The effect of tube diameters on evaporation heat transfer for ammonia falling liquid-film.

Abstract

The present study experimentally investigated evaporation heat transfer characteristics of ammonia falling liquid-film on horizontal stainless smooth tubes. The test tubes have outer diameters of 19.1 mm, 34.0 mm, 42.7 mm and 60.5 mm, respectively. Experiments were conducted using ammonia as the refrigerant at a saturation temperature of -5 °C, heat flux and film Reynolds number ranges of 3 to 20 kWm-2 and 100 to 500 respectively. Falling film evaporation heat transfer coefficients decreased with increasing film Reynolds numbers and are affected by tube diameters. Measured heat transfer coefficients were higher than pool boiling heat transfer coefficients of the correlation of Jung et al. in all heat flux ranges.