Flow through heaters

Abstract

A group head for an espresso machine comprising a water inlet 16, a flow-through heater comprising an integral body 40 having plurality of channels 15, and heating tracks (44, fig 7b) arranged to heat the integral body so as to heat the water flowing through the channel and means for distributing the heated pressurised water to a portafilter removably attached to the group head. Preferably the integral body comprises aluminium or ceramic material and may be formed as a single homogenous component with the channels, and preferably include hollow sections. Preferably group head includes housing portions 20a, 20b to house the integral body, which may be held together by fixing means passing through the integral body. Preferably group head includes manifolds 42b in housing portions, which may direct water to channels.

Description

Technical Field

[0001] The present invention relates to flow through heaters, particularly thick film flow through heaters for espresso coffee machines. Background

[0002] Espresso machines brew espresso coffee by passing hot water at high pressure through finely ground coffee. Their main components include a heater, a water pump, a group head and a portafilter. The heater heats water to the optimal temperature for brewing espresso, typically around 90°C to 96°C. In a conventional espresso machine, the heater is either a boiler that heats and stores water, or a flow-through heater that heats water on demand. The pump generates high pressure required to force water through the coffee grounds, either before or after the water is heated. Typically, the water pressure required for brewing espresso is 7-11 bar (700-1100 kPa).

[0003] The group head serves as the interface between the water and the coffee grounds, allowing water at the required temperature and pressure to pass through the coffee to create espresso. The group head typically contains a shower screen to distribute water evenly over the coffee grounds, a gasket to seal against the portafilter, and a connector such as a bayonet connector for connection to the portafilter. The portafilter is a removable device, typically with a handle, that holds a puck of tamped coffee grounds within a removable filter basket and attaches to the group head with a bayonet fitting that forces the portafilter against a gasket in the group head, thus creating a chamber in which espresso coffee is brewed. Brewed coffee flows out of the filter basket and is dispensed through a spout in the portafilter.

[0004] One problem with conventional espresso machines is that the water cools as it enters the group head, so that espresso is not brewed at the optimum temperature. Also, the brewing temperature may be inconsistent as it depends on the temperature of the group head and the portafilter, which varies depending on the time since the last use. Statements of Invention

[0005] Aspects of the invention are defined by the accompanying claims.

[0006] In some embodiments, a group head for an espresso machine includes a flow-through heater arranged to heat pressurised water passing through the group head. This may remove the requirement for a heater arranged upstream of the group head, although such a heater may additionally be provided. Heating the water within the group head allows the water to maintain optimum temperature for brewing.

[0007] In some embodiments, the flow-through heater is a thick film heater comprising a channel plate attached to an element plate to form one or more channels therebetween. This arrangement directs the flow of water in contact with the element plate, so improving the thermal efficiency of the heater.

[0008] There may be provided a diffuser plate arranged between one or more outlets of the one or more channels and a shower screen, so as to direct the flow of water over the outside of the channel plate and thereby improve thermal transfer to the water.

[0009] A water inlet may pass through the element plate so as to connect to the channel. This may allow a compact arrangement within the group head.

[0010] A temperature sensor may be located in the channel and electrical connections to the temperature sensor may pass through the element plate.

[0011] In other embodiments, the flow through heater comprises an integral body having a plurality of channels formed therein, and one of more heater tracks arranged to heat the integral body and hence the water flowing through the channels. The channels may be interconnected in series and / or parallel by one or more manifolds, which may be provided in one or more housing portions of the group head.

[0012] The heater tracks may be deposited on the integral body. The integral body may be formed of aluminium, with an anodised surface on which the heater tracks are deposited. Alternatively, the integral body may be formed of ceramic material. Brief Description of Drawings

[0013] Specific embodiments will now be described with reference to the accompanying drawings as identified below.

[0014] Figure 1 is a schematic diagram of an espresso machine in which embodiments of the invention may be incorporated.

[0015] Figures 2a and 2b are perspective views respectively from above and below of a flow-through heater in a first embodiment.

[0016] Figures 3a and 3b are perspective views respectively from above and below of a flow-through heater in a second embodiment.

[0017] Figure 4 is a cross-section of a group head including a flow-through heater in a third embodiment.

[0018] Figure 5 is a cross-section of a group head including a flow-through heater in a fourth embodiment.

[0019] Figures 6a and 6b are respectively exploded and assembled diagrams of a group head in a fifth embodiment.

[0020] Figures 7a to 7c are respectively perspective, exploded perspective and cross-sectional views of a group head in a sixth embodiment.

