US2030820A - Electric heater - Google Patents

Description

R. F. JAMES ELECTRIC VHEATER Filed Dec'. 5. 1931 /l//I//l//l//l/ Feb. 1l, 1936.

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Patented Feb. 1.1, 1936 UNITED STATES momo HEATER Robert F. James, Detroit, Mich., assignor, by mesne assignments, to Westinghouse Lamp Company, Bloomfield, N. J., a corporation of Pennsylvania Application December 5, 1931, Serial No. 579,232

4 Claims.

The invention relates to electric heaters of that type in which the heat passes from its source to the zone of utilization in the form of radiant energy. Heaters of this type have been extensively used where it is desired to distribute a small amount of heat over a relatively large absorption area, but have not, however, proved as eiiicient for the transfer of heat to a relatively small absorption area as other constructions in which the transfer is through conduction. This may b'e'due to several causes` first, the rate of radiation from the source may be too low; second, the rate of absorption by the receiving body may be too low; third, afportion of the radiant heat may not be so directed as to fall upon the absorption body.

It is the object of the present invention to obtain a construction of heater which is capable of transferring, in the form of radiant energy, a relatively large quantity of heat to a relatively small absorption body. This is accomplished, first, by increasing the temperature of the radiant body, thereby making use of the Aphysical law that the total radiation. of any body is proportional to the fourth power -of its vabsolute temperature; second,` by directing substantially all of the radiation to fall upon the absorption body -and third, by utilizing as" an absorption body a material approximating as closely as possible the properties of a black body. 'I o increase the temperature of the radiant body it is necessaryto select a material of a` highly refractory character and to protect the same from oxidation. This requires the enclosure of the radiant body in a hermetically sealed casing or bulb. To utilize all of the radiation a portion of the rays must be redirected by a suitably fashioned reector within the hermetically sealed casing and the absorption body must constitute one wall of the casing.

The invention therefore consists in the pe-v culiar construction of a heater conforming to the conditions as above given as hereinafter set forth.

Embodiments of the invention are illustrated in the accompanying drawing, and the views thereof are as follows:

Figure 1 is a central longitudinal section through an improved heater embodying principles of the present invention.

Figure 2 is a plan view of the heater of Figure 1.

Figure 3 is a view similar to Figure 1 showing a modified construction.

'I'he drawing will now beexplained.

A casing or bulb A is formed of a material impervious to gases and capable of withstanding a relatively high temperature without loss of rigidity. A suitable material for this purpose is black quartz, although other materials may be equally well adapted. 'I'he form ofthe casing is preferably that of a paraboloid with one wall or plate B in a plane perpendicular to the major axis. The plate or wall B is made of material capable of absorbing light and heat energy, hence the assembly will approach a true black body or one that is capable of absorbing and transmitting all incident radiation falling on it. By use of the black body plate B the source of heat is transferred from the element to the plate. The flat wall B is supported by a central post C of the same material and surrounding this post is arranged the radiant body or element, such for instance as a tungsten filament D. 'I'he electrical terminal conductors E for this element are carried out through a neck portion F similar in construction to that employed in electric light bulbs, and 'terminal contacts G and H of a similar character may also be provided. Thus the heater may be placed in any suitable socket of an `electrical service.

To concentrate all of the radiation` upon the fiat wall B, the filament D is suitably positioned atthe focus of the paraboloid, and the inner surface of the paraboloid may be silvered or otherwise formed into a reecting surface. Thus when in operation practically all of the radiant energy from the filament D will fall directlyy or by reilection on the wall B which if formed of quartz 'will have to a considerable extent, the properties of .a black body. l

It is, however, necessary-to maintain a neutral atmosphere within the casing which, is accomplished by filling it with a suitable inert gas and then exhausting to the desired degree of vacuum. It is preferable, however, to allow suiiicient gas to remain within the casing so that lwhen in operation the internal gas pressure will not vary greatly lfrom that of the external atmosphere, thereby relieving the walls of the casing from objectionable stresses. The gas Within the casing also serves for transferring a portion of the heat to the Wall B by convection.

