14 research outputs found
Stability and Thermophysical Properties of GNP-Fe<sub>2</sub>O<sub>3</sub> Hybrid Nanofluid: Effect of Volume Fraction and Temperature
No full textThe study focused on the impact of concentration and temperature on the electrical conductivity, viscosity, and thermal conductivity of GNP/Fe2O3 hybrid nanofluids. The study found that nanofluids have better electrical conductivity, viscosity, and thermal conductivity than water. The electrical conductivity and thermal conductivity increase linearly with concentration for a constant temperature. However, the nanofluid’s viscosity increases with the addition of the hybrid nanoparticles and decreases as the temperature increases. Furthermore, the study shows that the thermal conductivity of the nanofluid is enhanced with increased addition of hybrid nanoparticles in the base fluid and that the thermal conductivity ratio increases with increased addition of nanoparticles. Overall, the results suggest that GNP/Fe2O3 hybrid nanofluids could be used in various industrial applications to improve the heat transfer and energy efficiency of systems
Nanoindentation mechanical properties on spark plasma sintered 48Ti-48Al-2Cr-2Nb alloy
No full textThis study aims to investigate the microstructure, plastic (H) properties, elastic (E) properties, reduced elastic (Er) properties the strain-to-break parameter (H/Er), and the resistance to plastic deformation parameter (H3/Er2) of the Ti-48Al-2Cr-2Nb alloy by use of scanning electron microscopy, nanoindentation and micro-indentation techniques. The results show that the sintering parameters had significant effect on the resulting microstructure. Desirable mechanical properties were obtained with the sample sintered at temperature of 1200 °C, pressure of 50 MPa, holding time of 7.5 min and a heating rate of 50 °C/min which had a near lamellar structure, resulting from the grain boundary pinning effect of the fine equiaxed gamma grains and the impartation of ductility due to the coarsened lamellar colonies. The nano-hardness and elastic modulus were observed to be about 4GPa and 31GPa for the near lamellar microstructure, respectively, with the microhardness of about 4.4GPa. While the duplex and the near gamma microstructures possessed the least nano-hardness (3.65–3.78GPa) and elastic modulus (3.6–29.5GPa) with the exception of sample sintered at temperature of 1150 °C, pressure of 50 MPa, holding time of 7.5 min and a heating rate of 100 °C/min., with nano-hardness and elastic modulus of 4.05GPa and 31.25GPa, respectively, however it had the lowest micro-hardness of 2.7GPa. Furthermore, the ratios H/Er and H3/Er2 values were observed to be greater for the same sample suggesting good wear resistance of the alloy
Experimental study and ANFIS modelling of the thermophysical properties and efficacy of GNP‑Al2O3 hybrid nanofuids of different concentrations and temperatures
No full textDATA AVAILABITY STATEMENT: The datasets generated during and/or analysed during the current study are available from the corresponding author upon reasonable request.This study delves into an extensive investigation of the thermophysical properties and heat transfer efficacy of a
hybrid nanofluid incorporating graphene nanoplatelets and γ-Al2O3 nanoparticles dispersed in deionised water. The
nanofluids were characterised for their viscosity (µ), thermal conductivity (λ), and electrical conductivity (σ) over
a 15–40 °C temperature range for varying nanoparticle loading (0.1–0.4 volume%). The experimental results revealed
notable enhancements in µ, λ, and σ with increasing nanoparticle concentration, while µ decreased at elevated
temperatures as λ and σ increased. At the highest concentration (0.4 vol%), µ increased by 21.74%, while λ and σ
exhibited peak enhancements of 17.82% and 393.36% at 40 °C. An Adaptive Neuro-fuzzy Inference System (ANFIS)
model was devised to enhance predictive precision by meticulously optimising the number of membership functions (MFs) and input MF type. The ANFIS architecture that exhibited the most remarkable agreement with the
experimental data for µ, λ, and σ was found to utilise the Product of Sigmas, Difference of Sigmas, and Generalized
Bell MFs, respectively, with corresponding input MF numbers being 2–3, 3–2, and 3–2. The optimal ANFIS model
for µ, λ, and σ exhibits a higher prediction accuracy with an R2
value of 0.99965, 0.99424 and 0.99995, respectively.
