Heat transfer characteristics of microencapsulated phase change material slurry flows under a constant heat flux boundary

This paper investigates laminar heat transfer characteristic of two-phase microencapsulated phase change material (MPCM) suspension flows within mini-channels under a constant wall heat flux boundary. Capsules containing paraffin wax with phase change temperature between 35.1°C and 44°C are examined and found to be well suited for electronics cooling applications using liquid cold plate technologies. In particular, it is shown that the large thermal capacity of MPCM slurries around the phase change temperature can lead towards greater isothermality of isoflux systems, a characteristic of significant interest to telecommunication, laser and biomedical applications. The principal focus of the study is to examine heat transfer characteristics within standard tube flow geometries, quantify the heat transfer augmentation/degradation observed and finally, elucidate the mechanisms from which these result. Through the study volume concentrations of the MPCM slurry were varied between 30.2% and 5.03%. High resolution local heat transfer measurements were obtained using infrared thermography and results presented in terms of local Nusselt number versus inverse Graetz parameter. These spanned both the thermal entrance and the fully developed flow regions with inverse Graetz number ranging from 10^-3 to 10°. Results show that significant heat transfer enhancements are attainable via the use of MPCM slurries over conventional single phase coolants. Overall, the study highlights mechanisms that lead to significant heat transfer enhancements in heat exchange devices employing micro-encapsulated phase change material slurries.