Performance evaluation of single stage flash desalination system under different air intermittences and intake valve opening conditions

Abstract

Drinking water is produced inside the evaporator of thermal desalination plants through the critical processes of water vaporization and condensation. Any leakage in this unit can lead to substantial losses in thermal energy, reduced distillation efficiency, and potential contamination of the distillate product. Therefore, this study aims to introduce and investigate the thermal performance of single-stage flash desalination systems under different air intermittence and intake rates. An experimental system is fabricated, and experiments are performed with different operating conditions to simulate similar leakage conditions. The initial pressure inside the vacuum tank is set at 8.4 kPa, the water height is 60 mm, and the initial temperatures are 80 °C and 70 °C. The investigation explores the influence of different cycle lengths of air intake ($t_1$) and air removal periods ($t_2$), ranging from 6 s to 160 s for different intermittent periods. The study also explores different intake valve opening levels, including 0%, 25%, 50% and 100%, to understand how these different opening levels affect heat and mass transfer characteristics. The experiments examined and analysed the effect of different valve opening levels, air intake and removal periods, and initial liquid temperatures on measuring parameters such as temperature, pressure, water mass, and non-equilibrium factor (NEF). The results indicate that decreasing the air intake period and increasing the air removal period significantly improves the temperature and pressure drop. When the air removal period increases from 4 s to 6 s, the pool temperature drop increases from 18.6 °$C$ to 23.2 °$C$. With the increase of initial temperature by 10 °$C$,the temperature drop and evaporated mass are increased by 22.4% and 21.7%. The outcomes provided a comprehensive understanding of the effects of leakage on the flashing evaporation process.