GB2048382A

GB2048382A - Fan unit particularly for extractor hoods

Info

Publication number: GB2048382A
Application number: GB8010724A
Authority: GB
Original assignee: VORTICE ELETTROSOCIALI SpA
Current assignee: VORTICE ELETTROSOCIALI SpA
Priority date: 1979-04-23
Filing date: 1980-03-31
Publication date: 1980-12-10
Also published as: IT7922059A0; FR2455198A1; IT1166757B

Abstract

The fan unit 1 comprises a centrifugal impeller 5 about the periphery of which is formed an annular manifold chamber containing stationary blades 6 so shaped as to direct the discharged airflow in an axial direction past the impeller. <IMAGE>

Description

SPECIFICATION Fan unit particularly for aspiration hoods This invention relates to a fan unit, particularly for aspiration hoods, as used in household appliances.

Basically two types of fan are available for the aspiration of air, which have neatly differentiated operational and constructional features, namely the centrifugal type and axial flow or airscrew type.

Axial flow fans present a large unimpeded section to the flow and involve no deflections of the airflow pattern; thus, they are suitable for large flow rate requirements, although on account of their very nature they cannot provide high heads, but rather operate the better the lower is the head. By contrast, centrifugal fans, which have generally an axial suction side and a tangential delivery side, by imparting at least one deflection to the airflow, involve of necessity an appreciable pressure drop, which can be compensated for by the possibility of achieving high heads, as are inherent to centrifugal impellers. Thus, the fields of application of these two types of rotary fans are neatly differentiated. Obviously, there exist in the transition range of their fields of application, conditions where it is possible to choose arbitrarily from the two types in question.Naturally, in that transitory range of the fan operational characteristics, instances are frequently encountered where it would be desirable to combine the high flow rate capability of the axial flow fans, for a given size, with the capability for high heads which typifies the centrifugal fans. For example, this would be the case with aspiration hood fans for household appliances, such as used in kitchens, bathrooms, garages, and the like spaces. Strict space requirements would impose an axial fan, also in order to have it installed centrally and not off-centered as centrifugal fans require normally. But at the same time it may be necessary to discharge the air to remote exhaust systems, e.g. above the roof of a building, or to filter and strain the aspired air, thereby higher heads than those supplied by axial impellers are required.By increasing the blade number and imparting to the blades special foil sections it has been possible to increase the head of the airscrew blowers considerably, but this involves individual designing of the blades in each case, and a performance drop, especially if the operating conditions deviate, even slightly, from the ones anticipated. In practice, it must be recognized that there exists a need for a fan which is both suitable for the application just mentioned, and for several similar applications where the conditions outlined above prevail.

This invention sets out to fill the need just mentioned above.

Within that general aim, it is possible to arrange that the fan according to the invention is both suitable for operation in that transition range where the axial fan exhibits inadequate head, while the centrifugal one would restrict the duct excessively or be impossible to install within the outline of the duct.

It is further possible to arrange that this novel fan has a good performance within a wide range of flow rates.

It is further possible to arrange that the construction of this novel fan is as simple and easily carried out as those of the two conventional types mentioned above.

According to one aspect of the present invention, there is provided a fan unit, particularly for aspiration hoods, comprising a centrifugal impeller with axial suction,. and characterised in that it includes a manifold chamber along the periphery of said impeller, and a plurality of stator blades in said manifold chamber, said stator blades being configurated to direct the centrifuged airflow in an axial direction past the impeller.

The invention features and advantages will be next explained in detail through a description of a presently preferred embodiment thereof, with reference to the accompanying drawing, where: Figure 1 is a plan view, with portions removed, of a fan according to the invention; Figure 2 is an axial section, with portions visible and others removed, of that same fan; and Figure 3 is an elevational view of the fan in the direction Ill of Fig. 1.

With reference to all three of the drawing figures, a fan unit according to the present inventive concept is indicated generally at 1.

It comprises a housing 2, in which a rigid cup-like support 3 is installed in an axial position which carries an electric motor 4, a centrifugal impeller 5 of traditional shape, cantilevered from the motor. Between the housing and impeller, there are provided stationary or stator blades 6 extending in axialradial planes. The housing 2 is made in two parts, namely a lower body or pan 7 of substantially cylindrical configuration, and a substantially conical upper cap 8, which define together the inner path for the airflow.

