Freeze Desalination: Experimental Investigation and High-Fidelity Modeling

Abstract

This thesis is dedicated to the experimental and numerical scrutiny of saltwater freeze desalination. The primary goal is to examine salt trapping during seawater freeze desalination and seek strategies to enhance ice quality while improving desalination efficiency. Initially, the temperature evolution of brine during freezing and the salinity gradient within the formed ice are obtained in the brine freezing experiments to clarify the freezing dynamics and salt diffusion during the freezing. Subsequently, the impact of freezing source temperature and initial salinity on the salinity gradient of the ice is systematically studied, revealing an optimal freezing temperature of approximately -15°C for brine with a concentration of 35 g/L. Moreover, it is observed that supercooling in low-salinity brine exacerbates the reduction in desalination efficiency. Both bulk freezing and droplet freezing experiments are then conducted to investigate supercooling further. The findings indicate that regions near the cooling source experience the highest supercooling, leading to nucleation initiation. Strategies to minimize supercooling, such as increasing the cooling source temperature and brine initial salinity, are proposed based on droplet freezing experiments. However, these conditions may not be suitable for saltwater freezing operations, prompting further exploration of additional factors to enhance desalination efficiency. The lateral-center freezing direction is identified as yielding higher desalination efficiency compared to top-down and bottom-up freezing, with optimal stirring rates also identified. Subsequent experiments employing these optimal parameters demonstrate significant improvements in water recovery rates, reaching 23.8% in five-stage freezing of a 35 g/L NaCl solution, representing a 2180% increase compared to five-stage bottom-up freezing method alone. Additionally, low-fidelity and high-fidelity models are developed to investigate the freezing process and salt diffusion, providing valuable insights not directly observable in experiments. Overall, this research contributes to the advancement of freeze desalination methods by elucidating salt trapping mechanisms and proposing strategies to enhance desalination efficiency.

Date of Award	17 May 2024
Original language	American English
Supervisor	Isam Janajreh (Supervisor)