Longitudinal conductivity

For long lengths of anode it is sometimes necessary to extrude one material over another to improve a particular characteristic. Thus titanium may be extruded over a copper rod to improve the longitudinal conductivity and current attenuation characteristics of the former lead alloys may be treated similarly to compensate for their poor mechanical properties. It should he noted that these anodes have the disadvantage that, should the core metal be exposed to the electrolyte by damage to the surrounding metal, rapid corrosion of the former will occur. 

A substantial reduction in the amount of stray current picked up by nearby buried pipes or cables may be achieved by interrupting the longitudinal conductivity of the structure by means of insulating gaps or joints. Care must be taken in siting the gaps, and they should preferably be placed in localities where the current tends to enter the structure and at points on each side of the track where the pipe or cable crosses under the rails. 

Input of thermal energy by effective longitudinal conduction... 

Ljaschenko and Stepko have studied the decrease of the electrical conductivity of very thin CU2O films after these films had chemisorbed methyl alcohol, ethyl alcohol, acetone, and water vapor. Engell (18) has explained this decrease of conductivity by extending the explanation given above to the chemisorption on thin films whose total thickness is less than the thickness of the boundary layer. If is the conductivity before the chemisorption of any of the vapors listed above, the mean longitudinal conductivity after the chemisorption has taken place, and ifiH) then Ak is proportional to the number of the electron... 

In writing this equation, it has been noted that since be lies in the freestream where the temperature is constant, there can be no heat transfer into the control volume through it. Longitudinal conduction effects have also been ignored because the boundary layer is assumed to be thin. This is consistent with the neglect of the effects of longitudinal viscous forces in the derivation of the momentum integral equation. 

Figure 14 Longitudinal conductivity of a single crystal of TTF-TCNQ versus pressure at various temperatures showing the sharp dip at commensurability. (From Ref. 85.)...

ThermalGraph DKA X (0.2 mm), CKD X (50 mm), DKE X (0.003-0.005 mm), DKD X (0.2 mm) - pitch-based thermally conductive fibers which have 50% higher longitudinal conductivity than copper. The filament diameter is 10 pm for all fibers and their length is given in parentheses. 

The underlying substrate of AV nodal reentry is the functional division of the AV node into two (or more) longitudinal conduction pathways, or dual AV nodal pathways." Most practitioners now believe that there are not two distinct anatomic pathways inside the AV node itself. Rather, it is likely that a fanlike network of perinodal fibers inserts into the AV node and represents the second pathway. The two... 

Longitudinal conductivity of a semimetal in a very strong magnetic field [/S] ... 

In Sections 4,5 we used the scaling hypothesis to obtain the longitudinal conductivity. To verify this assumption in the framework of the method we use is very complicated since already... 

For a crossflow exchanger, temperature gradients in the wall exist in the x and y directions (two fluid flow directions). As a result, two longitudinal conduction parameters Xh and Xc are used to take into account the longitudinal conduction effects in the wall. Detailed tabular results are presented in Ref. 15, as reported by Chiou, on the effect of Xh and X, on the exchanger e for an unmixed-unmixed crossflow exchanger. 

Bahnke and Howard s results for C = 1 and C > 5 are the same as those shown in Fig. 17.31a provided that the abscissa NTU is replaced by NTU . The regenerator effectiveness due to longitudinal conduction decreases with increasing values of X and C, with the maximum effect at C -1. 

For C < 1, use the following Razelos method to account for the effect of longitudinal conduction in the wall. 

From the known heat capacity rates on each fluid side, compute C = Cmm/Cmax. From the known UA, determine NTU = fM/Cmin. Also calculate the longitudinal conduction parameter X. With the known NTU, C, X, and the flow arrangement, determine the crossflow exchanger effectiveness (from either closed-form equations of Table 17.6 or tabular/ graphical results from Kays and London [20]. 

Now calculate the core dimensions. In the first iteration, use NTU computed in step 2. For subsequent iterations, calculate longitudinal conduction parameter X and other dimensionless groups for a crossflow exchanger. With known e, C, and X, determine the correct value of NTU using either a closed-form equation or tabulated/graphical results [10], Determine A, from NTU using U, from previous step and known Cmm. 

Ak Total wall cross-sectional area for longitudinal conduction (subscripts c, h, and t... 

The idea of this method can be described in the following way. Let us imagine a set of surfaces Oj = const. In such a way a conducting medium can be presented as a system of sufficiently thin layers. Then each layer can be replaced by an infinitesimally thin shell located at the middle part of this layer, provided that the longitudinal conductance, S, of the layer and that of the corresponding shell are the same. Here the longitudinal conductance of the layer is a product of its conductivity and thickness. 

Within a certain range of a change of conductivity, a, and thickness, Ar, of shells, induced currents within them generate practically the same field if the longitudinal conductance, S = (jAr, remains constant. With an increase of the radius r, that is moving away from the borehole axis, this equivalence by S can be applied to shells with greater thickness. 

In contrary, thin low resistive layers have essential influence on curves of induction logging. In fact with an increase of ratio 02 the value of the apparent conductivity, a a, tends to a constant equal to S /2L S is the longitudinal conductance of the bed (TiH), and it can turn out to be much greater than 0-2 This fact is well seen from curves with index Oi/a2 > 1 (Fig. 5.8). Let us assume that the probe is located against a system of thin layers. Then an expression for apparent conductivity, CTo, can be obviously presented... 

Thus, for sufficiently large times the field becomes the same as in a uniform medium with resistivity of the surrounding medium p2 00, and it does not depend on the probe length. At the same time at the late stage induced currents are distributed uniformly within the formation along 2 axis, if the surrounding medium is not conductive, and the field is directly proportional to the cube of the longitudinal conductance (H/pi). ... 

We can assume that if the electric field is not uniform and changes along the layer, the longitudinal conductance is also a function of a frequency. Curves, presented in Fig. 11.3 characterize the influence of displacement currents on coefficient on anisotropy. 

Roth et al. [1988] recast the expression for the effective longitudinal conductivity in terms of spatial frequency, k (rad/m). This approach has two advantages. First, the temporal and spatial behaviors are both described using frequency analysis. Second, a parameter describing the size of a specific piece of tissue is not necessary the spatial frequency dependence becomes a property of the tissue, not the measurement. The expression for the DC effective longitudinal conductivity is... 

K (411,465,490b, 501). Figure 48 shows the temperature dependent conductivity. The data of Hsu and Labes (501) and Walatka et al. (411) were for samples which had significant C, H, and O impurities. They reported a longitudinal conductivity at room temperature of order 10 (maximum... 

FIGURE 10.6 Schwan general model of a, 3, and j dispersions. Dashed curve is an example of measured muscle longitudinal conductivity. 

Axial and longitudinal conduction are negligible (i.e. conduction only in the... 

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