US2863980A - Electric air heater - Google Patents

Description

Dec. 9, 1958 M. LOGAN ELECTRIC AIR HEATER Filed Aug. 8, 1957 IWJWW m A.

United States Patent ELECTRIC AIR HEATER Malcolm Logan, Laguna Beach, Calif.

Application August 8, 1957, Serial No. 676,997

3 Claims. (Cl. 219-39) This invention relates generally to heaters and more particularly to an improved portable type electric heater for supplying warm air in small rooms or automobile trailers.

Different types of portable electric air heaters are presently available on the market. Many of these heaters simply comprise a heating coil and suitable reflector, while others incorporate various heating coil arrays concealed in suitable grilled casings and the like. For maximum efficiency and heat transfer, forced draft or air blower type heaters are preferable inasmuch as greater heat transfer occurs when relative motion exists between the mass of fluid or air to be heated and the heat sources. Many forced draft electric heaters of this type, however, suffer the disadvantage of being noisy and relatively complicated in construction as well as expensive to manufacture. As a consequence of the present known constructions, it is relatively diflicult to replace the heating coils should they become inoperative. Usually, the procedure requires the disassembly of the entire heater which is not only time consuming but involves considerable labor.

Bearing the above in mind, it is a primary object of the present invention to provide an improved forced draft type electric air heater of portable size which is relatively uncomplicated in construction and silent in operation.

' Another object is to provide a heater of the above type which has a relatively large heating capacity for its size as compared to prior art heaters of similar size.

Still another important object is to provide a heater of the above type in which the heating coils may be readily removed and replaced without the necessity of dismantling the major portions of the heater.

Another object is to provide a heater which employs relatively few differently shaped components whereby it is relatively inexpensive to manufacture.

These and many other objects and advantages of the present invention are attained by providing a cylindrical casing having upper and lower end plates. Each of these end plates is provided with a plurality of open ended tubes arranged generally parallel to eachother with fixed ends secured to the plates and terminating in free ends. The axial length of the cylindrical portion of the casing is greater than the length of the tubes so that when the upper and lower end plates are positioned on the ends of the cylindrical casing with the various tubes projecting therefrom to pass within the casing, the free ends of the various tubes terminate short of the end plates. By such an arrangement, air entering the tubes associated with the upper end plate must traverse downwardly through the tubes into the lower region of the cylindrical casing and thence pass up through the cylindrical casing to the free ends of the plurality of tubes associated with the lower end plate and finally traverse these tubes out the end of the lower end plate. The air is thus caused to pass through the chamber along a path three chamber lengths -distance.- The upper and lower end plates and drawn into the suction chamber from the casing out into the enviromment of the heater.

. The cylindrical casing itself includes a central co-axial ceramic type rod wound with suitable electrical heating coils. To facilitate replacement of this electrical heating coil arrangement, the upper end plate is provided with a central opening through which the energizing leads for the heating coils pass and which is of sufiicient diameter to enable the entire ceramic rod and coils themselves to be removed. Because of the three passages which the air must follow through the axial length of the cylindrical casing, and as a consequence of a suction fan causing air flow to follow these paths, relatively large heat exchange takes place between the electrical heating coils and the tube walls themselves which are heated by radiation from the coils. Thus a relatively large heating capacity for the particular size of the heater is achieved. By enclosing the suction fan completely within the suction chamber and employing a spiral type cowling for passing the outlet air from the casing, the entire heater is relatively silent in operation.

A better understanding of the invention will be had by referring to the accompanying drawing illustrating a cutaway perspective view of a preferred embodiment of the heater.

As shown in the drawing, the heater comprises basically a cylindrical casing 10 provided with an .upper end plate 11 and a lower end plate 12. As shown, the upper end plate 11 is provided with a first plurality of open ended tubes only two of which are shown in complete detail as at 13 and 14. In an actual embodiment on the invention, there may be provided twelve such tubes similar to tubes 13 and 14 secured at their upper ends to the upper end plate 11 and passing downwardly into the casing 10. Inasmuch as all of these first plurality of tubes are identical in construction, description of the two complete tubes 13 and 14 will suflice for an understanding of the invention.

