Thermal-hydraulic characteristics of ethylene glycol aqueous solutions containing microencapsulated paraffin

The study involved investigating heat exchange performance with a microcapsule - ethylene glycol/water slurry for flow in a horizontal circular tube under constant heat flux boundary conditions. The microcapsule included paraffin as a phase change material and was 250 mu m in average diameter. The particle fraction in the slurry corresponded to 15 wt%. Measurements were performed for both cases with or without the phase change. The friction factor of the microcapsule slurry obtained by pressure drop measurements increase when compared with ethylene glycol/water, and this indicated increase in flow resistance. Interestingly, the heat exchange output of the microcapsule slurry at 10 wt% increased by up to 10% compared to that of the ethylene glycol/water solution under the same pressure drop conditions. This is due to the reduction in the boundary-layer thickness given the effect of particle agitation and the increase in heat capacity with latent heat. The heat exchange output of the microcapsule slurry under the same pressure-drop conditions decreased for a particle concentration exceeding 10 wt%, and this resulted from the increase in the negative effect of the flow resistance.