In this contribution, we present a transient, spatially resolved analysis of entropy generation and exergy destruction in adsorber heat exchangers for adsorption heat pumps. The objective is to quantitatively distinguish irreversibilities caused by heat and mass transfer, thereby providing a basis for the thermodynamic optimization of adsorber designs.
The study investigates an adsorber heat exchanger concept developed at ITFD using moulded bodies made from an activated-carbon composite material and methanol as the refrigerant. The adsorbent bodies are arranged between copper lamellae and connected to a flat-pipe heat exchanger. Two geometric variants are compared, one of which incorporates additional mass-transfer channels. These channels reduce the diffusion length of methanol and thereby accelerate mass transfer during adsorption and desorption.
The analysis is based on a transient, spatially resolved finite-element model describing the coupled heat- and mass-transfer processes. Adsorption kinetics are represented using a linear driving force approach. Based on the calculated local state variables, entropy generation is evaluated as a function of space and time and decomposed into contributions associated with heat and mass transfer.
The results show that the additional mass-transfer channels significantly reduce entropy generation associated with macropore diffusion. Consequently, the dominant source of irreversibility shifts from mass-transfer limitations towards heat-transfer-related losses. The proposed methodology therefore identifies not only where and when exergy is destroyed during the adsorption cycle, but also which transport mechanisms are responsible. It enables the systematic comparison of different adsorber geometries and provides a basis for the further optimization of high-performance adsorption heat pumps.