Investigation of pore size effect on thermally driven CO₂ sorption compressor performance, using molecular simulations

Thermally driven sorption compressors are a promising technology for utilizing low-grade waste heat for refrigeration and air conditioning, and their performance is highly dependent on the adsorption characteristics of the working materials. Existing optimization efforts typically focus on system design or maximizing adsorption capacity, while the fundamental impact of pore geometry on compressor performance remains unexplored at the molecular level. This study uses Grand Canonical Monte Carlo (GCMC) simulations to investigate the effect of carbon slit-pore width (10 Å to 60 Å) on the performance of a CO₂ sorption compressor, quantified by a Mass to Heat Ratio (MHR) relating delivered mass to total heat input. The research focuses on operating temperatures below 410 K. The results reveal a strong relationship between the MHR, pore size, and operating temperatures. Molecular-level analysis through density profiles and simulation snapshots reveals that peak performance at a 20 Å is driven by high packing density which maximizes mass release, effectively compensating for the energetic penalty. For larger pores, performance declines as the mass capacity diminishes while the relative energy cost rises. These findings suggest that adsorbent design should focus on creating a narrow pore size distribution in the optimal range to achieve the most energetically favorable structure for desorption, providing a direct means to enhance the Coefficient of Performance (COP) of sorption compressor based vapor compression systems.