Qatar Foundation Annual Research Forum Volume 2012 Issue 1

Over the past several years organic Rankine cycle (ORC) processes have become a promising technology for power production from low grade heat sources, such as solar, biomass, geothermal and waste heat. A key challenge in design is the selection of an appropriate working fluid. ORC systems that use single components as working fluids have two major shortcomings. First, in the majority of applications, the temperatures of the heat sink and source fluid vary during the heat transfer process, whereas working fluid evaporation and condensing is isothermal. As a consequence a pinch point is encountered in the evaporator and condenser giving rise to large temperature differences at one end of heat exchanger. This leads to irreversibility that in turn reduces process efficiency. A similar situation is also encountered in the condenser. A second shortcoming of the Rankine cycle is its lack of flexibility. For given operating conditions, a certain working fluid may be the optimum choice; however, as the operating conditions change another working fluid would become a more appropriate choice. The shortcomings result from a mismatch between thermodynamic properties of pure working fluids, the requirements imposed by the Rankine cycle and the particular application. In contrast, when working fluid mixtures are used instead of single component working fluids, improvements can be obtained in two ways: through the inherent properties of the mixture itself, and through cycle variations which become available with mixtures. The most obvious positive effect is decrease in exergy destruction, because occurrence of the temperature glide at phase change provides a good match of temperature profiles in condenser and evaporator. The paper presents detailed simulations analysis of organic Rankine cycle processes for energy conversion of low heat sources for various binary zeotropic mixtures. The rigorous and the most suitable thermodynamic models are applied in each mixture simulation. The paper explores the effect of mixture utilization on common ORC performance assessment criteria in order to demonstrate advantages of employing mixtures as working fluid as compared to pure fluids. In addition, several new criteria are developed in order to provide a new perspective on how ORC performance should be assessed from thermodynamic point of view.

Background: Sandwich panels with low density core constructions are a class of structural elements with superior structural performance compared to traditional solid panels. Sandwich panels, compared to solid panels of equal mass, generally have much higher bending stiffness and comparable stretching stiffness, thus undergoing smaller deformation under loading. The potential advantage of sandwich panels for mitigating shock and projectile loading has been established in literature. The previous studies related to understanding the mechanics and structural performance of sandwich structures are mainly focused on studying the behavior of the core construction or the performance of a single isolated sandwich panel. These studies have provided significant insight into the behavior of sandwich panels, which includes mechanisms of energy dissipation in the core, stages of deformation of sandwich panels as they get impinged by an intense shock, fluid-structure effects for shock waves transmitted in air and water, and the mechanism of deformation and failure of sandwich panels under shock and projectile loading. Objective: This study extends previous research by exploring the behavior and structural performance of structural systems made of sandwich walled panels. The objective is to explore the potential benefit of sandwich configurations in enhancing the overall behavior of structural systems under complex loading conditions that could occur in petrochemical industry settings and pipeline networks. Method: We considered three frame structures, (i) frames made of solid panels (ii) frames with sandwich panel side walls and (iii) frames where all walls are made of sandwich panels. We also considered sandwich walled cylinders resembling pipes and compared their performance with the mechanical behavior of traditional pipes made of solid metal hollow cylinders. We used detailed finite element models to simulate the response of these structural systems. Results: The results showed that sandwich walled frame and cylinder (pipeline) configurations, in general, undergo smaller deflection than traditional counterpart structures under both quasi-static and high intensity dynamic (shock) loadings. Conclusions: The results highlight the potential of sandwich walled structural systems for developing novel threat resistant structures especially for the petrochemical industry and pipeline networks.

Electrolyte solutions occur in many natural systems and are present in several industrial processes. Aqueous solutions of electrolytes are particularly important for designing water purification and treatment systems, among which water desalination processes. The design of processes with electrolyte solutions may require determining phase equilibrium conditions, and predicting volumetric and calorimetric properties. Equations of state (EOSs) are, in principle, capable of such predictions and, for this reason, a several equations of state (EOS) have been developed considering the ionic interactions in electrolytes solutions. An example is the electrolattice equation of state. This model evaluates the Helmholtz energy as the summation of three contributions: the first considers the short range interactions (by using the Mattedi-Tavares-Castier equation of state (MTC-EOS)); the second, the Born contribution term, accounts the solvation effects; the third, the primitive mean spherical approximation (MSA) term, describes the long range effects. In the electrolattice EOS, the diameters of cations and anions are considered to be equal. In this work, we calculate vapor pressures, mean ionic activity coefficients, osmotic coefficients, and densities of mixtures containing water and a single 2:1 strong electrolyte with a revised version of the electrolattice EOS, which is called Q-electrolattice EOS. The latter preserves the first and the second contributions of the electrolattice EOS, but includes another MSA term, which is an explicit mean spherical approximation under the assumption the ions have unlike diameters. The water molecule is assumed to have a dispersion region, an electron-donor region, and an electron-acceptor region. To reduce the number of adjustable parameters of the model, the ionic diameters are taken from the literature. Also, interactions between the each ion and each of the three regions of the water molecule are assumed to be equal. Finally, short range interactions between ions are neglected. With this set of assumptions, the inclusion of each ion only requires the fitting of one additional parameter. The work compares the performance of the electrolattice and Q-electrolattice models with respect to other equations of state for similar applications.

