Assessment of TiO2 water-based nanofluids with two distinct morphologies in a U type evacuated tube solar collector

In the present study two samples of water based nanofluids having suspended TiO2 species with spherical and wire-like geometry (TiO2 NPs-nanofluid, TiO2 NWs-nanofluid) were prepared and their thermophysical properties were experimentally determined. The results showed that adding TiO2 nanowires and TiO2 nanoparticles to the base fluid could respectively improve the thermal conductivity up to 12.4% and 5.4%. TiO2 NWs-nanofluid because of the particular configuration of the wire-like suspended species displayed better thermal properties. A thermal system included a U type evacuated tube solar collector, a circulating refrigerator bath, digital thermometers and a peristaltic pump was erected, in which, the working fluid flowed through the collector under a laminar regime in a closed loop. Several flow rates of 0.1, 0.2, 0.3, 0.4, and 0.5 L/min were considered for the collector testing. The collector performance results indicated that both the absorbed energy parameter F-R (tau alpha) and the removal energy parameter FRUL are significantly influenced using the nanofluids. Increasing flow rate makes the nanofluids more efficient due to the heat transfer coefficient enhancement. At 0.5 L/min, TiO2 NWs-nanofluid and TiO2 NPs-nanofluid could respectively enhance the maximum collector efficiency (eta(0)) up to 21.1% and 12.2%. Thermal-hydraulic results proved that TiO2 NWs-nanofluid, despite higher pressure drop due to its higher viscosity, was a better choice as compared to TiO2 NPs-nanofluid for working in the solar collector. In this superior fluid the enhancement in pressure drop as a penalty was not notable as compared to improvement in the heat transfer coefficient.

Automated summary

The study showed that adding TiO2 nanowires and nanoparticles can significantly improve the thermal conductivity of the base fluid, with TiO2 NWs-nanofluid exhibiting better thermal properties due to its unique wire-like suspended species. Increasing flow rate enhances nanofluid efficiency in a solar collector, with TiO2 NWs-nanofluid and TiO2 NPs-nanofluid enhancing maximum collector efficiency by up to 21.1% and 12.2% respectively at 0.5 L/min. Despite higher viscosity and pressure drop, TiO2 NWs-nanofluid is a better choice compared to TiO2 NPs-nanofluid in terms of thermal-hydraulic performance in the solar collector.