Heating elements

Abstract

A heating element and heating assembly for heating a fluid as part of a heating device, the heating element being formed from a high electrical resistance material, such as an FeCrAl-based material, the heating device including a heating block having a high heating surface area to volume ratio (HTVR) to achieve high heating density with a low surface load.

Description

[Technical Field] 【0001】 This disclosure relates to an electric heater for heating a fluid flow, and more particularly, to a heating element that can be mounted within the electric heater, formed from a high-resistance conductive material. [Background technology] 【0002】 Electric heaters for heating gas to high temperatures typically include a ceramic block or jacket having a longitudinally extending bore through which relatively thin heating wires extend, heating the gas as it flows through the block. The effectiveness and efficiency of the conversion of electrical energy (through the heating wires) to heat depends, for example, on the available voltage applied, the electrical resistance of the wires, the maximum operating temperature achievable by the wires, the resistance of the fluid flow, and the surface area of ​​the outer surface of the heating element in contact with the flowing fluid. Typically, the maximum gas temperature that can be achieved by conventional electric process heaters may be around 700°C to 900°C. 【0003】 Different types of electric heaters comprise one or more heating channel-forming elements for heating a fluid. International Publication 2009 / 071590, U.S. Patent Application Publication 2007 / 189741, European Patent 2784049, U.S. Patent Application Publication 2013 / 287378, and German Patent Application Publication 10012675 disclose various such heating systems comprising ceramic electroresistive heating elements that form one or more channels through which the fluid to be heated flows. 【0004】 U.S. Patent Application Publication 2007 / 189741 and European Patent No. 2784049 each disclose a heating element comprising several channels arranged for parallel flow of a fluid to be heated. An electric current for heating the heating element is applied in parallel across the channels. [Overview of the project] 【0005】 One object of this disclosure is to provide heating elements, heating assemblies and / or electric heaters configured to improve thermal energy transfer between a device and a fluid by having a high heating surface area per unit volume. A more specific object is to provide heating element configurations having improved structural and mechanical properties, in particular having bending strength to withstand vibrations and movements related to other components of the heating assembly / device, and whose heating configuration can operate in any orientation. A more specific object is to provide heating elements and electric heaters that are less susceptible to the effects of undesirable movement of the conductive heating element and "short circuits" resulting from contact with itself or other conductive components within the heating device. 【0006】 These objectives are achieved through heating elements and electric heating devices formed from conductive materials in the heating block, thereby eliminating the need for additional heating wires extending within the fluid flow bore of the heating block (as in existing configurations). Thus, the heating block formed from conductive materials represents a stable structure and is adapted via internal bores or channels for through-flow and direct / active heating of the fluid. Consequently, the internal hollow material structure can withstand the stresses and general physical requirements encountered during use, arising from large pressure differences, gravity, and periodic heating gradients. In particular, this configuration provides a high-strength heating assembly that eliminates the need for additional wire-type heating elements and ceramic channel-like structures. Thus, this configuration is more compact and lighter than conventional configurations and features a larger heating surface area per unit volume compared to conventional heating devices. 【0007】 This heating assembly is adapted to be an active heating assembly via a conductive material forming / defining a heating block, which serves the functions of a) defining a path through which current flows exclusively, primarily, or preferentially to any other conductor in the electric heater, and b) defining a structure through which fluid flows. However, this heating block can operate with additional structural elements such as ceramic components, sheaths, stabilizing rods, or spacers, which provide secondary and passive heating components to the heating element, and such secondary components are non-conductive to enable extended operating conditions. 【0008】 As used herein in the context of heating blocks, the term “block” is not limited to a specific cross-sectional geometric shape and may also refer to any relevant structural shape unless a further definition of the structure of a heating block is provided. 