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Solar distillation research at the University of California
Solar Abstracts M i l t o n D. L o w e n s t e i n Technical Research Service Center, AFASE, Arizona State University, Tempe, Arizona
All d o c u m e n t s in t h e T e c h n i c a l R e s e a r c h S e r v i c e Center l i b r a r y are classified a c c o r d i n g to the categories listed below. Reproductions of the d o c u m e n t s are a v a i l a b l e a t 15¢ per page (10¢ per page for A F A S E m e m b e r s ) .
I--Evaporative Processes (Distillation) B a u m , V. A., " S o l a r D i s t i l l e r s , " U n i t e d N a t i o n s C o n f e r e n c e on N e w Sources of E n e r g y , R o m e , 1961, 43 p. This article expounds certain methods for the solar distillation of salt water. Hot Box Stills--An elaborate system of equations is given that reveals, among other data, that the efficiency of this still is fairly stable. Charts permit the calculation of the still's charaeteristics. A modification of the still is one with a soaked fabric placed in a sloping flat box, the bottom of which is also a condensation surface. The advantages and several disadvantages of this still are discussed. Regenerative Stills--More economical of energy, this type of still uses the heat of condensation instead of letting it out into the ambient air. A three-stage still designed in 1952 at the Russian helio-laboratory had solar boilers heated by a 10-meter paraboloid mirror. The efficiency of the boiler amounted to 60 percent. Among the conclusions drawn from studying the installation are: (a) with paraboloid mirrors, stills have a capacity of 3.4 liters of fresh water per hour per square meter of mirror; (b) with accurate (K = 30) parabolo-cylindrieal aluminum mirrors, the stills can give a specific capacity of 2 to 2.2 liters per hour per square meter of mirror surface, using a 4- or 5-stage still; (c) the choice of boiler should be on a basis of comparative cost of the boiler. Another type of still discussed is one for obtaining fresh water in large quantities. The steam first operated a turbine to generate electricity and the spent steam is directed into a still, or by using a condensation turbine, the electricity could distill water by electrodialysis. H o w e , E v e r e t t D., " S o l a r D i s t i l l a t i o n R e s e a r c h a t t h e U n i v e r s i t y of C a l i f o r n i a , " U n i t e d N a t i o n s C o n ference on N e w Sources of E n e r g y , R o m e , 1961, 22 p. Illus. Experimental results are reported for seven units. Four of these were greenhouse-type units with symmetrical glass covers and horizontal water trays; two were flat-type units with inclined water trays; and the remaining one was a greenhousetype unit with an unsymmetrical glass cover, including a vertical mirror as its north face. The performance data for clear days only are used in comparing the efficiencies of the several units, since it is argued that cloudy-day data does not fit on the same performance curves as the clear-day data and reflects the local vagaries of weather rather than the true efficiency of the still. It is noted that the costs of solar distillation equipment are presently so high that the product water is more expensive than that produced using fuel heat. The paper suggests some economies of construction pertaining to the flat-type unit and, 28
it is hoped, may stimulate others to conceive further simplification that can make solar distillation feasible on a large scale.
II--Space Water Heating and Absorptive Collectors A n d r a s s y , Stella, " S o l a r W a t e r H e a t e r s , " U n i t e d N a tions C o n f e r e n c e on N e w Sources of E n e r g y , R o m e , 1961, l l p. Illus. A new type of solar water heater has been developed and tested. It combines sheet metal with durable plastic tubing. The metal sheet is corrugated in a special way, forming tubular openings. Plastic pipe is inserted into these grooves forming a continuous coil. The inherently low heat conductivity of plastic materials is increased by incorporating metal-powder into the plastic material before extrusion into tubing. The new panels show the following advantages as compared to all-metal panels: a) Not damaged by freezing temperatures, nor by heat, when heat-resistant tubing is used. b) Light weight and simplicity in installation. c) Low cost. d) Corrosion-proof and leak-proof. Material costs of the panels are $0.29 per square foot and the total cost, including labor is estimated at $0.35 per square foot. This is considerably lower than the cost of the usual collector panel, made of copper sheet with soldered copper coils. The durability of the panels is very good and they cannot be damaged by freezing water. M a t h u r , K. N ., a n d M . L. K h a n n a , " S o l a r W a t e r H e a t e r s , " U n i t e d N a t i o n s C o n f e r e n c e on N e w Sources of E n e r g y , R o m e , 1961, 19 p. Illus. An arrangement for heating water by solar energy has been described using a flat-plate collector. The conventional flatplate construction using a copper sheet with a length of copper pipe soldered on it has been replaced by a comparatively inexpensive arrangement consisting of a corrugated, galvanizediron sheet blackened on top and backed by a plane, galvanizediron sheet to form a compact sandwich in which water can flow through the channels between the plane sheet and the corrugations. Experiments were conducted to test the efficiency of the heating unit by passing a constant stream of water at various rates of flow from 6 to 21 gallons per hour. The arrangement is cheap and makes use of easily available materials and in the larger size costs about Rs.500/-($110.) giving a saving of up to Rs.36/-per month. Several of these units have been used experimentally for several years and have proved entirely satisfactory. R o b i n s o n , N a t h a n , a n d E l i y a h u N e e m a n , " T h e Solar S w i t c h : A n A u t o m a t i c D e v i c e for E c o n o m i z i n g A u x i l i a r y H e a t i n g of Solar W a t e r H e a t e r s , " U n i t e d N a t i o n s C o n f e r e n c e on N e w Sources of E n e r g y , R o m e , 1961, 19 p. Close examination of the actual proportion of auxiliary heating shows that the average consumer tends to use it ex-
Solar Energy
All d o c u m e n t s in t h e T e c h n i c a l R e s e a r c h S e r v i c e Center l i b r a r y are classified a c c o r d i n g to the categories listed below. Reproductions of the d o c u m e n t s are a v a i l a b l e a t 15¢ per page (10¢ per page for A F A S E m e m b e r s ) .
