GB2165888A

GB2165888A - Air swirl systems for fans

Info

Publication number: GB2165888A
Application number: GB08426635A
Authority: GB
Inventors: Vitold Vitoldovich Pak; Viktoria Ionovna Kovalevskaya; Vitaly Alexandrovich Sidorenko; Margarita Mikhail Kovalevskaya; Valery Prokofievich Peredery; Jury Valerievich Vasiliev
Original assignee: DO G PK I EXI KOMPLEXNOI MEK Z; Donetsky Politekhnichesky Institut
Current assignee: DO G PK I EXI KOMPLEXNOI MEK Z; Donetsky Politekhnichesky Institut
Priority date: 1984-10-10
Filing date: 1984-10-22
Publication date: 1986-04-23
Also published as: GB2165888B; GB8426635D0; FR2572140B1; DE3439218C2; SE8405068L; SE445061B; DE3439218A1; SE8405068D0; FR2572140A1

Abstract

The fan comprises an impeller 2 and a system for imparting prerotation swirl to the air flow entering the impeller. The swirl system includes a bypass conduit 6 and an adjustable baffle 9. Normally the baffle blocks the inlet 7 of the conduit 6 so that the entire airflow passes through the inlet box 5 and inlet cone 4 to the impeller. When the baffle is swung away from the inlet 7, the air flow is divided into two streams 10, 11, the stream 11 being swirled due to the tangential direction in which the air is supplied from the conduit 6 to the inlet cone 4. <IMAGE>

Description

SPECIFICATION Fan The present invention relates to devices for producing a current of air, and more specifically concerns fans, especially those centrifugal and axialflow fans as employed in power engineering, mining, metallurgical and chemical industries.

A known type of fan comprises a housing with an inlet tube and suction chamber arranged sequentially; an impeller disposed inside the housing; and a by-pass conduit connected to the chamber and having an air-flow regulator.

The by-pass conduit takes air from the outside.

According to a feature of this earlier invention, if the fan operation should become unstable, a choke of the flow regulator is opened, whereby, because of the influx of air from the outside, the flow rate is increased to result in stable operation of the fan and greater volume flow rate.

However, because of this non-productive suction of air the fan power has to increase and this results in a reduced fan efficiency.

Other known types of fans comprise an impeller disposed in a housing, an inlet tube, and guide vanes for prerotation swirling of the air-flow entering the impeller, arranged either in the inlet tube or in an inlet box. However, reliable adjustment of the operating conditions of such fan is difficult since the guide vane means for prerotation swirling of the air flow have an excessive number of parts arranged in the air flow and this air flow not infrequently carries dust and/or corrosive components.

In addition, the guide vanes provide resistance to the flow, which also affects the overall efficiency of the fan.

The present invention sets out to provide a fan having a construction such as to give increased reliability of adjustment to simplify the fan structurally.

The invention consists in a fan comprising an impeller disposed in a housing; an inlet tube for a current of air drawn in by the fan; and a means for imparting a prerotating swirling of the flow of air entering the impeller; the swirling means comprising at least one bypass conduit an inlet of which is located in the inlet tube of the fan, and an outlet of which is attached tangentially to the inlet tube at a relatively downstream portion closer to the impeller, and a baffle being movably disposed inside the inlet tube to separate the incoming flow into a main flow for the inlet tube and an additional flow entering the by-pass conduit.

The or each by-pass conduit may have the general form of a tube placing a relatively upstream part of the inlet tube of the fan in communication with a suction zone of the impeller. Alternatively, the or each conduit may have the general form of hollow lugs arranged on the walls of the inlet tube of the fan and placing in communication at their tangential outlets a relatively downstream portion of the inlet tube with a relatively upstream portion thereof. In the former case the baffle (which preferably has a height less than the height of the inlet tube in which it is disposed) is usually movable from a position covering the upstream end of the bypass conduit to a position at which it deflects some of the air into the said conduit.In the latter case the baffle is usually movable from a position generally across the inlet tube to a position at which it deflects some of the air into a said conduit.

The examples of the proposed construction as shown in more detail below make it possible to increase fan efficiency, to simplify and make less expensive the fabrication of the fan, and to improve the reliability of fan operation.

The invention will now be described in greater detail with reference to various specific embodiments thereof taken in conjunction with the accompanying drawings, in which: Figure 1 is a diagrammatic illustration of a proposed fan with a tangential air-flow inlet; Figure 2 is a section taken along the line ll-ll in Figure 1; Figure 3 is a section taken along the line Ill-Ill in Figure 1; Figure 4 is a diagrammatic illustration of a modified fan with an axial air-flow inlet; Figure 5 is a section taken along the line V-V in Figure 4; Figure 6 is a section taken along the line VI-VI in Figure 4 and Figure 7 is a part sectional diagrammatic plan view of the modified fan according to Figure 4.

