Abstract:
An apparatus and method for portably heating water for the purpose of showering or cleanup. A flow of water, originating from a supply container, is warmed as it passes through a heat exchanger transferring energy from a heat source. The heated flow of water is deposited into an accumulating container. The water temperature is actively and automatically controlled by a temperature-responsive valve. Responding to the temperature of the flowing water, the temperature-responsive valve varies the flow of water so as to produce an accurate water temperature within the accumulating container. The flow of water is gravitationally motivated by a pressure head differential between the supply container positioned at an upper elevation and the accumulating container positioned at a lower elevation.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims the benefit of U.S. provisional patent application Ser. No. 61/267,080, filed Dec. 6, 2009 by the present inventor. 
    
    
     FEDERALLY SPONSORED RESEARCH 
     Not Applicable 
     SEQUENCE LISTING OR PROGRAM 
     Not Applicable 
     BACKGROUND 
     1. Field of the Invention 
     This invention generally relates to water heaters, and more specifically, a portable temperature-controlled water heater. 
     2. Prior Art 
     Outdoor sports enthusiasts many times enjoy aspects of nature requiring a separation from modern amenities such as running water, hot showers, and many of the conveniences that are typically encountered during day-to-day living. Though these accommodations may be desired, they are generally not practical to employ in the outdoors. 
     A very basic method of heating water with a kettle over a fire or camp stove, though simple, is relatively inefficient in producing water in quantities sufficient for showering. In addition, it is difficult to obtain a precise water temperature suitable for contact with skin. 
     U.S. Pat. No. 6,877,461 to Long et al. (2005) discloses a method for heating water by mechanically pumping water through a heat exchanger warmed by a burner assembly. This method requires the transportation of bulky equipment, a supply of batteries, and fuel weighing upwards of 12 kg (26.4 lbs) or more. 
     A thermosiphon water heating system disclosed in U.S. Pat. No. 5,417,201 to Thomas et al. (1995) relies on density changes that occur as water is heated within a heat exchanger. The change in water density motivates the circulation of water through the heat exchanger. A single container of water is gradually heated taking a considerable amount of time, upwards of an hour or more. The user must monitor the water temperature in the container and judge when the time is right to remove the heat exchanger from the heat source. In addition, due to the nature of the thermosiphoning principle, stratifications in water temperature prevail vertically within the water container. During operation, the water towards the top of the container is likely to be as much as +10 C (+20° F.) warmer than the water on the bottom making it difficult to determine average bulk water temperature. 
     Other portable water heaters such as those disclosed in U.S. Pat. No. 5,460,161 to Englehart et al. (1995) and U.S. Pat. No. 3,246,644 to Peterson (1966) heat water to the boiling point within a heat exchanger. Upon boiling, water expands into steam driving the flow of water through the system similar to an automatic coffee maker. Water and steam temperatures up to 100 C (212° F.) can pose additional handling risks for the user during normal operation. Also, from a thermodynamic perspective, it is less efficient to heat water to the boiling point only to have to dilute or cool the water down to approximately 38 C (100° F.), necessary for contact with the skin. Heat energy is spent during the phase change of water from a liquid to a gas. 
     SUMMARY 
     The present invention fills the previously mentioned deficiencies by providing a portable, temperature-controlled, water heating system which advantageously allows for a compact and lightweight design. Coupled with a variety of possible heat sources, the present invention is capable of quickly heating a volume of water to an accurate, user-selected temperature appropriate for contact with the skin. Energy is absorbed efficiently from a heat source such as a camp fire, backpacking stove, or burner assembly, warming the water to the temperature setting selected. In one embodiment, the dry system, including water containers, weighs less than 0.9 kg (2 pounds) and packs to a size of 180 mm (7 in.) in diameter×5 cm (2 in.) in height. For a typical example, the water heating system is capable of heating 15 liters (4 gallons) of water from 15 C (60° F.) to 38 C (100° F.) in approximately 12 minutes. 
    
    
     
       DRAWINGS 
       Figures 
         FIG. 1  is a perspective view of a portable water heater shown in accordance with the first embodiment. 
         FIG. 2  is a top view of a heat exchanger shown in accordance with the first embodiment. 
         FIG. 3  is a front-side view of a heat exchanger shown in accordance with the first embodiment. 
