SOLAR ENERGY FOR WATER HEATING — BROOKS 



171 



with internal coils but without stratification shields can be connected 

 (fig. 6) with an expansion chamber for the separate nonfreezing cir- 

 culating fluid, but will not give high-temperature water quickly. 



Separate -fluids for nonfreezing solar-energy ahsorhers. — ^Various 

 ingredients can be added to water to lower its freezing point. The 

 most common solutions are alcohol mixtures and brines. Other fluids 

 not having the freezing characteristic of water might also be used, 

 notably oil. Addition of alcohol to water is the simplest nonfreeze 

 expedient ; but as the alcohol vaporizes rather easily in a solar heater 



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FiGDKB 6. — Commercial type nonfreezing solar-tieater-system tank. 



and the solution weakens, some addition should be made every fall. 

 Various brine solutions, widely used industrially for refrigeration, 

 are recommended for nonfreeze solutions only where the operator is 

 familiar with the operating technique to avoid corrosion in black iron 

 pipe. The lightest grade of highly refined spray oil is the most suit- 

 able of the petroleum products, but does not circulate readily under 

 thermal density differential head, being only one-fifth as effective 

 as water as a thermosiphon heat-transfer medium. This means that 

 the absorber when filled with oil would operate at much higher tem- 

 perature than when filled with water and would be less effective be- 

 cause of larger absorber heat losses unless forced circulation is used. 