【0009】 The heating element is further advantageous in that it allows for greater design flexibility regarding the shape and configuration of the heating block, also known as the heating structure. For example, the heating element can be manufactured using additive manufacturing, such as 3D printing, in which the conductive heating block is formed as a whole or as an assembly / assembly of additively printed individual heating elements that are electrically coupled and mechanically assembled to form the heating block. Advantageously, the heating element and / or heating block and / or heating structure are formed by additive manufacturing printing together with the integral manufacturing of additional mechanisms and components such as terminals for connection to a current source, stabilizing discs, rods, blocks, braces, brackets, flanges, and / or fins / surface area expansions and fluid flow perturbations that can disturb fluid flow through bores or channels. Alternatively, additional mechanisms and components such as terminals for connection to a current source, stabilizing discs, rods, blocks, braces, and / or brackets may be manufactured separately and assembled with the heating element and / or heating block and / or heating structure. 【0010】 According to the first aspect of this disclosure, A heating element comprising at least one heating element defining an axially elongated heating block having first and second longitudinal ends, A plurality of longitudinal bores or channels extending inward through the axially elongated heating block and opening at their respective first and second longitudinal ends, wherein at least one heating element is made of a conductive material for active resistance or two or more conductive materials for active resistance heating, First and second terminals provided on the heating block for connection to a current supply source and An electric heater for heating a fluid flow is provided, comprising the conductive material or two or more conductive materials, selected from the group consisting of iron-chromium-aluminum alloys, nickel-chromium alloys, copper-nickel alloys or iron-nickel-chromium alloys, and intermetallic materials. 【0011】 Therefore, a high power density can be achieved in the electric heater, and in addition, the electrical resistance heating of the heating element provides heating of the heating block up to a temperature of 1300 degrees Celsius. Thus, the fluid flow through the electric heater can be heated to a high temperature in a single step, for example from ambient temperature (e.g., 20°C) to a range of 1000-1250°C. Furthermore, the current supply to the heating block may be provided by a common line voltage. 【0012】 At least one heating element heats the fluid by guiding its flow as it passes through an electric heater. 【0013】 According to the embodiment, the heating element can be manufactured using additive manufacturing, in which the conductive heating block is formed as an assembly / assembly of additively printed individual heating elements, either as a single unit or as an assembly / assembly of electrically coupled and mechanically assembled heating elements to form the heating block. In this way, the heating element can be manufactured efficiently. That is, the materials that can be used are selected from one or more of the group consisting of iron-chromium-aluminum alloys, nickel-chromium alloys, copper-nickel alloys or iron-nickel-chromium alloys, and intermetallic materials that may be difficult or impossible to form using conventional manufacturing methods such as machining. Furthermore, complex geometric shapes inside channels, for example, can be achieved using additive manufacturing. 【0014】 According to one embodiment, the heating-surface area to volume ratio (HTVR) of the heating block defined above or below is given by formula (1): Σ(A) / V≧1m -1 …(1) Defined by the formula, where Σ(A) is the sum of the heated surface areas of at least the bores or channels extending between the first and second longitudinal ends, V is the total enveloping volume of the conductive material, which is the sum of the volumes of all the bores and channels and the conductive material. 【0015】 According to one embodiment, at least 80% of the electric heaters defined above or below also meet the following conditions (2): [Wetted perimeter or circumference] / [Enveloping cross-sectional area] ≥ 1m -1 (2) The following equation can be satisfied, where the wetted edge or circumference is the total length of all edges of the heating block that are in direct contact with the fluid flow in a given cross-section, and the envelope cross-sectional area is the sum of the cross-sectional areas of the heating block or heating structure and the bore or channel in the same longitudinal direction. 【0016】 According to the embodiment, for the heating block defined above or below, the HTVR and / or condition (2) is 1.0 to 4.0 m -1 , 1.0~3.0m -1 or 1.0~2.5m -1 It is within the range. 【0017】 According to this disclosure, at least one heating element is made of a conductive material for active resistance heating, but at least one heating element may also be made of two or more conductive materials for active resistance heating. The conductive material may have a homogeneous composition. As described above, the conductive material for active resistance heating is selected from the group consisting of iron-chromium-aluminum (FeCrAl) alloys, nickel-chromium (NiCr) alloys, iron-nickel-chromium (NiCrFe) alloys, copper-nickel (CuNi) alloys, and intermetallic materials. Intermetallic materials should also generate heat. Therefore, at least one heating element may be made of one of the above materials, or a combination of the above materials. The heating structure may also comprise heating elements of different materials. When additive manufacturing is used as the manufacturing method, the above materials are provided as powders or wires. 