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  • 1
    Electronic Resource
    Electronic Resource
    Numerische Berechnung der natürlichen Konvektion in einem waagerechten Kanal mit ungleichen Endtemperaturen (1980)
    Springer
    Heat and mass transfer 14 (1980), S. 269-280 
    Details
    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 Die Arbeit berichtet über eine Lösung mit finiten Differenzen der natürlichen Gegenströmung in einem horizontalen adiabaten Kanal mit kreisförmigem oder rechteckigem Querschnitt bei ungleichen Endtemperaturen. Die natürliche Gegenströmung soll voll ausgebildet sein. Das Ergebnis zeigt, daß die Strömung aus einer starken axialen Gegenströmung und vier überlagerten sekundären Wirbeln in den vier Quadranten des Querschnitts besteht. Man erhält auch die Temperaturänderung längs der Rohrwand, wie sie für mäßige Rayleigh-Zahlen bisher nicht mitgeteilt wurde. Die Verwendung der berechneten Wandtemperatur bei Untersuchungen über thermischen Spannungen wird diskutiert. Die numerischen Ergebnisse wurden auch verwendet, um die Anwendbarkeit analytischer Voraussagen über das Strömungsfeld in rechteckigen Kanälen abzuschätzen.
    Notes: Abstract The paper reports a finite difference solution for the natural counterflow generated in a horizontal adiabatic duct with different end-temperatures. Ducts with circular and rectangular cross-section are considered. The natural counterflow is modeled as fully-developed. The numerical results demonstrate that the flow consists of a strong axial counterflow superimposed on four secondary eddies situated in the four quadrants of the cross-section. The paper documents the temperature variation around the wall of a pipe, in a moderate Rayleigh number range not documented previously. The use of the wall temperature information in thermal stress analysis is discussed. The numerical results are also used to assess the applicability of analytical predictions for the flow field in ducts with rectangular cross-section.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01618358
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  • 2
    Electronic Resource
    Electronic Resource
    Constructal tree networks for the time-dependent discharge of a finite-size volume to one point (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 3042-3050 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This paper shows that the time needed to discharge a volume to a concentrated sink can be minimized by making appropriate changes in the geometry of the flow path. The time-dependent flow of heat between a volume and one point is chosen for illustration, however, the same geometric optimization method (the constructal principle) holds for other transport processes (fluid flow, mass transfer, conduction of electricity). There are two classes of geometric degrees of freedom in designing the flow path: the external shape of the volume, and the distribution (amount, location, orientation) of high-conductivity inserts that facilitate the volumetric collection of the discharge. The optimization of flow path geometry is executed in a sequence of steps that starts with the smallest volume elements and proceeds toward larger and more complex volume sizes (first constructs, second constructs, etc.). Every geometric feature is the result of minimizing the time of discharge, or the resistance in volume-to-point flow. The innermost details of the structure have only a minor effect on the minimized time of discharge. The high-conductivity inserts come together into a tree-network pattern which is the result of a completely deterministic principle. The interstices are equally important in this optimal design, as they are occupied by the low-conductivity material in which the energy charge was stored initially. The paper concludes with a discussion of the relevance on this deterministic principle—the constructal law—to predicting structure in natural flow, and to understanding why the geometry of nature is not fractal. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.368458
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  • 3
    Electronic Resource
    Electronic Resource
    Constructal-theory tree networks of "constant" thermal resistance (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 1136-1144 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this article we show that the global thermal resistance to flow between a volume and one point can be reduced to unprecedented levels by shaping the external boundary of each volume element. This degree of freedom is optimized, next to internal features such as the shape and volume fraction of the high-conductivity channels. The volume is covered in a sequence of optimization and assembly steps that proceeds toward larger sizes. The resulting architecture is a leaf-like tree structure with high-conductivity nerves and low-conductivity leaf material. The same constant resistance characterizes the flow from each point on the periphery of the structure to the common sink point. Nearly optimal structures in which the leaf shapes are replaced by needle-like (triangle-in-triangle) shapes are also developed. The fractal-like character of these designs and their relevance to the trend toward fractal-like properties in natural flow structures are discussed in the concluding section of the article. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370855
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  • 4
    Electronic Resource
    Electronic Resource
