Device for heating a fluid

Abstract

The invention relates to a device (1) for heating a fluid. It comprises a transformer core (2) comprising first and second transformer legs (3,4). An electrically conducting winding (5) is wound around the first transformer leg for connection to an AC power supply during use. The device has at least one electrically conducting heating element (6) having a hole (7) through which the second transformer leg extends. A housing (8) with at least one inlet and at least one outlet is arranged around the at least one heating element. When an alternating current is applied to the winding during use, a resulting alternating magnetic field in the transformer core induces an electric current in the at least one heating element, the current causing heating of the at least one heating element. When fluid flows through the housing during use, the fluid is heated by the at least one heating element.

Description

[0001] 84998PC01

[0002] 1

[0003] DEVICE FOR HEATING A FLUID

[0004] FIELD OF THE INVENTION

[0005] The present invention relates to a device for heating a fluid flowing through the device during use. In particular, it relates to such a device based on the overall working principle of an electrical transformer.

[0006] BACKGROUND OF THE INVENTION

[0007] Electricity can be used to heat a fluid in many different applications. In general, two different principles are used to transfer the supply voltage to heating elements used for heating the fluid.

[0008] One principle is based on direct coupling via a cable with at least two conductors to one or more heating elements that comes into direct / indirect contact with the fluid to be heated. If the fluid is electrically conductive, electrical current can flow in the fluid or electrical current can flow down to ground. This means that there must be an insulating material around the heating element, which means that the heating element becomes less efficient for the heating. Therefore, the temperature difference between the heating element and the fluid becomes large, such as more than 100 degrees Celsius, when the fluid is heated to high temperatures. This causes the heating element to wear-out and eventually burnout like an incandescent bulb. In addition, cables are required to conduct the electrical current to the heating element, which causes losses and thus reduces the efficiency. In addition, at least four connections must be made with the ends of the two cables to the heating element and the power supply. The connections can fail if an oxide layer, such as copper oxide, forms. Therefore, the connectors are often coated with precious metals, such as silver or gold. At least for some applications, the electrical current must be connected to the heating element through a housing, such as a house wall of the heat generator. This can cause problems, because the housing must be fluid-tight if loss of fluid is undesired, it must not be electrically conductive, and it must not conduct too much heat out to the cables. 84998PC01

[0009] 2

[0010] Another principle is based on induction heating which is best known from induction cookers. Here a liquid is heated by a special cooking pan arranged on an induction coil. Induction cookers typically use high frequency, e.g. 10kHz, to transfer power efficiently enough. But this means that advanced electronics is needed to create the alternating voltage. Another problem with this method is that the magnetic field must travel from the coil to the bottom of the pan through a plate that is not magnetically conductive, typically glass. This means that the magnetic field has difficulty passing therethrough, and therefore much more electric current is needed than if the magnetic circuit was closed by an iron core, as is the case with a standard 50Hz transformer. Induction heating typically relies on the heating elements being magnetically conducting, and hysteresis loss is formed in the heating elements. Hysteresis loss will cease to exist, if the material temperature is higher than the curie temperature (769°C for iron), because the material stops being magnetic, this setting a thermal limit of such devices.

[0011] Hence, an improved device for heating fluid would be advantageous.

[0012] OBJECT OF THE INVENTION

[0013] It is an object of the present invention to provide a device for heating a fluid, which device has a high efficiency.

[0014] It is another object of the present invention to provide a very high power device for heating a fluid in order to electrify the hard-to-abate fossil fuel burning industry where high temperatures (>500°C) are demanded. By "very high power" is preferably meant 1 MW or above.

[0015] It is another object of the present invention to provide a device for heating a fluid, which device has a low risk of malfunction caused by weak or broken electrical connections.

[0016] It is an object of at least some embodiments of the present invention to provide a device for heating a fluid, which device is compact. 84998PC01

[0017] 3

[0018] It is an object of at least some embodiments of the present invention to provide a device for heating a gas.

[0019] It is a further object of the present invention to provide an alternative to the prior art.

[0020] In particular, it may be seen as an object of the present invention to provide a device that solves the above-mentioned problems of the prior art.

[0021] SUMMARY OF THE INVENTION

[0022] The above-described object and several other objects are intended to be obtained in a first aspect of the invention by providing a device for heating a fluid flowing through the device during use, the device comprising:

[0023] - a transformer core comprising a first transformer leg and a second transformer leg,

[0024] - an electrically conducting winding wound around the first transformer leg and configured to be connected to an AC power supply during use,

[0025] - at least one heating element made of electrically conducting material and having a hole through which the second transformer leg extends,

[0026] - a housing arranged around the at least one heating element, the housing having:

[0027] - at least one inlet for allowing fluid to flow into contact with the at least one heating element during use of the device, and

[0028] - at least one outlet for allowing fluid to flow away from the at least one heating element during use of the device, so that when an alternating current is applied to the winding during use, a resulting alternating magnetic field in the transformer core induces an electric current in the at least one heating element, the current causing heating of the at least one heating element, and so that when fluid flows through the housing during use, the fluid is heated by the at least one heating element. 84998PC01

[0029] 4

[0030] The idea and work leading to the present invention is based on the fact that you typically need a transformer anyway when converting large amounts of electricity into heat. This is because electricity is most easily transported over long distances with very high voltage, typically 150kV or 400kV, but for many end applications, the heaters require a low voltage, typically between a few volts and up to a few 100V, and the voltage is adapted to the intended use with a 50 / 60Hz transformer. A device according to the present invention comprises a transformer, but the way it is used to heat a fluid differs significantly from a traditional way of heating as will be described in detail in the following.

[0031] With a traditional heater, electric wires are normally required to supply power to the heating elements; this is not necessary with the present invention. An advantage thereof is that such wires would cause electrical losses that result in poor efficiency. Another advantage is that it may be possible to obtain a more compact design, because there is no need for space for wires. Furthermore, with a device according to the present invention, there is no electrical connections between electric wires and the heating elements. In a traditional solution comprising wires, the electrical connections would typically be established by use of cable shoes and bolt-and-nut connections fastened thereto. During use, the connections will typically be exposed to varying thermal stresses which may result in damage or loosening of the nuts so that the electrical contact is weakened or lost. This disadvantage can be avoided with the present invention.

[0032] Another advantage of the present invention is that it is galvanically isolated from the power supply, so that no electric current can flow to ground. Furthermore, the voltage is very low, so it is very limited how much electric current can flow in the fluid compared to what flows in the heating element. The device can run at 50Hz, as the magnetic circuit is closed by a magnetically conductive material, typically soft iron. The voltage from one turn of winding around the transformer leg is given by:

[0033] U = 2 * pi * A * B * f

[0034] Where:

[0035] U is the amplitude of the voltage

[0036] A is the cross-sectional area of the transformer leg

[0037] B is the amplitude of the flux density in the transformer leg (typically 1.5-1.8T) 84998PC01

[0038] 5 f is the frequency (typically 50 or 60Hz)

[0039] For example, if:

[0040] A = 0.1m*0.1m = 0.01m2

[0041] B = 1.7T f = 50Hz Then U = 5.3V

[0042] 5.3V can cause electrical current to flow in the fluid if it is a good electrical conductor like most metals, but typically it is not. The fluid would e.g. be air or water. And even if the fluid was a good conductor, the electrical current would mostly just contribute to heating the fluid. Furthermore, a voltage of 5.3V would not be dangerous for humans to touch directly, and it is so low that it is not even covered by the Low Voltage Directive.

