GB2205901A

GB2205901A - Method and apparatus for adjusting the flow of air from a radial fan

Info

Publication number: GB2205901A
Application number: GB08812933A
Authority: GB
Inventors: Per Erik Gustafsson
Original assignee: Individual
Current assignee: Individual
Priority date: 1987-06-15
Filing date: 1988-06-01
Publication date: 1988-12-21
Anticipated expiration: 2008-06-01
Also published as: SE469760B; SE8702482D0; DE3820161A1; SE8702482L; GB2205901B; GB8812933D0

Description

METHOD AND APPARATUS FOR ADJUSTING THE FLOW OF AIR FROM A RADIAL FAN

2205901 Fans are generally utilised in series. The flow of each individual fan is generally adjusted by one means or another. It is often difficult to calculate the pressure drop in different passages and flow lines, which creates a need for fine adjustment of the flow and possibly an adjustment of the flow from a fan after other operations have been carried out. It is in this adjustment context that the present invention pres.ents a simple and economical method and apparatus for controlling the flow issuing from a radial fan.

The flow from a fan has previously been adjusted by means of simple baffles or throttle valves, which are inserted in selected numbers into passageways extending is to and/or from a fan. This meant that the fan built up an undesired pressure drop over the throttle valve, which in turn incurred extra cost. Efforts have been made to avoid such situation in view of increasing energy prices.

Different forms of revolution adjustment have been used for fan motors. Frequency control of the number of revolutions is a modern development, with electronic solutions which are relatively expensive both to install and to control.

The present invention relates to a radial fan having a central rotor or impellor which is driven by an electric motor and a casing surrounding same, said casing having a number of passages arranged in a spiral pattern. Air is drawn in at the centre of the casing by the rotor and flows through the passages. On flowing through such passages the air is given an acceleration and emerges from the spiral casing of the fan.

under pressure The present invention provides a method and a simple apparatus for controlling the flow within wide limits and at the same time with reduced energy consumption when the flow is to be reduced or throttled.

According to the present invention there is provided a method for adjusting the flow of air from a radial fan having a central rotor and a casing surrounding same, said casing having a number of passages arranged in a spiral pattern, wherein air is drawn in at the centre of the casing adjacent the rotor and emerges from the spiral casing of the fan at the widest part thereof, in which the flow of air is controlled by means of a throttle valve located in the widest part of the fan, wherein when the flow of air is at a minimum the throttle valve extends substantially from the edge of the casing at its widest part to the edge of the casing at the narrowest part of the fan.

Also, according to the present invention there is provided apparatus for adjusting the flow of air from a radial fan having a central rotor and a casing surrounding same, said casing having a number of passages arranged in a spiral pattern, wherein air is drawn in at the centre of the casing adjacent the rotor and emerges from the spiral casing at the widest part of the fan, in which a rotatable throttle valve is located in the passage at the widest part of the fan, said valve having an extension from one edge of the casing at its widest part to the edge of the casing at the narrowest part of the fan.

1 0 A distinguishing characteristic of the invention is that the flow is adjusted within the actual fan. A throttle valve is provided in the widest part of the spiral pattern, viz. the exhaust. the valve extending from one side of the casing to the other. The throttle valve, in a particularly preferred embodiment, has a rounded profile and is supported on an axle. Twisting of the axle causes the flow to be diverted, whereby, at the same time, a reduction in energy consumption can be observed if measuring instruments are available.

The present invention will be further illustrated, by way of example, with reference to the accompanying drawings, in which:- Fig. 1 shows, in diagrammatic form, a radial fan in accordance with the invention; Fig. 2 shows, in diagrammatic form, a side view of the fan of Fig. 1; Fig. 3 shows embodiments of types of throttle valve which may be used; and Fig. 4 shows a section through a part of the rotor.. wherein the direction of the blades is shown in relation to the direction of rotation.

Conventional supports and assembly instruments have not been included as they do not affect the invention itself.

The radial fan shown in Fig. 1 without a front gable, includes a rotor 1 having blades. The rotor is supported on an axle 2 in a known manner. This axle can 1 be driven by an electric motor in a known manner. The rotor is enclosed by a casing 3, which in a k -nown manner has a helical shape. The distance between the casing and the rotor increases continuously from the narrowest distance at 4 to the widest distance at the exhaust part of the fan. In a conventional way, air is drawn in adjacent to the axle of the fan. Four quadrants extend through the fan casing as shown in Fig. 2.

The narrow sector is in the second quadrant and the exhaust at the crossing between the first and second quadrant. The distance between the casing and the rotor is largest in the first quadrant.

is A throttle valve 5, supported on an axle 6, is inserted in this widest part. An anticlockwise twist of the valve shown in the drawings causes the front edge of the throttle valve, which faces towards the current of air, to rest against the casing, and the rear edge of the throttle valve comes close to the rotor.