I--Evaporative Processes (Distillation) B a u m , V. A., " S o l a r D i s t i l l e r s , " U n i t e d N a t i o n s C o n f e r e n c e on N e w Sources of E n e r g y , R o m e , 1961, 43 p. This article expounds certain methods for the solar distillation of salt water. Hot Box Stills--An elaborate system of equations is given that reveals, among other data, that the efficiency of this still is fairly stable. Charts permit the calculation of the still's charaeteristics. A modification of the still is one with a soaked fabric placed in a sloping flat box, the bottom of which is also a condensation surface. The advantages and several disadvantages of this still are discussed. Regenerative Stills--More economical of energy, this type of still uses the heat of condensation instead of letting it out into the ambient air. A three-stage still designed in 1952 at the Russian helio-laboratory had solar boilers heated by a 10-meter paraboloid mirror. The efficiency of the boiler amounted to 60 percent. Among the conclusions drawn from studying the installation are: (a) with paraboloid mirrors, stills have a capacity of 3.4 liters of fresh water per hour per square meter of mirror; (b) with accurate (K = 30) parabolo-cylindrieal aluminum mirrors, the stills can give a specific capacity of 2 to 2.2 liters per hour per square meter of mirror surface, using a 4- or 5-stage still; (c) the choice of boiler should be on a basis of comparative cost of the boiler. Another type of still discussed is one for obtaining fresh water in large quantities. The steam first operated a turbine to generate electricity and the spent steam is directed into a still, or by using a condensation turbine, the electricity could distill water by electrodialysis. H o w e , E v e r e t t D., " S o l a r D i s t i l l a t i o n R e s e a r c h a t t h e U n i v e r s i t y of C a l i f o r n i a , " U n i t e d N a t i o n s C o n ference on N e w Sources of E n e r g y , R o m e , 1961, 22 p. Illus. Experimental results are reported for seven units. Four of these were greenhouse-type units with symmetrical glass covers and horizontal water trays; two were flat-type units with inclined water trays; and the remaining one was a greenhousetype unit with an unsymmetrical glass cover, including a vertical mirror as its north face. The performance data for clear days only are used in comparing the efficiencies of the several units, since it is argued that cloudy-day data does not fit on the same performance curves as the clear-day data and reflects the local vagaries of weather rather than the true efficiency of the still. It is noted that the costs of solar distillation equipment are presently so high that the product water is more expensive than that produced using fuel heat. The paper suggests some economies of construction pertaining to the flat-type unit and, 28
it is hoped, may stimulate others to conceive further simplification that can make solar distillation feasible on a large scale.
II--Space Water Heating and Absorptive Collectors A n d r a s s y , Stella, " S o l a r W a t e r H e a t e r s , " U n i t e d N a tions C o n f e r e n c e on N e w Sources of E n e r g y , R o m e , 1961, l l p. Illus. A new type of solar water heater has been developed and tested. It combines sheet metal with durable plastic tubing. The metal sheet is corrugated in a special way, forming tubular openings. Plastic pipe is inserted into these grooves forming a continuous coil. The inherently low heat conductivity of plastic materials is increased by incorporating metal-powder into the plastic material before extrusion into tubing. The new panels show the following advantages as compared to all-metal panels: a) Not damaged by freezing temperatures, nor by heat, when heat-resistant tubing is used. b) Light weight and simplicity in installation. c) Low cost. d) Corrosion-proof and leak-proof. Material costs of the panels are $0.29 per square foot and the total cost, including labor is estimated at $0.35 per square foot. This is considerably lower than the cost of the usual collector panel, made of copper sheet with soldered copper coils. The durability of the panels is very good and they cannot be damaged by freezing water. M a t h u r , K. N ., a n d M . L. K h a n n a , " S o l a r W a t e r H e a t e r s , " U n i t e d N a t i o n s C o n f e r e n c e on N e w Sources of E n e r g y , R o m e , 1961, 19 p. Illus. An arrangement for heating water by solar energy has been described using a flat-plate collector. The conventional flatplate construction using a copper sheet with a length of copper pipe soldered on it has been replaced by a comparatively inexpensive arrangement consisting of a corrugated, galvanizediron sheet blackened on top and backed by a plane, galvanizediron sheet to form a compact sandwich in which water can flow through the channels between the plane sheet and the corrugations. Experiments were conducted to test the efficiency of the heating unit by passing a constant stream of water at various rates of flow from 6 to 21 gallons per hour. The arrangement is cheap and makes use of easily available materials and in the larger size costs about Rs.500/-($110.) giving a saving of up to Rs.36/-per month. Several of these units have been used experimentally for several years and have proved entirely satisfactory. R o b i n s o n , N a t h a n , a n d E l i y a h u N e e m a n , " T h e Solar S w i t c h : A n A u t o m a t i c D e v i c e for E c o n o m i z i n g A u x i l i a r y H e a t i n g of Solar W a t e r H e a t e r s , " U n i t e d N a t i o n s C o n f e r e n c e on N e w Sources of E n e r g y , R o m e , 1961, 19 p. Close examination of the actual proportion of auxiliary heating shows that the average consumer tends to use it ex-
Solar Energy