Aqueous Nanofluids based on Thioglycolic acid-coated copper sulfide nanoparticles for heat-exchange applications

In this work, a poly(vinyl pyrrolidone) (PVP)/poly(ethylene glycol) (PEG)/copper (Cu) nanocomposite was successfully synthesized using a one-pot method and dispersed in water to prepare aqueous nanofluids. The enhancement of the convective heat transfer coefficient was 20.86%, and the viscosity (0.949 mPa·s) was similar to that of pure water. The PVP and PEG shell effectively improved the thermal cycle stability by isolating the Cu cores from the environment. Particle size, morphology, elemental distribution, thermal stability, valence state, dispersion stability, viscosity, convective heat transfer coefficient, and thermal cycle stability were investigated using a scanning electron microscopy (SEM), ζ-potential analysis, energy-dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), an Ubbelohde viscometer, and an ultraviolet spectrophotometer. The convective heat transfer coefficient of the nanofluids was numerically calculated, and then, the interaction and dispersion mechanism of PVP/PEG/Cu was also discussed. 

Properties of Stable Aqueous Nanofluids Composed of Copper Nanoaggregates for Enhancing Heat Transfer

The present work proposes a method for synthesizing metallic copper (Cu) nanoparticles in aqueous solution. An aqueous colloidal solution of metallic Cu nanoparticles was prepared from Cu acetate by deposition of metallic Cu on metallic zinc (Zn) plate based on the difference in standard electrode potentials between Cu and Zn under ultrasonic irradiation in water, in which the ultrasonic irradiation was performed to disperse the nanoparticles in water. In the absence of the stabilizer and in the presence of polyvinylpyrrolidone (PVP), Cu2O was produced, even though metallic Cu nanoparticles were obtained. In addition, the nanoparticles with sizes of 60–80 nm formed aggregates in the absence of a stabilizer, and the nanoparticles with a size of several hundred nanometers were produced with PVP. In contrast, when cetyltrimethylammonium bromide (CTAB) was used as a stabilizer, metallic Cu nanoparticles with an average particle size of 22.7 ± 11.5 nm and a crystal size of 20.1 nm were fabricated, and no Cu2O was produced. CTAB probably formed a bilayer, and it stabilized the metallic Cu nanoparticles colloidally and chemically.

Fabrication of metallic copper nanoparticles by utilizing a difference in standard electrode potential

The effect of stability on the thermal conductivity of copper nanofluid at low particle loadings

\n In the present study, two-dimensional unsteady, incompressible flow around a square body that is being transformed into a vertex oriented towards the flow configuration of a triangular body is numerically investigated at Re =100 using ANSYS FLUENT 19.0 software. The purpose is to explore the effect of this transformation on the wake characteristics of a square body with l/d = 1 to a triangular body with l/d = 0; where l is the length of lateral and front surface, and d is the body height. The effect on the flow behavior caused by the leading-edge transformation from the prospect of wake width, recirculation length and stagnation pressure difference is discussed. It is seen that as the l/d ratio decreases, the vortex strength increases which is attributed to the higher stagnation pressure difference value resulting in more intense rolling of the shedding vortex and a smaller wake width. For lower l/d, the fluid traverses a longer distance along the lateral surfaces resulting in greater loss of momentum and hence the lower vortex formation length. The mean drag coefficient is found to be minimum for l/d = 0.75 with stagnation pressure difference and recirculation length being the more dominating factor on this variation. The flow in all the cases separates at the rear surface and the general trend of decrease in drag coefficient with decrease in wake width is not followed. However, such modification leads to better aerodynamic outcome by weakening the periodic drag and lift forces.

Rajashree Borah

Papers

The effect of stability on the thermal conductivity of copper nanofluid at low particle loadings

Flow Characterization of Bluff Bodies: A Two-Dimensional Transformation From Square to Triangular Cylinder