Abstract:
Devices for heating liquids have been known for a long time. The applications of these devices can also be of very diverse nature. Such heating devices are thus for instance already applied on a large scale as, or applied as component in, water kettles, dishwashers, washing machines, coffee-making machines, shower water heaters and the like. The invention relates to a device for heating liquids. The invention also relates to a base structure for use in such a device. The invention further relates to a method for heating liquids.

Description:
BACKGROUND OF THE INVENTION 
   1) Field of the Invention 
   The invention relates to a device for heating liquids. The invention also relates to a base structure for use in such a device. The invention further relates to a method for heating liquids. 
   2) Description of the Related Art 
   The device stated in the preamble has already been known for a long time. The applications of this device can also be of very diverse nature. Such heating devices are thus for instance already applied on a large scale as, or applied as component in, water kettles, dishwashers, washing machines, coffee-making machines, shower water heaters and the like. In for instance coffee-makers the device is adapted in particular for instant supply of heated water. For this purpose such a device is usually provided with a tubular body adapted for throughflow of a liquid for heating. During flow through the tubular body the liquid is heated by a heating element positioned on the tubular body or, conversely, close to the tubular body. Such a method of heating liquids has a number of drawbacks. A significant drawback of the known device is that heating of the liquid takes place with relative difficulty, among other reasons because of the relatively disadvantageous (low) surface to volume ratio. The tube length will therefore generally have to be relatively great to enable a desired heating result to be realized. Application of a relatively long tubular body generally results in a relatively long length of stay of the liquid in the device, required to allow the liquid to be heated sufficiently and as desired. It will therefore usually take a relatively long time before the heated water can be available to a user. The heating of the liquid will furthermore take place with relative difficulty due to the relatively inefficient heat transfer from the heating element, via the tubular body, to the liquid for heating, which also has an (adverse) effect on the relatively slow heating of the liquid. In addition, the cost of manufacturing the known device and for the use of the device (because of the relatively inefficient heating) is relatively high. 
   SUMMARY OF THE INVENTION 
   The invention has for its object to provide an improved device for heating liquids, with which a liquid can be heated in relatively efficient and rapid manner. 
   The invention provides for this purpose a device comprising a base structure and at least one heating element connected to the base structure, wherein at least one non-linear channel structure is arranged between the base structure and the heating element for throughflow of a liquid for heating, wherein the device comprises bias-generating means to enable the base structure to connect under bias to the heating element. Application of the bias-generating means will press the base structure under bias against the heating element, whereby the formation of gaps between the heating element and the base structure can thus be prevented, as a result of which permanent connection of the strip to the heating element is enabled and de facto compensation for deformation of the heating element is allowed. The bias can herein be realized by bias-generating means, such as for instance a diaphragm spring. A diaphragm spring is particularly advantageous here in enabling a homogeneously distributed bias to be realized. The channel structure is in fact bounded and formed here by both the base structure and the heating element. Heat can thus be transferred directly—without interposing another element—and therefore relatively efficiently from the heating element to the liquid for heating. Particularly in the case where liquid is driven through the channel structure at relatively high speed, a relatively efficient and rapid heat transfer per unit of volume of liquid can be achieved per unit of time. An additional advantage here is that precipitate, such as for instance limescale, cannot be deposited in the channel structure, or at least hardly so, as a result of the relatively high flow speed, which results in a relatively low-maintenance device. Because the channel structure does not take a linear form, the contact surface between the heating element and the liquid for heating situated in the channel structure can be maximized, which, in addition to a relatively rapid heating of the liquid to a desired temperature, also results in a relatively compact device for rapid and efficient heating of liquids. Furthermore, application of the device according to the invention functioning in energetically advantageous manner generally results in a cost saving. By applying the channel structure arranged between the base structure and the heating element, the surface area to volume ratio of the channel structure can moreover be maximized in relatively simple manner by for instance giving the channel or the channels of the channel structure a relatively flow (shallow) form, whereby the channel structure only acquires a limited volume, which can considerably improve the temperature increase of the liquid for heating per unit of time. The throughput time of the liquid through the device can be reduced considerably by the significantly improved heating of the liquid per unit of time, whereby the user can dispose of the heated liquid relatively quickly. The liquid can herein be guided through the channel structure at a flow rate of up to several meters per second, preferably between 1 and 3 meters per second. Such a relatively high flow rate is particularly advantageous in that vapour bubbles which may form in the channel structure are generally flushed immediately out of the device. Such a relatively high flow rate furthermore prevents deposition of contaminants, such as lime and the like, on the heating element and/or the base structure. The deposition of contaminants on the heating element is particularly adverse for the heat transfer from the heating element to the liquid for heating. It is noted that the non-linear channel structure is provided with one or more, optionally mutually parallel, non-linear channels, wherein the liquid for heating runs through a non-linear two-dimensional or three-dimensional route. It is however very well possible here to envisage parts of channel structure nevertheless taking a linear form, but wherein the liquid runs through the device via a labyrinthine route. 
