Experimental and CFD analysis of photocatalytic gas phase vinyl chloride (VC) oxidation

Photocatalytic destruction of gas phase vinyl chloride (VC) was examined using experimental and computational fluid dynamics (CFD) approaches. Experimental work involved using a differential photoreactor for determining kinetics of oxidation and an annular flow photoreactor for overall removal investigations as well as comparison with CFD models. The kinetic data obtained from differential photoreactor were used to model and predict the performance of the annular photoreactor using CFD. The photocatalytic oxidation of VC followed first order kinetics for inlet concentrations up to about and CFD was able to predict the removal of VC in the system. Both experimental and CFD modeling showed the removal of VC in the system increased with increasing the VC loading rate. CFD analysis of the photoreactor also provided insight into the detailed concentration gradient of VC within the reactor. The modeling results indicated significant radial VC concentration gradient and non-uniform flow distributions in the annular photoreactor. This non-uniform flow distribution, in turn, resulted in short circuiting of the VC contaminated gas and may have resulted in less than optimum removal efficiency for VC in the annular reactor over the entire range of inlet VC concentrations. Overall, the information provided by CFD modeling and simulation showed to be valuable for reactor design modification and for improving the reactor performance.     

Modeling of annular reactors with surface reaction using computational fluid dynamics (CFD)

A CFD-based model for predicting the performance of annular reactors with surface reaction was developed. The capability of several hydrodynamic models to predict successfully the kinetic behavior of the reactor under diffusion limiting conditions was assessed against experimental data. The evaluation included five models: laminar, standard k–ε, realizable k–ε, Reynolds stress (RSM), and Abe–Kondoh–Nagano (AKN). The catalytic decomposition of hydrogen peroxide over a Mn/Al oxide catalyst coated on the reactor surface was used as a model reaction. The reactor was tested within a range of flow rates corresponding to 530<Re<11,000 and intrinsic reaction rate constants of 5×10^?5 to 1 m/s. The results demonstrated that the performance of the hydrodynamic models is associated with their capability to predict external mass transfer and ultimately, the level of mass transfer limitation present in the reacting system. For laminar flow conditions, the laminar model is capable of predicting the experimental behavior of the system. For transient and turbulent flow regimes, all the analyzed turbulence models provided good predictions of the system when the process was controlled by surface reaction. When the system presented some degree of mass transfer limitation, AKN and RSM exhibited better performance.     

A hybrid fuzzy group decision support framework for advanced-technology prioritization at NASA

The prioritization of advanced-technology projects at the National Aeronautic and Space Administration (NASA) is a difficult task. This difficulty is due to the multiple and often conflicting objectives in addition to the inherent technical complexities and valuation uncertainties involved in the assessment process. As such, a systematic and transparent decision support framework is needed to guide the assessment process, shape the decision outcomes and enable confident choices to be made. Methods for solving Multi-Criteria Decision Making (MCDM) problems have been widely used to select a finite number of alternatives generally characterized by multiple conflicting criteria. However, applying these methods is becoming increasingly difficult for technology assessment in the space industry because there are many emerging risks for which information is not available and decisions are made under significant uncertainty. In this paper, we propose a hybrid fuzzy group decision support framework for technology assessment at NASA. The proposed objective framework is comprised of two modules. In the first module, the complicated structure of the assessment criteria and alternatives are represented and evaluated with the Analytic Network Process (ANP). In the second module, the alternative advanced-technology projects are ranked using a customized fuzzy Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS). We demonstrate the applicability of the proposed framework through a case study at the Kennedy Space Center.     

CHM: an annotation- and component-based hypervideo model for the Web

Hypervideos are hypermedia documents that focus on video content. While they have long been deployed using specialized software or even hardware, the Web now offers a ground for them to fit into standardized languages and implementations. However, hypervideo design also currently uses very specific models limited to a single class of documents, or very generic hypermedia models that may not appropriately express their specific features. In this article we describe such features, and we introduce CHM, an annotation-driven and component-based model to conceptualize hypervideos through a high level operational specification. An extensible set of high level components is defined to emphasize the presentation and interaction features modeling, while lower level components offer more flexibility and customization opportunities. Being annotation-based, the model promotes a clear separation between video content/metadata and their various potential presentations. We also describe WebCHM, an implementation of CHM with standard Web technologies that provides a general framework to experiment with hypervideos on the Web. Two examples are provided as well as a preliminary usage study of the model and its implementation to validate our claims and proposals.     

