Rotameters for

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. 

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. 

THEORY AND CALIBRATION OF ROTAMETERS. For a given flow rate, the equilibrium position of the float in a rotameter is established by a balance of three forces (1) the weight of the float, (2) the buoyant force of the fluid on the float, and (3) the drag force on the float Force 1 acts downward, and forces 2 and 3 act upward. For equilibrium... 

Aerating standpipes is sometimes necessary in order to achieve optimum solids flow through them. However, too much aeration is just as detrimental as too little aeration. Too much aeration leads to bubble formation and slugging. Often seal pots operate satisfactorily with no additional aeration added to the standpipe, especially with group B solids. However, it is usually wise to add aeration taps into the standpipe discharging into the seal pot. They will be there if needed and do not have to be used if they are not. An aeration point at the bottom of the standpipe and aeration points approximately every 2 to 3 m of solid seal height should be sufficient. It is also best to use a separate aeration control rotameter for each aeration point, especially in research units. In a commercial unit, restriction orifices are generally sufficient to ensure equal flows to each aeration location. 

Rotameters In many large-scale gas chromatograph installations, rotameters are used as visual indicators of gas usage. If the rotameter is of the proper size, so that gas use per bench suspends the float or ball midway in the rotameter tube, a quick glance will tell you if you are using the correct amount of gas. Leaks tend to push the float off scale—leaks can easily more than double or more your gas consumption. We recommend one rotameter for the entire lab and one for each bench (Figures 10.31). 

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. 

Instrument Society of America 400 Stanwix Street Pittsburgh, Pa. 15222 Standards l ibrary for Measurement and Control, 12th ed., 1994. Instmmentation standards and recommended practices abstracted from those of 19 societies, the U.S. Government, the Canadian Standards Association, and the British Standards Institute. Covers control instmments, including rotameters, aimunciators, transducers, thermocouples, flow meters, and pneumatic systems (see... 

Rotameter A rotameter consists of a vertical tube with a tapered bore in which a float changes position with the flow rate through the tube. For a given flow rate the float remains stationary since the vertical forces of differential pressure, gravity, viscosity, and buoyancy are balanced. The float position is the output of the meter and can be made essentially linear with flow rate by makiug the tube areavaiy hn-early with the vertical distance. 

Rotameters require no straight runs of pipe before or after the point of installation. Pressure losses are substantially constant over the whole flow range. In experimental work, for greatest precision, a rotameter should be cahbrated with the flmd which is to be metered. However, most modern rotameters are precision-made so that their performance closely corresponds to a master cahbration plot for the type in question. Such a plot is supphed with the meter upon purchase. 

The ratio of flow rates for two different fluids A aud B at the same rotameter reading is given by... 

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. 

For the tandem arrangement gas seal, a primary seal vent must be pro vided to vent the leakage across the process side seal. This vent ma> lie to flare or other suitable gas disposal point. The back pressure under nor mal conditions should be kept to a low value. A small amount of back pressure is recommended to keep a positive differential across the see ondaiy seal. Leakage measurement may be provided in the vent line to provide health monitoring of the primary seal. Unfortunately, the rotameter, which would be the obvious choice, should not be used because of its lack o reliability. If an orifice or needle valve is used to set the back pressure to the seal vent, pressure upstream of the restriction can be measured for a relative flow measurement. This type of reading does provide trend data that may be used to judge the seal s performance. 

The precision rotameter is a secondary calibration device. If it is to be used in place of a primary device such as a bubble meter, care must be taken to ensure that any introduced error will be minimal and noted. The precision rotameter may be used for calibrating the personal sampling pump in lieu of a bubble meter provided it is (a) Calibrated with an electronic bubble meter or a bubble meter, (b) Disassembled, cleaned as necessary, and recalibrated. It should be used with care to avoid dirt and dust contamination which may affect the flow, (c) Not used at substantially different temperature and/or pressure from those conditions present when the rotameter was calibrated against the primary source, (d) Used such that pressure drop across it is minimal. If altitude or temperature at the sampling site are substantially different from the calibration site, it is necessary to calibrate the precision rotameter at the sampling site where the same conditions are present. 

Hliiull. In v.tive B 5th ijifcni-.O pr< SM re ViilvL-. fail [jpai C)peration Excessive chlorine How to Tower Water Basin - high chlorine level to cooling water -potential for excessive corrosion in cooling water system Rotameter Relief valve an pressure check valve outlet in Nnilk-... 

To stop the process the circuit through the electromagnet (6) is broken at (18), so that air rushes into the injector and the glycerine in the pipe and in rotameter (3) runs back to (2). Mixed acid should be allowed to flow for 1 min in order to flush the pipes and cooling system. The separator is stopped about 10 min later and empties automatically... 

A typical meter of this kind, which is commonly known as a rotameter (Figure 6.21). consists of a tapered tube with the smallest diameter at the bottom. The tube contains a freely moving float which rests on a stop at the base of the tube. When the fluid is flowing the float rises until its weight is balanced by the upthrust of the fluid, its position then indicating the rate of flow. The pressure difference across the float is equal to its weight divided by its maximum cross-sectional area in a horizontal plane. The area for flow is the annulus formed between the float and the wall of the tube. 

This meter may thus be considered as an orifice meter with a variable aperture, and the formulae already derived are therefore applicable with only minor changes. Both in the orifice-type meter and in the rotameter the pressure drop arises from the conversion of pressure energy to kinetic energy and from frictional losses which are accounted for in the coefficient of discharge. The pressure difference over the float —AP. is given by ... 

Rate Meter Measures the instantaneous volume flow rate through the sampling systems. An example would be a rotameter or venturi meter. Used to set precise flow rate for flow sensitive sampling devices. 

Fig 18. Experimental trickle-bed system A, tube bundle for liquid flow distribution B, flow distribution packing of glass helices C, activated carbon trickle bed 1, mass flow controllers 2, gas or liquid rotameters, 3, reactor (indicating point of gas phase introduction) 4, overflow tank for the liquid phase feed 5, liquid phase hold-up tank 6, absorber pump 7, packed absorption column for saturation of the liquid phase 8, gas-liquid disengager in the liquid phase saturation circuit. (Figure from Haure et ai, 1989, with permission, 1989 American Institute of Chemical Engineers.)... 

The needle valves of Fig. 1 are operated choked, so that there is a constant flow independent of downstream resistances. However, the valve shown upstream of the bubble meter is very important. It is adjusted so that the pressures at the switching valve and upstream are hardly perturbed by a switch. The flows of both mixtures are adjusted to be identical by the needle valves and the bubble meter. When all is properly regulated, the ball in each rotameter makes a short, quick ( ls) excursion at the moment of the switch, and identically for the return to the first position of the valve. 

Are the proper maintenance materials (parts, etc.) available Yes. They include spare pigtails for the supply cylinders, as well as a rotameter and a pressure check valve. Other items must be ordered. 

---