Experimental investigation of solar evacuated tube collector with multi-walled carbon nanotube-water-based nanofluid

Abstract

ABSTRACT Improving the thermal performance of evacuated tube-type solar thermal collector has been attempted with different ways by various researchers, e.g. modifying absorber design, using heat pipe designs, concentrators and different heat transfer fluids, etc. In this work, an experimental investigation of multi-walled carbon nanotube-water (MWCNT-H2O)-based nanofluid as heat transfer fluid on the thermal performance of an evacuated tube solar collector has been performed. The effects of operating variables like nanoparticle volume concentrations, temperature and flow rate on the thermal conductivity of the nanofluid and the thermal efficiency of the collector are measured as well as compared with water-based evacuated tube collector. The nanofluid was prepared utilizing a probe sonicator for sonication time of 60 min. Before sonication, magnetic stirring was done for 2 h to obtain fine dispersion of the nanoparticles. The thermal conductivity of the nanofluid was measured using a KD2 probe by altering its temperature. Investigations are carried out at different nanoparticle volume concentrations (0.06–0.1 vol%), sonication temperature (0-–70°C), and flow rates (1 and 1.4 LPM). It is found that thermal conductivity of the nanofluid is increased as the nanoparticle volume concentration and sonication temperature are increased. A maximum enhancement of thermal conductivity by 20.37% is recorded for nanoparticle volume concentration 0.1% and temperature 70°C. Outlet temperature of the nanofluid is increased to 67.5°C with increase of nanoparticle concentration to 0.1 vol%, but at the lower flow rate condition (1 LPM). The thermal efficiency of the collector is also increased with increase of volume concentration to 0.1%, with a maximum efficiency of 64.13% recorded at 1.4 LPM flow rate. It is finally shown that at this volume concentration (0.1 vol %) and flow rate (1.4 LPM), the enhancement in thermal efficiency is 18.34% compared to the water-based collector.