CFD analysis of the tube bundle orientation impact on the thermal losses and vapor uniformity within the MED desalination plant

Thermal desalination still considered as a reliable technology, where the seawater characteristic is challenging in terms of high salinity, elevated temperature and high impurity level especially in the Gulf seawater case. Multi-effect distillation (MED) is an efficient thermal process for the commercial and large-scale desalination plants. Even though, minimization of the thermal losses within the evaporator is a matter of interest to improve the MED process. This work presents a computational fluid dynamic (CFD) simulation of vapor route for two conventional MED configurations named as long tube (MED-LT) and cross tube (MED-CT), respectively. The thermal losses and vapor uniformity are calculated at several vapor box lengths and process recovery ratios. An MED evaporator of 25 m ³ /d is considered for the CFD computational domain and conducted by COMSOL multiphysics. The CFD results show that compared by MED-LT configuration, the MED-CT configuration creates less uniform vapor flow at the tube sheet which indicates that some tubes will be admitted by amount of vapor higher than the designed, and accordingly will become overheated and lead to the scale deposition on the tube surface. The tube bundle losses represent 90% of the total losses while the rest is encountered in the demister and vapor box. This indicates that minimizing the thermal losses in the tube bundle is more effective and recommended for future work. The footprint of the MED-LT configuration is 25% lower than that the MED-CT configuration. It can be concluded that the MED-LT configuration is superior in terms of better vapor uniformity for reliable operation and lower foot print.