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Numerical Modeling of Sequential Segmentation for Enhancement of Mixing Inside Microchannels
No full textA Master of Science thesis in Mechanical Engineering by Ibragim Abu Dagga entitled, “Numerical Modeling of Sequential Segmentation for Enhancement of Mixing Inside Microchannels”, submitted in December 2019. Thesis advisor is Dr. Mohamed Abdelgawad. Soft copy is available (Thesis, Approval Signatures, Completion Certificate, and AUS Archives Consent Form).Microfluidics appeared recently as a new tool that facilitates many applications including chemical synthesis, electronics cooling and biological assays. However, flow on the microscale is characterized by laminar flow which renders mixing a challenge and reduces the effectiveness of mixing in many applications. Therefore, many techniques have been reported to enhance mixing inside microchannels. This thesis demonstrates the different mixing techniques inside microchannels and investigates sequential segmentation as an active mixing technique. In sequential segmentation, the solute and the solvent are divided into segments in the axial direction. Due to the parabolic velocity profile exhibited in laminar flow, Taylor-Aris dispersion can improve mixing by several orders of magnitude as compared with pure molecular diffusion. The present work comprises a comprehensive study to optimize this technique. A numerical model was built using COMSOL Multiphysics to calculate the concentration distribution by diffusion and advection in the entire microchannel. The different investigated parameters that were optimized are frequency, flow velocity, duty cycle (DC), aspect ratio, cross-sectional shape, and effect of inlet configuration of inlet branches. It has been found that changing the channel aspect ratio has the most significant effect on mixing efficiency. The analysis of aspect ratio (H:W) showed a moderate increase in mixing index for aspect ratio of 4:1. However, an aspect ratio of 1:4 is extremely inefficient. The best mixing efficiency achieved is that of sequential segmentation coupled with hydrodynamic focusing which is 99.7%. On the contrary, changing the shape of inlet branches to T-shape or arrow-head shape decreased the mixing index. Increasing segmentation frequency was found to increase the mixing efficiency up to a frequency of 150 Hz beyond which mixing efficiency decreased due to non-complete segmentation of both streams at higher frequencies. The duty cycle effect is mainly important for specific microfluidic applications that require different mixing fractions of the solutions. It is shown that by increasing the duty cycle of the solvent, mixing slightly increases, whereas decreasing it leads to a reduction in mixing. The effect of different cross-sectional shapes also has a small effect on the mixing index.College of EngineeringDepartment of Mechanical EngineeringMaster of Science in Mechanical Engineering (MSME
Formulation of heat conduction and thermal conductivity of metals
No full textThe well-known low-pressure monatomic gas thermal conductivity expression is based on the Maxwell-Boltzmann velocity distribution and involves the mean particle velocity, the gas heat capacity at constant volume and the particle mean free path. The extension of the formula to a free electron Fermi gas, using the Fermi velocity along with the Sommerfeld electronic heat capacity, was demonstrated in the literature using the Boltzmann transport equation. A different formulation of heat conduction in sufficiently pure metals, yielding the same formula for the thermal conductivity, is provided in the present investigation using the free electron Fermi gas energy distribution with the thermal conductivity determined from the net heat transfer occurring due to random motions of the free electrons in the presence of temperature gradient. Potential applications of this approach include extension of the present kinetic model incorporating quantum effects to cases in which electron scattering occurs such as in nanowires and hollow nanowires
Flexural Behavior of Concrete-Filled Steel Tubes (CFSTs) using Recycled Aggregate Concrete (RAC)
