EP0608569B1 - Continuous-flow heater - Google Patents

Abstract

A heater for fluids has a main housing part which is provided with flow channels for a fluid to be heated. The main housing part is surrounded by an auxiliary housing part, and the housing parts cooperate to define a compartment which is capable of containing sparks, flames and explosions. The compartment communicates with the atmosphere via one or more gaps too narrow to be penetrated by sparks and flames. The compartment further communicates with a chamber which is provided in the auxiliary housing part for switching elements. A heating foil is adhesively secured to one surface of the compartment so as to lie flat against such surface.

Description

The invention relates to a continuous-flow heater with a housing in which at least one material channel is provided for the flow of a fluid to be heated, and with a surface heating element which lies flat against a surface of the housing.

In a known instantaneous water heater of this type (US 4,866,250), a metallic housing is surrounded in the circumferential direction by a heating foil. The heating foil is enclosed by a thin metal foil, on which in turn an insulating wall made of foam or a similar insulating material is applied. The entire arrangement in turn is housed in a further housing, which can be covered by a further insulating layer. The known instantaneous water heater is used in particular for preheating liquid fuels.

Continuous-flow heaters are also used to heat paints with a higher viscosity. These varnishes can then be processed with less addition of thinners or solvents. The heating of the paints leads to a reduction in viscosity, which leads to fine atomization at lower spray pressures. However, when such paints are heated, vapors can form which, if ignited, can lead to explosions. It is obvious that such explosions are dangerous and that measures must be taken that such explosions do not occur at all or that the effects of such explosions do no harm.

This safety aspect is not dealt with in the known instantaneous water heater (US 4,866,250). It may be assumed here that a hazard can be excluded by embedding the heating element in other materials. However, this embedding has the disadvantage that the repair of the instantaneous water heater becomes very complex. In many cases, it will not be possible to replace or repair the heating element without destroying other parts.

DE-C-865 334 shows a pressure-resistant electric instantaneous water heater, in particular for a viscous oil mixture. A tubular heater is covered with an insulating jacket, which in turn is surrounded by a bandage. An insert is arranged in the radiator and is composed of axially stacked steatite rings. The steatite rings are held together by a clamping screw. The insert is located approximately centrally in the tube-like radiator, so that a free flow cross section is formed between the insert and the inner wall of the radiator, which has a small thickness. In this way, an oil flow through the water heater is formed, which is only a small one Has thickness. The oil is then heated evenly. A large amount of heat can be transferred to the oil without any heat-damaging effects on the heating material to be heated.

Continuous-flow heaters are also known which have heating cartridges or heating spirals between the material channels. These are either cast in or inserted into bores that run between the material channels. In this case, the basic structure is similar to that of the instantaneous water heater from US 4,866,250. The heating cartridges or spirals are completely enclosed by the housing, so that paint or liquid vapors cannot reach the heating cartridge in order to ignite there. A repair of the instantaneous water heater, for example after a heating element failed, was practically not possible, even if heating cartridges were inserted in the holes. To After a long period of operation, the heating cartridges can practically no longer be removed from their holes.

It is therefore the object of the present invention to be able to use a continuous-flow heater with a surface heating element even in an explosive environment.

This object is achieved according to the invention in a continuous-flow heater of the type mentioned at the outset in that the surface heating element is arranged on a boundary wall of a pressure-tightly encapsulated space.

The heating element is exposed to one side of an atmosphere into which flammable vapors can get. It is also permitted that these vapors ignite on the heating element and can lead to an explosion. The effects of this explosion are controlled. The boundary walls of the flameproof enclosure are designed so that they can withstand the pressure generated in the event of an explosion that may occur in the flameproof enclosure and prevent the explosion from being transmitted to the outside. Since the surface heating element is only connected to the boundary wall on one side, but is not loaded on the other side, the risk of thermal stresses with the risk of damage or destruction of the surface heating element is very small. The surface heating element is also freely accessible after opening the flameproof enclosure and can be easily repaired or replaced in the event of damage without having to destroy parts of the instantaneous water heater.

