HEATING UNIT AND METHOD FOR HEATING A MEDIUM

Abstract

Heating unit (2) with a housing (4), an air inlet (12) and a heating element (6) arranged in the housing (4) and with at least one guide element (20), wherein a line (14) is arranged as an air outlet for a heated medium on the housing (4), and wherein the guide element (20) directs a medium to be heated radially onto the heating element (6), characterized in that the guide element (20) is designed as a perforated sheet arranged concentrically around the heating element (6), the holes of which are the only outlet for the medium in the direction towards the heating element (6).

Description

[0001] The invention relates to a method for heating a medium and a heating unit.

[0002] Heating units for heating gaseous media are known, for example, from DE 10 74 056 A from 1960. Air to be heated flows radially past heating elements, and the heated compressed air exits radially from the heating unit. This heating unit is used as a radiator. Another heating unit is described in KR 10 0 993 877 B1. The air to be heated is conveyed essentially parallel to the outer surface of the heating unit; only discs inserted into the heating unit transversely to the heating elements cause a partial deflection of the air to be heated, which in this way repeatedly flows past a heating element.

[0003] The invention is based on the object of proposing a method for heating a liquid or gaseous medium and a heating unit that is compact, low-wear and efficient.

[0004] This object is achieved with a heating unit according to claim 1 and a method according to claim 12.

[0005] The heating unit according to the invention has a housing, a supply line, also referred to as an air inlet, and a heating element arranged therein, as well as at least one guide element arranged concentrically to the heating element. According to the invention, an outlet, also referred to as an air outlet, is provided, which is arranged radially, parallel, or tangentially to the heating element. The supply line or air outlet, usually a line or pipe, absorbs all of the heated air and directs it for subsequent use. This design makes the heating unit very compact. The guide element directs the medium to be heated radially onto the heating element.

[0006] The radial flow against the heating element results in particularly efficient heating of a liquid or gaseous medium. The medium to be heated, which flows radially against the heating element, then flows tangentially around the heating element, absorbing heat in the process. The heating unit according to the invention ensures that the medium to be heated flows only once against each heating element.

[0007] The housing of the heating unit is usually made of metal, but it can be made of any heat-resistant material, e.g., mineral or ceramic material or heat-resistant glass. It can be of any shape, but is preferably cylindrical, rectangular, or polygonal in cross-section, which allows for a very compact design. The housing accommodates heating rods and guide elements, as well as, if necessary, other elements that further improve the heating unit according to the invention. The housing is closed at the end faces, creating an enclosed space. The end faces can be flat or curved, in particular, domed. The outer surface of the housing extends between the end faces. The housing also has a supply line, usually in the form of a pipe for the pressurized or pressureless flowing medium to be heated, and an outlet for the heated pressurized or pressureless flowing medium.The air inlet is usually designed as a line that conveys the pressurized or unpressurized medium to be heated into the housing. The outlet is preferably designed as a line through which the heated pressurized or unpressurized medium is discharged. The lines for the air inlet and outlet are preferably mounted on the housing parallel or tangential to the longitudinal axis of the heating elements. However, they can also be mounted radially on the housing.

[0008] The inlet or supply line can be attached to the housing in any desired manner. According to an advantageous embodiment, the housing has a tangentially arranged supply line as an air inlet for the pressurized or unpressurized flowing medium. The supply line preferably opens into a dome-shaped end face of the housing, in which the pressurized or unpressurized flowing medium to be heated is distributed before it flows through the heating unit. The dome is advantageously attached to one end face of the housing. The supply line and the dome are preferably unheated, so that this section of the housing is cool. Advantageously, the connections for the heating rods are arranged on the end face with the dome, so that the connections do not come into intensive contact with the heated medium. Preferably, the supply line is designed as a pipe socket that extends into the housing and whose opening is directed towards an end wall of the housing.The pipe socket in the housing is usually designed as a 90° angle, especially when the supply line is located on the housing wall. Especially in combination with a domed end face, a particularly good distribution of the medium to be heated is ensured within the housing. The supply and discharge lines are preferably arranged on different, particularly opposite sides, preferably on the end faces of the housing.

