Performance evaluation of double slope solar still augmented with binary eutectic phase change material and steel wool fibre

Abstract

Solar still integrated with phase change material (PCM) as latent heat storage material proves to be the prominent solution for obtaining potable water from brackish water. However, none of the individual organic PCM possesses all the required favourable characteristics such as specific melting temperature, latent heat of fusion etc to operate the solar still in any environmental conditions. Therefore, development of binary eutectic PCM by mixing two or more different types of organic PCMs, enhances the thermo physical properties of PCM. In this experimental work, an effort was made to fabricate and compare the energetic and exergetic performances of traditional and modified double slope solar still. Two techniques were used to augment the yield of traditional solar still. First, binary eutectic PCM (mixture of palmitic acid and stearic acid) have been stored in copper tubes and copper cylinder. Second, Steel wool fibre (SWF) is embedded in solar still basin with PCM. Additionaly the effect of variation of basin water depth on still performance has also been studied. Hence, four different cases namely MDSSS-1 (PCM with 4 cm water depth), MDSSS-2 (PCM with 3 cm water depth), MDSSS-3 (PCM with 2 cm water depth) and MDSSS-4 (PCM + SWF with 2 cm water depth) have been compared with TDSSS (traditional still with 4 cm water depth) in the environmental condition of Bhopal city, Madhya Pradesh, India. The result reveals that total cumulative yields for TDSSS, MDSSS-1, MDSSS-2, MDSSS-3 and MDSSS-4 are approximately 1.82, 2.46, 2.78, 3.26, and 3.40 kg/m2, respectively. The average energy efficiency of MDSSS-4 is 41%, which was higher than TDSSS (22.21%), MDSSS-1 (30.42%), MDSSS-2 (33.88%) and MDSSS-3 (38.14%).Meanwhile, the daily average exergy efficiencies for TDSSS, MDSSS-1, MDSSS-2, MDSSS-3 and MDSSS-4 are found to be 3.1855, 5.47, 9.13, 10.1 and 11.8% respectively. Hourly variation of heat transfer coefficient and exergy fraction has also studied for different cases and it shows that mean value of coefficients of evaporation, convection and radiation heat transfer for MDSSS-4 is higher than TDSSS by 45.9, 36.2, and 35 % respectively.