【0018】 According to the embodiment, the surface load of the heating element is 1-3 W / cm² under atmospheric conditions. 2 The outlet temperature of the fluid flow may be within the range of 1000 to 1250°C. In this way, a relatively low surface load can be provided to the heating block while achieving a high outlet temperature during the use of the electric heater. This can provide a longer operating life compared to conventional electric heaters that utilize thin, high-electrical-resistance heating wires. 【0019】 Optionally, the heater may comprise multiple heating elements assembled together as a heating block, each heating element containing material and having a bore or channel that partially defines a bore or channel of the heating block. Specifically, each heating element may comprise only one bore or channel extending through it. 【0020】 According to one embodiment, the heater further comprises a plurality of stabilizing rods or spacers positioned between the heating elements and abutting against the heating elements along the respective lengths of the heating elements, and the heating elements are spaced apart from each other and indirectly contact via the rods or spacers. According to such a configuration, it is advantageous for the heater to provide both the inner and outer surfaces of the heating block as an active heating surface that contacts a fluid (such as a gas) flowing between the longitudinal ends of each of the heating block. The heating block may include a heat insulating material positioned adjacent to the outer surface. Such a heat insulating material may be provided in direct contact with the outer surface, or may be spaced apart from the outer surface so that the outer surface is exposed to the flow of the fluid flow / gas being heated to improve the size (surface area) of the all-active heating surface within the device. 【0021】 Thus, according to an embodiment comprising a plurality of heating elements assembled together, the plurality of longitudinal bores or channels extending internally through the axially elongated heating block may comprise channels formed in the gap regions between the outer surfaces between adjacent heating elements. In this way, the fluid flow can flow not only through the inside of the plurality of heating elements but also along the outer surfaces of the heating elements. Therefore, the heating block can provide a high HTVR. 【0022】 According to an embodiment, the stabilizing rods or spacers are dimensioned to create a gap region between the heating elements. In this way, the gap region can be conveniently provided while the stabilizing rods or spacers can provide a stabilizing function for the heating elements. For example, the rods or spacers may abut against only a part of the outer surface of the heating element. 【0023】 According to an embodiment, at least one of the stabilizing rods or spacers may be arranged in contact with three or four heating elements. In this way, one rod or spacer can support three or four heating elements, and at least contribute to providing a gap region between the three or four heating elements. For example, when each heating element has a substantially square cross-section, the rod or spacer may be arranged in contact with each of the four corners of four adjacent heating elements. For heating elements having a circular cross-section, corresponding positions of the rod or spacer with respect to the four heating elements may be provided. Alternatively, the rod or spacer may be in contact with three heating elements having a circular cross-section. 【0024】 According to an embodiment, each of the stabilizing rods or spacers may be non-conductive. In this way, the applied current is not short-circuited through any of the rods or spacers and flows only through the heating elements. For example, the rod or spacer may be made of a non-conductive ceramic material. Thus, the rod or spacer can withstand the high temperature within the electric heater. 【0025】 According to an embodiment, the heating elements of the plurality of heating elements may be electrically connected in series. In this way, an appropriate total resistance of the heating block can be achieved for the applied voltage. Further, such an applied voltage may be any of common line voltages such as 230, 400, 480 or 690 V. This simplifies the connection of the electric heater to the power grid. In particular, this can be achieved for materials selected from the group of iron-chromium-aluminum alloys, nickel-chromium alloys, copper-nickel-based alloys or iron-nickel-chromium alloys, and intermetallic materials. 【0026】 Optionally, the heater may comprise a single heating element defining a heating block having a plurality of bores or channels. In such a configuration, the inward-facing surfaces defining the bores or channels mainly provide an active heating surface for the fluid (gas). According to a particular embodiment, the active heating surface is the sum of the surface areas of the inward-facing surfaces of the bores or channels. 