   In a preferred embodiment, at least a part of the channel structure is arranged recessed into an outer surface of the base structure. The channel structure can already be arranged in the base structure beforehand during manufacture of the base structure, but can also be arranged in the base structure at a later stage. The base structure is generally formed here by a plastic and/or metal carrier layer, in which one or more non-linear channels are arranged. The channel structure can be arranged as cavity in the base structure. In another preferred embodiment, at least a part of the channel structure is arranged recessed into the heating element. Such a preferred embodiment is advantageous in that the contact surface between the heating element and the liquid for heating can thus be increased, which will generally result in a more intensive and more rapid heating. It is also possible to envisage arranging the channel structure in the base structure as cavity pattern, wherein the heating element is provided with a counter-cavity pattern connecting onto the cavity pattern. 
   The heating element preferably has a substantially plate-like form. Plate-like heating elements are already known commercially and are generally relatively cheap to manufacture. From a structural viewpoint it is moreover usually advantageous to apply a flat heating element. The heating element is then generally formed by an electric heating element which is preferably provided on a side remote from the channel structure with a track-like thick film for forced conduction of electric current so as to enable generation of a desired heat. 
   In another preferred embodiment, the channel length of the channel structure lies between 0.3 and 7 meters, in particular between 0.5 and 5 meters, and is more preferably substantially 2 meters. Such a length is generally sufficient to heat liquid such as water, oil, etc. from room temperature to a temperature of more than 90 degrees Celsius. Since the channel structure has a non-linear form, the volume taken up by the channel structure will be relatively limited, which enhances handling of the device according to the invention. 
   In yet another preferred embodiment, the cross-section of the channel structure has a surface area which lies between 1 and 100 mm 2 , in particular between 2 and 50 mm 2 . The exact area generally depends on the specific application of the device. A device for heating water for making tea or coffee thus preferably has a cross-section of between 2 and 5 mm 2 . For heating water which can then be drawn via a tap, usually a shower tap or bath tap, a channel structure with a cross-section of between 10 and 60 mm 2  is preferably applied. The same cross-section can for instance also be applied for heating frying oil. 
   The non-linear channel structure preferably has an at least partly angular form. By arranging one or more angles in the channel structure a two-dimensional or optionally three-dimensional flow progression of the liquid for heating can be realized. The liquid can thus be guided relatively efficiently along the (relatively compact) heating element to thus be heated to a required temperature. In another preferred embodiment, the channel structure has an at least partly curved form. Liquid can for instance also be heated to a required temperature in relatively compact and intensive manner by giving the channel structure a substantially spiral form. The base structure preferably takes an at least partly flexible form, wherein in particular a side of the base structure directed toward the heating element preferably takes a flexible, in particular elastic, form. For this purpose the base structure is preferably at least partly manufactured from an elastic material, in particular an elastomer. In an alternative preferred embodiment, the base structure comprises a composite strip of a metal band and a thermally insulating layer connected to the metal band, wherein the strip in spirally wound state does in fact form the channel structure. For this purpose the height of the metal band is preferably greater than the height of the insulating layer. The insulating layer is preferably formed by vulcanized rubber in order to also enable generation of a medium-tight sealing of the channel structure in addition to a thermal insulation. The thermally insulating layer is preferably manufactured from an elastomer. The thermally conductive metal band can for instance be formed from strip steel. A channel structure with a cross-section of 2×2 millimeters can for instance be formed by rolling up a composite strip of strip steel with a height of 6 millimeters and a thickness of about 0.6 millimeters, which has adhered thereto vulcanized rubber material with a height of 4 millimeters and a thickness of 2 millimeters. In an alternative embodiment, the composite strip can also be an integrated construction of a relatively high strip part and an adjacent relatively low strip part. 
