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Abstract
Several simple vapour cooling and pre-condensing concepts were assessed for the purpose of mitigating bubble column vapour temperatures, a critical aspect for the development of a bubble column driven greenhouse desalination system. Particular emphasis was on low-energy demand of the devices, ease of manufacture, low investment cost and technical and operational appropriateness for local people in remote places. Under laboratory conditions, the copper tube type I and II concepts achieved water recovery rates of between 65 and 75%. The water-tank cooled tube achieved 83% condensate recovery, albeit at the cost of large cooling water requirements, whereas the air cooled and passive sleeve-cooled bubble condenser columns achieved condensate recovery rates of at least 50% under favourable ambient conditions. A “self-cooling” effect was observed for the passive sleeve columns that could perhaps be tailored to produce small quantities of potable water in hot and arid regions. The effectiveness–NTU method was used to allow for a meaningful comparison between the devices. While the majority of the tested concepts represented a “single-stage” approach to the humidification–dehumidification cycle, it is stressed that a well-designed latent heat recovery system would be crucial for the economic viability of a bubble greenhouse.