Parametric Optimization of Ethanol-Based Adsorption Working Pairs for Sub-Zero Ice Production from Low-Grade Heat: A Source-Driven Design Framework

Thermally driven adsorption refrigeration offers a compressor-free pathway to sub-zero ice production from low-grade heat. Systematic design guidance for the 65–160 °C range remains limited: existing comparative studies lack consistent system-level constraints, rarely treat cycle time as a coupled variable, and have not addressed the thermodynamic penalties of sub-zero evaporator operation. This study presents a transient lumped-parameter model of a two-bed adsorption ice-making system comparing five ethanol-based working pairs: four activated carbon variants (Maxsorb III, ACF(A-20), KOH4-PR, KOH6-PR) and the metal–organic framework MIL-101(Cr). The Dubinin–Astakhov parameters of all five pairs reproduce the equilibrium measurements of their source studies, with a pooled coefficient of determination of 0.979 over 146 points. At the cycle level, the model reproduces two published chillers: MIL-101(Cr)/ethanol within 4.1% in coefficient of performance (COP) and 7.3% in specific cooling power (SCP), and ACF(A-20)/ethanol within 6.2% in cooling capacity and 5.5% in COP. Performance is mapped across a two-dimensional design space of regeneration temperature and adsorption half-cycle time. KOH4-PR/ethanol delivers the highest specific cooling power from 85 °C upward, reaching 136 W/kg at 160 °C, while Maxsorb III/ethanol activates from 65 °C and performs within 6% of KOH4-PR in SCP at 100 °C. A dual-optimum structure is identified. COP is maximized at long half-cycles and peaks at 0.541 across the swept temperature range, while the SCP-optimal half-cycle shortens as source temperature rises. At the 100 °C design point, the COP-optimal half-cycle of 1800 s gives COP = 0.535 and SCP = 104 W/kg, and the SCP-optimal half-cycle of 1200 s gives COP = 0.495 and SCP = 110 W/kg. The corresponding sorbent sizing for KOH4-PR/ethanol is 5.1 and 4.5 kg/kW. The combined results form a source-driven design framework that translates an imposed source temperature into a complete preliminary configuration: working pair, half-cycle time, expected ice production, and adsorbent inventory.