Abstract
In process engineering, optimization is usually carried out without the simultaneous consideration of material and process. This issue is addressed in the following contribution. A model-based optimization is presented to improve the performance of adsorption heat pumps. Optimization is carried out in two steps. First, we optimize the operational parameters, the cycle time, and the thickness of the adsorbent for a given adsorption material. In a second step we use a material model to predict heat and mass transfer and adsorption capacity from structural material parameters. This allows us to vary the structural material parameters and calculate the optimal operational parameters for each adsorbent. The two-step optimization thus identifies optimal material properties together with corresponding optimal operational parameters. As constraints, a minimum specific cooling power (SCP) and the passive mass of heat transfer pipes are used. The coefficient of performance (COP) is taken as the objective function. We exemplarily demonstrate the approach for a two-bed adsorption chiller, carbide-derived carbon as the adsorbent, methanol as the sorptive and boron-nitrate as additive to improve heat conductivity. The approach can be easily extended to multi-bed installations and more sophisticated material models.
Highlights
Driven adsorption chillers (ACH) are promising for sustainable cooling
We developed a two-step method for the combined optimization of process and material related parameters
The method was exemplified for an adsorption refrigeration process using carbide derived carbon as adsorbent and methanol as sorptive
Summary
Driven adsorption chillers (ACH) are promising for sustainable cooling. The necessary energy input can be supplied by solar heat or industrial waste heat, reducing primary energy consumption. Commonly used adsorption pairs are environmental friendly, compared to halogenated refrigerants used in conventional compression cooling machines. Numerous studies have focused on the improvement of adsorption cooling machines. One of the reasons why the potential is not fully exploited is the separation of research studies concerning either adsorbent properties or process parameters. Adsorbents for heat pump applications should allow for a high sorption capacity and low heat and mass transport resistance. Depending on the structural properties of the porous material, heat and mass transport and volumetric capacity are strongly related. Quantitative expressions for heat and mass transport as well as sorption capacity are a prerequisite. A material model that connects the structure of the porous adsorbent to effective material properties is needed
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