A conjugate heat transfer model for unconstrained melting of macroencapsulated phase change materials subjected to external convection. (March 2020)

• Record Type: Journal Article
• Authors: Hummel, Daniel; Beer, Stefan; Hornung, Andreas
• Is Part Of: International journal of heat and mass transfer. Volume 149(2020)
• Publication Date: 2020-03
• Subjects: Melting -- Transient conjugate heat transfer -- Fluid-structure interaction -- Mixed convection -- OpenFOAM®; Heat -- Transmission -- Periodicals; Mass transfer -- Periodicals; Chaleur -- Transmission -- Périodiques; Transfert de masse -- Périodiques; Electronic journals; 621.4022
• DOI: 10.1016/j.ijheatmasstransfer.2019.119205
• Languages: English
• ISSNs: 0017-9310

Abstract

Highlights: Model for interaction of phase change material, capsules and heat transfer fluid. Numerical solution by segregated and sequential conjugate heat transfer approach. Solid velocity based on isosurface, force balance and integration of acceleration. Wall temperatures of capsules immersed in fluid are transient and non-uniform. Assumption of constant and uniform wall temperatures induces significant error. Abstract: A new conjugate heat transfer model for unconstrained melting of macroencapsulated phase change material subjected to external convection is presented. Flow and heat transfer processes are modeled for the phase change material, the capsule wall and the external heat transfer fluid. The solvers for each region operate in a segregated and sequential manner and are coupled by mixed thermal boundary conditions. For the description of the solid body motion in unconstrained melting, the enthalpy-porosity method is modified. The solid body surface is reconstructed from the liquid volume fraction field for every time step by a triangulated isosurface using a marching tetrahedra technique. Based on computation of the forces exerted on the solid, the motion of the solid is determined iteratively in a strong coupling between solid velocity and pressure. The new conjugate heat transfer solver is utilized to simulate the commonly experimentally and numerically investigated scenario of a spherically encapsulated phase change material immersed in a water bath. The coupled flow and heat transfer is investigated for a natural convection dominated mixed convection problem with a Richardson number of 50 · 10 3 and Stefan numbers of 0.075, 0.1, 0.15, 0.2 and 0.25. Contrary to the commonly made assumption, the resulting capsule wall temperature is transient and highly non-uniform. The differences in melting times range from 50.7 to 67.5% between the consideration of external heat transfer and the assumption of constant uniform wall temperatures.