Evaporation and Condensation Heat Transfer Enhancement for Alternative Refrigerants Used in Air-Conditioning Machines

Abstract

The new advanced heat transfer tube called “Herringbone Heat Transfer Tube”, having a unique inner surface geometry, has been experimentally investigated with the aim to enhance the heat transfer and improve the heat exchanger performance with R407C. Experimental examinations have been carried out to obtain the heat transfer coefficient and pressure drop for R407C flowing inside the horizontal herringbone tube, and the data have been compared with those for the existing inner-grooved tube. The heat transfer enhancement mechanism for the herringbone tube has been proposed in that the thin film layer spots that occur inside the tube could cause the heat transfer enhancement. The heat exchanger performances of the herringbone tube and the standard inner-grooved tube are compared toassess thire impact on energy conservation. The heat transfer coefficients for the herringbone tube are much larger than those for the standard tube, but the significant increase in heat transfer has been accomplished with an increase in pressure drop. The circumferential local heat transfer measurements have suggested that the heat transfer mechanism proposed by the authors is qualitatively verified, but the quantitative verification of the enhancement for the herringbone tube is not sufficiently clarified. The practical comparison of the heat exchanger performance showed that the evaporator performance is improved only at relatively high refrigerant flow rates, while the condenser using the herringbone tube seems to be better than that using the standard inner-grooved tube for all the refrigerant flow rates.