Badawi W. Tleimat

Twenty years of work on solar distillation at the University of California

Abstract Solar distillation investigations at the Sea Water Conversion Laboratory, University of California, began in January 1952 and have continued to the present time. These studies have led to the development of still units of relatively small size, designed for furnishing potable water to isolated residences or small communities. Designs have been completed using wooden frames, precast concrete frames, and precast styrofoam basins. This paper gives information on the construction and performance of the several units; indicates the need for more effective utilization of solar energy; and offers a conceptual design of a solar collector for furnishing low-pressure steam for operation of a seawater distillation plant of advanced design with a capacity of 10,000 U.S. gal. (37·85 m 3 ) per day.

Nocturnal production of solar distillers

Abstract The accumulated production of the deep-basin solar still and that of the tilted-tray solar still with longitudinal baffles are compared. The comparisons show that evaporation in the deep-basin still continues during the entire 24-hour period while the tilted-tray still ceases to produce a relatively short time after sunset. Thus, nocturanal production is a maximum for the deep-basin type and nearly zero for the tilted-tray type. A small experimental still was constructed to determine the factors affecting the nocturnal production of solar stills. The experimental results indicate that a substantial increase of product water could be obtained from the continuous addition of warm water to the still. This increase was found to be a function of flow rate, feed-water temperature, evaporating and condensing areas, and ambient temperature. Using this data, an atmospheric still was laid out to use waste heat from a diesel-electric generator.

Comparison of plastic and glass condensing covers for solar distillers

Abstract This paper compares the productions of several solar stills of different designs, some with double-strength window-glass covers and others with plastic-film covers. Two small identical solar stills were designed and tested over a period of two years. One was covered with a double-strength window glass (0·125 in. thick) and the other was covered with a Tedlar plastic film (0·002 in. thick) which was mechanically treated to produce a wettable surface. Of the four other solar stills tested, three were covered with the Tedlar film and the fourth was covered with the double-strength window glass. These units were of differet designs. Three of them were of the same size (48 sq. ft) whereas the fourth was considerably larger (240 sq. ft). The data indicated that production of the stills covered with the Tedlar film was consistently less than that covered with glass for both small and large stills. The operating and design problems connected with both covers are reviewed.

Ion-exchange pretreatment for scale prevention in desalting systems

Abstract Ion exchange pretreatment can protect dependably against scaling from calcium sulfate and alkaline deposits in desalting equipment, and against acid corrosion. When a feedwater is “softened” by ion exchange to replace most of its calcium by sodium, use of the sodium-rich reject brine from desalination to regenerate the exchanger makes the treatment chemically self-sufficient. An inexpensive vessel construction using salt-resistant reinforced concrete appears suitable for large-scale use. For moderate concentration factors (up to around 5 for seawater feed), and moderately low sulfate/chloride ratios, regeneration can be carried out in fixed-bed mode, preferably counterflow (upflow). At higher sulfate levels, precipitation occurs, and regeneration must be done in fluidized- (expanded-) bed mode to keep calcium sulfate from collecting in the bed. When weak-acid cation exchange with acidified exchanger is used to eliminate bicarbonate, feedwater acidity excursions are avoided, and the total-dissolved solids level is reduced rather than increased.

A solar-assisted heat pump system for heating and cooling residences

Abstract A significant impact of solar energy applications on the total energy demand requires systems or devices which can be retrofitted to existing energy users. The all-electric residence unit, which includes about 10 per cent of all such units in the U.S.A. and constitutes over half of those completed in 1973, seems particularly suited to a solar modification. It is proposed that heating and cooling of the all-electric residence unit be accomplished by using a solar-assisted heat-pump system. The proposed system makes use of a conventional air-conditioning unit which would be modified by fitting controls to reverse the flow of refrigerant for the heating mode and by changing the outdoor heat exchanger from refrigerant-to-air to refrigerant-to-water. In addition, there would be provided a solar collector and two insulated water-storage tanks. Water from one tank would be circulated through the refrigerant-to-water heat exchanger when needed and then returned to the other tank, so that essentially a source of heat of constant temperature would be maintained, thus decreasing the temperature interval for the heat pump and thereby saving energy. In the cooling mode the stored water would be cooled by exposure of the solar collector to the night sky to decrease the temperature interval for the heat pump, thereby reducing energy consumption. Calculations were made for an existing residence unit for which the total energy input is known and to which the proposed solar-assisted heat-pump system is applied. An estimated cost of equipment and of its operation is compared with the cost of owning and operating fuel and electrically heated systems. It is concluded that the solar-assisted heat-pump system with current fuel prices can provide immediate economic benefit over the all-electric home and is possibly on par with residences using fuel oil or liquefied petroleum gas, but it yields higher cost over systems using natural gas. The effect of a two-phase expander to replace the expansion valve in the refrigerant circuit has been theoretically investigated. It shows a significant energy saving worthy of further economic and practical consideration.

The Development of the Vapor Phase Catalytic Ammonia Removal (VPCAR) Engineering Development Unit

This paper presents the results of a program to develop the next generation Vapor Phase Catalytic Ammonia Removal (VPCAR) system. VPCAR is a spacecraft water recycling system designed by NASA and constructed by Water Reuse Technology Inc. The technology has been identified by NASA to be the next generation water recycling system [1]. It is designed specifically for a Mars transit vehicle mission. This paper provides a description of the process and an evaluation of the performance of the new system. The equivalent system mass (ESM) is calculated and compared to the existing state-of-the art. A description of the contracting mechanism used to construct the new system is also provided.

Optimal water cost from solar-powered multieffect distillation

Abstract This paper presents a short review of solar distillation followed by a description of conventional distillation methods and associated energy consumption. The paper then presents a system where solar energy is used to generate steam to drive a multieffect distillation plant. The system is optimized on the basis of minimum water cost . The analysis shows that enhancement of heat-transfer coefficients in the distillation section and increasing steam temperature from solar boiler result in lower water cost as well as increase the output per unit area of solar collectors. This study shows that a solar boiler producing saturated steam at 60 C in combination with an evaporator-condenser, developed and tested at this Laboratory, resulted in minimum water costs ranging from

Developments in saline water distillation technology

1.40 to

Solar distillers for use on coral islands

3.70 per m3 for brackish water feed and

A novel 2500 GPD 5-effects wiped-film rotating-disk vapor-compression module; preliminary results

2.15 to