[0009] According to a further preferred embodiment of the invention, the outer surface of the housing is provided with vacuum insulation. A vacuum chamber encloses at least the outer surface of the housing. The vacuum chamber can advantageously be connected to a vacuum pump that constantly maintains a predetermined negative pressure.

[0010] The heating unit according to the invention is designed to heat a liquid or gaseous medium. According to a further development of the invention, the medium can be a pressurized liquid or gaseous medium, e.g., compressed air or another pressurized gas or a pressurized liquid such as water, aqueous solutions, or oil. Alternatively, the liquid or gaseous medium can simply be accelerated to flow through the heating unit without any differential pressure compared to the surroundings of the heating unit. This is also referred to below as pressureless flow through the heating unit. The medium can be heated to temperatures of up to 1,200°C, whereby the maximum temperature is determined solely by the technical equipment of the heating unit, e.g., by the power output of the heating element or the materials from which the housing or the guide element are made.Typically, the liquid or gaseous medium is heated to temperatures of 100 °C to 1,000 °C, especially 200 °C to 700 °C.

[0011] If the medium is under pressure, the pressure can be at least sufficient to convey the medium to be heated through the heating unit, e.g., using a fan. However, the medium to be heated is advantageously conveyed through the heating unit at a pressure of at least 0.5 bar, in particular at least 2 bar, typically at a pressure of up to 30 bar, in particular within a range of 2 bar to 10 bar, which is typical for compressed air. The maximum pressure of the medium to be heated is determined by the pressure resistance of the heating unit.

[0012] The heating rod is preferably elongated, although other shapes such as a curved or spiral arrangement are not excluded. The ends of the heating rod are preferably held by the housing or a holder attached to or in the housing. The heating rod can advantageously be held at only one end of the housing, but it is particularly preferably held at both ends. The heating rod can be heated in any desired manner, e.g., with gas, electricity, or oil, although an electrically heated heating rod is preferred. According to a particularly preferred embodiment, the heating rod has a winding of heating wire. This provides a large surface area for dissipating heat. The heating wire is preferably wound around an elongated, rod-shaped core so that the heating rod is stabilized and dissipates heat only outwards.The core is preferably permeable to the medium to be heated, so that the core is cooled by the medium to be heated, while the medium absorbs heat as desired. The heating rod or its core can advantageously be tubular or circular, so that a partial flow of the medium to be heated flows through the hollow center of the core. Alternatively, the core of the heating rod can have numerous channels through which a partial flow of the medium to be heated flows. The channels can be large or small as required; in particular, the core of the heating rod can be porous. This means that, on the one hand, the heat from the medium to be heated is completely absorbed by the heating element. It is also removed at the point of greatest heat, and on the other hand, the heating rod is protected against overheating. The core is preferably made of insulating material and can, for example, be made of mineral or ceramic material.The core of the heating element can be thermally insulated from the heating rod itself, e.g., with an insulating material or with vacuum insulation. The connections for the power supply are preferably located on one side of the rod, making connection to a power source particularly easy. The core is preferably made of insulating material and can be made of, for example, mineral, glass, or ceramic. The heating rod's heating coils are preferably not located near the connections to prevent the heat from the heating rod from placing stress on the power supply connections. This also contributes to the heating rods being low-wear and therefore long-lasting.

[0013] According to an advantageous embodiment of the invention, the heating unit has a plurality of heating rods, thus ensuring good efficiency in heating the medium. The heating rods are preferably aligned parallel to the casing surface to ensure uniform heating of the medium. Furthermore, it is advantageous to arrange a plurality of heating rods concentrically, as this results in a compact design and an easily controllable flow of the medium to be heated. With concentrically arranged heating rods, it is further preferred to arrange the heating rods radially one behind the other, so that the medium to be heated passes tangentially through a plurality of heating rods arranged one behind the other on a radius, one after the other, in particular without further reversal of direction, and absorbs heat from their surface, so that the medium is heated efficiently.The heating elements, which extend from end face to end face of the housing, are easy to replace; the heating unit according to the invention is therefore particularly easy to maintain.