    Three-dimensional tree constructs of "constant" thermal resistance (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 7107-7115 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This article extends to three-dimensional heat flow the constructal method of minimizing geometrically the thermal resistance between a heat-generating volume and one point. Optimized is the geometry of each volume element, and the shape and distribution of high-conductivity inserts. The new feature is the maximization of the amount of heat-generating material that operates at temperatures close to the hot-spot level (Tmax). Volume elements and subsequent constructs acquire optimal shapes where all the external surfaces are isothermal at Tmax. The same, constant thermal resistance separates each surface point (Tmax) and the common heat-sink point (Tmin). The optimized architecture is pine-cone-like, with high-conductivity nerves and low-conductivity filling (and heat-generating) material. The similarities between the constant-resistance structures and the three-dimensional tree networks found in nature are discussed. The analogy between evolutionary flow systems and evolutionary mechanical support systems is reasoned based on the same (constructal) principle of pursuing objective (purpose) subject to global and local constraints. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.371799
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  • 5
    Electronic Resource
    Electronic Resource
    Constructal tree networks for heat transfer (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 89-100 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This paper addresses the fundamental problem of how to connect a heat generating volume to a point heat sink by using a finite amount of high-conductivity material that can be distributed through the volume. The problem is one of optimizing the access (or minimizing the thermal resistance) between a finite-size volume and one point. The solution is constructed by covering the volume with a sequence of building blocks, which proceeds toward larger sizes (assemblies), hence, the "constructal" name for this approach. Optimized numerically at each stage are geometric features such as the overall shape of the building block, its number of constituents, and the internal distribution of high-conductivity inserts. It is shown that in the optimal design, the high-conductivity material has a distribution with the shape of a tree. Every aspect of the tree architecture is deterministic: the shapes of the largest assembly and all its constituents, the number of branches at each level of assembly, the relative position of building blocks in each assembly, and the relative thicknesses of successive branches. The finer, innermost details of the tree architecture (e.g., the branching angle) have a negligible effect on the overall thermal resistance. The main conclusion is that the structure, working mechanism, and minimal resistance of the tree network can be obtained deterministically, and that the constrained optimization of access routes accounts for the macroscopic structure in nature. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.365853
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  • 6
    Electronic Resource
    Electronic Resource
    Theory of instantaneous sinuous structure in turbulent buoyant plumes (1982)
    Springer
    Heat and mass transfer 16 (1982), S. 237-242 
    Details
    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 Diese Arbeit versucht, die flatternde Bewegung turbulenter Auftriebsfahnen und ihre großräumige gewundene Struktur aufzuklären. Man geht davon aus, daß der nichtzähe Bereich der Fahne (die „Fahnensäule“) elastische Eigenschaften besitzt ähnlich jener elastischer Stäbe, die longitudinalen Verdichtungen unterworfen sind. Die gerade Fahnensäule ist nicht stabil und verbiegt sich. Der Abstand zwischen zwei Krümmungen ist dem örtlichen Fahnendurchmesser proportional, d. h. die Formen aller gekrümmten Fahnen sind geometrisch ähnlich. Die gekrümmte Fahne bricht periodisch zusammen infolge der Wechselwirkung ihrer zeitlichen Krümmungen und der ruhenden Umgebung. Dadurch entstehen intermittierend großräumige Auftriebswirbel am Umfang turbulenter Auftriebsfahnen.
    Notes: Abstract This paper reports a theory which explains the flickering motion of turbulent plumes as well as their large-scale sinuous structure. The theory is based on the fact that the inviscid region of the plume (the “plume column”) possesses elastic properties analogous to those of elastic rods subjected to longitudinal compression. It is shown that the straight plume column is not stable and buckles. The distance between two consecutive elbows is proportional to the local plume diameter, in other words, the shapes of all buckled plumes are geometrically similar. A buckled plume collapses periodically due to the interaction of its lateral elbows with the stagnant ambient. This interaction is responsible for the intermittent formation of large-scale buoyant eddies on the periphery of the turbulent plume.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01375648
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  • 7
    Electronic Resource
    Electronic Resource
    Radioimmunoanalysis of the immune response and tissue lipoperoxidation of rats for low doses contaminated with tritiated water (1996)
    Springer
    Journal of radioanalytical and nuclear chemistry 204 (1996), S. 247-252 
    Details
    ISSN: 1588-2780
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Notes: Abstract The paper presents the evaluation of the humoral immune response and liver and kidney lipoperoxidation on rats acutely and chronically contaminated with low doses of tritiated water (HTO). The contamination doses for both situations were 0.5 cSv, 5 cSv and 10 cSv. By humoral immune response analysis we mean the measurement, through a radioimmunoanalysis (RIA) method, of the two intrinsic parameters of an antiserum, that is, the mean antibodies concentration and the mean antibodies affinity constant. We followed the liver and kidney lipidic peroxidation through malondialdehyde (MDA) formation assayed by the thiobarbituric acid (TBA) reaction. The humoral immune response and lipoperoxidation have been compared with the response of an uncontaminated group by the Studentt test.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02060313
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