Rotameters, flow measurement with

Fig. 12.15. Flow measurement with float (rotameter), a Conical flow pipe b float F gravity force Fe buoyancy force Fo- drag force [1].

Flow measurements using nonintrusive or low mechanical ac tion principles are desired, such as magnetic, vortex-shedding, or Coriolis-type flowmeters. Orifice plates are easy to use and reliable but have a limited range and may not be suitable for streams which are not totally clean. Rotameters with glass tubes should not be used. 

Many different techniques are available for flow measurement and for recording of respiratory functions or flow parameters in particular (e.g. [115,116]). However, not all methods are appropriate for measurement of inhalation flows, either because they have low frequency responses or they influence the shape of the inspiratory flow curve by a large volume or by the inertia of the measuring instrument (e.g. rotameters). They may also interfere with the aerosol cloud from the inhalation device during drug deposition studies. 

Variable-Area Meters Variable-area meters, which are also called rotameters, offer popular and inexpensive flow measurement devices. These meters employ a float inside a tube that has an internal cross-sectional area that increases with distance upward in the flow path through the tube. As the flow rate increases, the float rises in the tube to provide a larger area for the flowing fluid to pass. 

The pilot plant scale experimental unit, Fig. 2, described in previous papers [2,3] is provided with a blower that supplies a maximum air flowrate of 300Nm3/h at a pressure of 1500 mm of water column. The flow measurement is carried out with two rotameters, used in the ranges from 2.5 to 30 and from 30 to 250 Nm3/h. In the range from 0 to 4 Nm3/h a gas volume meter provided with paddles is used. A system of valves allows for choosing the suitable rotameter for the desired flowrate. This flowrate is fixed by closing or opening a butterfly valve. 

Air and gaseous S02 in the required ratio enter Mixer 6 to mix fully with each other, and the resulting pseudo flue gas is divided into two equal streams to enter Absorber 7. The air flow rate is adjusted by a butterfly valve in the pipeline and measured with a Pitot tube-pressure difference meter and that of S02 by the rotameter 5. The total gas flow rate is also monitored by a wind velocity meter of DF-3 type at the gas outlet of the reactor. For each run, gas-samplings are made at both inlet and outlet of the reactor, and the S02 concentrations in the samples are measured with the Iodine-quantitative method, a standard and authentic method of determining the integral amount of S02 absorbed in the reactor. 

Pumps, such as piston pumps, can meter liquids into a reactor fairly precisely, but the chemical engineer uses a flow measurement device for greater precision. The most commonly used flowmeters are rotameters that are calibrated to translate the lifting of a float in a vertical slightly tapered tube (small diameter at the inlet of the flowmeter) into a measure of the amount of liquid delivered in a given timeframe. For greatest precision the rotameter is calibrated with the specific fluid being metered. Most modem rotameters are provided with a calibration plot that corresponds to performance. 

Sulfur dioxide is contained in the feed and effluent streams of a chemical reactor, but it is neither a reactant nor a product. The volumetric flow rates of both streams (L/min) are measured with rotameters, and the concentrations of SO2 in both streams (mol/L) are determined with a gas chromatograph. The molar flow rate of SO2 in the reactor effluent (determined as the product of volumetric flow rate and concentration) is 20% lower than the molar flow rate of SO2 in the feed. Think of as many possible explanations for the discrepancy as you can. 

A condenser is then installed and run at the design temperature and pressure. The volumetric flow rates of the feed stream and the vapor and liquid product streams are measured with rotameters (see p. 46), and the MEK mole fractions in the feed and vapor effluent streams are measured with a gas chromatograph. The feed stream flow rate is set to 500 liters/s and enough time is allowed to pass for the product stream rotameter readings to reach steady levels. The feed and product gas flow rates are then converted to molar flow rates using the ideal gas equation of state, and the product liquid flow rate is converted to a molar flow rate using a tabulated MEK density and the molecular weight of MEK. Here are the results. 

A standard Pyrex vacuum apparatus is employed in this preparation. The system includes a fractionation train consisting of four U-tube traps, attached with ball joints, a mercury manometer, and several ball-joint connections on the manifold. The mercury in the manometer is covered with outgassed Kel-F-10 oil, and the stopcocks and ball joints are lubricated with Kel-F-90 grease. The fluorine metering system consists of a fluorine tank properly shielded and vented, a sodium fluoride scrubber (45 X 13 cm.), two calibrated rotameters for measuring flow rate and fluorine concentration, and a helium source, and is constructed of -J-in. copper tubing. 

