Abstract
In order to achieve process intensification for adsorption chillers and heat pumps, a new composite material was developed based on sintered aluminum fibers from a melt-extraction process and a dense layer of silico-aluminophosphate (SAPO-34) on the fiber surfaces. The SAPO-34 layer was obtained through a partial support transformation (PST) process. Preparation of a composite sample is described and its characteristic pore size distribution and heat conductivity are presented. Water adsorption data obtained under conditions of a large pressure jump are given. In the next step, preparation of the composite was scaled up to larger samples which were fixed on a small adsorption heat exchanger. Adsorption measurements on this heat exchanger element that confirm the achieved process intensification are presented. The specific cooling power for the adsorption step per volume of composite is found to exceed 500 kW/m3 under specified conditions.
Highlights
In the development of adsorption heat pumps and chillers over the past decades, it has been a persistent goal to increase the volume-specific cooling or heating power to achieve more compact and light-weight units
Perhaps the simplest concept of an adsorption heat exchanger is a bed of adsorbent grains in a volume, part of which is occupied by some kind of heat exchanger
The best heat transfer achievable as the limiting case of an adsorbent bed is obtained for a single layer of adsorbent grains on each heat exchanger surface, which is an approach taken, for example, in some zeolite/water heat pumps that have become available on the market recently ([2,3,4])
Summary
In the development of adsorption heat pumps and chillers over the past decades, it has been a persistent goal to increase the volume-specific cooling or heating power to achieve more compact and light-weight units. Jaeschke and Wolf [16] propose to glue a single layer of silica gel onto the surface of a finned-tube heat exchanger, whereas Freni et al [17] report an increase by a factor of 10 to 20 in power density for a binder-based coating with the silica gel/calcium chloride composite material. When using water as a working fluid, the low operating pressure restricts the thickness of compact layers, whereas other working pairs like ammonia/activated carbon with a high operating pressure show less sensitivity to this restriction [28] To overcome this issue, the surface area of the heat exchanger has to be enlarged considerably. The feasibility of the scale-up to a new type of compact adsorption heat exchanger is presented and its water uptake behavior is examined
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