It is also preferred that the boundary wall forms part of the housing. The heat emitted by the surface heating element can then reach the material channel or channels directly through the housing without having to traverse larger housing parts. The surface heating element is therefore arranged in the immediate vicinity of the material channel.

A flame-arresting gap is advantageously provided, which connects the pressure-tightly encapsulated space with the surroundings. On the one hand, this prevents a dangerous increase in pressure in the flameproof enclosure in the event of an explosion. On the other hand, the explosion cannot be transmitted outside. The flame-arresting gap prevents flames from escaping and causing further explosions in the outside environment. The gap, however, acts as a throttle, through which a pressure can escape from the pressure-proof, enclosed space. If necessary, several columns can also be provided. The individual dimensions depend on the intended use.

The flameproof enclosure is advantageously filled with a non-combustible material in powder form. This material can be sand, for example. This greatly reduces the volume available for the vapors or gases. Even if vapors or gases reach the heating element and ignite there, it is only small amounts that can explode. Accordingly, the force of the explosion is also small. On the other hand, such a powdery material can be easily introduced and also easily removed, so that the repair options are not significantly impaired.

The pressure-tightly encapsulated space advantageously has an extension perpendicular to the boundary wall which is in the range from two to twenty times the thickness of the surface heating element. The volume of the flameproof encapsulated space is therefore relatively small. This also keeps the amount of steam or gas that can explode small, which in turn keeps the force or force of an explosion at a low level. On the other hand, the surface heating element is at a distance from the non-touched boundary wall, which is opposite to its surface extension, which is at least as large as its thickness.

The surface heating element is preferably designed as a heating foil. Such heating foils are available, for example, under the name "MINCO foil heating elements" from Telemeter Electronic GmbH, Donauwörth, Federal Republic of Germany. Such heating foils are relatively thin. Their thickness ranges from 1/4 to 3 mm. Such films can be glued to the boundary wall. They adapt easily to the surface, even if this surface is not completely flat. When using heating foils, it is possible to keep the volume of the flameproof enclosure relatively small.

In a particularly preferred embodiment, a pressure-tightly encapsulated switchgear room is provided, in which electrical switching devices are arranged and which is connected to the pressure-tightly encapsulated space. The electrical switching devices can be temperature regulators and limiters, for example, which generate sparks during operation, for example when they switch the power supply of the electrically heated surface heating element on or off. Such a control room must be provided for instantaneous water heaters that are to be used in potentially explosive environments. This However, control room generally only takes up a relatively small proportion of the volume of the instantaneous water heater. By connecting the switch room with the flameproof encapsulated room, the switch room is now expanded so that it can take up the surface heating element.

It is preferred here that the control room completely surrounds the housing over part of its length in the circumferential direction, the pressure-tightly encapsulated room opening with its end face on the entire circumference into the control room. This ensures a large-scale transition between the flameproof enclosure and the control room. If an explosion spreads, pressure equalization between the flameproof enclosure and the control room can take place relatively quickly without dangerous local pressure increases due to constrictions.

It is also advantageous if the housing is essentially cylindrical, the material channel running essentially parallel to the cylinder axis. Both the flameproof enclosure and the switch room can then also be enclosed by an essentially cylindrical outer wall. There are no edges or knicks that can weaken the material of the outer walls. Rather, the cylindrical shape is well suited to easily absorb the resulting pressures.

It is particularly advantageous for the housing to have a recess in the region of the boundary wall, in which the surface heating element is arranged. This return has two advantages: On the one hand, it creates space for the flameproof enclosure without increasing the external dimensions of the instantaneous water heater. On the other hand, the surface heating element can also be closer to the material channel be arranged, whereby the heat transfer is improved.