Background: Many failures of engineering structures and equipment are attributed to the failure of a single component. It is of great importance to identify those critical components and understand how components' criticality changes over time under dynamic environments. Objective: In this paper, we investigate the criticality analysis for components with multi-dimensional degradation under time-varying environmental conditions. Methods: The component degradation is modeled as a k-dimensional Wiener process and a component fails when any of the k degradation processes attains a threshold level. Results: Since the degradation process is often influenced by the environmental conditions, we assume that both the mean and diffusion of the degradation process are time-dependent functions for a given environmental profile, which evolves either deterministically or stochastically. Conclusions: We derive expression for the criticality measure of the component with time, illustrate the analysis of component criticality under time-varying environmental conditions and demonstrate the necessity to consider the change of environmental conditions in analyzing component criticality.

It's been many years since the invention of the internal combustion engine. These engines are getting more challenging due to the concerns of ever increasingly harmful pollutions and limited energy sources. Environmental regulations have been more restrictive, and car manufacturers have invested more into reducing emitted pollutions and fuel consumption. It is well recognized that for spark ignition (SI) engines, the air-fuel ratio (AFR) is by far the most dominant factor in determining the engine exhaust gas mixture and the amount of lit/km characteristics. For many years this has been partially addressed due to the restrictions on the control approaches because of existence of a time delay in the control input. The control approach presented in this research provides a novel strategy based on the internal dynamics of SI engines. It compensates for the delay at each instant and follows the desired trajectory of AFR. This leads to a reduction of fuel consumption and keeps the actual AFR close to the stoichiometric AFR, which indeed minimizes the harmful pollutants. The research proposes a thorough design methodology that circumvents the previous limitations for industrial PID controllers in terms of noise attenuation. It is robust against canister purge disturbances, modeling uncertainties, parameter variations and time-varying engine operating conditions. The proposed controller has been implemented on experimental data collected at University of Houston on a FORD F-150 truck. The results have shown considerable improvements over the baseline controller and exhibited excellent performance for the noisy outputs of the sensor due to the aging factors.

Realization of multilevel inverters for multiphase high power AC drives with open-end windings is presented in this paper, with a specific case of five-phase five-level inverter configurations. The five-level voltage profile is realized by feeding both ends of the stator windings using a three-level five-phase flying capacitor inverter on one side and a five-phase two-level inverter on the other side. The flying capacitors' voltages are effectively balanced by utilizing the switching state redundancies. The capacitor voltages can be balanced at any modulation index, irrespective of the operating power factor. The operation of a drive at a higher voltage is preferred in many applications due to the advantages such as higher efficiency and reduction in size and weight. However, this demands higher DC link voltage in many topologies. The DC voltage magnitude required in the proposed topology is half of that required in the conventional multilevel neutral point clamped (NPC) topology, for a given output voltage. Hence, the scheme proposed in this paper can be advantageous in such applications where there is a limitation in obtaining DC voltage sources of higher magnitudes, such as in electric and hybrid electric vehicles. Another attractive feature of this topology is the enhanced reliability, as it is possible to operate the drive with half power even if any one of the inverters completely fails. The number of active switches used in this topology is lesser than that in equivalent five-level NPC inverters. Unlike the NPC inverter, this topology does not require any clamping diodes and is also free from issues like neutral point fluctuations. A carrier based pulse width modulation (PWM) technique combined with a hysteresis controller for balancing of the capacitors' voltages is used for the control of the inverter. The proposed drive topology can be applied to high power AC drives such as in oil and gas industries, electric/hybrid electric vehicles, ship propulsion, traction etc. The simulation and experimental results support the proposed idea.

