Abstract:
Embodiments provide systems and methods for improving in-line water heaters. Certain embodiments find particular use on board aircraft, other air travel vehicles (such as helicopters or aerospace vehicles), or any other vehicles that experience varying temperatures. The in-line water heaters described are self-regulating and use a temperature dependent resistance element to detect water temperature instead of a temperature sensor.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application Ser. No. 62/016,864, filed Jun. 25, 2014, titled “Self Regulating Inline Heater,” the entire contents of which are hereby incorporated by reference. 
     
    
     FIELD OF THE DISCLOSURE 
       [0002]    Embodiments of the present disclosure relate generally to heating systems that are self-regulating in-line heating systems. Certain embodiments find particular use on board vehicles, such as aircraft, which often experience fluctuations in temperatures that can be below freezing. Such low temperatures can cause damage to water lines. 
       BACKGROUND 
       [0003]    Water lines often have the possibility of freezing, particularly water lines onboard passenger transportation vehicles that experience extreme temperature changes. For example, water lines on board aircraft have the possibility of freezing during flight or on normal ground use in certain environments. If water freezes in a water line, this can cause pipe rupture, disruption of normal water flow, damage to end structures, as well as a number of other problems. It is thus desirable to protect water lines against freezing. 
         [0004]    Some solutions have been to provide spot heating on water lines in order to prevent them from freezing. One attempted solution has been to provide an external jacket around the water lines in order to keep them at a desired temperature that is lower than the freezing point. Other solutions have been to use an inline water heater that is routed inside the water line  10 . Examples of this solution are shown in  FIGS. 1 and 2 . 
         [0005]    The heater element may be resistance heating wire  12  that is sealed inside a tube  14  (e.g., in some instances, a Teflon tube). The wire  12  and a tube  14  combination is then inserted inside the water line  10 . The water system plumbing may have various lengths of in-line water heaters positioned in the water lines at various locations along the water system plumbing. These inline water heaters are operated by a controller  16  that monitors the temperature of the heater, which is determined by one or more temperature sensors  18 . The controller  16  is installed hardware that can control the heater element in order to avoid continuous operation of the heater. This is generally intended to maximize efficiency of the system so that they are not constantly heating, but instead, only heat when needed. The in-line heaters are not provided to heat the water in the water lines; they are provided to prevent freezing of the water in the water lines, so need only heat the water to a point above freezing. Accordingly, in-line heating may not be required in a warm environment and/or on a hot day. 
         [0006]    In use, when the controller  16  senses that the set point at which the heater element should turn on has been reached (i.e., the temperature is approaching freezing), the controller  16  activates the heater wires/elements. When the controller  16  senses that the set point at which the heater element should turn off has been reached (i.e., the temperature is at a safe level where freezing will not occur), it turns off the heater wires/elements. The controller  16  switches the in-line heaters on and off by commanding corresponding circuit breakers that power the heater wires/elements  12  on and off. The controller  16  communicates with the one or more temperature sensors  18  in order to make this determination. 
         [0007]    The temperature sensors  18  may be internal to the inline heater system or external to the heater system.  FIG. 1  illustrates an in-line heater with an external temperature sensor.  FIG. 2  illustrates an in-line water heater with an internal temperature sensor. 
       BRIEF SUMMARY 
       [0008]    The present inventors have sought to alleviate the need for the controller/temperature sensor in-line heater systems. It is generally desirable to reduce weight on board aircraft. Weight savings can be achieved by eliminating components. In turn, this can require a lesser need for maintenance because there are fewer components that are susceptible to damage and/or that may need periodic maintenance or repair. 
         [0009]    Embodiments of the disclosure provided herein thus provide systems and methods for improving in-line water heaters for use on-board aircraft or other vehicles where weight and space and considerations, but that may experience varying temperatures. The in-line water heaters described are self-regulating and use a temperature dependent resistance element that can change resistance in response to a change in water temperature, rather than using a temperature sensor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  shows a schematic view of a prior art in-line heater with an external temperature sensor. 
           [0011]      FIG. 2  shows a schematic view of a prior art in-line heater with an internal temperature sensor. 
           [0012]      FIG. 3  shows one embodiment of a self-regulating in-line heater system. 
           [0013]      FIG. 4  shows a cut away view of one embodiment of a self-regulating in line heater component. 
           [0014]      FIG. 5  shows an alternate embodiment including more than two heater wires. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    Embodiments of the present invention provide a self-regulating in-line water heater system  20 . The system  20  includes a temperature dependent resistance element  22  that connects two heater wires  24 ,  26 . One example is illustrated by  FIG. 3 . In a specific example, the two heater wires  24 ,  26  run parallel to one another, on either side of the temperature dependent resistance element  22 , such that the heater wires  24 ,  26  are not in contact with one another, but are both in contact with the temperature dependent resistance element  22 . The heater wires  24 ,  26  and the temperature dependent resistance element  22  are together sealed inside a tube  28 . In a specific example, the tube  28  may be a Teflon tube. In another example, the tube  28  may be an outer coating. 
         [0016]    One of the weaknesses with inline heaters in the market is that each inline heater has a single wire coiled or wound around a string. When the heater is powered and water is introduced around it, the wire material can expand/contract and become kinked or even break. By contrast, the design disclosed herein avoid this problem. It provides a wire material that is robust enough and that can stay within the limits of a given water system. 
