Electric fluid flow heater with heating element stabilizing fin
Patent Information
- Application Number
- JP2024196471
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2019-03-25
- Filing Date
- 2024-11-11
- Publication Date
- 2025-03-05
Smart Images
Figure 2025028882000001_ABST
Abstract
Description
[Technical field]
[0001] The present invention relates to electric heaters for heating a flow of fluid, and in particular, but not exclusively, to electric heaters having a jacket block housing a heating element including fins that positionally stabilize and center the heating element. [Background technology]
[0002] Electrical heaters for heating gases to high temperatures typically include a tube adapted for the flow of gas therethrough and an electric heating element (positioned within the tube) that heats the flowing gas.
[0003] Conventionally, a relatively thin wire is wound in a spiral configuration within the tube, whereby the heating effect is achieved by passing an electric current through the wire as the gas flows through the tube. Thus, the effectiveness of the conversion of electrical energy (via the heating wire) to heat depends, for example, on the available applied voltage and the resistance of the wire. In particular, this conversion to thermal energy depends on the maximum temperature achievable by the wire, the flow resistance, and the surface area available for heat exchange. Typically, the maximum gas temperature that a conventional electric process heater can achieve can be on the order of or about 700°C to 900°C. However, the higher the temperature, the greater the tendency for the wire to break and fail.
[0004] More recently, EP 2926623 A1 discloses an electric flow heater in which the heating wire has a larger cross-sectional surface area to provide a desired cross-sectional ratio with the tubular bore through which the rod extends. A single heating element extends through multiple bores (formed within an elongated tubular element) via multiple bent (or looped) ends. Gas heating temperatures of up to 1200°C are described.
[0005] Although conventional electric flow heaters may be capable of achieving high temperatures on the order of 1100°C, high gas velocities and large pressure differentials cause tension and movement or vibration of the heating element, as well as the surrounding tube or jacket block through which the element extends. The heating element is subject to mechanical shocks and stresses that inevitably result in destruction. This phenomenon is even more pronounced when the elongated tube (jacket block) is oriented vertically, with gravity further contributing to the stresses and physical demands on the heating element.
[0006] Furthermore, to maximize efficiency, the heating element typically passes through multiple bores within a surrounding elongated jacket block. The element, with its U-shaped bent axial end section, exits and returns to the adjacent bore at each axial end of the jacket block. Small positional deviations of the heating element, for example due to localized temperature fluctuations within the bore, can cause displacement of the bent end section, which can lead to the element contacting itself (at the bent end). This in turn causes short circuiting and failure of the electric heater. The risk of short circuiting is even greater for some of the most recent heaters due to their very small tolerances. What is needed, therefore, is an electric fluid flow heater that addresses these issues. Summary of the Invention
[0007] It is an object of the present invention to provide an electric fluid flow heater that will provide superior heating of a fluid, such as a gas, regardless of the shape of the bore or channel. It is a further object of the present invention to provide a flow heater with straight rods that will extend in the longitudinal direction (of the fluid flow), which will provide a fluid flow heater with controlled and efficient heat transfer without relying on an annular gap. It is a further object of the present invention to provide a flow heater that has low pressure drop while maintaining uniform heat transfer to the fluid.
[0008] It is a further object of the present invention to provide an electric fluid flow heater for heating fluids and particularly gases (gas phase media) that is capable of achieving moderate to high temperatures on the order of 700°C, such as up to 900°C, such as up to 1100°C, and possibly up to 1300°C, with minimal physical stress, fatigue, and damage to the heating element to enhance heater service life.
[0009] It is a further object to stabilize and center the heating element extending within at least one jacket element (which in turn forms the elongated jacket block) such that independent movement of the heating element relative to the jacket elements of the jacket block is minimized, and preferably eliminated.
[0010] It is a further specific object to stabilize the heating element positioned within the jacket block to avoid the heating element contacting itself at the bent axial end sections that extend axially beyond the jacket block and the longitudinal bore or channel extending through the jacket block.
[0011] It is a still further specific objective to increase the efficiency of heat transfer between the gas flowing through the jacket elements (jacket block and elongated bores or channels) and the heating element in order to maximize the efficiency of the electric heater.
[0012] Thus, an electric fluid flow heater is provided in which the heating element (at least partially contained within the jacket element / jacket block) is positionally stabilized internally within the heating element (jacket block) by a set of stabilizing and centering fins. Such fins project radially into each bore or channel (through which the heating element passes) to rest around the heating element and prevent lateral movement within each respective bore. Furthermore, the fins will center each channel or bore, thus providing a uniform temperature distribution.