The countries of the Gulf Co-operation Council (GCC) have established an interconnected power system network. The primary goal was to share the spinning reserve among the GCC power grids. The project considered the commercial use of the network by aiming to reduce the cost of power generation in the six GCC states while encouraging power trade in order to meet growing needs. The GCC interconnection authority proved its effectiveness and success when, after it was set up, the interconnection contributed in avoiding any partial or total blackout. This was done by passing supported power to any of the first phase connected states. After connecting the first phase of the project, none of the states were compelled to cut loads from their customers. Furthermore, the probability of having a blackout or power shortage has been reduced. The GCC's ambition did not stop at this point. The hope is to connect to neighboring power grids, which could potentially connect to the European Grid. The link, if it took place, would mean great commercial benefits, since peak load seasons in European countries are different from those in GCC countries. In this paper, a study includes an overview of the GCC interconnection, and its benefits are presented. This would emphasize the transfer capability in an interconnection, especially in Qatar, using PSSE program. Moreover, it considers maximizing this capability as a future need to transfer more power through the network. Flexible Alternating Current Transmission System (FACTS) devices are proposed for such purpose. A thyristor controlled series capacitor (TCSC) is selected for enhancing the power capability. This includes an overview, design, and simulation using MATLAB/SIMULINK of TCSC controller.

Cadmium is a naturally occurring metal and is usually present in the environment as a mineral combined with other elements, such as oxygen, chlorine, and sulfur, or as a minor component of most metal ores such as zinc, lead, and copper. Cadmium is also released in the environment from industrial activity; in particular, ore-smelting plants, industrial paints, and agricultural fertilizers. Over the last few decades, considerable attention has been paid to the evaluation and detection of cadmium contamination in the environment, mostly because of the relationship between cadmium exposure and the development of chronic health problems, including renal dysfunction, osteoporosis, and carcinogenesis, as well as developmental and reproductive problems. Water contamination by cadmium is of particular interest because of its high solubility in acidic conditions. Contamination of drinking-water may occur as a result of the presence of cadmium as an impurity in the zinc of galvanized pipes or cadmium-containing solders in fittings, water heaters, water coolers and taps. The aim of this study is to evaluate the availability of cadmium in drinking water in Qatar. Five samples of municipal water were collected from different locations in Doha--Al-Wakra, Dafna, Salwa Road, Al-Kharitiyat and Sailiya--to examine the availability of cadmium in drinking water. Analysis was performed by injecting the samples directly into an ICP-OES machine and obtaining the results. The results showed that the cadmium concentration in all samples was below detection (detection limit for Cd: 0.7 ppb). These low Cd concentrations in drinking water in Doha may be related to the fact that both dissolved and particulate matter are being removed from seawater during the desalination process. In addition, the absence of these toxic elements may be related to the water distribution system being relatively recent and containing cadmium-free pipes.

Qatar established it vision 2030 in October, 2008 (Ibrahim, 2009), adopting the concept of sustainable development. Thus the understanding of the impact of poor wastewater management and degrading sewage systems should be highlighted. Additionally, new technology should be developed to fully decrease the pollution while focusing concern on the economic benefits of the process. We have chosen to evaluate both poultry and slaughterhouse wastewater, since, if discharged into open waterways in an untreated form, it can cause great pollution stress on our environment. To be able to build a proper process for wastewater treatment, we had first to choose the characteristics needed to be identified for better understanding of the local wastewater, to later have informative values at the end. To help us fully understand the chemical and physical characteristics of the wastewater to be treated, we have chosen to measure initial parameters, including chemical oxygen demand (COD), total suspended solids, total dry solids, pH and conductivity. It is well-established that slaughterhouse wastewater is a moderate to low strength complex-type wastewater; thus, the biodegradability of this could be easily achieved if an adapted bacterial population is obtained. Interestingly, we showed that the anaerobic sludge from the Qatari environment is able to treat more than 95% of the wastewater at 38°C, which is favorable and beneficial to develop large-scale anaerobic digestion of the slaughterhouse waste waters given the conditions in Qatar. Consequently, it is possible to conclude that the anaerobic sludge and the temperature applied for the treatment are suitable to overproduce methane from slaughterhouses wastewaters in Qatar's conditions. Our findings showed that almost 1.3 L of methane can be produced by digesting 1 g of COD or dry matter in the slaughterhouse wastewater, which is a very high yield, unprecedented among levels reported for anaerobic digestion.