Experimental Study On Plate Heat Exchanger Used As Condenser Of R744/R290 Heat Pump System

The application of heat pump is of great significance for energy-saving and emission-reduction.The increasing environmental pollution and the limited use of Freon has made the replacement of eco-friendly refrigerant and the development of corresponding heat exchanger become the key to the popularization and application of heat pumps.Plate heat exchanger has extensive application potentiality in heat transfer fields because of its compact structure and excellent performance,but there are few researches on its application in direct thermal heat pump water heater system.The performance of plate condenser was studied by theoretical approach and experimental approach when it was used in non-azeotropic refrigerant mixtures direct thermal heat pump water heater in this paper.The main research contents are as follows:（1）Based on the established design model of plate condenser,the plate condenser for M3（the mass ratio of R744/R290 is 12/88）heat pump water heater was designed.Based on the design result,the structure of plate condenser was compared with that of the original double-tube condenser of the experimental system.（2）In the system,the performance of plate condenser and double-tube condenser under the nominal condition of water source heat pump water heater was compared.Based on the double-tube condenser,the applicability and advantages of plate condenser to M3 direct thermal heat pump water heater were evaluated.（3）The performance of plate condenser with the cooling water inlet temperature was studied when it is applied to the system using R744/R290 mixture with R744mass ratio of 8%（Code name M1）,10%（Code name M2）and 12%（Code name M3）and R22 as refrigerant,respectively.The performance of plate condenser with R744/R290 and R22 was compared.Based on R22,the effect of cooling water inlet temperature on the increase of the performance evaluation parameters was discussed when using these mixed refrigerants.（4）The effect of R744 mass ratio in the mixed refrigerant R744/R290 on the performance of the plate condenser was discussed,and the effect of the temperature glide on the performance of the plate condenser was explored.（5）Q/Q₀,K/K₀ and ΔP/ΔP₀（Q,K andΔP are the heat exchange,heat transfer coefficient and pressure drop of refrigerant R744/R290,respectively.Q₀,K₀andΔP₀are the heat exchange,heat transfer coefficient and pressure drop of refrigerant R22,respectively.）were used to evaluate the applicability of plate condenser to non-azeotropic refrigerant mixtures.The results of the plate condenser performance experiment in the R744/R290heat pump water heater system are as follows:（1）The plate condenser could be used in the direct thermal heat pump water heater system,and its structure and performance have been improved compared with the original double-tube condenser in the system.（2）When M1,M2,M3 and R22 were used as refrigerant respectively,the performance evaluation parameters of plate condenser decreased with the increase of cooling water inlet temperature.Compared with R22,the increase of the performance evaluation parameters increased with the increase of cooling water inlet temperature when R744/R290 was used,where the increase of heat transfer performance was positive,and the increase of pressure drop might be positive or negative,with the value not exceeding 18.6 k Pa.（3）The heat transfer rate,heat transfer coefficient and pressure drop increased with the increase of R744 mass ratio in the mixed refrigerant R744/R290,but the pressure drop was always less than 20 k Pa,in other words,the performance of plate condenser increased with the increase of temperature glide for mixed refrigerant.Therefore,the performance of plate condenser was the best when using mixed refrigerant M3.（4）The plate condenser could be used for zeotropic refrigerant mixtures.The plate condenser had better heat transfer performance than R22 when R744/R290 was used,where the range of Q/Q₀and K/K₀was 1.09-1.24 and 1.58-2.39 respectively.The ratio of refrigerant pressure drop increased with the increase of R744 mass ratio,and the maximum pressure drop was only 16.8 kPa.