Discipline: Technology and Engineering
Subcategory: Civil/Mechanical/Manufacturing Engineering
Fana Zewede - University of the District of Columbia
Co-Author(s): Henok Argaw and Jiajun Xu, University of the District of Columbia, DC
The need for advanced cooling technique has result many efforts on developing novel thermal management solutions including efficient heat exchangers, and new heat transfer fluids 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” that completely eliminates solid particles, and instead, uses liquid nanostructures has been proposed. The nanoemulsion can be formed spontaneously by self-assembly without the 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 ‘Ethanol/Polyalphaolefin (PAO) nanoemulsion’ using 12 circular mini-channels of 1mm diameter each. In this study, two nanoemulsions 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 and used 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 better.
Funder Acknowledgement(s): I thank Thanh Tran at Carderock Division of the Naval Surface Warfare Center, Bethesda, MD for his help. I also thank Yuwen Zhang at University of Missouri-Columbia for help in the field. Funding was provided by an NSF/HBCU-UP RIA grant to Jiajun Xu.
Faculty Advisor: Jiajun Xu, firstname.lastname@example.org
Role: I configured the system, collected and analyzed experimental data, prepared reports of the experimental results.