The role of contact angle in the thermal conductivity of microencapsulated phase change material suspensions

Abstract

The purpose of this article is to investigate the effect of the wettability on the thermal conductivity of microencapsulated phase change material suspensions. The wettability of the capsules, characterized by contact angle between solid capsules and carrier fluid, was modified by mixing two selected surfactants into the suspensions, that is, cetyltrimethylammonium bromide and sodium dodecyl sulfate, and changing such surfactants' additive amount. Meanwhile, the static thermal conductivity of the microencapsulated phase change material suspensions was measured. The results indicated the effect of the cetyltrimethylammonium bromide is more significant than the sodium dodecyl sulfate when the mass fraction of surfactants falls into the range of 0-0.05 wt%. However, when the mass fraction of surfactants continues to increase from 0.05 wt%, the significance of the sodium dodecyl sulfate exceeded the cetyltrimethylammonium bromide. It was also found that the decrease in the contact angle led to the growth in thermal conductivity for Maxwell model and tested results. When the contact angle fell into the range of 45°-95°, the Maxwell model could predict the thermal conductivity with a good accuracy, but inversely, when the contact angles were smaller than 45°, a significant gap was found between the two results. To remove such gap a correction factor ''A'' which is associated with contact angles was proposed.