Patent Application
20070212036
This invention relates to a heating element for use in a fluid heater. More specifically, this invention relates to a non-metallic heating element that is not susceptible to corrosion. This heating element may be inside the housing of a fluid heater and/or constitute the pipes that input fluid to and output fluid from the heater.
In the prior art, the storage-type fluid heater is comprised of a metallic or the less common plastic container. This describes the vast majority of vessels that are used for the purpose of heating a fluid. The source energy to raise the temperature of the fluid, within the container, to its desired predetermined level, the temperature setpoint, may be electric, combustible petroleum, or combustible gas. Regardless of the energy source the prior art has shown that metal(s) have been used to contain and apply heat to the fluid. This use of metal in constant contact with water has led to negative results. Specifically, the metallic heating elements are subject to failure due to corrosion. This corrosion is facilitated by the mineral build up within the base of the metallic storage tank as well as direct adherence to the internal metallic heating elements. The mineral build up is caused by the continuous heating of a fluid, such as water, under relatively low pressures and then having that hot fluid remain stagnant. This internal state of the fluid heating tank allows minerals to precipitate out of the fluid, to build up on the base of the tank, and to form onto the protruding internal electrical heating elements.
Fluid heaters that are heated by natural gas typically comprise a vertical, cylindrical tank having a centrally located gas flue passing vertically through the tank. The radial flame gas burner is located below the bottom of the metallic tank. This burner heats the water in the tank. Additionally heat is transferred to water in the tank from hot combustion gasses produced by the burner passing upward through the gas flue. Flue baffles and similar apparatuses are commonly employed in the gas flue for improving heat transfer from the combustion gases to the water in the tank. Combustion gases are exhausted from the gas flue near the top of the tank.
Fluid heaters that are electrically heated generally comprise a vertical cylindrical metallic or in this case a non-metallic tank having one or more electrical resistance heating elements mounted at intermediate elevations in the water tank. Heat is exchanged between the metallic heating elements and water in the tank.
Prior art attempts to resist corrosion included the placement of an anode within the tank. The anode is a metal rod usually made of magnesium or aluminum. Electrolysis eats away the metal anode instead of the other metal (heating elements or walls) of the tank. The benefit of this is limited, however, because once the anode is exhausted, the tank itself begins to corrode. Another deficiency found in prior art electric type fluid heaters is a reduction in heating efficiency due to the mineral content of the water. When water is heated under pressure, minerals will precipitate out of the water and adhere to the electric heating elements thus reducing their efficiency and eventually promoting their failure. Those deposits will also form into larger crystals and remain on the bottom of the tank; this is particularly troublesome for flame producing heaters, since the heat must transfer through large deposit layers.
The average life of a residential storage type water heater is about 13 years. The corrosion of the heating elements and tank of the heater can decrease the operating time and negatively impact performance during its functioning life.
The difficulties and limitations suggested in the preceding are not intended to be exhaustive, but rather are among many which demonstrate that although significant attention has been devoted to decreasing the amount of corrosion within fluid heaters and their resulting decreased function, the prior attempts do not satisfy the need for long term stability of the fluid heater.
It is therefore a general object of the invention to provide a fluid heating apparatus that will meet the objectives and minimize limitations of the type previously described.
It is a specific object of the invention to provide a heating element for use in a fluid heating system that is not susceptible to corrosion.
It is another specific object to provide a fluid heating system having pipes capable of heating incoming and outgoing fluid and also not being susceptible to corrosion.
In order to provide a solution to the deficiencies of the prior art, a preferred embodiment of the present invention provides a non-metallic heating element for use in a fluid heater. The heating element comprises a carbon black body that fully encases a set of one or more thin, flat metal strips. When a voltage is applied to the flat metal strips, a current is passed through the carbon black to the next strip, the resistance of the carbon black body produces heat for changing the fluid temperature.
Objects and advantages of the present invention will become apparent from the following detailed description of embodiments taken in conjunction with the accompanying drawings, wherein:
a is a schematic view of the heating element formed into a pipe.
b is a cross sectional view of a portion of the pipe to show detail.
