1,418 research outputs found
Difference points in extractive and reactive cascades. II — Generating design alternatives by the lever rule for reactive systems
No full textUsing linear combinations of vectors in composition space, we formulate a lever rule for reactive distillation columns. This lever rule facilitates the proposal of alternative sequences of reactive distillation systems by allowing us to visualize how material balance constraints move as a Function of reaction "turnover". our approach uses the concept of a pseudo-feed, which is the composition that results from mixing column distillate and bottom products. Our lever rule for reactive distillation columns uses linear combinations of so-called reaction difference points, stoichiometric coefficient vectors of reactants and products, and composition vectors. When a reaction causes no change in the total number of moles, the reaction difference point moves to infinity (Hauan, Omtveit & Lien (1996). Paper 5f, A.I.Ch.E. Annual Meeting, Chicago, Hauan, Westerberg & Lien (1999a). Chemical Engineering Science, 55(6), 1053-1075, Hauan, Ciric, Westerberg & Lien (1999b). Chemical Engineering Science, in press). We show how to carry out all geometric constructions entirely within a finite composition domain by decomposing the total stoichiometric coefficient vector into product and reactant stoichiometric coefficient vectors. In this case the lever rule compares distances along two parallel vectors. For an infinite extractive difference point (Westerberg & Wahnschafft (1996). Advances in Chemical Engineering, 23, 63-170) we can confine all geometric manipulations when proposing alternative reactive distillation processes to a finite composition domain by combining the vectors in a different order. (C) 2000 Elsevier Science Ltd. All rights reserved
Circumventing an azeotrope is reactive distillation
No full textUsing a McCabe-Thiele diagram, we explain nonintuitive behavior in a binary reactive distillation column where we react and separate two isomers displaying a maximum boiling azeotrope. Placing sufficient reaction on only two trays in the top section of the column, we shift the top operating line to Lie below the 45 degrees line. On lower nonreacting trays, we then easily step past the azeotrope. Once past the azeotrope, we even find that the column temperature decreases as we step down the column
A graphical method for designing reactive distillation columns II. The McCabe-Thiele method
No full textThis paper shows how to construct a McCabe-Thiele diagram for binary reactive distillation. We consider two types of reaction that are consistent with binary mixtures: isomerization (R1 <-> P1) and decomposition (R1 <-> 2P1). We can account for reaction by tracking only two features of the diagram while constructing it. First, the intersection point of the operating line with the y = x line can be called the reactive cascade difference point, and it moves in a manner directly determined by the ratio of the molar extent of reaction (or reaction turnover flowrate) to the product flowrate. Second, the heat supplied (removed) by reaction decreases (increases) the slope of the operating line while not changing the location of the reactive cascade difference point. By tracking these two features, one can quickly sketch such a diagram. We also show how to construct a McCabe-Thiele diagram if the reaction zone is only at the feed stage. Finally, we discuss a case in which the reactive cascade difference point moves past the feed composition and the bottom product composition is less pure than the feed composition
A graphical method for designing reactive distillation columns I. The Ponchon-Savarit method
No full textWe show how to construct a Ponchon-Savarit diagram for a binary reactive distillation column, illustrating it specifically for isomerization and decomposition reactions. We first show the properties needed for points to lie on a straight line in composition/enthalpy space. Then, for the isomerization reaction, we show how to step off the stages using a reactive cascade difference point. In the Ponchon-Savarit diagram, the reactive cascade difference point has two elements. One is the composition coordinate formed as a linear combination of stoichiometric coefficient vectors and the top product composition. The other is the enthalpy coordinate formed by combining the top product molar enthalpy, the condenser molar duty and the molar heat of reaction. Finally, and in a similar manner, we construct the Ponchon-Savarit diagram for a decomposition reaction.
