Conductance factor

Average errors are 5 percent when this equation is used. For pressures greater than 3.4 MPa, the thermal conduclivity from Eq. (2-135) may be corrected by the technique suggested by Lenoir. The correction faclor is the ratio of conductivity factors F/F, where F is at the desired temperature and higher pressure, and F is at the same temperature and lower pressure (usually atmospheric). The conduclivity Factors are calculated from ... 

Table 1 gives conductivity factors for common ions found in water supplies. 

Water Quality Conductivity Factors of Ions Commonly Found in Water... 

The general case is that of steady-state flow, and the thermal conductivity factor is a function of the temperature. In the unsteady state the temperature of the system changes with time, and energy is stored in the system or released from the system reduced. The storage capacity is... 

NOTE The specific conductance factor varies considerably, depending on several factors, including the concentration of ionic species present in the water. In general, the factor decreases with increase in the concentration of ionic species. Thus, for city water a factor of 0.65 is a good approximation for BW in higher pressure WT boilers, a factor of0.575 is preferred by the author, and for BW in lower pressure FT boilers, a factor of 0.5 is preferred by the author. 

The conductance of arbitrary axisymmetric particles may be approximated using the correlation given in Fig. 4.13. By analogy with the drag ratio, a conductance factor is defined as... 

Fig. 4.13 Correlation for conductance factor of axisymmetric particles in stagnant media (based on perimeter-equivalent sphere).

The photorefractive gain, shown in Figure 2b, is predominantly determined by two factors the trap density, NE, and the relative conductivity factor, . The latter factor accounts for the minimum... 

Also, the overall thermal resistance 1/U must include all thermal resistances, so that the denominator of the introductory expression for y given by Eqn. (23) must be corrected (since U as modeled by Eqn. (22) neglects the thermal resistances of the tubing wall and the two-phase side). The denominator of Eqn. (23) may be corrected by defining a thermal conductance factor... 

Besides the influence that the ligand has in determining the geometrical and electronic structure of the complex, there may also be the direct (but related) influence of affecting the distribution of the d electrons in the complex and thus the probability of barrier penetration. Unfortunately, there are no observations which expose separately the geometrical and conductivity factors, but the second factor will readily be discernible in some of the systems discussed in the next section. 

Heat transfer coefficient Heat transfer conductance factor... 

The phase diagrams and ionic conductivities of anion-deficient ZrO2 compounds have been widely investigated, to probe the influence of both dopant size and concentration (e.g.. Ref. [95]). Whilst Sc" + doped systems possess the highest values of ionic conductivity, factors such as cost and long-term stability have favored the use of (Zri j,Yj,)O2 x/2 as the current "best material, in which the m t and t c transitions are observed at x 0.05 and xw0.16, respectively [96]. On increasing dopant (anion vacancy) concentration, the ionic conductivity initially increases with X, but reaches a maximum close to the lower limit of stability of the c phase and then decreases rapidly [97]. Many theoretical studies have attempted to provide an explanation for this effect, and it is generally accepted that vacancies are trapped... 

Numerical examples follow. First, for flow of water, let the material of the dike have a conductivity factor or transmissivity of 2 x 10 kg/Pa-m-sec and let the difference in pressure from one side to the other be 0.008 MPa (for example, because of a difference in water level of about 30 inches or 75 cm). The average pressure gradient would be 0.002 MPa/m and the flow rate would be 0.04 kg/m -sec—a cupful in 5 seconds for every square meter of cross-section area material with such a high transmissivity would not be suitable for dike purposes. 

Second, for diffusion of salt, let the material of the dike have a conductivity factor or diflfusivity of 5 x 10 m sec. This is a value for the wet sand en masse regardless of the geometry of the tiny water pathways that permeate it. The salt content of seawater is about 3 g per 100 g or 3 kg per 100 kg a cubic meter of seawater has a mass of about 1100 kg so the salt content is about 33 kg/m if the concentration changes linearly from the salty side to the freshwater side, the change is 8.3 kg/m then the diffusion rate for salt is 4 X 10 kg/m -sec. A year is about 3 x 10 sec, so that this equals 1.2 kg or nearly 3 lb of salt crossing per square meter per year. 

The conductivity factor for salt difiusion has deceptively simple units. If we express the concentration gradient in mol/m and the transport rate of salt in kg/m -sec, the conductivity factor has units... 

The item here called a conductivity factor has various names— permeability, diffusivity, etc.— that sometimes emphasize the host material (e.g., permeability of sandstone ) and sometimes emphasize the traveling material (e.g., diffusivity of hydrogen ). The factor in reality always depends on both host and traveler it is a property of the transport situation as a whole. Sometimes it is useful to separate out two components such as mobility of the diffuser and tortuosity of the matrix but for present purposes we shall stay with a single comprehensive factor. The terms permeability and diffusivity may be used from time to time, but we shall try to maintain the view that any conductivity factor is acceptable, under whatever name, as long as its units are clearly in view. 

A transition from the conditions approximating a perfectly mixed (lumped) system to the realistic conditions with both the diffusion and conductive factors being involved in the process of attaining a steady state (in a distributed system) may bring about a destabilization of the previously stable uniform state. A qualitative picture of the destruction of the spatially uniform mode of a catalytic process appears as follows. A small local perturbation resulting in a local overheating is accompanied by an increase in the reaction... 

The tortuosity, r, of a porous medium is defined as the ratio of the distance between two fixed points and the tortuous passage followed by a fluid element of a single fluid saturated in the porous medium when traversing the two points. It may be viewed as a line porosity because, by definition, tortuosity is a one-dimensional property of the porous medium. It can be related to the formation factor, or formation conductivity factor, Ft by... 

Table 3.6. Conductivity factors for ions commonly found in water [4]... 

The moisture flux g (kg/(m, s)) in the bentonite has a liquid and a vapor component. The liquid flux g, is proportional to the gradient of the pore water pressure P with a hydraulic conductivity k(S) that is a function of the degree of water saturation S. The flux is inversely proportional to the viscosity rj(T). The water vapor flux g, is proportional to the gradient of the water vapor density in the gas phases in the pores with a vapor conductivity factor D,(5) that is a decreasing function of S. The heat flux q (W/m ) has a conductive part with a thermal conductivity. /i(S). There is also a negligible convective part. We have... 

Fig. 5. Conductance factors for directional free-molecule flow in cylindrical tubes.

The coefficient k is called the heat conductivity factor. In parallel with this, the factor of thermal diffusivity is frequently used in practice (sometimes also called the coefficient of heat conductivity)... 

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