Experimental Investigation On The Development And Characteristics Of Water Intake Device By Adsorption From Air

There are many parts of the world in short of fresh water resource, in northwest of China, perennial drought and rare rainfall makes water resource per capita in shortage, while fresh water supply is the prerequisite for human activities. Meanwhile, moisture in air is rich, renewable and not limited by zone, so atmosphere can be regarded as a good source of fresh water. Therefore, extracting water from air has a great potential to alleviate the shortage of water resource. Extracting water from air by adsorption is using adsorbents adsorb moisture from air first; then, the adsorbents are heated and water in adsorbents are desorbed; at last, the vapor is condensed to be fresh liquid water. There are two main issues of extracting water from air by adsorption:high adsorption performance adsorbents and adsorbent bed with good heat and mass transfer properties. Properties of adsorbents and adsorbent bed are studied in this paper.First, according to the request of adsorbent, it must be with high adsorption capacity、 high adsorption rate、low desorption temperature and short desorption time, considering the economic, calcium chloride is selected as the adsorption subject, expanded graphite is added to make calcium chloride/expanded graphite composite adsorbent. Weighing method is used to test kinetic curves of composite adsorbent with four different proportions (calcium chloride:expanded graphite were 1:1,2:1,3:1 and 4:1, respectively) in different environments (temperature of 25℃, relative humidity RH were 40%,50%,60%,70% and 80%, respectively), and the thermal conductivity of the composites with different densities are tested too. The results show that the water adsorption capacity and rate of composite rises as the relative humidity increases, the adsorption rate also increases with the increase of expanded graphite content. Thermal conductivity of composite adsorbent decreases with the increase of the calcium chloride content, meanwhile, increases with the rise of solid density.Secondly, a kind of casing type adsorption bed structure was designed, and its working process and thermodynamic process were analyzed. The adsorption performance of the adsorption bed under natural convection is studied theoretically and experimentally, and the results indicate that the adsorption bed needs external air supply to drive the air to flow through the adsorption bed to meet the requirements of adsorption. The influence of the fan power and diagram of mass transfer channel of the adsorption bed on the adsorption capacity of the double-pipe adsorption bed was studied. The results show that the adsorption capacity of sorption bed rises as the fan power increases and it improves with the increase of mass transfer channel diameter as well. Moreover, the size of mass transfer channel diameter has a bigger influence on sorption capacity compared to fan power.Finally, the structure of double-pipe adsorption bed was further optimized. It was found that when the volume of the mass transfer channel was constant and the number of the mass transfer channels increased, the contact area between the air and the adsorbent increased, the thickness of the adsorbent layer decreased, and the adsorption rate accelerated. The four-channel adsorption bed, each mass transfer channel diameter of which is 10mm, and adsorbent (calcium chloride/expanded graphite composite of 2:1) filling quality is 474.25g., adsorption capacity reach 88.4g after 12h in actual climate (average air temperature:12.9℃, relative humidity:52%).