Abstract:
A heating element for use in a portable humidifier is provided, which is at least partially disposed within a tray of water within the humidifier. The heating element includes a mounting portion, a leg portion and a foot portion. The mounting portion is coupled to the housing and an tipper end of the leg portion, which extends vertically downward from the mounting portion. The foot portion is coupled to a lower end of the leg portion, and extends horizontally therefrom. The leg portion is elongated and separates the mounting portion and the foot portion. The foot portion is shaped such that a line from the upper surface to the lower surface must pass through a perimeter of the heating element when viewed from above. A bottom surface of the foot portion is curved or slanted upward from a nadir to the perimeter of the heating element.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on and claims priority to U.S. Provisional Patent Application Ser. No. 60/147,984, which was filed on Aug. 9, 1999, the disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The field of the invention relates to humidifiers for generating steam, and more particularly relates to heating elements used in such humidifiers. 
     2. Brief Description of the Related Art 
     Humidifiers are commonly used in residential and commercial settings to increase the level of humidity in the air for various purposes, such as health, safety and reliability. For instance, it has been found that increased humidity reduces the amount of recuperation time required for upper respiratory infections. In addition, increased humidity reduces the amount of static charge which can build up on electrostatic sensitive devices, such as semiconductors and integrated circuits. 
     After operating a humidifier for a period of time, the components of the humidifier must typically be cleaned in order to control bacterial growth and remove mineral deposits. Mineral deposits caused by excess minerals in solution, such as calcium in the water used to generate steam is a problem, particularly when the deposits form on a heating element used to bring the water to a boiling point. 
     FIGS. 1A and B show a top and side view, respectively, of a heating element of the prior art. This conventional heating element includes a mounting portion  15  and a ring  11  having an open interior section  13 . The heating element is suspended in water within a boiling chamber of the humidifier. It has been found that the inner circumference of the ring  11  is particularly susceptible to the deposition of minerals, which in some cases causes a so-called “arch effect” wherein the deposited minerals create arches across the open interior section  13  of the ring  11 . These arches are particularly difficult to remove by the user, and removal often mars the external finish of the heating element such that additional minerals are deposited more quickly and are even more difficult to remove. 
     Some of the conventional heating elements include a flattened bottom surface, which becomes a collection point for small air bubbles that are created along a lower surface of the boiling chamber and float upwards as the water is boiled. As the smaller bubbles combine to form larger bubbles under the flattened bottom surface of the heating element, these larger bubbles eventually escape and float to the top of the boiling chamber creating an undesirable noise to the user upon bursting at the top of the boiling chamber. In addition, as the larger air bubbles burst, water droplets are projected onto additional surfaces surrounding the boiling chamber. These droplets leave additional mineral deposits or scaling upon evaporating. 
     Still other heating elements have a horizontally disposed lower portion that transfers excessive heat from the heating element to the remaining components of the humidifier. Since in most cases much of the remaining components are either plastic or not suitable for operating at high temperatures, this creates an undesirable and often dangerous situation. In addition, the proximity between the horizontally disposed portion and the mounting portion of the heating element provides restricted cavities which are prone to mineral deposits. 
     Therefore, it would be advantageous if a heating element could reduce the amount of mineral deposits on and around the heating element and/or reduce the noise created by air bubbles which collect underneath the heating element. 
     SUMMARY OF THE INVENTION 
     A humidifying apparatus formed in accordance with the present invention includes a housing, a tray for holding water and a heating element. The heating element is at least partially disposed within the tray and includes a mounting portion, a leg portion and a foot portion. The mounting portion is coupled to the housing and an upper end of the leg portion of the heating element. The leg portion extends substantially vertically downward from the mounting portion into the tray. The foot portion is coupled to a lower end of the leg portion and extends substantially horizontally therefrom. 
     The leg portion is elongated and separates the mounting portion and the foot portion, which reduces mineral deposition on the heating element. The foot portion is shaped such that a line from the upper surface to the lower surface must pass across a perimeter of the heating element when viewed from above. The bottom surface of the foot portion is preferably convex, partially spherical or curved upward from a nadir to the perimeter of the heating element. 
     The humidifying apparatus formed in accordance with the present invention can also include a gasket disposed around a cylindrical portion of the heating element located above a flange on the heating element. The gasket provides a seal between the heating element and the housing when the heating element is affixed thereto. The gasket includes an upper annular ring, a central annular ring, a lower annular ring and a side cross-sectional profile. The central annular ring is coupled to the upper annular ring and has a perimeter which is less than the perimeter of the upper annular ring. The lower annular ring is coupled to the central annular ring and has a perimeter which is about the same as the perimeter of the upper annular ring. Each of the annular rings have an inner circumference which is substantially the same, and defines a vertical conduit of substantially constant diameter extending through the gasket. 
