Hydrogen permeation model

All reduction coefficients dealt with in this chapter were calculated from the numerical solution of a complex hydrogen permeation model, opportunely validated by a number of experimental data, and reported in form of permeation reduction maps for several operating conditions. From these maps, the values of CPC, IC and PRC can be read directly and used simply in the modified forms of Sieverts law shown above to evaluate the hydrogen permeating flux, providing in this way a possible novel strategy of membrane module design. 

Ward, T.L. and Dao, T. (1999) Model of hydrogen permeation behavior in palladium membranes. Journal of Membrane Science, 153, 211-231. 

Caravella, A., Barbieri, G. and Drioli, E. (2008) Modelling and simulation of hydrogen permeation through supported Pd-alloy membranes... 

Due to their complexity, the model equations will not be derived or presented here. Details can be found elsewhere [Adris, 1994 Abdalla and Elnashaie, 1995]. Basically mass and heat balances arc performed for the dense and bubble phases. It is noted that associated reaction terms need to be included in those equations for the dense phase but not for the bubble phase. Hydrogen permeation, the rate of which follows Equation (10-51b) with n=0.5, is accounted for in the mass balance for the dense phase. Hydrodynamic parameters important to the fluidized bed reactor operation include minimum fluidization velocity, bed porosity at minimum fluidization, average bubble diameter, bubble rising velocity and volume fraction of bubbles in the fluidized bed. The equations used for estimating these and other hydrodynamic parameters are taken from various established sources in the fluidized bed literature and have been given by Abdalla and Elnashaie [1995]. 

Fabricate a "bench-top" model of a tri-layer, electrochemically-active protection device that greatly reduces hydrogen permeation through polymer "substrates"... 

Because the physical parameters such as the diffusivities and the equilibrium constants for the BCN membranes are not readily available in the literature, modeling analysis of hydrogen permeation through the MPEC membrane was carried out for the SrCe0.95Y0.05O3 X (SCY) perovskite membrane. The required physical parameters are taken from the literature [15-19] and are listed in Table 7.1. 

The concentration profiles of the 4 major defect species predicted from the model at 700°C are shown in Fig. 7.8. The feed is 4% hydrogen and the permeate is 0.488% hydrogen, the same conditions as in Fig. 7.7. Both the proton and the electron species dominate in the SCY membrane and the concentrations of the vacancy and the electron hole are very low. The results are reasonable because hydrogen permeation is mainly facilitated by both the proton and the electron while the vacancy and the electron hole are responsible for the oxygen transport. The proton and the electron concentrations decrease from the feed side to the permeate side as expected. Due to the low pressure operation, the proton concentrations generally are low. 

Song SJ, Wachsman ED, Rhodes J, Dorris SE, Balachandran U. Numerical modeling of hydrogen permeation in chemical potential gradients. Sohd State Ionics. 2003 164 107-16. 

Li L, Iglesia E. Modeling and analysis of hydrogen permeation in mixed proton-electronic conductors. Chem Eng Sd. 2003 58 1977-88. 

M. Ramasubramanian, B.N. Popov, R.E. White, Characterization of hydrogen permeation through zinc-nickel alloys under corroding conditions mathematical model and experimental study, J. Electrochem. Soc. 145 (1998) 1907-1913. 

Basic model for hydrogen permeation the lyer-Pickering-Zamanzadeh (IPZ) model 333... 

A basic hydrogen permeation mechanistic model was developed by Iyer, Pickering, and Zamanzadeh [13—15] on the basis of the following assumptions ... 

Using the model and data obtained from hydrogen permeation experiments one can compute hydrogen surface coverage and the rate constants. This model is only applicable for coupled discharge-recombination hydrogen evolution with constant cathodic side hydrogen concentration on the membrane. 

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