Carbon black is a generic term for the family of colloidal carbons. More specifically, carbon black is made by the partial combustion and/or thermal cracking of natural gas, oil, or another hydrocarbon. The incorporation of carbon black into polymers and the process for this incorporation is known in the art. Specifically, conductive fillers have been incorporated into polymers to make them electrically conductive with carbon black being the most common. In a preferred embodiment, the resistivity to alternating current is critical to generating heat by creating an electrical field internal to the surrounding carbon black material.
The heating element of a preferred embodiment ideally contains a centrally located pattern of direct conductors. The direct conductors are flat copper ribbon spaced and centered within the heating panel. The copper is a useful transmitting medium for an alternating current regardless of its frequency.
The copper tape is introduced to the carbon black body of the heating element via insert molding. Insert molding is an injection molding process whereby the carbon black polymer is injected into a cavity and around an insert piece placed into the same cavity just prior to molding. The result is a single piece with the insert encapsulated by the carbon black polymer. The insert of a preferred embodiment is a length of twenty (20) gauge copper tape (0.2500 inch width).
The insert molding technique was initially developed to place threaded inserts in molded parts and to encapsulate the wire-plug connection on electrical cords. Today insert molding is used quite extensively in the manufacture of medical devices. Typical applications include insert-molded encapsulated electrical components and threaded fasteners. Generally, there are few design limitations or restrictions on material combinations.
Another reason for the use of insert molding within a preferred embodiment is due to the type of bonding that will occur between the carbon black polymer and the copper tape conductor. There are two types of bonding that occur in insert molding: molecular and mechanical. Mechanical bonding is the only feasible option due to the dissimilar characteristics of the carbon black polymer and the copper tape electric conductor. The mechanical bonding of insert mold can take place in two forms. The first is the shrinking of the encapsulating carbon black polymer around the copper tape as the resin cools. In the second (the one implemented in the preferred embodiment), irregularities will be placed upon the surface of the copper tape to create a rough surface prior to any molding. This is done to facilitate the mechanical bond of the copper tape to the surrounding carbon black polymer. Although shrinkage of the carbon black polymer will occur, it alone is generally not sufficient to produce adequate physical strength or leak resistance of the copper tape conductor. In general, when insert molding dissimilar materials, the insert should offer some means of mechanical retention such as a rough surface.
The concept of the heating element is extended to the input and output fluid pipes servicing the fluid heater. These pipes are constructed in the same manner as the solid heating element, but they are molded to have a hollow center for the passage of water or other fluid. By applying current to the copper strips encased in the body of the pipe, the water can be heated as it moves in or out of the storage tank to increase efficiency.
The non-metallic heating elements described are not susceptible to corrosion as are the metal parts of prior art fluid heaters. As such, this will lead to longer life and better performance of the final product.
Referring now to
Turning to
The carbon black polymer of the heating element 208 is insert molded around copper conductors 216, 217, and 218 as described above. The preferred copper tape is of twenty (20) gauge copper having a width of 6.35 mm (0.25″). The tapes are generally spaced approximately 5.1 cm (2″) for optimal performance. This spacing may vary depending on the width of the tape and current that is used. Before injection molding, at least one surface of the copper tape is distressed. Two fourteen (14) gauge copper conductor wires 210 and 211 are attached to the copper tape by soldering, mechanical connection, or other suitable connection type. This connection is made at the intersection of the copper wire and the copper tapes shown at points 219, 220, and 221. The copper tapes 216, 217, and 218 are a set of three that are arranged in a pattern that repeats throughout the length of the heating element. The single copper tape 217 is attached to the line side of the input current. This tape is bordered on each side by tapes 216 and 218 which are both connected to the load side of the input current. Current is naturally going to flow from the line to the load side, so current will tend to flow from strip 217, through the carbon black material, to both strips 216 and 218. The resistance of the carbon black material to the current is what generates heat and allows the element to operate. This three tape configuration is repeated with the groups of tape labeled 223 and 224. This three tape configuration is referred to as a heat generation array. Connecting wires 210 and 211 are insulated at points 212 and 213 where they exit from the carbon black heating element wall. They are also insulated at points 214 and 215 where they pass through the wall.
