Heat Transfer to Non-azeotropic Mixtures of Refrigerants Flowing in a Horizontal Evaporator Tube

Heat transfer is experimentally investigated for refrigerant mixtures of R 22 and R 114 flowing in a horizontal evaporator tube. The heat transfer coefficients for the mixtures are always lower than the ‘ideal” values estimated from the heat transfer coefficients for pure refrigerants. This reduction is significant in the region where nucleate boiling contributes to the heat transfer, and is attributed to the mass transfer resistance in addition to the change of fluid properties. In the convection dominant region, the reduction in the heat transfer coefficient is assigned solely to the ‘unideal' effect of physical properties, and the heat transfer coefficients are approximately equal to those of an equivalent pure fluid with the same physical properties as the mixture. None of the correlations hitherto proposed for the heat transfer to binary mixtures successfully predict the present heat transfer coefficients.