     The heating element is disposed within the conduit of the gasket, and the annular rings are coupled such that the perimeter of the annular rings are substantially concentric when viewed from above. A side cross-sectional profile of the gasket substantially conforms to a side cross-sectional profile of the housing surrounding the heating element. A heating element having the features described above is also provided in accordance with the present invention. 
     A preferred form of the heating element and a humidifier including the heating element of the present invention, as well as other embodiments, objects, features and advantages of this invention will be apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A and 1B are top and side views, respectively, of a ring-shaped heating element of the prior art; 
     FIG. 2 is a cross-sectional view of a humidifier employing a heating element formed in accordance with the present invention; 
     FIG. 3 is an enlarged side cross-sectional view of a bottom portion of the humidifier shown in FIG. 2; 
     FIG. 4A is a top isometric view of the heating element formed in accordance with the present invention; 
     FIG. 4B is a rear view of the heating element formed in accordance with the present invention; 
     FIG. 4C is a side view of the heating element formed in accordance with the present invention; 
     FIG. 4D is a rear view of an alternative embodiment of the heating element formed in accordance with the present invention; 
     FIG. 4E is a rear view of an alternative embodiment of the heating element formed in accordance with the present invention; 
     FIG. 4F is a side view of an alternative embodiment of the heating element formed in accordance with the present invention; 
     FIG. 4G is a side view of an alternative embodiment of the heating element formed in accordance with the present invention; 
     FIG. 5A is a top plan view of the heating element formed in accordance with the present invention showing a cross-section line AA; and 
     FIG. 5B is a cross-sectional view of the heating element shown in FIG. 5A taken along the cross-section line AA. 
     FIGS. 6A,  6 B and  6 C are bottom, top and side views of a gasket which provides a seal between the heating element and remaining components of the humidifier. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 2 shows a portable humidifier  10  for use in the home, the office, or other suitable location. The humidifier includes a water tank  12 , a tray  14  or other suitable receptacle for receiving water from the tank, and a heating element  16  positioned within the tray. The water tank  12  is preferably removable to facilitate refilling and/or cleaning. A handle  18  is accordingly provided near the top of the tank, and may be integral with the tank. A tank cap  20  is mounted to the tank to enable filling of the contents thereof. Therefore, the tank cap  20  is preferably removable. While the tank  12  is preferably cleanable and reusable, a disposable tank could alternatively be employed. 
     A conventional tank valve  22  or other suitable means are provided for releasing water from the tank in a controlled manner. Tank valves are well known to the art, and are employed in commercially available humidifiers of various types. While more sophisticated water delivery means, such as a pump, could be employed, tank valves are economic and reliable for use in the consumer market. 
     The tray  14  is positioned within a base  24 . The base includes bottom and side walls which together define an enclosure for the tray  14  and other elements of the humidifier. As shown in greater detail in FIG. 3, an elongate, tortuous channel  26  is provided within the base  24 . One end  26 A of the channel is positioned beneath the taik valve  22 . The other end  26 B of the channel is in fluid communication with the tray  14 ., which has an opening in a side wall thereof for admitting water into the tray from the channel. The use of the tortuous channel  26  is preferred in order to substantially confine the hot water within the tray  14 . Backflow through the tortuous path is very limited. The tray  14  and the channel  26  are both preferably removable from the base  24  to facilitate cleaning. 
     Referring again to FIG. 3, a housing  30  is seated on the tray  14 . The housing  30  provides support for the heating element  16  which is preferably secured to the bottom of the housing  30  by screwing the heating element  16  into an opening in the bottom of the housing  30 . As shown in FIG. 3, a gasket  32  is inserted between the heating element  16  and the housing  30 , which provides for a water-tight seal between a boiling chamber  34  formed between the bottom of the housing  30  and the tray  14 . In addition, glue  28 , a sealant, or the like is preferably distributed between the gasket  32  and the housing  30 , and between the gasket  32  and the heating element  16  to further ensure that water will not enter the housing  30  from the boiling chamber  34  and that mineral deposits will not collect between the heating element  16  and the gasket  32 . 
     As shown in FIG. 2, an evaporator  36  is attached to an interior surface of the housing  30  near the top of the housing  30 . The evaporator  36  functions to guide the steam which results from water being boiled in the boiling chamber  34  through the housing  30  and out an outlet  38  at the top of the housing  30 . The outlet  38  is covered by an outlet grill  40 , which can preferably be used to both direct the steam as well as protect users from the interior of the housing  30 . Preferably, the outlet grill  40  is removable, which allows an optional medicine cup  42  to be seated over the outlet  38  and under the outlet grill  40 . The medicine cup  42  holds medication, and when the steam is passed over and around the medicine cup  42 , the medicine therein is heated, evaporated and joins with the steam as it escapes through the outlet  38 . 
