Flow drag and heat transfer reduction phenomena of non-ionic aqueous surfactant solutions flowing in helical and straight pipes have been experimentally investigated at surfactant solution concentration range of 250-5000ppm and temperature range of 5-20°C. The helically coiled pipes have curvature ratios range of 0.018–0.045. Experimental findings indicate that the friction factors and the heat transfer coefficients of the surfactant solution in helical pipes are significantly higher than in a straight pipe and lower than Newtonian fluid flow like water through the same coils in the turbulent drag reduction region. Drag reduction and heat transfer reduction increase with an increase in surfactant solution concentration and temperature in the measured concentration and temperature ranges. On the other hand, they decrease with increasing of the curvature ratio. A set of empirical expressions for predicting the friction factor and the average Nusselt number for the surfactant solution’s flow through helical and straight pipes have been regressed based on the obtained data in the present experiments.

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The present study has been performed for obtaining the heat transfer enhancement characteristics of the plural microencapsulated solid-liquid phase change materials (PCM) slurry having different sizes, which flows in a straight tube heated under a constant wall heat flux condition. In the turbulent flow region, the friction factor of the plural PCM slurry was found to be lower than that of pure water flow due to the drag reducing effect of the PCM slurry. The heat transfer coefficient of the plural PCMs slurry flow in the tube was increased by both effects of latent heat evolved in phase change process and micro-convection around plural microcapsules with different diameters. The experimental results revealed that the average heat transfer coefficient of the plural PCMs slurry flow was about 2∼2.8 times greater than that of a single phase of water.

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