Abstract:
A method and steam generator includes a steam generator container having a heated wall surface, an inlet for a liquid and an outlet for removing the vaporized liquid or steam, a rotor, which is mounted for rotation in the container and causes a rotational flow of the liquid outwardly against the heated wall to cause vaporization. During rotation of the rotor, outer edges of the blades of the rotor contact the wall surface to either abrade or wipe deposits, such as lime, from the wall surface.

Description:
BACKGROUND OF THE INVENTION 
     The invention is directed to a method for generating steam, particularly for a cooking device, whereby a liquid within a steam generating vessel is caused to boil by a method of heating at least one heatable wall surface of the steam generating vessel, placing the liquid into rotation while being heated and pressing the liquid against the heatable wall surface due to centrifugal forces due to the rotation, allowing the steam arising due to a vaporization of at least a part of the liquid to escape from the steam generating vessel through a steam outlet and separating drops of the liquid entrained with the steam from the steam. The invention is also directed to an apparatus for generating steam, particularly for a cooking device, which apparatus comprises a steam generating vessel that can be at least partially filled with a liquid via an admission or inlet and from which steam can proceed to a steam outlet, and has a heating device for heating the liquid in the steam generating vessel for the purpose of generating steam. 
     Traditional steam generators as particularly employed in cooking devices usually comprise a boiler that is partially filled with water that is brought to a boil with heating elements. The space requirement of such a steam generator is mainly defined by two factors, which are the volume part that is filled with liquid water and the volume part of the gas space located above the water. 
     The first volume part is thereby limited by the size of the heating elements and the space required between the heating elements for the flooding thereof and for carrying off the steam bubbles. The size of the heating elements for a prescribed heating capacity is in turn defined by the Leidenfrost effect, in accord wherewith a specific surface power density of a heating element dare not be exceeded when heating a vaporizable liquid since a closed intermediate steam layer that impedes the heat emission otherwise forms between the surface of the heating element and the liquid. The Leidenfrost effect is nicely demonstrated in the phenomenon that drops of water do not immediately vaporize on a red-hot plate but first move in a quasi dancing motion since, carried by a steam layer that is formed, they move irregularly on the plate. 
     The second volume part is required in order to separate the steam from entrained drops of water. The size and design of the second volume part, i.e. of the gas space above the liquid, are critical for the quality of the steam. The steam quality is particularly determined by the size of the water surface that the stream of steam must pass. The emerging steam, namely, entrains all the more water the larger the stream of steam is per water surface. 
     Given traditional steam generators, thus, a high space requirements derives overall from the above considerations when a high steam quality is to be produced. Additionally, however, it must also be pointed out that the time required to make a known, water-filled steam generator operational is also dependent on the amount of water filled in that is required for reliably covering the heating elements, and this, in turn, makes demands of the size of the steam generator. 
     Steam generators wherein a rotational flow is induced in a steam-generating liquid by injecting a further liquid are known in the field of power plants, particularly nuclear power plants. The centrifugal forces accompanying the rotational flow are thereby used for the precipitation of contaminants, as disclosed by U.S. Pat No. 4,972,804 or, respectively, DE 690 13 906 T2. 
     Steam generators are also known wherein the entire tubular or barrel-shaped steam generator vessel is placed into rotation. This involves high energy and cost outlays and requires a great structural complexity that makes a rotating bearing of the steam generating vessel necessary, whereby an admission or, respectively, discharge of liquid is necessarily only practical via the axis of rotation. DE 2 214 566, for example, discloses such a rotating steam generator that is designed for the vaporization of organic drive fluids in a closed circulation of a Rankine motor. The steam generator disclosed by German Letters Patent 904 653 works similarly and this, however, additionally comprises a regulation for the supply of liquid for the purpose of creating a liquid ring having a specific thickness. 
     DE 27 57 913 A1 discloses a rotating steam generator with a rotatably seated boiler that structurally foregoes rotatable lead-throughs for the introduction or, respectively, removal of a liquid work medium. 
