Heat Transport by Countercurrent Blood Vessels in the Presence of an Arbitrary Temperature Gradient

1990 ◽  
Vol 112 (2) ◽  
pp. 207-211 ◽  
Author(s):  
J. W. Baish
Keyword(s):  
Thermal Conductivity ◽  
Temperature Gradient ◽  
Vascular Tissue ◽  
Asymptotic Methods ◽  
Three Dimensional ◽  
Conductive Materials ◽  
Arbitrary Temperature ◽  
The Mean ◽  
Conductive Fibers ◽  
Arteries And Veins

This paper presents a three-dimensional analysis of the temperature field around a pair of countercurrent arteries and veins embedded in an infinite tissue that has an arbitrary temperature gradient along the axes of the vessels. Asymptotic methods are used to show that such vessels are thermally similar to a highly conductive fiber in the same tissue. Expressions are developed for the effective radius and thermal conductivity of the fiber so that it conducts heat at the same rate that the artery and vein together convect heat and so that its local temperature equals the mean temperature of the vessels. This result allows vascular tissue to be viewed as a composite of conductive materials with highly conductive fibers replacing the convective effects of the vasculature. By characterizing the size and thermal conductivity of these fibers, well-established methods from the study of composites may be applied to determine when an effective conductive model is appropriate for the tissue and vasculature as a whole.

scholarly journals The thermal conductivity of air

1934 ◽  
Vol 144 (853) ◽  
pp. 494-495 ◽  
Keyword(s):  
Thermal Conductivity ◽  
Temperature Gradient ◽  
Parallel Plate ◽  
Systematic Difference ◽  
Hot Wire ◽  
Plate Method ◽  
Metal Plates ◽  
Wire Method ◽  
The Mean ◽  
Plate Apparatus

When Miss Nelson and the writer prepared in 1929 an article for the 'International Critical Tables' on the thermal conductivity of gases, we found that the value for air had been measured by 19 observers and that the mean departure from the mean was 7%. Further the values obtained by the hot wire method by Weber, Gregory and Archer, and Schneider were higher than the value (5.40 X 10 -5 cal. cm. -1 sec. -1 deg. -1 ) which Hercus and the writer had found by a parallel plate method, and higher than 13 of the 14 determinations (including hot wire ones) made previous to 1918. In view of these facts it was desirable to repeat the parallel plate method and to obtain evidence as to whether or not there was a systematic difference between the two methods mentioned. The hot wire method, as used by the experimenters named, has the practical advantages measured, and it is convenient and simple. As carried out in the experiments referred to in which fine wires were used it has the disadvantages that the elimination of the convection effects is not attained with certainly, the temperature gradient in the gas is large (which introduces both theoretical and practical difficulties) and there is a temperature discontinuity at the surface of the wire which has to be determined. Hercus and Sutherland have nearly completed in this laboratory a measurement of the thermal conductivity of air with a parallel plate apparatus. This method has the inherent advantages that there are no convection currents in the horizontal lamina of gas used, that the temperature gradient may be made small, and the temperature disments now in progress radiation is eliminated by using the metal plates at two different separations and considerable improvements have been made us compared with the experiment of Hercus and in their measurement.

Thermal Conductivity of Metal Cloth Heat Pipe Wicks

1987 ◽  
Vol 109 (3) ◽  
pp. 775-781 ◽  
Author(s):  
J. R. Phillips ◽  
L. C. Chow ◽  
W. L. Grosshandler
Keyword(s):  
Thermal Conductivity ◽  
Heat Conduction ◽  
Heat Pipe ◽  
Effective Conductivity ◽  
Correction Term ◽  
Three Dimensional ◽  
Experimental Procedure ◽  
Conductivity Enhancement ◽  
Layer Contact ◽  
The Mean

Heat conduction through a metal cloth wick saturated with a fluid has been investigated. An apparatus used to measure thermal conductivity, in which the condition of wick packing geometry is carefully controlled, and the basic experimental procedure are described. Experimental results are presented and compared to a new mean-gap-conductance model based upon the wick geometry, and to the simple series model. The mean-gap-conductance model evaluates the effects of the mesh geometry, and with the addition of a correction term to account for three-dimensional effects and layer-to-layer contact, the effective conductivity can be accurately predicted. In addition, a correlation of the mean gap which directly includes three-dimensional and contact conductance effects is presented. The correlation predicts the data within 10 percent whereas the series model may be more than 40 percent in error. From a parametric study using the new model, theoretical limits on the maximum and minimum conductivity enhancement have been determined as a function of geometric parameters. The implications of the research on heat pipe wick design are discussed.