[0043] The transformer core will typically be made from laminated soft-magnetic material which is suitable for carrying an alternating magnetic field with a low hysteresis loss and eddy-current loss. The cross-sectional shapes of the first and second transformer legs may e.g. be rectangular, circular, or rectangular with rounded corners. A person skilled in the art of transformers will know how to design such a transformer core. The cross-sectional shape of the first and second transformer legs need not be the same. It may e.g. be possible to use a circular cross-section for the first leg and a rectangular cross-section for the second leg. The circular cross-section of the first leg allows for as short a winding as possible and thereby a low loss. On the contrary, loss resulting in heating is desired in the at least one heating element arranged around the second leg. This at least one heating element may typically have a shape matching the geometry of the second leg, and it may therefore be decided to use a cross-section, such as rectangular, of the second leg which both has such an effect, and which may also be easier to manufacture at least from some manufacturing processes.

[0044] In some embodiments of the invention, the first and second transformer legs are separate legs arranged in parallel. In other embodiments, the first and second transformer legs are arranged in extension of each other as is often the case in 3- phase transformers. 84998PC01

[0045] 6

[0046] The housing may have a shape and dimensions matching the outer geometry of the at least one heating element. Typically the housing will also carry the at least one heating element e.g. by comprising holders to which the at least one heating element is fastened. Furthermore, the housing may have a wall facing and surrounding the second transformer leg so that both that wall and the gap between the housing and second transformer leg provide thermal protection to the second transformer leg. An example of such an embodiment will be shown in the figures. In other embodiments, the housing may be arranged around both the at least one heating element and the second transformer leg provided that the second transformer leg can withstand the temperatures, chemistry and flow- induced forces of the flowing fluid. No matter which design is used, the flow path of the fluid must be sealed off from the surroundings. A person working within this technical field will know how such sealing can be ensured.

[0047] The housing may be made from a material that provides both thermal and electric isolation, such as ceramic, polymer or composite material. The housing may alternatively be made from metal. In such embodiments, it typically comprises at least one interruption in the metal material to prevent the induction of electric current in the housing due to the alternating magnetic field in the transformer core. At this at least one interruption, the housing is made from a material with very low, such as zero, electric conductivity, such as a semi-conducting material or a ceramic. In addition to the housing itself, further thermal and / or electrical isolation may be obtained by an isolating layer arranged at least partly around the at least one heating element as will be exemplified in the figures.

[0048] When the device is to be used for heating of pressurized fluid, it may be necessary or advantageous to provide the housing with a surrounding pressure shell designed to withstand the forces expected to arise during use of the device. Such a pressure shell may connect the at least one inlet and the at least one outlet to pipes through some transition zones. In some embodiments of the invention, this pressure shell may be integrated with the housing, such as being the housing itself configured to withstand high pressure. 84998PC01

[0049] 7

[0050] In some embodiments of the invention, more shells may be arranged around each other with free space in between. Such a design would provide good thermal insulation so that an isolating layer is unnecessary. However, there must be electrical insulation between the inner shell and the heating elements. This may e.g. be provided in the form of a thin ceramic plate on which the lowermost heating element rests.

[0051] In order to control a process in which the device is used, it may be possible to monitor at least the temperature, the pressure, and / or the flow rate at one or more locations within the housing. This may e.g. be done by use of sensors arranged within the housing. The sensors may either be configured to transfer measurements wirelessly to a receiver, or the sensors may be arranged through sealed holes in the housing and in the isolating layer, when present. The temperature can also be estimated by calculating the resistance of the at least one heating element, which typically has a resistivity that is temperature dependent. The resistance can be found by measuring available parameters, such as current and voltage, on the primary side of the transformer, i.e. in the electrical winding at the first transformer leg.

[0052] Each of the at least one heating element may be provided as a unitary element, such as an annular disc, or it may be made from sub-elements to be assembled before or during the process of assembling the device.

[0053] The choice of material for the at least one heating element depends on the intended use of the device. The material should be able to withstand the mechanical, thermal, and chemical conditions for which the device is designed. Furthermore, the material should have electrical properties making it suitable for the intended use. The choice will typically be based on a combination of computer simulations and physical experiments. As an example of design considerations, if the thickness of a heating element is doubled, the power output of the heating element also doubles, but the surface area that heats the fluid hardly changes as only the dimension of the surfaces oriented in the thickness direction is changed. Therefore, the thickness of the at least one heating element can be used as a parameter that can be varied in order to suit different materials used. 84998PC01

[0054] 8

[0055] The at least one heating element may e.g. be made by punching it out of a plate. It may alternatively be made by tape casting or by extruding powder metal which is then sintered. The at least one heating element can also be made from a strip of material which is welded into a tube, which tube is then rolled flat to obtain a disc. However, any suitable way of manufacturing the heating elements is covered by the broadest scope of protection.

[0056] The cross-sectional shape of the at least one heating element will typically be determined during the design of a device for a given application. The inner and the outer shape may e.g. be circular, rectangular, triangular, polygonal, or dropshaped. The inner and outer shapes may be the same or differ. Some examples of possible geometries will be shown in the figures. When heating elements are made by punching, the choice of shape will typically take into account that for geometrical reasons, the amount of scrap material can be minimized by using a rectangular or hexagonal outer shape. However, if other shapes are more optimal for the functionality of the heating elements for a given application, the choice will have to be balanced based on all relevant parameters.

[0057] In some embodiments of the invention, the at least one heating element has constant shape and dimensions in the circumferential orientation. By "constant" is meant that it may vary within the tolerances of the manufacturing process used. An advantage of such a design is that the induced current density and thereby the temperature will be substantially constant in the plane of extension of the heating element. Hereby it may be easier to ensure a uniform heating of the fluid, and the risk of hot spots in the heating elements is at least lowered and preferably minimized. In the present context, a hot spot is a localized heating to a temperature significantly higher than that of the surrounding material. Such a hot spot can potentially cause damage to the material.

[0058] In alternative embodiments of the invention, the at least one heating element has varying shape and / or dimensions in the circumferential orientation. As an example, a rectangular outer circumference and a circular inner circumference can provide four zones of low temperature supply and four zones of high temperature supply. Such a design may be used in combination with having more than one inlet and more than one outlet where it may be advantageous to generate heat in 84998PC01

[0059] 9 different zones in relation to the different inlets and or outlets in order to be able to control of the heating process. As an example, the temperature of the fluid will be highest at the at least one outlet, and it may therefore be desired to ensure that the electric power is relatively low at that location whereby - at least for some materials - the wear of the at least one heating element can be kept as low as possible for a given design.

[0060] In addition to selecting a given shape in the circumferential orientation, the shape of the at least one heating element may also be optimized in an orientation facing the fluid flowing through the housing, typically the thickness direction of the heating element. For some applications, it may be advantageous to use an aerodynamic shape ensuring as little flow resistance as possible in order to minimize the energy loss and allow for as high a flow rate as possible. In other applications, the shape is designed to obtain a turbulent flow in order to mix the fluid and obtain a uniform temperature.

[0061] The at least one heating element may be provided with one or more through- going openings in addition to the hole through which the second transformer leg extends. Such through-going openings may be provided to increase / adapt the electrical resistance of the at least one heating element, partly by increasing the distance that the current has to travel and partly by reducing the cross-sectional area of the material in which the current can flow. In embodiments comprising a plurality of heating elements, to be described below, the through-going openings can also be used to allow the fluid to pass from layer to layer, where layer refers to the space between two neighbouring heating elements. The shape of the through-going openings may be determined as part of the design process. They may e.g. be circular, rectangular or elongate, such as in the form of narrow slots.

