Control of air flows

Local supply, including air curtains (i.e., control of air flow using jets)... 

Some water-thinned industrial paints exhibit anomalous viscosity changes during drying and therefore need careful control of air flow and humidity to ensure satisfactory film formation. 

Figure 10.5. Simple ratio control of air flow rate.

Wels, C., Lefebvre, R. Robertson, A. 2003. An overview of prediction and control of air flow in acid-generating waste-rock dumps. Enviromine Online Journal, World Wide Web Address http //www.infomine.com/technology/enviromine/ publicat/A irflow Wels LcTebvre Robertson.pdf. 

Thermal Mass Flow Controller provides precise, automatic control of air flow... 

Three modes of control of air flow are shown in Figure 3.3(e). Precautions may need to be taken against subcooling to the freezing point in winter. 

Figure 10.13 is a schematic of a typical combustion air system. Ambient air is routed to the air preheater by the forced draught fan. Control of air flow may be means of a variable speed drive on the forced draught fan or by some form of throttling of fan discharge. Measurement of flow usually is by pitot tube or annubar. Air then divides to each of the burners adjustment to individual burners is performed manually by manipulation of air registers. The stack... 

Alternative configurations are possible which omit either of the fans. If both fans are omitted then recovery of heat from the flue gas is not possible using the type of air preheater shown. Control of air flow on such natural draught heaters is by manipulation of the stack damper, although only if this does not violate the need to keep firebox pressure negative. 

Finally, it should be mentioned that electrical fields can be used to influence fluid flows beyond the realm of combustion. Such is the case with the control of air flows by... 

Two-speed motors are typically used on noncondensing services where the process is not sensitive to temperature but mostly seasonal or variable throughput of fluids in the air cooler requires some degree of air flow control. This is a simple, rather inexpensive means to control air flow when volume air flow is not critical. Typical motor ratings are 1800/900 rpm, although 1800/1200 rpm types are available. 

Continuous recuperative furnaces employing metallic recuperators (heat exchangers) have been in use since the 1940s. Operation of these furnaces is simplified and the combustion process is more precisely controlled no reversal of air flow causes temperature variations. The recuperator metal must be caretiiUy selected because of chemical attack at high temperature. Recuperative furnaces are often used in the production of textile fiber glass because they maintain a constant temperature. 

Operating co.sts. Power requirements for air-cooled heat exchangers can be lower than at the summer design condition provided that an adequate means of air-flow control is used. The annual power requirement for an exchanger is a function of the means of airflow control, the exchanger seiwice, the air-temperature rise, and the approach temperature. 

Another type of classifier directs an air stream across a stream of the particles to be classified. An example is the radial-flow classifier Kennedy Van Saun Corp.), which Features adjustable elements to control the flow and classification. A further development on this principle is the Vari-Mesh classifier Kennedy Van Saun Corp.), which controls classification by adjustable flow baffles. A change in direction of air flow is the operating principle of the reverse-flow Superfine classifier Hosokawa Mineral Processing Systems). 

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. 

Controlling supply air flow in proportion to the square root of the change... 

Glove boxes have been described in Section 10.2.3.6 as systems with only exhaust air. There are glove boxes with both supply and exhaust air openings inside the closed volume (see Section 10.4.6.4) that look and function like the boxes described earlier. The use of supply air directly to the closed volume means that the control of the flow rates must be very accurate. Otherwise the box may be at a higher pressure than the surrounding areas, resulting in leakage of contaminants. 

Airflow rate controller Any mechanical, pneumatic, or electrical device that controls the air flow rare into Or out of a space by increasing or decreasing the flow resistance. See Dampers and Valve. 

Make no excuse for checking whether the sun shines on the thermostats or someone has washed the floor. Another common occurrence is that while the room is not being controlled as specified, the plant appears to be operating correctly. Here a series of simultaneous readings of air flows and wet and dry bulb temperatures should be taken around the whole of the air circuit - on and off coil, condition after fan, condition at inlet grilles, etc. Referring these to a psychrometric chart will usually indicate where the fault or leak lies. 

Many of the earlier studies of mass transfer involved measuring the rate of vaporisation of liquids by passing a turbulent air stream over a liquid surface. In addition, some investigations have been carried out in the absence of air flow, under what have been termed still air conditions. Most of these experiments have been carried out in some form of wind tunnel where the rate of flow of air and its temperature and humidity could be controlled and measured. In these experiments it was found to be important to keep the surface of the liquid level with the rim of the pan in order to avoid the generation of eddies at the leading edge. 

DAF is controlled under laminar hydraulic flow conditions using a very small volume of air flow amounting to about 1 to 3% of the influent groundwater flow. DAF only requires 3 to 5 min of detention time therefore it is a low-cost process for the decontamination of groundwater. 

Air and water streams are fed into a pressurized tank through two control valves. Air flows out of the top of the tank through a restriction, and water flows out the bottom through another restriction. The linearized equations deseribing the system are... 

Closely connected with control of the flow properties of Slurries is control of their density. For a given compn considerable variation in Slurry d can be achieved by introduction of small amounts of porous solids by air entrapment (aeration) and by inclusion of small amounts of gas producing ingredients. It is the latter approach (ie, gas-formers) that is... 

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