In this study, flow and heat transfer characteristics of the dilute oil-in-water emulsions containing micrometer-sized dimethyl silicone oil droplets with different concentrations are investigated experimentally in a helically coiled tube. Forced convective heat transfer of emulsions can be enhanced significantly by low-concentration oil droplets although thermal conductivity of oil is much lower than that of water. Pressure drop of low-concentration emulsions can be lower than that of the water base fluid in laminar flow region. Early onset of transition to turbulence for oil-in-water emulsions occurs compared to pure water in a heated tube. The largest thermal performance factor is 1.044 at oil mass fraction of 0.5% and at Re around 3500. This study could be helpful for exploring a new heat transfer media with large heat transfer enhancement at a slight or even negative increase of pumping energy consumption by adding low-concentration oil droplets.

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