Holdup volume

Z. 5-25-Y, large huhhles = AA = 0.42 (NG..) Wi dy > 0.25 cm Dr luterfacial area 6 fig volume dy [E] Use with arithmetic concentration difference, ffg = fractional gas holdup, volume gas/total volume. For large huhhles, k is independent of bubble size aud independent of agitation or liquid velocity. Resistance is entirely in liquid phase for most gas-liquid mass transfer. [79][91] p. 452 [109] p. 119 [114] p. 249... 

Correlations for mass transfer coefficients, gas holdup volume, and interfacial area, as functions of system physical properties and agitation rate or flow velocity, etc. 

Under well-mixed flow conditions, it is reasonable to assume that the mixer holdup volumes, VLmn ind Vomn will vary in direct proportion to the appropriate phase flow rate, and that the total liquid holdup in the mixer will vary as a function of the total flow rate to the mixer. 

Consider the binary batch distillation column, represented in Fig. 3.58, and based on that of Luyben (1973, 1990). The still contains Mb moles with liquid mole fraction composition xg. The liquid holdup on each plate n of the column is M with liquid composition x and a corresponding vapour phase composition y,. The liquid flow from plate to plate varies along the column with consequent variations in M . Overhead vapours are condensed in a total condenser and the condensate collected in a reflux drum with a liquid holdup volume Mg and liquid composition xq. From here part of the condensate is returned to the top plate of the column as reflux at the rate Lq and composition xq. Product is removed from the reflux drum at a composition xd and rate D which is controlled by a simple proportional controller acting on the reflux drum level and is proportional to Md-... 

Note that the above formulation includes allowance for the fractional phase holdup volumes, hL and ho, the phase flow rates, L and G, the diffusion coefficients Dl and Dq, and the overall mass transfer capacity coefficient Klx a, all to vary with position along the extractor. 

Column Length (cm) Internal Diameter (- P u tlcle Size (F ) Column Efficiency (n) Column Holdup Volume ( 1) Peak Stemdard Deviation (Ml) k > 0 k - 5 ... 

Kl is the mass transfer coefficient for the L phase (m/s), a is the interfacial area per unit volume (m2/m3), referred to the total liquid volume of the extractor, V is the total holdup volume of the tank, and is equal to (VL+VG). X is the equilibrium concentration, corresponding to concentration Y, given by... 

Fig. 2.4. Schematic of the microelution plate design. Tip design of the 96-well plate affords a smaller surface area and larger depth, more like an HPLC column, and permits good flow through the plate and low holdup volume on the order of nanoliters [36],...

Figure 1.3 A schematic chromatogram-. VR, retention volume VK-, adjusted retention volume V, elution volume of peak V0, void volume W, peak width VM, holdup volume OX, volume of injector XY, volume of detector, including volume of tubing.

The system is sketched in Fig. 3.1 and is a simple extension of the CSTR considered in Example 2.3. Product B is produced and reactant A is consumed in each of the three perfectly mixed reactors by a first-order reaction occurring in the liquid. For the moment let us assume that the temperatures and holdups (volumes) of the three tanks can be different, but both temperatures and the liquid volumes are assumed to be constant (isothermal and constant holdup). Density is assumed constant throughout the system, which is a binary mixture of A and B. 

A. LIQUID HOLDUPS. The most common and most important trade-off is that of specifying holdup volumes in tanks, column bases, reflux drums, etc. From a steadystate standpoint, these volumes should be kept as small as possible because this will minimize capital investment. The more holdup that is needed in the base of a distillation column, the taller the column must be. In addition, if the material in the base of the column is heat-sensitive, it is very desirable to keep the holdup in the base as small as possible in order to reduce the time that the material is at the high base temperature. Large holdups also increase the potential pollution and safety risks if hazardous or toxic material is being handled. 

Size the holdup volumes so that the closedloop time constants of the material-balance loops are a factor of ten bigger than the closedloop time constants of the product-quality loops. This breaks the interaction between the two types of loops. 

The concept of column void volume (Vg) is important for several reasons. Void volume is the volume of the empty column minus the volume occupied by the solid packing materials. It is the liquid holdup volume of the column that each analyte must elute from. Note that the void volume is equal to the void time multiplied by the flow rate (T). 

Vq is the column holdup volume (including the extra column breakthrough curve is the thick volume)... 

Figure 1.18. Types of chromatograms, (a) Differential chromatogram (b) integral chromatogram (c) peak resolution. O, injection point OX, injector volume OY, detector volume OA, holdup volume, VM OB, total retention volume, VR AB, adjusted retention volume,...

LC-6). Cells LC-1 and LC-2 have holdup volumes of 2.0 and 0.7 ml., respectively. In the case of LC-2 the platinum electrodes and mercury well side arms are part of a standard-taper joint assembly. Cells LC-3 and LC-4 have holdup volumes of 0.16 ml. and external copper electrode caps. Cells LC-3 and LC-4 were stacked so as to be able to shift scales during the demineralization and regeneration half cycles, but a more convenient design was achieved in the compound cells, LC-5 and LC-6, with effective holdup volumes between 0.25 and 0.55 ml. Figure 6 is a drawing of LC-4 and LC-5. By using several inputs into the recorder, a continuous record can be obtained over a wide concentration range. 

Roy, et al (2 ) empirically determined the gas velocity needed to completely suspend a given amount of solid in a 5 cm id x 1.52 m Lucite column using coal and quartz slurried in water, alcohol, or oil. The degree of suspension was found to depend on physical properties as well as gas holdup, volume fraction, bubble diameter, and the contact angle between the solid and liquid. 

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