Investigation on convective heat transfer of nanofluids: An application to solar collectors

One of the innovative methods of improving the heat transfer characteristics of solar heat exchangers is applying nanofluids as the working heat transfer fluids.Therefore, in this typical study the convective heat transfer of water-based TiO2 nanofluid flowing through a uniformly heated circular tube in laminar flow regimehas been investigated via experiment and numerical modeling. Using a two-step method, the nanofluids have been manufactured at different nanoparticle volumefractions of 1%, 1.6% and 2.3%. The thermal conductivity and dynamic viscosity of the preparednanofluids have been modeled based on the presentmeasured data at different temperatures and nanoparticle volume fractions. Furthermore, the single and two-phasenumerical approaches have been employed and modified to predict the heat transfer characteristics of the nanofluid. The results indicated that the convective heattransfer coefficient increases with an increase in nanoparticle concentration and flow Reynolds number.The numerical investigation proved that the predictedheat transfer coefficients via single-phase approach based on the thermophysical properties of nanofluids in a staticcondition are lower than the experimental data. Finally, it was concluded that employing the proposed nanoparticle Nusselt number correlation instead of the Ranz-Marshall correlation, the two-phase Eulerian-Eulerian model predicts heat transfer coefficient of nanofluids more accurately.

کلیدواژه ها:

Solar collector ، Nanofluid ، Convective heat transfer ، Experimental study ، Two phase modeling