Electric convection heater having a friction-type blower

Abstract

An electrical resistance convection heater has a friction-type blower rotor comprising a plurality of spaced annular fins in the form of a helix of substantially flat laminar material. The pitch of the helix is so small that each turn of the helix approaches a laminar annulus. The interior of the rotor forms an axial interior air inlet whereby when the rotor is rotated by an electric motor, air enters the interior of the rotor in an axial direction and flows through the exterior of the rotor in a radial direction through the spaces between the axially spaced rotor fins. A stationary annular electric heating element is mounted coaxially with respect to the rotor and located upstream thereof in the direction of air flow through the rotor for heating the air flow. The heating element may comprise a laminar metal strip in helix form, the turns of which constitute a plurality of axially spaced annular fins. In one embodiment such a heating element is arranged so that the fins of the heating element are substantially coplanar with respect to the rotor fins. Alternatively, the heating element may be a strip corrigated in zig-zig fashion.

Description

THE PRIOR ART

Portable fan heaters have found a wide application in the household, particularly for transition heating. A drawback of known appliances is that they generate an objectionable air noise. The fan system may be a noise source, and also so may the heating element.

THE OBJECT OF THE INVENTION

An aim of the invention is a low-noise fan heater which is effective and efficient. Further the rotary parts are such that the requirement of physical protection is reduced.

DESCRIPTION OF THE INVENTION

In an air-heating appliance with a blower driven by an electric motor, the invention resides in that the rotor is a friction blower rotor, with annular axially-spaced fins constituting a cylindrical figure of revolution and that a resistance heating element is arranged coaxial with and upstream of the rotor so that the air traverses this heating element before it is engaged by the annular discs. It has already been proposed to arrange the heating elements on the upstream side of a bladed centrifugal blower. This arrangement has the disadvantage that the blower must pass a greater volume and this results in lower pressure and delivery coefficients as well as lower efficiencies. This latter disadvantage is due to the fact that the Reynolds's number drops with rising temperature and thereby the larger viscosity forces lead to a worsening of the acceleration by the fan blades. For a given rate of delivery, the blower has to be larger than if it were to receive cold air, and of course it may have to be made of materials of high hot strength.

Thus, in an appliance according to the invention, the acceleration of the air is accomplished by virtually flat elements of continuous profile which frictionally, use the viscosity of the air to accelerate it tangentially. The friction between the elements and the air in the boundary layers is the operative energy-conversion force. This friction is a function of the air viscosity. The air viscosity increases substantially with the increase of temperature. Providing the fan downstream of the heating element uses the increased viscosity of and raised temperature of the air to advantage by providing an effective low-noise heating appliance. This is in contrast to known appliances in which the temperature effects lead to disadvantages.

The invention is described by way of example, with the help of Figures.

FIG. 1 shows diagrammatically, in cross-section along the axis, a heating appliance according to the invention.

FIGS. 2A and 2B show, in two cross-sections at right angles to each other, another embodiment of a heating appliance according to the invention.

FIG. 3 shows, in a cross-section similar to that of FIG. 1, a third embodiment of the heating appliance according to the invention.

FIG. 4 shows, in a diagrammatic cross-section, the possible correlation of a blower according to the invention with the blower casing parts which guide the air stream.

In FIG. 1, the motor 1 drives the hollow cylindrical rotor 3 via the wheel disc 2. The rotor 3 consists of a large number of virtually flat annular fins 4 which are preferably manufactured by helically coiling an aluminium strip. Although speaking exactly, there is only one fin comprised by a continuous helix of strip metal, for practical purposes it can be considered as a plurality of annuli and is described as such; indeed it may be desirable in some cases to manufacture the rotor by assembling a plurality of individual laminar annuli. The fins 4 are held axially spaced by bolts 5 which are placed as nearly as possible at minimum radius of the fin assembly, spaced by distance pieces (not shown). The distance can be ensured, for example, by washers or flanges around the bolt-holes in the fins 4. Room air is sucked in from below along the arrow 7, all around the appliance. The casing consists of the discs 11, 18 and 19 held assembled by bolts 24.

The resistance heating element 8 is also formed as a helical strip of suitable metal having a large ratio of width to thickness. The distance spacing of the helical turns is here maintained by insulating posts 9. The heated air proceeds as indicated by the arrow 10 into the inside of the rotor 3, and is thus engaged by the fins 4 by way of friction forces in a manner already described. The heated air is discharged with a radial velocity component indicated by the arrow 22. Slots 12 are provided to give access for cooling air for the motor 1. Furthermore, a cylindrical separating wall 13 is provided in the casing 19 protectively surrounding the motor 1. Air is sucked through the apertures 12 as indicated by the arrow 14. It then cools the motor 1 and emerges through a frustoconical slot 15 to be entrained and accelerated outwards as indicated by arrow 17.

