System-Level Adsorber Dynamics in Adsorption Heat Pumps: Equilibrium vs. Diffusion Mass-Transfer
Adsorption heat pumps (AHPs) convert low-grade thermal energy into cooling or heating, but their performance depends on coupled heat and mass transfer in the adsorber. Predictive yet hardware-agnostic models are needed to guide design and operation across different geometries and operating schedules. Here, we apply a dimensionless adsorber framework previously developed by the authors that captures both inter-component and intra-particle transport effects while remaining suitable for cycle-level performance metrics. Intra-particle transport in the adsorber module is treated analytically and embedded in the system balances via a causal convolution kernel. Using the silica gel–water working pair, we (i) compare equilibrium and diffusion-based mass-transfer closures, (ii) map dimensionless time against the governing dimensionless groups, and (iii) propagate the resulting dynamics to cycle-level metrics (specific heating/cooling power and coefficient of performance, COP) through the effective uptake swing, ???????????, and the cycle time, ??????????. Results show that equilibrium models overpredict specific power when the mass-transfer Biot number and adsorption Damköhler number are small; in contrast, the convolution-kernel closure captures film-limited early-time behavior and diffusive late-time tails. The cyclelevel model also indicates that, in the ideal loss-free limit, COP is only weakly sensitive to kinetics, whereas practical COP reductions correlate with the heat-release number and the heat-capacity ratio.