Linear flow velocity

When a gas or liquid flows over a surface, the pressure at the surface is reduced according to the formula shown in equation (1), in which d is the density and v is the linear flow velocity of the moving stream. 

Reduce linear flow velocities to eliminate static charge buildup during feed... 

The volume flow rate between different column dimensions can be calculated easily (assuming constant linear flow velocity) according to... 

Fig. 17.7. Fluidised bed adsorption of G3PDH from milled yeast homogenate onto zirconia-silica Cibacron Blue. The feedstock (20% w/v) was fed to the bead mill at a rate 4.05 dm3-h 1, which corresponded to a linear flow velocity of 250 cm-h 1 within the BRG contactor with a settled bed height of 21 cm. The disrupted baker s yeast homogenate from the bead mill was applied to the integrated fluidised bed directly and terminated when C/Ca = 0.65.

Fig. 17.8. Elution of L-asparaginase from CM HyperD LS in fluidised beds. The beds were washed with five settled bed volumes (SBVs) of buffer A at the loading flow velocity (BRG contactor 250 cm/h). Elution was achieved in fluidised bed mode at a linear flow velocity of 100 cm/h by a step of 1.0 M NaCl in buffer A.

Van Deemter equation An equation relating efficiency (HEPT in mm) to linear flow velocity in a chromatographic column. The efficiency is expressed as the height equivalent to a theoretical plate HEPT = A + BIV + Cv), where A, B, and Cv are constants and V is the linear velocity of the carrier gas. This equation tells us that to obtain maximum efficiency, the carrier gas flow must be optimized. 

The presence of two phases in the reaction mixture may seem to be a mass-transfer engineering problem, but even moderate stirring of the mixture produces an emulsion, which greatly facilitates the phase transfer steps of the reaction mechanism. In our fixed-bed reactor, the turbulence resulting from the flow rates used seemed to suffice to eliminate external mass transfer hmitations. At MeOH SA of 20 and identical LHSV values, similar acid conversions were observed for two linear flow velocities differing by a factor of two. 

Fig. 28. Effect of pH of the mobile phase on linear flow velocity (1) and electrical current (2) in the monolithic capillary column. (Reprinted with permission from [149]. Copyright 1998 American Chemical Society). Conditions monolithic capillary column 100 pm i. d. 30 cm, mobile phase 80 20 acetonitrile/5 mmol/1 phosphate buffer, pH adjusted by addition of concentrated NaOH, flow marker thiourea 2 mg/ml, UV detection at 215 nm, voltage 25 kV, pressure in vials 0.2 MPa, injection, 5 kV for 3 s...

Fig. 8. Effect of linear flow velocity of an L-benzoyl arginine ethylester solution (0.2 mol/1) on the enzymatic activity of trypsin immobilized on poly(glycidyl methacrylate-co-ethylene dimethacrylate) beads (curve 1) and monolith (curve 2) (Reprinted with permission from [90]. Copyright 1996 Wiley-VCH). Reactor 50 mm x 8 mm i.d., temperature 25 °C...

In liquid chromatography, the diffusion rates are slower than that in gas chromatography, and the values of DM and D are very small therefore, the minimum H value is obtained at a low flow rate, as shown by curve E in Figure 5.6. The value of H increases slowly at higher flow rates in liquid chromatography. An experimental result is shown in Figure 5.7. The HETP was minimal at a certain flow rate, and the measured optimum value was less than 10 pm for this column. The optimum flow rate was about 0.9 ml min - corresponding to a linear flow velocity of about 55 mm min -. ... 

Figure 5.6 Van Deemter curves relating H to linear flow velocity. A, eddy diffusion term ...

Figure 5.7 HETP of compounds with different k values related to linear flow velocity.

The advantages of pressure programming are demonstrated in Fig. 10 by comparing isobaric separations at 30 and 100 bar with a separation obtained by pressure-programming at column inlet pressures increasing from 30 to 225 bar (73). At low inlet pressure the early peaks are separated and eluted within 5 min, whereas the last one is eluted with tailing after an additional 5 min. The linear flow velocity is 1.1 cm/sec At 100 bar the... 

Type of slurry—linear flow velocity (settling)... 

An important measure concerning column characterization in LC is the column permeability, which represents the capacity of the support to transport the mobile phase as consequence of a pressure drop occurring over the column. In other words, the permeability of a column determines the required pressure to achieve the desired flow rate. The linear flow velocity (u) across an empty cylindrical column is given by... 

In RPC, as in all modes of chromatography, when a peptide is eluted under isocratic conditions, the retention can be expressed in either time, te, or volume, Ve, units. Expressions of the elution time or elution volume of a peptide, eluting with a peak width w (= 4ot=4ov), from a column packed with RPC particles of mean particle diameter dp, incorporate the physical aspects of the column (diameter dc, length L), the flow rate F (or linear flow velocity, v = LFIVm) and the phase ratio, mobile phase in the chromatographic column. Usually, retention dependencies for a peptide P, are represented in terms of a capacity factor k as follows ... 

Under conditions where the plug flow assumption is valid, that is, concentration gradients are negligible so that the linear flow velocity of the carrier gas is the same as that of the reactants, the time (t) for A and B to travel a distance d along the flow tube is given by... 

Consider a gas, near ambient pressure and temperature, forced by a small pressure gradient to flow through the channels of a packed bed of powder. At room temperature, a gas molecule can be adsorbed on a solid surface for an extremely short time but not less than the time required for one vibrational cycle or about 10 sec. When the adsorbed molecule leaves the surface it will, on the average, have a zero velocity component in the direction of flow. After undergoing one or several gas-phase collisions it will soon acquire a drift velocity equal to the linear flow velocity. These collisions and corresponding momentum exchanges will occur within one,... 

Another cell design that aids to minimize the effects of thermal diffusion is the capillary cell. Fig. 15.10c. By using capillary tubing on the vent side of the cell, a sufficiently high linear flow velocity is maintained to prevent... 

Figure 3. Separation of 1, -naphthol 2, resorcinol 3, hydroquinone 4, 2,6-di-aminotoluene 5, 2,4-diaminotoluene 6, 2,4-diaminoanisole and 7, 2,5-diamino-toluene. Mobile phase, 86.4/13.6 w/w % hexanes/ethanol linear flow velocity, 2.66 mm s 1 pressure drop, 380 psi X = 235 nm column, 250 X 4 mm Polygosil 10 fjjn CN.

Concentration of 500-L samples was usually performed at a flow rate of 150 mL/min and 500 lb/in.2. A piston-type pulse dampener (Hydrodyne) was used to minimize breakdown of resin particles. Flow rates did not exceed 250 mL/min (0.2-cm/s linear flow velocity). 

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