23 September 2011

EXPERIMENTAL INVESTIGATION OF FLOW BOILING HEAT TRANSFER OF HFO1234YF AND R32 REFRIGERANT MIXTURE IN A SMOOTH HORIZONTAL TUBE


: HFO1234yf has been proposed as a promising candidate to mobile air conditioner
due to its low GWP and comparable performance to R134a. However its performance is
inferior to that of R410A. That makes it difficult to be applied into residential air conditioners.
In order to apply the low GWP refrigerant to residential air conditioners, refrigerant mixtures of
HFO1234yf + R32 are proposed and their flow boiling heat transfer performances at two mass
fractions (80/20 and 50/50 by mass%) in a smooth horizontal tube with ID 2 mm were
investigated. The experiments were conducted under heat fluxes from 6kW/m
2
to 24kW/m
2
and mass fluxes from 100kg/m
2
s to 400kg/m
2
s at evaporating temperature of 15
o
C. The
measured heat transfer coefficients were compared with those of pure R32 and pure
HFO1234yf, respectively. The results showed that the heat transfer coefficients of the mixture
at R32 mass fraction of 20% are 10% ~ 30% lower than those of pure HFO1234yf at different
mass fluxes and heat fluxes. But results of the mixture are 10%-20% higher than those of
pure HFO1234yf at a high heat flux and high mass flux condition when the mass fraction of
R32 increases to 50%. Heat transfer coefficients of the mixture are about 20%-50% lower
than that of pure R32. It is indicated that mass diffusion and the temperature glide of the
mixture influence the heat transfer significantly. A correlation was proposed to predict heat
transfer coefficients of the mixture HFO1234yf+R32, pure R32 and pure HFO1234yf. The
deviation was confirmed be within ±20% for fitting over 80% data.