As will be clear from the drawing, the tubes 13 and 14 have their open upper ends 13' and 14 secured to the upper end plate 11 for receiving air from the environment. The lower ends designated 13" and 14" terminate short of the lower end plate 12, whereby air passing downwardly through the tubes 13 and 14 will be received in the lower region of the casing 10.

The lower end plate 12 is similar in construction to the upper end plate 11 and includes a second plurality of open ended tubes such as illustrated at 15 and 16 extending upwardly into the casing 10. The lower ends of the tubes 15 and 16 are secured to the plate 12 as indicated at 15' and 16. The upper ends of these tubes are free and open into the upper region of the casing 10 as indicated at 15" and 16". As in the case of the upper end plate 11, the lower end plate 12 may be provided with as many as twelve such tubes extending upwardly into the casing 10. The lower ends of these second plurality of tubes open out from the bottom of the lower end plate 12 into a suction chamber 17.

' The cylindrical casing 10 also includes a ceramic rod .18 having electrical heating coils 19 wrapped thereabout as shown. Electrical conductors for energizing the heating coils 19 are led in through a pair of insulating sleeves 20 passing through a top cover plate 21 positioned to cover a central opening in the upper end plate 11. This cover plate 21 serves the dual function of covering the central opening in the upper end plate 11 and also supporting the ceramic rod 18 in coaxial relationshipwithin the casing 10. To this end, there is provided a retaining plate 22 adapted to be secured to the underside of the cover plate 21 as by suitable screws 23. provided with wing nuts as shown. The ceramic tube 1t; itself is in turn secured to the underside of the retaining plate 22 by an annular flange portion thereof having openings for receiving screws 25. The lower end of the ceramic rod 18 is also provided with an annular flange 26 to provide a large seating surface on the lower end plate 12. The arrangement is such that simple manual removal of the wing nuts on the various screws 23 will enable the heating rod assembly to be removed through the upper end plate 11 Without the necessity of disassembling any of the other portions of the heater.

Referring now to the lower portion of the drawing, the suction chamber 17 includes a blower in the form of a centrifugal type rotor fan 27 mounted for rotation on a shaft 28 passing through a suitable bearing support housing 29 to a driving motor 30. A switch 31 may be provided for turning the motor 30 on and off. The centrifugal type fan blower 27 is arranged to suck air into its central portion and cause the air to flow towards the peripheral edges of the suction chamber 17 wherein it passes out through a spiral type cowling 32 in communication with the rear wall of the chamber 17 through an opening 33. The cowling 32 diverges into an enlarged opening 34 through which heated air passes to the environment.

The operation of the electric heater will be evident from the above description. Normally, the energizing conductors passing through the insulated sleeves 20 for the electrical heating coils 19 are in parallel with suitable lead-in conductors (not shown) for the motor 30 and the end terminals provided with a suitable attachment means for use with any conventional electrical source of energy. Thus, upon energization of the system, the heating coils 19 will serve to heat the entire interior of the casing and by radiation also heat the metallic tubes 13, 14, and 16. Actuation of the motor switch 31 will then cause the blower rotor 27 to rotate at high speed and suck air from within the casing 10 into the central portion of the rotor and out towards the peripheral portions of the suction chamber 17 to pass through the cowling 32 and outlet 34.

The reduced pressure created in the suction chamber 17 will result in environmental air passing into the upper open ends 13 and 14 of the tubes 13 and 14. This air will pass through the interior of these tubes and become heated through heat exchange with the tube walls in turn heated by radiation from the heating coils 19. The air will then pass out the. lower free ends of these tubes as at 13" and 145' as indicated by the arrows. This partially heated air will then rise within the interior of the casing 10 and be further heated through both radiation and convection from the heating coils 19 to pass to the upper region of the interior of the casing 10. The air will then pass into the free ends 15" and 16" of the tubes 15 and 16 and thence downwardly through these tubes where again further heat exchange will take place with the walls of the tubes. The air then passes out the lower ends 15 and 16 into the suction chamber 17 and thence out the cowling 32 to the environment in the form of heated air.