[0062] The device may comprise a plurality of heating elements that are preferably arranged spaced apart along a longitudinal extension of the second transformer leg. In this way, a larger surface area for a given volume of material is obtained. The transfer of heat from the heating elements to the fluid takes place at the surface of the heating elements, and therefore a larger surface area results in a more efficient device which has a low temperature difference between the heating elements. The fluid thereby minimizing the risk of hot spots and melting of the 84998PC01

[0063] 10 heating elements. For the same reasons, it is also important to have fluid convection on most of the heating elements' surface area, which is possible with the stacked heating element solution with fluid on both sides of the heating elements. In other words, the fluid nearly completely surrounds the heating elements and their surface area, and this results in a huge contact area and good thermal contact from the heating elements to the fluid. This will decrease the difference in temperature between heating elements and the fluid, and therefore it will decrease the risk of hot spots in the heating elements. Alternatively or in combination with heat transfer elements being arranged along a longitudinal extension of the second transformer leg, the heating elements may also be arranged concentrically around each other and thereby also around the second transformer leg.

[0064] The distance between the plurality of heating elements may be maintained e.g. with one or more of the following methods: a. The housing or the isolating layer, when present, can contain circumferentially arranged grooves to retain the heating elements in the desired locations. b. Spacers made from another material, e.g. bolts with nuts or pop rivets or clips. In such embodiments, holes can be made in the heating elements to provide a good mechanical construction. The spacers could be welded or mounted in a hole or embossing of the heating elements. c. Some or all of the heating elements themselves can have regions that are bent out of the plane, if they consist of plate-shaped elements, thus keeping the distance to the neighbouring heating elements. d. Some or all of the heating elements may have a wavy shape in the direction of extension so that they can abut neighbouring heating elements.

[0065] When determining how the distance is to be maintained, it has to be ensured as part of the design process that the mode of keeping the heating elements in place does not hinder the desired flow of fluid through the device. Furthermore, in order to have electrical insulation between the inner surface of the housing and the heating elements, option a) may require that the housing is made of material, such as ceramic, which can both retain heat and insulate both thermally and electrically. 84998PC01

[0066] 11

[0067] It is not a problem to have physical connection between the heating elements, because their electrical potential should be the same, or almost the same, if they are arranged around the same second transformer leg. A possible advantage of the electrical connections through the spacers, as in option b, may be that even if a heating elements does not work as intended, it may still be heated by its electrical connection to the neighbouring heating elements and thereby still provide at least some heating of the fluid.

[0068] In embodiments of the invention comprising a plurality of heating elements, the heating elements may be arranged with substantially the same distance between neighbouring heating elements. Hereby it may be easier to ensure a uniform flow of fluid and a uniform heating of the fluid, whereby the risk of hot spots in the heating elements can be minimized.

[0069] In alternative embodiments of the invention comprising a plurality of heating elements, the distance between neighbouring heating elements differs. In some embodiments of the invention, it may also be possible to adjust the distance between heating elements. This may be done either when the device is idle in order to adjust the device for a specific use, or during use to adjust the device in response to varying desired or undesired detected conditions in the fluid.

[0070] In embodiments of the invention comprising a plurality of heating elements, the arrangement of the at least one inlet and the at least one outlet as well as the design of the plurality of heating elements may be determined to result in the fluid flowing through the device along a meandering path during use. An example of such an embodiment will be illustrated in the figures and further explained in the detailed description thereof.

[0071] In some embodiments of the invention comprising a plurality of heating elements, at least some of the heating elements are provided with embossing which is shaped and dimensioned to ensure desired distances between the heating elements and / or to ensure a desired flow of fluid. The embossing may have several advantages, amongst other to guide the fluid or to create turbulence.

[0072] Such turbulence will increase the thermal convection and reduce the temperature 84998PC01

[0073] 12 difference between the heating elements and the fluid. Turbulence may also reduce the areas in which there would otherwise be a risk of hot spots.

[0074] In some embodiments of the invention comprising a plurality of heating elements, at least some of the heating elements are provided with spacers which are shaped and dimensioned to ensure desired distances between the heating elements and / or to ensure a desired flow of fluid. As mentioned above, such spacers may e.g. be bolts with nuts or pop rivets or clips. An example of such an embodiment will be shown in the figures.

[0075] In some embodiments of the invention comprising a plurality of heating elements, the shape of the heating elements is conical. Such a shape will be particularly advantageous in embodiments with a radial flow of fluid as will be described below.

[0076] The at least one heating element may be arranged to extend in a vertical orientation during use. For heating elements extending in a plane or substantially in a plane, this can e.g. be obtained by arranging tubular heating elements parallel to and surrounding the second transformer leg. Alternatively, the heating elements can extend perpendicular to a horizontally arranged second transformer leg. An advantage of such a vertical orientation is that fragments and dirt in the fluid will fall down due to gravity and can be removed e.g. via a cleaning door installed at the bottom of the housing.

[0077] In some embodiments of the invention, the at least one heating element is configured to be rotated around the second transformer leg during use. This may e.g. be obtained by the at least one heating element having a toothed periphery, which allows for rotation either manually or via an external, motor-driven rotator configured and arranged to engage with the toothed periphery and apply a rotational movement thereto. Such a rotation can be used to loosen fragments and dirt accumulated on the surface of the at least one heating element. The fragments may e.g. be biproducts arising from the heating process. A rotational movement may correspondingly be accomplished by having the at least one heating element mounted to isolation material which is provided with a toothed periphery and configured to rotate during use of the device. A rotational 84998PC01

[0078] 13 movement may also be used to allow the at least one heating element to be moved through different heating zones within the housing. The temperature near the at least one outlet is higher than near the at least one inlet, and therefore the at least one heating element may be more prone to wear on the heating elements near the at least one outlet. Furthermore, the at least one heating element can be rotated, cleaned and inspected manually or automatically all the way round e.g. via an opening at an inlet or outlet. For some embodiments of the invention, the at least one heating element may be configured to be vibrated, e.g. by manually applying a tapping motion thereto, in order to loosen any fragments or dirt therefrom. The loosened material may be flushed away by fluid flowing through the device.

[0079] In embodiments of the invention wherein the at least one heating element is configured to be rotated around the second transformer leg during use, the at least one heating element may be provided with vanes, and rotation of the at least one heating element during use may cause the vanes to assist and / or cause the flow of the fluid through the device. In embodiments of the invention comprising a plurality of heating elements, they may all be provided with vanes, or only some of them may be provided with vanes. The vanes may e.g. be mounted on the at least one heating element by welding. The rotation may e.g. be driven by a motor, such as an electromotor. The at least one inlet may be arranged at or near the second transformer leg, and the at least one outlet may be arranged at or near the periphery of the at least one heating element. Such embodiments comprising vanes may resemble a traditional centrifugal pump. There must be space for the second transformer leg in the centre. In some embodiments of the invention, the second transformer leg has a circular crosssection resembling a motor shaft and designed and arranged to rotate together with the heating elements. It just requires a small air gap at each end of the second transformer leg that connects to the primary side of the transformer. An example of such an embodiment will be shown in the figures.

[0080] In some embodiments of the invention, the at least one inlet and the at least one outlet are arranged:

[0081] - with the inlet(s) and the outlet(s) being located at different distances from the second transformer leg, and 84998PC01

[0082] 14

[0083] - at locations which result in the fluid flowing mainly radially, with respect to a central axis of the second transformer leg, across the at least one heating element.

[0084] The radial flow of fluid may be from close to the transformer leg and outwards, or it may be in the opposite direction. An example of an embodiment with a radial flow will be illustrated in the figures together with more detailed descriptions thereof.

[0085] In embodiments of the invention having a mainly radial flow of fluid, the fluid may flow along the following path through the device:

[0086] - from the at least one inlet into an inner space between an inner thermal insulation and inner periphery of the at least one heating element,

[0087] - mainly radially across the at least one heating element to an outer periphery of the at least one heating element, and

[0088] - to an outer space between an outer thermal insulation and an outer periphery of the at least one heating element, and

[0089] - leaving the device via the at least one outlet.

