Experimental study on falling film evaporation heat transfer of ammonia on horizontal tubes.

Abstract

The present study experimentally investigated falling film evaporation heat transfer characteristics of ammonia on horizontal stainless smooth tubes. Test tubes with diameters of 60.5mm and 42.7mm respectively and an effective heat transfer length of 300mm ware tested. Experiments were conducted using the ammonia as the refrigerant at a saturation temperature of -5 °C, heat flux range of 3 to 20 kWm-2 and film Reynolds number of 100 to 500. Falling film evaporation heat transfer coefficients increased with increasing heat flux and decreased with increasing film Reynolds numbers. Measured heat transfer coefficients were 4 times higher than values calculated by pool boiling heat transfer equations when heat flux was 10 kWm-2. Measured heat transfer coefficients were compared with predicted values calculated by previous correlations and found to be lower than the predicted ones.