A thermoelectric integrated membrane evaporation system

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A thermoelectric integrated membrane evaporation system

Trusch, R.B. / Roebelen, G.J.

A new urine water recovery subsystem is being designed to provide efficient potable water recovery from waste liquids on extended duration space flights. Low power, compactness, and gravity insensitive operation are featured in this vacuum distillation system which combines a hollow fiber polysulfone membrane evaporator and a thermoelectric (TE) heat pump. Application of these key elements have solved problems inherent in previous reclamation system designs. The hollow fiber elements provide positive liquid/gas phase control with no moving parts other than a waste liquid recirculating pump and a condensate pump. Tubular membranes also provide structural integrity, improving on previous flat sheet membrane designs. A thermoelectric heat pump was selected for heat recovery as opposed to a vapor compressor to elimiate moving parts and equipment noise. Optimum matching of the membrane evaporator area and the number of TE devices resulted in a low power requirement of less than 200 w-hr/kg (100 w-hr/lb) for the TE elements. This is 1/3 of the ideal heat of evaporation required for direct boiling of the liquid. System operation was verified in separate membrane endurance tests and in a scaled-down integrated system test. (Kursetz)