The present invention is related to heating devices, in particular to a heater for heating a flowing fluid, preferably air.

Heating devices for producing a stream of heated fluid, in particular heated air, are already known in the prior art. However, with regard to the achievable temperatures and the size and complexity of the known heating devices, there are still improvements necessary. Has been found that for achieving exit temperatures of more than 700 °C the heating devices known from the prior art have to be very large and complex.

It is therefore an object to the present invention to provide a heater which is capable of reaching high end temperatures of the heated fluid and in the same time has a compact and reliable design.

This object is achieved with a heater according to claim 1 . Preferred embodiments of the invention are defined in the depending claims.

According to the invention, a heater is provided, in particular for heating a streaming fluid, which comprises a frame, at least one heating wire, at least one heating block and a housing, wherein the housing comprises an inlet section and an outlet section which are arranged spaced apart from each other along a flow axis, wherein the heating block comprises a plurality of flow channels and is held by the frame such that the flow channels extend parallel to the flow axis, wherein said at least one heating wire comprises two terminals adapted to be connected to an electric power supply, wherein the heating wire is held by the frame and/or the housing in a position adjacent to the at least one heating block, wherein the electrically heated heating wire causes a temperature rise in the heating block, wherein i a fluid, preferably a gas like air, streaming from the inlet section to the outlet section, passes through the flow channels and is heated up by the heating blocks. The basic difference between the heater of the present invention and heaters known from the prior art is, that the heat transfer into the streaming fluid does not take place directly at the heating wires, which are for instance electrically heated, but is performed by the heating blocks which themselves are heated with thermal energy received from the heating wires. One main advantage of this arrangement is, that the surface area at which heat can be transferred into the gas is drastically increased. The heater comprises an inlet, which is adapted to receive streaming fluid from another entity, for instance a fan, blower or pump. This means that the heater according to the present invention must not necessarily have an own device or section to accelerate a fluid. Into the housing of the heater extends a plurality of heating wires which are adapted to be coupled to an electric power supply. The heating wires are thereby preferably not arranged within the fluid stream but are arranged adjacent to the heating blocks. The heat energy of the heated heating wires is transferred to the heating blocks preferably mainly via radiation. In the simplest embodiment of the invention one heating block is heated up by one heating wire, wherein the fluid streaming through the flow channels of the heating block is heated with certain temperature increase from the inlet to the outlet of the flow channel. This basic modular principle of the present invention allows to create heaters which are adapted to reach temperature increases of at least 500 K up to 1500 K. Furthermore, since the heating process does not rely on combustion processes, the heater according to the present invention avoids combustion-related pollutants and contributes to the reduction of the CO2 footprint.

Preferably the heating wires are not in direct contact with the heating blocks. This allows to use mechanically sensitive material for the heating wires, since the heating wires are arranged in a protected space. In particular the heating wires are projected from abrasion or other contaminations resulting from the direct contact to streaming fluid. This allows to heat even chemically aggressive fluids, in particular highly corrosive gases, with the heater according to the present invention. The heating blocks are thereby preferably heated mostly or only by radiation of heat energy transferred from the heating wires to the heating blocks. The heater of a preferred embodiment comprises at least four heating blocks, wherein the at least one heating wire is arranged adjacent to at least two heating blocks and is adapted to transfer heat to these adjacent heating blocks. Preferably, group of heating blocks is arranged such that heating wires arranged between the heating blocks are able to heat up several neighbouring heating blocks by radiation. This feature increases the efficiency of electric energy provided to the heating wires to be useable as thermal energy in the heating blocks. Furthermore, by arranging several heating blocks in a plane orthogonal to the flow axis of the streaming fluid, the mass flow can be increased compared to only one heating block. Preferably, by arranging a plurality of heating blocks successively along the flow axis, the overall temperature gain can be raised.

Preferably, at least four of the heating blocks are arranged in a first plane. In this preferred embodiment, at least four heating blocks form a first stage in the heating process of a fluid streaming orthogonal to the first plane. It is preferred that such group of heating blocks arranged in a first plane, such that the front faces of the heating blocks are parallel to the first plane, form a base module to build up an entire heater with several of such base modules.

In a preferred embodiment, at least four of the heating blocks are arranged in a second plane, at least four of the heating blocks are arranged in a third plane and at least four of the heating blocks are arranged in a fourth plane, wherein the flow channels of four heating blocks are arranged essentially coaxially to each other and essentially parallel to the flow axis. Arranging several groups of heating blocks consecutively behind each other along the flow axis allows for a higher temperature increase in the streaming fluid from the inlet to the outlet of the heater. The modular design of the heater according to the invention allows to build heaters for certain required temperatures, mass flows and available space for installing such specific heaters.

