Amro M. Al-Qutub

Spark plasma sintering of metals and metal matrix nanocomposites: a review

Metal matrix nanocomposites (MMNCs) are thosemetal matrix composites where the reinforcement is of nanometer dimensions, typically less than 100nm in size. Also, it is possible to have both the matrix and reinforcement phases of nanometer dimensions. The improvement in mechanical properties of MMNCs is attributed to the size and strength of the reinforcement as well as to the fine grain size of the matrix. Spark plasma sintering has been used extensively over the past years to consolidate wide range of materials including nanocomposites and was shown to be effective noneconventional sintering method for obtaining fully dense materials with preserved nanostructure features. The objective of this work is to briefly present the spark plasma sintering process and review published work on spark-plasma-sintered metals and metal matrix nanocomposites.

A Review of Hybrid Solar–Fossil Fuel Power Generation Systems and Performance Metrics

A literature review of hybrid solar―fossil fuel power generation is given with an emphasis on system integration and evaluation. Hybrid systems are defined as those which use solar energy and fuel simultaneously, thus excluding the viable alternative of solar thermal plants which use fossil fuels as backup. The review is divided into three main sections: performance metrics, the different concentrated solar receiver technologies and their operating conditions, and the different hybridization schemes. In addition, a new linear combination metric for analysis of hybrid systems, which considers trade-off of different metrics at the fleet level, is presented. This metric is also compared to alternative metrics from multi-objective optimization. Some previous work only evaluates the hybrid cycle at a certain point in time, which can be misleading as this evaluation would not take into account certain aspects of hybrid cycle, such as fluctuating solar supply. Furthermore, almost all previous work designs the hybrid solar―fossil fuel systems for a certain point in time and then evaluates the performance of the system for an entire year. By not taking into account fluctuating solar supply and selling price of electricity in the design of the system, the best possible annual performance of the hybrid cycle may not be reached.

A New Friction Factor Model and Entrance Loss Coefficient for Honeycomb Annular Gas Seals

A new experimental friction factor model for a honeycomb surface was developed using a static seal tester. Three clearances and three lengths were tested for the seals, and Reynolds number ranged from 3000 to 49,000. It was found that the friction factor was a function of Reynolds number and seal clearance only. The clearance effect was dominant and the friction factor was found to increase with increased clearance. A new uncertainty analysis was developed for the experimental friction factor when calculation friction factor using Mach number curve fit. The entrance loss coefficient was found to be constant for both smooth and honeycomb seals. The entrance loss coefficient of Honeycomb seals was found to be 50 percent higher than that of smooth seals.

Experimental Investigation of the Effect of Radial Gap and Impeller Blade Exit on Flow-Induced Vibration at the Blade-Passing Frequency in a Centrifugal Pump

It has been recognized that the pressure pulsation excited by rotor-stator interaction in large pumps is strongly influenced by the radial gap between impeller and volute diffusers/tongues and the geometry of impeller blade at exit. This fluid-structure interaction phenomenon, as manifested by the pressure pulsation, is the main cause of flow-induced vibrations at the blade-passing frequency. In the present investigation, the effects of the radial gap and flow rate on pressure fluctuations, vibration, and pump performance are investigated experimentally for two different impeller designs. One impeller has a V-shaped cut at the blades exit, while the second has a straight exit (without the V-cut). The experimental findings showed that the high vibrations at the blade-passing frequency are primarily raised by high pressure pulsation due to improper gap design. The existence of V-cut at blades exit produces lower pressure fluctuations inside the pump while maintaining nearly the same performance. The selection of proper radial gap for a given impeller-volute combination results in an appreciable reduction in vibration levels.

Age Hardening Behavior of Carbon Nanotube Reinforced Aluminum Nanocomposites

In the present work, age hardening behavior of CNT reinforced Al6061 and Al2124 nanocomposites, prepared by ball milling and spark plasma sintering, was investigated. The effect of CNT content, annealing time and temperature on the age hardening behavior of the nanocomposites was evaluated and compared to the monolithic alloys prepared and age hardened under the same conditions. It was found that CNTs have a negative influence on the age hardening of the alloys. The alloys displayed standard age hardening behavior i.e. a sharp increase in hardness during initial aging followed by a steady decrease in hardness. Whereas the nanocomposites did not only display initial softening during aging but also showed reduced age hardening efficiency. The hardening efficiency was found to decrease with increasing CNT content. The complicated behavior of nanocomposites was explained in terms of dislocation recovery, large thermal mismatch between matrix and CNTs and bulk microstructure of the composites.

