Fans, capacity characteristics

Figure 9-122. Plot illustrating combination of thermai and fan power characteristics to directiy determine flow capacities of a given size. Used by permission of Groitein, E. E., Combustion, Nov. (1957).

The axial fan is being built in larger capacities and for higher pressure characteristics and is finding increasing application. Figure 12-124 shows a vaneaxial unit. A tubeax-... 

Fans are used in parallel to obtain increased capacity in preference to a single large installation, to increase capacity at constant pressure, and for low-resistance systems requiring large capacities. It is important to study the effect of the addition or removal of fens on the system. This is done using the system resistance and the fan characteristics. 

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... 

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. 

Plot the control characteristics for the fans. Draw the fan head-capacity curve for the airflow... 

Plot the control characteristics for the fans. Draw the fan head-capacity curve for the airflow or gasflow range considered (Fig. 6.35). This plot shows the maximum capacity of 140,000 ft /min and required static head of 14 inH20, point P. 

The Champeyron Creek was chosen as a case study because of the availability of documentation on past debris flow events, of clearly visible tracks of past debris flow processes, and because of the presence of elements at risk. A geomorphological analysis of the basin, carried out through a multi-temporal photo interpretation, allowed to reconstruct the development of the debris flow in 3D. For this purpose also some photos of the period were used, together with interviews of witnesses and some specific field surveys. In particular the areas of debris supply for the 1981 event were identified. These latter corresponded to the extended screes visible in Fig. 24.2 and to some other areas prone to periodic rockfalls. The available DTM was adjusted to obtain the needed scale that allowed a simulation of the process. The characteristics of the debris flow mixture (solid fraction in % and dimensions of the largest boulders) were faithfully reconstructed, and this allowed to appreciate the dynamics of the process evolution and the mass transport capacity. Furthermore the expansion areas of the debris flow on the fan and the flow directions have been defined, which are essential components for the interpretation and numerical simulation of the 1981 event (Fig. 24.3). 

K, for example, the capacity (cfin) of a given fan were decreased by 50 percent (either by a reduction to half of design rpm, or by a reduction in blade pitch angle at constant speed), the capacity ratio would be 0.5. Conciurently, the static pressiu-e would become 25 percent of before, and the fan horsepower would become 12.5 percent of before. These characteristics afford imique opportunities to combine cold water temperatme control with significant energy savings. 

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