In-situ velocity

The volume fraction, sometimes called holdup, of each phase in two-phase flow is generally not equal to its volumetric flow rate fraction, because of velocity differences, or slip, between the phases. For each phase, denoted by subscript i, the relations among superficial velocity V, in situ velocity Vj, volume fraclion Rj, total volumetric flow rate Qj, and pipe area A are... 

The flow problems considered in the previous chapter have concerned either single phases or pseudo-homogeneous fluids such as emulsions and suspensions of fine particles in which little or no separation occms. Attention will now be focussed on the far more complex problem of the flow of miflti-phase systems in which the composition of the mixture may show spatial variation over the cross-section of the pipe or channel. Furthermore, the two components may have different in-situ velocities as a result of which there is shp between the two phases and in-situ holdups which are different from those in the feed or exit stream. Fiuthermore, the residence times of the two phases will be different. 

By applying hot-wire anemometry, in-situ velocity and concentration measurements enabled to evaluate the mixing time and the inner recirculation ratio of the gas phase, and to describe the mixing patterns in this novel unit. Mixing time was evaluated from the time the tracer gas injected to the state of uniform tracer concentration inside the reactor. At the impeller speed of 1200 revolution per minute (RPM), the mixing time was about 1.5 seconds. It was observed that... 

The slip velocity between gas and liquid is v, = Vc Vi. For two-phase gas/liqiiid flow, Ri + Rc = 1. A very common mistake in practice is to assume that in situ phase volume fractious are equal to input volume fraclions. 

In principle, there is no upper bound in measurements of particle velocity (or stress) using laser velocity interferometry. In practice, very high-pressure shock fronts can cause copious jetting of microparticles from the free surface (Asay et al., 1976), obscuring the surface from the laser beam. To alleviate this, optically transparent materials can be bonded to the specimen, and particle velocity measurements are then made at the specimen/window interface. This has the added advantage of simulating in situ particle velocity... 

In mechanistic studies of stress corrosion and also in the collection of data for remaining-life predictions for plant there is need for stress-corrosion crack velocity measurements to be made. In the simplest way these can be made by microscopic measurement at the conclusion of tests, the assumption being made that the velocity is constant throughout the period of exposure, or, if the crack is visible during the test, in situ measurements may be made by visual observation, the difficulty then being that it is assumed that the crack visible at a surface is representative of the behaviour below the surface. Indirect measurements must frequently be resorted to, and these... 

Because the gas always flows at a velocity greater than that of the liquid, the in situ volumetric fraction of liquid at any point in a pipeline will be greater than the input volume fraction of liquid furthermore it will progressively change along the length of the pipe as a result of expansion of the gas. 

Room temperature CO oxidation has been investigated on a series of Au/metal oxide catalysts at conditions typical of spacecraft atmospheres CO = 50 ppm, COj = 7,000 ppm, H2O = 40% (RH) at 25 C, balance = air, and gas hourly space velocities of 7,000- 60,000 hr . The addition of Au increases the room temperature CO oxidation activity of the metal oxides dramatically. All the Au/metal oxides deactivate during the CO oxidation reaction, especially in the presence of CO in the feed. The stability of the Au/metal oxide catalysts decreases in the following order TiOj > FejO, > NiO > CO3O4. The stability appears to decrease with an increase in the basicity of the metal oxides. In situ FTIR of CO adsorption on Au/Ti02 at 25 C indicates the formation of adsorbed CO, carboxylate, and carbonate species on the catalyst surface. 

Although NMRI is a very well-suited experimental technique for quantifying emulsion properties such as velocity profiles, droplet concentration distributions and microstructural information, several alternative techniques can provide similar or complementary information to that obtained by NMRI. Two such techniques, ultrasonic spectroscopy and diffusing wave spectroscopy, can be employed in the characterization of concentrated emulsions in situ and without dilution [45],... 

The evaluation of the parameters for this flow regime requires the calculation of the Reynolds number and hydraulic diameter for each continuous phase. The hydraulic diameter can be determined only if the holdup of each phase is known. This again illustrates the importance of understanding the fluid mechanics of two phase systems. Once the hydraulic diameter is known, the Reynolds number can be evaluated with the knowledge of the in situ phase velocity, and the parameters of the model equations can be evaluated. 

The transformation of n-Ci6, (Aldrich, > 99.9 % purity) was carried out in a fixed bed stainless steel reactor under the following conditions temperature = 220°C, total pressure = 30 bar, H2/n-alkane molar ratio = 20, WHSV (weight hourly space velocity) = 2-100 h 1. WHSV was changed by modifying the catalyst weight and/or the flow rates in order to obtain different conversion values. Before use, the catalysts were reduced in-situ under hydrogen flow at 450°C during 6h. 

Sensors based on acoustic principles are suitable for in-situ-measurements of gas concentration in industrial processes. They can even be used for aggressive media [1]. The velocity of sound - in the following formula marked as VOS - is taken as the characteristic criterion. 

The analysis can be made in situ using an optical, thermal, electrical or other method. The average time, during which the reaction proceeds before an element of volume and reaches a distance d along the reaction tube, is d/v, where v is the linear velocity. From the measurements made at various... 

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