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Abstract: This paper reports on the experimental research conducted to study the condensation of ammonia on smooth and integral-fin (32fpi) titanium tubes of 19.05mm outer diameter. Experiments were carried out at saturation temperatures of 30, 35, 40 and 45°C and wall subcoolings from 1 to 8°C. The results show that the condensation coefficients on the smooth tubes are well predicted by the Nusselt theory with an average error of +0.66% and within a deviation between −6.6% and +8.3%. The enhancement factors provided by the integral-fin tubes range from 0.77 to 1.22. The low enhancement factors are due to the high condensate retention between fins, which brings about flooded fractions of the tube perimeter from 62.9% to 73.2%, and the low thermal conductivity of titanium. The Briggs and Rose [1994. Effect of fin efficiency on a model for condensation heat transfer on a horizontal, integral-fin tube. Int. J. Heat Mass Transfer 37, 457–463.] model, which accounts for the conduction in the fins, predicts the experimental data with a mean overestimation of 20%. The analysis of the partial thermal resistances in the overall heat transfer process points out the convenience of enhancing the outside ammonia condensation when high water velocities are considered inside the tubes. [Copyright &y& Elsevier]

Abstract: Attention is drawn, to the fact that, while four different correlations for condensation in microchannels are in fair agreement for the case of R134a (on which the empirical constants in the correlations are predominately based) they differ markedly when applied to other fluids such as ammonia. A wholly theoretical model is compared with the correlations for both R134a and ammonia. [Copyright &y& Elsevier]