Journal of King Saud University, Engineering Sciences最新文献

The current study studies the drag reduction offered by the plate with protrusions to the swirling steam-water two-phase flows. Protrusions of different types, having triangular, sinusoidal, and trapezoidal shapes, are investigated. The variations and modifications were made in the dimensions and orientations (facing along or across, flush-mounted or protruded into the swirling flows), to test the effectivity of these protrusions. At 5 bars of inlet gauge pressure and rpm varying from 360 to 1440, the trapezoidal shape provides the most effective drag reduction. It is also found from the PIV images of the fluid region near the protrusions that the drag reduction in the trapezoidal-shaped protrusions occurs mainly due to the secondary flow structures formation over those protrusions.

On the one hand, the lateral spacing between the adjacent protrusions created the region of strengthening and expansion against the higher opposite inertial forces from the main swirling core fluids. While on the other hand, these spacings justify the impact of the axial elongation of the vortices above the protrusion tips. Further trends in drag reduction have also been investigated by observing the effect of the rise in the temperature of the fluid medium. Reduction in drag from 1.3 to 1.6% is noted using the trapezoidal protrusions for a temperature rise of 25–60 °C. It is also observed that the drag reduction profiles show a rising trend under the influence of the rising Nusselt Number. This trend is attributed to the decrease in viscosity. Whereas under the influence of a rising Prandtl number, the drag reduction shows a decreasing trend, mainly attributed to the rise in the pressure drop at the boundary layers and the pressure drop due to the friction.

In the activation of a heterogeneous catalyst, manipulating certain variables can affect its morphology, active sites and porosity which determine the efficiency of a heterogeneous catalyst. In this work, a highly efficient heterogeneous catalyst was synthesized from a waste turtle shell, which is a novel waste material. Using the experimental design, the influence of three parameters: calcination temperature, calcination time and KOH loading on the catalyst efficiency was studied. The catalyst efficiency was measured by taking the average biodiesel yields in four re-use cycles. Among others, an optimum catalyst efficiency of 81.2% was obtained at a calcination temperature of 807 °C, calcination time of 196mins and KOH loading of 33%(w/w). The obtained Catalyst was very efficient since it possessed high catalytic property, including activity and selectivity, even after being used in four transesterification reactions.

Results of fourteen two-span continuous deep beams made from ordinary reinforced concrete (ORC) as a reference and rubberized reinforced concrete (RRC) is presented and discussed in this research. The main parameters are the rubber ratios as a replacement with coarse and fine aggregate and the shear span/depth ratio (a/h) is 1.33 and 1.66. Chip and crumb rubbers were used to replace coarse and fine aggregate respectively in four different amounts by volume (5%, 10%, 15%, and 20%). The proposed mix shows an ability to replace 20% of the aggregate (coarse or fine), and the production is still structural concrete. All beams design to fail in shear. The main crack is formatted between the intermediate support and the applied load diagonally. In spite of the inclusion of waste tire rubber in concrete having specific apparent degradations, the potential benefit seems to overlook the adverse effects and also provides the primary significant value of resolution for rubber waste problems. The results show that 20% volumetric substitution of natural coarse or fine aggregates with tier rubber reduced the ultimate load of continuous deep beams by 32.06% and 32.65% but significantly increases the ultimate deflection by 83.07% and 106.28% respectively. The ductility of rubberized continuous deep beams increased up to 36.95% when the replacement ratio of crumb rubber is 20%.

The chip study can be the simile to the biopsy in the machining process, as it exposes physical phenomena that are generated in the machining process (heat transfer, hardening, phase changes, heat treatments, etc.). These physical phenomena are directly influenced by the cutting parameters applied to the process (feed, cutting speed, and depth). A chip analysis procedure is proposed to estimate some of the physical phenomena generated in the micro-end-milling in a conventional CNC machine on 7075 aluminium and Ti-6Al-4 V titanium alloys. The procedure is composed of hardness tests, metallography, scanning electron microscopy (SEM), and infrared thermography. A softened chip is observed in the Ti-6Al-4 V titanium a hardened one in 7075 aluminium alloy. The chip approach evaluation evidences a great variation regarded to thermal characteristics between micro-machining and meso-machining focused on the scale of the removed layer thickness.

A novel Log periodic patch with a circular slot antenna has been presented here, the perturbation of the shape of the antenna has been done by combining a triangular shape with a semicircular shape. The antenna proposed here is with a DGS structure on its ground plane and its effects on bandwidth and gain enhancement of the antenna are analyzed. The substrate of FR-epoxy material with length, breadth and height 170 mm, 50 mm and 1.6 mm, respectively is taken for implementation of the antenna on it. This proposed antenna operates at 12 GHz to 18 GHz which includes Ku-band with return loss below-10 dB. The parameters of antenna like S-parameters, antenna gain, directivity, VSWR, surface current distribution and radiation efficiency are determined one by one to ascertain its better performance. The simulation as well as the measurement results are comparatively analyzed.

