Effect of residual air on dynamics of temperature- and pressure-initiated adsorption cycles for heat transformation

Abstract

• Effect of air traces on dynamics of pressure-initiated (PI) adsorption is studied. • “Water - FAM-Z02″ and ”methanol - LiCl/silica“ working pairs are investigated. • PI adsorption is less sensitive to the air presence than temperature-initiated one. • Closed cooling cycles based on PI process are more robust against the air presence. It is well known that non-adsorbable gas, e.g. residual air, can dramatically slow down the adsorption stage of adsorption heat transformation cycles. So far, this effect has been studied for the cycles initiated by temperature change (temperature-initiated cycles). This work addresses the dynamic effect of residual air for another way of adsorption initiation, namely, by changing vapour pressure over adsorbent (pressure-initiated cycle). Comparison of the pressure- and temperature-initiated cycles is also made. The effects are studied for the working pairs “AQSOA FAM-Z02 – water” and “LiCl/(silica gel) – methanol” promising for adsorption heat transformation. The residual partial air pressure Δ P air was varied from 0 to 5 mbar. The main finding of this study is that the pressure-initiated adsorption is less sensitive to the presence of residual air than the temperature-initiated adsorption. This is especially true at a low partial air pressure Δ P air . For instance, at Δ P air ≤ 0.5 mbar, residual air has little or no effect on the pressure-initiated adsorption dynamics compared to the temperature-initiated one. A qualitative explanation of this finding is proposed. Thereby, closed adsorption heat transformation cycles based on the pressure-initiated process are more robust and resistant against the presence of residual air that could be a significant practical advantage.