   Although the metal strip is generally relatively rigid, the wound composite strip nevertheless has a certain flexibility in that mutually adjoining strip parts of the strip can slide relative to each other. Such a flexible character is particularly advantageous in making it possible to compensate (considerable) deformations of the heating element and height differences resulting therefrom during heating of the heating element, wherein the strip can connect to the heating element in reliable and medium-tight manner irrespective of the degree of deformation of the heating element, whereby leakage from the device of liquid and evaporation gases originating therefrom can be prevented. In order to enable permanent connection of the strip to the heating element and to allow for de facto compensation for deformation of the heating element, the base structure, in particular the strip, is pressed under bias against the heating element, whereby the formation of gaps between the heating element and the base structure can thus be prevented. The bias can herein be realized by bias-generating means, such as for instance a diaphragm spring. A diaphragm spring is particularly advantageous here in enabling a homogeneously distributed bias to be realized. 
   In yet another preferred embodiment, the base structure is formed by a plurality of separate, mutually connected base modules. The base modules can herein be of very diverse nature and can for instance be formed by partitions held at a mutual distance by spacers, wherein the relative orientation of the base modules determines the channel structure. 
   The device is preferably provided with a pump for pumping the liquid for heating under pressure through the channel structure. Because liquid can be heated relatively rapidly, intensively and efficiently using the device according to the invention, the liquid flow rate through the channel structure can be increased, on the one hand to prevent too intensive a heating of the liquid and on the other to increase the capacity of the device. The pump flow rate of the pump, i.e. the number of units of volume of liquid per unit of time, can preferably be regulated. It can be advantageous to regulate the pump flow rate so as to be able to satisfy the user need in relatively simple manner. If a large quantity of liquid is for instance required, the pump flow rate can be increased (temporarily) to enable the requirement of the user to be met relatively quickly. In a particular preferred embodiment, the device is provided with sensor means coupled to the pump to enable regulation of the pump flow rate subject to the liquid temperature in the channel structure. The sensor means are herein preferably positioned before the device in order to measure the temperature of the relatively cold liquid. Together with a desired end temperature of the liquid and the heat-transferring capacity of the heating element, the most ideal pump flow rate can thus be calculated and applied without delay occurring in the heating system, this latter in contrast to the situation in which the sensor means are positioned after the device and are adapted for detect the temperature of the heated liquid. By adjusting the pump flow rate it is for instance possible to prevent the liquid becoming overheated in the channel structure. When one or more critical temperatures are exceeded, the pump flow rate can be increased to prevent overheating. In the case that the liquid temperature in the channel structure is relatively low—if the heating element has for instance just been switched on—the pump flow rate can be (temporarily) reduced in order to increase to some extent the length of stay of the liquid in the channel structure, whereby an improved heating of the liquid can be achieved. 
   In a preferred embodiment, the heating element is displaceable relative to the base structure (and vice versa) between a (closed) position connecting to the channel structure and an (opened) position situated at least partially at a distance from the channel structure. The usual position will generally be formed by the position in which the heating element connects to the base structure, and thus in fact bounds the channel structure. The liquid for heating is then guided along the heating element via the channel structure and thus heated. Evaporation of the liquid in the channel structure can be prevented or at least be countered, by guiding the liquid under (some) pressure through the channel structure. In the opened position, in which the heating element lies at least partially at a distance from the channel structure (and thereby the base structure), the liquid guided in the device will no longer be guided only via the channel structure but, as a result of evaporation, will spread in a bounded evaporation chamber or steam chamber—which is relatively voluminous relative to the volume of the channel structure—formed by the heating element and the base structure, whereby vapour, usually steam, will form. It is therefore possible to generate a heated liquid as well as steam by means of a single heating element. The change in the relative orientation between the heating element and the base structure preferably takes place electromechanically, pneumatically, hydraulically or manually. In order to enable the change in orientation between the heating element and the base structure, the heating element can take a form which is pivotable or integrally displaceable in optionally vertical manner relative to the base structure. It is noted that the opened position can also be advantageous in the case of maintenance operations, due to the improved accessibility of both the heating element and the base structure, including the channel structure. In a particular preferred embodiment, the pump is coupled to the heating element and/or the base structure in order to change the relative orientation of the heating element and the base structure. In addition to supplying liquid under pressure to the base structure, the pump is thus also adapted to displace the heating element and the base structure relative to each other as required. 
