FLOW HEATER

Abstract: Flow heater for heating liquid, provided with a heat-conducting element (1) with a channel (5) for accommodating and guiding a liquid to be heated and a heater element (2) which is thermally coupled to the heat-conducting element (1). The heat-conducting element (1) is composed of a heat distribution plate (3) and a retaining element (4). The retaining element is thermally connected to a first side (13) of the heat distribution plate (3) such that the heat distribution plate (3) and the retaining element (4) enclose the channel (5). The heater element (2) is situated at a second side (14) of the heat distribution plate (3) which faces away from the first side (13). The flow heater has a simple construction and allows of a large freedom of choice as regards the shape of the path followed by the channel (5).

Description: Flow heater The invention relates to a flow heater as defined in the preamble of claim 1. Such flow heaters serve to heat a through-flowing fluid by means of heat originating from a heat source applied against the heat-conducting element. Such a flow heater is described in German patent application 39 25 549. The flow heater described in this cited patent application is provided with a heat-conducting element built up from a central profiled portion with mutually parallel channels. These channels extend in a longitudinal direction through the entire heat-conducting element and are open at two mutually opposed ends of the heat-conducting element. A connection for an inlet or outlet is mounted to each of the end faces, also interconnecting the channels such that the channel structure has a meandering shape. A thermal element in the form of one or several thin strips of high electrical resistance is provided against a side of the heat-conducting element between the channel ends. A current is passed through the thin strips and the electrical energy is partly dissipated into heat thereby, so that the water in the channels can be heated through heat transfer to the heat-conducting element. It is a disadvantage of this flow heater that the freedom of choice as regards the shape of the pattern in which the channels extend and as regards the outer contour of the region occupied by the channels, in which the channels extend, is limited. This is because the limitations as regards manufacturing cost imposed on such a flow heater, which is usually mounted in domestic appliances such as coffee makers and steam irons, imply in practice that extrusion is the only suitable manufacturing technique for the profiled central portion. It is an object of the invention to provide a flow heater which can be mass- manufactured at low cost. According to the present invention, this object is achieved in that a flow heater as defined in claim 1 is provided. The heat distribution plate and the closing element, between which the channels are closed in, render it possible to determine the shape of the channel or channels in a simple manner through the choice of the shape of the closing element, while the heat distribution plate, which comprises a comparatively large quantity of material for achieving a sufficient heat transfer capacity, can be of a simple construction. The fact that the closing element is in thermal contact with the first side of the heat transfer plate, moreover, promotes an even heat transfer. The heat-generating element may then be simply provided against the second side of the heat distribution plate facing away from the closing element and the channel or channels. The invention also relates to a device for preparing drinks such as a coffee maker, a steam iron, and a food steamer provided with a flow heater as described above. Advantageous embodiments of the invention are defined in the dependent claims. Further aspects, effects, details, and application examples will be described with reference to the annexed drawing, in which: Fig. 1 is a cross-sectional view of part of a flow heater in a first embodiment of the invention, Fig. 2 is a view taken as in Fig. 1 , but of a flow heater in a second embodiment of the invention, Fig. 3 is a view taken as in Figs. 1 and 2, but of a flow heater in a third embodiment of the invention, Fig. 4 is a diagrammatic plan view of a first example of a channel pattern of a flow heater according to the invention, Fig. 5 is a diagrammatic plan view of a second example of a channel pattern of a flow heater according to the invention, Fig. 6 is a diagrammatic cut-away side elevation of a coffee maker with a flow heater according to the third embodiment of the invention, Fig. 7 is a diagrammatic cut-away side elevation of an electric steam iron with a flow heater according to the third embodiment of the invention, and Fig. 8 is a diagrammatic cut-away side elevation of a steamer vessel with a flow heater according to the third embodiment of the invention. The invention will now be explained first with reference to the example shown in Fig. 1. The portion of a flow heater for heating water as shown in Fig. 1 is composed of a heat-conducting element 1 and a heater element 2 which is thermally coupled to the heat- conducting element 1. The heat-conducting element 1 is formed by a heat distribution plate 3 and a closing element 4. A meandering channel is present between the latter two components, which channel is intersected three times in the cross-sectional area shown in Fig. 1 and is enclosed at least circumferentially by the closing element 4 and the heat distribution plate 3. Although a single meandering channel