It is preferred that the recess is covered at least over part of its length by a wall pushed onto the housing from one end face. This wall then forms the outer wall of the flameproof enclosure. Because the wall can be pushed open, the wall can be closed all around. Axial connections can be avoided, so that a relatively high pressure safety can be achieved with this simple measure. By pushing it on, the flame-retardant gaps are created automatically if dimensioned accordingly.

It is also preferred here that the control room is provided in a housing part which is pushed onto the housing from the front side and at least partially covers the wall. It also applies to this housing part that it no longer has to be closed in the axial or longitudinal direction because it is already closed in a ring. This also results in a relatively high compressive strength. Sliding on the wall and the housing part automatically creates gaps with appropriate dimensions, which in turn can be designed so that they are flame-proof.

In another preferred embodiment, the housing part and the wall are made in one piece and in particular as a cast part. With such a configuration, assembly is simplified. Only a part has to be pushed onto the housing to form the flameproof enclosure and the control room.

In addition, a space of increased security can be provided in the housing part. Such a room is used, for example, to accommodate incandescent lamps or other display devices and to carry electrical cables through.

In a preferred embodiment, the space of increased security can be arranged on the outside in a direction perpendicular to the longitudinal axis of the housing. Another preferred design option is that the control room and the room for increased security each extend over a part of the circumference. As a third alternative, the switch room and the room of increased security can be arranged in the direction of the longitudinal axis of the housing at opposite ends of the housing part. The last two configurations in particular are very space-saving.

The housing is preferably made of stainless steel. With such a material, water-based paints can now also be used. Heating with surface heating elements is particularly advantageous for stainless steel housings because heating cartridges or heating spirals would be difficult to attach here.

Fig. 1

einen Axialschnitt durch eine erste Ausgestaltung eines Durchlauferhitzers,

Fig. 2

einen Schnitt II-II nach Fig. 1 in einer ersten Ausgestaltung,

Fig. 3

einen Schnitt II-II in einer zweiten Ausgestaltung,

Fig. 4

eine zweite Ausgestaltung eines Durchlauferhitzers,

Fig. 5

eine dritte Ausgestaltung eines Durchlauferhitzers,

Fig. 6

eine vierte Ausgestaltung eines Durchlauferhitzers,

Fig. 7

einen Schnitt VII-VII nach Fig. 6,

Fig. 8

eine fünfte Ausgestaltung,

Fig. 9

eine sechste Ausgestaltung und

Fig. 10

eine siebte Ausgestaltung eines Durchlauferhitzers.

The invention is described below on the basis of preferred exemplary embodiments in conjunction with the drawing. Show here:

Fig. 1

an axial section through a first embodiment of a water heater,

Fig. 2

2 shows a section II-II according to FIG. 1 in a first embodiment,

Fig. 3

a section II-II in a second embodiment,

Fig. 4

a second embodiment of a water heater,

Fig. 5

a third embodiment of a water heater,

Fig. 6

a fourth embodiment of a water heater,

Fig. 7

6 shows a section VII-VII according to FIG. 6,

Fig. 8

a fifth embodiment,

Fig. 9

a sixth embodiment and

Fig. 10

a seventh embodiment of a water heater.

A continuous-flow heater 1 has a housing 2 which is essentially cylindrical. Material channels 3 run parallel to the cylinder axis and are connected to one another via connecting grooves 6, 7 provided in an upper cover 4 and in a lower cover 5 such that a fluid entering through an inlet 8 alternately moves the housing 2 upwards and downwards interspersed from top to bottom until it has flowed through all material channels 3 and can exit again from an inlet 9. The material channels can have a circular cross section, as shown in FIG. 2. However, they can also have an approximately trapezoidal cross section, as is represented in FIG. 3 by material channels 3 '. If an odd number of material channels 3 or 3 'is provided, the inlet 8 and outlet 9 are arranged on opposite ends of the housing 2. If, on the other hand, an even number of material channels 3 or 3 'is provided (FIGS. 2 and 3), then there are input 8 and output 9 arranged at the same ends of the housing 2 or 2 '. For example, input 8 and output 9 are then provided in the lower cover 5.

