Abstract:
A flow-through heater ( 1 ) provided with a channel ( 2 ) for guiding a liquid to be heated. The flow-through heater ( 1 ) comprises a ferromagnetic wall ( 5 ) encasing an induction coil ( 4 ) for heating at least a wall portion of the ferromagnetic wall ( 5 ), wherein the channel ( 2 ) extends along said wall portion. In this construction, no additional electromagnetic shield is required.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a flow-through heater based on induction heating, particularly for heating water. 
       BACKGROUND OF THE INVENTION 
       [0002]    Induction heating is the process of heating a metal object by electromagnetic induction, where an electromagnetic flux generates eddy currents within the metal and resistance leads to heating of the metal. The heated metal can be used as a heating element for heating a substance, e.g., in flow-through induction heaters. In flow-through induction heaters water is heated by an induction coil surrounding a ferro-magnetic section of a water supply line. A high frequency magnetic flux in the coil generates heat in the ferro-magnetic section which in turn heats the water. Since the heat is generated in the ferromagnetic material, there is no energy loss due to thermal barriers. The contact-free way of heat transfer allows the use of thin walls and fast heating. Induction heaters can be controlled very effectively and directly. An induction heater in a water-supply device is for instance disclosed in JP 09-075219. 
         [0003]    For safety reasons such an induction coil must be shielded with an electromagnetic field shield, typically made of a ferromagnetic material such as ferrite. Such a shield performs no other function than protecting the environment against the impact of the electromagnetic flux. In such a construction, only part of the magnetic flux is used to generate heat for heating the water. 
         [0004]    The object of the invention is to provide a flow-through induction heater construction with improved heating efficiency. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0005]    The object of the invention is achieved with a flow-through heater provided with a channel for guiding a liquid to be heated, and comprising a ferromagnetic wall encasing an induction coil for heating at least a wall portion of the ferromagnetic wall, wherein the channel extends along said wall portion. 
         [0006]    This way, the induction coil is shielded by the ferromagnetic channel wall and no separate electromagnetic shield is needed. No heat is lost via an electromagnetic shield and highly efficient heat transfer to liquid is achieved. While so far induction coils are typically used for inducing eddy currents to heat objects placed in the interior of the coil, it has now been found that also a ferromagnetic heater wall along the exterior of the coil can be heated in a surprisingly effective manner. 
         [0007]    In a specific embodiment, the ferromagnetic wall is the outer wall of a double walled casing, e.g., a double walled cylinder, with an inner wall disposed at the interior of the induction coil, in such way that the induction coil is disposed between the ferromagnetic wall and the inner wall. Optionally, the channel extends also along at least a portion of the inner surface of the inner wall, so that the water to be heated flows along the outer wall as well as the inner wall of the double walled casing to further optimize heating efficiency. 
         [0008]    Alternatively, the ferromagnetic wall is formed by a casing, e.g., a cylinder, which has at least one closed end and which casing encases the induction coil, the casing being surrounded by a second wall, wherein the channel runs between the ferromagnetic wall and the second wall and wherein the channel is operatively connected to a supply line and a discharge line. The casing can for example be closed by a circular end wall. The surrounding second wall can, e.g., a coaxial cylindrical wall. This way, the heater can be configured to guide the water flow along the ferromagnetic wall, while the space enclosed by the coil is blocked from the flow path. This allows a simpler and cheaper construction of the heater. 
         [0009]    To further optimize heat transfer, the wall surrounding the induction coil can for example be provided with one or more partitions to define a flow path along the ferromagnetic wall, for instance by defining a spiral or helical flow path. In case the ferromagnetic wall is a body with a longitudinal axis, or forms part of such a longitudinal body, the partitions may extend radially relative to the longitudinal axis. The partitions can for example be radially extending partitions on a cylindrical ferromagnetic wall. 
         [0010]    The induction coil is usually made of 3 mm-5 mm diameter copper tubing. Diameter, shape, and number of turns can be selected to influence the desired efficiency and field pattern. 
         [0011]    The ferromagnetic material of the outer surface of a casing shielding the induction coil can be any suitable steel type generally used in the field of water supply lines. 
         [0012]    A high frequency electric power supply means can be used to supply high frequency AC power to the induction coil. The frequency of the alternating current can, e.g., be 50-400 KHz, for instance 100-300 KHz. 
         [0013]    Optionally, the supplied high frequency electric power can be adjusted in accordance with a preset temperature, e.g. using a thermostat. 