【0027】 This heating block is formed from a high electrical resistance material and is the primary or exclusive body through which current flows when a voltage is applied to its terminals. This heating block or structure serves its main purpose, namely heat generation and transfer, as well as guiding the flow of fluid (gas). 【0028】 Optionally, the heater may include fins or projections that project radially into the bore or channel. Such fins or projections are advantageous for increasing the active surface area for heating the gas / fluid in the region between the first and second longitudinal ends of the heating block. 【0029】 Optionally, the heating block may include perturbations that project radially into the bore or channel to disrupt the fluid flow through the bore or channel. Such perturbations can be formed by nodes, projections, flanges, ribs, ridges, crossbars or beams, meshes, etc., positioned within the bore or channel and restricting fluid flow from other longitudinal flow paths. Such perturbations can increase both the heating element surface area and fluid mixing characteristics in the boundary layer, and therefore increase the heat transfer coefficient accordingly. 【0030】 Optionally, a bore or channel is defined by the wall of the heating block, and the wall comprises one or a combination of a bore, notch, groove, or stopper that reduces the volume of material in the wall. This provides a configuration that increases the HTVR, surface load, and heating density of the heater. 【0031】 Optionally, in a plane perpendicular to the longitudinal axis of the heating block, the cross-sectional area of ​​the wall is non-uniform between the first and second ends and / or decreases between the first and second ends. Such a configuration may be advantageous in providing a longitudinal difference or heating gradient in the heating block. In particular, the heating block may be provided with a tube wall that becomes relatively thinner towards the first cooler end of the heating block compared to a relatively thick downstream end where the gas / fluid is heated and discharged from the device, maximizing / optimizing the HTVR and surface load (assuming a relatively cold inlet flow of gas is applied to this region of the heating block). Thus, the HTVR, surface load, and heating density may be longitudinally variable between the first and second ends of the heating block. 【0032】 According to one embodiment, at least one heating element is elongated in the axial direction. In such a configuration, the length of the heating element in the direction of fluid flow is greater than its width aligned perpendicular to the fluid flow. 【0033】 According to this disclosure, the heating device, in particular the internal heating assembly, does not contain any coiled wires or wire-based heating elements extending longitudinally within the bore or channel of the heating block. In particular, the current flow provided for the heating effect is supplied exclusively through the walls of the heating block, which are formed from a high electrical resistance material. 【0034】 According to one embodiment, the heater further comprises a casing positioned to at least partially surround a heating block, and at least one mounting portion extending radially from the casing, in contact with the heating block, and fixed in position within the heater. According to another embodiment, the heater may further include an insulating material positioned radially midway between the casing and the heating block. 【0035】 Optionally, the first and second terminals are positioned at or toward at least one of the first and second ends of at least one heating element. According to one embodiment, the terminals are formed integrally with at least one heating element and / or heating block. Optionally, the terminals are formed disintegrally with at least one heating element and / or heating block and are chemically or mechanically attached to the heating assembly. 【0036】 A further aspect of this disclosure provides a modular electric heater assembly comprising a plurality of heating blocks described and claimed herein, which are electrically connected in series and / or parallel. 【0037】 Herein, specific embodiments of the present disclosure will be described, merely as examples, with reference to the accompanying drawings. [Brief explanation of the drawing] 【0038】 [Figure 1] This is a cross-sectional side view of an electric heater incorporating a heating element according to a specific embodiment of the present disclosure. [Figure 2] Figure 1 is a perspective view of the heating assembly that forms part of the electric heater. [Figure 3a] Figure 2 is an enlarged view of one end of the heating assembly / heating block. [Figure 3b] Figure 2 is a cross-sectional view of the heating element AA that forms the heating block. [Figure 4] This is an end face perspective view of a heating block according to a further specific embodiment of the present disclosure. [Figure 5] This is a cross-sectional view of a heating element having inwardly protruding fins according to a further embodiment of the present disclosure. [Figure 6] This is a partial cross-sectional perspective view of a heating element according to a further specific embodiment, which has a section with reduced wall thickness according to a particular embodiment. [Figure 7] This is a partial cross-sectional perspective view of a heating element incorporating an internal perturbation section to disturb the fluid flow through the heating element, according to a further