Fans and blowers

That is, 843 W of heat removed for just 15 W of electrical power. Is that efficient It may be. But it is not, if more of that heat could be removed by natural convection and radiation, and we are using a larger fan than is necessary. The point is that the efficiency of the heat removal system depends more on the design of the airflow path, and how much temperature the air can pick up as it goes through, than on the performance of the motor. Rather than the efficiency of such a cooling system, it is more useful to define effectiveness as 

Small- to medium-sized PEM fuel cells are liable to be an important market for fuel cells in portable power systems. A problem with these cells is the pumps for circulating the reactant air, and the hydrogen fuel, if not dead-ended. In compact designs of, say, 200 W to 2kW, the back pressure of the reactant air is liable to be around lOkPa, equivalent 

An example of a published system design that nses this approach is for a 3(K)-W PEM fuel cell (Popelis et al., 1999). Using equation A2.4, and a stoichiometry of 2, and operation at about 0.6 V per cell, a 300-W cell would require a reactant air flow rate of 3.57 X 10 kg s which is equivalent to 18 SLM. The pnbhshed details give a flow rate of 15-20 SLM. 

This flow rate is delivered at a pressnre of between 1.10 and 1.15 bar. The pump unit is manufactured by KNF Neuberger and is driven by a 12-VDC motor. According to the published data, this motor/pump combination consnmes between 14 and 19 W. The parasitic power loss is thus about 6%. This represents abont as low a figure as can 

Perry R.H. and Green D.W. (1984) Perry s Chemical Engineer s Handbook, McGraw-Hill, New York, pp. 6-33. 

When a fan is placed at the end of a system so that most of the system pressure drop is on the suction side of the fan, it is commonly called an exhaust fan or an exhauster. This term may also be appHed to a ventilating fan where the primary function is to exhaust air from a room or an open hood. 

Kirk-Othmer Encyclopedia of Chemical Technology (4th Edition) 

Scroll side (scroll piece, side sheet, side plate) 

As the air leaves the blade tips, it contains kinetic energy by virtue of its velocity. The directional component of this velocity is both rotative and radial. When the fan blades ate inclined forward, these components are cumulative. With backward-iaclined blades, the components are ia opposition. The purpose of the fan volute or scroU-shaped casiag is to convert a portion of the kinetic energy of the air leaving the blades iato static pressure. 

Design operating efficiencies of fans under test conditions are ia the range of 40—80%. Actual efficiency can be affected appreciably by the arrangement of inlet and outiet duct connections. 

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The terms fans and blowers are often used interchangeably, and no distinction is made between them in the discussion that follows. Whatever is stated about fans equally applies to blowers. Strictly speaking, however, fans are used for low pressure (drop) operation, generally below 2 psi. Blowers are generally employed when pressure heads in the range of 2.0 to 14.7 psi are generated Operations at higher pressures require compressors. 

Fans and blowers ACGIH, AIHA, AMCA, ARI, ASME, FM, USCG... 

Centrifugal compressors usually have specific speeds of 1,500-3,000 rpm at the high efficiency point. The axial flow fans and blowers are high specific-speed wheels mixed flow units are lower and the centrifugal compressor wheels are the lowest in specific speed range because they have narrow impellers. 

Measurement locations should be permanently marked to ensure repeatability of data. If transducers are permanently mounted, the location can be marked with a center punch, paint, or any other method that identifies the point. The following sections give the recommended locations and orientations of measurement points for the following common machines or machine components compressors, electric motors, fans and blowers, gearboxes, process rolls, and pumps. 

As we discussed, fans and blowers are prone to aerodynamic instability. The indication of abnormal vanepass suggests that this may be contributing to the problem. The additional data provided by the narrowband readings help to eliminate many of the possible failure modes that could be affect the blower. However, we still cannot confirm the specific problem. 

Karassik, I.J. Pump Performance Characteristics, Hydrocarbon Processing, June 1972, p. 101. Doyle, H.E. Highlights of API 610 Pump Standard, Hydrocarbon Processing, June 1972, p. 85. Polcak, R. Selecting Fans and Blowers, Chemical Engineering, Jan. 22, 1973, p. 86. 

The amount needed, whether natural or mechanical (fans and blowers) depends upon the materials and the conditions involved. No dependence should be placed upon the odor of the material as a warning, because some flammable vapors are heavy and tend to settle and because smell is deceptive. The safe procedure is continual testing with an explosion or flammable vapor indicator... 

LHMA, FOULKES 6/19, Papers relating to filter fans and blowers for dug-outs (1917). 

Because the basic fuel cell needs no mechanical drive, its operation is quiet and involves no frictional losses (Figure 2.100). These characteristics should make it possible to locate them near the final user, producing a more even distribution of the generation capacity. Auxiliaries, particularly fans and blowers, must be quiet therefore, they should be well supported to prevent their motion and be provided with variable-speed drives. In addition, the feathering of the blade edges and the use of noise-reducing enclosures are recommended. 

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