No full textA Master of Science thesis in Civil Engineering by Yosri Izzeldin Hassan Abdelmageed entitled, “Flexural Behavior of Concrete-Filled Steel Tubes (CFSTs) using Recycled Aggregate Concrete (RAC)”, submitted in December 2019. Thesis advisor is Dr. Farid Abed. Soft copy is available (Thesis, Approval Signatures, Completion Certificate, and AUS Archives Consent Form).Concrete-filled steel tubes (CFSTs) can be considered as possible and promising alternative to conventional reinforced concrete members and steel structures since they have superior structural properties and economic advantages. In recent years, researchers have investigated the replacement of natural aggregate concrete (NAC) infill with recycled aggregate concrete (RAC) and utilizing the confinement provided by the steel tube in order to improve the mechanical properties of recycled aggregate concrete (RACFST). However, the research on RACFSTs has been limited to their behaviour under compression. The main goal of this research is to investigate the flexural response of RACFSTs experimentally and theoretically considering circular and rectangular cross-sections. For this purpose, a total of 12 circular and 8 rectangular CFST beams with different Diameter-to-thickness (D/t) and depth-to-thickness (h/t) ratios were tested under four-point bending. Concrete compressive strengths of 30 and 50 MPa and recycled coarse aggregate replacement percentages of 50 and 100% were used in the experimental investigation. The test results revealed promising outcomes on the feasibility of using RAC in CFST systems under flexure. The flexural behaviour of RACFSTs was found to be very similar to NACFSTs, and the change in the concrete compressive strength and the recycled coarse aggregate replacement percentage slightly affected the flexural behaviour of RACFSTs. In addition, the experimental flexural capacity of RACFST beams were compared to the theoretical nominal moments predicted by well-known design codes and methods including the AISC-LRFD, the Architectural Institute of Japan (AIJ), EuroCode4, the British Standard (BS) and Han’s method. The AIJ design code was the most accurate to predict the flexural capacity of RACFSTs followed by the EuroCode4 as they underestimated the flexural capacity of RACFST beams by an average of 5% and 12%, while the British Standard significantly underestimated the flexural capacity of the tested RACFST beams by an average of 34%.College of EngineeringDepartment of Civil EngineeringMaster of Science in Civil Engineering (MSCE
Corrosion Behavior of Common Metals in Eutectic Ionic Liquids
Get PDFThe corrosion behavior of six choline chloride-based eutectic solvents namely, ChCl-Ur, ChCl-EG, ChCl-Gl, ChCl-MA, ChCl-Ph and ChCl-TG towards copper, mild steel and stainless steel 316 have been investigated. The effect of temperature and moisture content was evaluated. The corrosion rates of the three materials increased with an increase in the temperature and moisture content. Stainless steel was found to be the most resistant under all experimental conditions. The experimental results demonstrated ChCl-Ph and ChCl-Gl to have high inhibition efficiency suggesting these to be a suitable candidate as green corrosion inhibitors for metal and alloys under extreme environments
Adsorptive Removal of Dyes from Aqueous Solutions Using Metal Organic Frameworks (MOFs)
No full textA Master of Science thesis in Chemical Engineering by Abdollah Karami entitled, “Adsorptive Removal of Dyes from Aqueous Solutions Using Metal Organic Frameworks (MOFs)”, submitted in April 2019. Thesis advisor is Dr. Rana Sabouni and thesis co-advisor is Dr. Ahmed Aidan. Soft and hard copy available.Synthetic dyes are commonly found in industrial wastewater due to their wide application as colorants in the textile, paper, food, leather and plastic industries. Among the various treatment methods, adsorption is generally considered to be the most efficient method for quickly lowering the concentration of dissolved dyes in an effluent. In recent years, there has been great interest in the use of Metal Organic Frameworks (MOFs) to remove dyes from contaminated water because of their diverse porous structures, high surface areas, and chemical tunability. In this thesis, the removal of methyl orange (MO) from aqueous solutions was investigated in batch and continuous setups using three MOFs, namely, Fe-BTC, Cu-BTC, and ZIF-8. The experimental results showed that at the same MO initial concentration (15 mg/L) and the same dosage (100 mg), Fe-BTC had the highest removal efficiency of 91%, followed by ZIF-8 (63%), and finally Cu-BTC (35%). Furthermore, pH effect experiments showed that Fe-BTC maintained consistent adsorption capacity over a wide range of pH suggesting that it could be a good candidate for dye removal from wastewater. The equilibrium study revealed that the experimental data could be best described by the Langmuir isotherm. The calculated maximum monolayer adsorption capacities were 100.3, 105, and 114 mg/g for Fe-BTC compared to 7.56, 5.62, and 4.65 mg/g for ZIF-8 at 298, 303 and 313 K, respectively. The calculated thermodynamic parameters indicated that the adsorption process was endothermic in the case of Fe-BTC (ΔH° was 16.86 kJ/mol) and exothermic in the case of ZIF-8 (ΔH° was -9.94 kJ/mol). In the continuous setup, a fixed-bed column was packed with Fe-BTC to study the performance of MO adsorption. The influent MO solution concentration was 15 mg/L, and the influent flow rate was 4.5 mL/hr. The adsorption performance was investigated at two different bed heights (0.75 and 1.5 cm). The results showed that as bed height increased the breakthrough time increased (20.0 hr at 0.75 cm to 46.2 hr at 1.5 cm). The bed maximum adsorption capacity also increased from 20.2 to 21.6 mg/g. The experimental data were found to best fit the modified dose response model (R2>0.99).College of EngineeringDepartment of Chemical EngineeringMaster of Science in Chemical Engineering (MSChE
A Multi-Objective Allocation Approach for Power Quality Monitoring Devices
No full textWith the inception of smart grids and the increased integration of renewable resources, the continuous monitoring of power systems becomes increasingly important to monitor power quality (PQ) and speed up the localization of faults. The optimal allocation of PQ monitoring devices to achieve 100% observability is one of the most important design problems that face the planning of any power system. However, for smart distribution networks (SDNs), the cost of achieving 100% observability is exorbitant. Therefore, for cost-effective monitoring, the SDN planers can sacrifice a percentage of the system observability. To that end, this paper proposes a multi-objective optimization approach for allocating the PQ monitoring devices with the aim of minimizing two conflicting objectives, namely, the cost and the loss of observability in the system. The proposed approach utilizes branch-and-reduce-based nonlinear programming global solver that minimizes both objectives. The analysis is first carried out for balanced systems and later extended to unbalanced systems. To validate the performance of the proposed approach, it is applied to different standard systems. The obtained results prove the effectiveness of the proposed approach
Transnational Links in Rhino Poaching and the Black Market Price of Rhino Horns
No full textThe trends of rhino poaching in South Africa and India – major range states – have been remarkably similar over time. Organized criminal syndicates manage an illegal supply chain of rhino horns from poachers, middlemen, and corrupt authorities, to East Asian black-markets. In this paper, we use rhino poaching data from South Africa and India to examine the plausibility of transnational links and coordination in their supplies of rhino horns. We develop an innovative model of oligopolistic collusion in supply and find empirical evidence to support the theory, while controlling for rhino horn demand features, corruption, governance quality, and conservation policy. Furthermore, we propose an inventory management model of a criminal syndicate that controls the horn supply chain. The method retraces and forecasts black-market prices, and has potential applicability in estimating supply or demand elasticities. This paper is a first to suggest an oligopolistic feature of the poaching industry. It highlights the need to reorient conservation policy to account for possible coordination of rhino horn supplies between range states
Internet of things based multi-sensor patient fall detection system
No full textAccidental falls of patients cannot be completely prevented. However, timely fall detection can help prevent further complications such as blood loss and unconsciousness. In this study, the authors present a cost-effective integrated system designed to remotely detect patient falls in hospitals in addition to classifying non-fall motions into activities of daily living. The proposed system is a wearable device that consists of a camera, gyroscope, and accelerometer that is interfaced with a credit card-sized single board microcomputer. The information received from the camera is used in a visual-based classifier and the sensor data is analysed using the k-Nearest Neighbour and Naïve Bayes’ classifiers. Once a fall is detected, an attendant at the hospital is informed. Experimental results showed that the accuracy of the device in classifying fall versus non-fall activity is 95%. Other requirements and specifications are discussed in greater detail
Effect of Flexural NSM-FRP Bars on the Shear Strength of Reinforced Concrete Beams
