Convective heat transfer in pipe flow for glycolated water-based carbon nanofluids. A thorough analysis

The exceptional thermal properties of graphene are maintained in a few orders of magnitude in its multi-layered structure, graphene nanoplatelets, with a considerably lower production cost. Ethylene glycol and water binary mixtures are commonly used as working fluids in different applications, such as the automotive sector, industrial cooling systems, renewable domestic heating systems, or solar and wind power plants, due to the protection provided against low freezing temperatures. In this work, the heat transfer performance of different-loaded sulfonic acid functionalized graphene nanoplatelet nanofluids (0.25, 0.50 and 1.0 wt%) based on an ethylene glycol:water 50:50 vol% mixture was experimentally assessed. Firstly, thermophysical and rheological evaluations for base fluid and nanofluids were developed in a wide temperature range (293.15 to 333.15 K). Densities, isobaric heat capacities, thermal conductivities and dynamic viscosities for base fluid and nanofluids were determined by vibrating tube, differential scanning calorimetry, transient hot wire and rotational rheometry methods, respectively. Subsequently, convective heat transfer coefficients and pressure drops/pumping powers were experimentally determined through a test rig with a concentric tube heat exchanger as main element at different working temperatures (from 298.15 to 318.15 K) and flow rates (from 300 to 700 dm(3).h(-1)). Furthermore, a dimensionless analysis from the obtained results was carried out. The proposed new 025 wt% nanofluid achieves the higher convective heat transfer performance. Finally, a summary and a comparison of the results for different glycolated water-based carbon nanofluids evaluated in the same experimental facility are reported. (C) 2019 Elsevier B.V. All rights reserved.