   The invention also relates to a base structure for use in such a device. 
   The invention further relates to a method for heating liquids using such a device, comprising the steps of: a) activating the heating element, and b) guiding a liquid for heating through a passage formed between the heating element and the base structure. The passage will usually be formed by the channel structure. However, as already described in the foregoing, it is also possible to place the heating element at least partially at a distance from the channel structure, whereby the volume of the passage through which flow takes place can be increased and vapour formation (steam formation) is thus made possible. The outlet opening for the generated voluminous steam will in that case usually be larger than the outlet opening for heated liquid so as to prevent obstructions during discharge of the generated steam from the device. While step b) is being performed the liquid for heating will however preferably be guided along the heating element in order to be able to ensure sufficient heating of the liquid. Guiding of the liquid for heating along the heating element via the channel structure as according to step b) preferably takes place under increased pressure. This increased pressure can vary from atmospheric pressure to higher pressures up to about 10 bar. Further advantages of the method according to the invention have already been described at length in the foregoing. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be elucidated on the basis of non-limitative exemplary embodiments shown in the following figures. Herein: 
       FIG. 1  shows a partly cut-away perspective view of a first embodiment of the device according to the invention, 
       FIG. 2   a  shows a partly cut-away top view of a second embodiment of the device according to the invention, 
       FIG. 2   b  shows a cross-section along line A-A as indicated in  FIG. 2   a,    
       FIG. 2   c  shows a cross-section along line B-B as indicated in  FIG. 2   a,    
       FIG. 3   a  shows a cross-section of a third embodiment of the device according to the invention, 
       FIG. 3   b  shows a cross-section along line C-C as indicated in  FIG. 3   a,    
       FIG. 3   c  shows a detail E as indicated in  FIG. 3   b,    
       FIG. 4  is a schematic representation of another embodiment of the device according to the invention, 
       FIG. 5   a  shows a partly cut-away top view of a fifth embodiment of the device according to the invention, 
       FIG. 5   b  shows a cross-section along line E-E as indicated in  FIG. 5   a,    
       FIG. 6  is a perspective view of a sixth embodiment of the device according to the invention, 
       FIG. 7   a  is a partly cut-away top view of a seventh embodiment of the device according to the invention, 
       FIG. 7   b  shows a cross-section of the device in a closed position along line F-F as indicated in  FIG. 7   a,    
       FIG. 7   c  shows a cross-section of the device in an opened position along line F-F as indicated in  FIG. 7   a,    
       FIG. 8   a  shows a cross-section of an eighth embodiment of the device according to the invention, 
       FIG. 8   b  shows a cross-section of the device in a closed position along line G-G as indicated in  FIG. 8   a , and 
       FIG. 8   c  shows a cross-section of the device in an opened position along line G-G as indicated in  FIG. 8   a.    
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows a partly cut-away perspective view of a device  1  according to the invention. Device  1  comprises a base structure  2  and a heating element  4  connecting thereto in substantially medium-tight manner. Heating element  4  and base structure  2  are clamped together by means of clamping means (not shown). Arranged between base structure  2  and heating element  4 , and in particular in an upper surface of base structure  2 , is a non-linear channel structure  3  for guiding a liquid for heating along heating element  4 . The liquid for heating is pumped into channel structure  3  via a feed opening  5  and, after heating, exits channel structure  3  via an outlet opening  6 .  FIG. 1  shows that channel structure  3  takes a zig-zag form and is furthermore provided with a plurality of angular transitions from the one linear channel part to the adjacent linear channel part. It will be apparent that the length of the channel structure comprises a multiple of the length of the heating element due to this angular, non-linear form, whereby liquid can be heated in relatively efficient and intensive manner. 
     FIG. 2   a  shows a partly cut-away top view of a second embodiment of device  7  according to the invention. Device  7  comprises a base structure  14  and a heating element  9  connecting thereto.  FIG. 2   a  shows that a sealing element  15  is provided for the purpose of a medium-tight seal between heating element  9  and base structure  14 . A thermo-resistant rubber O-ring can for instance be used as sealing element. Heating element  9  and base structure  14  are clamped together by means of clamping means (not shown). A plurality of guide elements  10 ,  11  are arranged in a recess in base structure  14  such that guide elements  10 ,  11  together form a flow route  12  for liquid. The liquid for heating is fed to flow route  12  via feed opening  8  and, after being heated by the heating element, is discharged via outlet opening  16 . 
