Measurement of properties and performance prediction of the new MWCNT-embedded zeolite 13X/CaCl<inf>2</inf> composite adsorbents

Abstract

© 2015 Elsevier Ltd. All rights reserved. In this study, MWCNT embedded zeolite 13X/CaCl<inf>2</inf> composite adsorbents with different MWCNT mass ratios were synthesized for use in adsorption cooling systems. XRF, XPS, BET, TGA and thermal conductivity tests were conducted and the properties of the composite adsorbents are presented. The MWCNT embedded composite adsorbent prepared with the highest MWCNT mass ratio, 100:1, has the highest carbon concentration, 12.91 wt%. The addition of MWCNT in the composite adsorbent can increase the overall specific surface area and total pore volume of the adsorbent. The useful range of water adsorption of composite adsorbents is much higher than for zeolite 13X. The operational range of water uptake for zeolite 13X is 0.09 kg/kg and that of the composite adsorbents is 0.5 kg/kg. It is possible that the composite adsorbents can perform 5 times better than zeolite 13X. The effective thermal conductivity is improved significantly, and reached 0.27-0.8 W/mK in the temperature range of 30-70°C, where the thermal conductivity of zeolite 13X is only 0.08-0.13 W/mK in the same temperature range. The addition of MWCNT does not have noticeable drawbacks on adsorption capacity and can improve the effective thermal conductivity of the composite adsorbent. A FEM simulation model of an adsorber was built to predict the performance of different adsorbents, namely zeolite 13X, zeolite 13X/CaCl<inf>2</inf> composite adsorbent and MWCNT embedded 13X/CaCl<inf>2</inf> adsorbent (CNT-CA-1). Under the same operation conditions, in which the evaporation pressure is 872.5 Pa, condensation pressure is 4247 Pa, heating water temperature is 80°C and cooling water temperature is 30°C, the CNT-CA-1 performs much better than zeolite 13X and the zeolite 13X/CaCl<inf>2</inf> composite adsorbent. The SCP of the adsorber using CNT-CA-1 is improved by 6.5 times to 1113.4 W/kg compared to zeolite 13X. The total cooling power is significantly enhanced by 13.4 times to 1783.2 W. By comparing the adsorber performance using CNT-CA-1 against that using zeolite 13X/CaCl<inf>2</inf>, simply adding the MWCNT can improve the COP and SCP by more than 20%.