The housing 2 has a recess 11 over part of its axial length on its outer circumference. This recess 11 is covered by a wall 12. The wall 12 is designed as a hollow cylinder and pushed onto the housing. The wall 12 thus, together with the housing 2, delimits a pressure-tight encapsulated space 15.

The wall 12 is guided in the region of the lower cover on the outer wall 13 of the housing, i.e. the housing 2 has the same outer diameter as the inner diameter of the wall 12 in this area. The housing 2 has a step 16 at the lower end against which the wall 12 abuts.

There is a flame-proof gap between wall 12 and outer wall 13 of the housing, i.e. a narrow gap through which gases can escape from the pressure-tightly encapsulated space 15, which is so narrow and long that it does not allow the passage of flames and also reduces the pressure of the gases to the outside due to its throttling effect.

In the area of the upper cover 4, a housing part 17 is provided which surrounds the housing 2 in a ring. The housing part 17 has a radially outwardly projecting extension 18, in which there is a switch space 20 closed by a cover 19 and a space 22 of increased security 22 separated by a partition 21. The increased security space 22 is closed by a cover 23. A flame-arresting gap 24 is also provided between the cover 19 and the housing part 17. In the control room 20 electrical switching devices such as temperature regulators or the like are provided. These switching devices can generate sparks when switching. Lamps or similar display instruments and cable glands are arranged in the area of increased security.

The pressure-tightly encapsulated space 15 and, if appropriate, the control room 20 can be filled with sand or the like.

The housing part 17 not only surrounds the housing 2 in a ring shape, the switching space 20 also being guided in a ring shape around the housing, but also the wall 12. The housing part 17 is pushed onto the wall 12. A flame-arresting gap 25 is also provided between the housing part 17 and the housing 2 in the area of the upper cover 4.

The housing 2 is made of stainless steel. In the recess, a heating foil 26, that is to say a surface heating element with a relatively small thickness, is glued to the housing 2. In this area, the distance between the heating foil and the material channels 3 is relatively small. The heating foil is electrically heated. As soon as current flows through the heating foil 26, it generates heat and emits this heat to the housing 2, from where it can penetrate to a fluid flowing in the material channels 3.

Due to its design, the heating foil is not intrinsically safe. It can become so hot that it can ignite an ignitable gas mixture. When processing liquid paints, vapors can easily form, which together with the ambient air form an ignitable mixture that can explode or even explode when ignited. Such a mixture can also penetrate up to the heating foil 26. Since the heating film 26 in the flameproof space 15 is arranged, explosions that arise in this flameproof space 15 can have no negative effects to the outside. A pressure rise resulting from an explosion in the pressure-tightly encapsulated space 15 can be reduced to the outside through the flame-arresting gaps 14, 24, 25 without the risk that flames can also reach the outside and ignite the ignitable mixture located there.

The pressure-tight encapsulated space 15 has only a relatively small thickness and thus a relatively small volume. The thickness is approximately two to twenty times the thickness of the heating film 26. This ensures on the one hand that not too much ignitable mixture can penetrate to the heating film 26. However, the less the mixture is ignited, the smaller the forces that occur during an explosion. On the other hand, it is ensured that the heating foil 26 is firmly connected to the housing 2 with only one surface. The other surface is free, so that due to different thermal expansions of different housing parts, no more stresses are applied to the heating foil 26, which can lead to damage or even destruction of the heating foil 26. On the other hand, by simply pulling off the housing part 17 and the wall 12 from the housing 2, access to the heating foil 26 can be gained, through which the heating foil 26 can be repaired or replaced.

The pressure-tightly encapsulated space 15 is connected to the switching space 20 over a relatively large area, namely over its entire upper end face. This ensures that a relatively good exchange of the gas can take place between the control room 20 and the pressure-tight encapsulated room 15. So if there are explosions in one room or another, can distribute the pressures evenly relatively quickly.

