Wael H. Ahmed

Bio: Wael H. Ahmed is an academic researcher from University of Guelph. The author has contributed to research in topics: Two-phase flow & Airlift. The author has an hindex of 17, co-authored 87 publications receiving 1119 citations. Previous affiliations of Wael H. Ahmed include Atomic Energy of Canada Limited & Alexandria University.

Thermoelectric Power Generation Using Waste-Heat Energy as an Alternative Green Technology

Abstract: In recent years, an increasing concern of environmental issues of emissions, in particular global warming and the limitations of energy resources has resulted in extensive research into novel technologies of generating electrical power. Thermoelectric power generators have emerged as a promising alternative green technology due to their distinct advantages. Thermoelectric power generation offer a potential application in the direct conversion of waste-heat energy into electrical power where it is unnecessary to consider the cost of the thermal energy input. The application of this alternative green technology in converting waste-heat energy directly into electrical power can also improve the overall efficiencies of energy conversion systems. In this paper, a background on the basic concepts of thermoelectric power generation is presented and recent patents of thermoelectric power generation with their important and relevant applications to waste-heat energy are reviewed and discussed.

Air-lift pumps characteristics under two-phase flow conditions

Abstract: Air-lift pumps are finding increasing use where pump reliability and low maintenance are required, where corrosive, abrasive, or radioactive fluids in nuclear applications must be handled and when a compressed air is readily available as a source of a renewable energy for water pumping applications. The objective of the present study is to evaluate the performance of a pump under predetermined operating conditions and to optimize the related parameters. For this purpose, an air-lift pump was designed and tested. Experiments were performed for nine submergence ratios, and three risers of different lengths with different air injection pressures. Moreover, the pump was tested under different two-phase flow patterns. A theoretical model is proposed in this study taking into account the flow patterns at the best efficiency range where the pump is operated. The present results showed that the pump capacity and efficiency are functions of the air mass flow rate, submergence ratio, and riser pipe length. The best efficiency range of the air-lift pumps operation was found to be in the slug and slug-churn flow regimes. The proposed model has been compared with experimental data and the most cited models available. The proposed model is in good agreement with experimental results and found to predict the liquid volumetric flux for different flow patterns including bubbly, slug and churn flow patterns.

Capacitance Sensors for Void-Fraction Measurements and Flow-Pattern Identification in Air–Oil Two-Phase Flow

Abstract: The design methodology of capacitance sensors for void-fraction measurement in adiabatic two-phase flow systems is presented in this paper. The effect of design parameters on the capacitance output has been theoretically and experimentally investigated for two types of sensor configurations: concave and ring types. Experiments were performed using air-oil two-phase flow to determine the signal-to-noise ratio, sensitivity, and time response of the capacitance sensors. The results show that the ring-type sensors are more sensitive to the void-fraction signal than the concave type for the same spatial resolution. The predictions from the theoretical model for the ring-type sensors are in better agreement with the experimental results than for the concave type. The mean value, time trace, power spectral density (PSD), and the probability density function (PDF) of the void-fraction signal from the capacitance sensors are used to objectively identify the flow pattern. The method was validated using high-speed video images of the flow and comparing the results to those from the signal analysis

Coplanar capacitance sensors for detecting water intrusion in composite structures

Abstract: Composite materials are becoming more affordable and widely used for retrofitting, rehabilitating and repairing reinforced concrete structures designed and constructed under older specifications. However, the mechanical properties and long-term durability of composite materials may degrade severely in the presence of water intrusion. This study presents a new non-destructive evaluation (NDE) technique for detecting the water intrusion in composite structures by evaluating the dielectric properties of different composite system constituent materials. The variation in the dielectric signatures was employed to design a coplanar capacitance sensor with high sensitivity to detect such defects. An analytical model was used to study the effect of the sensor geometry on the output signal and to optimize sensor design. A finite element model was developed to validate analytical results and to evaluate other sensor design-related parameters. Experimental testing of a concrete specimen wrapped with composite laminate and containing a series of pre-induced water intrusion defects was conducted in order to validate the concept of the new technique. Experimental data showed excellent agreement with the finite element model predictions and confirmed sensor performance.