     DE 37 83 361 T2 discloses a tandem separator for a steam/water mixture, whereby helically coiled baffles place the steam/water mixture into rotation. 
     DE 692 07 830 T2 discloses a steam generator arrangement for ovens wherein thin water jets or, respectively, small drops of water, which are placed into rotation, descend onto a heating device in order to be vaporized. 
     The known steam generators, however, do not work satisfactorily for the vaporization of tap water but exhibit the serious disadvantage that the dissolved minerals which are contained in the tap water, particularly lime, will deposit at the walls and built-in parts of the steam generator. This can lead to the outage of or damage to the steam generator, which can usually only be prevented by a regular chemical decalcification. The post-operation maintenance jobs that become necessary as a result thereof are in turn cost-intensive. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to develop a method of the species as well as the apparatus of the species for generating steam such that the disadvantages of the Prior Art are overcome in that, in particular, small steam generators for outputting high-quality steam can be offered that are also quickly operational, cost-beneficial, flexibly heatable and dependable without tending toward defervescences and without requiring a regular decalcification. 
     The object of the invention is achieved in that the liquid is placed into rotation by at least one first rotor that is rotatably seated in the steam generating vessel. 
     It is thereby inventively proposed that the centrifugal forces of the liquid and/or of the steam are higher than the gravitational forces of the liquid and/or of the steam. 
     It can also be provided in the region wherein the drops of liquid are separated that the liquid and the steam are at least partially forced against at least one diaphragm, so that potential eddies are at least partially generated in the liquid and/or the steam and/or no heating of the heatable wall of the vessel occurs. 
     It is inventively proposed that contaminants of the liquid are eliminated in that the liquid is forced against at least one diaphragm. 
     It is also proposed that the liquid is supplied into the vessel with a minimum velocity, preferably directed onto the heatable wall surface and/or onto the first rotor. 
     Alternatively, it is proposed that the filling level of the vessel is identified, preferably from outside the vessel, by measuring a centrifugal force-induced pressure against at least one wall surface of the vessel. 
     An inventive method is characterized in that liquid condensed and/or vaporized in the steam escaping from the steam generating vessel is placed into rotation by a second rotor in at least one further or additional liquid separation vessel following the steam generating vessel, and any condensate is separated and discharged from the liquid separation vessel, and is preferably resupplied to the steam generating vessel. 
     It can thereby be provided that the first rotor in the steam generating vessel and the second rotor in the liquid separation vessel are placed in rotation via a motor, preferably via the rotational axis. 
     It is also provided that the steam is at least partially supplied to the steam outlet through a pipe arranged in the steam generating vessel, preferably in the form of a hollow shaft in communication with the rotor or, respectively, rotors. 
     It can be preferably provided that at least one of the first and the second rotor comprises an at least regionally abradant contact with the wall surface or deposits on the wall surface of the steam generating vessel or, respectively, liquid separation vessel at least during the rotation, and at least partially strips the deposits, particularly in the form of lime incrustations, from the wall surface. 
     It can thereby be provided that the distance between the first and/or second rotor and the appertaining wall surface is dimensioned so slight that a deposit being formed, particularly a lime incrustation, is eroded upon rotation of the first or, respectively, second rotor. 
     It is also proposed that the first and/or second rotor comprises or, respectively, comprise no contact with the corresponding wall surface in the idle condition and is pressed at least regionally in the direction of the corresponding wall surface due to centrifugal forces upon rotation. 
     It is also proposed that the wall surface and/or the rotor is or, respectively, are dry-heated after an operating phase and/or a wetting with liquid given rotating and/or idle rotor, whereby an adhesion of the rotor to the wall surface due to deposits is prevented. 
     It is also inventively proposed that the steam generating vessel empties, preferably automatically, in the idle condition of the first rotor, particularly via a vapor-tight waste water drain. 
     It can preferably be provided that the admission or inlet is made of a flexible material and is deformed by the pressure of the incoming fluid in order to at least partially strip deposits from the inlet. 
