WO1995019529A1

WO1995019529A1 - An electric air heater

Info

Publication number: WO1995019529A1
Application number: PCT/US1995/000492
Authority: WO
Inventors: Dov Z. Glucksman; John A. Deros
Original assignee: Appliance Development Corporation
Priority date: 1994-01-18
Filing date: 1995-01-13
Publication date: 1995-07-20
Also published as: EP0740763A4; EP0740763A1; US5619612A

Abstract

A compact electric air heater is enclosed in a shockproof housing, cylindrical, and comprises a rear (9) and front wall (containing small air inlet openings preventing access to the electrical parts inside, and includes a circumferential air outlet between the front and rear walls. A motor (2) is located in the air inlet area facilitating its cooling. A centrifugal blower impeller (1) is mounted on the blower shaft with its inlet coinciding with the inlet openings. The impeller is surrounded by a cage-shaped heating element. The outlet comprises a plurality of guide vanes (4).

Description

An Electric Air Heater Background of the invention: In my U.S. patent # 4,090,061, I described and claimed an electrical air heater which combines a motor driven blower that is surrounded by an 5 electrical resistance heating element consisting of vane like strips which serve both to heat the air and also act as guide vanes to help and redirect the air imminating from the blower.

It was determined through recent testing that the air flow efficiency as claimed in my U.S. patent No. 4,090,061 is not realized due to the fact that the air imminating from the hearing element is at a high velocity and at a relatively shallow angle to the tangent.

The high air velocities, are responsible for pressure losses, they also generate a noise level that would be undesirable for certain domestic application.

In one embodiment of my above mentioned patent the blower heater combination is surrounded by a blower housing which would alleviate the problem mentioned above by providing a gradual diffusion of the high velocity. The heated air would thus be delivered out of a defined outlet which is very usable in some applications such as a hair dryer, but not so desirable in other applications, as would be discussed herewith. It has become apparent that there exist many application where a concentrated stream of heated air would not be required or even desired; instead a low-velocity heated air volume would be more appropriate. In such applications the concentric arrangement of the blower and heating element are still of a great advantage, due to the improved heat transfer properties of the turbulent air flow and the uniformity of the air flow along the entire heating element cylinder. In order to further enhance the aerodynamic efficiency of the system a concentric molded ring of guide-vanes are place around the heating element. The guide vanes further diffuse the heated air thereby reducing the tangential component of the air velocity converting it to static pressure, according to Bernouli's theorem.

Applications where a low velocity and therefore silent heated air flow would be of great benefit would include space-heaters, foot warmers, towel drying appliances, flat garment dryers etc. Further on in this specification some such applications would be discussed to illustrate the advantages of the system.

Summary of the invention It is the object of the invention to provide an air heater comprising a blower, heating element and guide-vanes in concentric alignment for the purpose of creating a compact source of heated air.

It is a further object of the invention to provide a source of heated air which is evenly imminating over the entire cylindrical circumference of the air heater.

It is another object to provide a low velocity silent air flow uniformly heated by a course of electric heat.

It is yet another object to provide a shock proof and fire proof housing surrounding the electrical components of the air heater unit.

Brief description of the drawings Fig. 1 is a longitudinal cross sectional view of an air heater according to the present invention.

Fig. 2 is a cross sectional view along lines 2-2 of Fig. 1.

Fig. 3 is an enlargement of the area marked 3 in Fig. 2.

Fig. 4 is a series of velocity vectors of the air flow illustrating flow conditions in the device according to the invention.

Fig. 5 is a longitudinal cross sectional view of a portable air heater embodying the air heater of the invention.

Fig. 6 is a longitudinal cross section through a combination light fixture, heater and exhaust fan, primarily for use in bathrooms, embodying the elements of the invention. Detailed description of the drawings Referring first to Figs. 1 through 4. The air heater according to the invention consists of a centrifugal blower wheel or impeller 1 comprising a back plate 12 and a six blades 11 integrally molded with said back plate which draws in the air in an axial direction and expels it along its cylindrical periphery. The impeller is driven by an electrical motor 2 and turns at a predetermined direction and speed. The air that is expelled from the impeller passes through the strips 4 of the heating elements which are positioned at an angle substantially parallel to the air flow so as not to cause any impedance of the air flow.

The heating element is similar to the heating element described in my U.S. patent # 4,694,142 and European patent #0183252B1 and it's various nationalized derivatives:

The heating element is in the form of a cylindrical cage consisting of many strip 4 of resistive metal alloy which is stamped to form a zig-zag pattern whereby these strips become connected to each other at their alternate ends 5 and 5' the ends of the strips are mounted on plastic rings 6 and 6' by partially melting plastic pins that are integral to the rings and forming mushroom heads 7 and 7' that secured the ends of the heater to the rings.

The electrical motor 2 is mounted on the plate 81 which is an integral a part of the front wall 8 the plate 81 is connected to the front wall by a series of integrally molded ribs 82 which are closely spaced to allow air in but to prevent contact with the motor or other electrically live parts.

The rest of the enclosure consists of the rear wall 9 which runs parallel the heater rings and the blower impeller. Plate 9 features a second cage consisting of a multitude of integrally molded guide vanes 91 that are inter connected at their free ends by a ring 92 which is integrally molded with the vanes.

Ring 92 is attached to front wall 8 by means of fasteners such as screws, not shown here.

The molded guide vanes that surround the heating element are fashioned in an arcuate manner so that physical access to the heating element is prevented yet the heated air will easily flow through the vanes.