[0013] Thus, at least three stabilizing fins are provided internally within each bore or channel, which is the minimum number to achieve sufficient stabilization and in particular centering of the heating elements on the axial center of each bore or channel. Thus, the heating elements are prevented from radial (lateral) deflection within each bore or channel, which in turn prevents the U-shaped looped ends of the heating elements (which extend axially beyond the jacket element, jacket block) from contacting each other, which would otherwise result in a short circuit and failure of the electric heater.
[0014] The present electric fluid flow heater will have a larger free flow cross-sectional area, typically having a square outer shape, within the fluid flow heater jacket element and / or jacket block due to the fins, which means that a larger area within the electric fluid flow heater can be used for heating the fluid, and also indirect heating of the flow will be possible since heat will be transferred by radiation. Furthermore, the fins will also provide proper centering of the jacket element and / or jacket block, leading to less exposure to failure, especially in cyclical operation.
[0015] According to a first aspect of the invention, an electric heater for heating a flow of a fluid comprises at least one axially elongated jacket element defining an axially elongated jacket block having first and second longitudinal ends; a plurality of longitudinal bores or channels extending internally through the jacket block and opening at each of the respective first and second longitudinal ends, each of the bores or channels being defined by an inwardly facing surface of at least one jacket element; and a plurality of longitudinal bores or channels extending axially through the bores or channels, and in particular extending axially straight and having respective bent axial end segments. and at least one heating element having a cross-section such that at least one heating element exits from and returns into an adjacent or nearby bore or channel at one or both of a respective first and second longitudinal ends, the at least one heating element and the jacket block forming a heating assembly, characterized by at least three fins projecting radially inwardly from the at least one jacket element towards the at least one heating element within each of the bores or channels. Thus, the electric heater is freeform, meaning that the fins allow the bore or channel to have any shape, thereby achieving the cross-sectional area ratio limits as described below.
[0016] According to one embodiment, the axially elongated jacket element can be a rod or wire. According to another aspect, the axially elongated jacket element has an axially straight alignment for at least 75% of its length. According to another embodiment, the entire elongated jacket element has a straight alignment.
[0017] The stabilizing and centering fins and especially the cross-sectional profile of the jacket element defining each bore are adapted to maximize the efficiency of thermal energy transfer from the heating element to the flowing gas. This is achieved by the internal geometric profile of each bore or channel, which can be considered to comprise a "lobe" defined in part by the centering fin. In particular, within the cross-sectional plane of the jacket element / jacket block, the inwardly facing surface of the bore or channel is set back from the outwardly facing surface of the heating element by a sufficient separation distance to allow an even and uniform flow of sufficient gas volume around the heating element. According to one embodiment, the surface area ratio, defined as the cross-sectional area of the heating element divided by the cross-sectional area of the bore or channel or cavity, is in the range of 0.12 to 0.72.
[0018] The centering fins thus enable uniform direction or channeling of the flow of gas around the heating element, which is advantageous for avoiding localized temperature differences axially along and radially around the heating element that would otherwise result in stresses and especially bending or distortion of the heating element. As will be appreciated, this in turn provides or contributes to lateral displacement of the U-shaped end section, increasing the risk of short circuits.
[0019] Additionally, the available free-flow surface area around the heating element will provide uniform and controlled heating and cooling along the cross-sectional area of the heating element.
[0020] Optionally, in a cross-sectional plane through the jacket block, the radial separation distance between the inwardly facing surface of each bore or channel and the outwardly facing surface of the at least one heating element is non-uniform between each of the fins in a circumferential direction around the at least one heating element. Preferably, in said cross-sectional plane, said separation distance is greatest at a central location between adjacent fins in the circumferential direction. Such an arrangement is advantageous for maximizing the volume and rate of gas flow through the bores or channels and avoiding undesirable localized heating.
[0021] References herein to "fins" and "stabilising fins" and "centering fins" and "stabilising and centering fins" encompass ribs, ridges, spines and protrusions that extend radially inward from the body of the jacket element / jacket block towards the heating element, and which ribs, ridges, spines and protrusions may change shape or even partially disappear in the axial direction.
[0022] The fins may be straight or may be curved or bent along their length. Optionally, the fins may be helical or partially helical along their length. Such an arrangement may help control the flow of gas through the heating assembly and reduce the tendency for localized heating variations along and around the heating element.
[0023] References herein to "at least one axially elongate jacket element" and "axially elongate jacket block" include covers, sleeves, and other jacket-type elements that have a length greater than a corresponding width or thickness to "elongate" in the axial direction of the heater. References to such "elongate" elements and blocks include bodies that are substantially continuous and solid between their respective longitudinal ends and do not include gaps, voids, spaces, or other separations between the longitudinal ends.