The fluid mixture coming out of the extractor is depressurized to atmospheric pressure by passing it through a heated metering valve and a back pressure regulator. The instantaneous flow rate of the gas leaving the extractor is measured using a rotameter and the total amount of gas flow is measured with a calibrated wet-test meter. 

The two identical nozzles and their dimensions described previously [2] had contractions of area ratio 9.0 and followed a fifth-order polynomial [3] to a diameter of 25 mm. Fig. 6.1. The nozzle separation was varied between 0.2 and 2.0 exit diameters with bulk velocities from 1.49 to 7.00 m/s, and, since these velocities corresponded to Reynolds numbers of 2,000 and 10,000, a perforated plate was located at the end of the contraction with 4-millimeter diameter holes and 50% solidity. A subsequent straight pipe, two exit diameters in length, allowed the wakes to diminish and the small-scale turbulence to develop [4]. The two jets were mounted on a frame that allowed the separation to be varied while maintaining the same geometric axis. The compressed air and gas supply of natural methane was filtered, and the flow was measured with calibrated rotameters to accuracy better than 3%, while the centerline velocities were matched within 0.1 m/s. 

Gas Atmosphere. Both the thin film and powder sample holders were surrounded by glass tubes which were part of closed systems. The total pressure over a sample was always close to 1 atm. The flow rates of the gases and the compositions of gas mixtures were measured with Brooks Rotameters. To obtain the 1.3% o-xylene feed, air or oxygen was bubbled through the liquid hydrocarbon to saturate the gas with vapor at room temperature. 

Conventional instrumentation is a rotameter on the demineralized water feed, with a manual valve for adjustment of the rate. Magnetically coupled flow indicators will not work properly in the strong electrical field of the cell room. The density of the caustic solution is measured with a nickel hydrometer. The hot, strong caustic would quickly destroy a conventional glass instrument. 

Figure 11.54 shows that the feed header is controlled at a selected pressure so that adjustment of the feed rate to any one electrolyzer does not affect the other flows. The pressure is measured with a Monel or nickel diaphragm seal connected to a pressure transmitter with a capillary system. The fail-open throttling valve is an all PTFE-lined butterfly, controlled by a reverse-acting, proportional-plus-integral controller. Control of the caustic flow to individual electrolyzers is by way of hand valves and local rotameters. This is similar to the arrangement described for brine feed and shown in Fig. 11.11. Again, bipolar systems are amenable to more complete automation.

Six temperature probes can be place inside each reactor and 13 probes can be places inside the column. There are also 4 scales (0-50 kg, 0-100 kg) with accuracy of 0.01 kg for measuring inlet and outlet flow rates. At the moment circulation flows are measured with rotameters. All measurements are connected to the Mitsubishi MELSEC logic and monitoring software to view and save the data. For safety reasons there are also locking system in automation and a separate alarm system. 

Rotameter Ultrasonic type Turbine flow meter Electromagnetic flow meter Good for upstream flow measurements Used in conjunction with variable inductance sensor Good for very high flow rates Can be used for both upstream and downstream flow measurements Not suited for fluids containing abrasive particles Relationship between flow rate and angular velocity is linear Least intrusive as it is noncontact type Can be used with fluids that are corrosive, contaminated, etc. The fluid has to be electrically conductive... 

If dilution water is used, this is generally measured with a rotameter variable orifice meter. However if this flow has to be integrated into a control system then an electronic method, as used for the feed, will be necessary. 

A classical installation for absorption and desorption experiments with packings is Prof. BiU s installadon described in his kt book [86]. The installaticm presented in Fig. 1 includes an absorber with a distributor and the investigated packings, two vessels for preparing of ribsorbent, respectively saturated liquid for desorption, a gas andyzer, manometers, a blower, a humidifier, a gas bottle, a colunm for mbdng of the absorbed gas fiom the bottle with air, and the nectary rotameters for measuring the flow rates of gas and liquid. 

Flow transmitters. Flow measurements are made in high-pressure lines by sensing the pressure drop across a calibrated orifice or venturi, or by the transmitting variable-area type of flowmeter. The latter meter resembles a Rotameter with float position transmitted electrically. It has the advantage of being an in-line element but is not readily applicable to large flows. 

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