Measurement of flowrate

On industrial plants, the instruments are therefore required not only to act as indicators but also to provide some link which can be used to help in the control of the plant. In this chapter, pressure measurement is briefly described and methods of measurement of flowrate are largely confined to those which depend on the application of the energy... 

The Doppler meter may be used wherever small particulate solids, bubbles or droplets are dispersed in the fluid and are moving at essentially the same velocity as the fluid stream which is to be metered. A continuous ultrasonic wave is transmitted, again at an acute angle to the wall of the duct, and the shift in frequency between the transmitted and scattered waves is measured. This method of measurement of flowrate is frequently used for slurries and dispersions which present considerable difficulties when other methods are used. 

Proper Measurement of Flowrates with Packed Columns and Appropriate Devices... 

LSI.) 7)45 1982. Determination of Flowrate of Fluids in Closed Conduits of Circular Cross Section—Method of Velocity Measurement at One Point of the Cross-section. Inteniational Organisation for Standardisation, 1982. 

In a series of experiments on the flow of flocculated kaolin suspensions in laboratory and industrial scale pipelines(26-27-2Sl, measurements of pressure drop were made as a function of flowrate. Results were obtained using a laboratory capillary-tube viscometer, and pipelines of 42 mm and 205 mm diameter arranged in a recirculating loop. The rheology of all of the suspensions was described by the power-law model with a power law index less than unity, that is they were all shear-thinning. The behaviour in the laminar region can be described by the equation ... 

For example, suppose a liquid is being pumped from one vessel into another vessel using a pump and under the action of flow control using an orifice plate to measure the flowrate. The head losses involved will be... 

Assume an orifice plate to measure the flowrate with diameter ratio of 0.4 and discharge coefficient of 0.62 ... 

In most problems, the concentration of contaminant is so small that there is virtually no difference between the concentration based on the mass flowrate of water and the mass flowrate of the mixture. However, it is important to be consistent and follow the convention given in Equation 26.1. The other point to note is regarding the units. It is convenient to define the flowrate in terms of metric tons (typically tons per hour or tons per day). It is also convenient to define the concentration in terms of parts per million (ppm). If the basic unit of flowrate is taken to be tons and concentration to be parts per million, then the mass load is measured in grams (typically grams per hour or grams per day). 

Data reconciliation is the process of adjusting or reconciling the process measurements to obtain more accurate estimates of flowrates, temperatures, compositions, etc., that are consistent with material and energy balances. 

RP-HPLC has been employed for the determination of flavonoids and other phenolic compounds in cranberry juice. The neutral and acidic analytes were preconcentrated octadecyl silica SPE cartridges conditioned with distilled water (neutral analytes) or with 0.01 M HC1 (acidic compounds). Hydrolysis of samples was carried out in aqueous methanol solution acidified with 6 M HC1 at 35°C for 16h. Chromatographic separation was performed in an ODS column (150 X 4.6mm i.d. particle size 5/.an). Solvents A and B were water-acetic acid (97 3, v/v) and methanol, respectively. The gradient started with 0 per cent B (flow rate, 0.9 ml/min), reached 10 per cent B in lQmin (flowrate, 1.0 ml/min) and increased to 70 per cent B in 40min (flowrate, 1.0 ml/min). Analytes were detected at 280 and 360 nm. Some typical chromatograms are presented in Fig. 2.71. The concentrations of flavonoids and phenolic acids are compiled in Table 2.69. It was stated that the SPE-HPLC procedure makes possible the simultaneous determination of phenolic compounds and flavonoids, therefore, it can be employed for the measurement of these classes of analytes in other fruit juices [188],... 

A detailed description of the various methods of measuring solids flowrates has been given by Liptak(17) and Table 1.2, taken from this work, gives a summary of the principal types of solids flowmeters in common use. 

The Carman-Kozeny equation relates the drop in pressure through a bed to the specific surface of the material and can therefore be used as a means of calculating S from measurements of the drop in pressure. This method is strictly only suitable for beds of uniformly packed particles and it is not a suitable method for measuring the size distribution of particles in the subsieve range. A convenient form of apparatus developed by Lea and Nurse 22 1 is shown diagrammatically in Figure 4.4. In this apparatus, air or another suitable gas flows through the bed contained in a cell (25 mm diameter, 87 mm deep), and the pressure drop is obtained from hi and the gas flowrate from h2. 

This equation relates the hold-up to the flowrates of the phases and column diameter through the characteristic velocity, u0. It therefore gives a method of calculating the holdup for a given set of flowrates if u0 is known. Conversely, equation 13.33 may be used to calculate uq from experimental hold-up measurements made at different flowrates. Thus, if hold-up data are plotted with L d + (J/( 1 — j))L c as the ordinate against j( 1 — j) as the abscissa, a linear plot is obtained which passes through the origin and which has a slope equal to fir, Wl. 

Van Harreveld measured the odour emission of a composting plant. As it was a composting plant with a surface of 4 ha it was impossible to measure the flowrate. He solved this problem in measuring the ratio mg NH3/m3 odour units/m3 in the air leewards of the plant. 

A(Ag ) is a measure of relative retention and is unaffected by flowrate, percent loading, or solvent molecular weight. 

If flow is cocurrent the lower sign is used if countercurrent the upper sign is used. Since the mass flowrate of the cooling fluid is based upon the cross-sectional area of the reactor tube the ratio G Ip Gq SpC(= H is a measure of the capacities of the two streams to exchange heat. In terms of the limitations imposed by the onedimensional model, the system is fully described by equations 3.9S and 3.96 together with the mass balance equation ... 

In contrast to the batch fermentation based methods of determining kinetic constants, the use of a continuous fermenter (Fig. 3.71) requires more experiments to be performed, but the analysis tends to be more straightforward. In essence, the experimental method involves setting up a continuous stirred-tank fermenter to grow the micro-organisms on a sterile feed of the required substrate. The feed flowrate is adjusted to the desired value which, of course, must produce a dilution rate below the critical value for washout, and the system is allowed to reach steady state. Careful measurements of the microbial density X, the substrate concentration S, and the flowrate F are made when a steady state has been achieved, and the operation is then repeated at a series of suitable dilution rates. 

Measured value of flowrate of concentrated sodium hydroxide... 

Air at 323 K and 152 kN/m2 flows through a duct of circular cross-section, diameter 0.5 m. In order to measure the flowrate of air, the velocity profile across a diameter of the duct is measured using a pitot-static tube connected to a water manometer inclined at an angle of cos-1 0.1 to the vertical. The following results are obtained ... 

Discuss the application of this method of measuring gas flowrates, with particular emphasis on the best distribution of experimental points across the duct and on the accuracy of the results. 

We note that Y/Y is a measure of the nonuniformity of flow experienced by a component in the system. It is a dimensionless constant reflecting the geometry of the flow space. It does not change with flowrate because, as noted in Section 4.4, all velocities in a given cross section subject to laminar flow maintain the same proportion to one another. Thus when flowrate increases, all individual velocities increase proportionately, as do 2 and A 5 ". The ratio remains constant. 

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