Thermal diffusion coefficient, definition

This inequality in (26-11) stems from the fact that the determinant of the 2 x 2 matrix of phenomenological transport coefficients [, y] mnst be positive to ensure a positive-definite quadratic form for sq- The contribution from thermal Soret diffusion in the final expression for Ja (see equations 25-76 and 25-77) provides a definition of P in terms of the thermal diffusion coefficient kr and the temperature dependence of cpA-... 

This definition is in terms of a pool of liquid of depth h, where z is distance normal to the surface and ti and k are the liquid viscosity and thermal diffusivity, respectively [58]. (Thermal diffusivity is defined as the coefficient of thermal conductivity divided by density and by heat capacity per unit mass.) The critical Ma value for a system to show Marangoni instability is around 50-100. 

The following symbols are used in the definitions of the dimensionless quantities mass (m), time (t), volume (V area (A density (p), speed (u), length (/), viscosity (rj), pressure (p), acceleration of free fall (p), cubic expansion coefficient (a), temperature (T surface tension (y), speed of sound (c), mean free path (X), frequency (/), thermal diffusivity (a), coefficient of heat transfer (/i), thermal conductivity (/c), specific heat capacity at constant pressure (cp), diffusion coefficient (D), mole fraction (x), mass transfer coefficient (fcd), permeability (p), electric conductivity (k and magnetic flux density ( B) ... 

These definitions introduce the binary molecular ( ab). thermal (kj), and pressure (kp) diffusion coefficients. The final form for the diffusional mass flux of species A in a binary mixmre with respect to the mass-average velocity v is... 

Comparing these forms with Equations (6) earlier, we can see definite and meaningful similarities. The Lewis number occurs in exactly the same way as the ratio of diffusion coefficients. The temperature rise can also be seen to provide an effective autocatalyst. In this case, the feedback is thermal rather than chemical, but enters the governing equation in exactly the same manner. 

In order to obtain a definite breakthrough of current across an electrode, a potential in excess of its equilibrium potential must be applied any such excess potential is called an overpotential. If it concerns an ideal polarizable electrode, i.e., an electrode whose surface acts as an ideal catalyst in the electrolytic process, then the overpotential can be considered merely as a diffusion overpotential (nD) and yields (cf., Section 3.1) a real diffusion current. Often, however, the electrode surface is not ideal, which means that the purely chemical reaction concerned has a free enthalpy barrier especially at low current density, where the ion diffusion control of the electrolytic conversion becomes less pronounced, the thermal activation energy (AG°) plays an appreciable role, so that, once the activated complex is reached at the maximum of the enthalpy barrier, only a fraction a (the transfer coefficient) of the electrical energy difference nF(E ml - E ) = nFtjt is used for conversion. 

Two other factors, however, combine to make a pressing need to reach a definitive experimental value for the thermal DR rate coefficient. The observation of Hj in diffuse interstellar clouds has made it possible to determine the abundance of The factor of 10 spread in the... 

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