CFD analysis of evaporation heat transfer for falling films application

Abstract

Multi-effect desalination (MED) uses less energy and has a smaller footprint than other thermal desalination systems. The MED plant consists of cascaded horizontal-tube falling film exchangers (HFFE), offering improved heat transfer at lower liquid loads. The MED plant’s current working temperature range is 40 °C–65 °C, for which 6–8 HFFE can be used. However, this limit can be extended to 5 °C–85 °C by using new antiscalants and an adsorption vapor compression system. Thus, more HFFE can provide enhanced water production. Furthermore, the heat transfer studies for this range are limited. Therefore, this work presents a 2-D computational fluid dynamics (CFD) model in Ansys fluent v19.0 to examine the film thickness, the temperature distribution, and the heat transfer coefficient for working temperatures of 5 °C, 65 °C, and 85 °C at various liquid loads. It is found that the heat transfer is improved at higher temperatures and liquid loads by 21 %–37 %, which indicates lower energy requirements and better distillate productivity.

Keywords

• CFD
• Desalination
• Evaporation
• Falling film
• Heat transfer coefficient
• Horizontal tube