         FIG. 4  is a section view along line  4 - 4  in  FIG. 3  of a heat exchanger shown in accordance with the first embodiment. 
         FIG. 5  is a top view of a temperature-responsive valve shown in accordance with at least one embodiment. 
         FIG. 6  is a front-side view of a temperature-responsive valve shown in accordance with at least one embodiment. 
         FIG. 7  is a section view of a temperature-responsive valve taken along line  7 - 7  in  FIG. 5 . 
         FIG. 8  is a section view of a temperature-responsive valve taken along line  8 - 8  in  FIG. 6 . 
         FIG. 9  is a section view of a temperature-responsive valve taken along line  9 - 9  in  FIG. 5 . 
         FIG. 10  is a section view of a temperature-responsive valve taken along line  10 - 10  in  FIG. 9 . 
         FIG. 11  is a section view of a temperature-responsive valve taken along line  11 - 11  in  FIG. 6 . 
         FIG. 12  is an exploded perspective view of a temperature-responsive valve shown in accordance with at least one embodiment. 
         FIG. 13  is a top view of a heat exchanger shown in accordance with an alternate embodiment. 
         FIG. 14  is a top view of a heat exchanger shown in accordance with an alternate embodiment. 
         FIG. 15A  is a front elevation view of a heat exchanger and heat source shown in accordance with an alternate embodiment. 
         FIG. 15B  is a section view of a heat exchanger shown in accordance with an alternate embodiment. 
         FIG. 15C  is a section view of a heat exchanger shown in accordance with an alternate embodiment. 
         FIGS. 16A-16C  are top views of three exemplary displacements of a temperature-responsive valve in accordance with at least one embodiment. 
         FIG. 17  is a chart showing typical operating temperatures of a portable water heater in accordance with at least one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     General—First Embodiment 
     Referring to  FIG. 1 , one embodiment of the portable water heater is shown in a typical state of use. An elevated supply container  100  is constructed of a flexible waterproof polymeric material ideally having one or more translucent sides. A translucent side allows a user to visually observe the water level within. Supply container  100  has a volume of approximately 8 to 20 liters which allows for a reasonable working quantity of water, at the same time limiting the filled weight to allow one person to lift and carry it. Many sizes of containers would be suitable, but presently I contemplate that a volume of 15 liters is a versatile working volume which can provide water for up to four people to use for showering. I contemplate that a flexible, sealed container which collapses upon emptying is preferred, however a rigid polymeric or metallic container would also be suitable, provided it has either an open or vented top to prevent a negative pressure from developing as water exits the container. 
     Supply container  100  has a drain port  104  which couples to a supply duct  106 . Alternately, drain port  104  may be eliminated and supply duct  106  placed directly into an opening near the top of supply container  100 , allowing for siphon feeding. Supply duct  106  is constructed from silicone tubing measuring 11.1 mm ( 7/16 in.) O.D.×7.9 mm ( 5/16 in.) I.D. and approximately 1.6 m (64 in.) in length. Although other flexible polymeric materials are suitable, presently I contemplate that silicone tubing is preferred due to its advantageous properties including high temperature resistance, flexibility and kink resistance. Also suitable, one or more segment of rigid metallic tubing may be substituted for a corresponding segment of flexible tubing. In addition, a filter means may be integrated into drain port  104  or added in-line in combination with duct  106 . 
     A heat exchanger  102  connects to supply duct  106  and to a heated water duct  20 . Heated water duct  20  is similar in cross section and material to supply duct  106 , however its length is shorter, approximately 0.81 m (32 in.). Heat exchanger  102  resides over a heat source  28 , which is shown as a wood fueled fire in this embodiment. A stove or burner assembly is also a suitable heat source. 
     Duct  20  connects to a temperature-responsive valve  22 . Temperature-responsive valve  22  couples to an accumulating container  26  through a container port  24 . Accumulating container  26  is preferably similar in construction to supply container  100  so that they could be used interchangeably, but it is not required that they are identical. Alternately, temperature-responsive valve  22  could deposit water directly into a rigid or flexible container with a closed or open top serving the same function as container  26 . Presently I contemplate that it is preferred to use a flexible, sealed container for water accumulation in order to prevent excessive evaporative cooling of the heated water as well as allowing for a compact stored size. Optionally, accumulating container  26  may be enclosed in an additional covering made of an insulating material such as closed cell polyethylene foam so as to further slow heat loss. 