Influence of temperature and sliding speed on the subsurface microstructure evolution of EN AW-6060 under sticking friction conditions
No full textThis article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in AIP Conference Proceedings 1896, 140012 (2017) and may be found at https://doi.org/10.1063/1.5008168.The microstructure evolution of the friction boundary layer of the aluminum alloy EN AW-6060 was investigated. Sticking friction tests at different temperatures and sliding speeds were carried out. A severe deformation below the friction surface was observed by means of LOM and EBSD mapping. Thus, the thickness variation and the grain structure of the high deformation zone could be described. Fibrous structure was observed at 300 °C and 400 °C, while equiaxed grains with high misorientation angle (>15°) were generated at higher temperatures. Additionally, abnormal grain growth and coarse grains were detected at high sliding speeds (10 mm/s, 42 mm/s) at 450°C and 500 °C respectively
Author-Suggested, Weighted Citation Index: A Novel Approach for Determining the Contribution of Individual Researchers
No full textA novel scientometric index, named ‘author-suggested, weighted citation index’ (Aw-index) is proposed to indicate the scientific contribution of any individual researcher. For calculation of the Aw-index, it is suggested that during the submission of a scholarly article, the corresponding author would provide a statement, agreed upon by all the authors, containing weightage factors against each author of the article. The author who contributed more to the article would secure a higher weightage factor. The summation of the weightage factors of all the authors of an article should be unity. The citation points a researcher receives from a scholarly publication is the product of his/her weightage factor for that article and the total number of citations of the article. The Aw-index of any individual researcher is the summation of the citation points he/she receives for all his/her publications as an author. The Aw-index provides the opportunity to the group of authors of a multi-authored article to determine the quantum of partial citations to be attributed to each of them. Through an illustrative example, a comparison of the proposed index with the major scientometric indexes is presented to highlight the advantages of the Aw-index
Influence of Process Parameters on the Quality of Aluminium Alloy EN AW 7075 Using Selective Laser Melting (SLM)
No full textAbstractSelective laser melting (SLM) is an additive manufacturing process, forming the desired geometry by selective layer fusion of powder material. Unlike conventional manufacturing processes, highly complex parts can be manufactured with high accuracy and little post processing. Currently, different steel, aluminium, titanium and nickel-based alloys have been successfully processed; however, high strength aluminium alloy EN AW 7075 has not been processed with satisfying quality. The main focus of the investigation is to develop the SLM process for the wide used aluminium alloy EN AW 7075. Before process development, the gas-atomized powder material was characterized in terms of statistical distribution: size and shape. A wide range of process parameters were selected to optimize the process in terms of optimum volume density. The investigations resulted in a relative density of over 99%. However, all laser-melted parts exhibit hot cracks which typically appear in aluminium alloy EN AW 7075 during the welding process. Furthermore the influence of processing parameters on the chemical composition of the selected alloy was determined
Zhedanov's Algebra AW(3) and the Double Affine Hecke Algebra in the Rank One Case. II. The Spherical Subalgebra
No full textThis paper builds on the previous paper by the author, where a relationship between Zhedanov's algebra AW(3) and the double affine Hecke algebra (DAHA) corresponding to the Askey-Wilson polynomials was established. It is shown here that the spherical subalgebra of this DAHA is isomorphic to AW(3) with an additional relation that the Casimir operator equals an explicit constant. A similar result with q-shifted parameters holds for the antispherical subalgebra. Some theorems on centralizers and centers for the algebras under consideration will finally be proved as corollaries of the characterization of the spherical and antispherical subalgebra
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Extensions and amplifications of a traffic model of Aw and Rascle
No full textIn a recent paper [1] Aw and Rascle introduced a new model of traffic on a uni-directional highway. Here the author studies an extension of this model, one which accounts for drivers attempting to travel at their maximum allowable speed. The author looks at a Lagrangian reformulation of this problem; a formulation that leads to an effective computational algorithm for solving the resulting system. He also investigates approximation scheme introduced by Dafermos [5] for scalar conservation laws and demonstrates that this Dafermos scheme works well on this 2 x 2 system
Automating the determination of wave speed using the pu-loop method
No full textThe PU-loop (pressure-velocity loop) is a method for determining wave speed and relies on the linear relationship between the pressure and velocity in the absence of reflected waves. This linearity of the PU-loop during early systole, which is directly related to wave speed, has always been established by eye. This paper presents a new technique that establishes this linearity and thus determining wave speed online. Pressure and flow were measured in the ascending aorta of 11 anesthetised dogs. The slope of the PU-loop, indicating wave speed was determined by eye and by using the new technique. The difference between the slopes of the two methods is in the order of 3%. The new technique is convenient and allows for the online assessment of wave speed, which could be used as a bedside tool for the assessment of arterial compliance
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