Direct passively operating

Figure 3.54. Direct methanol fuel cell designed for passive operation (no forced flows), with two membrane-electrode assemblies MEA) and a central fuel container.

Chan YH, Zhao TS, Chen R, Xu C (2008) A small mono-planar direct methanol fuel cell stack with passive operation. J Power Sources 178 118-124... 

Direct ethanol fuel cells (DEFCs) produce power directly from ethanol without prior reforming. Compared with methanol used as the fuel for DMFCs, ethanol is nontoxic, environmentally friendly, and universally available, and making the handling easy. Since ethanol is also a liquid alcohol like methanol, the technological issues of crossover, discharge of carbon dioxide, and passive operation are comparable. 

Eccarius, S., Krause, F., Beard, K., and Agert, C. (2008) Passively operated vapor-fed direct methanol fuel cells for portable applications. J. Power Sources, 182 (2), 565-579. 

All passive monitoring devices operate on the basis of diffusive transfer, regardless of whether they are classified as diffusion, permeation or unclassified (e.g., SPMDs), and the rate-limiting barrier is the step with the greatest resistance to mass transfer (see Figure 3.1). Pick s first law is the fundamental law of diffusion. It states that the flux of a chemical in the x-direction (j , e.g., ng cm d ) is proportional to the concentration gradient (9C/9x)... 

X. Ren, J. J. Becerra, R. S. Hirsh, et al. Direct oxidation fuel cell operating with direct feed of concentrated fuel under passive water management. US Patent 2004209136 (2004). 

A membrane reactor offers the possibility of combining two individual processes in the same unit operation. (1) Selective permeation (thus separation) can be coupled directly with the reaction by means of either a catalytically active membrane or of a passive membrane placed next to the... 

An important performance characteristic of passive samplers that operate in the TWA regime is the diffusion barrier that is inserted between the sampled medium and the sorption phase. This barrier is intended to control the rate of mass transfer of analyte molecules to the sorption phase. It is also used to define the selectivity of the sampler and prevent certain classes (e.g., polar or nonpolar compounds) of analytes, molecular sizes, or species from being sequestered. The resistance to mass transfer in a passive sampler is, however, seldom caused by a single barrier (e.g., a polymeric membrane), but equals the sum of the resistances posed by the individual media (e.g., aqueous boundary layer, biofilm, and membrane) through which analyte diffuses from the bulk water phase to the sorption phase.19 The individual resistances are equal to the reciprocal value of their respective mass transfer coefficients and are additive. They are directly proportional to the thickness of the barrier... 

Localized corrosion is the direct result of the breakdown of passivity at discrete sites on the material surface. As was stated above, once passivity is established on a surface, one might expect either that it would remain passive or that a complete activation of the surface would occur. However, what is often observed in practice is the appearance of discrete areas of attack that begin to corrode actively while the vast majority of the surface remains passive. These isolated regions of attack are more than mere annoyances the local penetration rates can be on the order of 10 mpy or higher, leading to rapid perforation of any reasonably sized container. Since the original intent in using passive materials (e.g., CRAs) in any application is to exploit their low dissolution rates, localized corrosion can be a major operational problem. 

The level of free calcium in the cytosol is affected by multiple mechanisms of active and passive transport. These are summarized in Figure 6.1. While the level of calcium in the cytosol varies in time, it is always much lower than in the extracellular space, or than in the mitochondria and ER. These two organelles function as intracellular buffers or reservoirs of calcium. Accordingly, calcium transport systems operating in both directions exist not only at the cytoplasmic membrane but also at the mitochondrial (iimer) membrane and the ER. 

Generally speaking, two principal mechanisms operate in the biology of membrane processes, such as membrane transport and permeation. One involves a network of active sites and operates by metabolic energy, and it is referred to as active another is directed by passive diffusion, and it is called passive. This passive mechanism is determined by various aspects of lipid dynamics and lipid-protein interactions, and it can be described in quantitative terms of chemical and phase equilibrium and molecular physics. However, in the highly anisotropic... 

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