specific embodiment. [Figure 8] This is a perspective view of a further embodiment of the present disclosure, in which the heating block is formed integrally via a single heating element. [Modes for carrying out the invention] 【0039】 Referring to Figure 1, the electric heater 10 comprises a casing in the form of a tubular sheath or housing 11 defining an internal chamber 17. The heater 10 includes a gas / fluid inlet pipe 21 and a gas outlet nozzle 14 having a discharge pipe 13. A fixed flange 20 is mounted on a current supply flange 19, which is coupled to an external electrical connection 18. An insulating material 37 is mounted inside the chamber 17 against or toward the inward-facing surface of the housing 11. The layer of insulating material 37 then defines an internal cavity 15 within the chamber 17 for housing a heating block, collectively indicated by reference numeral 23. The heating block 23 is mounted within a pair of hollow discs 40 that extend radially between the outer surface of the heating block 23 and the inner surface of the housing 11. 【0040】 The heating block 23 is formed from a plurality of elongated heating elements 26 assembled together to form a single heating assembly. The assembly of substantially linear heating elements 26 defines a substantially elongated heating block 23 having a first longitudinal end 23a and a second longitudinal end 23b. The heating block 23 further comprises first and second terminals 22a, 22b provided at / connected to the second end 23b, which are connected to an external electrical connection 18 (via a conduit 16) and supply current to the heating elements 26, and thus to the heating block 23. 【0041】 Referring to Figures 1, 2, 3a, and 3b, each heating element 26 is formed as a hollow, elongated tube, with an internal bore or channel 25 defined by an inward-facing surface 28 of a wall 32 representing the body of each heating element 26. The internal bore or channel 25 forms a single bore or channel 25 passing through each heating element 26. The wall 32 further comprises an outward-facing surface 29, defined between each inward-facing surface 28 and the outward-facing surface 29. Each heating element 26, and therefore the heating block 23, is elongated, with the heating block 23 centered on a longitudinal axis 12, and each heating element 26 centered on its own longitudinal axis 31. 【0042】 The heating element 26 is preferably formed from a high electrical resistance material such as iron-chromium-aluminum (FeCrAl). Examples of materials include alloys sold under the trade names Kanthal® APM or Kanthal® APMT, or powders sold under the trade name Kanthal® PM100 when additive manufacturing is used as the manufacturing method. These are all available from Kanthal GmbH in Sweden, and their chemical composition and physical and mechanical properties are incorporated herein by reference. Depending on the fluid composition, other resistance materials such as nickel-based alloys or molybdenum-based alloys may be preferred. 【0043】 A voltage / current can be applied to the block 23 using heating elements 26 connected to the external electrical connection section 18 via terminals 22a and 22b. Thus, the gas / fluid can be heated as it enters the chamber 17 from the tube 21 and flows through the block 23. In particular, the gas is adapted to flow through the internal bore 25 and be discharged from the device 10 via the nozzle 14 and discharge pipe 13. According to a specific embodiment, the block 23 (via the walls 32 of each heating element 26) is directly heated by the applied current, thereby providing direct active heating (of the gas flow) within the bore 25 and gap region 38. Thus, this heating assembly eliminates the need for internally mounted heating wires or conduits extending into the bore 25 (as is common in conventional fluid electric heaters). This configuration is advantageous for maximizing the efficiency and effectiveness of heat energy transfer between the heating elements 26 and the fluid flowing within the internal chamber 17. In particular, this configuration provides a large heating surface area to volume ratio (HTVR), which can be defined as the active surface area of ​​the heating material (surface area of ​​the wetted surface) divided by the envelope volume of the heating element 32. 【0044】 Within block 23, the heating elements 26 may be connected in series. That is, a current flows in series through the heating elements 26 due to the voltage applied to block 23 via terminals 22a and 22b. For this purpose, the heating elements 26 are sequentially connected via conductive elements not shown in Figures 1 to 3c. See the embodiment in Figure 4 and the description of the conductive element 41. 【0045】 In a specific embodiment, the insulating material 24 may be positioned to enclose or at least partially surround the outward-facing surfaces of the heating block 23 (defined by the regions of the outward-facing surfaces 29 of each heating element 26). In such a configuration, these covering regions of the outward-facing surfaces 29 are not active in heating the fluid flow, so that the inward-facing surfaces 28 can become the primary active heating surfaces. However, other unhidden / unobstructed regions of the outward-facing surfaces 29 may be considered active as the gas flows between adjacent heating elements 26. 