is provided in this example, it will be obvious to those skilled in the art that the invention may equally well be applied to a flow heater provided with several parallel channels. A single channel, however, is favorable for preventing major differences in throughput time between water flowing through one channel and water flowing through another channel. Water transported through the channel 5 is heated by heat given off by the heater element 2 and transferred to the water by the heat-conducting element 1. The heat distribution plate 3 and the closing element 4 then ensure an even transfer of heat, so that overheating and a locally intensified scale deposition are prevented. The heater element is connected to the heat distribution plate 3 by means of an electrically insulating, but heat-conducting intermediate layer 3'. The intermediate layer 3' may advantageously be provided on the plate 3 by means of a spin-coating method which is known per se. In the spin-coating process, a plate is quickly rotated, and a few drops of a liquid are applied to the center of the plate, which liquid will subsequently cover the entire surface of the plate under the influence of the rotation of the plate. The heater element 2 is constructed in a known manner as a resistance layer provided on the electrically insulating intermediate layer 3' of the heat distribution plate 3 with two electrical connections (not shown), the resistance layer being formed by a layer of synthetic resin with electrically conducting particles present therein. Such a heater element is described, for example, in European patent application 0 250 905. The closing element 4 is thermally connected to a first side 13 of the heat distribution plate 3 in regions 6 laterally of the channel. The heater element 2 is situated at a second side 14 of the heat distribution plate 3 facing away from the first side 13. The closing element 4 in this example is connected to the heat distribution plate 3 in the regions 6 alongside the channel 5 by means of welding. A very effective heat transfer through the heat distribution plate 3 to the closing element 4 is obtained thereby. It is also possible, however, to use alternative connecting techniques, such as soldering or gluing. The connections in the regions 6 between the closing element and the first side 13 of the heat distribution plate 3 are impermeable to liquids. Important boundary conditions are resistance to water at high temperatures and, especially in appliances used for preparing food and drink for human consumption, the prevention of generation of substances which are detrimental to human health. The pattern in which the channel 5 extends is determined in a simple manner by the shape of the closing element 4, which affords a wide freedom of choice for the shapes without additional manufacturing expenses being involved. The heat distribution plate 3, which comprises comparatively much material, is of a simple shape here, while it may nevertheless have a shape adapted for an intensive contact with the closing element 4, for example at the first side 13. The closing element 4 in this example is constructed as a plate with a substantially uniform thickness, which is advantageous for limiting the material cost. The shape required for achieving the desired shape of the channel 5 is provided in a simple manner here in that the plate is pressed into shape. It is alternatively possible, however, to provide a closing element of non-uniform thickness constructed, for example, as a casting product with a substantially planar surface at the side facing away from the heat distribution plate. In the embodiments shown in Figs. 2 and 3, a duct 27, 47 lies enclosed between the heat distribution plate 23, 43 and the closing element 24, 44, thus defining the channel 25, 45. In such a construction, the connection between the heat distribution plate 23, 43 and the closing element 24, 44 need not be watertight along the outer contour, and connecting of the lines upstream and downstream of the channel 25, 45 may be effected simply through connection to the duct 27, 47, or in that these lines are constructed as an extension of the duct 27, 47. The closing element 4, furthermore, is in thermal contact with a major portion of the surface of the duct 27, 47, which benefits the heat transfer from the heater element 22, 42 through the intermediate layer 23', 43' to the water flowing through the channel 25, 45. The closing element 24, 44, furthermore, keeps the duct 27, 47 in place against the heat distribution plate 23, 43. It is also advantageous if the duct 27, 47 is somewhat flattened at its side facing the heat distribution plate 23, 43. The contact surface area between the duct 27, 47 and the plate 23, 43 is enlarged thereby, which is favorable for the heat transfer. In the example of a flow heater as shown in Fig. 3, a heating plate 48 is additionally provided against a side of the closing plate 44 facing away from the heat distribution plate 43. The heating plate 48 is in thermally conductive contact with the closing plate 44 and can thus serve, for example, as a hot plate for keeping a jug of coffee placed thereon or a sole plate of an electric steam iron at the correct temperature. It is advantageous for safeguarding a sufficient supply of heat to the water flowing through the channel 25 if the channel 25 has a meandering or labyrinth shape in a plane substantially parallel to the heat distribution plate 23, as is shown in Fig. 4. Fig. 4 also shows an inlet 31 and an outlet 32 which are