[0090] The inlet(s) and the outlet(s) could be located at the top, at the bottom, on the inside, or on the outside of the housing. To ensure an even distribution of the fluid to all the heating elements, a space is necessary between the thermal insulation and the heating elements near the inlet(s) and outlet(s). Shaping of these spaces is essential to avoid hot spots and ensure an even distribution of fluid. The shape and dimensions of the space may e.g. be determined by computer simulation, typically combined with testing of physical prototypes. This could e.g. be a shape that changes as a function of the angle around the periphery of the at least one heating element to compensate for the pressure loss of the flow from the inlet(s) to other angular positions. Hereby a uniform radial flow across the at least one heating element independent of the angle is ensured.

[0091] In embodiments having a radial flow of fluid and a design as just described, it will be particularly advantageous to have conically shaped heating elements. In such embodiments, the temperature will be substantially equal circumferentially. When the fluid flows outwards, i.e. away from the transformer leg, the temperature will be highest at the larger radius. This may result in an upwards bending of the 84998PC01

[0092] 15 heating elements at the outer regions thereof, which deformation will typically disappear again upon cooling down of the device. An example of such a design and the advantages thereof will be further explained in relation to the figures.

[0093] The housing of the device in any of the above-described embodiments may be provided with more than one inlet and / or with more than one outlet. Hereby it will be possible to distribute possible heat-induced wear of the at least one heating element. The use of more than one inlet and / or outlet may also be relevant for special processes that require multiple heat levels or several independent loops with different flows. Furthermore, the presence of more than one inlet and / or outlet may facilitate inspection and cleaning of the at least one heating element due to the additional access points around the housing. In embodiments having more than one inlet and more than one outlet, one of these could be provided with an openable cover and be intended for use only in relation to inspection and cleaning but not for flow of fluid during use of the device.

[0094] The housing and / or the second transformer leg may be provided with one or more cooling channels through which cooling fluid can flow for active cooling of parts of the device during use. Furthermore, the electrically conducting winding on the first transformer leg may be submerged in transformer oil. In some embodiments of the invention, the whole device has an outer casing and both the windings and the housing are fully submerged in and cooled by transformer oil. In these embodiments there is at least one inlet and one outlet for fluid and at least one electrical connection to the electrical supply in the outer casing. The housing will then typically be arranged inside or integrated with the outer casing.

[0095] In some embodiments of the invention, the at least one heating element comprises a catalytically active material and / or coating allowing for one or more catalytic processes to take place in the fluid flowing through the device during use. A catalytically active material may e.g. be in the form of catalytically active materials elements arranged next to the at least one heating element, such as between two heating elements. A catalytic process, also referred to as catalysis, is a process that accelerates a chemical reaction that would otherwise be too slow for industrial purposes. Catalysis makes it possible to convert a large number of resources into important and necessary products. The speed of the chemical 84998PC01

[0096] 16 reaction is largely dependent on the activation energy, which refers to the amount of energy it takes to change the chemical bonds and angles of a reactant before it can become a desired product. The lower the activation energy, the faster the reaction. Therefore, an industrial catalytic process typically includes supplying heat in order to add energy to the chemical reactions and thereby increase the efficiency and speed of the production plant used for the production.

[0097] In some embodiments of the invention:

[0098] - the transformer core comprises at least one additional transformer leg,

[0099] - for each of the at least one additional transformer leg, the device comprises at least one additional heating element made of electrically conducting material and having a hole through which the respective additional transformer leg extends, and

[0100] - a) either the housing arranged around the at least one heating element is also arranged around the at least one additional heating element,

[0101] - b) or there is an additional housing arranged around each of the additional heating elements, the additional housing having:

[0102] - at least one additional inlet for allowing fluid to flow into contact with the at least one additional heating element during use of the device, and

[0103] - at least one additional outlet for allowing fluid to flow away from the at least one additional heating element during use of the device.

[0104] In embodiments comprising at least one additional transformer leg, the at least one corresponding additional heating element may be designed in accordance with any of the embodiments described above in relation to the second transformer leg and the corresponding at least one heating element. For a device comprising at least one additional transformer leg, all the transformer legs around which at least one heating element is arranged will typically be designed in the same way. However, the scope of protection also covers embodiments in which they are different. In some embodiments of the invention, each of the at least one heating element comprises holes for both the second transformer leg and all of the at least one additional transformer leg. The holes may e.g. be arranged in a row or in a triangular configuration with the transformer core having the second and at least one additional transformer leg arranged accordingly. 84998PC01

[0105] 17

[0106] In some embodiments of the invention, the device has a coaxial design, wherein each of the first, second, and, when present, at least one additional transformer leg is surrounded by:

[0107] - an electrically conducting winding, and

[0108] - at least one heating element arranged further away from the transformer leg than the electrically conducting winding.

[0109] An example of such an embodiment will be shown in the figures and described in relation thereto. From this description it is clear that such an embodiment could also be defined as:

[0110] The device has a coaxial design, wherein

[0111] - for the first transformer leg, there is at least one first heating element arranged further away from the first transformer leg than the electrically conducting winding,

[0112] - for the second transformer leg, there is a second electrically conducting winding arranged closer to the second transformer leg than the at least one heating element, and

[0113] - for the at least one additional transformer leg, when present, there is an additional electrically conducting winding arranged closer to the additional transformer leg than the at least one additional heating element.

[0114] Such a coaxial design provides a good magnetic coupling between the electrically conducting winding and the at least one heating element, which gives a cos(<|)), also known as power factor, close to 1. This means that the primary voltages and currents are nearly in phase and that the device does not draw much reactive power from the power grid. Reactive power generates loss and heat in the powerlines which should be avoided, if possible. For the same reasons, it is important that the transformer core makes a closed or almost closed path for the magnetic flux. Soft iron can be used as a material for the transformer core, and this material is typically a more than 1000 times better magnetic conductor than air. This also has the advantage that a very limited amount of flux flows in the surrounding air, which limits the electromagnetic disturbance of the surroundings around the transformer and reduces heat generating eddy currents in a 84998PC01

[0115] 18 transformer frame, the housing, and other conducting materials forming part of the device or any supporting elements.

[0116] In any of the embodiments of the invention, the transformer core may be made in a way that makes it possible to open it or to separate it into more parts so that it is possible to replace the at least one heating element in case of wear, malfunction or need for another type or number of heating element(s). This may e.g. be made possible by having the transformer core made from a plurality of parts that are assembled by releasable screw connections. An alternative to this way of allowing for replacement is to make each of the at least one heating element from more parts that are assembled and can be disassembled again. The condition of the at least one heating element can be monitored, e.g. continuously or at regular intervals, to determine when it needs replacement due to wear or malfunctioning. Such monitoring may e.g. include measuring or calculating the electrical resistance therein.

[0117] If considered relevant for any of the above-described embodiments, the device may be designed so that it is possible to change the power supplied thereto. This can e.g. be done by use of a tap changer or by providing additional electrical windings around the first transformer leg which allows for adding or removing electrical power. The functioning of such features and how to apply them will be well-known to a person skilled in the art.

[0118] In a second aspect, the invention relates to a method of heating a fluid, the method comprising the following steps:

[0119] - providing a device according to the first aspect of the invention,

[0120] - connecting the electrically conducting winding(s) to an AC power supply and switching on the power supply, and

[0121] - letting the fluid flow from the at least one inlet to the at least one outlet thereby heating the fluid.

[0122] In a method according to the second aspect of the invention, the fluid may be a gas. The gas may be CO2.

