Non-isothermal adsorption rate model of activated carbon-ethanol pair for solar cooling applications estimated through CFD simulation

Abstract

Adsorption cooling systems (ACS) are feasible alternative to vapor compression cooling system as they employ natural and benign refrigerants and could be driven by solar energy or waste heat. Performance optimization of ACS could be carried out using CFD simulations with lower cost and faster time comparing to experimental testing. One of the crucial parameters to obtain reliable CFD simulation results is the diffusion time constant of adsorption rate equation estimated from experimental data. This study presents transient CFD simulations of ethanol adsorption onto activated carbon powder of type Maxsorb III carried out by Ansys-Fluent v14.5 software using 2D-axisymmetric geometry. The mathematical model consists of mass, momentum and energy conservation equations as well as adsorption isotherm and adsorption kinetic equations implemented via user defined functions (UDFs). The conditions used were same as those employed in gravimetric adsorption analyzer that is 30˚C, 2.25 kPa and 3.32 kPa for temperature, initial and inlet pressures, respectively. Through multiple CFD simulations, we estimated the appropriate diffusion time constant of non-isothermal linear driving force (LDF) equation which led to simulated adsorption uptakes agreeing fairly with those measured experimentally. The mathematical model employing non-isothermal LDF equation could be implemented to simulate the heat and mass transfer in large scale adsorption/desorption bed and to optimize the performance of activated carbon-ethanol based adsorption cooling system.