Surface-exchange limitations

Fig. 2. (a) Penetration plot (top) obtained after 1.23 h anneal at 900 °C for system Lai-ySr MnC -s (y = 0.025). Solid line represents a fit to solution of diffusion equation, accounting for volume (equation (1)). (b). Penetration plot (top) obtained after 1.23 h anneal at 900 °C for system Lai-ySr MnC -s (y = 0.025). Solid line represents a fit to solution of diffusion equation, accounting for volume and surface exchange limited (equation (2)). 

Fig. 10.4. Thickness dependence of the dimensionless oxygen flux j 02 calculated using Eq. (10.18). The quantity / 02 is defined by the ratio of the oxygen flux over the maximum achievable oxygen flux in the surface exchange limited regime. Only if L Lo the oxygen flux becomes proportional to 1/L withy= 1 in agreementwifli tile Wagner theory.For smaller thicknesses, yrangesbetweenl andO...

Equation (3.103) (which is also known as Wagner s equation) may be transformed into the formula for steady-state oxygen permeation under conditions when the surface exchange limitations are negligible ... 

For shell-and-tube heat exchangers, limited fire protection may be provided during fire exposure by the liquid in the shell that provides some internal cooling for the shell wall. However, if a spill fire exposure exists and the shell side liquid has low heat capacity, then either water spray or fire resistive material should be applied to the surface of the exchanger itself. 

MAJOR limitation TO research on surface-exchange and flux measurements is the lack of sensitive, reliable, and fast-response chemical species sensors that can be used for eddy correlation flux measurement. Therefore we recommend that continued effort and resources be expended in developing chemical species sensors with the responsiveness and sensitivity required for direct eddy correlation flux measurements. This recommendation (I) was assigned the first priority in the report of the recent Global Tropospheric Chemistry workshop jointly convened by the National Science Foundation, the National Aeronautics and Space Administration, and the National Oceanic and Atmospheric Administration. The authors of the report recognized that the limited availability of fast, accurate chemical sensors is a major measurement challenge in the field of atmospheric chemistry. 

H.J.M. Bouwmeester, H. Kruidhof and A.J. Burggraaf, Importance of the surface exchange kinetics as rate limiting step in oxygen permeation through mixed-conducting oxides. Solid State Ionics, 72 (1994) 185-194. 

The 3D architecture of nanofibrous substrates may allow better nutrient exchange compared to flat surfaces because cells cultured on flat surfaces are limited to nutrient exchange on only one side. Specific nanofibrous orientations, such as aligned, can also offer different nutrient exchange potentials as compared to random orientations. 

This approximation is valid when A. is much less than the linear dimension of the liquid volume, that is for pores with low curvature. Therefore, experimental relaxation rates from a system in the fast exchange limit can provide information on the ratios of the surface-to-bulk volumes of liquid, given the relaxation rates of surface and bulk liquid are known as well as the value for A. If relaxation values are acquired for different stages of filling, it is possible to determine details of the filling process, like the formation of puddles within the pore structure [Alll, Bool]. 

---