Gases diffusivities

Graham s law of diffusion This law states that the rates at which two gases diffuse are inversely proportional to their densities, i.e. 

Graham s Law of Diffusion. The rates at which gases diffuse under the same conditions of temperature and pressure are inverseiy proportionai to the square roots of their densities ... 

Numerous systems in science change with time or in space plants and bacterial colonies grow, chemicals react, gases diffuse. The conventional way to model time-dependent processes is through sets of differential equations, but if no analytical solution to the equations is known, so that it is necessary to use numerical integration, these may be computationally expensive to solve. 

Molecular gases, diffusion through vitreous silica, 22 422... 

Making a Model Acid precipitation often falls to Earth hundreds of kilometers away from where the pollutant gases enter the atmosphere because the gases diffuse through the air and are carried by the wind. In this lab, you will model the formation of acid rain to observe how the damage caused by acid varies with the distance from the source of pollution. You also will observe another factor that affects the amount of damage caused by acid rain. 

Gases diffuse from areas of high concentration to areas of low concentration. The speed at which diffusion occurs in the body depends on partition coefficients. The faster the concentration in the lung and brain tissues reaches the inhaled concentration of an anesthetic, the sooner a patient is induced. 

Another way to use silicon wafers as DLs was presented by Meyers and Maynard [77]. They developed a micro-PEMFC based on a bilayer design in which both the anode and the cathode current collectors were made out of conductive silicon wafers. Each of fhese componenfs had a series of microchannels formed on one of their surfaces, allowing fhe hydrogen and oxygen to flow through them. Before the charmels were machined, a layer of porous silicon was formed on top of the Si wafers and fhen fhe silicon material beneath the porous layer was electropolished away to form fhe channels. After the wafers were machined, the CEs were added to the surfaces. In this cell, the actual diffusion layers were the porous silicon layers located on top of the channels because they let the gases diffuse fhrough fhem toward the active sites near the membrane. 

Because the mucus layer or the underlying cells may serve as either final accumulation sites of toxic gases or layers through which the gases diffuse en route to the blood, we need simplified models of these layers. Altshuler et al. have developed for these layers the only available model that can be used in a comprehensive system for calculating tissue doses of inhaled irritants. It assumes that the basement membrane of the tracheobronchial region is covered with three discrete layers an inner layer of variable thickness that contains the basal, goblet, and ciliated cells a 7-Mm middle layer composed of waterlike or serous fluid and a 7-Mm outer layer of viscous mucus. Recent work by E. S. Boatman and D. Luchtel (personal communication) in rabbits supports the concept of a continuous fluid layer however, airways smaller than 1 mm in diameter do not show separate mucus and serous-fluid layers. 

In the first instance (1,3) two types of nickel are used on the side exposed to the gas, large pores are produced in the metal and adjacent to this structure, a network of smaller pores are produced to hold back the electrolyte. The reacting gases diffuse rapidly in the large pores and come in intimate contact with the electrolyte present in the small pores. For the electrochemical reaction po occur, a three phases contact is needed since a gaseous reactant produces a solvated reactior oro uct nd in this process an electron is given or withdrawn from a solid conducting substrate. 

Gases diffuse from areas of high partial pressure to areas of low partial pressure thus, the tension of anesthetic in the alveoli provides the driving force to establish brain tension. In fact, the tension of anesthetic in all body tissue will tend to rise toward the lung tension as equilibrium is approached. Consequently, factors that control or modify the rate of accumulation of anesthetic in the lung (e.g., rate of gas delivery, uptake of gas from the lung into the pulmonary circulation) will simultaneously influence the rate at which tension equilibria in other body compartments is established. 

The results of the delayed stress on radiation studies presented above (Figure 7) are also consistent with the mechanism of gas buildup within the polymer specimens as the cause of the accelerated creep. An additional interesting conclusion is that applied stress should increase the rate at which gases diffuse out of a polymer specimen. This is not unreasonable in view of the fact that this conclusion is reached for stress application during irradiation, when expansion of the polymer matrix by the internally generated gas would be expected to facilitate gas diffusion. (Actually, one would expect increased gas diffusion in stressed glassy polymers, even in the absence of radiation, owing to the low Poisson ratio in such materials.)... 

When we put two gases together, the molecules diffuse throughout the container, so that within a short time the mixture is homogeneous, or of uniform concentration throughout. Not all gases diffuse at the same rate, however the lighter the molecule, the more rapid the diffusion process. 

The gases diffusing through the pellet obey the ideal gas law. 

All gases diffuse to fill the space available. In Figure 1.13, after a day the brown-red fumes of gaseous bromine have spread evenly throughout both gas jars from the liquid present in the lower gas jar. 

Gases diffuse at different rates. If one piece of cotton wool is soaked in concentrated ammonia solution and another is soaked in concentrated hydrochloric acid and these are put at opposite ends of a dry glass tube, then after a few minutes a white cloud of ammonium chloride appears (Figure 1.14). This shows the position at which the two gases meet and react. The white cloud forms in the position shown because the ammonia particles are lighter and have a smaller relative molecular mass (Chapter 4, p. 62) than the hydrogen chloride particles (released from the hydrochloric acid) and so move faster. 

Chapter 7 covers the kinetic theory of gases. Diffusion and the one-dimensional velocity distribution were moved to Chapter 4 the ideal gas law is used throughout the book. This chapter covers more complex material. I have placed this material later in this edition, because any reasonable derivation of PV = nRT or the three-dimensional speed distribution really requires the students to understand a good deal of freshman physics. There is also significant coverage of dimensional analysis determining the correct functional form for the diffusion constant, for example. 

Diffusion occurs when one material spreads into or through another. Gases diffuse rapidly and move from one place to another. 

Consider the system shown in Fig. 11-1. A thin partition separates the two gases A and B. When the partition is removed, the two gases diffuse through each other until equilibrium is established and the concentration of the gases is uniform throughout the box. The diffusion rate is given by Fick s law of diffusion, which states that the mass flux of a constituent per unit area is proportional to the concentration gradient. Thus... 

Graham s Law of Effusion states that at the same temperature and pressure, gases diffuse at a rate inversely proportional to the square roots of their molecular masses. What this translates to is that lighter (less dense) gases travel faster than heavier (more dense) gases. 

The permeability of concrete and the rates at which ions and gases diffuse in it are of major importance for durability. We shall consider only the behaviour of cement paste. 

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