     Referring to  FIGS. 2, 3 , &amp;  4  supply duct  106  connects to a heat exchanger inlet  114  by means of a friction fit. Duct  20  connects to a heat exchanger outlet  116  also by means of a friction fit. 
     Heat exchanger  102  is constructed of cylindrical aluminum tubing 9.5 mm (⅜ in.) O.D.×0.9 mm (0.035 in.) wall thickness with an uncoiled length of approximately 1.8 m (72 in.). Other thermally conductive materials such as copper or stainless steel are also suitable, although heavier and typically having a higher material cost. In this embodiment heat exchanger  102  is formed in such a manner to allow heat exchanger inlet  114  and a heat exchanger outlet  116  to be routed generally adjacent to each other with a formed overall outer diameter of approximately 180 mm (7 in.). Reversing inlet  114  and outlet  116  is also suitable. Referring to  FIGS. 2-3 , heat exchanger  102  is formed to have a height of approximately 38 mm (1.5 in.). Many other sizes, cross sections, and routings of tubes or vessels are suitable for constructing heat exchanger  102  but at the present time I contemplate the size and routing described above is advantageous in terms of compact storage which is described later. 
     A flexible duct insulator  108  surrounds a short length of both supply duct  106  and heated water duct  20 . Duct insulator  108  is beneficial in this embodiment for the purpose of insulating ducts  106  and  20  from heat source  28  ( FIG. 1 ). Flexible duct insulator  108  overlaps the connections made by duct  106  and inlet  114  as well as duct  20  and outlet  116 . Duct insulator  108  extends and protects approximately 250 mm (10 in.) away from ports  114  and  116  of heat exchanger  102 . 
     Duct Insulator—First Embodiment 
     Referring to  FIG. 4 , flexible duct insulator  108  is made up of a flexible and abrasion resistant duct sheath  70  and a flexible duct insulation sleeve  72 . Duct sheath  70  is an approximately 300 mm (12 in.) length of braided sleeve made of stainless steel wire. Duct sheath  70  has a nominal inner diameter of 22 mm (0.88 in.) with a 0.25 mm (0.010 in.) braided wire wall thickness. Duct insulation sleeve  72  is made of one or more plies of braided, resin-coated, fiberglass sleeve with a wall thickness of 1.1 mm (0.046 in.) and capable of withstanding a minimum continuous working temperature of 650 C. Other temperature-resistant, thermally insulating materials such as ceramic blanket are also suitable. Duct insulator  108  is joined to heat exchanger  102  by means of a clamp  74 . Clamp  74 , made of stainless steel, compresses around the perimeter of duct insulator  108  pinching it against heat exchanger  102 . Other methods of captivating duct insulator  108  to heat exchanger  102  such as a crimped stainless steel or brass ferrule are also suitable. 
     Temperature-Responsive Valve—First Embodiment 
     Referring to  FIGS. 5 and 6 , temperature-responsive valve  22  has an inlet  30 , an outlet  32  and a temperature selector  34 . Heated water duct  20  connects to inlet  30  by means of a friction fit. Outlet  32  couples to container  26  through container port  24 . An additional length of tubing between outlet  32  and port  24  is also suitable, as is depositing directly into container  26  without the use of container port  24 . 
     Referring to  FIGS. 7 and 8 , an inner lumen  36  of inlet  30  intersects a chamber  118 . Chamber  118  is formed between an upper housing  42  and a lower housing  44 . Upper and lower housings  42  and  44  are made of a rigid material such as polycarbonate, nylon, polypropylene, etc. Within chamber  118 , a movable valve member  40  having a displacement, variably blocks a valve aperture  120  forming a variable restriction for the flow of water. Aperture  120  intersects with an inner lumen  122  of outlet  32 . Aperture  120  has an I.D of approximately 6.4 mm (0.25 in.) Valve member  40 , having a head with a flange O.D. of 9.5 mm (0.38 in.), is made of a rigid material such as polycarbonate, nylon, polypropylene, etc. 