     Among other things, it is inventively proposed that the admission is cooled by a liquid stream that is continuously maintained via a control and/or regulating device, whereby the liquid is taken from a reservoir and/or from a feed conduit, and deposits are at least regionally prevented. 
     The invention is also directed to an apparatus for generating steam that is characterized by a first rotor in the steam generating vessel via which at least the liquid can be placed into rotation. 
     It is thereby provided that the vessel comprises two ends lying opposite one another, whereby the inlet and the steam outlet are either both arranged at one end or each is arranged at a different end. 
     It is also proposed that the steam generating vessel is rotationally symmetrical around an axis, preferably essentially tubularly, or is conically expanded from the inlet to the steam outlet. 
     An inventive apparatus can also be characterized in that the axis of the steam generating container coincides with the rotational axis of the first rotor, whereby the rotational axis preferably proceeds essentially parallel to the direction of the gravitational force. 
     It is also proposed that the heating device works with electrical heating coils, a gas burner, a heat exchanger, electrical induction, thermal radiation, direct or indirect flame charging, thick-film heating or an electrically conductive ceramic as material of the heatable wall surface of the steam generating vessel, whereby the outer surface of the steam generating vessel is enlarged, preferably by ribs, embossing and/or coils and/or the flow velocity of the combustion gas is increased. 
     The inventive apparatus is also characterized by at least one diaphragm for the elimination of drops of liquid entrained by the steam and/or contaminants in the liquid. 
     It is thereby also proposed that a first diaphragm is arranged downstream of the inlet and/or a second diaphragm is arranged upstream of the outlet. 
     An inventive apparatus can also be characterized by an opening for a preferably automatic emptying of the liquid given standstill of the rotor and/or by a third diaphragm in the region of the steam generating vessel with the least gravitation potential, whereby the opening is closed during rotation by a closure mechanism that preferably comprises a siphon trap. 
     It is also proposed that the first rotor can be driven by a motor via a shaft, whereby the shaft is, in particular, a hollow shaft with radial bores and/or slots that are arranged along the long side of the hollow shaft in order to enable a steam transfer from the steam generating vessel to the steam outlet. 
     Further, an inventive apparatus can be characterized by a liquid separation vessel between the steam generating vessel and the steam outlet, whereby a liquid return preferably proceeds from the liquid separation vessel to the steam generating vessel. 
     It can thereby be provided that a second rotor is rotatable in the liquid separation vessel, and is preferably mechanically coupled to the first rotor. 
     It can also be inventively provided that the first and/or the second rotor comprises a stripper device that strips deposits from at least regions of a wall surface of the steam generator vessel or, respectively, liquid separation vessel during rotation. 
     It can thereby be provided that the stripper device comprises brushes, lamellae, fringes and/or lips, which are preferably composed of foodstuff-fast, heat resistant material. 
     It is also proposed that the stripper device comprises a material reinforcement at least regionally at its side lying closest to the wall surface during rotation. 
     It is preferably inventively proposed that the stripper device comprises no contact with the wall surfaces in its idle condition but does upon rotation, preferably via employment of at least one spring system. 
     It can also be provided that the first and/or second rotor is or, respectively, are fashioned spirally, helically and/or star-shaped in the form of a paddle, which preferably has two paddle halves. 
     Finally, it is proposed that the rotor itself is implemented flexible, preferably in the form of brushes, lamellae, fringes and/or lips and exhibits no contact with the wall in its idle condition. 
     In that the invention is the first to have undertaken the step of rotating the built-in parts of the steam generating vessel instead of the steam generating vessel itself, the following advantages have, in particular, been achieved:
         i) recusation of the mass moment of inertia, as a result whereof the energy requirement is reduced at the same time, response times are shortened, control times are shortened, bearing forces are reduced and balancing problems are reduced; and   ii) simplification of the structure, for example by simplifying the installation and contacting of a heating device, as well as avoiding structurally complicated structures of a type that are standard given rotating outside vessels in order, among other things, to avoid rotatably implemented leads.       