[0021] Figure 7d is a perspective view of a manifold in the sixth embodiment. Detailed Description of Embodiments

[0022] As shown schematically in Figure 1, an espresso machine 1 to which embodiments of the invention may be applied comprises a water supply 2, such as a tank or a mains water supply, a pump 4 that increases the water pressure to an espresso brewing pressure (e.g. 7-11 bar, 700-1100 kPa), a group head 6 that received the pressurised water and a portafilter 8 that connects to the group head and includes a filter basket for containing finely ground coffee. The portafilter 8 has one or more outlets for dispensing brewed espresso e.g. into one or more cups.

[0023] Water for brewing espresso must be heated to brewing temperature, for example between 90° C and 96° C. Conventionally, this is done by heating the water supply 2 (for example in a boiler tank) and / or by means of a flow-through heater (not shown) arranged in the path between the water supply 2 and the group head 6. In embodiments of the invention, the water is heated within the group head 6, although in some applications one or more additional heaters may be provided upstream of the group head 6.

[0024] The pump 4 and the water heater may be controlled by a control 5 (such as an electronic control unit) so as to brew espresso at the required temperature and pressure, when initiated by a user by means of a user interface.

[0025] In the first to fourth embodiments as described below, the group head 6 includes a thick film flow through heater 11 comprising a channel plate 12 attached in a watertight manner (e.g. by brazing) to a planar thick film heating element 14, the latter comprising a substrate 13 of material with good thermal conductive properties such as a metal, an electrically insulating layer such as vitreous enamel and at least one heating resistor track 44 applied by a thick film technique. A channel 15, formed between the channel plate 12 and the planar heating element 14, guides water to be heated along the surface of the channel plate 12. The low thermal mass of this type of flow through heater 11 provides a fast response and a very controllable heater.

[0026] In the first embodiment as shown in Figures 2a and 2b, a water inlet 16 extends through the substrate 13, from a first side thereof on which one or more heating track 44 is provided, to an inlet 15a of the channel 15 which is provided on a second side of the substrate 13 opposite to the first side.

[0027] The channel plate 12 has a planar portion for attachment to the heating element 14 and a non-planar or raised portion that defines the channel 15. The channel 15 may run in a spiral path extending in a plane parallel to the surface of the substrate 13 on the second side. Preferably, the channel 15 is aligned with the arrangement of heating track(s) on the first side, to improve heat transfer into the channel 15. The length and shape of the channel 15, and of the heating track(s) on the opposite side, made be selected depending on the required performance of the flow through heater 11.

[0028] An outlet 15b of the channel 15 is provided in a central position of the substrate 13 and comprises one or more apertures in the channel plate 12 through which water passes to a diffuser and / or shower screen in the group head, as described in more detail below.

[0029] A sensor aperture 17 is provided through the central portion of the substrate 13, through which a temperature sensor 19, such as a negative temperature coefficient (NTC) resistor, senses the temperature of water entering the outlet 15b. The control unit 5 may control the heating power of the flow through heater 11 and / or the flow rate of the pump 4 so as to maintain the temperature sensed by the temperature sensor 19 within the brewing temperature range.

[0030] The second embodiment as shown in Figures 3a and 3b is similar to the first embodiment, except that the outlet 15b is offset from the central position of the substrate 13. A boss 18 is provided in the central position of the substrate 13, for fixing the heater 11 to a group head housing 20.

[0031] The channel 15 in the second embodiment has the form of a spiral extending over nearly two turns compared to the single turn in the first embodiment.

[0032] Figure 4 shows a cross section through the group head 6 in a third embodiment, including a flow-through heater 11 according to the first or second embodiments or variants thereof. The group head 6 comprises a disc-shaped housing 20. The arrangement of components of the group head 6 will be described below with reference to a notional axis A-A passing through the centre of the group head 6, about which the disc-shaped housing 20 has (approximately) rotational symmetry.

[0033] The housing 20 has a peripheral groove 21 containing a gasket or other seal 22 for sealing against an upper edge of the portafilter 8. The housing 20 also includes a connector or fitting (not shown), such as a bayonet fitting, for removable attachment of the portafilter 8 to the group head 6.

[0034] The flow through heater 11 is secured against the housing 20 by means of ferrule 30 that passes through the housing 20 in the direction of the axis A-A and is secured against the outside of the housing 20 by a clamp nut 31. Electrical connectors 32a, 32b extend through the ferrule 30 and are electrically connected to the temperature sensor 19. The ferrule 30 may also carry electrical power connectors for connection to the heating track(s) 44.