         [0017]    The temperature dependent resistance element  22  can be selected such that its resistivity varies as the temperature changes. For example, when the temperature is warm enough to allow water flow, the resistance of element  22  is generally high. However, when the temperature of the water lowers to a point where the water is close to or otherwise in danger of freezing, the resistance of element  22  decreases. As the temperature of the water increases, the resistance of element  22  increases. In other words, lower temperatures will decrease the resistance locally. This decrease in resistance connect the electrical bridge therebetween, causing the heater wires  24 ,  26  to heat locally. For example, when the temperature of the water flowing in the water line  10  reaches a particular set low point, contact between heater wires  24 ,  26  will be established. For example, the low set point may be about 40° F. The use of the temperature dependent resistance element  22  alleviates the need for temperature sensors or a controller to operate the system. Instead, the system is self-regulating and will heat as needed. When the temperature rises above a high set point, the contact between the heater wires is interrupted and their heating will turn stop. In one particular example, the high set point may be about 50° F. 
         [0018]    Traditionally, heater wires are provided within a cover or sleeve. Such may be the case with wires  24 ,  26 . In one example, the heater wires  24 ,  26  may be PTFE fluoro-polymer insulated heating wires. Additionally or alternatively, in one example of this disclosure, each of the heater wires  24 ,  26  may be coated with an inert chemical component that serves as a plastic “cover”  30 . 
         [0019]    The temperature dependent resistance element  22  may be provided as a cement-like mixture that bonds the two heater wires  24 ,  26  to the element  22 . This cement-like component/mixture may vary the resistance between the wires  24 ,  26 . In one example, the component may be a special alloy such as nickel chromium or another metallic-based cement or metal adhesive. The component acts as a binder between the two heater wires  24 ,  26  and may allow varied resistance between the wires  24 ,  26  based on temperature. The resistance of the heater wires  24 ,  26  does not change. The heater wires  24 ,  26  are only connective when the resistance of the inner element  22  decreases. In this example, the temperature dependent resistance element  22  is an “intelligent cement.” The metal ions in the cement provide varying resistance, depending upon the temperature of the environment. The metallic cement provides the function of a binder between the wires  24 ,  26 , as well as creating varied resistance therebetween. The use of this metallic cement/ temperature dependent resistance element  22  eliminates the need for a controller or temperature sensors. The resistance element  22  allows contact between the heater wires  24 ,  26  in order to create a circuit when the temperature reaches a certain low level. 
         [0020]    The metallic cement may be varied in metallic composition, depending upon the size of the system and the desired temperature points. The non-metallic binder of the cement may be a potting epoxy used with electrical circuits, other epoxies, silicone oxide, a polymer base, an organic or inorganic compound, or combinations thereof. The metallic component may be nickel chromium, alumina, titanium, mayenite, alkali metal, or combinations thereof. 
         [0021]    As is shown in  FIG. 4 , the temperature dependent resistance element  22  is not connected to the electrical circuitry, but is sandwiched between the wires  24 ,  26 . There is not a terminal connection point for the wires. The wires are only in communication with one another via a temperature dependent resistance element  22 . A coating or tube is positioned around these components. The combination of the element  22  and wires  24 ,  26  in the tube  28  may be referred to as a self-regulating heater component  34 . 
         [0022]    The self-regulating heater component  34  is intended to be a flexible component that can navigate curved water lines. The self-regulating heater component  34  is also designed to fit within a thin water line. For example, many water lines on board an aircraft are at less than 1 inch in diameter. In specific embodiments, they may be 3/8  inch thick or 1/2  inch in diameter. Thus, the self-regulating heater component  34  may be designed to have a diameter that is about 4-5 mm or less. It should be understood that the diameter of the self-regulating heater component  34  is dependent upon the diameter of the water line it is used to treat. If the water line has a larger diameter, then it is possible to use a self-regulating heater component  34  that has a larger diameter, such that it is scaled relative to the water line pipe. It is generally preferred that the self-regulating heater component  34  does not interrupt with the pressure or flow of water at the end point. 
         [0023]    The self-regulating heater component  34  may also be designed to be inserted into a pipe of water line and easily removed if necessary. This can ease cleaning of the self-regulating heater component  34 . This can also make any repairs that may need to be made to the self-regulating heater component  34  more efficient. The self-regulating heater component  34  is not designed to be wrapped around the waterline, which would add weight to the aircraft. Instead, it is positioned directly within the waterline, in the stream of water flowing therein. This allows the heater component  34  to be shorter and more efficient, as it is in direct contact with the water to be warmed. 
         [0024]    In other embodiments, it is possible to provide a plurality of shorter self-regulating heater components  34  that are positioned only along areas of the waterline that are more prone to freezing. 
         [0025]    As also shown in  FIG. 5 , two heater wires (or more than two heater wires, as shown) may be connected to electrical circuitry  36 . Each connection point may be bonded with epoxy or other compound to prevent fluid ingression into the electrical circuitry  36  and to provide a moisture barrier. The inner element  22  is not connected to the circuitry  36 . The heater wires are not connected to one another at a termination point. Activation of the heater wires  24 ,  26  is dependent only upon decreased resistivity of the temperature dependent resistance element  22  when the temperature decreases. The electrical circuitry  36  relies on signals from the top and bottom heater wires  24 ,  26 . Once power is applied to the heater wires  24 ,  26  via electrical circuitry  36 , the resistance of the wires increases, and electricity flows, generating heat. 
         [0026]    Although a single self-regulating heater component  34  is shown, it is understood that more than one or more heater components  34  may be positioned within a single waterline. It is also understood that more than one heater components  34  may be twisted or otherwise combined together in order to provide a more robust or a quicker burst of heat. In another embodiment, it is also possible for the heater wires  24 ,  26  to be split into other resistors, such that a plurality of heater wires (e.g., represented as wires W 1 , W 2 , W 3 , and W 4 ) may be provided, as shown in  FIG. 5 . In this embodiment, a temperature dependent resistance element  22  may be provided between each of the wires. 
         [0027]    Changes and modifications, additions and deletions may be made to the structures and methods recited above and shown in the drawings without departing from the scope or spirit of the disclosure or the following claims.