Shell-side two-phase pressure drop and evaporation temperature drop on falling film evaporation in a rotated square bundle

Abstract

An experimental investigation of steam flowing across a horizontal tube bundle and related calculations on falling film evaporation in a rotated square bundle were conducted to simulate flow characteristics in a large desalination plant. The experiments and calculations were performed under saturated temperature ranging from 50 °C to 70 °C and water-spray density ranging from 0.02 kg/m·s to 0.08 kg/m·s. The intertube pressure drop and the corresponding temperature drop were presented under various operating conditions. The effects of saturated temperature, water-spray density and steam mass velocity on the pressure drop as well as on the consequent temperature drop were analysed. A correlation for predicting the pressure drop of steam flowing across the horizontal tube bundle with falling film was proposed based on the experimental results. The experimental data were reproduced within ±10%. The rotated square bundle was selected as the physical model. The fitting coefficient of pressure drop based on previous experimental data was employed for calculating the temperature drop and the pressure drop in falling film evaporation. The calculations indicated that the temperature drop caused by the pressure drop increases with increasing spray density and tube column number, but decreases with increasing saturated temperature. Based on the aforementioned analysis, a new design on a same temperature drop in each effect evaporator for multi-effect distillation evaporators is proposed.