Existing schemes for correlating heat transfer coefficients for convective vaporisation in tubes and tube banks are reviewed briefly. The asymptotic model is selected as the most suitable for correlating both in-tube and tube bank data. The model contains a nucleate boiling and a forced convection term, and the vaporisation coefficient is asymptotic to pool boiling at low Reynolds numbers (Re) and to convective vaporisation at high Re. The model is used to correlate the authors' R11 and R123 data for a tube bank with enhanced tube geometry. The data span vapour qualities of 0 to 0.9, mass velocities of 10 to 20 kg/m2.s (7,369 to 14,738 lb/ft2.h, and heat fluxes of 15 to 45 kW/m2 (4,761 to 14,283 Btu/h.ft2). The data were taken in an apparatus that allows independent control of vapour quality, mass velocity, and heat flux. The two-phase convection multiplier is correlated with the two-phase friction multiplier and the liquid Prandtl number. The data show no suppression of the nucleate boiling coefficient because of convection. The exponent in the asymptotic model is chosen to provide the best fit. The model correlates heat transfer coefficients within + or - 20%.

KEYWORDS: refrigerants, vaporising, tubes, heat flow, heat transfer coefficient, calculating, boiling, Reynolds numbers, R11, R123, Prandtl number