Nano-second pulse laser treatment of Incoloy 800 HT alloy-corrosion properties

Incoloy alloy 800 HT is widely used material of construction for equipment that must resist corrosion. Moreover, the corrosion properties of the alloy reduce considerably when the alloy is heat treated. However, the short pulse laser treatment of the alloy may offer alternative technique to improve the corrosion properties of the alloy. In the present study, nano-second pulse heating of Incoloy 800 HT alloy is carried out using a Nd-YAG laser. The heating rate and the temperature rise during the laser treatment are predicted theoretically. Electrochemical techniques are applied to determine the corrosion rates of the laser treated and untreated Incoloy 800 HT samples. SEM and EDS are introduced for metallographic examination of the treated alloy surface. It is found that the fine dentritic structures occur at the surface after the laser treatment. The local pitting is observed for the laser melted and re-solidified regions while the scattering of the pits are resulted for the laser heated and unmelted regions. In addition, the corrosion rate reduces for the laser-treated samples.

Solar car optimization for the World Solar Challenge

This paper presents the details of an optimization method for the solar cars speed and battery management. The optimization method is demonstrated for the World Solar Challenge along a 3000km from Darwin to Adelaide, Australia. The optimization can be performed at any time during the race based on the current location, time, and battery status. The method predicts the required car speeds between the road land marks, taking into consideration the mandatory stops. The optimization includes the terrain inclination, the car rolling resistance and aerodynamic resistance, and predicts available solar energy as function of position and time.

Effect of increasingly metallized hybrid reinforcement on the wear mechanisms of magnesium nanocomposite

Strength and ductility of pure magnesium have experienced simultaneous improvement due to the presence of nanosize hybrid (yttria and copper) reinforcement. Increasing the vol% (i.e., 0.3–1.0) of ductile metallic copper particles in reinforcement has further enhanced the strength of magnesium. Wear behaviour of these magnesium hybrid nanocomposites was investigated using pin-on-disc dry sliding tests against hardened tool steel using a constant sliding speed of 1 m s−1 under a range of loads from 5 to 30 N for a sliding distance of 1000 m. Scanning electron microscopy identified abrasion and delamination as primary wear mechanisms in the hybrid nanocomposite. Oxidation was active in nanocomposite with higher copper content, tested under higher load and positively affected the wear resistance. Limited thermal softening was observed when tested at a relatively higher load. High frictional heat dissipation capacity couples with higher hardness resisted adhesive wear which is common mechanism for magnesium composite.

Premature Failure of an Industrial Mixer Timing Gears

A systematic and practical methodology was adopted to determine the root cause(s) of the premature failure of a pelletizer mixer timing gear. The investigation activities covered all possible causes of failure and included field examination, interview of engineers and operators, lubrication analysis, metallurgical examination. Fracture surfaces and microstructure of gear material were examined, and hardness profiles were developed. Analyses of shaft misalignment and teeth profiles were performed and found to be within acceptable limits. Results clearly indicate the surface hardness deficiencies in many locations specifically at center of the driven gear, area of severe pitting. The developed hardness profile for all locations is lower than that specified by the manufacturer. Fractographic analysis revealed that failure occurred by pitting followed by crack propagation. A number of cracks are seen to branch in different directions indicating the presence of high contact stresses combined with weak surface strength. Bending fatigue and pitting fatigue stress calculations revealed that the safety factor under contact is well below the desired value.

Performance Study of a Dimpled-Protruded Air-to-Air Plate Heat Exchanger

In the present study, the overall heat transfer coefficient, friction factors, and effectiveness of a dimple-protrusion air-to-air counter-flow plate heat exchanger have been measured at low Reynolds number (500 < Re < 4,000). The heat exchanger consists of 4 channels per flow direction built using 1 mm aluminum plates. Dimples are specially arranged such that protrusions are opposed for applications that require structural support to withstand high pressure difference between the two fluids. A maximum heat enhancement level of 3.2 was obtained with a penalty of increased friction factor by 9 times which leads to a maximum performance factor of 1.5. The effectiveness obtained was found to be almost independent of Reynolds number on most tested Re. A detailed uncertainty analysis has been performed to determine the uncertainty in the results.Copyright