[0024] Preferably, the elongated jacket element and the elongated jacket block are substantially straight / straight bodies with at least one respective internal bore or channel for housing the straight or straight section of the heating element. Thus, the present jacket element and jacket block are configured to substantially encase, surround, cover, house or contain the straight / straight section of the heating element substantially along the length of the straight / straight section between the U-shaped bent or curved end sections of the heating element. Thus, it is preferred that the bent or curved section of the heating element only protrudes from the heating element / jacket block and is not covered or housed by the heating element / jacket block.
[0025] Thus, references herein to "jacket" elements and and "jacket" blocks encompass the respective hollow bodies that contain, house, surround or cover the heating element substantially continuously between the bent or curved end sections of the heating element protruding from the respective longitudinal ends of the jacket element / block.
[0026] The effect of elongated jacket elements and jacket blocks having correspondingly axially elongated internal bores or channels is to maximize the efficiency of thermal energy transfer between the heating element and the fluid flowing through the bore or channel in close confinement around the heating element. The longitudinally elongated configuration of the heating elements and blocks allows the flowable fluid to be adequately contained within the bore or channel around the heating element over substantially the entire length of the straight / rectilinear section of the heating element.
[0027] Within this specification, references to the respective first and second longitudinal ends of the heating element exiting a bore or channel in the elongated heating element / jacket block may be considered to be distinct from the straight / rectilinear section of the heating element that is continuously contained within the bore or channel of the element / block. As will be appreciated, substantially all of the heat transfer between the heating element and the fluid occurs within the elongated bore(s) or channel(s).
[0028] Preferably, at least one jacket element (jacket block) comprises a non-electrically conductive material. Optionally, the jacket element (jacket block) is formed exclusively from a heat-resistant or ceramic material. Optionally, the jacket element may include a core material that is at least partially surrounded or enveloped by a heat-resistant or ceramic (i.e., non-electrically conductive) material formed as a coating in the outer region of the jacket element and within each elongated bore or channel. Thus, the jacket element (jacket block) is configured to be both heat-resistant and electrically insulating.
[0029] Preferably, the heater comprises multiple jacket elements assembled together as a unitary body and at least partially surrounded by spacers (extending between a surrounding casing and a jacket block). The jacket elements are assembled together and bonded as an assembly, optionally by spacers and / or other support members positioned at different regions along the length of the jacket block to positionally fix the jacket block relative to the casing and other components of the electric heater.
[0030] Optionally, the casing (alternatively referred to as a sheath) comprises a generally hollow cylindrical or hollow cubic shape that encloses the heating assembly. Preferably, a spacer is attached to a radially inner surface of the casing. Optionally, the spacer may be welded to the inner surface of the casing to facilitate manufacturing the heater and to provide structural strength to the heater. Thus, the spacer may be considered to form part of the casing.
[0031] References herein to a "heating element" encompass relatively thin wires as well as heating elements of larger cross section. Such heating elements, rods, bars, or wires may include iron-chromium-aluminum (Fe-Cr-Al) alloys or nickel-chromium-iron (Ni-Cr-Fe) alloys, although other suitable alloys or materials may be used. In many implementations, the maximum internal spacing between the heating element and the inwardly facing surface defining each bore or channel is between 0.5 mm and 20 mm, but may fall within a broader range between 0.2 mm and 20 mm. Optionally, particularly thicker walled heating elements, may comprise individual rods or wire bundles that are then optionally twisted or twisted together. With such a configuration, the internal spacings referred to above are defined by the internal spacing between the rods or wire bundles and the regions of the inwardly facing surface defining each longitudinal bore or channel that are further separated from the heating element.
[0032] Optionally, a width of each of the circumferential fins decreases in a direction toward the at least one heating element. Optionally, each of the fins may be approximately wedge-shaped in a cross-sectional plane of the boss or channel. Optionally, in a cross-sectional plane of the boss or channel, each fin may include a polygonal, rectangular, square, triangular, or semicircular cross-sectional shape profile.
[0033] Preferably, within said cross-sectional plane, the inwardly facing surface includes curved and straight or planar regions. In particular, the inwardly facing surfaces of the bores or channels between the circumferential fins are not continuously curved. The bores or channels positioned circumferentially between the stabilizing fins project radially outward beyond an imaginary circle centered on and extending around the heating element (positioned within each bore or channel). With respect to this imaginary circle, each channel can be considered to be enlarged with a larger cross-sectional area (by extending radially outward beyond the imaginary circle) to increase the available volume for the throughflow of gas. This configuration is beneficial for enhancing both the energy transfer and heating capacity of the subject invention while reducing localized temperature deviations along the length of the heating element.
