Experimental Study On The PvT Properties Of R1234yf And Its Theoretical Cyclic Performance Analysis In A Heat Pump System

The problem of energy shortage has become increasingly serious all over the world,and the environmental problems brought about by the sharp increase in energy consumption have also attracted the attention of countries.The large use of refrigerants is an important factor in the "depletion of the ozone layer" and the "greenhouse effect".With the enactment of environmental regulations and policies to reduce greenhouse gases worldwide,fourth-generation refrigerants have received much attention.R1234 yf is currently the most promising fourthgeneration refrigerant.This paper analyzes the thermophysical properties of R1234 yf and the theoretical cycle performance of two mixtures of R1234 yf in a heat pump system.The gas phase pvT properties of R1234 yf were measured according to the Burnett-isochoric method.The 171 groups of high precision experiments were carried out in the range of 253K-368 K.The second Vary coefficient and the third Vary coefficient on each isotherm are obtained by nonlinear fitting.On this basis,the high-precision three-truncated Vary equation is obtained.Comparing the experimental and calculated values of the pressure and the density,the relative deviation is ±0.8% and-1%-2.5%.The saturated vapor pressure of R1234 yf was measured in the temperature range of 253.141K-367.146 K and a total of 24 experimental data were obtained.A four-stage Wagner type vapor pressure equation was obtained.Comparing the experimental pressure value and the value calculated by the equation,the maximum absolute deviation is-0.5kPa,the maximum relative deviation is-0.09%,and the average absolute deviation is 0.02%.Energy and exergy analyses of a two-stage air-source heat pump system are carried out,using R513A(mixture of 44%R134a and 56%R1234yf)and R125/R1234 yf mixture(with a ratio of 20:80,by mass)as an alternative replacement for R134 a.A thermodynamic model has been derived for calculating heating capacity,pressure ratio,compressor work,compressor discharge temperature,coefficient of performance,exergetic efficiency and exergy destruction.Effects of evaporating and condensing temperature are also computed and discussed.Results obtained indicate that the coefficient of performance and exergetic efficiency of three refrigerants are similar.In other properties,the R125/R1234 yf mixture is superior to R134 a and R513 A.R125/R1234 yf mixture is a better substitute to R134 a compared to R513 A.Among the system components,the evaporator presents the highest exergy destruction,followed by the condenser,the compressor and the throttle valve.