As a consequence of the tube construction and easing as described, air received by the heater will traverse a path through the casing equivalent tolthree times the axial length of the casing whereby a large amount of heat transfer can take place. As a consequence, theheatingcapacity of the heater is relatively high although the overall dimensions may be of limited size. The provision of the particular type of fan blower wholly enclosed within the suction chamber 17 not only serves to provide asufiicient suction for circulating the air but further is relatively silent in operation.

The arrangement of the tubes with respect to the upper and lower end plates is such that the entire heater may be manufactured relatively inexpensively since the sets of tubes and their manner of attachment to the end plates are identical, it being only necessary to have the upper and lower end plates slightly displaced circumferentially with respect to each other to prevent interference between the tubes when assembling the structure. Finally, the provision of a central opening in the upper end plate and the simple securement of the heating rod and electrical heating coils will enable these coils to be easily removed and replaced without the necessity of disassembling other portions of the heater.

Various modifications that fall within the scope and spirit of the present invention will readily occur to those skilled in the. art. The electric air heater is, therefore, not to be thought of as limited to the particular embodiment chosen for illustrative purposes.

What is claimed is: I

1. An electric air heater comprising, in combination: a cylindrical casing having upper and lower end plates; a first plurality of separated, individual open ended tubes secured to and passing from said upper end plate down into said casing to terminate short of said lower end plate, the axes of said tubes being respectively radially spaced from the axis of said cylindrical casing and circumferentially spaced from each other; a second plurality of separated, individual open ended tubes secured to and passing from said lower end plate upwardly into said casing to terminate short of said upper end plate, the axes of said second plurality of tubes being respectively radially spaced from the axis of said cylindrical casing and circumferentially spaced from each other; a heating coil in said casing; and a suction fan in communication with the lower open ends of said second plurality of tubes whereby air is caused to flow through said first plurality of tubes to the lower interior of, said casing and thence to the upper interior of said casing to pass down said second plurality of tubes.

2. An electric air heater comprising, in combination: a cylindrical casing; upper and lower end plates secured to said casing; a first plurality of separated, individual open ended tubes secured to said upper end plate at their upper ends and depending downwardly into said casing to terminate short of said lower end plate at their lower ends whereby air may be introduced into the lower interior of said casing, the axes of said tubes being respectively radially spaced from the axis of said cylindrical casing and circumferentially spaced from each other; a second plurality of separated, individual open ended tubes secured to said lower end plate at their lower ends and projecting upwardly into said casing to terminate short of said upper end plate at their upper ends whereby air from the upper interior of said casingmay pass down said second plurality of tubes and out of the lower end plate on said casing, the axes. of said second plurality of tubes being respectively radially spaced from the axis of said cylindrical casing and circumferentially spaced from each other; electric heating coils in said cylindrical casing for heating air passing from the lower ends of said first plurality of tubes into the upper ends of said second plurality of tubes; a suction chamber below said casing in communication with the end openings in the lower ends of said secondplurality of tubes; a suction fan in said chamber; and a cowling defining an outlet duct from said chamber for passing air circulated through said tubes in said casing to the environment.

3. A heater according to claim 2, in which said upper end plate includes a central opening; a ceramic rod adapted to be passed through said opening to be positioned co-axially within said casing, said electric heating coils being wrapped about said rod and. supported thereby; v P a m a qv na d op inaan ec red 5 to the upper end of said rod; and insulated sleeves carry- References Cited in the file of this patent ing conductors passing through said cover plate means UNITED STATES PATENTS and connected to said coils for energizing the same, whereby said heating coils and rod may be readily re- 1319733 Terry 1919 moved from said cylindrical casing through said central 5 1,694,351 110mg 1928 opening 1,705,812 Flsher Mar. 19, 1929 2,119,161 Hay May 31, 1938

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