Use of membrane transport in an absorption thermal transfer cycle

Abstract

A thermal transfer cycle utilizing membrane osmotic transport of water against a pressure rise is investigated from the viewpoint of the operation of a conventional absorption heat pump using an aqueous solution as the working fluid. Physical sorption, similar or equivalent to condensation, of water vapor in the membrane material is considered to be an essential step in the overall process of water transport. The thermal nature of this step, during which the heat of sorption similar in amount to the heat of condensation for water vapor must evolve at the evaporator temperature or lower, disqualifies the system in performance as a heat pump. Simple flow relations for the aqueous sugar solution are derived under simplifying assumptions. A set of numerical calculations is given to show that the inferred steps are well within the limits of thermodynamics.