[0123] The method may be configured to perform the following reactions: 84998PC01

[0124] 19

[0125] CH4+CO2+2H2O— >2CH3OH

[0126] CH4+H2O— >CH3OH + H2

[0127] Thus, a method according to the second aspect of the invention may be used to transform methane and water to methanol. In such a method, the gas is CH4 or H2O. Such methods are called endotherm and require heat to occur.

[0128] In a third aspect, the invention relates to the use of a device according to the first aspect of the invention in one of the following processes: thermal storage of energy, catalytic conversion, manufacturing of slaked lime, manufacturing of glass, manufacturing of mineral wool, melting / manufacturing of metal / ceramics, oil refining, manufacturing of cement, heating of tar extracted from coal for use e.g. as roof coating, and heating of bitumen extracted from crude oil e.g. for the production of asphalt. Mineral wool may e.g. be rockwool or glass wool. For all the uses, the invention could also be referred to as a method; i.e. a method of storing energy, a method of catalytic conversion, a method of manufacturing slaked lime etc. The scope of protection of the first aspect of the invention covers a device suitable for any intended use, and such a use is not limited by the examples mentioned in relation to the third aspect of the invention.

[0129] These processes involve the use of a heated fluid, and the heating can be provided by a device as described. As an example, energy can be stored in thermally isolated stones after heating the stones by passing hot air past them. These steps can be preceded by converting electric energy to thermal energy in the form of air heated in a device according to the first aspect of the present invention. The energy can now be stored as heat, and when it is needed again, the stones can heat liquid water into vapour form used in a traditional steam engine with an electric generator, thereby providing the electricity again. The need for temporary storage of energy can e.g. be relevant in relation to energy production for which the amount of produced energy varies and not necessarily matches an actual need, such as for solar power plants or wind turbines.

[0130] Many of the other processes mentioned require the use of hot liquid, such as water, and this liquid may be heated by a device according to the first aspect of the present invention. In the same way, other types of fluid to be used in a heated condition can be provided by leading the fluid through a device according 84998PC01

[0131] 20 to the invention. The device can be used for other purposes than those specifically mentioned if the device is configured to provide the required amount of heating. Should a higher temperature be required than what is obtainable with one device, it will be possible to let the fluid flow through a series of such devices.

[0132] The device according to the invention has been developed for heating fluid, and therefore applications related thereto are used in the description. However, the device can also be used for heating materials that are solid at room temperature and can be transformed from solid to liquid form during the heating process taking place in the device. In such applications, it will also be possible to re-start the process after a possible temporary break in operation without damaging, such as burning, the heating elements. When the heating elements heat up again after cooling during the break, they form a closed circuit of solidified material around the heating elements that becomes liquid due to the heating and can be pumped around the heating elements. This liquid circuit can then be used to re-heat a larger loop of solidified material so that the entire process can be restarted. Such an application could e.g. glass wool or mineral wool production.

[0133] The first, second, and third aspects of the present invention may each be combined. This means that what has been described in relation to one of the aspects may also apply to the other aspects. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0134] BRIEF DESCRIPTION OF THE FIGURES

[0135] The device according to the invention will now be described in more detail with regard to the accompanying figures. The figures show one way of implementing the present invention and is not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

[0136] Figure 1 schematically shows a three-dimensional view of an embodiment of the invention.

[0137] Figure 2 schematically shows a partial view of the device in figure 1. 84998PC01

[0138] 21

[0139] Figure 3 schematically shows a partial view of the device in figures 1 and 2 where three fourths of the housing as well as the isolating layer has been removed.

[0140] Figure 4 schematically shows a partial view of the region around the inlet of the housing being provided with an inlet flange.

[0141] Figures 5. a and 5.b schematically show three-dimensional views of two different embodiments of the housing of the device in figures 1-3.

[0142] Figures 6. a and 6.b schematically show cross-sectional views of the region around the housing when seen from above in relation figures 1-3.

[0143] Figures 7. a and 7.b schematically show cross-sectional view of embodiments provided with cooling channels.

[0144] Figures 8.a-8.c schematically show two embodiments resembling the device in figure 1 but designed to be arranged in another orientation during use.

[0145] Figure 9 schematically shows an example of a heating element that is provided with through-going openings in addition to the central hole through which the second transformer leg extends.

[0146] Figure 10 schematically shows a three-dimensional view of an embodiment of a plate-shaped heating element.

[0147] Figure 11 schematically shows some examples of shapes of heating elements.

[0148] Figure 12 schematically shows a cross-sectional view of an embodiment having a design resulting in the fluid flowing through the device along a meandering path during use.

[0149] Figure 13 shows an example of a heating element provided with a toothed circumference. 84998PC01

[0150] 22

[0151] Figure 14 schematically shows an embodiment of the invention in which the heating elements are configured to be rotated around the second transformer leg during use.

[0152] Figures 15. a and 15. b schematically show two embodiments of the invention in which the transformer core comprises an additional transformer leg.

[0153] Figure 16 schematically shows a 1-phase model of a transformer having a plurality of heating elements arranged in parallel.

[0154] Figures 17.a-17.f schematically show examples of heating elements which are conical and provided with embossing.

[0155] Figures 18.a-18.g schematically show an embodiment of the invention in which the fluid flows mainly radially with respect to an axis of the transformer leg around which the heating elements are arranged.

[0156] Figures 19. a - 19. c schematically show an embodiment of the invention in which the electrically conductive windings and the heating elements are coaxially located on each transformer leg.

[0157] Figures 20.a-20.d schematically show an embodiment of the invention in which the distance between the heating elements is kept as desired by use of spacers in the form of clips.

[0158] DETAILED DESCRIPTION OF AN EMBODIMENT

[0159] Figure 1 schematically shows an example of a device 1 for heating a fluid flowing through the device during use. The device 1 comprises a transformer core 2 with a first transformer leg 3 and a second transformer leg 4. An electrically conducting winding 5 is wound around the first transformer leg 3 and configured to be connected to an AC power supply (not shown) during use. In relation to electrical transformers, this winding would typically be referred to as the primary winding. In the illustrated embodiment, the device 1 comprises a plurality of heating elements 6 made of electrically conducting material and having a hole 7 (see 84998PC01

[0160] 23 figure 9) through which the second transformer leg 4 extends. However, as described above, the scope of protection also covers embodiments with only one heating element 6. The heating elements 6 resemble what in relation to electrical transformers in general would be referred to as the secondary winding. When an alternating current is applied to the winding 5 arranged around the first transformer leg 3, a resulting alternating magnetic field in the transformer core 2 induces an electric current in the heating elements 6 in the same way as in a traditional transformer. This induced current causes heating of the heating elements 6. A housing 8 is arranged around the heating elements 6. In the embodiment in figures 1 and 2, the housing 8 has one inlet 9 for allowing fluid to flow into contact with the heating elements 6 during use of the device 1 and one outlet 10 (see figure 2) for allowing fluid to flow away from the heating elements 6 during use of the device 1. Thus, the invention is based on the idea that when fluid flows through the housing 8 during use, the fluid is heated by the heating elements 6. The connections between the device 1 and pipes (not shown) leading the fluid to the at least one inlet 9 and from the at least one outlet 10 may be designed according to known ways of establishing fluid-tight connections between the respective components of a fluid-conveying system; see also figure 4 and the description thereof.

[0161] Figure 2 schematically shows a partial view of the device 1 in figure 1. Half of the housing 8 and of the heating elements 6 have been removed to better illustrate some of the details inside the housing 8. In this embodiment, an isolating layer 11 is arranged in the housing 8 and around the heating elements 6. Such an isolating layer 11 may be used to provide both thermal and electrical isolation of the housing 8 and the second transformer leg 4. Figure 2 schematically illustrates that the transformer core 2 is made from more parts that can be separated to replace the heating elements 6 in case of wear, malfunction or need for another type or number of heating elements 6.

