A correlation of heat transfer for falling film evaporation on the horizontal tube with multiple-precision expansion method

Abstract

The falling film evaporation of water and seawater outside the horizontal tube is experimentally investigated under non-boiling condition, and the effects of spray density, evaporation temperature, tube pitch, circumferential position and seawater salinity on the falling film evaporation are studied. A competitive mechanism, based on the analysis of liquid film, is proposed to analyze the critical Reynolds number of the spray water, ReΓ, and the dual effects of liquid film on heat transfer coefficient. The experimental data covers tube diameter D=19∼38 mm, tube pitch s/D=1.3∼2.25, evaporation temperature Tsat=50∼70 °C, spray Reynolds number ReΓ=118∼1979, and salinity S=0∼60 g/kg. By summing up a large number of experimental data, the heat transfer coefficient correlation applying both water and seawater falling film evaporation on horizontal tubes is proposed. The correlation is also compared with previous studies about water and seawater, which shows a better and wider adaptability to experimental conditions.