Performance investigation of an auto-tuning area ratio ejector for MED-TVC desalination system

In Multi-Effect Distillation with Thermal Vapor Compression (MED-TVC) desalination system driven by low-grade thermal energy, it is arduous for conventional fixed geometry ejectors to operate efficiently with unstable feeding motive steam. In this paper, a variable geometry ejector named auto-tuning Area Ratio (AR) ejector equipped with a bellows-driven spindle is proposed to enhance the performance of MED-TVC desalination system under varying operating conditions. A Computational Fluid Dynamics (CFD) model has been built and validated to investigate the influence of AR on the system performance. A correlation to calculate the optimal opening degree under varying primary pressure with different critical back pressures is established and identified by data regression method. Moreover, with this correlation, an optimization strategy for auto-tuning AR ejector in MED-TVC desalination system is presented. Simulation results show that by using the auto-tuning AR ejector, relatively higher entrainment ratios (Er) can be achieved under varying motive steam. When the pressure of motive steam fluctuates from 800 kPa to 2000 kPa, the average Er of auto-tuning AR ejector is 1.39, higher than fixed geometry ejector of 0.69 with a critical back pressure of 20 kPa. The proposed auto-tuning AR ejector would have wide applications in MED-TVC desalination systems and other systems driven by low-grade energy.