     A temperature sensitive element  38  is contained within chamber  118 . A temperature sensitive element exhibits a repeatable response function as a result of applied temperature. In this embodiment, element  38  is a bimetallic strip formed into a coil with a strip width 9.5 mm (0.375 in.), a strip thickness 0.5 mm (0.020 in.) and a formed outer coil diameter 25 mm (1 in.). The radial outer end of element  38  forms a linkage  124 . The inner end of element  38  attaches rigidly to a cylindrical shaft  52 . The distance from the center axis of shaft  52  to the center axis of linkage  124  is 16.5 mm (0.65 in.). The lower end of shaft  52  is located within a blind bore  126  of lower housing  44  and is allowed to rotate freely. The upper end of shaft  52  extends through a bore  128  in upper housing  42  passing into a bore  130  of temperature selector  34 . Shaft  52  is locked rigidly to selector  34  with a set screw  58 . Shaft  52  is constructed of corrosion resistant metal such as brass, stainless steel or aluminum with a diameter of 6.4 mm (0.25 in.). The mid portion of shaft  52  is slightly larger in diameter, creating an upper shoulder  132  and a lower shoulder  134 . A stainless steel flat washer  50  is oriented such that its lower face mates against shoulder  132  of shaft  52 , while the upper washer face mates against upper housing  42 . This arrangement allows rotation of shaft  52  relative to upper housing  42  but prevents axial movement. A seal  46  prevents fluid leakage between shaft  52  and upper housing  42 . A gasket  48  prevents fluid leakage between lower housing  44  and upper housing  42 . 
     Referring to  FIGS. 9 and 10 , valve member  40  is shown in a closed position centered over aperture  120 . A stop  54  restricts clockwise rotation (viewed from top) of valve member  40  about shaft  52  any further than the center of aperture  120 . Stop  54  is attached rigidly to upper housing  42 . This present closed or zero-displacement position of valve member  40  provides a maximum degree of flow restriction. A fixed orifice  56 , a three-sided furrow formed into surface  136 , intersects with aperture  120 . Orifice  56  serves as a constant leak path which allows a minimum flow of water through temperature-responsive valve  22 . In addition, orifice  56 , having only 3 sides is advantageously self-cleaning minimizing the risk of becoming clogged with debris. Orifice  56  has a cross section of approximately 2.3 mm 2  (0.0035 in 2 ) in this embodiment. 
     Referring to  FIGS. 8, 9 and 11 , temperature selector  34 , made of a rigid material such as polycarbonate, nylon, polypropylene, etc., has two cylindrical protrusions  68  and  68   a  which are captivated within two slots  64  and  64   a . Slots  64  and  64   a  are formed channels within upper housing  42 . Shaft  52 , locked to selector  34 , is allowed to rotate within bores  126  and  128 . Slots  64  and  64   a  provides positive stops to limit rotation of selector  34 . In this embodiment, selector  34  is allowed to rotate plus or minus 25 angular degrees from the center position. On the underside of selector  34  are formed two hemispherical detents  62  and  62   a . Two mating detent receptacle troughs  66  and  66   a  allow for a plurality of discrete resting positions of detents  62  and  62   a . In this embodiment there are nine discrete positions representing nine different temperature settings. 
     It is suitable to produce the temperature-responsive valve with a different number of temperature settings by adding or removing detent positions or changing the spacing. It is also suitable to remove the adjustable temperature feature altogether and have a fixed temperature setting. 
       FIG. 12  shows an exploded perspective view of temperature-responsive valve  22 . This view provides additional clarity of components contained in temperature-responsive valve  22  in this embodiment. 
     Operation 
     General—First Embodiment 
     Referring to  FIG. 1 , the use of this portable temperature-controlled water heater requires a source of water, a heat source  28 , and finally, a means of supporting elevated supply container  100 . Possible methods for suspending container  100  may include a natural or man-made structure near the heat source such as a tree limb, rock etc. If no structure is conveniently located near heat source  28 , a field constructed or prefabricated tripod may be used as another option of supporting supply container  100 . 
     In preparation for heating a batch of water, supply container  100  is detached from duct  106 , filled with water, and set aside. Drain port  104  is temporarily capped off to prevent loss of water. Heat source  28  is ignited and allowed to develop in intensity. Filled supply container  100  is suspended so that drain port  104  is at a height of 0.81-1.01 m (32-40 in.) higher than accumulating container  26  and horizontally approximately 0.9 m (3 ft) from heat source  28 . This elevation differential between supply container  100  and accumulating container  26  produces a column of water pressure suitable for motivating a flow of water through the system during operation. 
