Air Flow Measurement

The temperature and pressure can be measured in an air stream. The pressure can be the barometric pressure adjacent to the test point and the gage pressure or the pressure difference between the reference atmosphere and the still air within a small hole positioned at the required point in the air stream. If the air is flowing parallel to the surface in which the hole is made, it will be the static pressure of the air stream. These pressures can be measured as follows  

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The air pollution control solutions that are available to control these emissions are normally dictated by the volume of air that is to be processed. The volume of air flow, measured in cubic feet per minute, is designated as ACFM for Actual Cubic Feet per Minute of SCFM where "S" stands for standard cubic feet per minute, at 70°F, sea level, and one atmosphere. 

ASHRAE 41.2-1987. Methods for Laboratory Air Flow Measurement. American Societv of Heating, Refrigerating, and Air-conditioning Engineers, Atlanta, 1987. 

The rate of air flow, measured with a precalibrated mercury flow meter in the gas inlet tube, was adjusted to 400- 50 ml. per minute. 

It is important to note that it is common in the reticulated foam industry to use air flow-through to define pore size. Manufacturers calculate average pore sizes from air flow measurements. Presumably, one would do this via a microscope either by counting pores or using an optical scanning device, but given the problems of sampling a bulk material with a microscope, it has become standard to use an empirically derived correlation between air flow and pore size. This serves as an indirect confirmation of the effect of the quality of the foam and its dynamic... 

The most important sensors for control of the drying process are those for inlet-air and exhaust-air temperature and the sensor for air flow measurement, located in the ah transport system. Other sensors for the spray agglomeration process include those for atomization air pressure and volume, pressure drops (across... 

If only small quantities of powder are available, columns down to 2 in (50 mm) in diameter can be used but diameters not less than 4 in (100 mm) are recommended whenever possible. This is to minimize the wall effects and also to increase the accuracy of air flow measurement. 

For calibration of the air mass and temperature signal a measurement is performed at zero air-flow at a temperature of 20 °C and at 80 °C. The output signal of air mass is measured at five different air-flow rates at 20 °C. Then a correction map is calculated for an optimal approach to the target characteristic. The digital concept with correction maps enables high precision air-flow measurement. The precision depends on the calibration procedure. 

Air flow measurement technique at different hood surfaces, volumetric flow rate, transport and capture velocity, hood static pressure, pitot tube, thermal anemometer, and magnehelic gauge. 

There are many other types of flow meters that can be used such as venturi meters, vortex shedder flow meters, and Coriolis flow meters. Any of these may be preferred depending on the application. Fluid flow can also be measured indirectly using chemical analysis and mass and energy balance calculations. Air flow measurements are commonly made this way since an oxygen analyzer is generally more accurate than a thermal mass flow meter. 

Air-flow measurement A mask and measuring apparatus can be used for measuring air flow from the mouth and separately from the nose. This is particularly useful in that we can measure the outputs from the nose and mouth separately, and we can do this in terms of air-flow signals rather than the pressure signals which microphones record. 

The outlet methane concentration bias in the objective function was heavily weighted (to drive it toward zero, since the objective function is the sum of the weighted squares biases) and therefore explains the good agreement between calculated and observed values. The process air flow measurement bias (difference between measured and calculated) was a parameter, so the calculated nitrogen composition is precisely equal to the measured value. The air flow measurement bias was 4.4% of the measured value at the solution. The calculated outlet temperature is surprisingly close to the measured value. The heat balance around the high pressure steam drum required only a 1.2% heat loss to close in this case. That balance is of course affected by numerous other measurements, so the calculated secondary reformer outlet enthalpy can only be said to be part of the overall consistent set of information. 

For unsteady-state operation the control scheme is more complex. A high selector is used to set the set point on the airflow controller, and a low selector is used to control the ratio controller on the fuel side (Figure 7.32) [12]. For an increase in heat demand, the demand signal will be higher than either the fuel or air flow measurements. This will be passed by the high selector (>) to the airflow controller [12]. The increase in air flow will then be transferred through the low selector (<) to the ratio controller on the fuel side [12]. This ensures no excess in fuel, since airflow leads fuel flow for an increase in steam demand. 

Humidity must be measured to document the experimental conditions and may be so to correct the air flow measurements to STPD conditions, if applicable. The significance of errors in humidity measurements on the accuracy of the detection of the gaseous exchange and EE, however, is relatively small. 

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