Geometrical analysis of thermo-compressors in multiple-effects distillation units based on the second law of thermodynamics

摘要

Thermo-compressors are used instead of mechanical compression devices in many industries and play a main role in the process. Through the process of designing desalination systems, amount of exergy dissipation is a very important economical factor. Most of the exergy losses in multi-effect distillation systems with thermal vapor compression (multiple-effect desalination-TVC) occur in the thermo-compressor. The aim of this article is to investigate geometrical effects in thermo-compressors by numerical methods based on the second law of thermodynamics to obtain lower exergy loss and consequently, higher entrainment ratio. A lot of geometrical parameters such as converging and diverging angles in mixing section, dif-fuser, nozzle location and also its throat area ratio affect thermo-compressors' performance. The modifications in the above-mentioned parameters were applied to a thermo-compressor established in a desalination unit in Kavian petrochemical company which is working with 15barg of motive pressure. Numerical simulation of the base model has an accurate agreement with experimental data with about 1.3% discrepancy in maximum discharge pressure and just 6.7% in entrainment ratio. Results of the analysis indicate that thermo-compressor's performance is sensitive to the mixing area converging angle. The other parameter which mostly affects the performance is the location of nozzle in thermo-compressor's body.