The mode control unit 302 has an alphanumeric digital display 403 that is visible to the user. The alphanumeric display will show the operating mode as well as allow the user to view and change the setpoint temperature. The mode control unit control panel 302 comprises three momentary on pushbutton switches. The first pushbutton switch 412 toggles between normal operating mode and setpoint temperature setting mode. Pushbutton switch 413 is the positive temperature increment switch, when pressed, it will cause the setpoint temperature to rise by one degree. Pushbutton switch 414 is the temperature decrement switch which will lower the setpoint temperature by one degree when pressed. After the user has selected the desired setpoint temperature, the mode select pushbutton 412 is pressed to return the mode control unit 302 to the normal operating mode. The mode control panel 302 communicates to the central processing unit (CPU) 407, a dedicated application microprocessor. This CPU communicates with the mode control display 403 and generates the alphanumeric characters. The CPU 407 stores its variable instructions within a battery backed up memory chip 406 whose purpose is to ensure that the setpoint temperature is not lost if the main power source is lost due to a power outage. The CPU 407 receives the current fluid temperature from two locations, thermistor 409 in the outflow pipe and thermistor 410 in the storage tank. The thermistors transmit the current analog fluid temperature to the analog to digital converter 411. The converter 411 converts the analog temperature value to a digital value that can be used by CPU 407.
Normal operating mode of a preferred embodiment occurs during times of active user demand for heated fluid, typically water. The CPU 407 determines normal operations when the tank fluid temperature is below the user defined setpoint temperature and less than 30 minutes have elapsed since closure of the main tank switch 415 (this switch causes heating of the tank fluid). This short time period between closures of the switch indicates that there is a high demand for hot water from the storage tank. When this condition is met, switch 415 is closed and alternating current flows to the carbon black heating element via wires 418 and 419. If the tank utilizes heated pipes, CPU 407 will simultaneously close switch 417 sending alternating current to the heated inflow pipe via wires 422 and 423.
Another mode is a low temperature mode and it occurs if the fluid in the storage tank has not reduced temperature for a period of thirty minutes since the last closure of switch 415. In this instance, CPU 407 will allow the temperature of the fluid in the tank to decrease by a predetermined amount. In a preferred embodiment, this predetermined amount is forty degrees lower than the setpoint temperature. This lower temperature state will continue until the introduction of fluids colder than the predetermined low temperature. When these fluids are introduced, the CPU 407 signals the switch 415 to close, sending alternating current to the tank internal heating element. At the same time, if heated pipes are in use, CPU 407 will close switches 416 and 417 to send alternating current to both the inflow and outflow pipes via wires 420, 421, 422, and 423. In this situation, the CPU will monitor the temperature of the fluid in the outflow pipe and maintain this fluid at the user setpoint. In doing this, the end user will not experience colder water due to the tank being in low temperature mode. CPU 407 does this by turning on and off the switch 416 that controls alternating current being sent to the outflow pipe. This is possible due to the relatively small internal diameter of the outflow pipe and the limited rise in temperature required given that the fluid has been heated above its lowest temperature before entering to the outflow pipe. The CPU 407 will only stop the flow of alternating current to the outflow pipe and tank heating element when the tank fluid temperature reaches the user defined setpoint temperature thus ending the low temperature cycle and beginning a new thirty minute time period.
It is advantageous in some implementations to heat fluid as it is input into the fluid heater and as it exits the tank. In order to accomplish this, a pipe can be constructed using carbon black and inserting copper tape as described in relation to
Thermistor 616 is inserted into outflow pipe 618 via wall sleeve 615. Wire lead 617 connects thermistor 616 to the mode control unit 302 and CPU 607 via the digital to analog converter 411.
In describing the invention, reference has been made to preferred embodiments and illustrative advantages of the invention. The subject invention, however, is not limited to residential water heaters. Those skilled in the art and familiar with the instant disclosure of the subject invention may recognize additions, deletions, modifications, substitutions, and other changes which fall within the purview of the subject invention and claims.
After reading and understanding the foregoing detailed description of an inventive fluid heating apparatus in accordance with preferred embodiments of the invention, it will be appreciated that several distinct advantages of the subject fluid heating apparatus are obtained.
At least some of the major advantages include providing a body 208 made of carbon black and encasing in this body a plurality of metal strips 216, 217, and 218 by injection molding. A portion of the strips are connected to line side 212 of the input alternating current 222. These strips are bordered on each side by strips connected to the load side 214 of input alternating current 222. When a voltage is applied, current tends to flow from the strip connected to the line side, to the strips connected to the load side. The resistance to this current produces heat. This is advantageous because heat is generated and no metal is in contact with the fluid so corrosion is avoided.