     Referring to  FIGS. 1 and 5 , temperature-responsive valve outlet  32  is then connected to port  24  of accumulating container  26  and temperature selector  34  is set to a desired water temperature setting. Supply duct  106  is then connected to drain port  104  following removal of the temporary cap or plug blocking drain port  104 . Water begins to flow through duct  106 , heat exchanger  102 , duct  20 , temperature-responsive valve  22 , and finally into container  26 . After a couple seconds any air will have purged through the system. After flow of water has begun, heat is applied to heat exchanger  102  by placing on heat source  28 . The water heating system is now in operation and after 10-15 minutes the process will deplete supply container  100  having transferred its contents to accumulating container  26 . Factors that influence the amount of time required to heat the water include: the volume of water, the initial cold water temperature, the intensity of heat source  28 , and the water temperature set by the user on temperature-responsive valve  22 . Before supply container  100  is completely depleted of water, heat exchanger  102  must be removed from heat source  28  to avoid boiling stagnated water within heat exchanger  102  which would undesirably force steam out of the system through ducts  106  and  20 . When heating is complete, temperature-responsive valve outlet  32  is disconnected from port  24  of container  26 . Port  24  may be temporarily capped off. The user now possesses a quantity of warm water within container  26  that is at the desired temperature reflective of the temperature setting chosen. The user may then position the container at a place of their choosing to provide hot water for a shower or other cleanup function. 
     Temperature-Responsive Valve—First Embodiment 
     Referring to  FIG. 1 , temperature-responsive valve  22  automatically adjusts the flow rate of water during operation in order to produce an accurate temperature of water within accumulating container  26 . In order to function properly, temperature-responsive valve  22  requires a minimum flow-through to ensure thermal feedback is provided to element  38 . This minimum flow rate is determined primarily by the cross sectional opening of fixed orifice  56  and the height of supply container  100 . When fully closed, valve  22  allows a minimum flow of approximately 20 fluid ounces/minute (0.6 liters/minute). 
     Heat is absorbed from heat source  28  into heat exchanger  102  and transferred to the minimum flow of water within, thus raising the temperature of water exiting heat exchanger  102 . Referring to  FIGS. 7 and 9 , as the temperature of water flowing through temperature-responsive valve  22  rises to within approximately 3 C (5° F.) below the temperature setting, temperature sensitive element  38  begins to cause valve member  40  to move counter-clockwise about shaft  52  away from stop  54 . As valve member  40  moves away from stop  54 , aperture  120  is gradually uncovered, thus decreasing restriction and increasing the flow rate of water. As the flow rate increases, the dwell time of the water flowing through heat exchanger  102  is shortened and so the temperature of the water flowing begins to fall again. As the water temperature falls, temperature-responsive valve  22  conversely causes an increase in restriction and thus a decrease in flow as valve member  40  is moved toward stop  54 . 
     Element  38  exhibits a response function such that an increase in temperature produces a counter-clockwise rotation of linkage  124  about the center axis of shaft  52  at an approximate change of 1.25 angular degrees for every 0.55 C (1° F.). As the water temperature in contact with element  38  climbs approximately 3 C (5° F.) above the temperature setting, temperature-responsive valve  22  gradually displaces valve member  40  to a fully opened state allowing the maximum flow rate through the system of approximately 1.9 liters/min (64 fluid ounces/minute). Again, as the water temperature drops to a level of 3 C (5° F.) below the temperature setting, element  38  displaces valve member  40  clockwise, to a fully closed state producing the minimum flow rate mentioned above. Likewise, when the water temperature in contact with element  38  is approximately equal to the temperature setting, valve member  40  is displaced to cause a 50% flow restriction flowing approximately 42 fluid ounces/minute (1.2 liters/minute). Referring to  FIG. 17 , this thermal oscillation repeats many times during the 10-15 minutes of operation. Though the instantaneous temperature of water flowing through the system may vary as much as 15 C (28° F.), the bulk water temperature collected in accumulating container  26  is generally within 1.5 C (3° F.) of the temperature setting chosen by the user. 