The Figure of Merit analysis using Mouromtseff Number identified an optimal nanoparticle concentration range of
0.1–0.2 volume% for enhanced heat transfer performance with a reasonable µ increase. This range guides practitioners
in utilising hybrid nanofluids effectively while managing potential drawbacks.The University Research Council of the University of Johannesburg.https://www.springer.com/journal/42452Mechanical and Aeronautical EngineeringSDG-09: Industry, innovation and infrastructur
Effects of temperature and nanoparticle mixing ratio on the thermophysical properties of GNP-Fe2O3 hybrid nanofluids : an experimental study with RSM and ANN modeling
No full textThis study investigated the impact of temperature and nanoparticle mixing ratio on the thermophysical properties of hybrid
nanofluids (HNFs) made with graphene nanoplatelets (GNP) and iron oxide nanoparticles (
Fe2O3). The results showed
that increased temperature led to higher thermal conductivity (TC) and electrical conductivity (EC), and lower viscosity in
HNFs. Higher GNP content relative to Fe2O3
also resulted in higher TC but lower EC and viscosity. Artificial neural network
(ANN) and response surface methodology (RSM) were used to model and correlate the thermophysical properties of HNFs.
The ANN models showed a high degree of correlation between predicted and actual values for all three properties (TC, EC,
and viscosity). The optimal number of neurons varied for each property. For TC, the model with six neurons performed the
best, while for viscosity, the model with ten neurons was optimal. The best ANN model for EC contained 18 neurons. The
RSM results indicated that the 2-factor interaction term was the most significant factor for optimizing TC and EC; while,
the linear term was most important for optimizing viscosity. The ANN models performed better than the RSM models for
all properties. The findings provide insights into factors affecting the thermophysical properties of HNFs and can inform the
development of more effective heat transfer fluids for industrial applications.The University Research Council (URC) of the University of Johannesburg. Open access funding provided by University of Pretoria.https://www.springer.com/journal/10973am2024Mechanical and Aeronautical EngineeringSDG-09: Industry, innovation and infrastructur
Stability and thermophysical properties of GNP-Fe2O3 hybrid nanofluid : effect of volume fraction and temperature
No full textDATA AVAILABILITY STATEMENT : The data presented in this study are available in the article.The study focused on the impact of concentration and temperature on the electrical conductivity,
viscosity, and thermal conductivity of GNP/Fe2O3 hybrid nanofluids. The study found that
nanofluids have better electrical conductivity, viscosity, and thermal conductivity than water. The
electrical conductivity and thermal conductivity increase linearly with concentration for a constant
temperature. However, the nanofluid’s viscosity increases with the addition of the hybrid nanoparticles
and decreases as the temperature increases. Furthermore, the study shows that the thermal
conductivity of the nanofluid is enhanced with increased addition of hybrid nanoparticles in the
base fluid and that the thermal conductivity ratio increases with increased addition of nanoparticles.