     FIGS. 2   b  and  2   c  show cross-sections along line A-A and B-B respectively, which are indicated in  FIG. 2   a . Flow route  12  is in fact formed by the different dimensions of guide elements  10  and  11  placed adjacently of each other in the recess of base structure  14 . This is achieved in that the width of guide element  10  is smaller than the width of the recess in base structure  14 , and in that the height of guide element  11  is smaller than the height of the recess in base structure  14 . By positioning the space in the width of the guide element  10  alternately on the one and on the other side of the recess in the base structure, the spaces situated above guide element  11 , on either side of guide element  10 , are mutually connected. A zig-zag-shaped flow route  12  is thus obtained, wherein the liquid for heating flows substantially in a direction transversely of the longitudinal direction of heating element  9 . Guide elements  10  and  11  are herein preferably connected to each other by means of a connecting element  13 , which connecting element  13  can for instance be formed by a rubber cord. In order to bring about a substantially medium-tight connection of guide elements  10 ,  11  to heating element  9 , guide elements  10 ,  11  are placed on elastic elements  17 . 
     FIG. 3   a  shows a cross-section of a third embodiment of a device  18  according to the invention. This cross-section represents a view along line D-D as shown in  FIG. 3   b . Device  18  comprises a base structure  71  and a heating element  23  connecting to base structure  71 . Base structure  71  herein forms a spiral channel  20  for liquid for heating which is opened on one side. In the shown exemplary embodiment the channel  20  is however sealed medium-tightly by the adjacent heating element  23 . In order to have base structure  71  connect to heating element  23  in stable, reliable and medium-tight manner, device  18  comprises a pressing element  24 , in particular a diaphragm spring, for pressing base structure  71  under bias onto the heating element in order to enable a reliable sealing of spiral-shaped channel  20  to be realized. Base structure  71  is in fact constructed from a metal wound in a spiral shape, in particular strip steel, or plastic strip  25 , and an adjacent insulating (rubber) strip  26  connected to this plate. In the wound-up situation of base structure  71  the base structure has a certain flexibility, despite the generally rigid character of band  25 , since mutually adjacent parts of base structure  71  are mutually displaceable, which is particularly advantageous when heating element  23  deforms as a result of heating of heating element  23 . In this manner a permanent and medium-tight sealing of channel  20  can be guaranteed, wherein deformations of device  18 , in particular of heating element  23 , can be compensated relatively easily and effectively. A seal (not shown) can be applied to prevent possible flow of liquid out of channel  20  and along pressing element  24 . An annular seal  21  adapted to clamp heating element  23  connects heating element  23  to device  18  and holds it in position relative to channel  20  and thereby pressing element  24 . As already noted, pressing element  24  is preferably manufactured from a resilient material, such as a diaphragm spring, so that base structure  71  connects fully and permanently to heating element  23  despite possible variations in the flatness of heating element  23 . Such elements in any case generally have a slightly concave shape in respect of the desired compression strength thereof. Channel  20  is open on one side and is adapted to be fully covered by the plate-like heating element  23  (see  FIG. 3   b ). Channel  20  is herein provided with a feed  19  and a discharge  22  for liquid, which is preferably pumped through channel  20  under a pressure above atmospheric. The cylindrical pressing element  24  is enclosed in substantially medium-tight manner by an inner wall of the device. It is however also possible here to envisage realizing the separation between relatively cold and hot liquid in other manner.  FIG. 3   b  herein shows a cross-section along line C-C as indicated in  FIG. 3   a . Liquid can be carried into device  18  via feed  19  and exits the device via discharge  22  after passing through the spiral-shaped channel  20 . While passing through channel  20  the liquid is heated directly, i.e. without interposing of any other element, by the plate-like heating element  23  bounding channel  20 . Since the channel cross-section  20  is rather small (generally between 2 and 50 mm 2 ) the liquid volume of device  18  is likewise relatively small. Owing to the efficient and intensive heat transfer from heating element  23  to the liquid, the liquid will however be able to reach a desired temperature relatively quickly. In order to prevent overheating of the liquid and to increase the capacity of device  18 , the liquid will generally be pumped through device  18  under a pressure of about 10 bar. The liquid will preferably cover a channel length here of 0.5, 1, 2, 4, 5 or 6 meters.  