Non-isothermal adsorption kinetics of water vapour into a consolidated zeolite layer

Abstract

A one-dimensional model for the kinetics of water vapour adsorption into a consolidated zeolite layer is presented. The combined heat and mass transfer problem is modelled and simulated using the software packet gPROMS ® (general PROcess Modelling System). The centered finite difference method approximation is employed in solving the obtained set of partial differential, ordinary differential and algebraic model equations. Mass transfer is described by micro-pore diffusion, while heat transfer is described in terms of conduction. The temperature dependence of the diffusion coefficient is defined by an Arrhenius relationship, whereas the concentration dependence is accounted for by the Darken factor. The validity of the developed model has been checked against an experimental study, in which the kinetics of water vapour adsorption into a consolidated zeolite layer has been investigated in a constant volume-variable pressure test rig. The starting pressure has been changed in the range of 10–30 mbar, while the wall temperature has been adjusted to 35 and 50 °C. The measured characteristic half time for the adsorption kinetics varies between 13 and 21 s, while the required time to reach 90% of the equilibrium water loading lies between 70 and 94 s depending on the adsorption boundary condition. These times are quite short and promise highly compacted adsorption heat pump appliances. Fitting the results of the experimental investigations against the numerical simulation model gives a micro-pore diffusion coefficient ( D ∞) of 1.58 × 10 - 4 (m 2 s −1) and an activation energy of 32.41 (kJ mol −1). Furthermore, a measuring cell wall heat transfer coefficient ( α W) of 230 (W m −2 K −1) has been estimated.