The reliability of the result significantly affects the use of the Coefficient of Variation (within the test variation), which reflects the variability of the concrete properties rather than the standard deviation. For the estimation of reliability and precision, comprehensive statistical analysis (within test variation) is conducted on 534 test samples using a rebound hammer. Different standards, like BIS, EN, ACI, and ASTM, are used in this study to compare the test results. Empirical research revealed that there are contradictions in literature as well as the standards used in many countries. The present paper focuses on detailed investigations of uncertainty measurements of the surface hardness test by statistical parameters (range of rebound index, standard deviation, and Coefficient of Variation). The unbiased estimate of the variability parameters from the published results has been verified concerning to the European standard. Concrete parameters namely cement type, water to cement ratio, compaction deficiency, curing condition, and elevated temperature have an impact on the output of the rebound hardness in terms of the variability of the compressive strength. Based on the results, the authors are willing to propose amendments to the Indian code graciously in compliance with the variability of the rebound hammer.

In an effort to further improvement of LSCF hollow fiber membrane properties in oxygen purification applications, this work studied the use of polyethylene glycol (PEG) with a different molecular weights of 2000, 3400 and 6000 Da as a pore former. A well-prepared hollow fiber membrane was successfully fabricated via extrusion followed by a sintering method. The results showed that the addition of PEG increased the viscosity of the dope suspension and formed a constant asymmetric pore configuration of the membrane after sintering at 1250 °C. The increasing molecular weight of PEG also leads to a decrease in the mechanical strength of the membranes, indicating that finger-like pores were sacrificed by forming irregular pores. The gas tightness was also examined under room temperature which showed that membrane with PEG 3400 achieved the best tightness with the nitrogen permeability of 3.55 × 10⁻⁵ mol·m⁻²·s⁻¹·Pa⁻¹. The oxygen permeation of the membranes was also influenced by the addition of PEG, where the highest oxygen permeation flux of 6.07 × 10⁻⁸ mol·cm⁻²·s⁻¹ was obtained using a hollow fiber membrane with PEG 3400 due to the existence of the lowest dense layer thickness.

The compatibility problems become the main concern in the utilization of biodiesel especially regarding degradation and corrosion. The present study is conducted to describe the corrosion behaviour that occurs in steel tanks after contact with palm-based biodiesel for a period of 7 months. The storage tank used is respectively made of galvanised steel (GS), carbon steel (CS) and stainless steel (SS). It is performed in vertical cylinders with a floating-roof model. In every 30 days of storage time, the profile changes in the wall, roof and base surface of each tank were observed. The oil fuel properties were monitored in the parameter of viscosity, acid numbers, water content and oil colour. The topographic profiles on the surface of the walls and bottom of each tank wetted by biodiesel were examined over three zones inside the tanks using an endoscope imager. The main results of this study indicate that tank steel with different protective layers exhibits different types of corrosion. The corrosion was localized in SS tanks but generalized in GS and CS tanks. The oil contamination in SS tanks was relatively lower than that in CS and GS tanks. The type of corrosion performed differently in different zones on the inside of the tank. The potential for leaks is greater at the base than on the walls and roof of the storage tank.

Monitoring the degradation of induction motors is an essential concern for industries, especially when there are high costs related to maintenance and their stops. Nowadays, there are many non-invasive ways to monitor the health status of induction motors, including sensors to measure temperature, magnetic field, vibration, current, and power. However, installing these sensors may not be a simple task since intrusive procedures such as engine disassembling, wire separation, and engine interruption are commonly observed. Thus, we propose MUCLA (Multiphase Clamp and Tracking - patent pending) as a new device and methodology for monitoring motor degradation by analyzing its stator current. MUCLA introduces a non-invasive current sensors array on a proposed clamp in the hardware perspective, while a spectral tracking methodology refers to our novelty in the software viewpoint. For end-users, the main MUCLA contribution relies on the combination of the simplicity of installation and the possibility of using the proposed device even when considering Variable-Frequency Drive powered engines. The results obtained with both simulation and practical tests show encouraging results over different input workloads and emulated degradation. Compared to the current initiatives, we can classify MUCLA as a better solution for industrial plants in terms of installation time, installation complexity, and cost.

Amidst a world of never-ending waste production and waste disposal crises, scientists have been working their way to come up with solutions to serve the earth better. Two such commonly found trash deteriorating the environment are glass and tin can waste. This study aims to investigate the comparative suitability of response surface methodology (RSM) and artificial neural network (ANN) in predicting the mechanical strength of concrete prepared with fine glass aggregate (GFA) and condensed milk can (tin) fibers (CMCF). An experimental scheme has been designed in this study with two input variables as GFA and CMCF, and two output variables compressive and splitting tensile strength. The results show that both variables influenced the compressive and splitting tensile strength of concrete at 7, 28, and 56 days (p < 0.01). The maximum compressive and splitting tensile strength was found at 20% GFA with 1% CMCF and 10% GFA with 0.5% CMCF, respectively. The model predicted values in both techniques were in close agreement with corresponding experimental values in all cases. The results of different statistical parameters in terms of coefficient of correlation, coefficient of determination, chi-square, mean square error, root mean square error, mean absolute error, and standard error prediction indicate the functionality of both modeling approaches for concrete strength prediction. However, RSM models yield better accuracy in simulating the compressive and splitting tensile strength of concrete than ANN models.