FIG. 2A shows another embodiment of the fan heater according to FIG. 1 in which the heating element 20 is formed of strip corrugated in zigzag formation. The major area of the heat dissipating regions lies radially. In the rotor 3', shown in FIG. 2A, the fins 4' are so formed that their surfaces lie on frustoconical nested surfaces concentric with the rotor axis. By this means, the air flow which enters into the fan heater and heated by the heating element during movement along radial paths indicated by the arrows 28 is delivered from the rotor in flow paths with an axial velocity component indicated by arrow 28". Within the fan heater the heated air flows generally axially as indicated by the arrow 28'. The cooling of the motor is accomplished by means of an auxiliary blower carrying radial blades 16 by which air is conveyed through the aperture 12' as indicated by the arrow 14' over the motor.

FIG. 2B shows a cross-section along the section line IIb-IIb of FIG. 2A from which the radial arrangement of the resistance heater 20 can be seen. The air is sucked in radially from the outside as indicated by the arrows 28. In FIG. 2A the motor 21 is attached to the coverplate 23 which is mounted on the baseplate 25, as in FIG. 1, by bolts or studs 24 which may be so numerous as virtually to form a protective cage.

FIG. 3 shows diagrammatically an embodiment according to FIG. 1 in which, however, the heating element 8' comprising a helical strip, on its posts 9' is located inside the rotor 3' and is substantially coplanar with the rotor which comprises a helical strip 4. By this modification the cylindrical wall 13 ceases to be necessary. The motor 1' is attached to the annular floor portion 31 by spoke-like arms 30. By provision of feet 32 extending downward from the portion 31, the annular portion affords passage for the entry of air to the inside space 33. Air flows axially into the rotor along the path indicated by arrow 34, through inlet openings between the arms 30 and then radially out of the rotor between the axially spaced fins 4 along the path indicated by arrow 35.

FIG. 4 shows diagrammatically in cross-section an appliance according to the invention in which the rotor 40 is arranged in a volute casing so that the emerging air stream is directed as indicated by the arrows 42 and 46. This formation may be applied with simple design modification, to the earlier described embodiments.

Claims

I claim:

1. An electrical resistance convection heater having a friction-type blower rotor comprising a plurality of axially spaced annular fins in the form of a helix of substantially flat laminar material where the pitch of the helix is so small that each turn of the helix approaches a laminar annulus and where the annular interior forms an axial interior air inlet whereby when said rotor is rotated air enters the interior of the rotor in an axial direction and flows to the exterior of the rotor in a radial direction through the spaces between the axially spaced fins, a motor for rotating the rotor, and a stationary annular heating element mounted coaxially with respect to the rotor and located upstream of the rotor with respect to the direction of air flow through the rotor.

2. Heating appliance according to claim 1, characterised in that the rotor fins are virtually frustoconical surfaces nested concentrically with the rotor axis.

3. A heater according to claim 1 in which the heating element is constituted by laminar strip metal formed sinuously in zigzag manner and so as to have a generally hollow cylindrical shape coaxial with the axis of the rotor, the surfaces of major area of the strip lying substantially radially to the axis.

4. A heater according to claim 1 in which the motor is surrounded by a wall which is itself surrounded by the heating element.

5. A heater according to claim 1 in which the motor is exposed to a flow of cooling air for which passages are provided separately from the flow of air heated by the appliance.

6. A heater according to claim 5 in which blower means are provided for the flow of cooling air which flow of cooling air is independent from the flow of air caused by the said rotor.

7. An electrical resistance convention heater according to claim 1 wherein said heating element comprises a laminar metal strip in helix form with axially spaced turns wherein substantially plane surfaces of the strip extend radially of the axis of the rotor.

8. An electrical resistance convection heater according to claim 7 having an axially extending insulative post supporting the metal strip.

9. An electrical resistance convection heater according to claim 1 wherein the heating element is surrounded by the rotor.

10. An electrical resistance convection heater according to claim 1 having a spoke-like structure mounting said motor on one side thereof and legs on the other side of said spoke-like structure opposite said motor whereby air flowing into said rotor passes around said legs and through the spoke-like structure.

11. An electrical resistance convection heater according to claim 1 having in addition a casing structure comprising disc-like parts located axially exterior of said rotor and heating element with said disc-like parts interconnected coaxially in parallel planes and having axially extending bolts connecting said disc-like parts near their outer peripheries to form a cage protecting said rotor and said heating element and where one said disc-like part has an opening therein through which air may enter the interior of said rotor in an axial direction.

12. An electrical resistance convection heater according to claim 11 wherein one of said supports said disc-like parts motor.

13. An electrical resistance convection heater having a friction-type blower rotor comprising a plurality of axially spaced annular fins the annular interior of which forms an axial interior air inlet whereby when said rotor is rotated air enters the interior of the rotor in an axial direction and flows to the exterior of the rotor in a radial direction through the spaces between the axially spaced fins, a motor for rotating the rotor, and a stationary annular heating element mounted concentrically and substantially coextensively with respect to the rotor and located upstream of the rotor with respect to the direction of air flow through the rotor, said annular heating element constituting a plurality of axially spaced annular metallic fins, said heating element fins being substantially coplanar with respect to said rotor fins.

14. A heater according to claim 13 in which a volute casing surrounds at least the rotor so as to deliver the heated air therefrom in a directed stream subtending substantially less then 360.degree. referred to the axis.