Session: 11-10-01 Single/ Two-Phase Heat Transfer in Active and Passive Systems

Paper Number: 70712

Start Time: Tuesday, 06:40 PM

70712 - Development of a Topology-Optimized Structure for Thermal Energy Storage Under Natural Convection Conditions 

A topology-optimized structure for thermal energy storage is developed. The topology optimization is performed based on the minimization of objective functions under natural convection in two-dimensional space. The design domain is of a rectangular shape with a heat source placed at the bottom, while the remaining walls have the Dirichlet boundary condition. The solid volume fraction is set to 0.15. A symmetry boundary condition is applied in the middle of the design domain in order to reduce the computational time needed. Since the study takes natural convection into account, the Boussinesq approximation is included in the momentum equation to simulate natural convection. A RAMP-style function is applied to the thermal conductivity in the design domain so as to clearly define the solid and liquid regions. The solid region represents the AlSi10Mg, a high thermal conductivity aluminum alloy that is used for additive manufacturing, while the liquid region represents the phase change material (PCM). The optimization was computed with COMSOL Multiphysics at different temperature differences at the bottom and the top walls. By varying the temperature difference, it can be shown that the topology-optimized structures do not differ significantly from one another. The final generated optimized structure resembles a tree. The structure is successfully fabricated by Selective Laser Melting (SLM) using AlSi10Mg powder at a laser power of 250 W, and a scanning speed of 1300 mm/s. SLM is used to fabricate the structure as such technology is capable of fabricating complex geometries with a high apparent density.

Experimental investigations of these structure were compared with two conventional designs fabricated with Al-6061; one with five longitudinal fins positioned radially from the heat source and the other with no surface enhancements. The PCM used in the experiments is RT44HC, a pure PCM that is mainly used for heat storage applications. The experiments involved allowing the PCM to completely melt at two heat rates of 27 and 48 W. All structures were placed in the horizontal orientation, where the PCM can flow toward the heat source placed at the bottom of each structure. One side of each structure is sealed with an acrylic plate to allow visualization of the melting process, while the remaining sides are insulated to minimize heat loss to the surroundings. Our preliminary experimental studies suggest that the topology-optimized structure has a lower rate of increase in base temperature during post-melting compared to the two conventional designs, primarily due to the efficient transfer of heat by natural convection.

Presenting Author: Yao Song See Nanyang Technological University Singapore

Authors:

Yao Song See Nanyang Technological University Singapore
Jin Yao Ho Nanyang Technological University Singapore
Kai Choong Leong Nanyang Technological University Singapore
Teck Neng Wong Nanyang Technological University Singapore