Abstract
A novel thermodynamic cycle for adsorption heat pumps and chillers is presented. It shows a significant improvement of the internal heat recovery between the adsorption and the desorption half cycle. A stratified thermal storage, which allows for a temperature-based extraction and insertion of storage fluid, is hydraulically coupled with a single adsorber. The benefit is an increased efficiency by reusing the released heat of adsorption for regeneration of the adsorber and by rendering possible low driving temperature differences. For investigating the second law of this cycle, a dynamic model is employed. The transient behavior of the system and the respective losses because of driving temperature differences at the heat exchangers and losses due to mixing within the storage and to the surroundings are depicted in this one-dimensional model. The model is suitable both for analyzing this advanced cycle as well as for comparisons with other cycles.
Highlights
Typical coefficients of performance (COP) attainable employing a standard adsorption heat pump cycle are significantly lower than those using a standard single stage absorption cycle [1]
We comprehensively described the Stratisorp cycle concept and introduced a model suitable for the dynamic simulation of such advanced adsorption cycles
The second-law-analysis of the cycle reveals that the entropy generation due to external-temperature-coupling in the adsorber is strongly reduced compared to a standard two-adsorber-cycle
Summary
Typical coefficients of performance (COP) attainable employing a standard adsorption heat pump cycle are significantly lower than those using a standard single stage absorption cycle [1]. These differential heat curves are derived from a pure adsorption equilibrium model integrated over an ideal cycle with two isobars and two isosteres (cf [10] (Section 3.2), [8,14]). When searching for novel adsorbents for standard adsorption cycles (which are not suitable to achieve a high internal heat recovery), an S-shaped adsorption isotherm is desired [13,16,17] This leads to sharper peaks in the differential heat curves and a reduced temperature overlap and recoverable heat. The advantage of any cycle allowing for a large internal heat recovery over a standard two-adsorber cycle can be expected to be higher for the type of working pair with a loading field stretched evenly across a wide temperature range (that is linear rather than S-shaped isotherms and isobars)
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