Heat transfer performance of a nano-enhanced propylene glycol:water mixture

Propylene glycol:water mixtures are usually employed as heat transfer fluids because of their protection against low freezing temperatures and non-toxicity. They are used as working fluids in different applications, like those based on renewable sources such as solar thermal or geothermal energy. In this work, the convection heat transfer coefficients and the pressure drops of various functionalized graphene nanoplatelet nanofluids with a propylene glycol:water mixture at 30:70% mass ratio as base fluid have been experimentally determined. Thus, the heat transfer performance of nanoadditive mass concentrations up to 1.0% at different working temperatures from (298.15-313.15) K and flow rates from (0.2-0.7) m(3).h(-1) has been evaluated by means of an experimental setup whose main element is a double pipe heat exchanger of stainless steel. Enhancements of the convection heat transfer coefficient reaching 15.3% have been found for the 0.75% mass concentration. Furthermore, a dimensionless analysis has been carried out and new correlations were provided in order to predict Nusselt number and friction factor as a function of other dimensionless parameters. Maximum deviations for Nusselt number and friction factor of 2.5% and 1.5% were achieved, respectively. Finally, thermal performance factors were also obtained for each condition with the aim of evaluating the thermal effectiveness of all the prepared nanofluids with respect to the base fluid.