Improvement of both adsorption performance of silica gel and heat transfer characteristics by means of heat exchange modulation for a heat pump

In order to provide high performance silica gel for an adsorption heat pump (AHP), gels were synthesized using the sol-gel process modified with a new method of controlling the primary gel particle growth by the addition of aluminum ion. In this process, the pores of the silica gel synthesized became smaller when aluminum ion was added in the washing process. Furthermore, this silica gel adsorbed more water at a low region of water vapor pressure and its adsorption ability did not change after 100 repetitive times of adsorping/desorping water vapor. The experimental results from the water vapor adsorption on the silica gel agreed well with theoretical results obtained under the Lump model for heat transfer and intraparticle diffusion model for mass transfer. A new direct heat exchange silica gel module (DS-module) for the AHP was provided, and the heat transfer characteristics during the operation for the adsorption of water vapor were both experimentally and theoretically determined. The period of the adsorption for the DS-module was shorter than that for a silica gel/tube module. Therefore, with the addition of the DS-module the heat transfer in the AHP adsorber was sufficiently enhanced and the maximum heat generation power for the 2-mm-thick DS-module was obtained. © 1997 Scripta Technica, Inc. Heat Trans Jpn Res, 25(7): 420–433, 1996