     The heating element  16  has two electrodes  44  which are an electrical connection with a positive line and a return line of a power cord  46 . When the power cord  46  is plugged in, current passes between the electrodes  44  which creates heat in the heating element  16 . The heating element  16  is preferably a thermal and electrical conductor, such as a metal. If the water in the boiling chamber  34  is maintained at a minimum water level  48 , the heat created by the heating element  16  is transferred to the water. When the water reaches a boiling point, the resulting steam rises upward and passes through a conduit  28  in the bottom of the housing  30  and is guided by the evaporator  36  to the outlet  38 . An optional thermo-fuse  50  is electrically connected in series between one of the electrodes  44  and one of the lines of the power cord  46 . The thermo-fuse  50  disconnects or open-circuits the corresponding electrode  44  from the power cord  46  when a signal from a thermostat  52  indicates that the temperature of the heating element  16  has exceeded a maximum pre-determined threshold considered to be safe. The thermostat  52  is seated in the heating element  16  and continuously monitors the temperature thereof. The thermo-fuse  50  is positioned above and is removably affixed to the heating element  16  by a clip  54 . 
     An optional humidistat  56  is affixed to the top of the interior surface of the housing  30 , and extends through an opening therein. The humidistat  56  monitors the level of moisture in the air surrounding the humidifier  10  and interrupts the power supplied to the electrodes  44  from the power cord  46  upon reaching a desired level of humidity preferably set by the user. The user can modify the desired level of humidity by adjusting a knob  58  located on top of the humidistat  56 . Rubber feet  61  located on the bottom of the humidifier  10  function to provide a stable base for the humidifier  10  on a variety of surfaces. 
     The humidifier may be equipped with a microprocessor or other electronics for controlling its operation. The options of manual and automatic operation are preferably, though not necessarily, provided. Displays showing power on, high and/or low modes or operation, and humidity are also preferred. Use of the humidistat  56  allows automatic operation of the humidifier. In the automatic mode, the user would set the desired humidity. If the room humidity is less than the desired humidity level, the heating element  16  would be powered until the humidity reaches the set level. Whether used manually or automatically, power to the heating element  16  is shut off when the water tank  12  is below a preselected level or empty. Additionally or alternatively, a water gauge or separate float in the tank  12  and/or tray  14  may be provided in conjunction with a switch for the purpose of shutting off power to the heating element  16  under low water level conditions. Such float/switch assemblies have been used in prior art warm mist humidifiers. 
     A top isometric view, a rear view and a side view of the heating element  16  are shown in FIGS. 4A,  4 B and  4 C, respectively. The heating element  16  includes an upper threaded portion  60  which is screwed into the bottom of the housing  30 ; an upper cylindrical portion  62  around which the gasket  32  is positioned; a flange  64  against which the gasket  32  is seated; a vertical portion or leg  66 ; and a horizontal portion or foot  68 . The heating element  16  is preferably manufactured from an integral piece of solid metal such as aluminum. The upper threaded portion  60  extends vertically upward from and is coupled to the upper cylindrical portion  62 , which extends vertically upward from and is coupled to the flange  64 . The upper cylindrical portion  62  includes a shoulder  63 , which protrudes radially beyond the upper threaded portion  66 . The leg  66  extends downward from and is coupled to the flange  64  on an opposing side of the flange  64  from the upper cylindrical portion  62 . The foot  68  extends horizontally from and is coupled to a lower portion of the leg  66 . 
     The leg  66  is elongated, which represents an improvement over heating elements of the prior art since such a leg  66  enables greater separation between the flange  64  and the foot  68 . This greater separation reduces the amount of mineral deposits on and the flange  64  and the foot  68 . Such separation also positions the mass of the foot  68  at a greater distance from the bottom of the housing  30  such that less heat is transferred from the foot  68  to the remaining elements of the humidifier including the gasket  32 . In the preferred embodiment, a dimension A, shown in FIG. 4B from a bottom surface  70  of the foot  68  to a top of the flange  64 , is preferably about 2.25 inches, and a dimension B, from a top of the threaded portion  60  to the bottom  70  of the foot  68 , is preferably about 3.00 inches. Also, in the preferred embodiment, a dimension C from an outer circumference of the flange  64  to a front or toe of the foot  68  shown in FIG. 4C, is preferably about 2.95 inches, and a dimension D, being a width of the foot  68  as shown in FIG. 4B, is preferably about 2.10 inches. A dimension E, being a diameter of the upper threaded portion  60  shown in FIG. 4B, is preferably about 1.50 inches. It is anticipated that the dimensions provided above preferably remain in substantially the same proportion to each other if the size of the heating element  16  is changed. 
