单选题
Not a plant to be seen, the desert ground is too dry. But the air contains water, and research scientists have found a (51) of obtaining drinking water from air humidity. The system is based completely on renewable energy and is therefore autonomous.
Cracks permeate the dried-out desert ground and the landscape bears testimony to the lack of water. But even here, where there are no lakes, rivers or groundwater, considerable quantities of water are stored in the air. In the Negev desert in Israel, for example; annual average relative air humidity is 64 percent-in every cubic meter of air there aye 11.5 milliliters of water.
German research scientists have found a way of converting this air humidity autonomously into drinkable water. "The process we have developed is based exclusively on renewable energy sources (52) thermal solar collectors and photovoltaic ceils, (53) makes this method completely energy-autonomous. It (54) will function in regions where there is no electrical infrastructure." says Siegfried Egner, head of the research team. The principle of the (55) is as follows: hygroscopic brine-saline solution which absorbs moisture runs down a tower-shaped unit and absorbs water from the air. It is then sucked (56) a tank a few meters off the ground in which a vacuum prevails. Energy from solar collector (57) up the brine, which is diluted by the water it has (58) .
Because of the vacuum, the boiling point of the liquid is lower than it would be under (59) . atmospheric pressure. This effect is known from the mountains: as the atmospheric pressure there is lower than in the valley, water boils at temperatures distinctly below 100℃. The evaporated, non-saline water is condensed and runs down through a completely filled tube in a controlled manner. The gravity of this water column (60) produces the vacuum and so a vacuum pump is not needed. The reconcentrated brine (61) down the tower surface again to absorb moisture from the air.
"The concept is suitable for various water (62) . Single-person units and plants supplying water to entire hotels are conceivable, "says Egner. Prototypes have been built for (63) system components-air moisture absorption and vacuum evaporation-and the research scientists have already (64) their interplay on a laboratory scale. In a further (65) the researchers intend to develop a demonstration facility.