Unsteady-state modeling and analysis of a spray-assisted low-temperature desalination system

Abstract

The spray-assisted low-temperature desalination (SLTD) technology driven by low-grade heat sources has demonstrated excellent thermodynamic and economic performances. However, existing studies are based on steady-state analyses and cannot describe dynamic system performance under fluctuations of the operating conditions. This work presents an unsteady-state analysis of the SLTD system driven by low-grade waste-heat sources. A dynamic model is developed and validated against experimental data. The model is observed to predict dynamic temperature profiles accurately with a maximum absolute error of ±0.3 °C. Then, the model is applied to analyze the responses of the SLTD system to different disturbances. Results show that the first evaporator is the most sensitive to the heat source temperature fluctuation, while locations farther away from the disturbance have longer response times and smaller fluctuations. When the heat source temperature for a 4-effect system fluctuates by 10 %, the response time and temperature fluctuation amplitude of the 1st effect are 579 s and 8 %, respectively, while those of the 4th effect are 1007 s and 3 %, respectively. Besides, the systems with smaller heat transfer areas, fewer numbers of effect, and higher heat source temperatures have faster response speeds. The results provide useful information for system operation and control strategy exploitation.