Fig. 4 shows a further embodiment of a water heater 101, which differs from the water heater 1 according to Fig. 1 in that the wall and the housing part are integrally formed. Corresponding parts are provided with reference numbers increased by 100. The wall and the housing together form a casting 112 which is pushed onto the housing 102. As a result, the pressure-tight encapsulated space 115 in the recess 111 is covered. Otherwise, the instantaneous water heater 101 corresponds to the instantaneous water heater 1 according to FIG. 1.

FIG. 5 shows a third embodiment of a water heater, in which corresponding parts are provided with reference numerals increased by 200 compared to the water heater 1 from FIG. 1.

The material channels 203 are no longer circular, but are arranged along a line in an essentially rectangular housing 202. The housing 202 has a pressure-tightly encapsulated space 220 in the middle, in which the heating foil 226 is arranged, i.e. the heating foil 226 is glued to a boundary wall of the pressure-tightly encapsulated space 220. On the side of the pressure-tightly encapsulated space 220 facing away from the material channels 203, a space of increased security 222 is provided, separated from it by a partition wall 221.

A fourth embodiment is shown in FIGS. 6 and 7, corresponding parts being provided with reference numerals increased by 300 compared to FIG. 1. In contrast to FIGS. 1 and 4, the control room 320 no longer surrounds the housing 302 in a ring. Rather, the control room 320 is only in one half (in the circumferential direction) provided, while the increased security room 322 is provided in the other half. The housing 302 is otherwise unchanged from the housing 2 of FIG. 1. The pressure-tight encapsulated space 315 is also closed by a wall 312. However, this wall extends over the entire axial length of the housing 302. It has a window 27 through which the pressure-tightly encapsulated space 315 is connected to the control space 320. Two flameproof gaps 324, 325 allow explosion pressures to escape from the pressure-proof encapsulated space 315 on the one hand and from the control room 320 on the other. In both cases, however, the escape of flames or sparks is prevented.

A fifth embodiment of a water heater 401 is shown in FIG. 8. The housing 402 and the wall 412, which together delimit the pressure-tight encapsulated space 415, are unchanged from the embodiment according to FIG. 1. However, the housing part 417 has changed. The housing part 417 has a switching space 420 which surrounds the housing 402 in a ring shape. The housing part 417 has an axial extension 418, in which a space 422 of increased security 422, which is also annular, is arranged, which is closed by a cover 423. Since the extension 418 does not allow the fluid to exit in the radial direction, the outlet 409 is now essentially axially aligned.

FIG. 9 shows a sixth embodiment of the water heater 501, in which corresponding parts are provided with reference numerals increased by 500 compared to FIG. 1. The housing 502 and the wall 512 are unchanged from the embodiment according to FIG. 1. Only the housing part 517 has changed, which has an annularly extending end at its end facing the upper cover 504 Has control room 520 and at its other end the room of increased security 522. The housing part 517 has an outer wall 28 which connect the two sections, which accommodate the control room 520 and the increased security room 522, with each other. This outer wall is at a small distance from the wall 512 over most of its length. This makes it easier to push the housing part 517 onto the wall 512.

A seventh embodiment of a water heater 601 is shown in FIG. 10. This corresponds to the configuration according to FIG. 9 with the exception that no room with increased security is provided. Rather, only one control room 620 is provided, which is connected to the pressure-tightly encapsulated space 615 over the entire end face of the pressure-tightly encapsulated space 615. The heating foil 626 is arranged in the pressure-tightly encapsulated space 615. This is glued to the boundary wall of the pressure-tightly encapsulated space 615, which at the same time forms the outer boundary of the housing 602 in the recess 611.

