Flow boiling heat transfer with HFC mixtures in a smooth horizontal tube. Part II: Assessment of predictive methods

In tube heat transfer characteristics of R410A and R404A have been experimentally investigated in a smooth horizontal tube made of stainless steel with an inner diameter of 6 mm and a length of 6 m, uniformly heated by the Joule effect. The evaporation pressures has been varied within the range from 3 to 12 bar, the refrigerant mass flux within the range from 290 to 1100 kg/m2 s and the heat flux within the range from 11 to 39 kW/m2. In this paper attention is focused on the comparison between experimental results and theoretical results predicted with the most known correlations from literature. The best agreement was found with the results of the correlation of Kandlikar [J. Heat-Transfer, 112 (1990) 219]. A modification of the Kandlikar correlation has been proposed in the present paper to predict the local heat transfer coefficients obtained with the test facility. A correction factor that enhance the influence of the nucleate boiling term has been introduced to take into account the influence of the reduced pressure on the heat transfer coefficients.