Abstract:
A portable heater includes a radiator having multiple tubular units and an electric heating element in the radiator for heating the diathermal fluid. A fan positioned above the sealed radiator directs air on the upper portions of the tubular units to enhance convection of the fluid.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to portable heating devices.  
           [0003]    2. Brief Description of the Prior Art  
           [0004]    As home heating oil and natural gas prices fluctuate upward, there is an increasing need for efficient, inexpensive portable heaters. Portable heaters provide flexibility to enhance the comfort of specific rooms within a centrally-heated home, without incurring the cost of employing the central furnace to heat the entire home, including unoccupied rooms.  
           [0005]    Portable heaters are well known in the art. One well-known type of portable heater is the portable radiator-type heater. Examples of portable radiator-type heaters are disclosed in U.S. Pat. Nos. 4,493,974, 4,870,253, 5,966,498, and D 341,654.  
           [0006]    Portable radiator heaters typically include a set of flattened, tubular radiator units filled with a diathermal fluid such as mineral oil. The radiator units are joined proximate their tops by an upper header and proximate their bottoms by a lower headers. The headers permit the thermal fluid to flow between radiator units. An electric heating element is provided in the lower header. The heating element serves to warm the diathermal fluid so that the fluid circulates through the radiator units by thermal convection, to warm the air adjacent to the exterior surfaces of the tubular radiator units.  
           [0007]    U.S. Pat. No. 4,879,253 discloses a portable radiator-type heater equipped with an air-circulating fan under the radiator units. The fan optionally includes resistive heating elements for preheating air expelled by the fan. The orientation of the exhaust of the fan can be varied from a generally vertical position in which the fan exhaust is directed upward through the radiator units, to a generally horizontal position in which the exhaust is directed outward away from the radiator units.  
           [0008]    The greater the number of radiator units, the greater their collective surface area, the greater the rate of heat transfer from the radiator unit to the surrounding air. Thus, it is desirable to employ as many radiator units as practical. On the other hand, each additional radiator unit adds to the cost of manufacturing the portable heater. Thus, there is a need for a portable radiator-type heater that employs a reduced number of radiator units, yet provides effective heat transfer from the radiator units to the room air.  
         SUMMARY OF THE INVENTION  
         [0009]    The present invention provides a portable heater comprising a sealed radiator containing a diathermal fluid. The radiator includes a plurality of tubular radiator units. Each of the tubular radiator units has respective upper portions and respective lower portions. The portable heater further includes at least one electric heating element positioned within the sealed radiator, as well as a fan positioned above the sealed radiator for directing air on the upper portions of the tubular radiator units. The fan is effective to cool the upper portions of the tubular units. This enhances thermal convection of the diathermal fluid within the tubular radiator units.  
           [0010]    The present invention thus advantageously reduces the surface area required for transferring heat from the electric heating element via the diathermal fluid to the room air. Thus, at least one fewer tubular radiator unit is required, with a concomitant reduction in the cost of manufacturing the portable heater. In addition, the radiator can be maintained at a cooler temperature. It has been calculated that for every 10 degrees Celsius that the operating temperature can be reduced, the power consumption per tubular radiator unit can be concomitantly reduced by 250 watts. Thus, the power consumption of the portable heater can be advantageously reduced. Further, the present invention provides more rapid heat distribution from the portable heater to the room.  
           [0011]    Preferably, the heater includes a centrifugal fan driven by an electric motor. It is also preferred that a quiet fan be employed. To that end, it is preferred that the electric motor operates at low rpm, preferably at less than 2500 rpm, and more preferably at less than 1000 rpm. Preferably, the portable heater includes a cover enclosing the fan. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0012]    [0012]FIG. 1 is a perspective view of a portable heater according to the present invention.  
         [0013]    [0013]FIG. 2 is a side elevational view of the heater of FIG. 1.  
         [0014]    [0014]FIG. 3 is a top plan view of the heater of FIG. 1.  
         [0015]    [0015]FIG. 4 is a front elevational view of the heater of FIG. 1.  
         [0016]    [0016]FIG. 5 is an exploded perspective view of the heater of FIG. 1, showing assembly of the heater and the major components thereof. 
     
    
     DETAILED DESCRIPTION  
       [0017]    Referring now to the figure in which like reference numerals represent like element in each of the several views, there is shown in FIG. 1 a portable heater  10  of the present invention. As can be seen in the exploded view of FIG. 5, the portable heater  10  includes a central radiator  20  formed from a plurality of generally flat, tubular radiator units  22  formed from a suitable material such as sheet metal.  