Flow and mass transfer downstream of an orifice under flow accelerated corrosion conditions

Abstract: Local flow parameters play an important role in characterizing flow accelerated corrosion (FAC) downstream of sudden area change in power plant piping systems. Accurate prediction of the highest FAC wear rate locations enables the mitigation of sudden and catastrophic failures, and the improvement of the plant capacity factor. The objective of the present study is to evaluate the effect of the local flow and mass transfer parameters on flow accelerated corrosion downstream of an orifice. In the present study, orifice to pipe diameter ratios of 0.25, 0.5 and 0.74 were investigated numerically by solving the continuity and momentum equations at Reynolds number of Re = 20,000. Laboratory experiments, using test sections made of hydrocal (CaSO 4 ·½H 2 O) were carried out in order to determine the surface wear pattern and validate the present numerical results. The numerical results were compared to the plants data as well as to the present experiments. The maximum mass transfer coefficient found to occur at approximately 2–3 pipe diameters downstream of the orifice. This location was also found to correspond to the location of elevated turbulent kinetic energy generated within the flow separation vortices downstream of the orifice. The FAC wear rates were correlated with the turbulence kinetic energy and wall mass transfer in terms of Sherwood number. The current study found to offer very useful information for FAC engineers for better preparation of plant inspection scope.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Recent advances in thermoelectric materials

Abstract: Thermoelectric materials are crucial in renewable energy conversion technologies to solve the global energy crisis. They have been proven to be suitable for high-end technological applications such as missiles and spacecraft. The thermoelectric performance of devices depends primarily on the type of materials used and their properties such as their Seebeck coefficient, electrical conductivity, thermal conductivity, and thermal stability. Classic inorganic materials have become important due to their enhanced thermoelectric responses compared with organic materials. In this review, we focus on the physical and chemical properties of various thermoelectric materials. Newly emerging materials such as carbon nanomaterials, electronically conducting polymers, and their nanocomposites are also briefly discussed. Strategies for improving the thermoelectric performance of materials are proposed, along with an insight into semiconductor physics. Approaches such as nanostructuring, nanocomposites, and doping are found to enhance thermoelectric responses by simultaneously tuning various properties within a material. A recent trend in thermoelectric research shows that high-performance thermoelectric materials such as inorganic materials and carbon nanomaterials/electronically conducting polymer nanocomposites may be suitable for power generation and energy sustainability in the near future.

A review of waste heat recovery technologies towards molten slag in steel industry

Abstract: Molten slag exhausted with critically high temperature of about 1450–1550 °C is a potential resource of energy and raw materials. Water quenching is a traditional heat recovery technology, which uses cold water to cool down slag so as to achieve the desired glassy by-products. However, this technology consumes a huge amount of water and fails to recover the sensible heat of slag. To save energy and reduce water consumption, some other heat recovery technologies have thus been proposed. Generally, current heat recovery technologies can be classified into physical and chemical methods. Regarding the physical methods, mechanical crushing, air blast and centrifugal granulating process, etc. are widely investigated. With respect to chemical methods, methane reforming reaction and coal gasification process, etc. are proposed. Unfortunately, all these methods cannot fulfill the sustainable requirement. This paper aims to review the proposed granulation and heat recovery technologies. Their working principle, current research status, challenges and future prospects are presented. The waste heat recovery and utilization technologies, which give consideration to both heat recovery rate and cooled slag particles with high quality and high additional value, will be a key to achieve sustainable development for the iron and steel industry.

Challenges of Sustainable and Commercial Aquaponics

Abstract: The world is facing a number of serious problems of which population rise, climate change, soil degradation, water scarcity and food security are among the most important. Aquaponics, as a closed loop system consisting of hydroponics and aquaculture elements, could contribute to addressing these problems. However, there is a lack of quantitative research to support the development of economically feasible aquaponics systems. Although many studies have addressed some scientific aspects, there has been limited focus on commercial implementation. In this review paper, opportunities that have the potential to fill the gap between research and implementation of commercial aquaponic systems have been identified. The analysis shows that aquaponics is capable of being an important driver for the development of integrated food production systems. Arid regions suffering from water stress will particularly benefit from this technology being operated in a commercial environment.

Influence of Bubbles on the Energy Conversion Efficiency of Electrochemical Reactors

Abstract: Summary Bubbles are known to influence energy and mass transfer in gas-evolving electrodes. However, we lack a detailed understanding on the intricate dependencies between bubble evolution processes and electrochemical phenomena. This review discusses our current knowledge on the effects of bubbles on electrochemical systems with the aim to identify opportunities and motivate future research in this area. We first provide a base background on the physics of bubble evolution as it relates to electrochemical processes. Then we outline how bubbles affect energy efficiency of electrode processes, detailing the bubble-induced impacts on activation, ohmic, and concentration overpotentials. Lastly, we describe different strategies to mitigate losses and how to exploit bubbles to enhance electrochemical reactions.