【0046】 Specifically, referring to FIGS. 3a and 3b, the heating elements 26 are positionally stabilized and held as an integral assembly via intermediate elongate rods 27 that extend between the edges / surface regions of adjacent heating elements 26 and abut against the adjacent heating elements 26. The rods 27 are dimensioned to create a gap region 38 that is effective to increase the HTVR via the available active heating surface defined by both the inner surface 28 and the outer surface 29. The rod 27 may extend over the entire axial length of the heating element 26 or only over a portion of the total length. Thus, the rod 27 may be formed as a relatively short bushing or spacer to further maximize the available active heating surface area and thus improve the HTVR. 【0047】 Thus, the HTVR of the heating block 23 can be defined as the sum of the active / exposed heating surfaces (including both the regions of the inward-facing surface 28 and the outward-facing surface 29) divided by the total enveloping volume of the heating block that forms / generates the wall 32. Thus, the present heating assembly (heating block 23) includes a high heating surface area per volume, i.e., a high heating density. Thus, such a configuration provides a heating configuration with a relatively low surface load expressed in W / m 2 Advantageously, the present heating configuration / device is adapted for a relatively long operating life in addition to a higher outlet temperature in the discharge regions 13, 14. A maximum heating temperature of about 1300° C. in air is enabled by using heating elements 26 formed from a high electrical resistance material sold under the trade name Kanthal® APM or Kanthal® APMT, both available from Kanthal of Sweden, or in the case where additive manufacturing is used as the manufacturing method, from a powder sold under the trade name Kanthal® PM100. The surface load of the heating element may be in the range of 1-3 W / cm 2 in atmospheric conditions and 30 W / cm in a system operating at 100 bar pressure 2The number can reach up to 20 W / cm². The electric heater according to this disclosure can have an HTVR (1 / m) of 1 to 2.5 via the configuration described herein. This is in contrast to conventional process electric heaters in which a thin, high-electrical-resistance heating wire is fitted and passed through an internal bore of a ceramic heating block. Such conventional configurations typically have a power output of 3 to 20 W / cm². 2 With a surface load of the element and an HTVR of 0.2 to 0.5, a maximum heating temperature of 1100°C in air is achieved. 【0048】 Figure 4 shows a further embodiment of the heating block 23 of Figures 1 to 3b, where the individual heating elements 26 are formed as tubes having a circular cross-sectional profile relative to the rectangular cross-sectional profile shown in Figure 3b. As noted, the cross-sectional profile through AA is defined in a plane aligned perpendicular to the longitudinal axes 12, 31. 【0049】 Here too, the heating elements 26 are electrically connected in series. For this purpose, an appropriate number of conductive elements 41 are provided, each connecting two heating elements 26, thereby connecting the heating elements 26 in series across the entire heating block. 【0050】 Therefore, one such conductive element 41 may connect one end of the first heating element 26 to the end of the second heating element 26. The opposite end of the second heating element 26 is connected to the end of the third heating element 26, forming a single unit throughout the heating block 23. The first and last heating elements 26 in this chain of interconnected heating elements 26 are provided with terminals 22a and 22b, respectively. 【0051】 The conductive element 41 may be manufactured together with the heating element 26 during the manufacturing of the heating block 23 in an additive manufacturing process. In this way, the entire heating block 23 can be manufactured in a single manufacturing step. If a stabilizing rod 27 is used, the stabilizing rod 27 may be inserted after the manufacturing of the heating block 23. Optionally, terminals 22a and 22b (see also Figure 2) may also be manufactured in an additive manufacturing process. 【0052】 Alternatively, the conductive element 41 may be manufactured separately from the heating element 26, or it may be joined to the heating element 26 in a separate manufacturing step. 【0053】 In this embodiment of the heating block, the heating elements 26 may be held as a single assembly, positionally stabilized, via intermediate elongated rods (not shown) that extend between the edges / surface regions of adjacent heating elements 26 and abut against the adjacent heating elements 26. In this embodiment, each rod abuts against three adjacent heating elements 26. Again, gap regions are maintained / formed between the individual heating elements. 【0054】 Figure 5 shows a further embodiment of the present disclosure, in which each heating element 26 has fins 30 projecting radially inward. Each fin 30 extends from the wall 32 toward the axial center 31 of the internal bore 25. The fins 30 are advantageous for increasing the active surface area, and thus the HTVR, heating density, and therefore the available output operating temperature of the heated gas from the outlets 13, 14, or for further reducing the size of the heater mechanism at a constant fluid outlet temperature. 