Water adsorption dynamics on representative pieces of real adsorbers for adsorptive chillers

Dynamic optimization of adsorbent-heat exchangers (Ad-HExs) represents a key issue for the broader diffusion of adsorption cooling and heating (ACH) technologies. This paper is a sequel to an earlier one (et al., 2014) that described the study of an ideal Ad-HEx configuration (loose adsorbent grains placed on a flat metal plate) by a new gravimetric version of the large temperature jump method. In the present paper, the study is extended to analyse the dynamic behaviour of HExs with much more complex geometry, namely, small but representative pieces of a finned flat-tube HEx. The Ad-HEx configuration tested is obtained by filling these small HExs with loose grains of AQSOA FAM Z02. The aim of the study is to evaluate the effect of the HEx geometry, grain size and flow rate of heat transfer liquid. The results obtained are compared with a reference flat Ad-HEx configuration. The ad-/desorption dynamics is found to be nearly exponential that proves the applicability of a modified Linear Driving Force model to characterize the water ad-/desorption rate. The majority of the tests have revealed the existence of the ''grain size insensitive'' regime for grains of 0.3-0.7 mm size. Under this mode, the dynamic behaviour is only function of the ratio (S/m) = [heat transfer surface]/[absorbent mass]. This leads to a practically important conclusion that it is not necessary to precisely select the adsorbent grain size. When the grain size becomes too small or too large the rate reduction was found that is due to inter- or intra-grain mass transfer resistances. The tested Ad-HEx configuration is proved to be quite efficient: the specific cooling power amounts to 50-66% of that obtained with the reference (ideal) one, and the average specific cooling power W-80% can reach 2.3 kW kg(-1). This power is 6-8 times higher than those reported in the literature for full scale Ad-HExs with similar cell geometry. Thus, the study showed that there is still a big room for significant dynamical improvement of real ACH units. (C) 2014 Elsevier Ltd. All rights reserved.