Gaseous Flow

Selective catalytic reduction is based on selective reactions of a continuous gaseous flow of ammonia or similar reducing agents with the exhaust stream in the presence of a catalyst. The reaction that occurs is as follows ... 

The subject of this chapter is single-phase heat transfer in micro-channels. Several aspects of the problem are considered in the frame of a continuum model, corresponding to small Knudsen number. A number of special problems of the theory of heat transfer in micro-channels, such as the effect of viscous energy dissipation, axial heat conduction, heat transfer characteristics of gaseous flows in microchannels, and electro-osmotic heat transfer in micro-channels, are also discussed in this chapter. 

Two-dimensional compressible momentum and energy equations were solved by Asako and Toriyama (2005) to obtain the heat transfer characteristics of gaseous flows in parallel-plate micro-channels. The problem is modeled as a parallel-plate channel, as shown in Fig. 4.19, with a chamber at the stagnation temperature Tstg and the stagnation pressure T stg attached to its upstream section. The flow is assumed to be steady, two-dimensional, and laminar. The fluid is assumed to be an ideal gas. The computations were performed to obtain the adiabatic wall temperature and also to obtain the total temperature of channels with the isothermal walls. The governing equations can be expressed as... 

Asako Y, Toriyama H (2005) Heat transfer characteristics of gaseous flows in micro-channels. Microscale Thermophys Eng 9 15-31... 

Dehydrochlorination of a 1-chlorosilanamine by vacuum gas solid reaction (VGSR). The presence of the iminosilane was confirmed by direct analysis of the gaseous flow.7... 

When a gaseous flow of cyclopropylcarbinyl chloride is passed over NaY zeolite at room temperature, formation of cyclobutyl chloride and allylcarbinyl chloride was observed (scheme 4), as well as cyclopropylcarbinyl chloride (product and unreacted starting material). These data are consistent with formation of the C4H7+ cation with internal return of the chloride ion. 

Lozano, A., B. Yip, and R. K. Hanson. 1992. Acetone A tracer for concentration measurements in gaseous flows by planar laser-induced fluorescence. Experiments Fluids 13 369-76. 

Extensive reviews of active instability suppression techniques are found in McManus et al. [18] and Candel [19]. Also, Zinn and Neumeier [20] provide an overview of research and developmental needs for practical applications. Most of the previous studies have used actuators impractical in liquid-fueled systems, such as loudspeakers that impose acoustic perturbations on gaseous flow. The major emphasis in the present study was to establish active instability suppression using liquid-fuel injection. According to Rayleigh s criterion [21, 22], combustion-acoustics interaction can be used to damp the undesirable oscillations provided that pressure fluctuations p and heat release fluctuations q satisfy the proper phase relation such that... 

In combustion experiments, there are two key considerations first, generating a flame and second, detecting the species of interest. Gaseous flows in a flame can be classified as laminar (streamlined layers) or turbulent. While these flames can be analyzed directly, it is less confounding to study flame chemistry through controlled generation of reactive species in one of a wide variety of experimental apparata. 

In order to be able to design even the most elementary vacuum line, it is necessary to know something of the basic theory concerning the movement of molecules within the system. No attempt will be made here to instruct the reader in the details of vacuum physics and therefore the formulae given below have been kept simple. A more detailed discussion of the theory of gaseous flow can be found in Bushman s excellent review (Bushman, 1962). The object of the following discussion is simply to allow the reader to assess, without too much effort, the approximate efficiency of the system he is planning. 

Unsteady gaseous flow in rectangular microchannels frequency response of one or two pneumatic lines connected in series, Eur. J. Mech. B/Fluids 1998, 17, 79-104. 

One can evaluate this phenomenon by periodically subjecting the catalyzed material to gaseous flows at temperatures anticipated in service and noting weight losses. Monoliths can be mounted on a rotating carousel that moves in and out of streams of heated gas. 

There are four well-known types of diffusion in solids [10] gaseous or molecular diffusion [75], Knudsen diffusion [76-80], liquid diffusion [10], and atomic diffusion. In Figure 5.27, the possible transport mechanisms in porous media are schematically shown [77], Gaseous flow (Figure 5.27a)... 

