Experimental Investigation on Charging and Discharging Behavior of Paraffin Wax Capsules for Thermal Energy Storage

Abstract

This study presents an experimental analysis of charging and discharging characteristics of paraffin wax encapsulated in red sand for thermal energy storage applications. Paraffin wax with a melting temperature range of 45–75 °C was used as the core material because of its non-toxicity, chemical stability, and high latent heat capacity. Red sand, available locally, was chosen as the shell material owing to its low cost and ability to form mechanically stable structures when mixed with water and dried. Although multiple capsules were fabricated, one representative unit was chosen for detailed analysis. During charging at 60 °C, the capsule required approximately 220 minutes to reach steady state. Distinct sensible and latent contributions were observed, with a total energy storage of about 2.35 kJ, comprising 1.92 kJ sensible heat and 0.43 kJ latent heat. The discharging process, conducted at 25 °C, lasted nearly 350 minutes. During this period, the capsule gradually cooled, releasing approximately 2.03 kJ of energy, consisting of 1.65 kJ latent heat and 0.38 kJ sensible heat. These findings demonstrate that paraffin wax encapsulated in red sand provides stable and repeatable thermal energy storage. The encapsulated system shows potential for low- to medium-temperature applications requiring long-duration heat release, including solar water heating and waste heat recovery systems.