No full textA Master of Science thesis in Civil Engineering by Rayyan Bashar Saleh entitled, “Effect of Flexural NSM-FRP Bars on the Shear Strength of Reinforced Concrete Beams”, submitted in May 2019. Thesis advisor is Dr. Rami Haweeleh and thesis co-advisors are Dr. Jamal Abdalla and Dr. Elias Saqan. Soft and hard copy available.Strengthening of reinforced concrete (RC) members in flexure and shear, using fiber-reinforced polymer (FRP) laminates and near surface mounted (NSM) bars has been developed over the last few decades. Conventionally, FRP composite laminates are attached to the vertical sides of RC beams to increase their shear strength. However, in some cases, the sides of the beam might be inaccessible or shallow. According to the ACI 318-14 guidelines and other codes of practice, longitudinal reinforcement contributes to the shear strength of RC beams. The objective of this study is to assess experimentally the effect of longitudinal NSM bars, which are mounted to the beam’s sides, on the shear strength of RC beams. The variables of the experimental program included the beam’s depth to evaluate the size effect, the concrete compressive strength, and the flexural FRP reinforcement ratio. A total of 18 shear deficient RC beams were built, strengthened with longitudinal NSM bars, and tested under three-point bending until failure. It was observed that the strengthened beam specimens exhibited an increase in shear capacity that ranged from 10 to 35% over the control beams. It was also observed that the increase in the concrete shear strength with longitudinal FRP bars for the high strength concrete specimens was not as effective as that with normal concrete strength specimens. The results have also revealed that the size effect phenomena has a significant effect on the test results, in which the increase in shear strength has decreased from around 35% to 10%, with the increase of beam’s height from 230 to 650 mm, respectively. It was concluded that equation 22.5.5.1 of the ACI 318-14 code, which gives a simplified expression for the concrete contribution to the shear strength of beams, is not conservative for beams with large depths. Thus, other published analytical shear strength models that account for size effect were utilized in this study to predict the strength of the tested specimens. This study utilized 10 different analytical models in predicting the shear strength of the tested RC beam specimens. The models that showed the closest agreement with the tested data were the University of Houston method and the model based on the second order simplified modified compression field theory. It can be concluded that flexural longitudinal NSM bars could be used as a viable solution to enhance the shear strength of RC beams.College of EngineeringDepartment of Civil EngineeringMaster of Science in Civil Engineering (MSCE
Refinancing the Rentier State: Welfare, Inequality, and Citizen Preferences toward Fiscal Reform in the Gulf Oil Monarchies
No full textMiddle East oil producers are today pursuing profound transformations of their rentier economies, including through new taxes and reductions in state spending and welfare subsidies that have supported citizens for generations. Reforms aimed at deficit reduction are expected to pose serious challenges for authoritarian states whose citizens are accustomed to generous financial patronage in return for political allegiance. However, the dominant rentier state theory does not offer clear expectations about citizen preferences or priorities surrounding welfare retrenchment, beyond the basic assumption that citizens should oppose reductions in state largesse. This paper proposes a general framework for understanding how citizens relate to welfare benefits in the rentier state, and then tests some observable implications using original survey data from the quintessential rentier state of Qatar. We distinguish between nonexcludable benefits that are available to all rentier citizens and personalistic benefits that disproportionately flow to elite citizens and the ruling class, the latter giving rise to inherent inequality. Using two novel choice experiments, we ask Qataris to choose between competing forms of economic subsidies and state spending, producing a clear and reliable ordering of welfare priorities. Finally, expectations derived from the experiments about the individual-level determinants of rentier reform preferences are tested using data from a follow-up survey. Findings demonstrate the importance of nonexcludable public goods, rather than private patronage, for upholding the rentier bargain. Our study has important implications for understanding how citizen preferences may serve to constrain the domestic and foreign policy options available to rentier governments as they seek to reshape their societies away from reliance upon oil. It also invites a larger conceptual reorientation of key aspects of the prevailing rentier state paradigm.Qatar National Research Fun