Experimental Analysis of the Influence of Residual Air on Water Adsorption–Desorption Dynamics of Natural Zeolite

Non-condensable gases are a significant factor limiting the performance of adsorption cooling systems, yet their quantitative impact on adsorption–desorption dynamics remains poorly understood. This study experimentally investigates the effect of residual air on a natural zeolite–water adsorption system under controlled conditions, varying residual air pressure, and evaporator/condenser temperatures. The results show that increasing air content significantly reduced both adsorption and desorption capacities, with desorption being markedly more sensitive. At 0 mbar residual air pressure, the adsorption capacities were 0.0553 and 0.0573 kg/kg at 10 °C and 20 °C, respectively, while the corresponding desorption capacities were 0.0277 and 0.0256 kg/kg. At 50 mbar nominal residual air pressure, the adsorption capacity decreased by 14% and 8% at 10 °C and 20 °C, respectively, whereas the corresponding reductions in desorption capacity were 57% and 52%. When the pressure increased to 100 mbar, the adsorption capacity reductions further increased to 82% at 10 °C and 18% at 20 °C, whereas the desorption capacity decreased dramatically by 99% and 77%, respectively. Furthermore, the desorption-to-adsorption capacity ratio remained within the range of 4–50% across all operating conditions, indicating severe kinetic limitations in the desorption process. Performance degradation was more pronounced at lower operating temperatures due to the higher ratio of partial air pressure to saturation pressure. Residual air also alters transient pressure–temperature behavior and can induce ice formation, further suppressing system performance. These findings emphasize the necessity of leak-tight design and optimized operating conditions for efficient and stable system operation.