Performance analysis and experiment of solar hot water and pure water co-production system

Abstract: In this paper, the solar hot water and pure water co-production system was built and the mathematical model of energy conversion and transmission was established based on the system's operation, which aimed to improve the thermal performance and water productivity of the system experimentally and theoretically. The double evacuated tube solar collector was integrated into the desalination stills to ensure the continuity production of distillate. The evaporation-condensation tank and the heat storage water tank were designed and built with a φ58 mm×1.8 m×24 double evacuated heat pipe, a hot water tank capacity of 109.2 L, an evaporation area of 0.6235 m2, a condensation water tank capacity of 124.8 L, a condensation area of 0.7092 m2, and a heat storage water tank of 200 L. The governing energy balance equations were solved analytically with Matlab software and compared with the experimental results. The results indicated that water productivity and performance coefficient increased first and then decreased with the increase of temperature at a certain temperature range (50-70℃). It was found that the productivity of water and the coefficient of performance increased to a maximum at 60℃. The constant temperature (60℃) heat storage had a significant advantage in terms of superior performance as compared to quantitative heat storage at 60℃. The increments of the distilled water productivity, the total coefficient of performance, and the gained output ratio were 950 mL, 0.102 and 0.056 respectively. Furthermore, the system performance was conducted without heat storage. The distilled water productivity, the overall system coefficient of performance, and the gained output ratio were 5 978.4 mL, 1.2498 and 0.468, respectively. The decrease of the coefficient of performance and the gained output ratio were 0.1979 and 0.219, compared with constant temperature heat storage at 60℃. Finally, the water quality of the distilled water was also tested It was found that each parameter test result of water quality reached the standard of drinking water, including the sensory index, chemical index, bacteriological index, and toxicology index. The pH of distilled water was increased from 6.98 to 7.6, and its weakly alkaline properties excellently accorded with human body physiological needs. The chromaticity of the distilled water was reduced from 12 to 4.2, and chloride content and fluoride content were reduced from 360.3 to 2.5 mg/L and from 1.38 to 0.08 mg/L, respectively. The total hardness and total soluble solids were reduced from 275.62 to 4 mg/L and from 639.6 to 12 mg/L, oxygen consumption was decreased from 2.8 to 0.54 mg/L, the iron and manganese content had been reduced from 0.29 to 0.2 mg/L and from 0.16 to 0.04 mg/L as well, and total coliforms and toxicity index in water were not detected. The percent of pass of the system was obtained as 100%. The proposed method could be used to provide living hot water and drinking water for brackish water areas, coastal areas, and overseas islands, and has very good social and economic value.