Drift velocity effective

Effective drift velocity The velocity re suiting from air flowing from one zone to another due to a pressure differential. 

Fig. 2. Electron drift velocities as a function of electric field for A, GaAs and B, Si The gradual saturation of curve B is characteristic of all indirect semiconductors. Curve A is characteristic of direct gap semiconductors and at low electric fields this curve has a steeper slope which reflects the larger electron mobiUty. The peak in curve A is the point at which a substantial fraction of the electrons have gained sufficient energy to populate the indirect L minimum which has a much larger electron-effective mass than the F minimum. Above 30 kV/cm (not shown) the drift velocity in Si exceeds that in...

According to this approximation, the drift velocity is proportional to the square of the electric field. This is a clear indication of the importance of the electric field inside an electrostatic precipitator. Equation (13.60) is a valid approximation for large particles [dp > 0.5 m), provided that particle charge is close to the saturation level. In the case of small particles, the effect of diffusion charging must be taken into account. 

Silinsh et al. (1989) applied their thermalization procedure to naphthalene and anthracene at low temperatures, 35 K or less. A stationary state was envisaged in the presence of an external field. Calculations have been performed for the saturation drift velocity, friction coefficients, and effective mass as functions of the external field. The conclusions are almost the same as for pentacene. 

Here, Vd = pE is the drift velocity. The recombination and escape probabilities are now given by PR = NR /n+° L0 and Pkc = 1 - Pr. Since Vd = i, but T /r1 these probabilities are independent of mobility. However, the initial separation r0 is expected to depend (increase) with electron mobility, thus making the escape probability indirectly dependent on the mobility. These effects are quite similar to those in the Onsager theory... 

Since there are (Tf + Tt) 1 cycles of trapping and detrapping per unit time, the drift velocity is (Ax)/(xf + tt), from which the effective mobility is derived to be... 

Up to now, only hydrodynamic repulsion effects (Chap. 8, Sect. 2.5) have caused the diffusion coefficient to be position-dependent. Of course, the diffusion coefficient is dependent on viscosity and temperature [Stokes—Einstein relationship, eqn. (38)] but viscosity and temperature are constant during the duration of most experiments. There have been several studies which have shown that the drift mobility of solvated electrons in alkanes is not constant. On the contrary, as the electric field increases, the solvated electron drift velocity either increases super-linearly (for cases where the mobility is small, < 10 4 m2 V-1 s-1) or sub-linearly (for cases where the mobility is larger than 10 3 m2 V 1 s 1) as shown in Fig. 28. Consequently, the mobility of the solvated electron either increases or decreases, respectively, as the electric field is increased [341— 348]. 

The IMS system is in effect a modification of the CEDC system. It distinguishes ionized molecules on the basis of differences in their drift velocity as they pass countercurrent thru a flowing gas stream. An electric field provides the driving force for the flow of ionized molecules... 

Mobility — The (ionic or electric) mobility u of an ion is given by the drift velocity v (the velocity of an ion at equilibrium between the accelerating effect of the electric field and the decelerating effect of the viscous medium (Stokes friction)) of an ion and the effective electric field E v... 

Theoretical calculations will always overestimate precipitator efficiencies, probably because of reentrainment. This overestimation could be as large as a factor of 2 or more (Rose and Wood, 1966). Even so, drift velocity or effective migration velocity is the basis for all precipitator calculations and does provide a good base for the comparison of various designs. 

Ions drifting through a buffer gas under the influence of a weak uniform electric field E quickly reach an equilibrium between forward acceleration due to the electric field and retarding effect due to collisions with the buffer gas resulting in a constant drift velocity vD. The drift field is weak when the steady flow of ions along the electric field is much slower than the random motion leading to diffusion. The low field mobility K is the proportionality constant between vD and E [9] ... 

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