     Referring to  FIGS. 16A-16C , three displacements of valve member  40  are illustrated. Each displacement is a function of the water temperature in contact with element  38 .  FIG. 16A  shows element  38  at a temperature several degrees or more below the chosen temperature setting. Valve member  40  is fully closed with the exception of the minimum flow rate allowed by fixed orifice  56 .  FIG. 16B  shows valve member  40  at a displacement creating an approximately 50% flow restriction created by an opening of approximately 9.5 mm 2  (0.015 in 2 ). This displacement corresponds with a water temperature of approximately equal to the temperature setting.  FIG. 16C  shows the temperature-responsive valve approximately fully open and corresponds with a water temperature several degrees above the chosen temperature setting. 
     Referring to  FIGS. 7 and 11 , the water heating system is generally able to control the water temperature within a range of 27 C (80° F.) to 49 C (120° F.) and is determined by the position of selector  34 , set by the user. In this embodiment, when selector  34  is set to the center or middle position, the corresponding control temperature is 37 C (100° F.). Adjusting selector  34  to the next detent position increases or decreases the temperature setting by 2.8 C (5° F.) depending on the direction of rotation. Clockwise rotation of selector  34  produces an increase in temperature setting; counter-clockwise rotation produces a decrease in temperature setting. In this embodiment the detent spacing is 6.25 angular degrees with a total of 9 discrete positions again ranging from 27 C (80° F.) to 49 C (120° F.). 
     In this embodiment, the heating system is sized for a broad range of initial water temperatures of 4 C (40° F.) to 27 C (80° F.) and net absorbed heating intensities of 3000 BTUH to 10,000 BTUH. When using low heat intensities (3000 BTUH absorbed), the maximum increase in water temperature that can be expected is approximately +22 C (+40° F.). Conversely, very high heat intensities (10,000 BTUH absorbed) should be reserved for use when the supply water is below 15 C (60° F.). These limits are dictated by the elevation of supply container  100  and the effective diameters and lengths of the components. The operating range limits could be varied by changing one or more of these parameters, however presently I contemplate that the current sizing provides a practical operating range. 
     In this embodiment, the upper temperature setting limit of 49 C (120° F.) could be changed by adjusting the length of slots  64  and  64   a  in  FIG. 7  and adding or removing detent positions, however presently I contemplate that an upper limit of 49 C (120° F.) provides a practical upper temperature setting limit. In addition, it should be noted that it is advantageous to leave a reasonable margin of temperature between the upper temperature setting limit and the boiling point of water. If, during operation, the flowing water should reach the boiling point within heat exchanger  102  ( FIG. 1 ) the steam generated would disrupt the flow of water and undesirably force water and steam out of ducts  106  and  20 . An upper temperature setting limit of 49 C (120° F.) provides an adequate margin to avoid this behavior. 
     Calibration of Temperature-Responsive Valve 
     Referring to  FIGS. 7 and 9 , a one-time initial calibration of temperature-responsive valve  22  is performed with lower housing  44  removed. Temperature selector  34  is set to a predetermined calibration position, for example the center position representing 38 C (100° F.). Set screw  58  is loosened. The partial assembly is placed in a bath of water controlled to 38 C (100° F.). Shaft  52  is then adjusted within bore  130  of selector  34  (still in the center temperature position) such that a gap of 3 mm (0.12 in.) is present between linkage  124  and stop  54 . Temperature selector  34  is locked to shaft  52  by tightening set screw  58  and lower housing  44  is assembled to upper housing  42  thus completing initial calibration. 
     Duct Insulator—First Embodiment 
     Referring to  FIGS. 2-4 , flexible duct insulator  108  allows flexibility at the same time providing thermal protection of ducts  106  and  20 . Duct insulator  108  allows this encompassed length of ducts  106  and  20  to be in direct contact with flames produced by heat source  28  ( FIG. 1 ). Insulation sleeve  72  provides a means for maintaining a large temperature gradient between the outer surface of sheath  70  and the O.D. of ducts  106  and  20 . This temperature gradient is required to prevent damage of ducts  106  and  20  due to excessive temperature. Heat migration inward toward ducts  106  and  20  is slowed by insulation sleeve  72 . Heat that reaches ducts  106  and  20  is effectively absorbed into the flowing water within. Water is required to be flowing at all times through ducts  106  and  20  to prevent thermal damage. 
     Storage—First Embodiment 
     In this embodiment, flexible duct insulator  108  along with ducts  106  and  20  may be coiled within the concave portion of heat exchanger  102  during storage and transportation, resulting in a relatively compact size of approximately 180 mm (7 in.) in diameter×50 mm (2 in.) height. 
