Dynamic study of adsorbers by a new gravimetric version of the Large Temperature Jump method

Abstract

This paper presents a new experimental setup devoted to measure the ad-/desorption kinetics of an Ad-HEX (adsorbent+heat exchanger) under typical boundary conditions of an Adsorption Heat Transformer (AHT) as well as the results of the first test campaign carried out. The experimental apparatus can be considered as a gravimetric version of the known Large Temperature Jump method. In fact, the dynamic evolution of the uptake during the isobaric ad-/desorption stages is directly measured by a weighing system suitable to work in the range of 5–600g of sample mass (adsorbent+HEX) with the accuracy ±0.1g and the time response shorter than 0.1s The experimental campaign was conducted on an Ad-HEX composed of granules of a commercial SAPO-34 adsorbent placed on a flat type aluminum HEX, under operating conditions reproducing two different thermodynamic cycles (Th=90°C, Te=10°C, Tc=30 and 35°C), typical for adsorption air conditioning.The influence of the grain size (ranging from 0.350 to 2.5mm) on the adsorption dynamics both in monolayer and multilayer configurations at variable and constant “heat transfer surface/adsorbent mass” ratios (S/m) was studied. The results showed that, for the Ad-HEX configurations tested, the adsorption dynamics can be properly described by a modified Linear Driving Force approach by the use of a single temperature-invariant characteristic time τ. The invariance of the specific cooling power was revealed when the S/m ratio was kept constant (S/m=1.23m2/kg). This ratio is found to be a useful parameter for both assessment of the dynamic perfection and optimization of various Ad-HEX configurations.