3879 -- R-502 and Two Near-Azeotropic Alternatives. Part II - Two-Phase Flow Patterns PDF

Flow patterns for horizontal in-tube flow boiling have been studied for new refrigerants R402A and R404A and the conventional refrigerant R502. The flow pattern observations were compared with several criteria utilised in horizontal flow boiling correlation for determining whether the entire circumference of a horizontal evaporator tube is all wet or partially wet. Use of only the liquid Froude number (utilised in numerous flow-boiling correlations) is shown to be completely unreliable. Stratified (partially wet wall) flow was found to occur at liquid Froude numbers up to 16 times those of the recommended threshold values utilised by the correlations. A semi-empirical method for predicting stratification proposed by Klimenko and Fyodorov is an improvement but still is not very successful in predicting the present data.

KEYWORDS: year 1995, refrigerants, mixtures, R502, R402A, R404A, replacing, fluid flow, calculating, boiling, horizontal, comparing, evaporators, tubes, Froude numbers, testing, experiment, properties.