Sonochemical preparation of rGO-SnO2 nanocomposite and its nanofluids: Characterization, thermal conductivity, rheological and convective heat transfer investigation

In the present study, rGO-SnO2 nanocomposite of different rGO:SnO2 ratio (1:7, 1:8 and 1:10 on mass basis) was synthesized using ultrasonic assisted method. The nanofluid prepared with the use of the rGO-SnO2 nanocomposite dispersed in water was investigated at lab-scale for its application for convective heat transfer using a heat exchanger consisting of a straight tube. The successful formation of the rGO-SnO2 nanocomposite particles was proved through UV/vis spectrophotometry, XRD, Raman spectroscopy and TEM analysis. Further, rGO-SnO2 nanocomposite based nanofluids were prepared using distilled water as the basefluid, varying its volumetric concentration (0.01 to 0.1%). The rGO-SnO2 nanocomposite based nanofluid with 0.07 vol.% concentration (1:7 ratio) exhibited 102.97% enhancement in thermal conductivity at 40.. Further, rheology of the prepared nanofluids was studied at various concentrations and temperatures. It has been found that the prepared nanofluid exhibits non-Newtonian rheological behaviour. The obtained experimental data were tested with the available viscosity models to find the one that predicts the experimental to an acceptable degree. The influence of volume percent of rGO-SnO2 nanocomposite and Reynolds number over the heat transfer coefficient presented by nanofluid was investigated and was found to be increasing with an increase in the volume % of rGO-SnO2 nanocomposite in it and also with rise in Reynolds number. A 0.01 vol. % rGO-SnO2 nanocomposite based nanofluid with 1:7 rGO-SnO2 mass ratio showed 3671.19 W/m(2)K heat transfer coefficient at a Reynolds number of 7510 at the exit of the test section. Various other equations and analogies were tested so as to find the one that satisfactorily predicts the experimental Nusselt number.