Abstract:
An apparatus for heating fluid includes a tank for holding fluid to be heated, and a fuel wafer in fluid communication with the fluid. The fuel wafer includes a fuel mixture including reagents and a catalyst, and an electrical resistor or other heat source in thermal communication with the fuel mixture and the catalyst.

Description:
FIELD OF DISCLOSURE 
     This disclosure relates to heat transfer systems, and in particular to devices for transferring heat to a fluid. 
     BACKGROUND 
     Many heat transfer systems use hot fluids as a heat transfer medium. Such systems include a heat generator for generating heat, a heat transfer medium in thermal communication with the energy source, and a pump to move the heated medium to wherever the heat is needed. Because of its high heat capacity and its abundance, a common heat transfer fluid is water, both in its liquid and gas phase. 
     A variety of heat generators are in common use. For instance, in nuclear power plants, nuclear fission provides energy for heating water. There also exist solar water heaters that use solar energy. However, most heat transfer sources rely on an exothermal chemical reaction, and in particular, on combustion of some fuel. 
     SUMMARY 
     In one aspect, the invention features an apparatus for heating fluid, the apparatus including a tank for holding fluid to be heated, and a fuel wafer in fluid communication with the fluid, the fuel wafer including a fuel mixture including reagents and a catalyst, and a heat source, for example an electrical resistor, in thermal communication with the fuel mixture and the catalyst. 
     Among the embodiments are those in which the fuel mixture includes lithium and lithium aluminum hydride, those in which the catalyst includes a group 10 element, such as nickel in powdered form, or in any combination thereof. 
     In other embodiments, the catalyst in powdered form, has been treated to enhance its porosity. For example, the catalyst can be nickel powder that has been treated to enhance porosity thereof. 
     In those embodiments that include an electrical resistor, the apparatus can also include an electrical energy source, such as a voltage source or current source in electrical communication with the resistor. 
     Among the other embodiments are those in which the fuel wafer includes a multi-layer structure having a layer of the fuel mixture in thermal communication with a layer containing the electrical resistor. 
     In yet other embodiments, the fuel wafer includes a central heating insert and a pair of fuel inserts disposed on either side of the heating insert. 
     A variety of tanks can be used. For example, in some embodiments, the tank includes a recess for receiving the fuel wafer therein. Among these are embodiments in which the tank further includes a door for sealing the recess. In yet other embodiments the tank includes a radiation shield. 
     Also included among the embodiments are those that further include a controller in communication with the voltage source. Among these are controllers that are configured to cause vary the voltage in response to temperature of the fluid to be heated. 
     In another aspect, the invention features an apparatus for heating a fluid, the apparatus including means for containing the fluid, and means for holding a fuel mixture containing a catalyst and a reagent, and means for initiating a reaction sequence mediated by the catalyst to cause an exothermic reaction. 
     Another aspect of the invention is a composition of matter for generating heat, the composition including a mixture of porosity-enhanced nickel powder, lithium powder, and lithium aluminum powder, and a heat source in thermal communication with the mixture for initiating a nickel catalyzed exothermic reaction. 
     Another aspect of the invention is a method of heating a fluid, the method including placing a mixture of nickel powder, lithium powder, and lithium aluminum hydride in thermal communication with the fluid; and heating the mixture, thereby initiating an exothermic reaction in the mixture. 
     These and other features of the invention will be apparent from the following detailed description and the accompanying figures, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  shows a heat transfer system having a heat source; 
         FIG. 2  is a cut-away view of the heat source in  FIG. 1 ; 
         FIG. 3  is a cross-section of the wafer for use in the heat source of  FIG. 2 ; 
         FIG. 4  shows an exemplary resistor in the central layer of the wafer shown in  FIG. 3 . 
         FIG. 5  shows the heat source of  FIG. 1  operating with a conventional furnace. 
         FIG. 6  shows plural heat sources like that in  FIG. 2  connected in series. 
         FIG. 7  shows plural heat sources like that in  FIG. 2  connected in parallel. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a heat transfer system  10  includes a pipe  12  for transporting a heated fluid in a closed loop between a heat source  14  and a thermal load  16 . In most cases, for example where there is hydraulic resistance to be overcome, a pump  18  propels the heated fluid. However, in some cases, such as where the heated fluid is steam, the fluid&#39;s own pressure is sufficient to propel the fluid. A typical thermal load  16  includes radiators such as those commonly used for heating interior spaces. 
     As shown in  FIG. 2 , the heat source  14  is a tank  20  having a lead composite shield, an inlet  22  and an outlet  24 , both of which are connected to the pipe  12 . The interior of the tank  20  contains fluid to be heated. In many cases, the fluid is water. However, other fluids can be used. In addition, the fluid need not be a liquid fluid but can also be a gas, such as air. 
     The tank  20  further includes a door  26  that leads to a receptacle  28  protruding into the tank  20 . Radiating fins  30  protrude from walls of the receptacle  28  into the tank  20 . To maximize heat transfer, the receptacle  28  and the fins  30  are typically made of a material having high thermal conductivity, such as metal. A suitable metal is one not subject to corrosion, such as stainless steel. 
     The receptacle  28  holds a multi-layer wafer  32  for generating heat. A voltage source  33  is connected to the wafer  32 , and a controller  35  for controlling the voltage source  33  in response to temperature of fluid in the tank  12  as sensed by a sensor  37 . 
     As shown in  FIG. 3 , the multilayer fuel wafer  32  includes a heating section  34  sandwiched between two fuel sections  36 ,  38 . The heating section  34  features a central layer  40  made of an insulating material, such as mica, that supports a resistor  42 .  FIG. 4  shows an exemplary central layer  40  having holes  44  through which a resistive wire  42  has been wound. This resistive wire  42  is connected to the voltage source  33 . First and second insulating layers  46 ,  48 , such as mica layers, encase the central layer  40  to provide electrical insulation from the adjacent fuel sections  36 ,  38 . 
     Each fuel section  36 ,  38  features a pair of thermally conductive layers  50 ,  52 , such as steel layers. Sandwiched between each pair of conductive layers  50 ,  52  is a fuel layer  54  that contains a fuel mixture having nickel, lithium, and lithium aluminum hydride LiAlH 4  (“LAH”), all in powdered form. Preferably, the nickel has been treated to increase its porosity, for example by heating the nickel powder to for times and temperatures selected to superheat any water present in micro-cavities that are inherently in each particle of nickel powder. The resulting steam pressure causes explosions that create larger cavities, as well as additional smaller nickel particles. 
     The entire set of layers is welded together on all sides to form a sealed unit. The size of the wafer  32  is not important to its function. However, the wafer  32  is easier to handle if it is on the order of ⅓ inch thick and 12 inches on each side. The steel layers  50 ,  52  are typically 1 mm thick, and the mica layers  40 ,  48 , which are covered by a protective polymer coating, are on the order of 0.1 mm thick. However, other thicknesses can also be used. 
     In operation, a voltage is applied by the voltage source  33  to heat the resistor  42 . Heat from the resistor  42  is then transferred by conduction to the fuel layers  54 , where it initiates a sequence of reactions, the last of which is reversible. These reactions, which are catalyzed by the presence of the nickel powder, are:
 