Overall, the results suggest that GNP/Fe2O3 hybrid nanofluids could be used in various industrial
applications to improve the heat transfer and energy efficiency of systems.https://www.mdpi.com/journal/nanomaterialsam2024Mechanical and Aeronautical EngineeringSDG-09: Industry, innovation and infrastructur
Implications of the use of cannabis in the South African workplace
No full textAbstract: The study entitled: “Implications of the use of cannabis in the South African workplace”, is a comparative study, situated within the labour law fraternity. This area of law regulates the “employer-employee relationship” which often comes into conflict. The author casts light on the conflicting interests of the employer to ensure safety in the workplace, against the employee’s right to privacy. On the one hand, employers’ have an overarching duty to enhance workplace safety by putting in place of drug testing policies. On the other spectrum, employees may challenge drug testing policies on the ground of the right to privacy. This conflict arose after the Constitutional Court legalised “private use” of cannabis in Prince. The concern is, inter alia, that urine drug test detects cannabislong after it has been consumed. It only discloses presence of drug metabolites and not the likelihood of impairment at the time of the test. Therefore, employees may be dismissed even though their actions took place in private and could in no way affect their ability to perform duties safely. In light that Prince legalised the private use of cannabis, the study questions whether dismissal is an appropriate sanction following a positive drug screening, where an employee had used cannabis privately at home. It is not clear how our courts should construe the LRA by weighing the conflicting interests of the employer (to ensure safety) and employees (privacy) to reach the balance required by “fair labour practices”. The case of Mthembu is subject to constitutional scrutiny for upsetting a “fair” balance, as the CCMA upheld dismissal as an appropriate sanction following a positive drug screening. Mthembu is a totally misleading judgment for ignoring that urinalysis has the disadvantage of showing past impairment. This policy is declared unjust by foreign courts. A comparative legal analysis is utilised to examine how the US, Canada and German courts assess reasonableness to ascertain which drug testing policies may be declared reasonable, and those which constitutes a prima facie unlawful invasion of privacy. Foreign courts argue that the limitation (testing policy) must rationally be capable of achieving its purpose (ensuring safety). Therefore, a testing method which detects current impairment is capable of achieving safety, as opposed to that which shows past impairment. The study argues that South African courts may seek guidance from foreign case law to positively influence our legal system, to maintain equilibrium between the conflicting interests of employer(s) and employee(s). This promotes the achievement of social justice in the workplace and a shift towards a transformative society.LL.M. (Labour Law
Development of city logistics maturity model for municipality performance measurement
No full textMunicipalities play an important role in tackling city logistics related matters, having many instruments at hand. However, it is not self-evident that all municipalities use these instruments to their full potential. A method to measure city logistics performance of municipalities can help in creating awareness and guidance, to ultimately lead to a more sustainable environment for inhabitants and businesses. Subsequently, this research is focused on a maturity model as a tool to assess the maturity level of a municipality for its performance-related city logistics process management. Various criteria for measuring city logistics performance are studied and based on that the model is populated through three focus fields (Technical, Social and Corporate, and Policy), branching out into six areas of development: Information and communication technology, urban logistics planning, Stakeholder communication, Public Private Partnerships, Subsidisation and incentivisation, and Regulations. The CL3M model was tested for three municipalities, namely, municipality of Utrecht, Den Bosch and Groningen. Through these maturity assessments it became evident the model required specificity complementary to the existing assessment interview, and thus a SWOT analysis should be added as a conclusion during the maturity assessment.Transport and Logistic
Zero-Emission Zone (ZEZ) Maturity Model: First Results
No full textWith the approach of the zero-emission zone implementation in 30-40 cities mandated by the Dutch climate agreement in 2025, comes the need to determine whether the SMEs located within these zones are aware of the coming changes. The zero emission zones are set to change how city logistics is currently being executed with the aim of decreasing emissions in the city centre by transitioning to zero emission vehicles and optimizing deliveries to create less flows. However, it is currently unclear whether small to medium businesses located within these zones know about the new regulations within their local municipalities. This article delves into the initial results of The Zero-Emission City Logistics Maturity QuickScans which are used to facilitate the determination of the maturity of small to medium enterprises in light of zero-emission city logistics operations.Transport and Logistic
The effect of alloying additions on the mechanical properties of nickel aluminide NiAl — A review
No full textLactones from Unspecific Peroxygenase-Catalyzed In-Chain Hydroxylation of Saturated Fatty Acids
No full textγ- and δ-lactones are valuable flavor and fragrance compounds. Their synthesis depends on the availability of suitable hydroxy fatty acid precursors. Three short unspecific peroxygenases were identified that selectively hydroxylate the C4 and C5 positions of C8-C12 fatty acids to yield after lactonization the corresponding γ- and δ-lactones. A preference for C4 over C5 hydroxylation gave γ-lactones as the major products. Overoxidation of the hydroxy fatty acids was addressed via the reduction of the resulting oxo acids using an alcohol dehydrogenase in a bienzymatic cascade reaction.BT/Biocatalysi