[0162] Figure 3 schematically shows a partial view of the device 1 in figures 1 and 2. In this figure, three fourths of the housing 8 as well as the isolating layer 11 has been removed to more clearly show a possible design of the heating elements 6. Possible ways of fastening the heating elements 6 were described above and are omitted from this figure. In this embodiment, the heating elements 6 have 84998PC01

[0163] 24 constant shape and dimensions in the circumferential orientation. They are arranged spaced apart along a longitudinal extension of the second transformer leg 4, and there is substantially the same distance between neighbouring heating elements 6.

[0164] If the heating elements 6 have a large dimension, compared to that of the second transformer leg 4, in a plane perpendicular to the longitudinal axis of the second transformer leg 4, the current distribution in the heating elements 6 may be inhomogeneous and thus the heating elements 6 may be warmer near the second transformer leg 4 than further away. If this is undesired or unacceptable, it can be counteracted by making the distance between neighbouring heating elements 6 and / or the thickness of the heating elements 6 variable. Another way of the counteracting may be to make the heating elements 6 corrugated in the regions near the second transformer leg 4 or by making slits / holes in the heating elements as will be shown in figure 9. All these parameters and possible adjustments thereof can be analysed during the design of a device 1 for a given application, such as one of those mentioned above in relation to the second aspect of the invention. Such analysis will typically be made by use of computer simulations, possibly combined with tests on physical prototypes.

[0165] Figure 4 schematically shows a partial view of the region around the inlet 9 of the housing 8 being provided with an inlet flange 12 to which an inlet pipe (not shown) can be connected.

[0166] Figures 5. a and 5.b schematically show two different embodiments of the housing 8 of the device 1 in figures 1-3. As described above, when the housing 8 is made from an electrically conducting material, such as metal, it preferably comprises at least one interruption 13 in the metal material to prevent the induction of electric current in the housing 8 due to the alternating magnetic field in the transformer core 2. At this at least one interruption 13, the housing 8 is made from a material with very low, such as zero, electric conductivity, such as a semi-conducting material or a ceramic. In the illustrated embodiments, there is one such interruption 13, but there may be more than one, if desired. The housing 8 in figure 5. a is provided with an interruption 13 which is shown arranged flush with the walls of the housing 8. In the embodiment in figure 5.b, the housing 8 is 84998PC01

[0167] 25 provided with flanges 14 next to the interruption 13, and a gasket of electrically isolating material is arranged between the flanges thereby forming the interruption 13.

[0168] Figures 6. a and 6.b schematically show cross-sectional views of the region around the housing 8 when seen from above in relation to the previous figures. In figure 6. a, the housing 8 has one inlet 9 and one outlet 10. In figure 6.b, the housing 8 has two inlets 9 and two outlets 10. The arrows indicate possible orientations of the flow of fluid.

[0169] If it is necessary to provide cooling, this may e.g. be done by blowing cooling air or pumping transformer oil into the space between the second transformer leg 4 and the wall of the housing 8 facing towards the second transformer leg 4. Alternatively or in combination therewith, cooling channels in the form of cooling tubes 15 may be arranged around and along the second transformer leg 4 as shown schematically and in cross-sectional view in figure 7. a. The cooling tubes 15, in which cooling fluid flows, may be gathered in a manifold (not shown) in each end of the second transformer leg 4. Cooling may also be provided as shown schematically and in cross-sectional view in figure 7.b. Here the second transformer leg 4 has been provided with inner cooling channels 16 through which cooling fluid can flow. The size of such cooling channels 16 should be carefully selected to ensure the overall functioning of the transformer.

[0170] Figures 8.a-8.c schematically show two other embodiments resembling the device in figure 1 but designed to be arranged in another orientation during use. The housing 8 comprises one inlet 9 for fluid, one outlet 10 for fluid, and one outlet 10a through which it is possible to remove fragments and dirt 17 loosened from the surface of the at least one heating element 6 as described above. The fragments and dirt 17 are collected in a collection chamber 18 from which it can be removed. In the embodiment in figure 8.b, the collected fragments and dirt 17 are collected in a tray that moves in a direction perpendicular to the plane of the paper. In the embodiment in figure 8.c, the collection chamber 18 has a rotation mechanism 19 seen as the central cross-shaped element. By rotating the rotation mechanism 19 around its axis, the fragments and dirt 17 can be removed and collected below the device 1. In the illustrated embodiments in figures 8.a-8.c, the 84998PC01

[0171] 26 device 1 is oriented with the first and second transformer legs 3,4 being horizontally arranged, and with the at least one heating element 6 arranged to extend in a vertical orientation during use. However, if desired, it may also be arranged at an inclined angle as long as the fragments and dirt 17 can fall into the collection chamber 18 by gravity.

[0172] Figure 9 schematically shows an example of a heating element 6 that is provided with through-going openings 20 in addition to the central hole 7 through which the second transformer leg 4 extends. Different possible reasons for having such openings 20 in the one or more heating elements 6 were described above. In the illustrated embodiment, the openings 20 are circular and evenly distributed around heating element 6, but they may have other shapes or arrangements depending on the desired electric properties of the heating elements 6 and the way they influence the flow of fluid.

[0173] Figure 10 schematically shows an embodiment of a plate-shaped heating element 6 having regions near the edges 21 bent out of the plane of extension of the heating elements 6. These bent regions form tabs 22 that can be used to maintain the distance to a neighbouring heating element 6 resting on the tabs 22.

[0174] In all the previous figures, the heating elements 6 have been illustrated as being annular with a circular inner and outer circumference. However, as mentioned above, the scope of protection covers any suitable geometry, and some examples are schematically shown in figure 11. In embodiments in which the fluid is flowing along the surfaces of the heating elements in the manner shown in the previous figures, the housing 8 should preferably have a geometry matching the shape of the heating elements 6 to ensure that all the fluid flowing through the housing 8 is heated. Furthermore, there should preferably be thermal insulation between the heating elements and the surroundings to limit the heat loss to the surroundings.

[0175] Figure 12 schematically shows a cross-sectional view of an embodiment of the invention having four heating elements 6, and wherein the arrangement of the inlet 9 and the outlet 10 as well as the design and arrangement of the heating elements 6 are determined to result in the fluid flowing through the device 1 along a meandering path during use. The temperature of the fluid increases along the 84998PC01

[0176] 27 path so that T1<T2<T3<T4. In such embodiments, the heating elements 6 can advantageously be made of different materials, as the materials that can withstand the highest temperatures (T3, T4) may be very expensive. Cheaper material can be used for the lower temperatures (Tl, T2). The distance between the heating elements 6 may be different e.g. to take into account possible differences in the thermal properties of the materials used for the heating elements 6. The design and resulting meandering path shown in figure 12 is given as an example, but the scope of protection also covers other types of meandering paths as can be understood by a person working within this technical field.

[0177] Figure 13 schematically shows an example of a heating element 6 for use in embodiments of the invention in which the at least one heating element 6 is configured to be rotated around the second transformer leg 4 during use. As described above, this can be obtained by the at least one heating element 6 having a toothed periphery 23, as shown in figure 13, which allows for rotation either manually or via an external, motor-driven rotator (not shown) configured and arranged to engage with the toothed periphery 23 and apply a rotational movement thereto.

[0178] Figure 14 schematically shows an example of an embodiment in which the heating elements 6 are configured to be rotated around the second transformer leg 4 during use. In this embodiment, the heating elements 6 are provided with vanes 24, and the rotation is obtained by an electromotor (not shown). The rotation of the heating elements 6 during use causes the vanes 24 to assist and / or cause the flow of the fluid through the device 1. In this figure, the housing is not shown to better illustrate the vanes 24.

