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  • 1
    ISSN: 1432-1181
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Description / Table of Contents: Zusammenfassung In dem vorliegenden Beitrag wird die numerische Berechnung der Druckverluste bei nichtisothermer, laminarer Rohrströmung von nicht-Newtonschen Potenzgesetz-Flüssigkeiten und für verschiedenartige, thermische Randbedingungen behandelt (konnstante und veränderliche Rohrwandtemperatur sowie konstanter und veränderlicher Wärmestrom längs der Rohrwand). Dabei werden sowohl die temperaturabhängigen Stoffwerte des strömenden Mediums als auch die Reibungsdissipation berücksichtigt. Die Ergebnisse numerischer Berechnungen sind graphisch in 7 Abbildungen wiedergegeben und ausgewählte, numerische Daten werden in einer Tabelle zusammengestellt. Als Endergebnis wird eine verallgemeinerte Formel für die Berechnung der Widerstandszahl hergeleitet, die für alle hier betrachteten, thermischen Randbedingungen gilt. Zusätzlich wird eine Näherungsformel für die Berechnung der Widerstandszahl vorgeschlagen, welche ermöglicht, die örtliche Widerstandszahl zu errechnen, vorausgesetzt, daß die sogenannte “Filmtemperatur” an nur einer Stelle des Rohrquerschnittes gemessen wurde. Die Ergebnisse dieses Beitrages mögen von Nutzen sein für diejenigen Forschungsingenieure, die sich mit der Berechnung der Druckverluste bei der Auslegung von Wärmeaustauschern sowie Rohrleitungen für den Transport der Polymerschmelze befassen.
    Notes: Abstract This work is concerned with numerical computations of pressure-drops in non-isothermal, laminar flow of power law fluids in circular tubes with various thermal wall conditions (constant and variable wall temperature as well as constant and variable wall heat flux). In the paper both temperature dependent rheological fluid properties and viscous dissipation are included. The results of numerical computations are plotted in 7 figures and selected numerical data are presented tabularly. As a result an extended friction factor formula is derived similar to that one introduced by Metzner and Reed. In addition, an approximative friction factor formula is proposed which enables the calculation of local friction factor if only one value of the so called “film temperature” has been previously measured. This formula is valid for all the thermal wall conditions considered in this work. The results of the present paper are intended to be very helpful for design engineers while calculating the pressure losses in some heat exchangers and pipes for transporting polymer melts.
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  • 2
    ISSN: 1432-1181
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Description / Table of Contents: Zusammenfassung In dem vorliegenden Beitrag wird die nichtisotherme, laminare, stationäre Spaltströmung einer Newtonschen Flüssigkeit untersucht. Dabei wird gleichzeitige Temperaturabhängigkeit der dynamischen Viskosität und des Wärmeleitkoeffizienten angenommen. Zur Lösung der für solche Strömung geltenden Differentialgleichungen (Impuls- und Energiegleichungen) werden zwei analytische Näherungsmethoden eingesetzt und zwar: das “Gauss'sehe Prinzip des kleinsten Zwanges” sowie die “Methode der optimalen Linearisierung.” Die erzielten Ergebnisse werden-im Sonderfall der Temperaturabhängigkeit allein der dynamischen Viskosität -mit den entsprechenden Resultaten verglichen, die im Aufsatz [9] nach der Näherungsmethode von Slezkin und Targ ermittelt wurden.
    Notes: Abstract In the present paper a nonisothermal laminar steady flow of a Newtonian fluid in a flat gap is considered. It is assumed that both the dynamic viscosity and thermal conductivity vary with temperature. For solving the differential equations (momentum and energy principles) governing the problem in consideration two approximate methods are applied, i.e. the “Gauss' principle of least constraint” and the “method of optimal linearization”. In the case when only the dynamic viscosity varies with temperature the results obtained in this paper are compared to the results achieved in paper [9] by using the approximate method of Slezkin and Targ.
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  • 3
    ISSN: 1432-1181
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Description / Table of Contents: Zusammenfassung In dem vorliegenden Beitrag wird die Wärmeübertragung bei laminarer Rohrströmung von denjenigen nicht-Newtonschen Flüssigkeiten untersucht, die dem Potenzansatz nach Ostwald-de Waele gehorchen. Es werden Grundgleichungen für den zu behandelnden Vorgang hergeleitet, unter besonderer Berücksichtigung viskoser Dissipation sowie der Temperaturabhängigkeit rheologischer Parameter des strömenden Mediums. Der Einfluß innerer Wärmequellen wird hingegen vernachlässigt. Zur numerischen Lösung der hergeleiteten Differentialgleichungen wird die Methode der finiten Differenzen eingesetzt, unter der Voraussetzung, daß die Temperatur der Rohrwand unverändert bleibt (Randbedingungen erster Art). Die gewonnenen Ergebnisse wurden graphisch dargestellt sowie mit den von anderen Autoren erarbeiteten Resultaten verglichen. Es wurde dabei eine recht gute Übereinstimmung festgestellt. Der hier vorliegende Beitrag soll als eine Verallgemeinerung des Aufsatzes [5] gehalten werden, der neulich in dieser Zeitschrift von Krishnan und Sastri veröffentlicht wurde.
    Notes: Abstract This work is concerned with laminar heat transfer in circular tubes to power law fluids with temperature-dependent rheological properties. Basic equations governing the problem under consideration are derived including effects of viscous dissipation but neglecting internal heat generation. The derived equations are solved numerically by means of finite-difference scheme and for the boundary conditions of constant wall temperature. The results are presented in form of graphs and compared to the computations carried out by other authors. A very good agreement is stated. The present work is intended to be an extension of the paper which has been recently published by Krishnan and Sastri [5].
