Liquid displacement

Hindered Settling When particle concentration increases, particle settling velocities decrease oecause of hydrodynamic interaction between particles and the upward motion of displaced liquid. The suspension viscosity increases. Hindered setthng is normally encountered in sedimentation and transport of concentrated slurries. Below 0.1 percent volumetric particle concentration, there is less than a 1 percent reduction in settling velocity. Several expressions have been given to estimate the effect of particle volume fraction on settling velocity. Maude and Whitmore Br. J. Appl. Fhys., 9, 477—482 [1958]) give, for uniformly sized spheres,... 

In the top (clarifying) zone the relatively clear liquid moves upward and overflows the top. In the middle zone the solid particles settle as the displaced liquid moves upward, and both the local solids concentration and the settling velocity vary from point to point. In the bottom (compressed) zone, the solids and liquid both move downward at a rate that is determined mainly by the underflow draw-off rate. For a given feed rate and solids... 

Because the batch flux data are obtained in a closed system with no outflow, the net solids flux is zero in the batch system and Eq. (14-40) reduces to FL = —(pV%/ 1 — cp). Note that FL and Vs are of opposite sign, because the displaced liquid moves upward as the solids settle. The relative velocity between the solids and liquid is Vr = Vs — VL which, from Eq. (14-20), is Vr = Fs/(1 — relative velocity that controls the dynamics in the thickener. If the underflow draw-off rate from the thickener is gu, the additional solids flux in the thickener due to superimposition of this underflow is qu = Qu/A = Vu. Thus, the total solids flux at any point in the thickener (qs) is equal to the settling flux relative to the suspension (i.e., the batch flux qsb) at that point, plus the bulk flux due... 

The three most common ways of obtaining true density measurements are gas pycnometry (gas displacement), liquid displacement, and flotation in a liquid. These three techniques have been compared based on accuracy, ease of use, and instrumentation [63], and the results are summarized in Table 4. Gas pycnometry will be discussed in this section because of its wide use and ease of operation. 

Reservoir method This method makes use of the displacement principle. Brine or any other saturated solution in which a gas has low solubility is used as the liquid. Gas from the column is collected in a burette from which the displaced liquid flows to a reservoir. As the gas collection proceeds, the gas is collected under increasing pressure conditions, thereby changing the flow rate as well as the frequency of bubble formation. In order to collect gas under atmospheric conditions, the levels of the liquid in the burette and the reservoir must always be kept equal. This requires manual adjustments. 

The force due to the movement of the liquid surrounding the bubble is m (dt>ldt). For a sphere moving in an infinite medium of an inviscid fluid, the mass of the liquid m is equal to half the mass of the displaced liquid. The authors, however, assumed merely a direct proportionality between m and the mass of the displaced fluid, instead of the above relationship, because they considered their flow not to be irrotational. 

Fig. 9. Apparatus for sluijy packing of columns. After the properly fittul column tube is attached to the bottom of the reservoir, both are filled up with the slurry ofthe micropartic-ulate stationary phase. Thereafter a displacement liquid is pumped into the reservoir by the constant pressure pump, e.g., Haskel Model DST>I00, which is driven by preuurized air. Upon displacement, the slurry from the reservoir is filtered over the porous etal frit at the bottom of the column tubing which becomes densely packed with the partic s. By intermit-tently operating the liquid shut-off valve between the pump and the reservoirpressure waves can te generated in order to flirther compact the column packing. Reprinted from Bakalyar et at. U05) with permission from Spectra-Physics.

Plunger pumps differ from piston pumps in that they have one or more constant-diameter plungers reciprocating through packing glands and displacing liquid from cylinders in which there is consider-... 

During SIVE applications, traditional soil vapor extraction (SVE) is augmented by steam, which is injected into the subsurface. The steam vaporizes volatile and semivolatile contaminants and displaces liquids in soil pores. Both vapor and liquids are then pumped to the surface via extraction wells. 

If the powder has no porosity the true density can be measured by displacement of any fluid in which the solid remains inert. The accuracy of the method is limited by the accuracy with which the fluid volume can be determined. Usually, however, the solid particles contain pores, cracks or crevices which will not be completely penetrated by a displaced liquid. In these instances the true density can be measured by using a gas as the... 

Liquid chromatography is two decades more mature than capillary electrophoresis. As trained electropherographers become more common, more separations will be handled by electrophoresis. For example, electrophoresis displaced liquid chromatography as the preferred method for forensic analysis of alkaloids in opium and heroin.51 The enabling technology for this application was dynamic coating of the capillary between runs to eliminate adsorption of analytes on the silica surface and decrease variations in migration times to less than 0.5%. 

A buoyant spherical particle of diameter D floating in a liquid which has no tendency to wet, ie, pull the shoreline up, or to reject, ie, push the shoreline down, the solid submerges to a depth d at which the downward force of gravity on the sphere equals the upward buoyancy force of the displaced liquid. This occurs when... 

A hydrometer is used to determine the density or specific gravity of a liquid using the principles of buoyancy. Buoyancy results from the upthrust on any object immersed or partially immersed in a liquid. Upthrust is developed as a consequence of the weight of the displaced liquid. At the point of partial immersion at... 

Positive displacement Liquids only 20 (See Volume 1, Section 6.3.9) Hydrocarbon liquids, glues, food products (jams, chocolate, etc.) Suitable for high viscosity fluids. High accuracy and wide range... 

Rose examined the flow pattern in a capillary tube where one immiscible liquid displaces another one. In the front end of the displacing liquid the flow pattern is one he termed fountain flow, and in the other reverse fountain flow. In polymer processing the significance of the former was demonstrated in the advancing melt front in mold filling (see Chapter 13). 

Much has been written about solid metal electrodes, which have now largely displaced liquid mercury. Those most often used as redox ( inert ) electrodes for studying electron transfer kinetics and mechanism, and determining thermodynamic parameters are platinum, gold, and silver. However, it should be remembered that their inertness is relative at certain values of applied potential bonds are formed between the metal and oxygen or hydrogen in aqueous and some non-aqueous solutions. Platinum also exhibits catalytic properties. 

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