Viscosity Evaluation of Carbon-Nanotube-Dispersed Phase Change Material as Latent Heat Storage Material

Latent heat storage with a high heat storage density owing to the phase change is a promising method. Melting convection is a dominant process in the phase change progression during latent heat storage. To reduce latent heat storage time, thermal conductivity and melting convection should be increased and promoted, respectively. Dispersed fluids have a continuous fluid phase that can be convected; hence, the heat exchange performance can be improved using a high thermal conductivity material as the dispersoid. Carbon nanotubes (CNTs) are promising materials for dispersoids, owing to their high thermal conductivity. However, the inclusion of dispersoids obstructs convection because of the increased viscosity and flow complications owing to the change to a non-Newtonian fluid. Therefore, understanding the viscosity properties of latent heat storage materials with dispersed systems is essential for system design. This study evaluates the viscous properties of a multi-walled CNT (MWCNT) dispersed phase change material (PCM). The test sample consists of MWCNT as the dispersoid, latent heat storage material in the continuous phase and surfactants for dispersion. Moreover, this study carries out a flow analysis of latent heat storage by melting. Shear-rate dependence of the shear stress was measured using a rotational viscometer. The experimental data are obtained for a temperature range of 60–84 °C, a shear rate of 500 1/s or below, and an MWCNT content of 0–1.0 mass%, which are arranged as an experimental equation based on the power law.