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William D. Sellers and Carl N. Hodges


A “fluxometer” has been developed for estimating the fluxes of latent and sensible heat from bare soil and short grass in any type of terrain. The fluxometer consists of two polyethylene-covered tunnels 50 cm long, 30 cm wide, and 6 to 12 cm high. The floor of one is exposed to the soil surface; the floor of the other is covered with plastic, as a control. The latent and sensible heat fluxes can be determined from the wet-and dry-bulb temperatures of the air entering and leaving the exposed tunnel at a known rate.

A comparison of hourly evaporation rates measured simultaneously with the fluxometer and with three precision weighing-type lysimeters at Tempe, Ariz., showed that the fluxometer usually gave lower evaporation rates than the lysimeters.

A second experiment was conducted in a dry river channel in southeastern Arizona. Evaporation rates were measured during 18 days and agree well with estimates by other investigators. For 33 hourly periods, during which all energy balance components were measured, the average absolute error was 2.4 ly hr−1; the average relative error was 11.0 per cent.

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Carl N. Hodges, T. Lewis Thompson, John E. Groh, and William D. Sellers


The University of Arizona has developed a sea water desalinization system which can economically utilize low temperature solar energy. The system consists of a horizontal plastic-covered solar collector, a packed-tower evaporator, and a finned-tube surface condenser. Incoming sea water is preheated in the surface condenser and then pumped to the solar collector where it is heated 5 to 10C. The heated sea water is pumped from the collector to the packed-tower evaporator, where a small fraction is evaporated into a circulating air stream and condensed as distilled water in the finned-tube surface condenser.

To evaluate the system a pilot plant has been constructed in cooperation with the University of Sonora at Puerto Peñasco on the Gulf of California. This plant is designed to produce between 2500 and 5000 gallons of fresh water daily.

The energy for evaporation in the system is derived from ocean water heated in the solar collector during the day. In order to allow design optimization for the entire plant the temperatures in the collector must be accurately predicted. It is shown that this can be done by a simple manipulation of the energy balance equation for the collector.

The resulting theory is applied to a number of cases involving a double glazing collector filled with 2 inches of water. Such a collector will utilize about 24 per cent of the available solar energy if the warm water in the collector in the late afternoon is flushed out and stored for nighttime use in the evaporator.

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