[0179] Figures 15. a and 15. b schematically show two embodiments of the invention in which the transformer core 2 comprises two additional transformer legs 4a, and three windings 5 connected to a three-phase supply voltage (not shown), i.e. the power grid. The design of these transformers differs from those of the previous figures in that the first and second transformer legs 3,4 are arranged in continuation of each other. Such a design may also be used in any of the previously described embodiments. The device 1 comprises at least one additional heating element 6a made of electrically conducting material and having a hole 84998PC01

[0180] 28 through which the additional transformer legs 4a extend. In figure 15. a, the heating elements 6,6a are arranged around all of the transformer legs 4,4a, and in figure 15. b, the heating elements 6,6a are each arranged on one transformer leg 4,4a. In the illustrated embodiments, the housing (shown with dotted lines) arranged around the heating elements 6 is also arranged around the additional heating elements 6a. As described above, the scope of protection also covers embodiments wherein there is an additional housing arranged around each of the additional heating elements, the additional housing having:

[0181] - at least one additional inlet for allowing fluid to flow into contact with the at least one additional heating element during use of the device, and

[0182] - at least one additional outlet for allowing fluid to flow away from the at least one additional heating element during use of the device.

[0183] Figure 16 schematically shows a 1-phase model of a transformer having a plurality of transformer legs arranged in parallel. This type of diagram is used to design and calculate the transformer electrically. In such an embodiment there is a primary side with an electric winding, shown on the left, with equivalent resistance and leakage inductance and a transformer coupling to the secondary side, shown on the right, where there are N heating elements. Each heating element consists of a leakage inductance and a resistance which provides the heat.

[0184] Figures 17.a-17.f schematically show examples of heating elements which are conical and provided with embossing 25. Advantages of conical heating elements 6 will be described in relation to the following figure. Figures 17. a and 17. c are three-dimensional and top views, respectively, of a heating element 6 provided with six pairs of embossing 25, and figures 17. b and 17. d are three-dimensional and top views, respectively, of a heating element 6 provided with five pairs of embossing 25. Figure 17. e shows a three-dimensional cross-sectional view of a stack of heating elements 6 arranged alternatingly with those on figures 17. a and 17. b. Figure 17. f is an enlarged view of section B in figure 17. e. As seen from these figures, this is an example of how embossing 25 of the heating elements 6 can be used to arrange a stack thereof at a predetermined distance determined by the size and shape of the protrusions and indentations formed by the embossing 25. By using an alternating arrangement of heating elements 6 with different 84998PC01

[0185] 29 numbers of protrusions and / or depressions, marked as X and Y in the figure, it is ensured that the distance is kept as desired no matter the mutual orientation of the heating elements 6. The embossing 25 may also have other shapes than those shown in the figures. It may e.g. comprise ribs used to control the flow of fluid into a desired flow path, such as to obtain turbulence and thereby a more efficient and / or uniform heating of the fluid.

[0186] Figures 18.a-18.g schematically shows an embodiment of the invention comprising two inlets 9 and two outlets 10, and wherein the inlets 9 and outlets 10 are located at different distances from the second transformer leg 4. The embodiment in figures 18.a-18.g is one in which the electrically conducting winding 5 and the heating elements 6 are coaxially located on one transformer leg, the transformer leg thereby constituting a combined first and second transformer leg 3,4. It will be referred to as the second transformer leg 4 in the following description. Typically the housing 8 comprises both thermal insulation 11a, lib and a load carrying shell structure. In these figures it is shown as one unit. Figure 18. a is a three-dimensional view of a part of the heating device mainly illustrating the housing 8 in which the heating elements 6 are arranged around the second transformer leg 4. Figure 18. b is a side view, figure 18. c is a top view, and figure 18. d is a bottom view of what is shown in figure 18. a. Figure 18. e is a cross-sectional view along line AA in figure 18. b, and figure 18. f is a cross-sectional view along line BB in figure 18. d. Since figure 18. d is a bottom view, figures 18. e and 18. f are arranged in opposite orientations and therefore show the inlets 9 facing upwards and downwards, respectively. Figure 18. g is an enlarged view of the encircled region in figure 18. e. Figures 18. e and 18. f show that the illustrated embodiment has a coaxial design as will be further described in relation to figure 19. The inlets 9 and outlets 10 are arranged to result in the fluid flowing mainly radially, with respect to a central axis of the second transformer leg 4, across the heating elements 6. As shown with arrows in figure 18. g, the fluid flows along the following path through the device:

[0187] - from the inlets 9 into an inner space 26 between an inner thermal insulation 11a and the inner periphery of the heating elements 6,

[0188] - mainly radially across the heating elements 6 to an outer periphery of the heating elements 6, and 84998PC01

[0189] 30

[0190] - to an outer space 27 between an outer thermal insulation lib and an outer periphery of the heating elements 6, and

[0191] - leaves the device 1 via the outlets 10.

[0192] In the illustrated embodiment, the thermal insulation 11a, lib is provided unitary with the housing 8, but it may also be provided as a separate member.

[0193] As explained above, in embodiments having a radial flow of fluid and a design as described in relation to figures 18.a-18.g, it will be particularly advantageous to have conically shaped heating elements 6 to ensure a uniform deformation and thereby width of the free space next to the heating elements when the temperature of the heating elements 6 changes. This rotationally symmetrical shape means that when the fluid flows outwards, i.e. away from the transformer leg 4, the temperature will be highest at the larger radius. This may result in an upwards bending of the heating elements 6 at the outer regions thereof, which deformation will typically disappear again upon cooling down of the device 1. Or in other words, the illustrated shape of the heating elements 6 means that the temperature is only dependent on the radius and not the angular location with respect to the transformer leg, this giving freedom for any thermal expansion to lead to mechanically stable deformations that will maintain the geometries of the inner and outer spaces 26,27. Likewise, this expansion will be reversible when the heating elements 6 cool down. Due to the inner and outer spaces 26,27 surrounding the heating elements 6, the deformation of the heating elements 6 will not cause any damage, because there is free space for the deformation.

[0194] At least for some embodiments of the invention, it is extremely important to have the same radial flow of fluid in each of the slots 28 between neighbouring heating elements 6 in the entire stack of heating elements 6 in order to ensure a uniform temperature, an efficient heat transfer, and no hot spots. Therefore, the same static pressure difference must be established between Pl and P3 as between P2 and P4, as this will ensure the same flow of fluid in each of the slots 28; see figure 18. g. This can be done by making the pressure loss from Pl to P2 the same as from P3 to P4. It should be noted that the inner space 26 with width W1 is located at a smaller radius in the rotationally symmetrical heating elements 6, and the outer space 27 with width W2 is located at a larger radius. Likewise, the fluid has a higher temperature at W2, as it has been heated by passing between the 84998PC01

[0195] 31 heating elements 6. A warmer fluid has, among other things, a different density and thus a different flow resistance. Thus, there are several factors to consider when establishing and determining the correlation between W2 and Wl. In the literature, these inlet and outlet challenges are described as Z-inlet-outlet, which is well known from heat exchanger design. The skilled person would therefore know how to perform this part of the design process.

