Adsorption cooling systems utilize the principle of adsorption to generate cooling effect. Composite adsorbents synthesized from zeolite 13X and CaCl2 have previously been shown to have a high adsorption capacity and high adsorption rate with lower desorption temperature where the adsorption capacity and adsorption rate are 420% and 122% of zeolite 13X under the same condition respectively. This results in more compact design and a lower temperature waste-heat source can be used. The system performance is, however, limited by the low thermal conductivity of the 13X/CaCl2 composite adsorbent which is common for many adsorbents. Due to the low thermal conductivity of the adsorbent, poor heat transfer and slow temperature change in the adsorbent bed lead to longer time for the adsorbent to achieve the adsorption/desorption temperature. This directly reduces the adsorption/desorption rate of the adsorbate on the adsorbent, such as water on zeolite, and results in lower system coefficient of performance (COP) and specific cooling power (SCP). It was proposed that embedding carbon nanotube (CNT) into the 13X/CaCl2 composite absorbents can increase the thermal conductivity of the adsorbent bed to improve the system performance. Thus, the properties of the multi-wall CNT (MWCNT) embedded zeolite 13X/CaCl2 composite adsorbents were investigated to find out the optimized composition for the cooling system. The material properties of the MWCNT embedded zeolite 13X/CaCl2 composite adsorbent were measured. The thermal conductivities of the MWCNT embedded 13X/CaCl2 composite adsorbents were predicted by developing a new theoretical model modified based on area contact model. The performance of the adsorption cooling system using zeolite 13X and MWCNT embedded composite adsorbent were studied numerically. It is found that the COP and SCP are improved by 3.6 and 26 times respectively. This results in a much more compact and energy efficient cooling system.

Volume Subject Area:
Heat Transfer in Energy Systems
Topics:
Carbon nanotubes, Composite materials, Thermal conductivity, Cooling systems, Multi-walled carbon nanotubes, Temperature, Desorption, Cooling, Absorbents, Design, Heat transfer, Materials properties, Waste heat, Water
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