It is preferred that nine heating blocks are arranged in at least each of a first, a second, a third, a fourth and a fifth plane. This particular design of nine heating blocks to be arranged in each of the five heating planes allows for temperature increases and fluid stream of air of about 1200 K to 1500 K. It will as well be understood that increasing the number of heating planes will allow for even higher temperatures, even though the temperature difference between the fluid and the heating block will be restricted by the maximum temperature, the material of the heating block is able to withstand.

In a preferred embodiment the heating wire comprises a U-shaped section, wherein the sides of the U-shaped section extend preferably orthogonal to an axis parallel to the flow axis. The U-shaped section allows to arrange the terminals of the heating wires on one side of the housing. This allows in particular for a compact design of the power supply to the heating wires, since all necessary terminals can be arranged within small space. It may furthermore be preferable if the heating wires not only have a U-shaped but a couple of consecutive U-shaped selections which provides a wave-shaped or W- form of the heating wires. By increasing the length of the heating wires, it is possible to heat a greater volume of the heater with one heating wire. However, the maximum power output of the heater is limited to the maximum electric energy that can be transferred into heat energy by the heating wire(s), which may make it preferable to increase the number of heating wires.

It is preferred that at each end of the U-shaped section there is arranged one of the first or second terminal. The design of a U-shaped heating section of the heating wire together with two terminals arranged at the end portions of the U-shaped portion allows for a very compact design of the heating wires and makes the arrangement of the respective terminals at the outer side of the housing simple.

The heater of any of the preceding claims, wherein the heating wire comprises a section made of tungsten. It is preferred that at least the portion of the heating wire, which transfers heat energy to the heating block, is made of tungsten wherein the terminal portions may for instance be made of less heat resistant material. Preferably the frame comprises a plurality of web sections which hold at least one heating block in position, wherein the web sections comprise guide faces which are adapted for guiding the fluid into or out of a heating block. The frame is preferably built as holding structure to hold the heating blocks in position relative to the housing and relative to the heating wires. In particular, the frame comprises a plurality of web sections which form rectangular openings to receive the heating blocks. A further function of the frame is to guide the fluid flow into the heating blocks. Therefore, the web sections of the frame comprise guide faces which are inclined relative to the fluid flow direction, to allow for a mostly laminar flow of fluid into the flow channels.

Thereby it is preferred that each heating block is supported by at least four surrounding web sections. The four web sections of the frame prevent the heating block from movements relative to the housing and the other heating blocks. In a further preferred embodiment eight web sections are adapted hold one heating block, four at the front face and four at the rear face of the heating block relative to the fluid flow direction.

Furthermore preferred, the flow channels have a polygonal or circular cross section which is constant along the flow axis. The design of the flow channels as an important impact of the flow characteristics within the flow channel. Furthermore, it is preferred to provide a cross shape, that is easy to produce and sustainable when high temperatures and high fluid velocities are present. Preferably the flow channels have a rectangular cross shape. In a preferred, alternative embodiment the flow channels may have a hexagonal shape, which gives the heating block honeycomb shape.

Preferably the at least one heating block has a rectangular front face lying orthogonal to the flow axis, wherein the heating block preferably has a cubic shape. The rectangular shape and in particular preferred cubic shape of the heating block eases production of the heating blocks and allows for a very compact design of the heater. In particular, a plurality of heating blocks can be arranged adjacent to each other with small gaps in between to form a group of heating blocks allowing for high temperature increases achieved by the heater.

It is preferred that the flow channels have an average cross-sectional area, wherein the ration of the sum of the cross-sectional areas of all flow channels of one heating block to the total area of the front face heating block is about 0,2 to 0,8, preferably about 0,3 to 0,6. The preferred range of 0,2 to 0,8 was found to allow fluid temperature increases of 200 K and more within one heating block. While at the same time high mass flows are possible.

Preferably the fluid enters the inlet section with an inlet temperature and exits the outlet section with an outlet temperature, wherein the heater is adapted to provide a difference between the outlet temperature and the inlet temperature of at least 500 K to 1500 K, preferably of at least 800 K to 1200 K and preferably at least 1100 K. The Heater, in particular the plurality of heating blocks, the heating wires and the arrangement of the heating blocks is configured to reach temperature increases by the heater of at least 1100 K. This is achieved by the chosen materials, number and arrangement of heating blocks and the electric power which can be transformed into heat by the heating wires.

In a preferred embodiment the at least one heating block is made of silicone carbide (SiC). Silicon carbide has the advantage of being very resistant to high temperatures and is easy to manufacture and to shape.