FIG. 3   c  shows a detail E as indicated in  FIG. 3   b  and clearly shows that channel  20  is formed in modular manner by a metal (steel) or plastic strip  25  wound in a spiral shape and an adjacent insulating (rubber) strip  26 . Test results have shown that specific ratios between parameters a, b, c and d (see  FIG. 3   c ) have an advantageous effect on the heating of the liquid. The heating of the liquid to a desired temperature can be optimized if the ratio 30:10:1:5 is applied for ratio a:b:c:d. It is particularly advantageous to minimize parameter c in order to be able to maximize the contact surface between heating element  23  and the liquid for heating. The modular construction of a base structure for forming of a spiral-shaped channel provides a high degree of flexibility in that the base structure can then be replaced relatively easily by another base structure, and therewith another channel with a different dimensioning. In the shown exemplary embodiment the band  25  and/or strip  26  will for this purpose be replaced by a plate respectively a strip with a different dimensioning. Since the flow rate of the liquid through channel  20  will usually be constant, the dimensioning, in particular the length and the cross-section, of channel  20  determines the heat transferring capacity, whereby device  18 , and in particular the capacity of device  18 , can be modified relatively simply to the specific application for which device  18  is being used. Heat can moreover be transferred in relatively efficient and effective manner using the device, since the thermally insulating strip  26  prevents heat loss, which stimulates the accumulation of heat in the liquid for heating. 
     FIG. 4  shows a schematic representation of another embodiment of a device  27  according to the invention. Device  27  herein comprises a pump  33  and a non-linear channel structure  31  connected to pump  33 . Channel structure  31  is formed here by a single channel which has a both curved and angular form. Channel structure  31  herein connects to a thick film element (not shown) for heating a liquid, such as water or oil, flowing through channel structure  31 . To this end relatively cold liquid is first guided to pump  33  via a conduit  34 , whereafter the relatively cold liquid is guided under pressure in the direction of channel structure  31  via another conduit  32 . The liquid is heated in channel structure  31 . Via an outlet conduit  29  the heated liquid can be removed from device  27  and consumed by a user or be used for other purposes. Device  27  is also provided with a temperature sensor  30  which is coupled to pump  33  via a conduit  28  and positioned in or close to outlet conduit  29  of channel structure  31 . If sensor  30  detects that the liquid temperature exceeds a critical limit, sensor  30  will increase the pump flow rate of pump  33  via a regulator (not shown) coupled to the sensor such that the (over)heated liquid will be flushed relatively quickly out of device  27 , whereby further overheating can be prevented. A similar (reverse) situation can occur when the liquid is heated insufficiently, whereafter the pump flow rate can be (temporarily) reduced. 
     FIG. 5   a  shows a partly cut-away top view of yet another embodiment of a device  35  according to the invention. Device  35  comprises a support structure  36 , which support structure  36  is provided on the top side with a plurality of parallel oriented, non-linear channels  37 , which channels are mutually coupled on either side of support structure  36  by means of a collector  39 . Channels  37  are adapted for throughflow of liquid and are provided with an inlet  38  and an outlet  41  for liquid. The upper side of the non-linear channels  37  is wholly covered as channel structure by a plate-like electrical heating element  42 . Arranged between support structure  36  and heating element  42  is a seal  40  to prevent, or at least counter, leakage of liquid from device  35 .  FIG. 5   b  shows a cross-section along line E-E as indicated in  FIG. 5   a .  FIG. 5   b  shows that a side of heating element  42  directed toward support structure  36  is also provided with (three) non-linear, identical (zig-zag-shaped) channels  43 . Channels  37  of support structure  36  herein connect over substantially the entire length to channels  43  of heating element  42 . In this manner the channel volume of device  35  can still be increased to some extent, wherein the heat transfer capacity of device  35  is at least maintained. 