     Second Embodiment—FIG.  13   
     A combination temperature-responsive valve and handle assembly  22   a  is located at the ends of a heat exchanger inlet extension  114   a  and a heat exchanger outlet extension  116   a . Inlet and outlet extensions  114   a  and  116   a  are made of similar metallic tubing as a heat exchanger  102   a  and are approximately 250 mm (10 in.) to 380 mm (15 in.) in length. A supply duct  106   a  connects to inlet extension  114   a  within assembly  22   a . Outlet extension  116   a  connects to assembly  22   a  which functions similarly to temperature-responsive valve  22  described in the first embodiment. An optional pair of brass, aluminum, stainless steel, etc. detachment couplings  138  and  140  provides a disconnecting point and allows for a more compact overall storage size. Suitable coupling types for couplings  138  and  140  are compression, flared, telescoping, etc. 
     Third Embodiment—FIG.  14   
     A supply duct  106   b  connects to a heat exchanger inlet extension  114   b . A heated water duct  20   b  connects to a heat exchanger outlet extension  116   b . An insulating non-metallic handle  142  is attached to the ends of extensions  114   b  and  116   b . An optional pair of brass, aluminum, stainless steel, etc. detachment couplings  138   a  and  140   a  provides a disconnecting point and allows for a more compact overall storage size. 
     Additional Embodiments—FIGS.  15 A- 15 C 
     Heat exchanger  102  is shown in combination with a heat source  28   a  in  FIG. 15A . In the embodiment shown, heat source  28   a  is a conventional liquid fueled burner of which may consume one of many liquid fuels such as propane, butane, petroleum, naphtha, etc. A typical fuel burn rate of 7,500-15,000 BTUH provides a suitable heating rate for the shown embodiment. The general operation is much the same as with the previous embodiments, however a higher heating efficiency may be obtained by placing heat exchanger  102  in a concave-up position as shown in  FIGS. 15A and 15B . In addition, an optional heat deflector  138  ( FIG. 15B ), may be used to further improve heating efficiency by directing the hot exhaust gases outward, maximizing the contact with heat exchanger  102 . Deflector  138  is approximately 125 mm (5 inches) in diameter and constructed of a heat resistant material such as stainless steel. 
     A heat exchanger  102   c  ( FIG. 16C ) in an alternate configuration is shown with heat deflector  138  and an outer enclosure  140  constructed of a heat resistant material such as aluminum, steel, fiberglass, etc. The use of enclosure  140  further improving efficiencies by channeling combustion gases around the surfaces of heat exchanger  102   c . At this time I contemplate that it is preferred that heat exchanger  102   c  is constructed to allow removal from heat source  28   a  ( FIG. 15A ), however exchanger  102   c  could also be permanently joined to a dedicated burner assembly. 
     CONCLUSION, RAMIFICATIONS, AND SCOPE 
     Thus, the reader will see that a portable water heating system described through the various embodiments has several practical advantages for a wide range of users spending time in the outdoors. In at least one embodiment, the total weight of the system including containers is less than 0.9 kg (2 pounds) and packs to a size of 180 mm (7 in.) in diameter×50 mm (2 in.) height. With few moving parts and a small total number of components, the cost to manufacture is relatively low compared to other water heating devices. When used properly, the water heating system is relatively fast and accurate and has the capability of heating hundreds of gallons of water without failure or need for batteries. Furthermore, the heating system provides exceptional versatility, adapting to multiple heat sources in at least one embodiment. 
     While my above description contains many specifics, these should not be construed as limitations on the scope of the invention, but rather as an exemplification of several preferred embodiments thereof. Many other variations are possible. 
     Alternate temperature-responsive valve constructions are possible. For example, an expanding wax pellet temperature sensitive element is suitable although generally slower responding which limits the allowable ranges of inlet temperatures and heat intensities applied to the system for proper operation. Alternately, an electro-mechanical temperature-responsive valve incorporating a temperature sensor, a microprocessor and a valve actuator provides exceptional control and programmability; however it is accompanied by additional manufacturing cost, increased physical size, and the inconvenient need for batteries in the field. 
     Individual dimensions of components and/or the overall scaling of the water heating system could be sized up or down for a trade-off in heating performance and overall package size. 
     Accordingly, the scope of the invention should be determined not by the embodiments illustrated, but by the appended claims and their legal equivalents.