[0035] In use, pressurised water enters the group head 6 through the inlet 16, as shown by a dashed arrow in Figure 4, flows through the channel 15 while being heated by the flow-through heater 11, and then flows out of the outlet 15b towards a shower screen 23, comprising a perforated bottom surface 23a extending perpendicularly to the axis A-A, which distributes heated, pressurised water evenly through the ground coffee within the portafilter 8. The shower screen 23 has a peripheral wall 23b extending parallel to the axis A-A and attached to the housing 20 so as to define an internal chamber within which the flow-through heater 11 is fixed, with the planar substrate 13 extending perpendicularly to the axis A-A. In the space between the channel plate 12 and the bottom surface 23a of the shower screen 23 is provided a diffuser plate 25 which is arranged to direct the flow of water from the outlet 15b to pass over an outer surface of the channel plate 12, before passing through apertures 25a, 25b in a radially outer region of the diffuser plate 25, as shown by the dashed arrows in Figure 4. This arrangement improves the thermal efficiency of the flow-through heater 11, because the water passes twice over the channel plate 12, first within the channel 15 and then outside the channel 15, before passing through the perforated bottom surface 23a of the shower screen 23.

[0036] Figure 5 shows a cross section through the group head 6 in a fourth embodiment, which differs from the third embodiment in that there is no diffuser plate 25, although this may optionally be included in the space between the channel plate 12 and the bottom surface 23a of the shower screen 23. The channel plate 12 has a plurality of outlets 15b at different outer positions in the channel 15 so as to distribute water over the shower screen 23. Alternatively or additionally, the bottom surface 23b of the shower screen 23 may have a section free of perforations opposite the outlet(s) 15b, so that water flowing through the outlet(s) 15b passes along the outside of the channel plate 12 in a direction perpendicular to the axis A-A before passing through the perforations. Alternatively of additionally, the outlet(s) 15b may have one or more flow deflectors connected or arranged proximate thereto, to direct the flow of water in a direction perpendicular to the axis A-A along the outside of the channel plate 12 before passing through the perforations.

[0037] In this embodiment, the inlet 16 is provided centrally within the housing 20 and is used to secure the flow through heater 11 against the housing 20 by means of clamp nut 31. The ferrule 30 and temperature sensor 19 are provided adjacent one of the outlets 15b of the channel 15.

[0038] Fifth and sixth embodiments will now be described, in which the flow through heater 11 comprises an integral body 40 having a plurality of channels 15 formed therein, and one or more manifolds are provided to interconnect the channels 15 in a flow path. The integral body 40 may be formed as a single, homogenous component with the channels 15 passing therethrough. In this way, the sides of the channels 15 are defined by the form of the integral body 40 rather than being formed by different components that are fixed together. Advantageously, the use of an integral body 40 may avoid the need to connect components together in order to form the flow channels, thus avoiding the risk of stagnation, corrosion and / or leakage along the flow channels. Additionally or alternatively, the problems involved in joining processes, such as brazing, soldering or welding, may be avoided.

[0039] The integral body 40 may be formed of aluminium. Aluminium is resistant to corrosion, and may be anodised to further increase its corrosion resistance. Aluminium also has a high thermal conductivity, which improves heat transfer to the channels 15. The use of aluminium instead of steel may reduce the cost of manufacture. The aluminium integral body 40 may be formed by extrusion, diecasting or metal injection moulding. Alternatively, the integral body 40 may be formed of ceramic material, for example by extrusion, ceramic injection moulding or isostatic pressing.

[0040] One or more thick film heating tracks 44 may be deposited directly onto the integral body 40. Where the integral body 40 is made of aluminium, the thick film heating track(s) 44 may be deposited on an anodised surface of the integral body 40, so that there is no need to deposit a separate insulating layer on the integral body 40 before depositing the track(s).

[0041] In the fifth embodiment shown in Figures 6a and 6b, the integral body 40 is cylindrical and the plurality of channels are distributed circumferentially and extend in an axial direction through the integral body 40. The housing 20 comprises first and second housing parts 20a, 20b, which are held together by a bolt which passes through the first housing part 20a, through a central axial aperture of the integral body 40 and through the second housing part 20b, with the distal end being secured by a nut and washer. Sections of the integral body 40 radially inward from the channels 15 may be hollow so as to reduce the mass and material costs of the integral body 40.

[0042] The first and second housing parts 20a, 20b each include a corresponding manifold 42a, 42b which interconnects the channels 15 within the integral body 40 so that the flow of pressurised water entering inlet 16 is directed by a first manifold 42a into one or more of the channels 15 and passes into the second manifold 42b which directs the flow of water back to the first manifold 42a through another one or more of the channels and / or directs the flow of water through a water outlet 26 to the diffuser plate 25 and / or shower screen 23.