【0055】 Referring to Figure 6, the HTVR can be further improved by reducing the volume of the high-resistance material forming the wall 32. In particular, the thickness of the wall 32 region may be reduced through recessed grooves 33 or channels 34 on each or at least some of the outer surfaces 29 of the heating element 26. Additionally or alternatively, the wall 32 may have through bores 39 extending between the outward-facing surface 29 and the inward-facing surface 28 to further reduce the mass of the conductive material and thus increase the HTVR. The above mechanism can also allow for an artificial increase in the overall resistance of the entire flow heater, thereby making the flow heater 10 even more suitable for direct connection to line voltage. 【0056】 Referring to Figure 7, according to a further optional embodiment, at least some of the heating elements 26 may be provided with perturbations 35, 36 in the form of obstacles projecting radially inward from the inward-facing surfaces 28 of the walls. Such perturbations 35, 36 are positioned in the flow path of the bore 25 and are effective in disturbing the gas flow and generating eddy currents, thereby improving the mixing effect in the boundary layer and thus increasing heat transfer to the fluid. Such perturbations can further increase the active heating surface area for the reasons described above. 【0057】 Referring to Figure 8, a further embodiment of the heating block 23 is formed as a single, integrated unit, with a single heating element 26 comprising a plurality of internal bores 25 extending between first and second longitudinal ends 23a and 23b (shown in Figure 1). Electrical terminals 22a and 22b (shown in Figure 1) are connected to, or provided in or toward, one or both of the longitudinal ends 23a, 23b, to electrically connect to an external current source. The heating block 23 of the further embodiment is also formed from a high electrical resistance material such as an FeCrAl alloy. All other mechanisms and functions of the heating block 23 in Figure 8 are as described in the embodiments of Figures 1 to 7, in which gas is adapted to flow through the bores 25 and is heated by the passage of current through the resistive material forming the heating block wall 32. 【0058】 The heating block 23 / heating element 26 can be conveniently manufactured through conventional techniques such as 3D printing and other computer model-based engineering manufacturing methods. Such techniques enable the manufacture of complex shapes and configurations of the heating element, such as those shown in Figures 5 to 8, including fins 30, grooves and channels 33, 34, bores 39 and perturbations 35, 36, in a single manufacturing process. 【0059】 In this embodiment, a high electrical resistance material such as a FeCrAl alloy is described with reference. However, embodiments may be formed from any suitable conductive material, including NiCr alloys, NiCrFe alloys, CuNi alloys, or Mo alloys. All components may be formed from powder-based materials and processes. 【0060】 The electrical terminals 22a and 22b may be formed integrally with the heating element 26 and / or the heating block 23. According to a further embodiment, the terminals 22a and 22b may be attached to or connected to the respective regions of the heating block 23 via chemical or mechanical attachment. Preferably, the terminals 22a and 22b are formed integrally with one longitudinal end of the heating block 23.

Claims

[Claim 1] An electric heater (10) for heating a fluid flow, A heating element (26) defines an axially elongated heating block (23) having a first longitudinal end and a second longitudinal end (23a, 23b), Multiple longitudinal bores or channels (25) extend inward through the axially elongated heating block (23) and are open at their respective first and second longitudinal ends (23a, 23b), so that the fluid flows through multiple longitudinal bores or channels (25), The heating block (23) is provided with a first terminal and a second terminal (22a, 22b) for connecting to a current supply source. Equipped with, The at least one heating element (26) is made of a conductive material for resistance heating or two or more conductive materials for resistance heating. The conductive material or the two or more conductive materials are selected from the group consisting of iron-chromium-aluminum alloys, nickel-chromium alloys, copper-nickel alloys, iron-nickel-chromium alloys, and molybdenum alloys. The electric heater (10) is given by the following formula: 4.0 m －１ ≧ Σ(A) / V ≧ 1.0 m －１ The heating block (23) satisfies the heating surface area to volume ratio (HTVR) per unit length, as defined by the formula, where Σ(A) is the sum of the heating surface areas of at least the multiple longitudinal bores or channels (25) extending between the first longitudinal end (23a) and the second longitudinal end (23b), and V is the total enveloping volume of the conductive material. Multiple heating elements (26) are assembled together as a heating block (23), and each heating element (26) is formed as a hollow, elongated tube and contains the conductive material or two or more conductive materials. The plurality of longitudinal bores or channels (25) of the heating block (23) include bores or channels (25) defined by the inward-facing surfaces of each heating element (26) and channels (25) formed in the gap region between the outward-facing surfaces (29) of adjacent heating