Abstract
Active transport caused by the temperature gradient is discussed from the viewpoint of energy transformation. When a membrane can adsorb a specific solute and the equilibrium constant for the adsorption changes significantly with temperature, the solute is adsorbed at the low temperature side and desorbed at the high temperature side. Simultaneously, the heat of adsorption is required at the high temperature side and is evolved at the low temperature side, giving rise to net flow of heat from the high temperature solution to the low temperature one.
The concept of exergy is applied to analyse the energy transformation in such a nonisothermal system. The exergy required to transport a mol of solute from a dilute solution of concentration Cl to a concentrated one of Ch can be expressed as ΔεT=RTo in Cl/Ch' while the exergy consumed is Δεad, =To [(ΔH) /Tl- (-ΔH) /Th]. Hence, the ideality index ηI in this case is given by ΔεT/ (Δεad+Δεcond), where Δεcond is the exergy loss by the heat conduction. It is found that ηI becomes unity when the system is operated ideally and ηI obtained experimentally for a Sirotherm ion-exchange resin membrane was 0.0745.
