The Metallographic Study of Corrosion of Metals with Latent Heat Storage Materials Suitable for Solar Hot Water System

In the present study three most commonly considered metals in thermal equipment such as copper, aluminium and stainless steel have been considered to study the corrosion rate with latent heat storage materials suitable for solar hot water system. The latent heat storage materials (LHSMs) considered are paraffin wax, myristic acid, stearic acid, palmatic acid, lauric acid and sodium acetate trihydrate. The compatibility of these metals with selected LHSMs is evaluated by immersion corrosion test on a short term basis. The experiment is performed at 70°C to make sure it is above the melting points of selected LHSMs. During the experiment, it is made sure that the metal specimen is totally immersed in the LHSM to avoid contact with air, thereby creating a more practical and realistic situation of thermal energy storage system. The corrosion rate is measured for a span of 20 days. Results are presented in terms of corrosion rate, physical and microscopic appearance of the metal specimens. Based on the experiments, it is observed that several pairs can be ruled out. The study could reveal that a good amount of metal loss can be seen on both copper and aluminium. Stainless steel is found to be the best out of three metals (almost immune to corrosion) and can be used as a container material for solar water heating system.