elements (26). Electric heater (10). [Claim 2] An electric heater (10) for heating a fluid flow, A heating element (26) defines an axially elongated heating block (23) having a first longitudinal end and a second longitudinal end (23a, 23b), Multiple longitudinal bores or channels (25) extend inward through the axially elongated heating block (23) and are open at their respective first and second longitudinal ends (23a, 23b), so that the fluid flows through multiple longitudinal bores or channels (25), The heating block (23) is provided with a first terminal and a second terminal (22a, 22b) for connecting to a current supply source. Equipped with, The at least one heating element (26) is made of a conductive material for resistance heating or two or more conductive materials for resistance heating. The conductive material or the two or more conductive materials are selected from the group consisting of iron-chromium-aluminum alloys, nickel-chromium alloys, copper-nickel alloys, iron-nickel-chromium alloys, and molybdenum alloys. Multiple heating elements (26) are assembled together as a heating block (23), and each heating element (26) is formed as a hollow, elongated tube and contains the conductive material or two or more conductive materials. The plurality of longitudinal bores or channels (25) of the heating block (23) include bores or channels (25) defined by the inward-facing surfaces of each heating element (26) and channels (25) formed in the gap region between the outward-facing surfaces (29) of adjacent heating elements (26). Electric heater (10). [Claim 3] The electric heater (10) according to claim 1 or 2, wherein the heating block (23) is formed as an assembly / collection of individual heating elements (26) manufactured by additive manufacturing, which are electrically coupled and mechanically assembled to form the heating block (23). [Claim 4] The electric heater (10) is given by the following formula: 3.0 m －１ ≧ Σ(A) / V ≧ 1.0 m －１ An electric heater (10) according to any one of claims 1 to 3, satisfying the heating surface area to volume ratio (HTVR) per unit length of the heating block (23) as defined by the formula, wherein Σ(A) is the sum of the heating surface areas of the plurality of longitudinal bores or channels (25) extending between at least the first longitudinal end (23a) and the second longitudinal end (23b), and V is the total enveloping volume of the conductive material. [Claim 5] The electric heater (10) is given by the following formula: 25 m －１ ≧ Σ(A) / V ≧ 1.0m －１ The electric heater (10) according to claim 4, which satisfies the heating surface area to volume ratio (HTVR) per unit length of the heating block (23) as defined by the formula, wherein Σ(A) is the sum of the heating surface areas of the plurality of longitudinal bores or channels (25) extending between at least the first longitudinal end (23a) and the second longitudinal end (23b), and V is the total enveloping volume of the conductive material. [Claim 6] The surface load of the heating element is 1-3 W / cm² under atmospheric conditions. ２ An electric heater (10) according to any one of claims 1 to 5, wherein the outlet temperature is within the range of 1000 to 1250°C. [Claim 7] An electric heater (10) according to any one of claims 1 to 6, comprising a plurality of stabilizing rods or spacers (27) positioned between the heating elements (26) along their respective lengths and in contact with the heating elements (26), such that the heating elements (26) are supported spaced apart from each other via stabilizing rods or spacers (27). [Claim 8] The electric heater (10) according to claim 7, wherein each of the stabilizing rods or spacers (27) is sized to create the gap region between the heating elements (26). [Claim 9] The electric heater (10) according to claim 7 or 8, wherein at least one of the stabilizing rods or spacers (27) is positioned in contact with three or four of the heating elements (26). [Claim 10] The electric heater (10) according to any one of claims 7 to 9, wherein each of the stabilizing rods or spacers (27) is non-conductive. [Claim 11] The electric heater (10) according to any one of claims 1 to 10, wherein the heating elements (26) among the plurality of heating elements (26) are electrically connected in series. [Claim 12] The electric heater (10) according to any one of claims 1 to 11, wherein the heating block (23) comprises fins or projections (30, 35, 36) that project radially into the plurality of longitudinal bores or channels (25). [Claim 13] The electric heater according to any one of claims 1 to 12, wherein the plurality of longitudinal bores or channels (25) are defined by the walls (32) of the heating block (23), and the walls (32) include one or a combination of bores (39), notches, grooves or stoppers (33, 34) that reduce the volume of the material in the walls (32). [Claim 14] A casing (11) positioned to at least partially surround the heating block (23), Extending radially from the casing (11), contacting the heating block (23), and positionally fixing the heating block (23) within the electric heater (10), An electric heater (10) according to any one of claims 1 to 13, comprising: [Claim 15] The electric heater (10) according to claim 14, further comprising an insulating material positioned between the casing (11) and the heating block (23).

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