Wall boundary between different phases

The mathematics of the wall boundary model slightly changes if the media on either side of the interface are different. As an example, consider the volatilization of a dissolved chemical into the well-mixed atmosphere from a shallow puddle of water in which advective and turbulent motion is completely suppressed. Another example is the transport between a solid phase and a turbulent water body. 

Here, the Zn/Zn pair constitutes the left half-cell and the Cu/Cu pair the right half-cell. The vertical bar, as between Zn(s) and Zn (aq) and Cu (aq) and Cu(s), is a symbol for phase boundary. What is a phase boundary It is the place - point, line, surface - where materials of different phases meet. Think of a glass beaker filled with water the glass wall is a phase boundary. The double vertical line, 11, represents a salt bridge in electrochemical cells, that is, a conduit for ions. 

Phase-averaged values of 4 in a plane midway between two baffles of a stirred tank have been plotted in Fig. 1 (from Hartmann et al., 2004a) for two different SGS models (Smagorinsky and Voke, respectively) in LES carried out in a LB approach. The highest values, i.e., the strongest deviations from isotropy, occur in the impeller zone, in the boundary layers along wall and bottom of the tank, and at the separation points at the vessel wall from which the anisotropy is advected into the bulk flow. In the recirculation loops, the turbulent flow is more or less isotropic. 

Here A a represents the difference between the interfacial tension at the end and at the beginning of the path. When the refreshing of the elements of liquid is complete, A a is equal to the difference between the interfacial tension at the equilibrium concentration at the interface and the interfacial tension between the liquid phases at their bulk concentrations. The problem of the boundary layer that develops when a solid planar surface moves continuously was treated by several authors. Tsou et al. [115] have derived the following expression for the local wall shear stress r ... 

The simplest technique is to use separate numerical solvers for the fluid and solid phases and to exchange information through the boundary conditions. The use of separate solvers allows a flexible gridding inside the solid phase, which is required because of the three orders of magnitude difference in thermal conductivities between the solid and gas. It is also easy to include various physical phenomena such as charring and moisture transfer. Quite often, ID solution of the heat conduction equation on each wall cell is sufficiently accurate. This technique is implemented as an internal subroutine in FDS. 

A Galvani potential difference can form not only across the interface electrode/ electrolyte solution but also across the interface between two electrolyte solutions. There is usually a fine-pored wall (made of sintered glass or ceramic), a so-called diaphragm, to stabilize the phase boundary so that the solutions do not mix too... 

---