[0014] In a simple embodiment, the heating unit according to the invention is designed such that the heating rods are arranged parallel around a central rotational axis or longitudinal axis. However, if greater output is desired or the heating unit is to have more than one discharge line, the heating unit can also have more than one longitudinal axis, e.g., two spaced-apart longitudinal axes, so that the heating unit has, for example, an elliptical or rectangular cross-section. With three longitudinal axes around which heating rods are arranged, the heating unit has an approximately triangular cross-section, or the three longitudinal axes are arranged in series, resulting in a rectangular cross-section. The term "longitudinal axis" is used here to refer to a central axis for each group of heating rods in a heating unit. It is clear that the heating unit according to the invention can be individually designed to meet different requirements.Either an air outlet is assigned to each individual longitudinal axis, or the heating unit has a central air outlet. This also demonstrates the flexibility of the heating unit according to the invention.

[0015] Furthermore, a guide element or, as a rule, several guide elements are arranged in the housing. The guide element(s) are preferably arranged concentrically around the heating element. More preferably, one or more heating elements extend essentially over the length of the heating element. According to the invention, the guide element(s) have holes which, on the one hand, cause a reversal of movement or a change in direction of the medium and, on the other hand, cause the medium to pass through a heating element only once. The perforated plate can have small or large holes; the holes can, for example, be round, elongated or slit-shaped. The size of the holes depends on the quantity of the medium to be heated flowing through the heating unit, and in particular on the pressure and velocity conditions in the heating unit. The optimal size for the holes can be determined in a few tests.The guide element can also be composed of two or more sub-elements between which holes or slots are formed.

[0016] The medium or a main stream of the medium flows towards the heating rod in an almost radial direction due to the guide element, then flows tangentially around the heating rod and in doing so absorbs heat given off by the heating rod. This deflection of the medium to be heated from a movement tangential or parallel to the longitudinal axis of the heating rod into a radial movement ensures efficient heat transfer to the medium to be heated. Depending on the power of the individual heating rod or the temperature to be reached of the medium, this process can be repeated if either two or more heating rods are present, preferably arranged one behind the other in a radial direction. To ensure that the medium is supplied to the heating rod in a radial direction, another guide element can be arranged between the heating rods. It is to be seen as a particular advantage of the invention that the heating rod(s) can be heated by inserting the guide element(s).The guide elements are particularly evenly exposed to air flow because the heating element is always exposed to equally cool or equally preheated air along its entire length. As a result, the heat from a heating element is dissipated particularly evenly across its entire length, unlike other heating element designs. This extends the service life of the heating element. The heating unit according to the invention is therefore particularly wear-resistant.

[0017] According to the invention, the guide elements are designed as perforated plates, whereby according to an advantageous embodiment the holes are each arranged directly adjacent to a heating rod. The holes are preferably small in relation to the volume of the medium so that the medium is directed specifically onto the heating rod. The medium to be heated, which flows through the housing under pressure or without pressure tangentially or parallel to the longitudinal axis of the heating rod, is deflected through the openings directly in an approximately radial direction onto the heating rod. If the medium to be heated is introduced radially into the housing, the medium is initially distributed in the housing and flows parallel to the heating rod, before also reversing its direction and being deflected by the guide element in a radial direction onto the heating rod. The medium to be heated then flows tangentially around the heating rod.

[0018] In addition to the perforated plate, the guide element can be designed as a baffle which, like a fixed blade or vane, deflects the pressurized medium to be heated so that it flows essentially radially towards the heating rod, then flows around it tangentially and absorbs heat in the process. The baffle is well suited to setting optimal flow conditions in the heating unit. For this purpose, the baffle can be shaped according to aerodynamic or fluid dynamic aspects. It is particularly preferred if a first guide element, e.g. a baffle, extends between the heating rod and the outer wall of the housing, and if a second guide element, e.g. a wedge-shaped baffle, is arranged between tangentially adjacent heating rods.In particular, the apex of the wedge-shaped baffle is positioned toward the center axis of the housing, while the vanes of the wedge-shaped baffle extend toward the outer wall. This ensures that the medium to be heated impinges on the heating elements in an approximately radial direction, particularly when the heating elements are arranged radially one behind the other in the housing.