Comparison between fluid electron-temperature-gradient driven simulations and Tore Supra experiments on electron heat transport

2007 ◽  
Vol 73 (2) ◽  
pp. 199-206
Author(s):  
B. LABIT ◽  
M. OTTAVIANI
Keyword(s):  
Thermal Conductivity ◽  
Temperature Gradient ◽  
Electron Temperature ◽  
Heat Transport ◽  
Three Dimensional ◽  
High Electron ◽  
Present Contribution ◽  
Electron Thermal Conductivity ◽  
Electron Temperature Gradient ◽  
Electron Heat

Abstract.In recent years, much attention has been devoted to the electron-temperature-gradient (ETG) driven instability as a possible explanation for the high electron thermal conductivity found in most tokamaks. The present contribution assesses whether a specific three-dimensional fluid ETG model can reproduce the conductivity observed in the Tore Supra tokamak [Equipe Tore Supra (presented by R. Aymar) 1989 Plasma Physics and Controlled Nuclear Fusion Research (Proc. 12th Int. Conf., Nice, 1988, Vol. 1.) Vienna: IAEA, p. 9]. Although the model reproduces fairly well the observed critical gradient, a large discrepancy factor, of the order of 50, is found for the ratio between the experimental and the simulated conductivity. On the basis of this study, one must conclude that the electron heat transport cannot be explained only with a fluid ETG turbulence model.

Structure and Thermoelectric Properties of New Quaternary Tin and Lead Bismuth Selenides, K1+xM4-2xBi7+xSe15 (M = Sn, Pb) and K1+xSn5-xBi11+xSe22

2000 ◽  
Vol 626 ◽  
Author(s):  
Antje Mrotzek ◽  
Kyoung-Shin Choi ◽  
Duck-Young Chung ◽  
Melissa A. Lane ◽  
John R. Ireland ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Single Crystal ◽  
Thermoelectric Properties ◽  
Three Dimensional ◽  
Structure Type ◽  
Narrow Gap ◽  
Low Thermal Conductivity ◽  
Seebeck Coefficients ◽  
Metal Atoms ◽  
Anionic Framework

ABSTRACTWe present the structure and thermoelectric properties of the new quaternary selenides K1+xM4–2xBi7+xSe15 (M = Sn, Pb) and K1-xSn5-xBi11+xSe22. The compounds K1+xM4-2xBi7+xSe15 (M= Sn, Pb) crystallize isostructural to A1+xPb4-2xSb7+xSe15 with A = K, Rb, while K1-xSn5-xBi11+xSe22 reveals a new structure type. In both structure types fragments of the Bi2Te3-type and the NaCl-type are connected to a three-dimensional anionic framework with K+ ions filled tunnels. The two structures vary by the size of the NaCl-type rods and are closely related to β-K2Bi8Se13 and K2.5Bi8.5Se14. The thermoelectric properties of K1+xM4-2xBi7+xSe15 (M = Sn, Pb) and K1-xSn5-xBi11+xSe22 were explored on single crystal and ingot samples. These compounds are narrow gap semiconductors and show n-type behavior with moderate Seebeck coefficients. They have very low thermal conductivity due to an extensive disorder of the metal atoms and possible “rattling” K+ ions.

Electron Holographic Nano-Characterization of Gold Catalyst at Interface

2002 ◽  
Vol 727 ◽  
Author(s):  
S. Ichikawa ◽  
T. Akita ◽  
M. Okumura ◽  
M. Haruta ◽  
K. Tanaka
Keyword(s):  
Contact Angle ◽  
Titanium Oxide ◽  
Gold Catalyst ◽  
Three Dimensional ◽  
High Resolution Electron Microscopy ◽  
Electron Holography ◽  
Gold Particles ◽  
Oxide Support ◽  
The Mean ◽  
A Charge

AbstractThe catalytic properties of nanostructured gold catalyst are known to depend on the size of the gold particles and to be activated when the size decreases to a few nanometers. We investigated the size dependence of the three-dimensional nanostructure on the mean inner potential of gold catalysts supported on titanium oxide using electron holography and high-resolution electron microscopy (HREM). The contact angle of the gold particles on the titanium oxide tended to be over 90° for gold particles with a size of over 5 nm, and below 90° for a size of below 2 nm. This decreasing change in the contact angle (morphology) acts to increase the perimeter and hence the area of the interface between the gold and titanium oxide support, which is considered to be an active site for CO oxidation. The mean inner potential of the gold particles also changed as their size decreased. The value of the inner potential of gold, which is approximately 25 V in bulk state, rose to over 40 V when the size of the gold particles was less than 2 nm. This phenomenon indicates the existence of a charge transfer at the interface between gold and titanium oxide. The 3-D structure change and the inner potential change should be attributed to the specific electronic structure at the interface, owing to both the “nano size effect” and the “hetero-interface effect.”

