Simulation analysis of flow velocity and liquid film of saline wastewater in falling film evaporation

Abstract

It is an important way to promising treatment strategy to use the Multiple Effect Distillation(MED) system for saline wastewater treatment by numerical simulation. In the paper, the flow and heat transfer process’s difference of saline wastewater and pure water in falling film evaporator was simulated based on the volume of Fluid(VOF) multiphase flow model and the SIMPLE algorithm. Analysis results show that the temperature of pure water and saline wastewater reached 373.15 K at 226.3 mm from the evaporation pipe inlet. Compared with pure water, saline wastewater has slightly lower axial velocity, higher liquid film temperature and faster evaporation rate under the same conditions. In order to improve the heat transfer performance of saline wastewater in falling film evaporator, a comparison of tube diameter and length is made. At the same unit width flow, increasing tube diameter can improve heat transfer performance. In the tube diameter range of 35–50 mm, the heat transfer effect is best when the tube diameter is 50 mm. Under the condition of the same average circumferential flow and considering economy and efficiency, 1000 mm tube length is considered appropriate.