Velocity characteristic value

Physical Properties. Most of the physical properties discussed herein depend on the direction of measurement as compared to the bedding plane of the coal. Additionally, these properties vary according to the history of the piece of coal. Properties also vary between pieces because of coal s britde nature and the crack and pore stmcture. One example concerns electrical conductivity. Absolute values of coal sample specific conductivity are not easy to determine. A more characteristic value is the energy gap for transfer of electrons between molecules, which is deterrnined by a series of measurements over a range of temperatures and is unaffected by the presence of cracks. The velocity of sound is also dependent on continuity in the coal. 

In the so-called "wrinkled flame regime," the "turbulent flame speed" was expected to be controlled by a characteristic value of the turbulent fluctuations of velocity u rather than by chemistry and molecular diffusivities. Shchelkin [2] was the first to propose the law St/Sl= (1 + A u /Si) ), where A is a universal constant and Sl the laminar flame velocity of propagation. For the other limiting regime, called "distributed combustion," Summerfield [4] inferred that if the turbulent diffusivity simply replaces the molecular one, then the turbulent flame speed is proportional to the laminar flame speed but multiplied by the square root of the turbulence Reynolds number Re. ... 

In forced convection, the velocity of the liquid must be characterized by a suitable characteristic value Vih e.g. the mean velocity of the liquid flow through a tube or the velocity of the edge of a disk rotating in the liquid, etc. For natural convection, this characteristic velocity can be set equal to zero. The dimension of the system in which liquid flow occurs has a certain characteristic value /, e.g. the length of a tube or the longitudinal dimension of the plate along which the liquid flows or the radius of a disk rotating in the liquid, etc. Solution of the differential equations (2.7.5), (2.7.7) and (2.7.8) should yield the value of the material flux at the phase boundary of the liquid with another phase, where the concentration equals c. ... 

Straightforward calculation of the characteristic values of the velocity, Coulomb potential and kinetic energy in the stationary states gives... 

The reported study on gas-liquid interphase mass transfer for upward cocurrent gas-liquid flow is fairly extensive. Mashelkar and Sharma19 examined the gas-liquid mass-transfer coefficient (both gas side and liquid side) and effective interfacial area for cocurrent upflow through 6.6-, 10-, and 20-cm columns packed with a variety of packings. The absorption of carbon dioxide in a variety of electrolytic and ronelectrolytic solutions was measured. The results showed that the introduction of gas at high nozzle velocities (>20,000 cm s ) resulted in a substantial increase in the overall mass-transfer coefficient. Packed bubble-columns gave some improvement in the mass-transfer characteristics over those in an unpacked bubble-column, particularly at lower superficial gas velocities. The value of the effective interfacial area decreased very significantly when there was a substantial decrease in the superficial gas velocity as the gas traversed the column. The volumetric gas-liquid mass-transfer coefficient increased with the superficial gas velocity. 

The characteristic values of the above bursting charge are shown in table 19. As we see in the table, the starting velocity of stars propelled by KP can be increased to the same value as H3 by increasing the number of pasted layers of paper to 1.2 times more than is required for H3. 

More precise relationships for /Jdisp were discussed earlier, in the previous section (see Eqs. 6.91a, 6.91b, and 6.91f). A and B in the equation above are characteristic of the packing material and Pe — udp/Dm is the particle Peclet niunber, with u the interstitial velocity, hi the chromatographic literature, the particle Peclet number is frequently named the reduced velocity. Typical values of A and B in a well-packed column are 1.5 and 1.6, respectively [56]. For such a column, used at a moderate to high Peclet munber, hdisp is a small contribution to the overall reduced plate height of the column. 

In our problem, the characteristic air velocities in the thin gap are determined by the normal airflow through the porous lower surface. An appropriate characteristic value for this velocity is... 

Now transform the system (5.99)-(5.102) to a dimensionless form. To this end, introduce the characteristic values of length I, velocity U and time z. Notice that the characteristic time is natural in problems, in which processes under the external, time-varying actions are considered. We denote as z the characteristic time of such an action. In many problems z is not an independent value, and is determined as T = I/U. 

