| Pressure drop experiments were performed in small channels with three refrigerants: R-134a, R-12, and R-113. The channel size simulates flow passages in compact evaporators. The pressure drop results were obtained for quality up to 0.95, a mass flux range of 33 to 832 kg/m2s, a heat flux range of 2.2 to 90.8 W/m2, and in the range of pressure from 138 to 864 kPa. Flow boiling heat transfer experiments of R-134a were also conducted over a range of quality up to 0.9, a mass flux range of 33 to 502 kg/m2s, a heat flux range of 2.2 to 49.8 W/m2, and in the range of pressure from 342 to 856 kPa. Local heat transfer coefficients were determined experimentally as a function of heat flux. The effects of pressure and fluid properties on heat transfer and pressure drop performance, as well as insights relative to heat transfer mechanisms in small channels, are presented. The heat transfer results are presented for both nucleate boiling and convective boiling heat transfer regimes and are compared with large-channel predictions. New correlations for pressure drop and heat transfer are proposed for small channels based on data of R-134a, R-12, and R-113. The relationship between pressure drop and heat transfer of flow boiling was also presented. |