The Influence of Blade Wakes on the Performance of Interturbine Diffusers

1996 ◽  
Vol 118 (2) ◽  
pp. 347-352 ◽  
Author(s):  
R. G. Dominy ◽  
D. A. Kirkham
Keyword(s):  
Performance Modeling ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Two Dimensional ◽  
Correct Performance ◽  
Analysis Methods ◽  
Flow Factor ◽  
The Mean ◽  
Lp Turbine

Interturbine diffusers provide continuity between HP and LP turbines while diffusing the flow upstream of the LP turbine. Increasing the mean turbine diameter offers the potential advantage of reducing the flow factor in the following stages, leading to increased efficiency. The flows associated with these interturbine diffusers differ from those in simple annular diffusers both as a consequence of their high-curvature S-shaped geometry and of the presence of wakes created by the upstream turbine. It is shown that even the simplest two-dimensional wakes result in significantly modified flows through such ducts. These introduce strong secondary flows demonstrating that fully three-dimensional, viscous analysis methods are essential for correct performance modeling.

scholarly journals Proximity of the middle meningeal artery and maxillary artery to the mandibular head and mandibular neck as revealed by three-dimensional time-of-flight magnetic resonance angiography

2021 ◽  
Author(s):  
Daphne Schönegg ◽  
Raphael Ferrari ◽  
Julian Ebner ◽  
Michael Blumer ◽  
Martin Lanzer ◽  
...  
Keyword(s):  
Magnetic Resonance ◽  
Magnetic Resonance Angiography ◽  
Three Dimensional ◽  
Time Of Flight ◽  
Middle Meningeal Artery ◽  
Individual Variability ◽  
Maxillary Artery ◽  
Condylar Process ◽  
The Mean ◽  
Meningeal Artery

Abstract Purpose The close topographic relationship between vascular and osseous structures in the condylar and subcondylar region and marked variability in the arterial course has been revealed by both imaging and cadaveric studies. This study aimed to verify the previously published information in a large sample and to determine a safe surgical region. Methods We analyzed the three-dimensional time-of-flight magnetic resonance angiography images of 300 individuals. Results The mean distance between the middle meningeal artery and the apex of the condyle or the most medial point of the condyle was 18.8 mm (range: 11.2–25.9 mm) or 14.5 mm (range: 8.8–22.9 mm) respectively. The course of the maxillary artery relative to the lateral pterygoid muscle was medial in 45.7% of cases and lateral in 54.3%. An asymmetric course was evident in 66 patients (22%). The mean distance between the maxillary artery and condylar process at the deepest point of the mandibular notch was 6.2 mm in sides exhibiting a medial course (range: 3.7–9.8 mm) and 6.6 mm in sides exhibiting a lateral course (range: 3.9–10.4 mm). The distances were significantly influenced by age, gender, and the course of the maxillary artery. Conclusion Our study emphasizes the marked inter- and intra-individual variability of the maxillary and middle meningeal arterial courses. We confirmed the proximity of the arteries to the condylar process. Extensive surgical experience and thorough preparation for each individual case are essential to prevent iatrogenic vascular injury.

scholarly journals Interactions between Tandem Cylinders in an Open Channel: Impact on Mean and Turbulent Flow Characteristics

Water ◽  
2021 ◽  
Vol 13 (13) ◽  
pp. 1718
Author(s):  
Hasan Zobeyer ◽  
Abul B. M. Baki ◽  
Saika Nowshin Nowrin
Keyword(s):  
Turbulent Flow ◽  
Open Channel ◽  
Recirculation Zone ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Flow Recirculation ◽  
Tandem Cylinders ◽  
Flow Development ◽  
The Mean ◽  
Recirculation Length

The flow hydrodynamics around a single cylinder differ significantly from the flow fields around two cylinders in a tandem or side-by-side arrangement. In this study, the experimental results on the mean and turbulence characteristics of flow generated by a pair of cylinders placed in tandem in an open-channel flume are presented. An acoustic Doppler velocimeter (ADV) was used to measure the instantaneous three-dimensional velocity components. This study investigated the effect of cylinder spacing at 3D, 6D, and 9D (center to center) distances on the mean and turbulent flow profiles and the distribution of near-bed shear stress behind the tandem cylinders in the plane of symmetry, where D is the cylinder diameter. The results revealed that the downstream cylinder influenced the flow development between cylinders (i.e., midstream) with 3D, 6D, and 9D spacing. However, the downstream cylinder controlled the flow recirculation length midstream for the 3D distance and showed zero interruption in the 6D and 9D distances. The peak of the turbulent metrics generally occurred near the end of the recirculation zone in all scenarios.

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