formed by portions of the duct 27 which bounds the channel 25, which portions project from the heat distribution plate 3. Tubing elements, for example made of rubber, may be connected to the inlet 31 and the outlet 32 in a known manner for the supply of water and the discharge of water and/or steam. The connections 31, 32 for the supply and discharge of water in the flow heater shown in Fig. 4 are situated next to one another at one and the same side of the flow heater. This is convenient for mounting of the flow heater. Fig. 5 shows an alternative arrangement of the channel as compared with Fig. 2, the channel 25 now following a spiraling course. Such a shape offers the advantage that the duct 27 need not be bent with a small radius and that accordingly the flow resistance is small. Furthermore, it is now possible through a suitable connection of the inlet and outlet to obtain a temperature which increases or decreases in a substantially radial direction from the center to the outside, as desired. This may be utilized, for example, if the flow heater is used in a filter- type coffee maker, in which case the flow heater also heats a hot plate for the coffee jug. The hot plate may be designed such that the coffee jug makes contact with the hot plate in certain locations such as, for example, an inner or outer region; a good heat transfer between the plate and the jug will then take place only in the regions of contact. The amount of heat supplied to the jug may thus be controlled. Since the insulating intermediate layer 3 ' in the form of a polymer with an imide structure is provided on the heat distribution plate by means of spin-coating, the processing temperature is considerably lower than for known insulating layers such as, for example, enamel. This means that the heat distribution plate 23 can be manufactured from aluminum or an aluminum alloy. This material is a good heat conductor, is light in weight, and is easy to process. Preferably, the heat distribution plate is round in shape, so that the spin- coating process can be more efficiently performed. The side of the heat distribution plate facing away from the channel structure is preferably planar, partly also for reducing the manufacturing cost and for facilitating the provision of the intermediate layer through spin- coating and the subsequent application of the heating layer. The flow heater proposed may be used to particular advantage in mass- produced consumer products in view of the great freedom as regards its shape and its low manufacturing cost. Fig. 6 shows by way of example a drinks preparation device in the form of a filter-type coffee maker with a water reservoir 55, a water feed line 56 with a non-return valve 57 arranged therein, a flow heater in accordance with Fig. 3, a hot water line 58, a filtration device 59 in which the water is brought into contact with ground coffee 60, and a coffee jug 61 for catching the coffee flowing from the coffee holder 60. The coffee jug is placed on the hot plate 47 of the flow heater. The operation of such a filter-type coffee maker is presumed to be generally known and is accordingly not explained any further here. Fig. 7 shows a steam iron with a flow heater in accordance with the basic configuration shown in Fig. 3. The steam iron has a water reservoir 62 with a fill opening 63. A pump 64 is connected to the water reservoir 62, and to an electrical supply circuit with a control switch which can be operated via a pushbutton 67 in a handle 68 of the iron. The flow heater is situated downstream of the pump 64, the heating plate 48 at the same time forming the sole plate, and is provided with steam outlet openings 69 which are in communication with the flow heater and which are situated downstream thereof. If steam supply is desired, the switch 66 is energized for activating the pump 64, whereby water is pumped into the flow heater. The latter is kept at a temperature of more than 100 °C, so that at least a major portion of the water introduced into the flow heater is converted into steam, which issues with force from the outlets 69. The flow heater accordingly acts as a steam generator here. The heat distribution plate 43 in this application is at the same time a heat storage medium, achieving that the power of the heater element 42 can be lower than is necessary for generating a sufficiently forceful steam output. Fig. 8, finally, shows an application of the flow heater of Fig. 2 in a food steamer. The food steamer or steam pan is provided with a water reservoir 70. The water reservoir 70 is connected to the flow heater via a water feed line 71. A non-return valve 72 is included in the water feed line. A steam line 74 is connected downstream of the flow heater and issues into a preparation space 75 in which food 76 to be steamed is placed. The steam generated in the flow heater is used for cooking the food in the preparation space 75. Although water was heated in the embodiments of the flow heater according to the invention discussed above, the invention is not limited to the use of this liquid. Indeed, the invention may also be applied to the heating of alternative liquids such as, for example, oil. Neither is the invention limited to the devices mentioned; it will be obvious to those skilled in the art that the invention may be used to advantage in a plurality of other appliances, for example steaming devices for facial treatment, wallpaper removal steamers, radiators, steam cleaning devices, vacuum cleaners with a steam supply, and appliances for making tea.