With the construction as thus far described, to utilize the heater, it is preferably mounted in a suitable stand with the socket I spring supported, as indicated at J, to permit yielding. The stand K has an annular supporting portion surrounding the casing A and normally slightly below the plane of the flat top B. 'I'hus when any article to be heated is placed on the stand it will force the casing A downward against the tension of the spring J, thereby permitting the weight of this article to be supported by the annular casing K while at the same time mainltaining the wall B in pressure contact against the bottom of the article. In this way the heat absorbed by the wall B will pass directly by conduction into the body to be heated.

Figure 3 shows a modied construction to facilitate heat exchange by convection and to add strength to thestructure. Specifically, this construction substitutes for the solid post C a tubular post C which extends completely through the casing A establishing communication between .the space within the neck F andthe space above the wall B. This construction is also preferably provided with a. series of radial grooves or utes L in the wall B which form channels connecting with the tube C' through which the heated air may pass radially outwardly. This construc-k tion also strengthens the wall B by providing the same with reinforcing ribs by which the channels L are formed. Thuswhere a 'flat bottom vessel to be heated -is placed on the stand it will force downward the wall B to the plane of the annular support K, but the channels L will still permit the heated air traveling upward through the tube C' to travel outwardly beneath the bottom of the vessel imparting heat thereto. The cool air enters the column C at the base, passes upwardly where it is heated in. the column and flows along the base of the article on the plate in the grooves or utes L.

The provision of the tubular post C in addition to providing strength for the plate B provides for air circulation between this plate and the base or bottom of the vessel for the purpose eliminating hot air pockets.

The hollow post furthermore provides means for relieving heat from the central zone of the heater. It is apparent that the center of the heater would naturally acquire appreciable heat which should be relieved in order to increase the elciency of the unit and to decrease the possibility of excessively heating the element. The provision of the hollow post provides relief for this heat in that air circulates through the post in the manner heretofore stated.

It is obvious that many modiflcations of the structure as above specifically described may be made, and that equivalents may be substituted,

without departing from the spirit and scope of the invention.

The invention is claimed as follows:

1. An electric heater`comprising a hermetically sealed bulb having a portion of'concave conguration provided with a reflecting surface on the interior wall thereof, an end wall integral with said concave portion con..tituting a heat absorption body adapted to be disposed in surface engagementwith an object to be heated, an electrically heated radiant element integral with-said bulb comprising a lament symmetrically disposed about and extending longitudinally of the normal vertical axis of said concave por# tion of said bulb and positioned substantially at the focus thereof in order to cause the majority of all radiant energy reflected by said reflecting surface to be reflected but once before being absorbed by the heat absorption end wall of said bulb and those radiations striking said reflecting surface whose angle of incidence is substantially with respect thereto to be confined to a minimum. I

2. An electric heater comprising a hermetically sealed casing provided with one wall forming a heat absorption body, a concave wall joining said absorption wall and completing the enclosure, a tubular post extending through-said casing in the axis of said vconcave wall, an electrically heated radiant element within said casing surrounding said tubular post, means for directing the radiant heat from said element against said heat absorption wall, and said heat absorption wall, having radial channels therein' connecting with said tubular post for transfer of heat through convection.

3. An electric heater comprising a hermetically sealed casing provided with a dat wall forming a heat absorption body, a concave wall joining said flat wall and completing the enclosure, a tubular post extending through said casing, said post having the interior thereof open to the atmosphere through its ends and serving as a duct for air circulation, the circulation of air through said post serving to relieve the heat in the interior of the casing and about said post.

4. An electric heater comprising a hermetically sealed casing having one wall thereof forming a heat absorption body and being flat for receiving a dish, a hollow post extending through u said casing and having one end open to the atmosphere through said one wall and the other end open to the atmosphere through the bottom of said casing for air circulation, an electrically u passes through said utes when a dish is on u said one at wall. v

ROBERT F. JAMES.

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