Horizontal flow boiling heat transfer experiments with a mixture of R22/R114

Abstract

An experimental study on horizontal flow boiling heat transfer for pure R22, R114 and their mixtures under uniform heat flux condition is reported. More than 1200 local heat transfer coefficients are obtained for annular flow at a reduced pressure of 0.08. The ranges of heat flux and mass flow rate are 1045 kW m −2 and 16–46 g s −1, respectively. The results indicate a full suppression of nucleate boiling for pure and mixed refrigerants beyond transition qualities and the majority of the data belongs to the convective evaporation region. The heat transfer coefficients of mixtures in this region are as much as 36% lower than the ideal values under the same flow condition. Non-ideal variations in physical properties account for 80% of the heat transfer degradation seen with mixtures and the other 20% (less than 10% of the heat transfer coefficient) is believed to be caused by mass transfer resistance in this region. A composition variation of up to 0.07 mole fraction in the annular liquid film was measured between the top and bottom of the tube, which causes a corresponding circumferential variation of wall temperature with mixtures.