A hood 7 has an axial aspiration or suction port 9, located directly beneath the impeller 5, the cap 8 being provided with a coaxial delivery port 10. The entire housing is overlaid by ribs 11 extending in a longitudinal, i.e. axial, direction, excepting for a flattened portion 1 2 intended for resting against a supporting wall, e.g. the wall of an aspiration hood. The impeller 5 is carried cantilever fashion by the driveshaft 1 2a protruding downwards from the motor 4 through the support 3, and comprises shaped blades 1 3 which are backed and stiffened by a disk 14 and have a typical foil section profile for centrifugal impellers. The difference from ordinary centrifuges is evidenced in the path followed by the intake air downstream of the impeller, from the stator blades 6.Instead of the usual volute type of manifold, forming a conveying scroll which encircles the impeller tangentially, there is provided herein a cylindrical annular manifold chamber 15, in which the stator blades 6 are arranged in the form of as many partitions evenly distributed along the circumference. The stator blades 6 define in pairs flow channels on the wall which are parallel to the axis.

The operation, from a fluid dynamics standpoint, will be self-evident when compared to the operation of conventional centrifugal fans.

In fact, while the shape reminds that of an axial fan, the principles underlying it are substantially centrifugal ones, as required by the blades of the rotor or impeller. By centrifugal effect, as favored by the foil section profiles of the blades 13, the air entrained rotatively is transferred into the peripheral manifold chamber 15; here, the partitions forming the stator blades 6 hinder the rotary component of the airflow, deflecting its direction from tangentcrosswise to axial. Thus, the rotary knetic energy of the fluid is converted into rectilinearly axial kinetic energy. The shape of the partitions, or stator blades 6, is such as to cause that deflection without inducing local or stationary eddies, which would result in dissipated energy, to the detriment of both the head and flow rate.In the absence of such blades, the airflow would follow a circular pattern in the manifold chamber 1 5 along with the impeller. By providing a single partition or baffle 6, that circulating movement would be stopped, but the streamlines would be strongly compressed against the partition, thus resulting in a poor energetic recovery and strong dissipation through eddy formation. It is only by defining several channels in the desired direction that the streamlines are not slowed down but only deflected, to substantially retain their kinetic energy. Thus, a fan is provided which combines the advantages of an axial flow direction with a rational pattern of the streamlines and a simple construction, and the centrifugal operation mode which can afford higher heads than the mere suction provided by the airscrew.In other words, the more effective principle of centrifugal fans has been combined with the more functional arrangement of the streamline patterns which is typical of the axial fans. Actual tests have confirmed in practice these theoretical assumptions.

But at the same time, further advantages have been provided with the novel combined solution according to the invention. The motor being located aligned with the flow axis as in conventional axial fans, it only restricts a small fraction of the flow section, whereas with conventional impellers of the airscrew type even the central area is "blown", and the motor is a material obstruction to the airflow.

Moreover, the motor, when arranged as mentioned, is lapped externally by the airflow and is accordingly more effectively cooled, while leaving the flow unrestricted. Further advantages, such as the construction of the body 2 in two parts 7 and 8, and the tapering of the body 2 around the motor to utilize even the slight compression of the air, with attendant transitory volume reduction, which occurs on account of the centrifugal effect, are also ascribable to the invention.

The instant inventive concept obviously affords other design and construction embodiments in addition to the one described. Thus, for example, it will be obvious to modify and bend the stator blades 6 which deflect the airflow to optimize the performance of the fan unit, or maximize the flow rate, in certain conditions. Such modifications, inasmuch as they do not affect this inventive concept, are well within the purview of this invention.

Claims

1. A fan unit, particularly for aspiration hoods, comprising a centrifugal impeller with axial suction, and characterised in that it includes a manifold chamber along the periphery of said impeller, and a plurality of stator blades in said manifold chamber, said stator blades being configurated to direct the centrifuged airflow in an axial direction past the impeller.

2. A fan unit according to Claim 1, characterised in that said manifold chamber along the periphery of said impeller has a substantially cylindrical annular configuration, and said stator blades are partitions dividing said chamber in several channels.

3. A fan unit according to Claims 1 or 2, characterised in that the motor is mounted in alignment with the impeller axis, downstream thereof in the direction of the intake airflow.

4. A fan unit according to Claim 3, characterised in that the motor contacts and is cooled by the airflow generated by said impeller.

5. A fan unit according to any Claims 1 to 4, characterised in that said manifold chamber is connected, on its delivery side, to a converging conical cap or shroud.

6. A fan unit according to any Claims 1 to 5, characterised in that it comprises at two opposite ends provided for suction and delivery two ports positioned in alignment with the axis of said impeller.

7. A fan unit, particularly for aspiration hoods, substantially as herein described with reference to the accompanying drawing.

8. Any novel element, or combination of elements, herein described and/or shown in the accompanying drawing, irrespective of whether the present Claim is within the scope of, or relates to the same invention as, any of the preceding Claims.