Study on flow boiling heat transfer characteristics of R161/oil mixture inside horizontal micro-fin tube

The research on alternative refrigerants has been one of the urgent issues in the refrigeration and air conditioning industry for the sake of reducing ozone depletion and global warming effect. R161, as a refrigerant with good environmental acceptability (GWP = 12, ODP = 0), good thermo-physical properties, good heat transfer and flow characteristics, and highly similar thermo-physical properties to R22, has attracted broad attention as a substitute of R22 and R407C. In this paper, the boiling heat transfer and pressure drop characteristics of R161/POE mixture in a 7 mm O.D. horizontal micro-fin tube were investigated by experimental methods. The local heat transfer coefficients and pressure drops were measured at mass flux range of (100 ∼ 250) kg/(m2·s), heat flux range of (11.76 ∼ 52.94) kW/m2, bubble point temperature range of (−5 ∼ 8) °C, and oil concentration range of (0 ∼ 5)%. The results showed that: (1) at low vapor quality region, the local heat transfer coefficient increased with oil concentration, while at the high vapor quality region, it decreased rapidly with the increase of oil concentration; (2) the pressure drop increased with the increase of oil concentration, mass flux and heat flux; (3) the influence of oil on heat transfer coefficient and pressure drop decreased with the increase of mass flux. A new correlation to predict the local boiling heat transfer of R161/oil mixture inside small micro-fin tubes was developed on the basis of the local properties of refrigerant/oil mixture and structure of enhanced tube, and the predicted data agreed with the experimental data within the deviations of (−15 ∼ +20)%.