Distribution of heat transfer coefficient in the vertical tube of falling film evaporator treating saline wastewater based on micro flow and experimental verification

Abstract

It is still one of the significant solutions to treat saline wastewater with thermal desalination technology, especially falling film evaporators. To improve the performance of the falling film evaporator, a numerical study on the gas–liquid two-phase flow characteristics of saline wastewater in the vertical pipe was conducted using the VOF model. The results showed that the inlet velocity of the saline wastewater increased under the same operating conditions, resulting in the thickening of the liquid film and the increase of the average convective heat transfer coefficient. Increasing the inlet temperature of the working liquid reduced the temperature difference, which led to a decrease of the average convective heat transfer coefficient. In addition, as the inlet concentration of the working liquid increased, the film flow rate and the average convective heat transfer coefficient first decreased and then increased slightly. The experimental results verified the accuracy of the numerical simulation, and the average error was 9.27%. HIGHLIGHTS The study of fluid microflow combined with heat transfer was proposed.; The distribution of heat transfer coefficient based on numerical simulation.; The distribution of heat transfer coefficient is correctly verified by experiments.; The effects of the various operating parameters on the heat and mass transfer processes are studied.;

Keywords

• convective heat transfer coefficient
• falling film evaporation
• numerical simulation
• saline wastewater