[0019] After passing the heating elements, the heated medium is again deflected so that the medium flows preferably close to the longitudinal axis of the heating unit, more preferably parallel to the jacket surface in the direction of the outlet or discharge line of the heating unit.

[0020] According to a further development of the invention, the heating unit has a storage unit. The storage unit, which is preferably arranged centrally, serves to store heat. In this way, during industrial use of the heating unit, in the event of a production interruption, it is ensured that a heated, liquid or gaseous medium can be made available again as quickly as possible. The storage unit is preferably arranged downstream of the heating elements so that the already heated medium can transfer heat to the storage unit. The storage unit is advantageously made of a material with a high heat storage capacity. Preferably, a solid is used that does not soften, melt, or sublimate even at maximum temperature in the heating unit. Aluminum is used in particular. The solid can be used, for example, in solid form, e.g., as coarse aluminum granulate, or as a porous material, e.g., as loosely poured lumps of aluminum foam.A storage tank with a larger surface area is preferred, allowing it to quickly absorb and release heat. The capacity of the heat storage tank can be determined not only by the choice of storage material but also by the quantity of storage material used. On the one hand, the storage tank keeps the medium in the heating unit, e.g., air or water, at the desired temperature. On the other hand, it ensures the release of heated medium, e.g., air or water, when the heating unit is restarted for the short period during which the heating element has not yet heated up to the specified temperature.

[0021] According to a further preferred embodiment, the heating unit has a cooling system. Cooling is advantageously designed such that partition walls in the housing, which preferably run parallel to the housing wall, initially guide the medium that is not yet heated, e.g., at room temperature, parallel to an outer wall of the housing, and optionally also through another partition wall at a greater distance from the housing, again parallel to the outer wall. In this way, the medium to be heated cools the housing, in particular the outer surface of the housing, by means of a meandering guide defined by the partition walls. While the housing is being cooled, the medium to be heated is heated by the medium to be heated absorbing heat from the surface of the partition wall or the outer wall of the housing, so that it impinges on the heating rod already preheated.According to an advantageous development, the partition wall does not extend the entire length of the housing, but is delimited at least at one end by a separate partition wall arranged parallel to an end wall of the housing. In this way, the medium to be heated follows a closed path without mixing with incoming or already heated medium. However, the cooling system can also be arranged externally around the outer wall of the housing.

[0022] In addition to or as an alternative to cooling, the housing can be insulated to prevent the ambient temperature from heating up or the heating unit from cooling down. The insulation preferably comprises an inorganic material, e.g., silicate, ceramic, or glass-like material, such as aerogel, glass wool, or mineral wool. The insulation can be installed inside or outside the housing. Alternatively or additionally, vacuum insulation can be installed.

[0023] The pressurized or pressureless flowing medium heated in the heating unit according to the invention is preferably used in conjunction with a tool for machining a workpiece, for example for heating an edge strip to be applied to the narrow surface of a panel. According to an advantageous development of the invention, the heating unit is used in conjunction with a heat exchanger, which is advantageously arranged upstream of the heating unit. The medium still containing residual heat after leaving the tool is at least partially captured and fed to the heat exchanger. Medium that has not yet been heated is passed in countercurrent past the air that still contains residual heat, so that at least part of the residual heat is transferred to the medium still to be heated. This reduces the energy or heat input required to heat the medium.

[0024] According to an advantageous development of the invention, a detection device is arranged in or on the heating unit, which detects the state and / or quantity of the pressurized medium to be heated or of the heated medium. Preferably, one or more detection devices are used, which detect the temperature, quantity, pressure, or velocity of the medium flowing through the heating unit. Advantageously, the detection device(s) are connected to a controller that ensures a desired or specified output of the heating unit.

