Graphene Platinum Nanoparticles Research Articles

Predicting entropy generation of a hybrid nanofluid containing graphene–platinum nanoparticles through a microchannel liquid block using neural networks

This study investigates the characteristics of first and second laws of thermodynamics including the convective heat transfer coefficient, entropy generation rate, and Bejan number for the hybrid nanofluid having graphene–platinum nanoparticles through a cylindrical microchannel liquid block. The geometry contains thirty-six microchannels having hydraulic diameter of 564 μm. The maximum values of the convection heat transfer coefficient, thermal entropy generation, and frictional entropy generation are obtained as 7653 W/m2K, 9.7 × 10−5 W/K, and 6.2 × 10−6 W/K, respectively. With increase of the particle concentration, the heat transfer coefficient and frictional entropy generation increase whereas the thermal entropy generation reduces. Furthermore, by increment of the heat load, the entropy generation due to the heat transfer increases, whereas the entropy generation due to the friction reduces. The influence of Reynolds number on the entropy production rates is more noticeable than the effect of particle fraction. Also, the entropy generation due to the heat transfer diminishes by raising the Reynolds number, while the entropy generation due to the friction intensifies. Furthermore, the Bejan number reduces with increment of the particle fraction and Reynolds number. Eventually, the entropy generation is modeled in terms of the Reynolds number, particle fraction, and heat flux by a neural network.

Second law analysis of a hybrid nanofluid in tubes equipped with double twisted tape inserts

Entropy generation rates for flow of a novel hybrid nanofluid containing graphene–platinum nanoparticles in tubes equipped with double twisted tapes, which can develop diverse swirling flows, are analyzed based on the second law of thermodynamics. The twisted tapes under study include double co-twisted tapes and double counter twisted tapes with various twisted ratios. Based on the obtained results, using the double counter twisted tapes is recommended since they demonstrate the lower entropy generation rate (i.e. smaller overall irreversibility) compared with the double co-twisted tapes. The double counter twisted tapes are able to create more intense swirl flows, disturb boundary layer and reduce total entropy generation rate more than double co-twisted tapes. Smaller irreversibility for the double counter twisted tapes is a pleasant outcome based on the second law of thermodynamics. Furthermore, using lower twisted ratios is suggested since although with the twisted ratio reduction, the frictional entropy generation augments, the thermal entropy generation reduces and due to dominance of thermal entropy generation, total entropy generation decreases. In the case of double counter twisted tape, the global thermal entropy generation rate reduces around 10% with decreasing the twisted ratio from 3.5 to 2.5 at concentration of 0.06%. Moreover, the results reveal that using the nanofluid instead of the base fluid decreases total entropy generation and consequently overall irreversibility. Indeed, adding the graphene–platinum nanoparticles, even in low concentrations, profoundly reduces the thermal entropy generation while the frictional entropy generation increases slightly. Thereby, in the case of double co-twisted tapes with twisted ratio of 3, increasing the concentration from 0% to 0.1% causes 14% decrement in the global thermal entropy generation.

Second law analysis for flow of a nanofluid containing graphene–platinum nanoparticles in a minichannel enhanced with chaotic twisted perturbations

The second law and entropy generation characteristics of a new hybrid nanofluid containing graphene nanoplatelets decorated with platinum nanoparticles are evaluated in a chaotic twisted channel. Although several investigations have been carried out on flows inside chaotic channels in the relevant literature, very few studies have employed nanofluids as working fluids in such configurations. The geometrical perturbations cause formation of counter rotating Dean roll-cells which intensify mixing in the flow and disturb the boundary layer. The intensity of perturbations considerably enhances at higher Dean numbers. The maximum velocity is shifted toward the outer wall due to the centrifugal force, and the maximum frictional entropy generation occurs there. Because the roll-cells lead to more uniform temperature distribution, thermal entropy generation reduces with increase of distance from the inlet of each bend. Moreover, by increasing concentration and Dean number, thermal entropy generation and Bejan number decrease while frictional entropy generation intensifies, however, due to dominance of thermal entropy generation, overall irreversibility of the nanofluid flow reduces. Besides, the temperature gradients become greater at higher wall heat fluxes which lead to the more intense thermal entropy generation. In addition, the difference between the Bejan numbers related to different wall heat fluxes is more noticeable at higher concentrations.

Application of a novel hybrid nanofluid containing graphene–platinum nanoparticles in a chaotic twisted geometry for utilization in miniature devices: Thermal and energy efficiency considerations

This study aims to research the flow, heat transfer and energy efficiency of a novel hybrid nanofluid containing graphene nanoplatelets decorated with platinum nanoparticles in a chaotic twisted minichannel. This geometry develops chaotic advection owing to geometrical perturbations. Dean roll-cells are formed in the channel, and are the cause for irregular trajectories of fluid particles. The channel includes four bends, such that the chaotic motions are strengthened gradually along the bends, and reach a maximum rate at the exit of them, which causes minimum wall temperature in those regions. To better evaluate the merit of chaotic channel, simulations are also performed in a simple channel. The convective heat transfer and pumping power in both channels augment by increasing either concentration or Dean number. The chaotic channel has higher heat transfer and pressure drop than the simple one. Due to the excellent attributes of graphene, not only heat transfer enhances significantly but also pressure drop does not increase noticeably by adding nanoparticles. Figure of merit, i.e. ratio of enhancement in convective hear transfer to enhancement in pumping power in the case of employing the chaotic channel rather than the simple channel, is always greater than 1.5, which demonstrates a promising outcome.

Electrocatalytic oxidation of formaldehyde on direct electrodeposited graphene–platinum nanoparticles composites electrode

The one-step electrochemical deposition of highly dispersed platinum nanoparticles on graphene to fabricate a new Pt/EG/GC modified electrode for formaldehyde determination in aqueous solution. Catalyst surface morphology was characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM), the composition analysis was carried out on energy-dispersive X-ray spectroscopy (EDS). The electrochemical performances of the electrode were investigated by cyclic voltammetry, and clear amperometric responses were obtained in the scan process. The correlation coefficient was 0.998 of the linear relation between current values and concentrations, the Pt/EG/GC electrode exhibited a low limit of detection (0.04 mM), high sensitivity (0.0162 mA mM−1) and long working life. These characteristics make the Pt/EG/GC electrode appropriate for the formaldehyde determination based on formaldehyde electric catalytic oxidation.

A graphene–platinum nanoparticles–ionic liquid composite catalyst for methanol-tolerant oxygen reduction reaction

We report here that graphene-supported Pt nanoparticles impregnated with the ionic liquid [MTBD][bmsi] which is more oxygen-philic and less methanol-philic than the exterior aqueous solution can exhibit both enhanced electrocatalytic activity and excellent methanol tolerance for oxygen reduction reaction.