Graphite oxide (GO) and cetyltrimethylammonium bromide (CTAB) modified multi-walled carbon nanotubes (m-MWCNTs) are utilized to fabricate “Line-Plane”-like hetero-structured thermally conductive [email protected] fillers by electrostatic self-assembly, which are then introduced into polydimethylsiloxane (PDMS) to fabricate thermally conductive [email protected]/PDMS composites. When the mass ratio of GO to m-MWCNTs is 2:1, [email protected] fillers have optimal morphologies and thermal conductivity contribution. When the mass fraction of [email protected] is 20 wt%, the thermal conductivity coefficient (λ) of [email protected]/PDMS composites reaches 2.10 W/(m·K), 950% higher than that of pure PDMS (0.20 W/(m·K)), which is also superior to the λ of MWCNTs/PDMS (0.68 W/(m·K)), GO/PDMS (1.59 W/(m·K)) and (GO/MWCNTs)/PDMS (1.28 W/(m·K)) composites with the same amount of single or hybrid thermally conductive fillers. Meantime, the [email protected]/PDMS composites also present good thermal conduction stability (average λ after 15 heating-cooling cycles in the temperature of 21 to 100°C is 2.14 W/(m·K)) and thermal stability (heat resistance index is 249.3°C). 

Highly efficient thermal conductivity of polydimethylsiloxane composites via introducing “Line-Plane”-like hetero-structured fillers

Nanofluids, due to their superior thermal properties, have immense applications in heat transfer process. In view of this, nanofluids, as working fluids in solar thermal systems, have gained importance. This review emphasizes the properties of nanofluids for solar thermal applications as well as typical nanomaterials and analyses experimental and numerical investigations on solar thermal systems utilizing nanofluids along with typical experimental setups and calculation methods used for determination of the performance of nanofluids in the same. The effect of nanoparticles concentration, flowrate, ambient temperature, solar intensity and inlet temperature on the solar thermal system performance utilizing nanofluids is also discussed. Further, challenges occurring during application of nanofluids in solar thermal systems are specified along with recommendations for scaling up of nanofluid-based solar thermal systems.

Performance evaluation of nanofluids in solar thermal and solar photovoltaic systems: A comprehensive review

State-of-the-art review on water-based nanofluids for low temperature solar thermal collector application

Technologies for wastewater remediation have been growing ever since the environmental and health concern is realized. Development of nanomaterials has enabled mankind to have different methods to treat the various kinds of inorganic and organic pollutants present in wastewater from many resources. Among the many materials, semiconductor materials have found many environmental applications due to their outstanding photocatalytic activities. TiO2 and ZnO are more effectively used as photocatalyst or adsorbents in the withdrawal of inorganic as well as organic wastes from the wastewater. On the other hand, graphene is tremendously being investigated for applications in environmental remediation in view of the superior physical, optical, thermal, and electronic properties of graphene nanocomposites. In this work, graphene-TiO2 and graphene-ZnO nanocomposites have been reviewed for photocatalytic wastewater treatment. The various preparation techniques of these nanocomposites have been discussed. Also, different design strategies for graphene-based photocatalyst have been revealed. These nanocomposites exhibit promising applications in most of the water purification processes which are reviewed in this work. Along with this, the development of these nanocomposites using biomass-derived graphene has also been introduced. PRACTITIONER POINTS: Graphene-TiO2 and graphene-ZnO nanocomposites are effective for wastewater treatment through photocatalysis. These nanocomposite photocatalysts have been used in the form of membrane as well as antibacterial agents. Synthetic strategies and design considerations of graphene-based photocatalyst play a major role. Biomass-derived graphene-TiO2 and graphene-ZnO nanocomposites have also found application in wastewater treatment.

A review of graphene-TiO2 and graphene-ZnO nanocomposite photocatalysts for wastewater treatment.

Ag-doped TiO2 hybrid nanoparticles have been synthesized by ultrasonic-assisted method for nanofluid application for heat transfer in minichannel heat exchanger at constant wall temperature condition. Prepared nanoparticles were dispersed in water by ultrasonication to form an extremely stable nanofluid. Thermal conductivity of the nanofluid was found to be 1.84 W/mK at 45 ℃ for nanofluid concentration of 0.25 vol%. The overall heat transfer coefficient increased from 1211.71 to 2727.38 W/m2K as the nanofluid concentration increased form 0.01 vol% to 0.1 vol% at Reynolds number of 3480 ± 3. A new correlation for Nusselt number has been proposed. The pressure drop and friction factor of the nanofluids were also advantageously lesser than that of water. The overall performance of the Ag-doped TiO2 hybrid nanoparticles based nanofluid was assessed by comparing the heat transfer with the pumping power and by determining the entropy generation and thus the Bejan number.

Investigation on thermophysical properties, convective heat transfer and performance evaluation of ultrasonically synthesized Ag-doped TiO2 hybrid nanoparticles based highly stable nanofluid in a minichannel

Investigation of thermophysical properties of reduced graphene oxide-Al2O3 (rGO-Al2O3) nanocomposite based nanofluid along with convective heat transfer study and associated pressure drop has been done in the present work. Formation of the rGO-Al2O3 nanocomposite was confirmed with the help of various characterization techniques like UV/Vis, XRD, FTIR, Raman spectroscopy, TEM, Elemental mapping and XPS analysis. Thermal conductivity at different temperatures of various volume % (0.01−0.1%) of the prepared rGO-Al2O3 nanofluid was measured by dispersing and ultrasonicating the nanocomposite in deionized water. Thermal conductivity increased with increase in temperature as well as concentration of the rGO-Al2O3 nanofluid. These nanofluids exhibited non-Newtonian behavior as found from their rheological study. Different viscosity models also were employed to predict the viscosity at a range of applied shear rate (0-2000 s−1). Convective heat transfer study at a wall condition of constant heat flux was done at different concentration and Reynolds number of the rGO-Al2O3 nanofluid. Maximum value of heat transfer coefficient of 5461.602 W/m2℃ was achieved at the exit of test section by using 0.05 vol.% rGO-Al2O3 nanofluid flowing at Reynolds number of 7510.

Synthesis, characterization and heat transfer study of reduced graphene oxide-Al2O3 nanocomposite based nanofluids: Investigation on thermal conductivity and rheology

Kamalnayan Singh

Papers

Synthesis, characterization and heat transfer study of reduced graphene oxide-Al2O3 nanocomposite based nanofluids: Investigation on thermal conductivity and rheology