[0025] The method according to the invention for heating a pressurised or pressureless flowing, liquid or gaseous medium is carried out in a heating unit having a housing and a heating rod and at least one guide element, with the steps: introducing the pressurised or pressureless flowing, liquid or gaseous medium to be heated into the housing, guiding the medium by means of the at least one guide element designed as a perforated plate onto the heating rod, radial flow of the medium to be heated onto the heating rod and tangential flow around the heating rod to heat the medium, and outflow of the heated liquid or gaseous medium from the heating unit in a line which is attached to the housing as an air outlet.

[0026] The medium to be heated is preferably introduced into the heating unit parallel to the outer wall of the housing, or alternatively tangentially or radially to the outer wall of the housing. As already described, the pressurised or unpressurised medium to be heated preferably flows tangentially into a dome, which is preferably attached to an end face of the housing. The dome creates space for distributing the medium over the entire cross-section of the heating unit. According to a particularly preferred embodiment, the medium to be heated is introduced into the housing in such a way that it flows in towards an end wall of the housing. The air inlet can advantageously be designed as a pipe or pipe bend, which introduces the medium to be heated in the direction of an end wall, in particular in the direction of a dome-shaped end wall of the housing.This ensures a particularly even distribution of the medium to be heated within the housing, especially along the outer wall. As the introduced air initially flows along the outer wall of the housing, it is effectively cooled.

[0027] From there, the unheated medium is initially guided along the outer wall of the housing by guide elements, with the desired side effect of cooling the outer wall of the housing, because the heat energy emitted by an external heating element is dissipated toward the center of the housing. The medium to be heated is then guided radially toward the heating element by a guide element, where it flows tangentially around it. The medium to be heated absorbs heat emitted by the heating element. The tangential flow around the heating elements heats the pressurized or unpressurized medium particularly effectively.

[0028] Details of the invention are described below with reference to the drawings. They show: Fig. 1 is a schematic representation of the heating unit according to the invention according to a first embodiment in longitudinal section; Fig. 2 a schematic representation of the heating unit according to the invention according to a second embodiment in cross section; Fig. 3 a cross-section through a heating unit according to the invention according to a third embodiment; Fig. 4 a longitudinal section through a heating unit according to the invention according to a fourth embodiment.

[0029] The following exemplary embodiments deal with the heating of a pressurized, gaseous medium, here in particular compressed air. However, the same design of the heating unit 2 can also be used according to the invention for a pressurized liquid medium or for gaseous or liquid media flowing through the heating unit without pressure. Typical media to be heated are air or compressed air, water, steam, or oil.

[0030] A heating unit 2 according to the invention according to a first embodiment with a housing 4 and heating elements 6 is shown in a first embodiment in Fig. 1. The housing is made of metal. It is cylindrical. The outer wall 10 and the end faces 8a, 8b are sealed, except for a supply line 12 and a discharge line 14, which open into the end face 8a parallel to the outer wall 10.

[0031] The heating rods 6 are arranged near the rotational axis R of the housing 4. They extend parallel to each other and to the rotational axis R of the housing 4. They have a core made of ceramic material and a winding of electrically heated heating wire. They are screwed to the end faces 8a, 8b. Preferably, the heating rods 6 are screwed to the cold end face 8a, i.e., to the end face 8a that has the air inlet.

[0032] In the housing 4, two intermediate walls 16a, 16b are arranged parallel to the outer wall. The intermediate wall 16a, which is closer to the outer wall 10, extends from the end wall 8a to just in front of the end wall 8b. The intermediate wall 16b, which is closer to the heating elements 6, extends from the end wall 8b to just in front of the end wall 8a. The intermediate walls are therefore arranged concentrically and they guide the inflowing gaseous, pressurized medium, here e.g. compressed air at a pressure of approx. 6 bar, alternatively also a pressureless flowing, liquid or gaseous medium such as water, oil or a pressureless, accelerated air stream, in a meandering shape, initially through a first guide channel 18a, which is delimited by the outer wall 10 and the first intermediate wall 16a. At the end wall 8b, the flow direction of the medium is reversed, indicated by the arrows, and is directed towards the end wall 8a. It passes through the guide channel 18b, which is limited by the two intermediate walls 16a 16b.At the end wall 8a, the flow direction of the medium is reversed again. Up to this point, the medium flows parallel to the outer wall 10 of the heating unit 2.