[0196] Figures 19. a -19. c schematically show an embodiment of the invention in which the electrically conducting windings 5 and the heating elements 6 are coaxially located on each transformer leg of a transformer having a first, a second, and one additional transformer leg. In figure 19. a the housing and the insulation has been left out from the figure to more clearly illustrate the other parts. Figure 19. b schematically shows the same device 1 as in figure 19. a but now including the housing 8. Figure 19. c shows a cross-sectional view resembling the one shown in figures 6.a-7.b. In such an embodiment with a coaxial design, the thermal insulation 11 around the heating elements 6 should be thick enough to prevent, or at least limit, the heat from the heating elements 6 from heating the windings 5, which heating could otherwise potentially destroy the windings 5. Therefore it might also be an advantage with extra space for a cooling fluid, which may be gas or liquid, to pass between the inner side of the insulation or housing and the outside of the windings 5. Such cooling was described above in relation to figures 7.a-7.b. As described above, a coaxial design gives a good magnetic coupling between the windings 5 and the heating elements 6. This gives a cos(4>) close to 1 which indicates an efficient us of the electrical power. It minimizes the losses and ensures that the transformer and the whole system operate efficiently and economically.

[0197] Figures 20.a-20.d schematically show an embodiment of the invention in which the distance between a plurality of heating elements is kept as desired by use of spacers in the form of clips 29 designed to engage with corresponding holes 30 in the heating elements. Figure 20. a shows a stack of heating elements 6 with clips 29 arranged there between. Figure 20. b is a three-dimensional view of a clip 29, figure 20. c is an enlarged view of the encircled region marked C in figure 20. a, and figure 20. d is an enlarged view of the encircled region marked D in figure 84998PC01

[0198] 32

[0199] 20. a. As seen in the figures, the clips 29 both keep the desired distance between the heating elements 6 and also assist in keeping the heating elements 6 aligned. Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms "comprising" or "comprises" do not exclude other possible elements or steps. Also, the mentioning of references such as "a" or "an" etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.

Claims

84998PC0133CLAIMS1. Device (1) for heating a fluid flowing through the device during use, the device (1) comprising:- a transformer core (2) comprising a first transformer leg (3) and a second transformer leg (4),- an electrically conducting winding (5) wound around the first transformer leg (3) and configured to be connected to an AC power supply during use,- at least one heating element (6) made of electrically conducting material and having a hole (7) through which the second transformer leg (4) extends,- a housing (8) arranged around the at least one heating element (6), the housing (6) having:- at least one inlet (9) for allowing fluid to flow into contact with the at least one heating element (6) during use of the device (1), and- at least one outlet (10) for allowing fluid to flow away from the at least one heating element (6) during use of the device (1), so that when an alternating current is applied to the winding (5) during use, a resulting alternating magnetic field in the transformer core (2) induces an electric current in the at least one heating element (6), the current causing heating of the at least one heating element (6), and so that when fluid flows through the housing (8) during use, the fluid is heated by the at least one heating element (6).

2. Device (1) according to claim 1, wherein:- the at least one heating element (6) has constant shape and dimensions in the circumferential orientation, or- wherein the at least one heating element (6) has varying shape and / or dimensions in the circumferential orientation.

3. Device (1) according to any of the preceding claims, wherein the at least one heating element (6) is provided with one or more through-going openings (20) in addition to the hole (7) through which the second transformer leg (4) extends.84998PC01344. Device (1) according to any of the preceding claims, wherein the device (1) comprises a plurality of heating elements (6) that are preferably arranged spaced apart along a longitudinal extension of the second transformer leg (4).

5. Device (1) according to claim 4, wherein the heating elements (6) are arranged with substantially the same distance between neighbouring heating elements (6).

6. Device (1) according to claim 4, where the distance between neighbouring heating elements (6) differs.

7. Device (1) according to any of claims 4-6, wherein the arrangement of the at least one inlet (9) and the at least one outlet (10) as well as the design of the plurality of heating elements (6) are determined to result in the fluid flowing through the device (1) along a meandering path during use.

8. Device (1) according to any of claims 4-7, wherein at least some of the heating elements (6) are provided with embossing (25) which is shaped and dimensioned to ensure desired distances between the heating elements (6) and / or to ensure a desired flow of fluid.

9. Device (1) according to any of claims 4-8, wherein at least some of the heating elements (6) are provided with spacers which are shaped and dimensioned to ensure desired distances between the heating elements (6) and / or to ensure a desired flow of fluid.

10. Device (1) according to any of claims 4-9, wherein the shape of the heating elements (6) is conical.

11. Device (1) according to any of the preceding claims, wherein the at least one heating element (6) is arranged to extend in a vertical orientation during use.

12. Device (1) according to any of the preceding claims, wherein the at least one heating element (6) is configured to be rotated around the second transformer leg (4) during use.84998PC013513. Device (1) according to claim 12, wherein the at least one heating element (6) is provided with vanes (24), and wherein rotation of the at least one heating element (6) during use causes the vanes (24) to assist and / or cause the flow of the fluid through the device (1).

14. Device (1) according to any of the preceding claims, wherein the at least one inlet (9) and the at least one outlet (10) are arranged:- with the inlet(s) (9) and the outlet(s) (10) being located at different distances from the second transformer leg (4), and- at locations which result in the fluid flowing mainly radially, with respect to a central axis of the second transformer leg (4), across the at least one heating element (6).

15. Device (1) according to claim 14, wherein the fluid flows along the following path through the device (1):- from the at least one inlet (9) into an inner space (26) between an inner thermal insulation (11a) and inner periphery of the at least one heating element (6),- mainly radially across the at least one heating element (6) to an outer periphery of the at least one heating element (6), and- to an outer space (27) between an outer thermal insulation (lib) and an outer periphery of the at least one heating element (6), and- leaves the device (1) via the at least one outlet (10).

16. Device (1) according to any of the preceding claims, wherein the housing (8) is provided with more than one inlet (9) and / or with more than one outlet (10).

17. Device (1) according to any of the preceding claims, wherein the housing (8) and / or the second transformer leg (4) is provided with one or more cooling channels (15,16) through which cooling fluid can flow for active cooling of parts of the device (1) during use.

18. Device (1) according to any of the preceding claims, wherein the at least one heating element (6) comprises a catalytically active material and / or coating allowing for one or more catalytic processes to take place in the fluid flowing through the device (1) during use.84998PC013619. Device (1) according to any of the preceding claims, wherein:- the transformer core (2) comprises at least one additional transformer leg (4a),- for each of the at least one additional transformer leg (4a), the device (1) comprises at least one additional heating element (6a) made of electrically conducting material and having a hole through which the respective additional transformer leg (6a) extends, and- a) either the housing (8) arranged around the at least one heating element (6) is also arranged around the at least one additional heating element (6a),- b) or there is an additional housing arranged around each of the additional heating elements (6a), the additional housing having:- at least one additional inlet for allowing fluid to flow into contact with the at least one additional heating element (6a) during use of the device (1), and- at least one additional outlet for allowing fluid to flow away from the at least one additional heating element (6a) during use of the device (1).

20. Device (1) according to any of the preceding claims, the device (1) having a coaxial design, wherein each of the first, second, and, when present, additional transformer leg (3,4,4a) is surrounded by:- an electrically conducting winding (5), and- at least one heating element (6) arranged further away from the transformer leg (3,4,4a) than the electrically conducting winding (5).

21. Method of heating a fluid, the method comprising the following steps:- providing a device (1) according to any of the preceding claims,- connecting the electrically conducting winding(s) (5) to an AC power supply and switching on the power supply, and- letting the fluid flow from the at least one inlet (9) to the at least one outlet (10) thereby heating the fluid.

22. Method according to claim 21, wherein the fluid is a gas.

23. Method according to claim 22, wherein the gas is CO2.84998PC013724. Use of a device (1) according to any of claims 1-20 in one of the following processes: thermal storage of energy, catalytic conversion, manufacturing of slaked lime, manufacturing of glass, manufacturing of mineral wool, melting / manufacturing of metal / ceramics, oil refining, manufacturing of cement, heating of tar extracted from coal for use e.g. as roof coating, and heating of bitumen extracted from crude oil e.g. for the production of asphalt.

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