     FIG. 6  shows a perspective view of a sixth embodiment of device  44  according to the invention. Device  44  comprises a base structure  45  in which there is arranged a channel structure  46  adapted in the first instance to guide a liquid for heating. Device  44  also comprises a heating element  47  adapted to heat liquid fed to device  44 . The relative orientation of base structure  45  and heating element  47  can be changed, wherein heating element  47  is displaceable relative to the base structure  45 , which (in this exemplary embodiment) is in a stationary disposition, by means of a displacing member  50  coupled to heating element  47 .  FIG. 6  shows device  44  in an opened position, wherein the heating element does not connect directly onto channel structure  46 . A liquid fed to channel structure  46  via a feed opening  49  arranged in base structure  45  will in this case evaporate out of channel structure  46  in the direction of a space formed between base structure  45  and heating element  47 , while forming steam. Via an outlet opening  48  formed in base structure  45  the formed steam can then be discharged and usefully employed. In the case that the heating element is placed against base structure  45 , wherein heating element  47  in fact bounds channel structure  46  on one side, the liquid fed under some pressure to channel structure  46  will only be heated and further discharged from device  44  via outlet opening  48 , whereafter use can be made of the heated liquid. Using device  44  according to  FIG. 6  liquid can thus be heated or steam can be generated using a single heating element  47 . Device  44  can be applied particularly advantageously in a coffee-making machine (or other device for preparing drinks), whereby espresso coffee and the like can also be prepared using steam. Due to the relatively efficiently constructed, relatively compact device  44  according to the invention, the coffee-making machine can herein likewise be given a relatively compact form. 
     FIG. 7   a  shows a partly cut-away top view of a seventh embodiment of device  51  according to the invention. Device  51  comprises a base structure  56  provided with a flow route  55 , and a heating element  54  connected hingedly to base structure  56  via a hinge element  53 . Liquid can be fed to flow route  55  via a feed opening  52 . In the case that heating element  54  connects to base structure  56  via a sealing element  57 , the liquid supplied to device  51  will be heated in flow route  55  by heating element  54 , whereafter the heated liquid will be removed from device  51  via outlet opening  58  and can thus be employed for determined purposes. In the case that heating element  54  is pivoted in a direction away from base structure  56 , the flow route  55  will be left clear for a substantial part, thereby making possible evaporation of liquid fed to device  51 , and thus formation of steam in device  51 . 
     FIG. 7   b  shows a cross-section of device  51  in a closed position along line F-F as indicated in  FIG. 7   a . Device  51  shown in  FIGS. 7   a - 7   c  is structurally almost identical to the device  7  shown in  FIGS. 2   a - 2   c , wherein base structure  56  is provided with an assembly of a plurality of guide elements  68 ,  70  mutually coupled by a connecting element  59 , wherein the assembly supports on elastic elements  60  arranged in base structure  56 . The difference with the embodiment shown in  FIGS. 2   a - 2   c  is that heating element  54  is connected hingedly on one side to base structure  56  by means of hinge  53 . In the shown situation heating element  54  closes flow route  55 , whereby formation of steam in flow route  55  can be prevented or at least be countered, and wherein liquid will be heated only to a desired temperature.  FIG. 7   c  shows a cross-section of the device in an opened position along line F-F as indicated in  FIG. 7   a . In this opened situation steam will form between base structure  56 , or at least the guide elements  68 ,  70 , and heating element  54 , which steam can then be usefully employed, for instance to prepare drinks, clean surfaces and so on. 
     FIG. 8   a  shows a cross-section of an eighth embodiment of device  61  according to the invention. Device  61  is structurally similar to the embodiment of the device  18  shown in  FIGS. 3   a - 3   c . Device  61  comprises a spiral-shaped channel  63  provided with a feed  62  and a discharge  64 . Channel  63  can be pushed against a plate-like heating element  67  by means of a pressing element  66  connected to channel  63  in order to enable relatively efficient heating of liquid fed to channel  63 . Heating element  67  is herein held in stationary position by an annular seal  65 . Pressing element  66 , and therewith also channel  63  can, as stated above, be pressed against heating element  67  in a first (closed) position (see  FIG. 8   b ), but can be displaced in a direction away from heating element  67  in an (opened) second position, whereby formation of steam can be realized in a steam chamber  69  formed between channel  63  and heating element  67  (see  FIG. 8   c ). The formed steam can further be removed from device  61  via discharge  64 . It is thus possible to heat liquid or generate steam, or at least vapour, in relatively effective and efficient manner by means of changing the relative orientation of the (single) heating element  67  and channel  63 . 
   It will be apparent that the invention is not limited to the exemplary embodiments shown and described here, but that numerous variants, which will be self-evident to the skilled person in this field, are possible within the scope of the appended claims.