Heat Transfer Enhancement in Laminar Graetz and Taylor Flows Using Nanofluids

This paper focuses on heat transfer in mini scale tubes under laminar developing flow conditions for a constant wall temperature boundary condition. An experimental study was preformed using Aluminum Oxide nanoparticles (< 50nm) for continuous and segmented fluid streams. A two step method was employed to prepare several samples of aluminum oxide nanofluid with different concentrations 0.25, 0.5 and 1% by volume. Heat transfer enhancement in mini scale tubes (∼1 mm) was assessed using the dimensionless Graetz parameter L*, dimensionless mean wall heat flux q*, and Nusselt number Nu. In this study we investigate the effect of nanofluid concentration on laminar heat transfer enhancement in mini-scale circular tube under continuous and segmented flow using gas as a segmenting medium. The initial results show a maximum of 10–65% enhancement of Nusselt number as compared with pure water under the same conditions as a function of L*. For the upper limit of concentration of 1% Al₂O₃ nanofluid, the friction factor was found to be less than 5% greater, which means a small sacrifice on pumping power is to be expected. This study provides new insights on the thermal behaviour of nanofluids under laminar developing flow and segmented flow conditions in straight tubes.