[0033] The heating elements 6 are surrounded by a concentrically arranged guide element 20, which is designed here as a perforated sheet. The holes are formed as rows of holes located exactly above a heating element 6.

[0034] The medium, which reverses its flow direction again at the end of the guide channel 18b at the end face 8a, enters the flow channel 18c, which is defined by the second partition wall 16b and the guide element 20. The medium has the holes of the guide element 20 as its only outlet and passes through these holes. The flow direction is reversed, also indicated by arrows, into a radial flow direction relative to the heating elements 6.

[0035] The medium flows around the surface of a heating element 6, absorbing heat from the surface of the heating element 6. This section can be described as tangential flow with respect to the heating element 6. The heated medium then flows into the outlet and reverses its direction again. The medium flows, indicated by the arrows, parallel to the outer wall 10 of the housing 4 through the outlet 14 out of the heating unit.

[0036] In the present embodiment, the compressed air is heated from ambient temperature (approx. 20°C) to 600°C. Heating is carried out very efficiently in a compact heating unit because the heating elements are freely accessible, and the compressed air or other liquid or gaseous pressurized or unpressurized media can absorb the heat directly from the heating wire. The device is maintenance-friendly because the heating elements 6 can be easily replaced as needed.

[0037] Fig. 2 shows a second embodiment of the heating unit 2 according to the invention. In the further description, the reference numerals for the same features are used as previously introduced.

[0038] Fig. 2 shows a second embodiment in cross section, in which the structure of the housing 4 with intermediate walls 16a, 16b and guide element 20 as well as guide channels 18a, 18b and 18c are arranged in the same way as in the embodiment according to Fig. 1. Fig. Figure 2 further shows nine heating rods 6 arranged parallel and concentrically. The guide element 20, again a cylindrical perforated plate, has rows of holes. The rows of holes each extend directly above a heating rod 6, so that the medium to be heated flows radially relative to the heating rod 6 and is then guided tangentially around the heating rod 6, allowing heat to be transferred from the surface of the heating rod 6 to the medium, which may be gaseous in this case, but alternatively also liquid, flowing under pressure or without pressure.

[0039] Unlike the embodiment according to Fig. 1, a reservoir 22 is inserted here in the discharge line, parallel to the rotation axis R. The reservoir 22 is composed of lumps of open-pore aluminum foam, i.e., lumps of sintered aluminum particles. The heated, pressurized medium flowing in the discharge line 14 flows past or through the reservoir 22, thereby transferring a portion of the heat just absorbed by the heating element 6 to the reservoir 22. During a brief standstill in the consumption of the heated medium, e.g., during a brief production stoppage in piece-related production processes, when no new heat is supplied to the heated medium and the medium to be heated in the heating unit 2, the reservoir 22 transfers heat, thereby facilitating the provision of heated medium at the desired temperature when production is restarted.

[0040] If the storage tank is designed to absorb a large amount of heat, the heating unit is referred to as slow-acting because it heats up slowly and cools down slowly. If the storage tank is designed to absorb a small amount of heat, the heating unit is referred to as nimble because the storage tank quickly absorbs the intended amount of heat and also releases it quickly, for example, in the event of a production interruption.

[0041] Fig. 3 shows a third embodiment of the heating unit 2 according to the invention. The housing 4 encloses, with its outer wall 10, a first intermediate wall 16a and a guide element 20, which are arranged concentrically and which guide the medium to be heated, as described above, first in a guide channel 18a and then in a guide channel 18c parallel to the outer wall 10 of the housing 4. From the guide channel 18c, the medium to be heated is deflected through the holes of the guide element 20, which is designed as a perforated plate, so that it flows in a radial direction towards the heating rod 6 arranged immediately behind the hole and flows tangentially around it.

