Diffusion driving force

Can the Chemical and Electrical Work Be Determined Separately In the case of transport processes, the total driving force for the flow of a particular species j, i.e., the gradient of electrochemical potential. 3pj./3bc, was considered split up into a chemical (diffusive) driving force dp/dx and an electrical driving force for conduction, ZjFdty/dx,... 

The term d is called the diffusion driving force. For a low-density ideal gas it is given by [178]... 

The diffusion driving force d was given by Eq. 12.167 for a low-density, ideal gas. This expression is generalized as [83,178]... 

For a dense gas or liquid, Eq. 12.191 may be used, with the more general diffusion driving force calculated by Eq. 12.184. 

It is believed that the formation of fat soluble ion pairs is responsible for the increased permeation in the above cases. However, additive interactions with stratum corneum or increases in the diffusive driving force in the film may also contribute to the increase. 

The effect of the phase-diffusion driving force enters through the (generally energy-dependent) effective temjjerature Teff( ). 

We see that T,tt goes through a maximum near the resonance condition cuj, = CO, where co is the oscillator frequency. The phase-diffusing driving force results in thermallike kinetics with a renormalized temperature, which is resonantly enhanced relative to the bare temperature. 

Therefore, the diffusion driving force has three important parts which express the concentration diffusion (caused by composition gradient), the barodiffusion (by pressure gradient) and the third member is the forced diffusion by the body forces. ... 

The most important case of concentration diffusion is that with isobaric diffusion driving force (4.535), without external forces and with corresponding neglection noted above, i.e. with the following driving force... 

An extended Stefan-Maxwell diffusion equation can be constructed by setting up a homogeneous, linear relationship between the vector of diffusion driving forces and the vector of species velocity differences. 

It is a drawback that transport constitutive laws in the form of Eq. 4 make it difficult to identify the effect of convection. Also, analyses based on analogies to systems described by Fourier s law, Ohm s law, or Fick s law are confounded by the fact that Eq. 4 is explicit in the diffusion driving forces, rather than the fluxes (cf. Eq. 1, a more familiar formulation in which Ni = Ci Vi stands alone on the left side). 

Nevertheless, the most rigorous, thermodynamically complete understanding of ion mobility or diffusivity in concentrated electrolytic solutions is provided by the extended Stefan-Maxwell transport theory, which can be applied to electrolytic solutions [13, 17-22], ionic melts or ionic liquids [23, 24], and ion-exchange membranes [25-28]. The diffusion driving force in any system involving ion transport is taken to be a gradient of electrochemical potential /i, typically expressed in terms of a chemical part and an electrical part as... 

One of the main goals of the GDL is the transport of gaseous species. From an experimental point of view the determination of the gas permeability (pressure-driven flow) is easier than the determination of the diffusion (driving force concentration difference) of gases. This might be the reason that, in the literature, values for the permeability for GDL material can be found much more often than diffusion coefficients or structural parameters of the materials necessary for the determination of the effective diffusion coefficient. Especially when looking in the specification for GDLs provided by manufacturers, one will find values for gas permeation but no data relevant for gas diffusion. 

Here it is noted that terms in the perturbation function that allow for departures from the local equilibrium because of temperature gradients and velocity gradients must be taken into account as well as those for the possibility of composition gradients, which is done by including the diffusion driving force Aq>. The quantities A, B, and... 

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