         [0014]    The heater according to the present invention is suitable for use in commercial, domestic and industrial environments. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1A  in cross section a heater according to the present invention; 
           [0016]      FIG. 1B  the heater of  FIG. 1A  in perspective cross section; 
           [0017]      FIG. 2  second embodiment of a heater according to the invention in perspective cross section; 
           [0018]      FIG. 3  third embodiment of a heater according to the invention in perspective cross section; 
           [0019]      FIG. 4  fourth embodiment of a heater according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0020]      FIG. 1A  shows in cross section a flow-through heater  1 . This cross section is shown in perspective in  FIG. 1B . The flow-through heater  1  comprises a channel  2  for guiding liquid to be heated, in particular water. A double walled cylinder  3  encases an induction coil  4 . The double walled cylinder  3  comprises an outer cylinder  5  of a ferromagnetic metal surrounding the induction coil  4 , and an inner pipe line  6  surrounded by the induction coil  4 . The inner pipe line  6  is in open connection and in line with a discharge line  7 . Two annular end walls  8 ,  9  close off the space  10  between the outer and inner walls  5 ,  6 . The outer cylinder wall  5  surrounding the induction coil  4  forms an inner wall of an annular section  11  of the flow path channel  2 . The outer wall of the annular channel section  11  is formed by a casing  12  comprising a cylindrical wall  13  capped by a circular end wall  14 . The cylindrical wall  13  stands proud of the double walled cylinder  3  encasing the induction coil  4 , resulting in a space  15  between the circular end wall  14  on the one end and the annular end wall  9  of the double walled cylinder  3  on the other hand. At the other end, an annular end wall  16  closes off an annular space  17  between the double walled cylinder  3  and the cylindrical casing wall  13 . Near the annular end wall  16 , a supply line  18  is joined to the cylindrical casing wall to form an open connection with the annular space  17  between the double walled cylinder  3  and the cylindrical casing wall  13 . 
         [0021]    The flow path for water to be heated is indicated in the drawings by the arrows. Water flows from the supply line  18  via the annular channel formed by the annular space  17  between the double walled cylinder  3  and the cylindrical casing wall  13 , and further via the space  15  between the circular end wall  14  and the annular end wall  9  of the double walled cylinder  3  into the inner pipe line  6  of the double walled cylinder  3  and further into the discharge line  7 . 
         [0022]    At the inner side of the induction coil  4 , the generated magnetic flux heats the inner pipeline  6 , thus heating passing water. At the outer side of the coil  4 , the flux is shielded by the wall  5 . Heat is generated in the wall  5  which is absorbed by the water passing the flow path. 
         [0023]      FIG. 2  shows in perspective a cross section of a second embodiment of the heater  1  according to the invention. The heater  1  has a similar construction as the heater shown in  FIGS. 1A and 1B . Parts common to both embodiments will be referred to by identical reference numerals. The embodiment of  FIG. 2  differs with the embodiment of  FIGS. 1A  and B in that the outer surface  5  of the double walled cylinder  3  is provided with a radially extending spiral partition  19 . The spiral partition  19  defines a spiral flow path, serving to maximize heat transfer from the shield  5  to passing water. 
         [0024]      FIG. 3  shows a further embodiment of the heater  1  according to the invention. Again, parts common to both embodiments are referred to by identical reference numerals. In contrast to the embodiment of  FIGS. 1A and 1B  and the embodiment of  FIG. 2  a double walled cylinder  3  is capped with a circular end wall  20  closing off the inner pipe line  6 . A discharge line  21  is joined to a cylindrical casing wall  13  opposite a supply line  18 . Water flows from the supply line  18  to the discharge line  21  via an annular space  17  between the double walled cylinder  3  and the inner surface of the cylindrical casing wall  13 . 
         [0025]      FIG. 4  shows a further embodiment of the heater  1  according to the invention. The heater  1  has a channel  2 . Fluid to be heated enters the channel via a supply line  18  and exits the channel via a discharge line  21 . The fluid is guided by a second wall  13  and a coil encasing wall  55  around an induction coil  4 . Before flowing through the discharge line  21  the fluid is guided through an inner pipeline  6 . The inner pipe line  6  is surrounded by the induction coil  4 . The second wall  13  has a ferromagnetic wall  5 . The coil encasing wall  55  may comprise ferromagnetic material, but this is not necessary as will be explained hereafter. Ferromagnetic wall  5  serves as a shield protecting the environment against the impact of the electromagnetic flux. At the same time a part of the magnetic flux produced by the induction coil  4  may produce eddy currents in portions of the ferromagnetic wall  5  which portions comprise ferromagnetic material. In this embodiment the ferromagnetic wall  5  combines the electromagnetic shielding function with the possibility of heating the fluid which flows through the channel  2  of heater  1 . 
         [0026]    While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. 
         [0027]    Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. Devices, elements and components, known per se, have not been described in detail, as the skilled person is familiar with the matter. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single mechanism or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.