Preferably, the housing comprises an insulation which preferably comprises a layer of alpha wool and/or a layer of aerogel. To increase the efficiency of the heater, the housing comprises at least one insulation layer, to prevent heat from exiting the heater without heating up the streaming fluid. In other words, the insulation provided to the housing reduces the thermal losses of the heater.

Furthermore preferred, the frame and selected parts of the housing comprise or are built of an aluminum alloy. The advantage of utilizing an aluminum alloy to form the frame and furthermore preferred the housing of the heater lies in the relatively low costs and mechanical abilities of aluminum. Furthermore, aluminum allows for lightweight constructions, which optimizes the heater for the use in moveable energy generation systems.

Further features of preferred embodiments of the present invention are described below with reference to the enclosed figures.

Figures 1 and 2 show cut views of a first preferred embodiment of the present invention. The heater comprises a frame 1 formed of web sections 11 between which heating blocks 3 are arranged and held. The frame 1 and the heating blocks 3 are enclosed by a housing 4, while a plurality of heating wires 2 enter topside of the housing 4. It is preferred to arrange all entry points of the heating wires at only one side of the heater, to allow for a compact design of the heater itself and also of the electrical periphery, as for instance the cables or a respective manifold to supply electric current to the heating wires 2. Each of heating wires 2 comprises a first terminal section 21 and second terminal section 22 which are adapted to be connected to an electric power supply. The housing 4 comprises an inlet section 41 , through which fluid F enters the heater along a flow axis A, and an outlet section 42 at which the heated fluid F exits the heater. Preferably, the inlet section 41 is formed as diffuser to decelerate the entering cold fluid F at inlet temperature T1 and distribute it to the heating blocks 3 adjacent to the inlet 41 . The outlet section 42 is formed as nozzle to accelerate the leaving and heated fluid F which has an outlet temperature T2. As can be seen particular from figure 2, several groups of heating blocks 3 are arranged each within one of a first plane H1 , a second plane H2, a third plane H3, a fourth plane H4 and a fifth plane H5. This modular construction of the heater allows to adapt the heater for certain temperature raise requirements and given space the heater may occupy. In case a lower temperature increase is sufficient, only four or three planes (H1 , H2, H3) of heating blocks 3 may be sufficient. Accordingly, a higher number of planes with heating blocks 3 can be used if higher temperature gradient is required. Figure 3 shows a view on a preferred embodiment of the heater according to the present invention with the housing 4 not shown. In particular the U-shaped section 23 of the heating wires 2 is shown, which extends into the area between the heating blocks 3 to heat up the adjacent heating blocks 3. Thereby, both sides of the U-shaped sections 23 preferably extent orthogonal to a parallel axis to the flow axis A.

Figure 4 shows a front view on the inlet section 41 of the housing 4 of the heater according to the present invention. In particular the preferred shape and arrangement of the web sections 11 is visible. In this preferred embodiment, one heating block 3 is held by 4 neighbouring web sections 11. Furthermore, the web sections 11 comprise guide faces 12 which guide the fluid flow into the heating block 3 and in particular into the flow channels 31 .

Figure 5 shows a cut view of a preferred embodiment of the heater wherein the frame 1 , the housing 4 and in particular the insulation 43 of the housing 4 is shown. The housing 4 and particular the insulation 43 of the housing surrounds the frame 1 and the heating blocks 3 to prevent heat from leaving the heater in an orthogonal direction relative to the flow axis A.

Figure 6 shows a detailed view on a preferred embodiment of a holding system to hold the heating wires 2 at the other side of the housing 4. It is preferred that adjacent to the terminals 21 , 22 but heating wires 2 are clamped by holding blocks 24, which preferably are made of material with low thermal conductivity. These holding blocks 24 are clamped against the heating wires 2 by brackets 25 which are held together for instance in a conventional manner by a screw.

Figure 7 shows a detailed perspective view on a preferred embodiment of a heating block 3. In particular preferred the heating block 3 comprises a plurality of flow channels 31 that are distributed uniformly within the heating block 3. In particular preferred each of the flow channels 31 extends parallel to the flow axis A. This preferred embodiment the flow channels 31 have rectangular cross-sectional shape with a cross-sectional area 32. It is preferred that the sum of the cross-sectional areas 32 of the flow channels lie within a range of 0,2 to 0,8 times the total front surface 33 of the heating block 3.

Reference numerals:

1 - frame

11 - web sections

12 - guide faces

2 - heating wire

21 - first terminal

22 - second terminal

23 - U-shaped section

24 - holding block

25 - bracket

3 - heating block

31 - flow channel

32 - cross-sectional area

33 - total area

4 - housing

41 - inlet section

42 - outlet section

43 - insulation

A - flow axis

F - fluid

H1 , H2, H3,(...) - first, second, third, (... ) plane

T1 - inlet temperature

T2 - outlet temperature