[0043] The first and second manifolds 42a, 42b may be configured so that the water flows first through a first plurality of the channels 15 in parallel for optimum heating efficiency, and then through one or more second channels 15, fewer in number than the first channels, to increase the flow resistance and thereby maintain water pressure. Other configurations of the first and second manifolds 42a, 42b may provide other series and / or parallel configurations of channels 15 to achieve the desired heating and / or pressure parameters.

[0044] Figures 7a-7d show a group head in a sixth embodiment, in which the first housing part 20a is integral with the group head housing. As shown in Figure 7d, the first manifold 42a connects adjacent channels 15 together so that water flows through each channel 15 in turn before passing to the water outlet 26.

[0045] Figures 7a and 7b show heater tracks 44 arranged around the sides of the integral body 40 so as to heat water as it flows through the channels 15. The heater tracks 44 may comprise thick film heater tracks deposited on the sides of the integral body 40. Alternative Embodiments

[0046] Alternative embodiments which may occur to the skilled person on reading the above description may nevertheless fall within the scope of the invention as defined by the following claims. Alternative Statements of Invention

[0047] Alternative statements of invention are recited below as numbered clauses. 1. A group head for an espresso machine, the group head comprising a water inlet, a heater for heating the water, and means for distributing the heated water to a portafilter removably attachable to the group head; wherein the heater comprises a flow-through heater comprising a thick film heater element and a channel plate attached to the heating element to form one or more channels therebetween, such that water is heated by the thick film heating element as it flows through the one or more channels. 2. The group head of clause Error! Reference source not found., including means for directing a flow of water from one or more outlets of the one or more channels, such that the water flows along the outside of the channel plate before being distributed to the portafilter. 3. The group head of clause 2, wherein the means for directing comprises a diffuser plate. 4. The group head of clause 3, wherein the means for distributing the heated water comprises a shower screen, the diffuser plate being located between the one or more outlets of the one or more channels and the shower screen. 5. The group head of any preceding clause, wherein the thick film heater element comprises a substrate with one or more thick film heater tracks formed on a first side thereof opposite a second side to which the channel plate is attached. 6. The group head of clause 5, wherein the water inlet passes through the substrate to the channel. 7. The group head of clause 5 or clause 6, including a temperature sensor located in an aperture extending through the substrate to at least one said channel, for sensing the temperature of water within the channel.

Claims

1. A group head for an espresso machine, the group head comprising a water inlet, a heater for heating the water, and means for distributing the heated pressurised water to a portafilter removably attachable to the group head; wherein the heater comprises a flow-through heater comprising an integral body having a plurality of channels formed therein, and one or more heating tracks arranged to heat the integral body so as to heat water flowing through the channels.

2. The group head of claim 1, wherein the integral body comprises aluminium.

3. The group head of claim 1, wherein the integral body comprises ceramic material.

4. The group head of any preceding claim, wherein the integral body is formed as a single,homogenous component with the channels passing therethrough.

5. The group head of any preceding claim, wherein the integral body includes one or more hollow sections.

6. The group head of any preceding claim, wherein the one or more heating tracks are deposited onto the integral body.

7. The group head of claim 6 when dependent directly or indirectly on claim 2, wherein the one or more heating tracks are deposited on an anodised surface of the integral body.

8. The group head of any preceding claim, wherein the integral body is cylindrical and the channels extend in an axial direction through the integral body.

9. The group head of claim 8, wherein the channels are distributed circumferentially in the integral body.

10. The group head of any preceding claim, including one or more housing portions in which the integral body is housed.

11. The group head of claim 10, including first and second said housing portions held together by fixing means that passes through the integral body.

12. The group head of any preceding claim, including one or more manifolds arranged to interconnect the channels in series and / or in parallel.

13. The group head of claim 12 when dependent directly or indirectly on claim 10, wherein the one or more manifolds are provided in the one or more housing portions.

14. The group head of claim 13, wherein first and second said manifolds are provided respectively in first and second said housing portions such that water entering the water inlet is directed by said first manifold into one or more of the channels and passes into the second manifold which directs the water back to the first manifold through another one or more of the channels and / or directs the water through a water outlet.

15. The group head of claim 14, wherein the first and second manifolds are configured so that the water flows first through a first plurality of the channels in parallel and then through one or more second channels, fewer in number than the first channels.

16. The group head of any one of claims 13 to 15, wherein at least one of the housing portions is integral with a housing of the group head.

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