Gas flow measurement

Both gas flow rates and liquid flow rates can be measured by a wide variety of devices such as bellow meters, Venturi nozzles, nutating disk meters, orifice meters, rotameters, weirs (for liquids), Pitot tubes, and magnetic meters among others. Some devices measure volumetric flow directly as with meters in which the space between rotating paddles incorporates small volumetric displacements of fluid. Other device measure the flows indirectly by measuring the pressure drop caused by an orifice between two different sites in the pipe, or the change in voltage of a heated wire. 

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The simplest calibration procedure for a gas flow-measuring device is to connect it in series with a reference meter and allow the same flow to pass th tough both instruments. This requires a reference instrument of better metrological quality than the calibrated instrument. One fact to consider when applying this method is that the mass flow rate in the system containing both instruments is constant (assuming no leakage), but the volume flow rate is not. The volume flow rate depends on the fluid density and the density depends on the pressure and the temperature. The correct way to calibrate is to compare either the measured mass... 

Pulsed hot wire anemometer A device used for gas flow measurement, similar to the hot grid anemometer, in which measurement, are made by pulses of hot air at a downstream sensor. 

Velocity vectors of the gas flow measured using laser Doppler anemometry inside a closed chamber during the formation of a tulip flame. Images of the flame are also shown, though the velocity measurements required many repeated runs, hence, the image is only representative. The chamber has square cross sections of 38.1mm on the side. The traces in the velocity fields are the flame locations based on velocity data dropout. The vorticity generated as the flame changes shape appears clearly in the velocity vectors. 

There are many ways to measure the concentrations of reacting species or species formed during the reaction, such as there are gc, UV-visible spectroscopy, IR spectroscopy, refiactometry, polarometry, etc. Conversion can be monitored by pressure measurements, gas-flow measurements, calorimetry, etc. Data are collected on a computer and many programmes are available for data analysis [3,4], The two-reaction system described above can be treated graphically, if it fulfils either the Bodenstein or Michaelis-Menten criteria. 

Gimson, C. Processing (April, 1993), 14. Guide to techniques for gas flow measurement. 

The hot-wire anemometer, principally used in gas flow measurement, consists of an electrically heated, fine platinum wire which is immersed into the flow. As the fluid velocity increases, the rate of heat flow from the heated wire to the flow stream increases. Thus, a cooling effect on the wire electrode occurs, causing its electrical resistance to change. In a constant-current anemometer, the fluid velocity is determined from a measurement of the resulting change in wire resistance. In a constant-resistance anemometer, fluid velocity is determined from the current needed to maintain a constant wire temperature and, thus, the resistance constant. 

Head-type flow measurement derives from Bernoulli s theorem. Work on the conventional orifice plate for gas flow measurement was commenced by Weymouth in the United States in 1903. 

In a typical analysis the columns are cooled to about —75° C. by dry air precooled by liquid N2. Then the gas sample is injected into one column by a Perkin-Elmer sampling valve the second column is for reference. After sampling is complete, the liquid N2 is removed, and the air flow is continued for about 5 minutes or long enough to warm the columns to about —10° C. and remove the 03. Yields, as percent of current, are calculated from the gas chromatographic, amperage, sample volume, and total gas flow measurements. 

Fig. 2.16 Gas flow measurement device using the soap bubble principle.

The principle of this gas flow measurement device is simple. A push on the gummy bubble leads to soap bubble rising in the measurement cylinder. The gas flow pressures up the soap bubble. The time it takes for the bubble to pass through a defined volume of the measurement cylinder is measured by a timer. The principle of soap bubble gas flow measurement is the direct measurement of the average gas flow velocity. The advantage of this device is that a very accurate average value for the gas flow velocity can be calculated from the measurements. This... 

Fig. 2.17 Gas flow measurement device using principle of heavy sphere floatation.

The last device for measuring gas flow and for calibrating mass flow controllers that is discussed in this chapter is called the capillary gas flow measurer. The principle of this device is used in many modem automatic calibration devices for mass flow controllers. The scheme of such a device is shown in Figure 2.18. 

Yu Dun, Hsieh H Y and Zemel J N 1993 MicroChannel pyroelectric anemometers for gas flow measurements Sensors Actuators 39 29-35 Pfahler J, Harley J C, Bau H H and Zemel J N 1990 Liquid transport in micron and submicron channels Sensors Actuators A 21-23 431 Wilding P, Pfahler J, Bau H H, Zemel J N and Kricka L J 1994 Manipulation and flow of biological fluids in straight channels micromachined in silicon Clin. Chem. 40 43-7... 

While measuring the combustion air flow may not be necessary to calculate the exhaust gas flow, measuring only the O2 in the stack (either wet or dry) only tells how much air has gotten into the furnace. It does not tell where it came from so it is possible that the burners are running fuel rich with a large amount of air infiltration. Therefore, it is usually desirable to measure the combustion air flow to ensure the operating conditions of the burners. 

GAS FLOW MEASUREMENT CALIBRATION FACILITIES AND FLUID METERING TRACEABILITY AT THE NATIONAL BUREAU OF STANDARDS... 

Olsen, L., and Baumgarten, G.P., Gas Flow Measurement by Collection Time and Density in a Constant Volume, Proceedings Symposium on Flow Its Measurement and Control in Seienee and Industry, Paper No. 

Gas flow measurement device is composed of S-type pitot tube, the pressure tube, differential pressure measurement, pressure measurement, temperature measurement, ARM processor unit, liquid crystal display components. Architecture block diagram looks like this. 

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