Fan performance

Fig. 2. Fan performance (a) a typical test arrangement (b) performance curve where the soHd line showing data points is the pressure the dashed line is the power. At point A the duct is blanked off, and at point B the flow is wide open the data points in between represent progressively less restricted flow.

Fig. 7. Control of fan performance with inlet vane control. SoHd lines marked A and N show normal performance without vanes (vanes wide open). As vanes are progressively closed, static and power curves are modified as indicated by dashed lines. Intersection ( - ) of the system resistance curve with these reduced pressure curves at points B, C, D, and E shows how imparting more spin to the inlet air reduces flow. Projecting points A to E vertically downward to the corresponding power curve locates fan power points A through E7 Power savings achieved over throttling control can be estimated by projecting points B through E vertically downward to the A power curve and comparing the value with that from the proper reduced power curve. To...

Performance Curves. Pan manufacturers furnish fan performance curves for each type fan available. These are typically based on 61 m/s (12,000 ft/min) tip speed and 1.20 kg/m (0.075 lb /ft ) density. To select a fan for a specific duty requires knowledge of the flow, static pressure resistance, and density of the actual operating conditions. Usually the fan diameter is known as well as some idea of operating speed a 61 m/s tip speed can often be assumed. 

Fan Performance The performance of a centrifugal fan varies with changes in conditions such as temperature, speed, and density of the gas being handled. It is important to keep this in mind in using the catalog data of various fan manufacturers, since such data are usually based on stated standard conditions. Corrections must be made for variations from these standards. The usual variations are as follows ... 

The measured pressure differences in ventilation applications are low or very low. The measurement range varies from a few pascals to several thousand pascals. At the lower end are typically building leakage and air movement-related measurements, where only a few pascals can cause a remarkably large air-tlow. The largest pressure differences probably occur in fan performance determination and similar applications. This wide range requires special demands on the measuring equipment and selection of the correct instrument for each application (Fig. 12.15). 

Vane control Fan inlet vanes alter fan perform.ance by controlling the swirl. 

Inlet vanes Specially-designed adjustable vanes inserted in the airstrearn entering a fan inlet to control fan performance by producing a swirl of the gas in the direction of the rotation of the impeller. 

Correct gas/air stream for other than standard density (0.075 Ib/fF) because the manufacturer s fan performance tables are based on dry air at 70°F at sea level at a density of 0.075 Ib/fF. For flow densities other than 0.075, corrections need to be made. 

The amount of sand and other particles sucked from the soil must be viewed as a possible cause for bearing failure or for the generation of bearing noise (such effects can also be caused by the moisture). Noise can directly influence the occupant to shut down the SSD system. Sandblasting of the fan blades or plateout on the fan blades by particles sucked into the mitigation system could lead to degradation of fan performance over the long term. 

Legend Organic fanning performs ++ much better, + better, o the same, - worse, -... 

Fans are made either with axial propellers or with a variety of radial vanes. The merits of different directions of curvature of the vanes are stated in Figure 7.24 where the effect of flow rate of pressure, power, and efficiency also are illustrated. Backward curved vanes are preferable in most respects. The kinds of controls used have a marked effect on fan performance as Figure 7.23 shows. Table 7.4 shows capacity ranges and other characteristics of various kinds of... 

FIGURE 6 Fan performance curve. Source Courtesy of Fluid Air Incorporated. 

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