     The foot  68  represents an improvement over heating elements in the prior art in that the foot  68  provides a continuous surface on all sides without an aperture which passes from a top surface to the bottom surface of the heating element  16 . Many of the conventional heating elements, such as those that are ring-shaped, have an inner circumference which is prone to mineral deposits that are extremely difficult to remove during cleaning. In addition, the mineral deposits within the ring often create an “arch effect” wherein the minerals bridge across the ring at numerous locations. Removal of these deposits typically results in permanent damage to the surface of the heating element  16  that renders the heating element even more prone to further buildup of minerals. 
     A bottom surface  70  of the foot  68  is curved, which also represents an improvement over heating elements in the prior art. It was found that a foot having a flat bottom surface provided an area for the collection of small air bubbles, which were generated along the lower surface of the boiling chamber  34  as the water boiled. The small air bubbles combined to form larger air bubbles, which escaped around the outer perimeter of the foot and created an undesirable popping noise upon reaching the top of the boiling chamber  34 . The curvature of the bottom surface  70  of the foot  68  prevents the collection of these air bubbles. Thus, the smaller air bubbles reach the top of the boiling chamber  34  in substantially the same size, and do not create an unacceptable amount of noise upon bursting. 
     In the preferred embodiment of the invention, the bottom surface  70  is substantially convex between a front (or toe) and a rear (or heel) portion of the foot  68  as shown in FIG.  4 C and/or substantially convex between a right and a left side of the foot  68  when viewed from the rear of the heating element as shown in FIG.  4 B. Alternatively, the bottom surface  70  can be slanted substantially upward or downward from a left side to a right side of the foot  68  as shown in FIGS. 4D and 4E, respectively. In addition, the bottom surface  70  can be slanted substantially upward or downward from the front to the rear of the foot  68  as shown in FIGS. 4F and 4G, respectively. Substantially any shape of the bottom surface  70 , which does not cause the air bubbles to collect under the heating element  16 , or which promotes the rolling off of air bubbles is considered to be within the scope of the present invention. 
     FIG. 5A shows a top plan view of the heating element  16  through which a cross-section line AA has been drawn. A cross-sectional view of the heating element  16  is shown in FIG. 5B taken along the cross-section line AA. The heating element  16  is preferably manufactured from a substantially solid piece of metal which is resistant to corrosion, such as aluminum. 
     As shown in FIGS. 6A,  6 B and  6 C, the gasket  32  includes an upper annular ring  72 , a central annular ring  74  and a lower annular ring  76  having a circumferential lip  78 . As shown in FIG. 3, the upper annular ring  72  is positioned between a sealing compression washer  80  located at the bottom of the housing  30 , and a circumferential shoulder  82  integral with the bottom of the housing  30  and protruding from the housing  30  located under the sealing compression washer  80 . The shoulder  63  of the upper cylindrical portion  62  comes into contact with or bottoms out against the sealing compression washer  80 , and thus limits the compression of the gasket  32  to a constant amount. Stated differently, the action of the solid shoulder  63  coming into contact with the solid sealing compression washer  80  provides a constant compression of the gasket  32 . The constant compression of the gasket  32  ensures that the gasket  32  will not be overly compressed, which would eventually decrease the resiliency of the gasket  32 , and thus the ability of the gasket  32  to create a water-tight seal. The constant compression of the gasket  32  also ensures that the gasket  32  will be compressed enough to maintain the water-tight seal between the heating element and the bottom of the housing  30 . 
     The upper, central and lower annular rings  72 ,  74 ,  76  are preferably manufactured as an integral unit, and follow the contour of the shoulder  82  creating a water-tight seal between the flange  64  of the heating element  16  and the bottom of the housing  30 . The heating element  16  is placed through a central conduit  84  in the gasket  32  and is screwed into the bottom of the housing  30 . The action of the heating element  16  being screwed into the housing  30  creates a force which compresses the lower annular ring  76  of the gasket  32  between the flange  64  of the heating element  16  and the shoulder  82 . This force also compresses the circumferential lip  78  of the gasket  32  between the flange  64  and a vertically downward protruding portion  86  of the shoulder  82  as shown in FIG.  3 . 
     While there have been described what are presently believed to be the preferred embodiments of the invention, those skilled in the art will realize that various changes and modifications may be made to the invention without departing from the spirit of the invention.