Quantification of heat and mass transport limitations in adsorption heat exchangers: Application to the silica gel/water working pair

Developing strategies to reduce mass and heat transport limitations is one of the most important challenges in adsorption heat exchanger technology. Due to the strong coupling of mass and heat transport in these systems, it is difficult to determine the individual transport limitations quantitatively. In order to find an optimal design where heat and mass transport are balanced, a quantitative method that enables a direct comparison of these two transport phenomena is needed. In the present work, a novel experimental approach to discriminate between mass and heat transport is proposed based on the measurement of adsorbent temperature, heat exchanger surface temperature and vapor pressure. The methodology is applied to micro/mesoporous silica spheres arranged in a monolayer or bilayer loose grain configuration or in a monolayer configuration adhesively bonded to the substrate. While the monolayer configuration exhibits balanced heat and mass transport, we find that the bilayer and the thermally enhanced configurations are limited by heat and mass transport, respectively. The application of the proposed methodology to compare heat and mass transport limitations in other industrially-relevant adsorbent materials should greatly aid the design of more efficient adsorption heat exchangers for a wide range of applications.