Note that in the small double layer thickness approximation, the character of motion of liquid in the capillary is that of plug flow with the velocity U. If the thickness of the double layer is small, but finite, the velocity profile looks like the one shown in Fig. 7.9. For the characteristic values C = 0.1 V, = 10 m, we have for water U = m/s. Thus, electroosmotic motion has a very low velocity. 

With the initial conditions of ds/dt = 0 at t = 0 and s = So at t = 0, Eq. 23 can be numerically solved to yield the displacement and velocity characteristics of the advancing capillary meniscus. Since the effect of added mass is not incorporated in Eq. 22, a nonzero value of sq is required to avoid the prediction of an unrealistic initial burst at t = 0, as explained earlier. One major cmiclusimi that can be drawn from the numerical simulatimi studies of Yang et al. [8] is, based on the above model, that while liquid slip on hydrophobic surfaces may increase the flow velocity, the presence of a capillary pressure across the liquid—vapor interface can suppress the electroosmotic flow and significantly decrease the flow performance. 

The Backgroimd document (1999) provides additional information about experimental measurements of temperatures which formed the basis for the development of the models of thermal actions given in Eurocodes. The characteristic values of temperature components are based on the fifty years return period like other climatic actions (snow, wind velocity, icing). Presently, the Eurocodes recommend a unique value of partial factor yg = 1,5 for most variable actions Q with respect to the ultimate limit states. However, the reduced factor yr = 1, 2 may be applied for thermal actions in some national standards, CSN 73 6203 (1986). It appears that the partial factors for some variable actions might be differentiated taking into account their characteristics. 

In addition according to BERMAN [l9] the product of the velocity gradient at the wall u /v for the onset-point and the relaxation time at the same shear rate (s. fig. 2) was calculated. The product does not have a characteristic value like that found by BERMAN for homogeneous polymer solutions. The Reynolds number in all experiments is based on the solvent kinematic viscosity v. 

To identify characteristic values of j/, such as the boundary layer thickness, one must consider the flow fleld profiles near the wall. To that end the flow fleld was time-averaged along lines of = constant, using the last 3625 cycles of the calculation t = 16 to 592 ms). Examples of the mean-flow profiles in the wall jet re on are shown in Fig. 7. The mean velocity profiles (Fig. 7a) do indeed resemble those expected for a wall jet the stream-wise velocities reach a peak value of about 5.3 km/s in the jet and decay to a value of about 3.5 km/s far above the wall. Mean density profiles are shown in Fig. 7b. The fluidized bed was compressed somewhat (p 65 mg/cm ) by the Mach stem shock. The profiles converge at a height of z 2.15. As... 

In general, the settling velocity function is of the form Wg = Wsof iC, ), where Wso is a characteristic value of Wg and /"(C, 7) denotes a function of C and a representative value of flow shear rate 7. Substituting these relations in Eq. (27.25) (and assuming = 0) yields... 

The conditions behind a detonation initiated at a free surface are similar to those behind a detonation intiated at a fixed wall. This is illustrated in Fig. 11. Here the Prandtl-Meyer region II extends up to the free surface which itself is an / characteristic. At the free surface, it is supposed that the temperature is zero so that both c and a are zero. The particle velocity, the value of the / characteristic. 

Figures 8 and 9 show applications of NMR microscopy in the rheological investigation of complex viscoelastic fluids. In Figure 8 comparative velocity and diffusion profiles are shown across the diameter of a 700 p,m diameter capillary though which is pumped a solution of high-molecular-mass polymer undergoing laminar flow. The velocity profile is distinctly non-Poiseuille, consistent with shear thinning, while the polymer self-diffusion coefficients exhibit a dramatic enhancement once the shear rate (the velocity gradient) exceeds a characteristic value. This value corresponds to the slowest relaxation rate of the molecule where rj is the so-...

Eq. (3.26). Now diffractive scattering occurs in a very narrow forward cone (assuming the atoms are not moving too slowly) and so the accompanying velocity changes are small. Let dv be the characteristic value of the velocity change v - v in the diffractive region. A coherence which is prepared at time t = 0 will subse-... 

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