Problem outer mass transfer

The inner problem of convective mass and heat transfer is essentially different from the similar outer problem, primarily, by the streamline pattern. This leads to a corresponding qualitative distinction between the dynamics of processes of transient mass transfer inside and outside a drop. In the outer problem considered in Section 4.12, all streamlines are open. The lines near the flow axis carry the... 

In the inner problems of the convective mass transfer for kv - 0(1) as Pe —> oo, the concentration is leveled out along each streamline. The mean Sherwood number, by virtue of the estimate (5.4.8), is bounded above uniformly with respect to the Peclet number Sh < const kw. This means that the inner diffusion boundary layer cannot be formed by increasing the circulation intensity alone (i.e., by increasing the fluid velocity, which corresponds to Pe - oo) for moderate values of kv. This property of the mean Sherwood number is typical of all inner problems. For outer problems of mass transfer, the behavior of this quantity is essentially different here a thin diffusion boundary layer is usually... 

In studying the sublimation of naphthalene into an airstream, an investigator constructed a 3-m-long annular duct. The inner pipe was made from a 25-mm-OD solid naphthalene rod this was surrounded by a 50-mm-ID naphthalene pipe. Air at 289 K and 1 atm flowed through the annular space at an average velocity of 15 m/s. Estimate the partial pressure of naphthalene in the airstream exiting from the tube. At 289 K, naphthalene has a vapor pressure of 5.2 Pa and a diffusivity in air of 0.06 cm2/s. Use the results of Problem 2.7 to estimate the mass-transfer coefficient for the inner surface, and equation (2-74), using the equivalent diameter defined in Problem 2.7, to estimate the coefficient from the outer surface. 

Use the following boundary condition at the outer edge of the mass transfer boundary layer in the liquid phase Ca = 0 at r = t2. At the solid-liquid boundary where r = ri, Ca is given by its equilibrium solubility in the liquid. The thickness of the mass transfer boundary layer is T2 — n. Hint Think about your experience with heat transfer coefQcients because you have used the solution to this problem several times in the past in other courses that focus on heat transfer. 

P. A film of cationic solute Af+ in phase 1 (Figure 7.16) deposits on the sheet by diffusion on the outer surfaces and the film is constantly saturated with the electrolyte. Film thickness growth occurs in the xi and X2 directions having a thickness Li in phase 1 and L2 in phase 2, respectively. Thus, the spaces occupied by the d sited film on each side of the sheet are 0 < xi < Li and -L2 < 2 2 < 0. Thus, motion of one or two phases relative to the boundary is caused by the mass transfer diffusion across the interface. This diffusion problem resembles the tarnishing reactions forming an oxide film on a metal surface [25]. 

The MSR reaction is affected by several limitations, such as thermodynamic equilibrium constraint, mass and heat transfer limitation, and coke formation. Heat transfer is one of the most important problems. Indeed, as well known, the MSR reaction is strongly endothermic and, in order to furnish an adequate heat transfer rate from the outer zone of bed catalyst to the inner one, the catalyst needs to be packed in long, narrow tubes composed of super-aUoys, which are, furthermore, very expensive (Rostmp-Nielsen, 1984, chap. 1). 

---