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Full Description
Adsorption energy systems can be driven by thermal energy from waste heat or the sun and thereby allow reducing fossil energy consumption and thus reduce global greenhouse gas emissions. Adsorption heat pumps and chillers can provide heating or cooling, adsorption thermal energy storage allows storing thermal energy. However, adsorption energy systems suffer from high investment costs due to low performance.
Performance of adsorption energy systems strongly depends on the equilibrium properties of the working pair as well as heat and mass transfer mechanisms of the adsorption material in the adsorption energy system (adsorbent configuration).
Evaluating new working pairs and adsorbent configurations is rather challenging: While the working pair's equilibrium properties can be determined with standardized measurement equipment, heat and mass transfer mechanisms cannot easily be determined, since they strongly depend on the full-scale adsorption energy system. Construction and operation of full-scale experiments requires high effort. Besides, often only small amounts of an adsorbent configuration are available, which are insufficient for full-scale experiments.
To resolve these drawbacks, this thesis provides and validates a comprehensive method to determine the performance of working pairs and adsorbent configurations in adsorption energy systems from simple small-scale experiments. As a representative class of adsorption energy systems, adsorption chillers are investigated in this thesis. A small-scale Large-Temperature-Jump experiment is combined with dynamic modeling of the transient heat and mass transfer processes. Additionally, the experiment is extended by an infrared camera. The additional temperature information allows to distinguish and to determine the time-resolved effective heat transfer coefficient and diffusion coefficient in the heat and mass transfer model.
The heat transfer and diffusion coefficients are inserted into a full-scale adsorption chiller model to predict the performance. Exemplarily, a commercial available silica gel and the adsorbent class of metal-organic frameworks (MOFs) are evaluated for an adsorption chiller application.
The method is validated with experimental data of a full-scale prototype adsorption chiller and shows high accuracy. Furthermore, the method allows optimizing the adsorption chiller for a given working pair or adsorbent configuration and allows identifying bottlenecks and potential for improvement of the working pairs. In summary, this thesis bridges the gap between small-scale experiments and modeling of full-scale adsorption energy systems. The method allows for a comprehensive and reliable evaluation of working pairs and adsorbent configurations for adsorption energy systems.
