Application of Carbon-based Nanofluids in Heat Exchangers: Current Trends

Abstract : The thermal performance of a heat exchanger can be enhanced by adding carbon nanostructured materials such as carbon nanotubes and graphene to the conventional working fluid. When nanomaterials are suspended in the working fluid, the fluid is known as Nanofluid. The enhancement in the thermal and rheological properties of the fluid is responsible for the augmentation in heat transfer performance. The influence of carbon nanomaterial on the thermophysical properties, heat transfer characteristics and flow properties are reviewed. The current trends on the utilization of carbon-based nanofluids in heat exchangers were reported. The study shows that carbon-based nanofluids have the potential to improve the performance of heat exchanger and reduce the cost of fabrication by reducing heat exchange area. The study identifies the scope for future study

Wear and corrosion of wrought a6061 aluminium alloy in dot3 brake fluid

Abstract: The twofold impact of wear and corrosion on wrought A6061 alloy in hydraulic DOT3 brake fluid environment was studied. The wear studies were performed on the samples using a developed wear-jig. Weight loss corrosion test method was used to determine the corrosion rate of the wrought A6061 alloy samples immersed in the brake fluid for a total of 1680 hours. From the results of wear tests carried out on the A6061 alloy sample with brake oil, the highest wear value of 5.24x10-7 mg/mm2/cycle (approx.) was obtained from 6 N (approx) force after 130 minutes. The wrought A6061 alloy material demonstrated the highest corrosion rates nearly 3.0 x10-2 mg/mm2/yr within the early 168 hours of immersion in brake fluid. The result is practically lower than the corrosion rate of cast specimen in DOT3 brake oil or some other alloys immersed in other corrosive media that were previously reported in the literature. The results show that small amount of chemical corrosion is sufficient to cause and accelerate mechanical wear of the material in usage

Effect of heat treatment on wear behaviour of rolled carbon steel in DOT4 brake fluid

Abstract : The wear of heat-treated rolled carbon steels (HTRCSs) were performed under dry and wet sliding in DOT4 brake fluid is successfully investigated and reported in the study. The HTRCSs samples were obtained by heating to and soaking the as-rolled carbon steel (ARCS) at 950 oC prior to quenching or cooling in different media at different selected temperatures between (20 and 250 oC) and atmospheric conditions. The microstructures and wear track patterns of specimens were evaluated using SEM and high-resolution metallurgical microscope. The sliding wear behaviour and wear track patterns of the specimens impressed under 10N normal loads and reciprocating mode was used to assess the wear damages. The obtained wear properties were compared in air and DOT4 fluid environments using Anton Paar TRB tribometer. The results obtained showed that enhanced wear behaviours were obtained from the oil and water quenched samples as compared with the air and furnace cooled samples. The HTRCSs samples are more tolerable than as-rolled sample (ARCS) under dry sliding. However, beside the influences of the heat treatments, the lubricating effect of DOT4 is more pronounced in the results. The CoF ranges from 0.105 to 0.137 for wet sliding while higher CoF values (0.378-0.934) were obtained in the dry sliding

Stability Assessment of Pipeline Cathodic Protection Potentials under the Influence of AC Interference

Abstract: Metallic pipelines are protected from induced corrosion by the application of coating and Cathodic Protection (CP) systems. The latter is achieved by keeping the pipeline at a constant Direct Current (DC) voltage in relation to the surrounding soil. While this is conventionally meant to arrest corrosion, the Alternating Current (AC) interference from high voltage transmission lines has been a major problem to the CP potential systems of buried steel pipelines. Several research studies dealing with this problem have been published, and a lot of research work is still on going. This work focuses on assessing the stability of the CP potentials under the influence of AC interference. Seven different CP potentials varying from −800 mV to −1200 mV were applied on steel pipe specimen exposed to the AC interference with a varying AC voltage from 0–50 V. The results of the laboratory investigation revealed that CP potential of −1150 mV was more stable under the influence of AC interference, with just a minimal shift from the set value. The results from the corrosion morphology tests on the pipelines using Scanning Electron Microscope (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) reveal the need for optimising the CP potential to provide adequate or optimum protection to the pipelines. Thus, more research studies involving simulation and field studies may lead to a major breakthrough in improving protection potentials

Characterisation and wear behaviour of rolled carbon steel in Dot 4 brake fluid

Abstract : The wear behaviour of as-rolled carbon steel (ARCS) in DOT4 brake fluid is investigated and reported in this study. Sample was characterised using chemical analysis, hardness, impact and tensile strength tests. Arc-spectrometry and the Energy Dispersive X-Ray (EDS) facilities were used to ascertain the chemical compositions. The microstructures and wear track patterns of samples were evaluated using Scanning Electron Microscopy (SEM) and High-resolution metallurgical microscope. The wear of as-rolled carbon steel (ARCS) samples subjected to reciprocating motion of loads at room temperature and constant wear time were compared in air, DOT4 fluid and water. The frictional behaviour and wear track patterns of the specimens subjected to varied normal loads (3, 5 and 10N) under reciprocating sliding wear were employed to assess the wear damage of samples in the three different environments. The coefficient of friction (CoF) obtained tends to be in the order of µDOT4 brake fluid < µwater < µair comparatively for the three test environments

Electrochemical corrosion behavior of copper in graphene-based thermal fluid with different surfactants

