Thermoelectric Membrane Distillation System Engineering Design Improvement Concepts

All of the membrane distillation technologies that NASA has examined to date require external heating and cooling subsystems to drive the distillation and condensation processes. Since energy is added to the system to change liquid water into vapor, and energy is rejected from the system to convert vapor back into a liquid, a higher efficiency is achieved when the enthalpy of liquefaction is recaptured for use in supplementing the enthalpy of vaporization. The Thermoelectric Membrane Distillation (TMD) system embeds thermoelectric devices acting as heat pumps directly at the membrane surface into a self-contained device, thereby heating the rententate while simultaneously cooling the permeate. A flexible testing apparatus has been developed to quickly validate the TMD concept and to characterize different key performance parameters, which have been utilized to develop models for the design of engineering prototypes. This paper describes the validation of our proof-of-concept work, the design improvements implemented to improve performances, and the degradation of performances observed during long-duration testing.