Investigation on the performance of a natural convection solar dryer with novel palmitic and sebacic acid eutectic phase change material for thermal energy storage applications

Abstract

Solar drying has got enormous opportunity in the agricultural sector for hygienic processing of various crops which leads to value addition and high return to farmers. One of the drawbacks associated with solar drying is its usage during non-solar hours. This demerit could be effectively alleviated by integrating latent heat thermal energy storage system based on PCM with the solar dryer and extend its usage beyond sunshine hours. The present study encompasses the development of a novel eutectic phase change material (PCM) consisting of palmitic and sebacic acids (PA-SA) with an individual composition of 80 wt% and 20 wt%, respectively. Using a differential scanning calorimeter, the melting point and enthalpy of fusion of the PA-SA eutectic mixture were determined as 61.10 °C and 161.14 J g−1, respectively. Fourier transform infrared spectroscopy analysis ensured the chemical durability of the fresh eutectic materials and 1000 thermal cycled samples, which proved the suitability of the material for long-term applications. Accelerated thermal cycles up to 1000, and thermal conductivity tests accentuated the superior thermal reliability, and competency of the developed PA-SA PCM. Thermo-gravimetric analysis observed a degradation temperature of 215.13 °C, which is >3 times higher than the operating temperature and hence qualifies the thermal stability test. Corrosion analysis carried out as per ASTM G O1 using three metals such as stainless steel, aluminium and copper revealed the compatibility of using stainless steel as heat exchanger material. Corrosion rates were found to be zero, 0.4015 and 8.6505 mg cm−2 year−1 over 365 cycles respectively for stainless steel, aluminium and copper. Extensive experimental analysis was undertaken to compare the effectiveness of a natural convection solar dryer with and without PA-SA eutectic PCM. The study conducted with 3 kg of eutectic PCM encapsulated in stainless steel cylindrical tubes as heat exchanger elucidated the use of solar with PCM for a duration of four and half hours after sunshine. For solar drying applications, an organic PA-SA eutectic PCM has been developed with a melting range of 61.1 °C and a latent heat of 161.14 J g−1.