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  • 4
    ISSN: 0945-3245
    Keywords: AMS (MOS): 65R20 ; CR: G1.9
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Summary The boundary element method (BEM) leads to a system of linear equations with a full matrix, while FEM yields sparse matrices. This fact seems to require much computational work for the definition of the matrix, for the solution of the system, and, in particular, for the matrix-vector multiplication, which always occurs as an elementary. In this paper a method for the approximate matrix-vector multiplication is described which requires much less arithmetical work. In addition, the storage requirements are strongly reduced.
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  • 5
    ISSN: 1432-0630
    Keywords: 72.40.+w ; 85.60.Gz
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract This paper considers the Hg1−x Zn x Te alloy system as a potential material for the fabrication of infrared photodiodes. The influence of different junction current components (diffusion, tunneling and depletion layer currents) on the R 0 A product of n+-pHg1−x Zn x Te photodiodes is analysed. The upper theoretical limits of the R 0 A product and detectivity are determined. Results of calculations are compared with experimental data reported by other authors and those measured in our laboratory. Preliminary results on related technology and the properties of Hg1−x Zn x Te prepared by the ion-etching technique are presented.
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  • 6
    ISSN: 1588-2780
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The effect of stable iodine on the radiolysis of the TBP-dodecane solvent was examined at two nitric acid concentrations. The results obtained indicate that presaturation of the solvent with stable iodine causes marked increase in the yields of organic nitrites and hydroxy-compounds and decrease of the yield of HDBP, carbonyl and nitro-compounds. The mechanisms of observed effects are discussed.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    ISSN: 1588-2780
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The effect of iodine on the radiolysis of TBP-dodecane-HNO3 systems and the same systems containing the uranium, zirconium and palladium salts was examined. The results obtained indicate that the effect of iodine on the radiolysis products in the systems with and without uranium salt is similar. It has been found also that the effect of iodine on the retention of uranium and zirconium in organic phase depends on nitric acid concentration and is particularly high in the systems with low concentrations of HNO3 containing uranium salt.
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  • 8
    ISSN: 1619-6937
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Description / Table of Contents: Zusammenfassung In der vorliegenden Arbeit wird die Wärmeübertragung bei laminarer Rohrströmung nicht-Newtonscher Potenzgesetz-Flüssigkeiten mit temperaturabhängigen, rheologischen Parametern behandelt. Es werden Grundgleichungen für den zu untersuchenden Vorgang unter besonderer Berücksichtigung der Reibungsdissipation hergeleitet. Der Einfluß innerer Wärmequellen wird hingegen vernachlässigt. Zur numerischen Lösung der hergeleiteten Gleichungen wird die Methode der finiten Differenzen eingesetzt, unter der Voraussetzung, daß die Temperatur der Rohrwand veränderlich ist (Randbedingungen erster Art). Die ausgewerteten Ergebnisse wurden graphisch dargestellt. Der hier vorliegende Beitrag soll als eine Verallgemeinerung der von denselben Autoren verfaßten Arbeit betrachtet werden, die baldmöglichst in [1] veröffentlicht wird.
    Notes: Summary This paper is concerned with laminar heat transfer in circular tubes to power law fluids with temperature-depedent rheological properties. Basic equations governing the problem under consideration are derived including the effect of viscous dissipation but neglecting the internal heat generation. The derived equations are numerically solved by means of finite-difference scheme and for boundary conditions of variable wall temperature. The results are presented in form of graphs. The present work is intended to be an extension of the paper which will be shortly published by the same authors in [1].
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  • 9
    ISSN: 1619-6937
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary This paper deals with laminar, steady heat transfer in flat gaps formed by two wide parallel plates to power law fluids with temperature dependent rheological properties. Basic equations governing the problem to be discussed here are derived including the effects of viscous dissipation but neglecting the internal heat generation. The derived equations of motion, energy and continuity (the last in integral form) have been solved numerically by means of Dufort-Frankel scheme for various thermal wall conditions (constant and variable wall temperature as well as constant and variable wall heat flux). The results of numerical computations are presented in form of graphs illustrating the changes in temperature and velocity profiles as well as in local and mean Nusselt numbers and pressure drops with increasing distance from the inlet cross section. A special attention has been paid to the effects of viscous dissipation and temperature dependent rheological fluid properties on the changes mentioned above. The present work is intended to be an extension of the classical Graetz-Nusselt problem on non-Newtonian power law fluids with temperature dependent rheological properties flowing through a narrow gap formed by two wide parallel plates.
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  • 10
    ISSN: 1619-6937
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary In this paper a new approximative method of calculating the pressure drops in laminar forced convection heat transfer to power law fluids with temperature dependent rheological properties is proposed. These fluids exhibiting a non-Newtonian rheological behaviour are assumed to flow through a flat gap formed by two wide, parallel plane plates. The method to be proposed here makes it possible to calculate the values of local Fanning's friction factor if only one value of the so called “film temperature” has been previously measured. The main advantage of the procedure presented is that it holds for various thermal wall conditions (constant and variable wall temperature as well as wall heat flux). In addition, the effects of viscous dissipation on pressure drops have been taken into account. The results of numerical computations are shown in form of graphs and some comparisons are presented tabularly. The present work is intended to be a supplement to the previous paper by the same authors [1].
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