Flow of suspensions of carbon nanotubes carrying phase change materials through microchannels and heat transfer enhancement

Abstract

This work explores the potential of nano-encapsulated phase change materials (PCMs) in applications related to microelectronics cooling. PCMs (wax or meso-erythritol) were encapsulated in carbon nanotubes (CNTs) by a method of self-sustained diffusion at room temperature and pressure. These nano-encapsulated wax nanoparticles alone allowed heat removal over a relatively wide range of temperatures (different waxes have melting temperatures in the range 40-80 degrees C). On the other hand, nano-encapsulated meso-erythritol nanoparticles allowed heat removal in the range 118-120 degrees C. The combination of these two PCMs (wax and meso-erythritol) could extend the temperature range to 40-120 degrees C, when both types of nanoparticles (wax and meso-erythritol intercalated) would be suspended in the same carrier fluid (an oil). The nanoparticles possess a short response time of the order of 10(-7) s. Such nano-encapsulation can also prevent the PCM from sticking to the wall. In this work, experiments with wax-intercalated CNTs, stable aqueous suspensions of CNTs with concentrations up to 3 wt% with and without nano-encapsulated wax were prepared using a surfactant sodium dodecyl benzene sulfonate (NaDDBS). These suspensions were pumped through two channels of 603 mu m or 1803 mu m in diameter subjected to a constant heat flux at the wall. It was found that the presence of the surfactant in CNT suspensions results in a pseudo-slip at the channel wall which enhances the flow rate at a fixed pressure drop. When aqueous solutions of the surfactant were employed (with no CNTs added), the enhanced convection alone was responsible for a similar to 2 degrees C reduction in temperature in comparison with pure water flows. When CNTs with nano-encapsulated wax were added, an additional similar to 1.90 degrees C reduction in temperature due to the PCM fusion was observed when using 3 wt% CNT suspensions. In addition, suspensions of meso-erythritol-intercalated CNTs in alpha-olefin oil were used as coolants in flows through the 1803 mu m-diameter microchannel. These suspensions (1.5 wt% CNT) revealed a temperature reduction due to the PCM fusion of up to 3.2 degrees C, and a fusion temperature in the range 118-120 degrees C.