FIGURE 5.27 Transport mechanisms in porous media molecular or gaseous flow, (a) Knudsen flow, (b) surface diffusion, (c) multilayer diffusion, (d) capillary condensation, and (e) configurational diffusion. 

B = characteristic constant of gaseous flow D°, D, D = effective, apparent effective (Equ.3) and e e effective Khudsen diffusivities respectively. 

Significant temperature gradients in the furnace chamber will cause gaseous flow from hot to cold, which may apply a spurious force to the specimen pan. This is a more severe effect for chambers under moderate vacuum ( thermomolecular flow [3]). Purge gas flow direction may be an important consideration, in order to avoid condensation of gaseous products on the hangdown wire, or along the balance beam, as the gas flows out of the hot zone of the furnace. 

This inaccuracy stems from their calculation of molecular transport effects, such as viscous dissipation and thermal conduction, from bulk flow quantities, such as mean flow velocity and temperature. This approximation of microscale phenomena with macroscale information fails as the characteristic length of the (gaseous) flow gradients approaches the average distance travelled by molecules between collisions - the mean path. The ratio of these quantities is referred to as Knudsen number. 

Gaseous flow in microchannels was experimentally analyzed by Shih et al. [44] with helium and nitrogen as the working fluids. Mass flow rate and pressure distribution along the channels were measured. Helium results agreed well with the results of a theoretical analysis using slip flow conditions, however there were deviations between theoretical and experimental results for nitrogen. 

Hydrodynamically fully-developed laminar gaseous flow in a cylindrical microchannel with constant heat flux boundary condition was considered by Ameel et al. [2[. In this work, two simplifications were adopted reducing the applicability of the results. First, the temperature jump boundary condition was actually not directly implemented in these solutions. Second, both the thermal accommodation coefficient and the momentum accommodation coefficient were assumed to be unity. This second assumption, while reasonable for most fluid-solid combinations, produces a solution limited to a specified set of fluid-solid conditions. The fluid was assumed to be incompressible with constant thermophysical properties, the flow was steady and two-dimensional, and viscous heating was not included in the analysis. They used the results from a previous study of the same problem with uniform temperature at the boundary by Barron et al. [6[. Discontinuities in both velocity and temperature at the wall were considered. The fully developed Nusselt number relation was given by... 

In the study of Fan, et al. [If], a numerical simulation of gaseous flows in microchannels by the DSMC was carried out. Several unique features were obvious to maintain a constant mass flow, the mean streamwise velocity at the walls was found to increase to make up for the density drop caused by the pressure decrease in the flow direction, which is in contrast to the classical PoisueUe flow. In addition, the velocities at the walls were found to be nonzero and to increase in the streamwise direction, which highlights the slip-flow effect due to rarefaction. The results of the DSMC simulations were validated by an analytical solution in the slip regime. It was observed that the two results showed remarkable agreements. 

ArkUic, E.B., Breuer, K.S. and Schmidt, M.A., Gaseous Flow in Microchaimels, Ap-plieation of Mierofabrication to Fluid Meehanies, ASME FED-197, 1994, 57-66. 

Fan, Q., Xue, H. and Shu, C., DSMC Simulation of Gaseous Flows in Microchannels, 5 ASME/JSME Thermal Engineering Joint Conference, San Diego, U.S.A, AJTE99-6519, 1999. 

Kakag, S., Vasiliev, L.L., Bayazitoglu, Y. and Yener, Y., (eds.). Microscale Heat Transfer - Fundamentals and Applications, 2005, Kluwer, The Netherlands. Kavehpour, H.P., Faghri, M. and Asako, Y., Effects of Compressibility and Rarefaction on Gaseous Flows in Microchannels, Numerical Heat Transfer, 1997, Part A, 32, 677-696. 

Tunc, G. and Bayazitoglu, Y., Heat Transfer for Gaseous Flow in Microtubes with Viscous Heating, Proceedings of the ASME Heat Transfer Division, HTD 366-2, 2000, 299-306. 

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