This paper documents the testing of a vacuum membrane distillation system intended for use with liquid desiccants. Liquid desiccants offer the possibility for low-energy, ambient temperature dehumidification. Effective desalination and purification of diluted desiccants outputs two important products: a concentrated desiccant for reuse in dehumidification and fresh water. In this study, vacuum membrane distillation was used in the laboratory to purify diluted liquid desiccants. Calcium chloride and magnesium chloride were the desiccants selected for testing. Desiccant solutions were pumped through the lumens of poly(vinylidene fluoride) (PVDF) hollow fiber membranes at varying feed inlet temperatures, solution velocity rates and vacuum set points during membrane distillation. An average flux of 8 kg m-2 h-1 was obtained using 30 wt% magnesium chloride solution at a temperature of 50 °C while applying vacuum to achieve 25 mbar absolute pressure on the air side of the membrane. The results are promising for the development of a full-scale vacuum membrane distillation process for desiccant solution regeneration and fresh water recovery. In addition, the recovered condensate was of sufficient quality for use in agricultural irrigation or drinking water.
20Agriculture accounts for ~70% of freshwater usage worldwide. Seawater desalination alone cannot meet 21 the growing needs for irrigation and food production, particularly in hot, desert environments. 22Greenhouse cultivation of high-value crops uses just a fraction of fresh water per unit of food produced 23when compared with open field cultivation. However, desert greenhouse producers face three main 24 challenges: fresh water supply, plant nutrient supply and cooling of the greenhouse. The common 25 practice of evaporative cooling for greenhouses consumes large amounts of fresh water. In Saudi 26Arabia, the most common greenhouse cooling schemes are fresh water-based evaporative cooling, 27 often using fossil groundwater or energy-intensive desalinated water, and traditional refrigeration-28 based direct expansion cooling, largely powered by the burning of fossil fuels. The coastal deserts have 29 ambient conditions that are seasonally too humid to support adequate evaporative cooling, 30 necessitating additional energy consumption in the dehumidification process of refrigeration-based 31cooling. This project evaluates the use of a combined-system liquid desiccant dehumidifier and 32 membrane distillation unit that can meet the dual needs of cooling and fresh water supply for a 33 greenhouse in a hot and humid environment. 34
a b s t r a c tDehumidification is responsible for a large part of the energy consumption in cooling systems in high humidity environments worldwide. Improving efficiency is therefore essential. Liquid desiccants offer a promising solution for dehumidification, as desired levels of humidity removal could be easily regulated. The use of membrane contactors in combination with liquid desiccant is attractive for dehumidification because they prevent direct contact between the humid air and the desiccant, removing both the potential for desiccant carryover to the air and the potential for contamination of the liquid desiccant by dust and other airborne materials, as well as minimizing corrosion. However, the expected additional mass transport barrier of the membrane surface can lower the expected desiccation rate per unit of desiccant surface area. In this context, hollow fiber membranes present an attractive option for membrane liquid desiccant contactors because of their high surface area per unit volume. We demonstrate in this work the performance of polyvinylidene fluoride (PVDF) based triple-bore hollow fiber membranes as liquid desiccant contactors, which are permeable to water vapor but impermeable to liquid water, for dehumidification of hot and humid air.
Global changes in mean surface temperatures are driving increased extreme environmental events which are beyond the tolerance of traditional agricultural practices, creating concerns of food insecurity (
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.