximum COP of the cycle can be increased by 0.8% in the direct contact condensation two-stage cycle.Compared with the R404 A conventional cascade vapor compression refrigeration cycle,the average power consumption of the compressor can be reduced by 1.5%,and the maximum COP of the cycle can be increased by 0.7% in the direct contact condensation cascade cycle.(4)By the experiment test,the performances of single stage R404 A direct contact refrigeration cycle and conventional R404 A vapor compression refrigeration cycle under different conditions of evaporator freezing liquid temperature and condenser cooling liquid temperature was compared.