Volume 63

Kinetic Study of the Water/MIL-101(Cr) Pair under Adsorption Chiller Operating Conditions: Influence of Adsorbent Layer Height Mohd Abdullah Khan, Sourav Mitra

Abstract

Understanding the adsorption/desorption kinetics of adsorbate-adsorbent is critical for optimising the adsorption-based cooling systems, where heat and mass transfer strongly affect specific cooling power (SCP). In an adsorption chiller, adsorption and desorption occur at constant pressure and are driven by temperature swing of the adsorbent. In this study, the kinetics of the water/MIL-101(Cr) pair are experimentally investigated under such conditions using the Large Temperature Jump (LTJ) method. MIL-101(Cr) powder loosely packed in an aluminium pan. Adsorbent layer height is varied (1.3, 2.6, and 3.9 mm) while maintaining a fixed mass of 0.3 ± 0.001 g. Measurements are performed at water vapour pressures of 1.2 kPa and 5.6 kPa, corresponding to evaporator and condenser temperatures of 283 K and 308 K, respectively. The pan base temperature is changed from 320 K to 298 K (adsorption) and 324 K to 338 K (desorption). Instantaneous uptake data are fitted using the Linear Driving Force (LDF) equation, which provides good agreement across all tested heights. The characteristic time(τ) increase with adsorbent bed height, indicating greater mass transfer resistance in thicker layers. The highest SCP (5.1 kW/kg) is achieved for the thinnest bed (1.3 mm), while SCP decreases nearly linearly with increasing bed thickness. Under conservative operation (80% cycle utilization), the SCP remains substantial at 3.2 kW/kg for the thinnest bed. This study further demonstrates that assigning shorter duration to desorption than adsorption enhances SCP. This strategy aligns with the faster desorption kinetics and enables more frequent cycling without compromising net water uptake. These findings underline the potential of MIL-101(Cr) as a high-performance adsorbent and provide useful design guidance for optimizing MOF-based adsorption chillers. However, practical implementation must account for the trade-off between enhanced kinetics and increased system thermal mass in thin-layer configurations, reinforcing the need for integrated system-level optimization.

Keywords Adsorption kinetics, Adsorption chiller, MIL-101(Cr), Specific cooling power, Water