Claims (18)

1. Instantaneous heater with a casing (2, 102, 202, 302, 402, 502, 602) in which there is provided at least one material channel (3, 103, 203, 303, 403, 503, 603) for the through passage of a fluid to be heated, and with a surface heating member (26, 126, 226, 326, 426, 526, 626), which lies flat on one surface of the casing (2, 102, 202, 302, 402, 502, 602), characterised in that the surface heating element (26, 126, 226, 326, 426, 526, 626) is disposed on one defining wall of a pressure-tight encapsulated space (15, 115, 215, 315, 415, 515, 615).
2. Instantaneous heater according to claim 1, characterised in that the defining wall forms part of the casing (2, 102, 202, 302, 402, 502, 602).
3. Instantaneous heater according to claim 1 or 2, characterised in that a flame-proof gap (14, 24, 25, 324, 325) is provided, which connects the pressure-tight encapsulated space (15, 315) with the environment.
4. Instantaneous heater according to one of claims 1 to 3, characterised in that the pressure-tight encapsulated space (15, 115, 215, 315, 415, 515, 615) is filled with a non-combustible material in powder form.
5. Instantaneous heater according to one of claims 1 to 4, characterised in that the pressure-tight encapsulated heater (15, 115, 315, 415, 515, 615) has an expanded portion vertical to the defining wall, which lies in a range of two to twenty times the thickness of the surface heating element (26, 126, 326, 426, 526, 626).
6. Instantaneous heater according to one of claims 1 to 5, characterised in that the surface heating element (26, 126, 226, 326, 426, 526, 626) is in the form of a heating film.
7. Instantaneous heater according to one of claims 1 to 6, characterised in that a pressure-tight encapsulated switch chamber (20, 120, 320, 420, 520, 620) is provided in which there are located electrical switch devices, and which is connected with the pressure-tight encapsulated space (15, 115, 315, 415, 515, 615).
8. Instantaneous heater according to claim 7, characterised in that the switch chamber (20, 120, 420 520, 620) totally surrounds the casing (2, 102, 402, 502, 602) over a portion of its length in the circumferential direction, the pressure-tight encapsulated space (15, 115, 415, 515, 615) opening with its end face over the entire circumference into the switch chamber (20, 120, 420, 520, 620).
9. Instantaneous heater according to one of claims 1 to 8, characterised in that the casing (2, 102, 302, 402, 502, 602) is substantially cylindrical, the material channel (3, 103, 303, 403, 503, 603) extending substantially parallel to the axis of the cylinder.
10. Instantaneous heater according to one of claims 1 to 9, characterised in that the casing (2, 102, 302, 402, 502, 602) has in the region of the defining wall a return (11, 111, 311, 411, 511, 611) in which the surface heating element (26, 126, 326, 426, 526, 626) is disposed.
11. Instantaneous heater according to claim 10, characterised in that the return (11, 111, 311, 411, 511, 611) is covered over at least a portion of its length by a wall (12, 112, 312, 412, 512, 612) pushed from an end face on to the casing (2, 102, 302, 402, 502, 602).
12. Instantaneous heater according to claim 11, characterised in that the switch chamber (22, 122, 322, 422, 522) is provided in a casing portion (17, 117, 317, 417, 517, 617) which is pushed from the end face on to the casing (2, 102, 302, 402, 502, 602), and at least partly covers the wall (12, 112, 312, 412, 512, 612).
13. Instantaneous heater according to claim 12, characterised in that the casing portion (117) and the wall are integrally formed, especially as a cast metal part.
14. Instantaneous heater according to claim 12 or 13, characterised in that there is provided in the casing portion (17, 117, 317, 417, 517) a high-security chamber (22, 122, 322, 422, 522).
15. Instantaneous heater according to claim 14, characterised in that the high-security chamber (22, 122) is externally located in a direction perpendicular to the casing longitudinal axis.
16. Instantaneous heater according to claim 15, characterised in that the switch chamber (320) and the high-security chamber (322) respectively extend over a portion of the circumference.
17. Instantaneous heater according to claim 14, characterised in that the switch chamber (520) and the high-security chamber (522) are disposed in the direction of the casing longitudinal axis at opposed ends of the casing portion (517).
18. Instantaneous heater according to one of claims 1 to 17, characterised in that the casing (2, 102, 202, 302, 402, 502, 602) is made from stainless steel.

Images