Prediction of void in graphite foam infiltration with phase change materials using Volume-of-Fluid method

Conference Name: 48th annual technical conference of the Society of Engineering Sciences
Location: Evanston, Illinois, USA
Date: 10/2011

List of Authors:

Mahmoud Moeini Sedeh, J. M. Khodadadi

Abstract

Infiltration process is one of the fundamental steps in production of composite energy storage systems. In this research, the fundamental capabilities of volume-of-fluid (VOF) method in simulation of infiltration process were studied. The infiltration is one of the primary mechanisms that seriously contribute in void formation in foam or graphite/phase change material (PCM) composites. The presence of void, even in low volume percentages, in open cells of the foams or inside the graphite pores, greatly alters the thermal behavior of such composites. Therefore, it is crucially important to investigate the formation of void and its effects on thermal behavior and phase change cycles in energy storage systems. In order to predict the formation of void during the infiltration process, a porous structure with interconnected cylindrical pores was considered. A two-dimensional model was developed and different unstructured grid systems were generated for grid independence study. The VOF model was utilized for simulation of infiltration process. The modeled pore is initially filled with air and then the PCM (cyclohexane) enters the pore from a boundary due to a combination of gravity, pressure gradient and surface tension effects. The simulation is transient and continues in time until it reaches the steady state condition of cyclohexane exchange with neighboring pores. This simulation firstly shows that the considered VOF multiphase model is able to predict void. Additionally, it can be concluded that formation of void is greatly due to the structure of the porous structure and the amount of stable void for this model was evaluated to be about 4.9 % (based on the surface) which is comparable to the experimental reported values. As a result, precise modeling of the geometry in a representative elementary volume (REV) in porous structures is crucially important for reliable prediction of void formation during the infiltration process.