Claims: CLAIMS: 1. A flow heater for heating a liquid, comprising: a heat-conducting element (1; 21; 41) with at least one channel (5; 25; 45) for accommodating and guiding liquid to be heated, and with a heater element (2; 22; 42) thermally coupled to said heat-conducting element (1; 21; 41) for heating said heat-conducting element ( 1 ; 21 ; 41 ), characterized in that said heat-conducting element (1; 21; 41) comprises a heat distribution plate (3; 23; 43) and a closing element (4; 24; 44), in that the closing element (4; 24; 44) is thermally connected to a first side (13) of said heat distribution plate (3; 23; 43) in at least a portion of regions situated adjacent said at least one channel (5; 25; 45) such that said heat distribution plate (3; 23; 43) and said closing element (4; 24; 44) enclose said at least one channel (5; 25; 45), and in that said heater element (2; 22; 42) is situated at a second side (14) of said heat distribution plate (3; 23; 43) facing away from the first side (13). 2. A flow heater as claimed in claim 1, wherein the closing element (4; 24; 44) is constructed as a plate of substantially uniform thickness. 3. A flow heater as claimed in claim 2, wherein the closing element (4; 24; 44) is constructed as a metal plate pressed into shape. 4. A flow heater as claimed in any one of the preceding claims, further comprising at least one duct (27; 47) having a wall which bounds said at least one channel (5; 25; 45). 5. A flow heater as claimed in any one of the preceding claims, wherein said at least one channel (5; 25; 45) follows a meandering or labyrinth course in a plane substantially parallel to said heat distribution plate. 6. A flow heater as claimed in any one of the claims 1 to 4, wherein said at least one channel (5; 25; 45) follows a spiraling course in a plane substantially parallel to said heat distribution plate. 7. A flow heater as claimed in any one of the preceding claims, further comprising a heating plate (48) in thermally conductive contact with the closing element (44) and situated at a side of the closing element (44) facing away from said heat distribution plate (43). 8. A flow heater as claimed in any one of the preceding claims, wherein said heat distribution plate (3; 23; 43) is manufactured from aluminum or at least an aluminum alloy. 9. A drinks preparation device with a flow heater as claimed in any one of the preceding claims and with a holder (59) for bringing substances into contact with water, which holder is provided with openings (60) downstream of said flow heater. 10. An electric steam iron with a flow heater as claimed in any one of the preceding claims 1 to 8, further comprising a sole plate (48) to be heated, with steam outlet openings (69) which are connected downstream to the channel (45) of said flow heater. 11. A food steamer with a flow heater as claimed in any one of the claims 1 to 8, further comprising a preparation space (75) which can be substantially closed and in which food (76) to be steamed can be accommodated, and a steam line (74) downstream of the flow heater, through which steam line (74) the flow heater is in communication with the preparation space (75).

Inventors: BLIEK MARINUS, VAN DER WOUDE RENE H, BLIEK, MARINUS, VAN DER WOUDE, RENE, H.
Applicants: KONINKL PHILIPS ELECTRONICS NV, KONINKLIJKE PHILIPS ELECTRONICS N.V.
Application year: 2001
Main classification: F24H1
IPC codes: F24H1