Dynamic response analysis of wind turbines under blade pitch system fault,grid loss,and shutdown events

This study focuses on the dynamic responses of land‐based and floating wind turbines under blade pitch system fault and emergency shutdown conditions. The NREL 5 MW turbine is studied. A hydraulic pitch system is considered, and the faults under study are events with a seized blade or a blade running out of control. Emergency shutdown is defined as a fast pitch‐to‐feather maneuver of the blades. Load cases with power production and grid fault with ensuing shutdown are also analysed for comparison. The fault scenarios and the blades' fast pitching activity are simulated using HAWC2 through external Dynamic Link Libraries. On the basis of the time‐domain simulations, the response characteristics of the land‐based and the floating turbines in the four design load cases are compared. The load effects from the fault conditions are compared with the operational cases. Strong system dynamics and resonant responses, such as the tower elastic mode and the yaw resonant response, are elicited during shutdown. If the pitch system has a fault and one blade is hindered from normal pitching, the uneven load distribution of the blades leads to large structural and motion responses. For both turbines, the response maxima vary cyclically with the instantaneous azimuth when the blades start pitching to feather. For the floating wind turbine, the interaction of waves and wind also affects the results. The effect of the pitch rate during shutdown is analysed. The responses of the land‐based turbine in grid loss and shutdown conditions are proportional to the pitch rate, whereas decreased sensitivity is found in the cases with pitch system faults. For the floating turbine, the effect of the pitch rate is small, and reduced pitch and yaw motion extremes are observed as the pitch rate increases. Copyright © 2013 John Wiley & Sons, Ltd.     

Positive and normative use of fuzzy DEA‐BCC models: A critical view on NATO enlargement

Data envelopment analysis (DEA) is a widely used mathematical programming approach for comparing the input and output of a set of comparable decision‐making units (DMUs) by evaluating their relative efficiency. The traditional DEA methods require accurate measurement of both the inputs and outputs. However, the real evaluation of the DMUs is often characterized by imprecision and uncertainty in data definitions and measurements. The development of fuzzy DEA (FDEA) with imprecise and ambiguous data has extended the scope of application for efficiency measurement. The purpose of this paper is to develop a fuzzy DEA framework with a BCC model for measuring crisp and interval efficiencies in fuzzy environments. We use an α‐level approach to convert the fuzzy Banker, Charnes, and Cooper (BCC) (variable returns to scale) model into an interval programming model. Instead of comparing the equality (or inequality) of the two intervals, we define a variable in the interval to satisfy our constraints and maximize the efficiency value. We present a numerical example to show the similarities and differences between our solution and the solutions obtained from four fuzzy DEA methods in the literature. In addition, a case study for NATO enlargement is presented to illustrate the applicability of the proposed method.     

Autonomous vehicles: challenges,opportunities, and future implications for transportation policies

This study investigates the challenges and opportunities pertaining to transportation policies that may arise as a result of emerging autonomous vehicle (AV) technologies. AV technologies can decrease the transportation cost and increase accessibility to low-income households and persons with mobility issues. This emerging technology also has far-reaching applications and implications beyond all current expectations. This paper provides a comprehensive review of the relevant literature and explores a broad spectrum of issues from safety to machine ethics. An indispensable part of a prospective AV development is communication over cars and infrastructure (connected vehicles). A major knowledge gap exists in AV technology with respect to routing behaviors. Connected-vehicle technology provides a great opportunity to implement an efficient and intelligent routing system. To this end, we propose a conceptual navigation model based on a fleet of AVs that are centrally dispatched over a network seeking system optimization. This study contributes to the literature on two fronts: (i) it attempts to shed light on future opportunities as well as possible hurdles associated with AV technology; and (ii) it conceptualizes a navigation model for the AV which leads to highly efficient traffic circulations.

     

Using UV pretreatment to enhance biofiltration of mixtures of aromatic VOCs

Mixtures of airborne toluene and o-xylene, two relatively recalcitrant volatile organic compounds (VOCs), were treated effectively using integrated UV-biofiltration. The set-up consisted of a biofilter receiving UV-pretreated stream and a reference biofilter receiving no pretreatment. Experimental conditions included UV fluences of 6 and 12 mJcm(-2) as well as air flow rates of 6.3 and 9.4 Lmin(-1), corresponding to biofilter empty bed retention times (EBRTs) of 45 and 30s, respectively. The inlet concentration of organics (toluene and o-xylene) ranged between 70 and 650 mg(carbon)m(-3). The UV-biofilter consistently provided removal efficiencies of greater than 95% over the range of toluene and o-xylene inlet concentrations. Also, the coupled UV-biofiltration system provided up to 60% additional contaminant removal compared to the sum of that offered by UV and reference biofilter, demonstrating the synergistic effect of UV on biofilter performance. The UV photooxidation partially oxidized a fraction of toluene and o-xylene into water soluble and more biodegradable intermediates, such as acetaldehyde and formaldehyde, which were readily removed in the downstream biofilter. These intermediates along with up to 20ppmv ozone, formed through the photolysis of oxygen by 185 nm UV, contributed to the enhanced degradation of parent VOCs in the biofilter as well as the absence of any inhibitory effects of the VOCs on one another. Also, the presence of ozone helped control the growth of excess biofilm in the UV-coupled biofilter. While the standalone biofilter showed significant pressure drop increase (of up to 14 mm H(2)Om(-1) of the bed) over the course of experiment, the UV-coupled biofilter maintained a relatively low pressure drop of less than 3 mmH(2)Om(-1) of the bed.