Abstract
We considered problems of water scarcity elimination in arid regions of the planet and analyzed modern water producing systems. We showed the prospects of obtaining of water from atmospheric air directly while cooling it below the dew point using refrigeration units. We proposed to use absorption-type cooling systems with a water-ammonia solution as a working liquid as cooling units in regions with an excess of solar energy. We noted that low energy characteristics of heat-using refrigeration cycle, with main problems associated with non-calculated losses of refrigerant (ammonia) during transportation through AWRU refluxer hamper a widespread use of absorption water-ammonia refrigerating units (AWRU) in systems for obtaining of water from atmospheric air. This contribution is particularly noticeable in operation of AWRU in a wide range of outdoor air temperatures. We performed modeling of heat and mass exchange processes of a lifting section of an AWRU refluxer to find methods for elimination of ammonia transportation losses. At the heart of model representations were equations of heat and mass balances, and we took into account resistance of a diffusion process at radial movement of a vapor flow to a wall of a refluxer in modeling. A preliminary analysis of thermal resistance of reflux film showed its small contribution to the total resistance and we ignored it subsequently. As a result of modeling, we found a significant (up to 36 °C) temperature difference between a flow inside a refluxer and its wall. Experimental studies of a serial AWRU confirmed the modeling results. The obtained results made possible to propose the original design of a heat-insulating casing of an AWRU refluxer with variable thermal resistance with a corresponding change in the outside air temperature. This gave possibility to increase energy efficiency from 18 to 36 % and productivity of systems for obtaining of water from atmospheric air.
Highlights
Water will become the most valuable resource on the planet very soon: this trend will only grow in the near future [1]
Estimating calculations showed that a heat flow in the section of the refluxer of 0.20 m length with a temperature difference between a WAM BAC flow and the outside air of 60 °C will be 0.15 W, that is, one can speak about almost adiabatic mode in the area of installation of the additional casing at a typical thermal load of an AWRU refluxer of 12‒15 W
We developed a technique for modeling of heat and mass exchange modes of AWRU refluxers in the composition of solar water producing systems from atmospheric air
Summary
Water will become the most valuable resource on the planet very soon: this trend will only grow in the near future [1]. Absorption water-ammonia refrigeration units (AWRU) can solve cooling problems in systems for obtaining of water from atmospheric air in absence of sources of electrical energy effectively. There is no information on internal processes of heat and mass transfer, which makes impossible to use them for the design of real structures of AWRU and systems for obtaining of water from atmospheric air, in papers [29,30,31]. Authors of work [35] propose to intensify proce s ses of natural circulation of a vapor-gas mixture in AWRU using a jet ejector installed at the output of a gene r ator They assume that forced convection will arise in the internal evaporator-absorber circuit because of ejection and, intensity of heat and mass exchange processes during absorption and evaporation will increase substantially, and in general, cooling capacity of a cooling unit w ill increase . Authors of paper [35] do not consider changes in temperature of the outside air, and this change is sufficiently critical for efficient operation of an ejector
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