[0042] In the third embodiment of the heating unit 2, two heating rods 6 are arranged one behind the other in a radial direction relative to the rotational axis of the cylindrical housing 4. To ensure that the second heating rod 6, which is arranged closer to the rotational axis R, is also exposed to the medium to be heated as completely as possible, thus enabling optimal heat transfer, a second guide element 24 is inserted into the housing 4. The second guide element 24 is shaped as an angle, the bending line 26 of which is directed towards the rotational axis, while the wings 28 of the angle are anchored to the guide element 20. These angles are placed between the rows of heating rods 6, forming a radial guide channel 30 that begins at the guide element 20 and also encloses the heating rod 6 arranged closest to the rotational axis R of the housing. The flow direction of the medium to be heated in this radial guide channel 30 is indicated by arrows.

[0043] In the present case, four groups of two radially arranged heating rods 6 are separated by four second guide elements 24, wherein the four second guide elements 24 form four radial guide channels 30. It is obvious that the number of heating rods 6 can be varied as desired, both in the number of the circularly arranged radially arranged heating rods 6 and in the number of rows in which the heating rods 6 are arranged. It is also obvious that the features of the embodiments described above can be freely combined. For example, a storage unit can be incorporated into the embodiments of the heating unit according to the invention according to Fig. 1 or Fig. 3 or second guide elements can be inserted between the heating elements according to Fig. 1 or Fig. 2. Each of the embodiments of the Fig. 1 to 3 may also comprise insulation, preferably insulation applied externally to the outer wall of the housing, which prevents or reduces the release of heat to the environment.

[0044] Fig. Figure 4 shows a longitudinal section of a fourth embodiment of the heating unit according to the invention. For explanation purposes, the same reference numerals are used here where they refer to the same components. The arrangement of the partition wall 16a with the guide channels 18a, 18b and the guide element 20 is comparable to the arrangements according to the first to third embodiments of the heating unit 2.

[0045] The heating unit 2 here comprises a housing 4, on whose end wall 8a a dome 32 is formed. The dome, which is delimited by a partition wall arranged parallel to the end wall 8a, creates a space 34 that covers the entire cross-section of the housing 4. The supply line 12 radially introduces pressurized air (compressed air) to be heated into the space 34. In addition, the supply line is angled at 90° and directed toward the end wall 8a, so that the compressed air is distributed within the dome.

[0046] The compressed air to be heated is then guided parallel to the heating elements through the guide channel 18a located between the outer wall and the partition wall and the adjoining guide channel 18b, before being directed radially through the guide element 20 to the heating element 6. The heating elements 6, of which only one is shown here for the sake of clarity, are arranged in the housing 4 such that their connections 36 are located on the end wall 8a. The end wall 8a and the connection 36 of the heating element 6 are cooled by the not yet heated compressed air.

[0047] The heating unit according to the fourth embodiment is designed such that a partial flow of the compressed air to be heated flows through the interior of the tubular core of the heating rod 6. The heating rod 6 is porous and thus permeable to a partial flow of the compressed air to be heated. Alternatively, an opening in the partition wall can direct a partial flow of the compressed air to be heated into the interior of the tubular heating rod 6. After flowing through the heating unit 2, the heated compressed air leaves the heating unit via the discharge line 14, which is arranged on the end wall 8b. The end wall 8b is warmer than the end wall 8a.

[0048] The Fig.The heating units 2 described in Figures 1 to 4 can optionally be designed to be cooled or insulated, particularly when other tools or devices are arranged adjacent during operation that are not to be heated. The insulation is advantageously designed as vacuum insulation, e.g., as a vacuum chamber, which is optionally constantly maintained at a predetermined negative pressure by a vacuum pump.

[0049] Alternatively, sheaths made of insulating material can surround the outer wall 10 of the housing 4. Cooling in which a cooling medium flows through a cooling chamber surrounding the outer wall of the housing is also available.

[0050] The above exemplary embodiments each show a heating unit 2 with only one axis of rotation R or longitudinal axis, around which heating rods 6 are arranged in a circular ring. Other embodiments, not shown in detail here, can have two or more axes of rotation or longitudinal axes, around which heating rods 6 are preferably arranged concentrically or in a circular ring at least on circular segments. In particular, when a high heating output is required, the heating rods 6, comparable to exemplary embodiment 3, can be arranged in a circular ring in several circles with increasing distance from the axis of rotation R or a longitudinal axis. The heating rods 6 are preferably arranged one behind the other, i.e. on a radius relative to the axis of rotation R. If the distance between two axes of rotation R or longitudinal axes is smaller than the largest radius in which the heating rods 6 are arranged, then heating rods 6 are preferably arranged between the axes of rotation R orLongitudinal axes at least on the outer radii no heating rods 6 are arranged.