         [0018]    Proximate the top of each of the radiator units  22  and symmetrically extending outwardly of each side thereof there are formed a pair of upper header elements  23 , each in the form of a truncated cone. Similarly, proximate the bottom of each of the radiator units  10  and symmetrically extending outwardly from each side thereof there are formed a pair of lower header elements  25 , each in the form of a truncated cone.  
         [0019]    When the radiator  20  is assembled, each of the upper header elements  23  are collinear, thus forming an upper header section  24 , and providing a flow path for fluid in between the interiors of the tubular radiator units  22 , the exterior-facing upper header elements of the first and last radiator units  22  being sealed. Similarly, when the radiator  20  is assembled, each of the lower header elements  25  are collinear, thus forming a lower header section  26 , and providing a flow path for fluid in between the interiors of the tubular radiator units  22 . The portion of the radiator  20  proximate the top of the radiator  20  can be referred to as the upper portion  28  and the portion of the radiator  20  proximate the bottom of the radiator  20  can be referred to as the lower portion  30 .  
         [0020]    An electrical resistance-heating element  40  is positioned inside the radiator  20  within the lower header section  26 . The radiator  20  is filled with a diathermal fluid such as an inert oil, for example, mineral oil, for transferring heat from the electrical resistance heating element  40  to the exterior surfaces of the radiator units  22 . The interior of the radiator  20  is sealed against leakage of the diathermal fluid.  
         [0021]    A wiring harness  32  connects the heating element  40  with a source of external electrical power via a power cord  34  and with various electric control devices. A thermostat  42  controls operation of the electrical resistance-heating element  40 . A thermal fuse  44  is also provided positioned proximate the radiator  20  as a safety device against overheating of the radiator  20 . In addition, a tip-over switch  46  is provided to cut off current to the heating element  40  should the portable heater  10  be accidentally tipped over. A temperature limiter  48  is also provided as a safety measure. A power switch  50  is provided to control overall operation of the portable heater  10 .  
         [0022]    A fan  52  is provided proximate the top of the radiator  20 . The fan  52  includes a generally cylindrical housing  56  with a downwardly directly outlet for blowing air over the upper portion  28  of the radiator  20 . The fan also includes a generally cylindrical “squirrel cage”-type fan blade assembly  54 , supported at one end by a suitable bearing  62 . The fan  52  includes a motor  62  that drives the fan blade assembly  54  through a suitable drive  58 . A baffle plate  64  is provided in between the fan housing  56  and the fan motor  62 . The fan motor  62  is mounted above an insulation plate  66  for thermally insulating the fan motor  62  from the radiator  20 . Preferably, the fan motor  62  is of a low rpm type, preferably having an operating speed of less than 2500 rpm and more preferably less than 1500 rpm, so that the fan  52  operates quietly.  
         [0023]    The portable heater  10  also includes a front cover  68  (FIG. 4) and a rear cover  74  (best seen in FIG. 5) each formed from a suitable material, such as by molding a suitable heat-resistant thermoplastic material. The front cover  68  is adapted to receive a control panel  70  proximate the top of the front cover  68 , the control panel  70  having a plurality of apertures formed therein for receiving knobs  92  for controlling the power switch  50  and the thermostat  42 , as well a pilot lamp  94  for indicating operation of the portable heater  10 . The control panel  70  also includes a molded-in handle  72 , and the rear cover  74  includes an aperture for receiving a corresponding handle  76 , to permit the portable heater  10  to be moved. The front panel  68  is also adapted to receive a cord wrap plate  96  proximate the bottom of the front panel for wrapping the electrical power cord  34 . A pair of wheel units  96  fitted with suitable wheels or castors is provided under the radiator  20  to facilitate moving the portable heater  10 . In addition, a generally “U”-shaped top cover  80  (FIGS. 2 and 3) is provided for covering the upper portion  28  of the radiator  28  and enclosing the fan  52 . The top cover  80  is provided with a plurality of louvers  82  adapted to cool the top cover  80  and to permit air to drawn into the fan enclosure. The front cover  68  and the rear cover  74  are also provided with a plurality of louvers  78  to permit air circulation and cooling.  
         [0024]    It will be recognized by those skilled in the art that changes may be made in the above described embodiment of the invention without departing from the broad inventive concepts thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but is intended to cover all modifications, which are within the scope and spirit of the invention.