Heat transfer and pressure drop of Al2O3 nanofluid as coolant in shell and helically coiled tube heat exchanger

In this investigation, the heat transfer and pressure drop analysis of Al2O3/water nanofluid in a shell and helically coiled tube heat exchanger are studied. The Al2O3/water nanofluid at 0.1%, 0.4%, and 0.8% particle volume concentration was prepared by two-step method and characterized. It was found that the enhancement of experimental inner Nusselt numbers of 0.1%, 0.4% and 0.8% nanofluids are by 21%, 28% and 42%, respectively, higher than in water under laminar flow condition. This may be due to better mixing of the flow particles and higher effective thermal conductivity of the nanofluid. The inner Nusselt number correlation was proposed based on the experimental data. It is found that the deviation between the predicted and experimental Nusselt numbers in the range of 7.5%. The pressure drop in 0.1%, 0.4% and 0.8% nanofluids was by 8%, 12% and 20%, respectively higher than that in water. This is due to the improved viscosity of the nanofluids. It is concluded that the Al2O3 nanofluid can be applied as coolant in a helically coiled tube at 0.1% and 0.4% particle volume concentrations without significant pressure drop.