     Overall, thus, the manufacturing and maintenance costs are reduced given a simultaneous enhancement of the use time. 
     Developments according to the invention are also based on the surprising perception that involved and cost-intensive maintenance work for decalcification at the steam generators becomes superfluous and that a maximum heat transfer from the walls to the liquid remains is assured during operation because the inside, rotating units function, so to speak, as a stripper device with which the deposits at the walls are instantaneously abraded during operation, i.e. during rotation. 
     Further features and advantages of the invention derive from the following description wherein three exemplary embodiments of the inventive apparatus are explained in detail on the basis of schematic drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view through a first embodiment with rotor at rest; 
         FIG. 2  is a cross-sectional view through a second embodiment with rotor at rest; and 
         FIG. 3  is a cross-sectional view through a third embodiment with rotor at rest. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As can be derived from  FIG. 1 , an inventive steam generator  1   a  comprises a steam generating vessel in the form of a tubular boiler  2  with an admission or inlet in the form of a water inlet  3  and a steam outlet  4  at the upper end of the boiler  2 , a diaphragm  5 , which diaphragm separates the boiler  2  from the steam outlet  4 , for condensate and contaminant separation, heating elements  6  in the form of a thick-film heater surrounding the tubular boiler  2 , and a rotor in the form of a paddle  8  rotatable around a rotational axis  7  that coincides with the longitudinal axis of the boiler  2 . The paddle  8  is seated with two bearings  9  and is driven with a motor  11  via a clutch  14 , which is intended to compensate for adjustment errors, and a shaft  13 . The paddle  8  comprises two paddle halves  8   a , which have respective long paddle sides or edges  8   b  neighboring the wall surface  12  of the boiler  2 , a recess  15  in the region of the diaphragm  5  and an impact disk  16  in order to generate a potential eddy in front of the diaphragm  5 . A waste water drain  17  is located at the lower end of the boiler  2 , and it has a collar  18  in order to avoid water losses due to flowing in a boundary layer. The waste water drain  17  is closed only with a siphon trap  19  in order to avoid steam losses, so that the boiler  2  automatically empties given standstill of the paddle  8 . 
     With the steam generator  1   a  described with reference to  FIG. 1 , water is supplied to the boiler  2  via the water inlet  3  and is placed in rotation by the paddle  8 , which is rotating around the rotational axis  7  in order to force the water against the wall surface  12  of the boiler  2 , which is heated via the heating elements  6 , and leads to a fast and uniform heating of the water. At the same time, the paddle halves  8   a  that are held in their idle position shown in  FIG. 1  by springs (not shown) and at whose long sides  8   b  fine, flexible lips (not shown) are located are pressed against the wall surface  12  of the boiler  2  due to the rotation. The pressing power is thereby dimensioned such that the lips wipe the wall surface  12  only lightly. Salt deposits, particularly lime incrustations, are thereby avoided. In addition, the long sides  8   b  can comprise reinforcements in order to achieve an optimally long-lasting stripping effect given low wear or with a flexible design of the rotor of the stripper device, the ends of the elastic lips of the sides  8   b  can be reinforced in order to increase the pressing power against the wall surface  12  during the rotation. Via the diaphragm  5 , moreover, both contaminants of the water as well as drops of water entrained with the generated steam, which are forced against the wall surface  12  of the tubular boiler  2  due to the rotation of the paddle  8 , are prevented from emerging from the steam outlet  4  together with the steam. 
     The geometry at the diaphragm passage or opening can be designed for enhancing the separation rate of the steam and the liquid so that a potential eddy that can be reinforced by the preceding impact disk  16  is induced. 