[0051] All designs show that the medium to be heated passes through each heating element 6 only once. In this way, each heating element 6 is exposed to the medium at the same temperature only once at each point along its entire length. This is different from known heating units, where cold air flows in, initially absorbs large amounts of heat from the beginning of the heating element, heats up quickly, and therefore hardly absorbs any more heat from the heating element toward the outlet. Thus, a conventional heating element is subjected to significant stress along its length due to the varying heat absorption and wears out much faster than a heating element used in a heating device according to the invention. List of reference symbols: 2 heating units 4 housings 6 heating elements 8a, 8b end walls 10 Exterior wall 12 supply line 14 Derivation 16a, 16b Partition walls 18a, 18b, 18c guide channel 20 Guide element 22 storage 24 second guide element 26 Bending line 28 wings 30 radial guide channel 32 Dome 34 Room 36 Connecting the heating element R rotation axis

Claims

[1] Heating unit (2) with a housing (4), an air inlet (12) and a heating rod (6) arranged in the housing (4) and with at least one guide element (20), wherein a line (14) is arranged on the housing (4) as an air outlet for a heated medium, and wherein the guide element (20) guides a medium to be heated radially onto the heating rod (6), characterized by that the guide element (20) is designed as a perforated plate arranged concentrically around the heating rod (6), the holes of which are the only outlet for the medium in the direction of the heating rod (6). [2] Heating unit (2) according to claim 1, characterized by that the housing (4) has a dome (32). [3] Heating unit (2) according to claim 1 or 2, characterized by that the guide element (20) is arranged concentrically to the heating element (6). [4] Heating unit (2) according to at least one of the preceding claims, characterized by that the guide element (20) is designed as a guide plate. [5] Heating unit (2) according to one of the preceding claims, characterized by that the heating rod (6) is made as a winding from a heating wire. [6] Heating unit (2) according to one of the preceding claims, characterized by that the heating element (6) has a core. [7] Heating unit (2) according to one of the preceding claims, characterized by that the heating unit (2) has several heating rods (6) which are preferably arranged concentrically. [8] Heating unit (2) according to at least one of the preceding claims, characterized by that it has a memory (22). [9] Heating unit (2) according to claim 8, characterized by that the storage tank (22) is arranged centrally in the heating unit (2). [10] Heating unit (2) according to one of the preceding claims 8 or 9, characterized by that the reservoir (22) is made of porous material. [11] Heating unit (2) according to at least one of the preceding claims 1 to 10, characterized by that the heating unit (2) has a cooling and / or insulation, in particular a vacuum insulation. [12] Method for heating a pressurised, gaseous medium in a heating unit (2), comprising a housing (4) and a heating rod (6) as well as at least one guide element (20), comprising the steps - Introducing the pressurised gaseous medium to be heated into the housing (4), - guiding the medium by means of the at least one guide element (20) onto the heating rod (6), wherein the guide element (20) is designed as a perforated plate arranged concentrically around the heating rod (6), -radial flow of the medium to be heated onto the heating element (6) and tangential flow around the heating element (6) to heat the medium, - The heated gaseous medium flows out of the heating unit (2) in a line (14) which is attached to the housing (4) as an air outlet. [13] Method according to claim 12, characterized by that, with respect to the heating element (6), the medium to be heated is introduced into the housing (4) parallel or tangentially. [14] Method according to claim 12 or 13, characterized by that in the housing (4) at least one change of direction of the medium to be heated takes place in the radial direction with respect to the heating rod (6). [15] Method according to at least one of claims 12 to 14, characterized by that the heated medium, after passing the heating element (6), passes through a storage (22) and there releases at least some of the heat to the storage (22). [16] Method according to claim 15, characterized by that the storage (22) transfers the stored heat to the medium to be heated.

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