The fan of Figures 1-3 comprises a housing 1 for an impeller 2 disposed inside the housing 1 and secured on a shaft 3. The fan has an inlet cone or tube 4 and an attachable inlet box 5. The inlet box 5 accommodates a means for prerotation swirling of the flow of air entering the impeller 2. This means comprises a by-pass conduit 6, inlet 7 of which is disposed inside the inlet box 5, and outlet 8 (Figure 2) of which is connected tangentially to the inlet cone 4 in proximity to the impeller 2 if viewed along the air inflow. The means for prerotation swirling of the incoming flow of air also comprises a baffle 9 (Figure 1) arranged in the inlet box 5 to separate the incoming air into the main and additional flows indicated by numerals 10 and 11, respectively. The outlet 8 of the bypass conduit 6 is divided by stationary vanes 12 (Figure 2) into several parts.The bypass conduit 6 has the general form of a tube placing a relatively upstream part of the inlet tube in communication with the suction zone of the impeller 2.

The baffle 9 (Figure 3) has a height "h" which is less than the corresponding height "H" of the section of the inlet box 5 in which the baffle 9 is disposed. The value e =H-h amounts to between 0.15 and 0.3 the diameter of the impeller 2 (Figure 1).

Figure 4 shows a modification of the proposed fan but with an axial inlet. In this modification an inlet tube 13 is provided with substantially hollow lugs 14 (Figure 5) outlets 15 of which are connected to the inlet tube 13 such that the additional flow 11 of air passing through the lugs enters the inlet tube 13 tangentially. Inlet holes 16 of the hol low lugs 14 (Figure 6) are connected to the inlet tube 13 upstream of the impeller 2 (Figure 4). Baffles 17 are disposed in the inlet tube 13 between the inlets and outlets 15 and 16 of the hollow lugs 14 (Figure 7). Figure 7 also illustrates by a dashed line an alternative (intermediate) position of the baffle 17.

The proposed fan of Figures 1 to 3 operates in the following manner.

When operating in a mode corresponding to the rated "capacity-pressure characteristic the baffle 9 blocks the inlet 7 of the by-pass passage 6. The air flow is thus fully delivered through the inlet box 5 and inlet cone 4 to the impeller 2.

Adjustment of fan operating conditions is made necessary by swinging the baffle 9 at a required angle for the air flow to divide into two flows, namely the main flow 10 and the additional flow 11. The main flow 10 is conveyed in the same direction as before, axially through the inlet box 5 and inlet cone 4 toward the impeller 2. The additional flow 11 passes through the inlet 7 in the bypass conduit 6 and thereafter flows through the outlet tangentially to the inlet cone 4 thereby swirling the flow entering the impeller 2 to coincide with the direction of rotation of the latter. This results in a drop of pressure developed by the fan, that is, the fan starts operating in conditions corresponding to the adjusted characteristics.

The provision of the gap "4" (Figure 3) between the baffle 9 and the wall of the inlet box 5 enables part of the main flow 10 to be directed along the wall of the inlet box 5, which produces an added swirling of this flow 10.

The proposed fan illustrated in Figures 4 to 7 operates in a manner similar to the aforedescribed one using vanes 17 to deflect at least part of the entering air.

By dispensing with a complicated guide vane apparatus the proposed invention makes it possible: (a) considerably to simplify the construction of the fan, reduce the amount of labour and expenses associated with its manufacture; (b) increase its peak efficiency by eliminating resistance to the flow caused by the prior art guide vanes; (c) expand the range of adjustment through preventing flow separation from the vanes; and the pressure losses associated therewith; and (d) improve the reliability of the flow adjustment means by way of substantially reducing the number of its parts.

Claims

1. A fan comprising an impeller disposed in a housing; an inlet tube for a current of air drawn in by the fan; and a means for imparting a prerotating swirling of the flow of air entering the impeller; the swirling means comprising at least one by-pass conduit an inlet of which is located in the inlet tube of the fan, and an outlet of which is attached tangentially to the inlet tube at a relatively down stream-portion closer to the impeller, and a baffle being movably disposed inside the inlet tube to separate the incoming flow into a mainflow for the inlet tube and an additional flow entering the bypass conduit.

2. A fan as claimed in claim 1 in which the or each by-pass conduit has the general form of a tube placing a relatively upstream part of the inlet tube of the fan in communication with a suction zone of the impeller;

3. A fan as claimed in claim 1, 2 or 3 in which the baffle is movable from a position covering the upstream end of the bypass conduit to a position at which it deflects some of the air into the said conduit.

4. A fan as claimed in claim 1, 2 or 3 in which the baffle has a height substantially less than the height of the cross-section of the inlet tube in which it is disposed.

5. A fab as claimed in claim 1 in which the or each bypass conduit has the general form of hollow lugs arranged on the walls of the inlet tube of the fan and placing in communication at their tangential outlets a relatively downstream portion of the inlet tube with a relatively upstream portion thereof.

6. A fan as claimed in claim 5 in which the or each baffle is movable from a position generally across the inlet tube to a position at which it deflects some of the air into a said conduit.

7. A fan substantially as described with reference to Figures 1 to 3 or 4 to 7 of the accompanying drawings.