Gas-particle exchange

Ideal gas particles exchange energy only by means of perfectly elastic collisions — collisions in which the total kinetic energy of the particles remains constant. 

Uptake and release of water is an important special case of gas-particle exchange. The importance of water arises because of its ubiquity and abundance, sensitivity of equilibrium liquid water content to RH, and frequent rapid changes of RH in response to changes in temperature associated with vertical motions of air parcels (cf. Section 4.04.3.3 and Figure 14). 

Fig. 2.1 Gas particles exchanging momentum through collisions with the molecules of the container wall...

The pressure of a fluid on a surface is defined as the normal force exerted by the fluid per unit of surface area. Assuming a gas within a cylinder, gas particles exchange momentum through collisions and interactions with the molecules of the container walls (Fig. 2.1). 

Thus the atmospheric component of the planet s radiation budget is strongly modulated by the indirect effects of oceanic gas and particle exchange. As will be... 

Heterogeneous processes play a role in several ways including gas-particle conversions, gas uptake by cloudwater and precipitation, exchange of gases into or from the oceans, and exchange of gases into or from soil. 

Figure 10. Continuous particle-gas heat exchange. (Kwauk and Tai, 1964.)...

The second transformation is again Schofield s, and the first one has been added to assure the exact reproduction of the quantum mechanical ideal gas behavior if particles exchange symmetry effects may be neglected [318, 286]. 

The three main processes by which atmospheric deposition of pesticides to the lakes occurs are wet deposition (rain and snow), dry deposition (particulates), and air-water gas exchange. For many of the banned pesticides, gas exchange across the air-water interface, in particular, is often the dominant deposition process, when compared with precipitation and dry particle exchange [42-44], The physicochemical considerations, as well as descriptions of calculation models for atmospheric deposition to lakes, rivers, and the oceans, have been reviewed extensively [45-47]. 

Pankow, J.F. 1988. The calculated effects of non-exchangeable material on the gas-particle distribution of organic compounds. Atmos. Environ. 22 1405-1409. 

Each particle exchanges energy due to radiation with its neighbours. To take into account reflection between the particles it is assumed that each particle contributes its radiative loss to a global radiation field. The radiation field is related to the flow model, and the cell each particle is contributing its radiative heat loss to, is determined by the position of the neighbour particles. It is assumed that no radiation due to short ray travelling distances is absorbed in the gas phase between the particles. 

A numerical model is presented to describe the thermal conversion of solid fuels in a packed bed. For wood particles it can be shown, that a discretization of the particle dimensions is necessary to resolve the influence of heat and mass transfer on the conversion of the solid. Therefore, the packed bed is described as a finite number of particles interacting with the surrounding gas phase by heat and mass transfer. Thus, the entire process of a packed bed is view as the sum of single particle processes in conjunction with the interaction of the gas flow in the void space of a packed bed. Within the present model, neighbour particles exchange heat due to conduction and radiation with each other. 

When the gas flow 0je reaches the TPB (x = 5), the ionization of the atom or molecular gas takes place depending on the correlation of the speed of exchange reactions as well as the concentration and diffusion coefficients of various forms of the adsorbed gas particles. Different scenarios of extension of the electrode process zone are also possible. 

In the framework of this description an attempt to model an effect of spatial non-uniformity of real catalytic systems was made (Bychkov et al., 1997). It was assumed that reaction proceeds in a heterogeneous system represented by two active infinite plane surfaces and in the gas gap between them. Surface chemistry was treated as for the Li/MgO catalyst (see Table III). Because of substantial complexity of the kinetic scheme consisting of several hundred elementary steps, the mass-transfer was described in this case as follows. The whole gas gap was divided into several (up to 10) layers of the same thickness, and each of them was treated as a well-stirred reactor. The rate of particle exchange between two layers was described in terms of the first-order chemical reaction with a rate constant ... 

Pankow, J. F., and Bidleman, T. F. (1991) Effects of temperature, TSP and percent non-exchangeable material in determining the gas-particle partitioning of organic compounds, Atmos. Environ. 25A, 2241-2249. 

---