An Experimental Study on Flow and Heat Transfer Characteristics of Ethanol/Polyalphaolefin Nanoemulsion Flowing Through Circular Minichannels

An Experimental Study on Flow and Heat Transfer Characteristics of Ethanol/Polyalphaolefin Nanoemulsion Flowing Through Circular Minichannels Fana Zewede1, Henok Argaw 1, Jiajun Xu1 1 Department of Mechanical Engineering, University of the District of Columbia, DC 20008 USA The need for advanced cooling technique has result many efforts to develop novel thermal management solutions including efficient heat exchangers, new heat transfer fluids and etc. Developing heat transfer fluids with improved thermal properties over those currently available is one of most challenging tasks in the heat transfer community. Therefore, more efforts must be made in this field to better understand how to enhance heat transfer using nanostructured materials and surface structures. Recently, a radically new design for thermal fluids, "nanoemulsion fluids" that completely eliminates solid particles, and instead, uses liquid nanostructures has been proposed. The nanoemulsion fluid can be formed spontaneously by self-assembly without need of external shear-induced rupturing. The phase changeable nanodroplets inside the nanoemulsion fluids have been experimentally discovered that their nucleation can enhance the heat transfer coefficient dramatically. However, it is urgently needed to characterize and understand the how the liquid nanostructure affects the convective flow and heat transfer properties. This work experimentally studied the convective flow and heat transfer characteristics of a novel heat transfer fluid "Ethanol/Polyalphaolefin nanoemulsion" using 12 circular mini-channels of 1mm diameter. In this study, two nanoemulsion fluids with different concentrations of ethanol were used as working fluids and the effect of flow modes on the heat transfer is also investigated. The Reynolds number was varied from 100 to 5000 to cover the laminar to turbulent regions. Moreover, base fluid PAO flowing through the same mini-channels was tested as the baseline data. The experimental results show that: at same Reynolds number, the Nusselt number of Ethanol/PAO nanoemulsion is higher than that base fluid PAO. There is an increase of the pressure drop and earlier induction of the laminar-turbulent transition for the Ethanol/PAO nanoemulsion compared to base fluid PAO. At transitional flow regime, an oscillation of surface temperature has been observed and it has been attributed to the temperature dependent viscosity and thermal conductivity. The difference of viscosity and thermal conductivity between the PAO and nanoemulsion will affect the thermal boundary layer and that might be the reason for the increase of Nusselt number in transitional region. Future research involves more data on the fully developed turbulent region and different heat inputs may help understand the convective heat transfer of nanoemulsion.