Development and experimental study of a small-scale adsorption cold storage prototype with stable and tunable output for off-grid cooling

Comfort cooling is a growing demand in summer outdoor activities and work. Adsorption cold storage (ACS) can achieve long-term cold storage without insulation measures and release cold without requiring electricity input. However, the challenges, including unstable cooling output and huge volume, hinder its wide applications. In this study, a small-scale silica gel-water ACS prototype for off-grid cooling is developed and experimentally investigated under typical summer conditions. The heat pipe structure is employed in the adsorption bed for heat transfer enhancement and volume reduction. Valve opening control is utilized for cooling output stabilization and adjustment. The experimental results show that the prototype achieves 6.36 h of cooling output with the outlet air temperature of 25 °C and the average cooling power of 107.67 W under the environment conditions of 35 °C and 40 % RH, indicating an effective cold storage capacity of 685 Wh and an operating efficiency of 0.30. Furthermore, the stable output air temperature can be flexibly adjusted from 19 °C to 27 °C while maintaining the inlet air temperature at 35 °C during the discharging process. Notably, the charging environment temperature shows a minimal influence on the cooling output performance. The prototype's design is novel and applicable for portable cooling in outdoor off-grid scenarios.