Chapter 2.23 – A Numerical Study on Phase Change Inside a Spherical Capsule

Abstract In this study, the transient thermal behavior of a phase change material inside a spherical capsule is investigated under various working conditions. A two-dimensional axisymmetric model is considered using ANSYS-Fluent software. A definition of enhanced thermal conductivity is used to incorporate the effect of natural convection in the mathematical model. Validation of the code is proven by comparing the prediction with results obtained from the literature. As a result, it is found that increasing the free stream temperature and convective heat transfer coefficient improves heat transfer inside the sphere and decreases the time for complete melting. The required time for complete melting is reduced by almost one-half for T m  + 30°C and T m  + 20°C when enhanced thermal conductivity is implemented. It is clear that neglecting the effects of convection causes significant underestimations regarding the liquid fraction even for lower free-stream temperature values, i.e., T m  + 10°C. On the other hand, the definition of enhanced thermal conductivity becomes effective when the liquid fraction reaches 0.4. The slope of the liquid fraction improves as improved thermal conductivity is defined. Implementation of enhanced thermal conductivity reduces the complete time of melting by almost one-fourth.