3LiAlH 4 →Li 3 AlH 6 +2Al+3H 2  
 
2Li 3 AlH 6 →6LiH+2Al+3H 2  
 
2LiH+2Al→2LiAl+H 2  
 
     Once the reaction sequence is initiated, the voltage source  33  can be turned off, as the reaction sequence is self-sustaining. However, the reaction rate may not be constant. Hence, it may be desirable to turn on the voltage source  33  at certain times to reinvigorate the reaction. To determine whether or not the voltage source  33  should be turned on, the temperature sensor  37  provides a signal to the controller  35 , which then determines whether or not to apply a voltage in response to the temperature signal. It has been found that after the reaction has generated approximately 6 kilowatt hours of energy, it is desirable to apply approximately 1 kilowatt hour of electrical energy to reinvigorate the reaction sequence. 
     Eventually, the efficiency of the wafer  32  will decrease to the point where it is uneconomical to continually reinvigorate the reaction sequence. At this point, the wafer  32  can simply be replaced. Typically, the wafer  32  will sustain approximately 180 days of continuous operation before replacement becomes desirable. 
     The powder in the fuel mixture consists largely of spherical particles having diameters in the nanometer to micrometer range, for example between 1 nanometer and 100 micrometers. Variations in the ratio of reactants and catalyst tend to govern reaction rate and are not critical. However, it has been found that a suitable mixture would include a starting mixture of 50% nickel, 20% lithium, and 30% LAH. Within this mixture, nickel acts as a catalyst for the reaction, and is not itself a reagent. While nickel is particularly useful because of its relative abundance, its function can also be carried out by other elements in column  10  of the periodic table, such as platinum or palladium. 
       FIGS. 5-7  show a variety of ways to connect the heat source  14  in  FIG. 1 . 
     In  FIG. 5 , the heat source  14  is placed downstream from a conventional furnace  56 . In this case, the controller  35  is optionally connected to control the conventional furnace. As a result, the conventional furnace  56  will remain off unless the output temperature of the heat source  14  falls below some threshold, at which point the furnace  56  will start. In this configuration, the conventional furnace  56  functions as a back-up unit. 
     In  FIG. 6 , first and second heat sources  58 ,  60  like that described in  FIGS. 1-4  are connected in series. This configuration provides a hotter output temperature than can be provided with only a single heat source  58  by itself. Additional heat sources can be added in series to further increase the temperature. 
     In  FIG. 7 , first and second heat sources  62 ,  64  like that described in  FIGS. 1-4  are connected in parallel. In this configuration, the output volume can be made greater than what could be provided by a single heat transfer unit by itself. Additional heat transfer units can be added in parallel to further increase volume.