The axle 6 may be supported in position in the fan in many known ways. It has proved successfulto cause the bearing to rest substantially in the centre of the free space between the rotor and the casing. It has also proved advantageous for the angle which is formed with the rotor axle 2 and throttle valve axle and the narrowest part 4, which is marked with a 7 in Fig. 2, not to exceed 450. This causes the throttle valve to check close to the exhaust 30 in the widest part of the fan.

In Fig. 2, the throttle valve is assumed to be a thin plate fixed to a cylindrical axle. The diameter of the axle is larger than the thickness of the plate. This 1 z embodiment does not prove to function particularly well. It appears probable that a large flow is circulating and the adjustment does not produce any reduction of the power requirement on the axle 2. A plane sheet, as shown for example in Fig. a, is also known to cause the formation of eddies in the flow which is generated by the fan. In Fig. 3b the throttle valve has been given another profile. The side of the throttle valve facing towards the rotor is plane, whilst that facing towards the cover is bent. Here it is easiest to give the band a circular cross-section.

In this embodiment it emerges that the power requirement reduces if the flow from the fan is throttled by twisting the throttle valve anticlockwise. It appears to be most favourable for both sides of the throttle valve to have a bend as shown in Fig. e, preferably having a cross-section of a part of a circle. Its centre will then lie an the rotor side of the throttle valve. Most successful is the embodiment wherein at the same time the rear edge of the throttle valve is on a level with the casing in its narrowest part and the front edge of the throttle valve rests against the casing. The flow is then throttled completely and the power requirement is lowest.

The blades on the rotor 8, which are shown diagram--matically in Fig. 1, can be directed radially and plane. This is shown in Fig. Aja, which is a section through one part of the rotor in Figs. 1 and 2. The blades can slope forwards or backwards in the direction of rotation of the rotor, as marked with a 9 in Fig. 4. In Fig. 4b the blades slope forwards in the direction of rotation. The blade which is shown in Fig. 4, b has also been given a bend or curve in a known manner, which improves the function of the fan and is particularly favourable when adjusting the flow, which can be executed with the throttle valve 5.

The fan cover could be made of galvanised sheet metal. It has therefore not been considered necessary to show the plate with thickness, but only as a simple spiral. The rotor may also be made of thin sheet metal in the blade 8 and somewhat thicker in the rotor's gables. These details are not covered by the invention. The galvanised surface can often be relatively rough, causing smaller eddies, which could disturb the existing flow adjustment. It has therefore proved advantageous to coat the surface, particularly if the fan is to operate in a dirty environment.

It has proved valuable to take some care in finishing the surface of the throttle valve, as otherwise dirt can stick and cause eddies. Besides sheet metal which is coated, different known plastics can also be used advantageously in a dirty environment.

The band or curve an the throttle valve has proved to be most advantageous if this coincides with a centre line on the distance between the rotor surface and the casing. The flow is then least disturbed when the throttle valve is placed in the open position.

With very simple means it is made possible to adjust.

the flow from a radial fan without expensive electronics or throttle of the flow.

41

Claims

1. A method for adjusting the flow of air from a radial fan having a central rotor and a casing.surrounding same, said casing having a number of passages arranged in a spiral pattern, wherein air is drawn in at the centre of the casing adjacent the rotor and emerges from the spiral casing of the fan at the widest part thereof, in which the flow of air is controlled by means of a throttle valve located in the widest part of the fan, wherein when the flow of air is at a minimum the throttle valve extends substantially from the edge of the casing at its widest part to the edge of the casing at the narrowest part of the fan.

2. A method as claimed in claim 1, in which at least one of the two lateral sdrfaces of the throttle valve is curved, with the centre of curvature situated at the side of the throttle valve which faces the rotor.

3. A method as claimed in claim 2, in which the throttle valve is provided with a rotatable axle located substantially midway between the casing and the rotor.

4. A method as claimed in claim 1, in which the rotor has blades, the front edge thereof being curved forwards in the direction of rotation.

5. Apparatus for adjusting the flow of air from a radial fan having a central rotor and a casing surrounding same, said casing having a number of passages arranged in a spiral pattern, wherein air is drawn in at the centre of the casing adjacent the rotor and emerges from the spiral casing at the widest part of the fan, in which a rotatable throttle valve is located in the passage at the widest part of the fan, said valve having an extension from one edge of the casing at its widest part to the edge of the casing at the narrowest part of the fan.

t 0 1

6. Apparatus as claimed in claim 5, in which at least one of the two lateral surfaces of the throttle valve is curved, with the centre of curvature situated an the side of the throttle valve which faces the rotor.

7. Apparatus as claimed in claim 5, in which the.rator has blades, the front edge thereof being curved forwards in the direction of rotation.

1 Puclished 1988 at The Fatert 0Mce. Statc House. 66 1 High Folborn. London WC1R 4TP. Further c-pies may be obtained from The Patent Office, Sales Branch. S,. Lia-,v Cray. Orpington. Kent BW 3RD Printed by Multiplex teel=ques ltd. St Mary Cray, Kerit. Con. 1187-