As can be seen in Fig. 1 the entire electrical components are thus enclosed to prevent access. The plastic material that the enclosure is molded of is classified as "flame-retardant" thus fire hazzard is minimized. "Flame-retardant" plastics are much more expensive than other plastic materials. The present design allows that just a small amount of "flame- retardant" plastic is used in comparison with the rest of the plastic materials that constitute the entire appliance. This is obvious if compared to the size of the blower housing in my patent No. 4,090,061 and to the size of the entire fan heater in my U.S. patent No. 4,694,142. Referring now to Fig. 3 & 4 in which the air flow directions are illustrated. Air that flows through the impeller follows the contour of the blade and will immerge from the impeller at an angle and velocity as shown in the vector diagram of Fig. 4. Here the air velocity Vo is the resultant of Vr, which is the relative velocity between the air and the blade and Vt, the tangential velocity of the tips of the blades.

The vanes 4 of the heating element are positioned so that they coincide with the direction of the air velocity Vo to minimize loss of momentum. It should be noted that the vanes 4 are slightly curves; this is done primarily to increase the rigidity of the vanes which are made of very thin metal strips.

The velocity vector of the air emerging from the heater vanes is substantially the same as Vo that immerged from the impeller blade. The leading edge 92 of the guide vaned 91 substantially coincides with the angle of the vector Vo.

As the air passes through the guide vanes it will change in direction and diminish in velocity, which will result in an increase of it's static pressure, as would follow from Bernulli' [s equation, as follows :

V₀ ²/2g+P₀/ = V_e ² /2g+P_e/

Thus Δp= ( P_e-P₀= /2g (V₀ ² -V_e ² ) The gain in pressure (Pe-Po) diminishes the amount of pressure by which the blower needs to raise the air flow thus resulting in a quieter operation, and requiring less power to drive the blower.

Referring back to Fig. 1 and 2, it becomes apparent that the configuration allows the motor to be cooled by the air being drawn in by the blower wheel. It can also be observed that the whole package becomes very compact since the electric motor partially fits inside the blower cavity.

Figs. 5 and 6 illustrate a few applications of the air heater according to the invention that demonstrate the advantages of the system.

Fig. 5 illustrates a free-standing space heater employing the air heater according to the invention. Air is being drawn into the space heater from the rear through the opening 51, after passing through the heating element the heated air is reintroduced into the space through an annular opening 52. The space heater also features a stand 53 that supports the main body 54 of the heater and permits the heater to be tilted in relationship to the base.

Fig. 6 illustrates a combination appliance that incorporated the air heater according to the invention: A ceiling mounted heater, light and exhaust fan suitable for use in bathrooms.

The center portion of the lower face of the appliance features an inlet grill 101 with a filter 102 behind it. The inlet grille is removable for cleaning. Surrounding the grille is a florescent circular light bulb 103 shielded by a clear or "frosted" lense 104 and provided with a reflector 105 to enhance the efficiency of the light source. The air heater according to the invention is positioned coaxially and above the inlet grille 101 and the light bulb 103. The air exiting from the guide vanes 91 can only exit along the annular opening 106 and will thus be returned to the room which will gradually be heated.

When the appliance is to be used as an exhaust fan the heater will not be energized and the solenoid 107 will pull the bar 108 which is attached to the two arms which in turn would lower the annular disc 110 to block the air from returning to the room, in stead the air, would be expelled through the new annual opening 106 that was created by the downward movement of the annular disc 110.

It should be borne in mind that the above mentioned applications are only a sampling of the broad use this air heater would have in domestic and industrial fields of heating air.

Claims

WHAT IS CLAIMED IS: 1. An electric air heater configured to operate at a low noise level and to provide a shock proof enclosure for electric current carrying portions of said heater, said heater including, a housing of a non-conductive material of generally cylindrical configuration, comprising a rear wall, a front wall containing central air inlet means in the form of adjacent perforations and a circumferential air outlet between said rear wall and said front wall, an electric motor in said housing rigidly fastened to said front wall in concentric alignment with air inlet means and with it's shaft extending ^" towards said rear wall, a centrifugal blower impeller mounted on said motor shaft, having its air inlet in continuation of said air inlet means in said housing, an electric heating element in the form of a cylindrical first cage surrounding said blower impeller, said cage comprising a plurality of interconnected strips of electrical resistance material of equal width and equal length inclined to the ideal surface of said cage at an angle substantially coextensive with the air flow created by said impeller, said heating element being held in position by non-conductive members supporting the two ends of said strips, a plurality if air guide vanes of non-conductive material positioned in and across said air outlet in the form of a second cage concentrically surrounding said blower impeller and said heating element, said guide vanes having a leading edge and a trailing edge and being of 10 generally equal length and of equal cross section and their leading edge being inclined to the ideal surface of said cage at an angle substantially coextensive with the air flow created by the vanes of said heating element, electric switching and controlling means. 2. The electric air heater of Claim 1, wherein said conductive strips of said 15 heating element in cage form are interconnected by bridging portions of conductive material jointing the alternate end of proximate strips, said cage being held in positioned between two annular members of a non-conductive material affixed to said housing walls. 3. The electric air heater of Claim 1, wherein said air inlet means are in the 20 shape of flat strips of a non-conductive material, radially and concentrically aligned across said air inlet of said housing, with their flat surfaces substantially perpendicular to said air inlet opening. 4. The electric air heater of Claim 1, wherein cool air inlet air flows along said electric motor. 5. The electric air heater of claim 1, wherein the trailing edge of said guide vanes is inclined to the ideal surface of said second cage at an angle substantially greater than that of the leading edge.