Experimental study on silica gel/ethanol adsorption characteristics for low-grade thermal driven adsorption refrigeration systems

Abstract

• Silica gel/ethanol adsorption pair is promising for EVs and PV/T applications. • Ethanol is highly attracted to silica gel through chemical adsorption. • The silica gel/ethanol presents minor hysteresis owing to condensation. • The theoretical cyclic performance of silica gel/ethanol were calculated 0.97. There has been an increasing interest in adsorption cooling and heat pumps as the most feasible green alternative to the widespread vapor compression technology. Recent developments in adsorption cooling highlighted the need for cost-efficient adsorption pairs of advanced adsorption characteristics. In response, this article experimentally investigates and models silica gel/ethanol pair adsorption characteristics that can utilize low-temperature heat sources, such as those available in the emerging electric vehicles and PV/T systems. The investigated characteristics are the porous structure stability, isosteric heat of adsorption, adsorption diffusion energy, adsorption isotherm, and adsorption kinetic under extended operating conditions 15–55 °C. The results showed the high affinity of silica gel towards ethanol to provide sub-zero cooling. Silica gel showed no structure deterioration during the repetitive adsorption/desorption cycles of net 22 % cyclic ethanol uptake. The chemical adsorption of silica gel/ethanol showed a high level of adsorption/desorption reversibility with minimal hysteresis, which the Langmuir model best simulated. The heat of adsorption was determined to be 4.49 × 10 4 J/mol, which was higher than the diffusion energy of 1.80 × 10 4 J/mol due to the slow physical mobility of ethanol molecules inside silica gel pores. The Elovich kinetic model was the most suitable for simulating the chemical adsorption/desorption processes. The material level cyclic analysis showed the potential of 22 kJ/kg ads cooling effect and 0.97 coefficient of performance by utilizing a 55 °C heat source, widely available in PV/T systems and electric vehicles.