Abstract: This study investigates the effect of different surfactant-dispersed graphene nanofluid on the electrochemical behavior of copper. This study was achieved by measuring the open circuit potential and potentiodynamic polarization of copper in the nanofluids at room temperature. The test media includes surfactant-free graphene nanofluid and graphene nanofluid dispersed using four different surfactants, which are sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, Gum Arabic, and Tween 80. The surface characterization and elemental composition of the copper sample before and after the corrosion tests were determined using a scanning electron microscope coupled with energy-dispersive X-ray spectroscopy. The phase formation after corrosion was also evaluated by measuring X-ray diffraction. The quantity of copper dissolved in the test media was evaluated using an inductively coupled plasma mass spectrometry (ICP-MS). The open-circuit potential measurements revealed that the current free corrosion potential of copper in the different surfactant-aided graphene nanofluids are different. The electrochemical corrosion potential, Tafel slopes, and corrosion rates revealed the better corrosion performance of copper in the nanofluid of different surfactants in the increasing order GA, SDS, Tween 80, and SDBS. Copper in GA-based graphene nanofluid was found to have the lowest corrosion rate while that of SDBS has the highest corrosion rate. However, the ICP-MS result revealed a discrepancy in the corrosion behavior and quantity of copper dissolved in the different test media. This could be attributed to the dissimilar dissolutionredeposition rate of copper in different media

Influence of single and double-atom metal doping on the electrocatalytic hydrogen evolution activity of 2D-MoS2 surface

Abstract: The Hydrogen evolution reaction (HER) is an important process during electrocatalytic water splitting for hydrogen energy generation. Two dimensional (2D) MoS2 has been considered as a promising alternative to Pt-based catalysts in the hydrogen evolution reaction. However, the highest contribution for the catalytic activity of 2D-MoS2 is from its edge sites, this in turn leaves many in-plane domains useless. In this study, the effect of single atom metal (Pt, Ni and Pt-Ni) doping on HER catalytic activity of in-plane atoms was investigated using density functional theory calculations. The Gibbs free energy of adsorbed hydrogen on pristine MoS2 decreased from 1.86eV to -0.08eV in PtNi co-doped MoS2. This demonstrates enhanced catalytic activity of MoS2 due to atomic doping. The enhanced catalytic activity may also be attributed to the observed changes and increase in the density of electronic states near the Fermi energy level

Fabrication of forced air cool austempered ductile iron and exploring its corrosion behaviour in a simulated mine water

Abstract: The production of austempered ductile iron (ADI) with uniform microstructure and properties is constrained by the austempering process vis-à-vis the quenching medium. This is as a result of the stringent operating parameters with costly facilities. This limitation has restricted the application of ADI, despite its inherent mechanical and chemical properties. An emerging technology of overcoming this limitation is by austempering with force air cooling equipment, which is accessible, available and cost-efficient. This work characterizes the behaviour of the forced air cool ADI in simulated mine water due to the strategic importance of the mining industry in the global economy. The study establishes the influence of sample section thickness on the corrosion performance. The sample’s thickness were 5, 15, and 20 mm. Electrochemical experiments were performed on the forced air cool ADI at atmospheric pressure and room temperature with method such as open circuit potential (OCP). The post-corrosion analyses were performed using X-ray diffractometry (XRD) and field emission scanning electron microscopy (FESEM). The research highlighted that small section thickness has a more favourable performance compared with larger section. Consideration is also accorded to the capability of the ADI in the studied environment

Structural characterization and mechanical properties of pearlite – Enhanced micro-alloyed ductile irons

Abstract: The structural characteristic and mechanical properties of ductile irons micro alloyed with lean additions of molybdenum, nickel, copper and chromium was investigated. This was aimed at assessing the potentials of the utilization of lean ferro alloy additions (which offers reduced processing and product costs) for enhancing pearlite phase proportion, which is required for improved mechanical performance of ductile irons. The ductile irons contained a maximum of 0.2% each of Mo, Ni, Cu, and Cr and were processed using a crucible furnace. They were characterized using optical microscopy and X-ray diffractometry while hardness and tensile testings were used to evaluate the mechanical properties. The results show that the micro alloyed samples contain new compound of alloying elements with iron and the base alloy phase (FeSi, a Fe). It was also observed that the micro alloy additions resulted in significant increase in pearlite proportion from 30.63% in the base alloy to as much as 59.38% in the composition containing Mo, Ni and Cu as micro addition. Increase in hardness within the range 1.4–36.5% was obtained, while tensile strength increase within the range 35.89–80.55% with the use of the micro alloying additions. Overall, the best combination of mechanical properties was achieved for the ductile irons composition containing chromium and copper, as well as the one containing molybdenum, nickel and chromium as micro alloy additions

Influence of processing parameters on the densification and the microstructure of pure zinc oxide ceramics prepared by spark plasma sintering

Due to the sensitivity of nanopowders and the challenges in controlling the grain size and the density during the sintering of ceramics, a systematic study was proposed to evaluate the densification and the microstructure of ZnO ceramics using spark plasma sintering technique. Commercially available ZnO powder was dried and sintered at various parameters (temperature (400–900 °C), pressure (250–850 MPa), atmosphere (Air/Vacuum) etc.). High pressure sintering is desirable for maintaining the nanostructure, though it brings a difficulty in obtaining a fully dense ceramic. Whereas, increasing the temperature from 600 to 900 °C results in fully densified ceramics of about 99% which shows to have big impact on the grain size. However, a high relative density of 92% is obtained at a temperature as low as 400 °C under a pressure of 850 MPa. The application of pressure during the holding time seems to lower the grain size as compared to ceramics pressed during initial stage (room temperature)