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  • 1
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 1041-1059 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A quantitative, model-based approach to the safety verification problem for general processing systems operating in the discrete time domain is presented. It is recognized that the operation of most of these systems involves both discrete and continuous characteristics. Therefore, an appropriate modeling framework is proposed, within which models of purely discrete, purely continuous and hybrid systems of arbitrary complexity can be constructed consistently. The models developed can then be incorporated into a safety verification formulation, which allows the identification of potential hazards that may occur while operating such systems, together with the combinations of events that lead to them. Apart from the dynamic process model, the data required for carrying out the analysis include the space of possible disturbances and the set of operating regimes that are considered to be unsafe or undesirable from the operability point of view. The formulation results in a mixed-integer optimization problem. A number of simple example problems presented illustrate the main ideas of the proposed technique, and the solution of an industrial-scale case study demonstrates its applicability.
    Additional Material: 22 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 12 (1972), S. 317-322 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The dependence of true stress on the extension ratio of PVC threads has been determined for a wide range of extension rates. Since the polymer subjected to deformation was in the high-elastic state (at temperatures from 90 to 160°), the deformations were predominantly high-elastic. The dependence of true stress on the amount of high-elastic deformation is described by the Mooney-Rivlin equation.Relaxation moduli have been found on the basis of measurements of stress relaxation at constant deformation after various extension ratios were attained at different rates. Within the limits of deformation regimes at which the true stress is an increasing function of extension ratio the relaxation moduli do not depend on extension ratio and rate of extension. This enables one to arrive at a master curve of the relaxation modulus versus relaxation time with the reservation indicated above concerning the increasing character of the dependence of true stress on extension ratio. The relaxation spectrum represented by the high-elasticity plateau has been determined from the relaxation moduli according to the first approximation.The experimental data for a very wide range of deformation regimes and temperatures are presented in the form of an invariant dependence of the ratio of true stress to the rate of deformation on the product of deformation time by extension ratio.The ultimate strength of the specimens frozen rapidly after the attainment of definite extension ratios is determined by the accumulated high-elastic deformation.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 24 (1978), S. 869-879 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The characteristics of a vortex found at the entry of a 2:1 and 4:1 contraction for viscoelastic fluids is investigated. Two distinct flow regimes are identified in the contraction flow field: a vortex growth regime and a divergent flow regime. In the vortex flow regime, rheological forces are found to dominate the flow, with the vortex detachment length being a linear function of the Weissenberg number. In the divergent flow regime, the flow is found to diverge at the center line upstream of the vortex detachment plane, and the vortex size decreases with increasing flow rates. Inertial forces are important in the divergent flow regime. The entry flow characteristics for the 2:1 and 4:1 contraction are quantified in terms of the vortex detachment length as a function of Reynolds and Weissenberg number over the range of 0:2 〈 N′Re 〈 200 and 0.10 〈 NWS 〈 0.7.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 21 (1975), S. 550-553 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Experimental data are presented to verify the numerical model discussed in Part I. The experimental techniques employed for recovering flow patterns and for point velocity measurement are described and justified. The measured reattachment lengths, the recorded flow patterns, and the developing axial velocity field all show excellent agreement with the model predictions.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 25 (1979), S. 152-159 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: For every viscoelastic fluid studied in the contraction geometry, it was found that increasing the flow rate beyond a certain limit resulted in disturbance to the stable entry flow patterns described in Parts I and II. An examination of the development of the entry flow disturbances was carried out using still and cine photography. Still photographs are presented to illustrate the characteristics of the unstable flow patterns. The time varying nature of the flow has been recorded on a cine film Flow Patterns in Abrupt Entry Flow of Viscoelastic Fluids which is available for loan. Critical condition criteria for the onset of the periodic flow disturbances were obtained in terms of the fundamental fluid properties and are presented and compared with other suggested criteria for the onset of unstable entry flow of viscoelastic fluids.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 31 (1985), S. 215-221 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: It is shown that the conventional Smith dead-time compensator can be modified in a fashion which leads to significant improvements in its regulatory capabilities for measurable disturbances or inputs. The proposed modification utilizes effectively the existing prediction capabilities of the conventional dead-time compensator and eliminates the need for a separate feedforward controller in many circumstances under which it is normally employed. The modified dead-time compensator possesses simultaneous feedforward and feedback actions. An additional tuning parameter which controls the degree of dead-time cancellation allows the designer to shape the response according to requirements. Illustrative examples show the advantages of the modified scheme.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 16 (1970), S. 1088-1091 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 24 (1978), S. 992-999 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Center-line velocities and developing velocity profiles are presented for viscoelastic fluids flowing in a 2:1 and 4:1 abrupt entry contraction. Two flow regimes are clearly identified: a vortex growth regime and a divergent flow regime. Dramatic differences in the velocity field are observed and discussed for the two flow regimes. A kinematic model based on the velocity field data is proposed for vortex growth flow.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 37 (1991), S. 871-885 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Waxy crude oils are highly non-Newtonian materials known to cause handling and pipelining difficulties and whose flow properties are time- and history-dependent. Experimental techniques are described that enable reproducible steady-state flow property data to be obtained from rotational viscometers. The flow properties are shown to depend strongly on the shear rate applied during cooling (shear history effect). This leads to a definable minimum operating point below which flow in a waxy crude oil pipeline would cease. Modified pipeline design techniques are presented for both laminar and turbulent flow at temperatures below the pour point, and it is shown that existing techniques overestimate the flow rate in laminar flow by the order of 100%. The modified design techniques can be used to quantitatively assess the performance of flow improver (pour point depressant) additives under steady-state conditions.
    Additional Material: 17 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 21 (1975), S. 540-549 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A numerical solution for the axisymmetric flow of an inelastic power-law fluid through an abrupt circular expansion is presented. The equations of motion were solved using an Alternating Direction Implicit method. Both a stream tube-real tube and a real tube-real tube model were investigated and the conditions for significant upstream diffusion of momentum were specified. Secondary flow characteristics and the bulk flow field development are predicted as a function of the flow behavior index (n) and of the Reynolds number. Some results are presented to show the influence of the expansion ratio.
    Additional Material: 13 Ill.
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