| Nowadays,the concept of energy conservation and environmental protection has prevailed.As the sythetic refrigerants are one of the main contributing factors of greenhouse effect,the research of their substitutions has gradually become an important issue.R410A,which is widely used in a variety of air conditioning products,will be faced with the situation of being phased out in the coming days due to its high global warming potential(GWP).The new ternary mixed working medium R447A has similar physical properties with R410A,while its GWP value is only 30%of R410A.Therefore,the eco-friendly refrigerant R447A is regarded as the potential substitute of R410A.The heat transfer characteristics of refrigerants have a very important impact on the design of heat exchangers.However,the researches on flow boiling heat transfer characteristics of R447A are not enough.In this paper,by studying the heat transfer characteristics of the new mixed working medium R447A,the heat transfer data of this refrigerant are supplemented,which provided a basis for the transformation and design of the heat exchanger and this is of great significance for enhancing the promotion and application of the alternative refrigerant.The heat transfer characteristics of the mixed refrigerant R447A is the main research object in this study.Flow boiling heat transfer characteristics of R447A were investigated in the smooth tube with inner diameter(I.D.)of 10.6 mm.The heat flux ranged in 5～20 k W/m~2,the evaporating temperature ranged in 5～25℃,and the mass flux ranged in 100～300 kg/(m~2·s).Based on the results of study,this research not only analyzed the influence of different experimental factors on heat transfer theoretically,but also compared the experimental results of R447A with R410A and R134a.In addition,a new correlation for predicting heat transfer coefficient of R447A was proposed.The primary results and conclusions are as follows:(1)Under the conditions of this experiment,the heat transfer coefficients of R447A are between 800～3500 W/(m~2·K).Experimental results show that the heat transfer coefficient of R447A increases slowly with the vapor quality,but with the increase of mass flux,the effect of vapor quality on heat transfer is enhanced.In addition,mass flux and heat flux can promote the heat transfer performance.(2)By comparing the heat transfer coefficients of R447A with those of R410A and R134a under same experimental conditions,the results present that the heat transfer coefficients of R410A are 10～30%higher than those of R447A,and the heat transfer coefficients of R134a are 7～18%higher than those of R447A.The effect of the mass flux on the heat transfer of R447A is stronger than that on R410A,but weaker than R134a.The impact of heat flux on R447A is slighter than that on both R447A and R134a.(3)Some existing prediction models were used to predict the heat transfer coefficients of R447A,R410A and R134a.The calculation results indicate that these correlations utilized in this paper have a good agreement with the results of pure refrigerants,except refrigerant mixtures,especially ternary work fluid R447A.Based on the previous work of other researchers,the difference between the heat transfer coefficient of R447A and pure refrigerants caused by mass transfer resistance and temperature slip was analyzed qualitatively.This paper proposed a new method that divides vapor quality into two part to predict heat transfer coefficients.A new prediction correlation was developed with a mean deviation of+6.21%,an absolute deviation of+12.96%,which provides theoretical basis for prediction of heat transfer coefficients of R447A. |
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