Column volumetric flowrate

The ratio of the volumetric flowrate out of the purge vent to the volumetric flowrate in the capillary column is termed the split ratio and provides an estimate of and control over the actual volume of sample entering the column. Care should be taken when using the split ratio to estimate actual injected sample volume, or when using it in comparisons between methods on different instruments. There are subtle differences between instruments and measurement techniques that may affect the measured flows. For example, the column volumetric flowrate measured by injecting a nonretained substance is the average column flowrate, not the flowrate at the inlet, while a flowmeter connected to the split purge vent measures the volumetric flowrate at the vent, not in the inlet. With newer, electronically controlled systems, the flows are measured directly at the inlet, or are calculated from the entered inlet conditions and column dimensions. 

The column diameter is normally determined by selecting a superficial velocity for one (or both) of the phases. This velocity is intended to ensure proper mixing while avoiding hydrodynamic problems such as flooding, weeping, or entrainment. Once a superficial velocity is determined, the cross-sectional area of the column is obtained by dividing the volumetric flowrate by the velocity. 

Linear flowrate. F(v). The volumetric flowrate of the carrier gas (mobile phase) divided by the area of the cross section of the column. It is expressed as cm3cm 2/min or cm/min. 

The dynamic losses can only be estimated by first sizing the pipe diameter of the line between the absorption column and the bleaching column. This is performed using recommended liquid velocities (Ref. P1, p. 163) in conjunction with the known volumetric flowrate. The area calculated can be translated into a standard pipe diameter. The dynamic losses are then estimated by two methods. The first employs Genereaux s formula (Ref. P1, p. 160) ... 

Molar concentrations are converted into mole fractions, and volumetric flowrates are converted to molar flowrates for the tray-to-tray calculations in the column. The fresh feedstream F0 is 0.03506 kmol/s with a composition zo = 1 mole fraction A. Since the reaction is equimolar (one mole of A produces one mole of B), the molar flowrate of the bottoms from the column P is equal to the fresh feed flowrate F(). The overall conversion is set at 98%, so the concentration of reactant in the column bottoms (the product stream P) is xP = 0.02 mole fraction A. 

Bed volume of design column, where Q is the fluid volumetric flowrate of the design column... 

Note If you are given the cross-sectional area of the pilot column, you can calculate the diameter of the design column. The volumetric flowrate of each column is known and the velocity in each column is the same. The design column length can then be calculated since the bed volume is known. 

If the design fluid volumetric flowrate (Q) is sufficiently low that equiUbriiun is rapid in comparison, the Equation (7.17) below is a good approximation of the concentration profile for the breakthrough curve as a function of fluid volume (V) put through the column [11], A Langmuir isotherm is assumed where k is the adsorption rate constant for this isotherm. When q M )g> CoV, the effluent solute concentration is approximately zero. For qoM Co V, the effluent solute concentration is C. See for yourself why this makes sense physically. 

Volumetric flowrate, F. The residence time for fluid in the column is ve/F. The linear flowrate is given by U = F/Se, and the superficial flow-rate is Ue = F/S. 

Figure 1.1 shows the surface area generated as a function of power input per unit volume of contactor for a number of different GL contactors. Also shown in Fig. 1.1 is the surface area/gas volumetric flowrate as a function of the power per gas volumetric flowrate. Thus, the lowest values for an ejector or jet loop column correspond to a, the surface area/gas volumetric flowrate, = 1000 s/m and a power per gas volumetric flowrate = 1 kW s/m. ... 

Gas-liquid Residence time, short. Use for very fast reactions, all reaction is in the liquid film and is mass transfer controlled. Gas-liquid surface area max. observed area 800 m /m with the usual range 200-500 m /m or slightly higher than a bubble column. Target species Henry s law constant < 10 kPa/mol fraction feed gas concentration < 1 vol%. Not for foaming. Limited in handling corrosive or particulates. Some flexibility in varying the gas/liquid volumetric flowrates. Related topic about surface area Section 1.6.1. 

The column in this example has 22 stages, so Stage 22 is the column base (or sump ). Figure 4.2c shows a volumetric flowrate of 0.320 m /min leaving Stage 21 and entering the... 

Flowrate F. The volumetric flowrate of the mobile phase, in milliliters per minute, is measured at the column temperamre and outlet pressure ... 

For example, the linear velocity of carrier gas through a 30-m column where methane has a retention time of 2 min is 3000 cm/120 s or 25 cm/s. If desired, the volumetric flowrate F (mL/min) can be computed from the relationship... 

When using a split inlet, there are several flows that provide the exact injected sample amount. The most important of these is the split ratio, which is the ratio of the volumetric flowrate at the split purge vent to the volumetric flowrate in the GC column. Classically, this was measured manually, using a flowmeter to obtain the purge vent flow and by injecting a nonretained substance to obtain the column flowrate. With electronically controlled systems, these values are... 

In practice, however, the liquid velocity relative to fixed particles, Uf, is not very useful. Instead, the velocity of settling relative to the walls of an apparatus, Uf - u, is of practical importance. The volume of the solid phase moving downward should be equal to that of liquid moving upward. This means that volume rates of these phases must be equal. Consider a column of slurry having a unit cross section and imagine the liquid and solid phases to have a well defined interface. The column of solid phase will have a base 1 - e, and the liquid column phase will have a base e. Hence, the volumetric rate of the solid column will be (1 - e)u, and that of the liquid column will be (Uf - u)e. Because these flowrates are equal to each other, we obtain... 

Flowrate. Fc- The volumetric flow rate of the mobile phase (carrier gas), in cm3/min, measured at the column temperature and outlet pressure. 

It may be tempting to increase the loop volume to increase the amount of sample for trace analysis. Before this is done, the system should be examined. If g-in.-diameter columns are used, a reasonable flowrate is 30 mL/min at atmospheric pressure. But if the pressure at the head of the column is at 3 atm (300 kPa) (which is not unreasonable), the volumetric flow at the head and through the sample loop is only 10 mL/min, or 6 s/mL. If the loop volume is increased to 5 mL, it will take 30 s to sweep the sample onto the column. Thus no peak can be any narrower than 30 s. A large-volume loop can completely destroy the separating efficiency of the chromatographic process. Again, as with any analytical problem, a common sense, logical examination of the whole picture will pinpoint problem areas. 

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