     Despite the counter-measures, an entrainment of drops of water due to high flow velocities can nonetheless occur given a small diameter of the boiler  2 . In the embodiment of the inventive steam generator  1   b  described in  FIG. 2 , the boiler  2  is therefore followed by a water separation chamber  20  that again separates entrained water from the steam and that is limited by a second diaphragm  21  with an opening. A second paddle  22  rotates in this water separation chamber  20 , which paddle  22  is driven by the same shaft  13  as the paddle  8  and likewise has a recess  23  and an impact disk  24  in order to generate a potential eddy. The drops of water separated from the steam due to the rotation generated by the paddle  22  are returned into the boiler  2  via a water return  25  in the form of a tube or hose conduit. All other components of the inventive steam generator  1   b  according to  FIG. 2  correspond to the inventive steam generator  1   a  according to FIG.  1 . 
       FIG. 3  shows another inventive steam generator  1   c  wherein additional measures are implemented in order to reduce the water entrainment given a small boiler diameter, and identical components of this generator are provided with identical reference characters. Here, the paddle  8  is driven by a hollow shaft  26  that simultaneously serves the purpose of conducting the generated steam out of the boiler  2 . In order to move the steam into the inside of the hollow shaft  26 , the latter must be provided with radial bores or slots  29   a  over its entire moistened length in the vaporizer space, i.e. the boiler  2 . The diameters or density of the bores or slots  29   a  are varied in axial direction so that the flow-conditioned pressure drop in the hollow shaft  26  is compensated and, thus, the flow component in the direction of the rotational axis  7  in the boiler  2  outside the hollow shaft  26  is minimized, as is the entrainment of water at the same time. Outside the boiler  2 , the steam can in turn be coupled out, for example, through further radial bores  29   b  in the hollow shaft  26  or through an axial opening (not shown) at the end of the shaft  26 . 
     The shaft  26  is seated at the lower end of the boiler  2 , whereby it can taper into a correspondingly thinner, solid shaft. At the upper end of the boiler  2 , the hollow shaft  26  is conducted out of the boiler  2  through a seal or a vapor-tight bearing  27  into a steam discharge chamber  28  lying thereabove. In this steam discharge chamber  28  above the boiler  2 , the hollow shaft  26  has the bores  29   b  in order to allow the generated steam to emerge in turn and be supplied to the steam outlet  4 . The hollow shaft  26  is in turn conducted out at the other end of the steam discharge chamber  28  with a seal or vapor-tight bearing  27 ′, and the hollow shaft  26  can merge into a thinner, solid shaft in or above the steam discharge chamber  28 . Above the steam discharge chamber  28 , the hollow shaft  26  is coupled to the motor  11  via a clutch  14  for compensating alignment errors between the motor shaft and the hollow shaft  26 . 
     Additionally, the filling level of the steam generator  1   a ,  1   b  or  1   c  can be acquired by measuring a centrifugal force-induced pressure at the outside walls of the boiler  2 . 
     A decalcification of an inventive steam generator  1   a ,  1   b  or  1   c  is effected by the flexible lips at the long paddle sides  8   b  of the paddle halves  8   a  that continuously erode the deposits from the outside wall during operation. The lips themselves do not thereby wear significantly since they themselves calcify in the region of immersion into the water film and it is thus mainly lime scraping against lime. However, an excessive amount of lime can also not collect at the paddle  8  since this is driven outward by the centrifugal force and is ultimately scraped off thereat. The lime meal that occurs must merely be removed from the boiler by being regularly rinsed or, respectively, by changing the water. The employment of flexible lips as stripper device or the flexible design of the rotor in and of itself yields the advantage that no adhesion of the rotor to the wall surface  12  can occur in the idle condition due to potentially existing deposits since the centrifugal force upon rotation produces the contact of the rotor or the stripper device with the wall surface  12 . In order to enable an automatic emptying, the lower end of the boiler  2  can be provided with an additional diaphragm or a closure mechanism (not shown). The diaphragm  5  can thereby be combined with just such a diaphragm upstream of the steam outlet  4 . 
     Both individually as well as in arbitrary combination, the features of the invention disclosed in the above specification, in the claims as well as in the drawings can be critical for realizing the various embodiments of the invention.