On the thermodynamic analysis of a novel low-grade heat driven desalination system

Thermally-driven desalination technologies are ideal for mitigating the problem of water scarcity using sustainable and renewable energy sources. This paper presents a novel technology for thermal desalination: a spray assisted low-temperature desalination. It applies direct contact heat and mass transfer mechanism for both evaporation and condensation, which markedly enhances heat and mass transfer while eliminating the need for a metallic surface inside the chambers. To perform an in-depth analysis on this novel technology, a detailed thermodynamic model has been developed. The model is based on the principles of appropriate heat balance, mass balance and salt balance, and judicious heat transfer and mass transfer in the system. Key input parameters that affect system performance are taken into account in formulating the model. Simulations were conducted for top brine temperatures spanning 55-90 °C for low-grade heat utilization. Key results from the model revealed that more operating stages and higher top brine temperatures are essential to enable higher production rates and realizing better thermal efficiencies, while a cooling water flowrate close to the feed water flowrate is at the optimal. A system performance ratio of 6.5 can be achieved for a 14-stage system with a top brine temperature of 90 °C.