[0034] Optionally, the linear or planar regions of the inwardly facing surface represent an imaginary polygonal region surrounding at least one heating element, the imaginary polygon being interrupted in the circumferential direction by the fins. Optionally, in the circumferential direction, the curved regions are located at central positions between adjacent fins, with respective linear or planar regions on either side. Preferably, in said cross-sectional plane, the shape of the inwardly facing surface between the circumferential fins is discontinuously curved. Preferably, in said cross-sectional plane, the shape of the inwardly facing surface between the circumferential fins is not exclusively formed by an arc of a circle having a radius larger than the radius of at least one heating element. The leaf or petal shaped configuration of the bores or channels around the heating elements controls the flow of gas and prevents undesirable localized heating fluctuations.
[0035] Preferably, the fins extend over a majority of the length of each bore or channel between the first and second longitudinal ends. Preferably, the fins extend over the entire length of each bore or channel between the first and second longitudinal ends. Preferably, each of the fins has the same depth radially towards the at least one heating element. Optionally, each of the fins projects radially inwardly from a planar region of the inwardly facing surface. Preferably, in the cross-sectional plane, each of the fins includes a wedge-shaped profile, with the thinnest portion of each wedge positioned radially closest to the at least one heating element.
[0036] Optionally, the heater may include three, four, five, or six fins projecting radially inward in each respective bore or channel. However, the number of fins will be design dependent and therefore it will be possible to have more than six fins. As such, it will be appreciated that any number of fins may be provided to achieve a desired direction of flow of gas through the heater, center the heating element, and prevent undesirable temperature gradients around the heating element. The fins may be straight along their length, or may bend, curve, or follow a non-linear direction along the length of the bore or channel. Optionally, the fins may be helical or partially helical along their length between the respective ends of the heating element / jacket block.
[0037] Optionally, the electric heater may further comprise a casing positioned to at least partially surround the heating assembly, the casing comprising an outer sheath and a plurality of spacers extending radially between the outer sheath and the jacket block. Optionally, the spacer comprises a partial disk-shaped member having a central aperture through which a portion of the jacket block extends. Preferably, the heater may further comprise a plurality of jacket elements assembled together as a unitary body and at least partially surrounded by the spacers. Optionally, the elongated jacket block may comprise a single elongated jacket element having a plurality of longitudinal bores or channels extending through the jacket block.
[0038] Particular implementations of the present invention will now be described, by way of example only, and with reference to the accompanying drawings, in which: [Brief description of the drawings]
[0039] [Figure 1] FIG. 2 is a cross-sectional side view of a heating assembly within an electric heater according to one embodiment of the present invention. [Diagram 2] 2 is a further cross-sectional side view of an electric heater incorporating the heating assembly of FIG. 1. [Diagram 3] FIG. 2 is a cross-sectional perspective view of a portion of a jacket element surrounding a heating element / wire according to one embodiment of the present invention. [Figure 4] FIG. 4 is a cross-sectional perspective view of the jacket element of FIG. 3 without the heating element. [Diagram 5] FIG. 5 is an end view of the jacket element of FIG. 4 without the heating element. [Figure 6] FIG. 13 is a cross-sectional perspective view of a jacket element surrounding a heating element / wire according to a further specific implementation of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0040] 1 and 2, the electric heater 1 comprises a casing 2 or housing 3 (having an inwardly facing surface 3b and an outwardly facing surface 3a) in the form of a tubular sheath defining an internal chamber 4 open at both axial ends. The heater 1 comprises a gas feed tube 22, a gas outlet nozzle 16 having an inlet tube 15, and a fixed flange 20 attached to a current feed flange 21. The gas feed tube 22 opens into a cylindrical cavity 19 through which extend parallel current connection tubes 18 (only one tube is shown). The current connection tube 18 forms a passage for connecting the end of the mated electric heating element 11 with the electrical connection flange 21 from which an external electrical connection 23 extends. A centering extension 17 (which may be part of the heating element) projects into the tube 18 to help stabilise the heating assembly 5.
[0041] The heating assembly, generally indicated by reference 5, is mounted within the chamber 4 and is formed from a plurality of longitudinally elongated jacket elements 6 assembled and held together to form a longitudinally elongated jacket block 7. Each elongated jacket element 6 includes a longitudinally extending internal bore or channel 8 extending the entire length of each jacket element 6 to open at first and second axial ends 7a, 7b of the jacket block 7. The jacket elements 6 and jacket block 7 are formed as hollow bodies within which the solid mass and volume extend continuously between the first and second axial ends 7a, 7b. That is, the jacket elements 6 and jacket block 7 are not discontinuous between the respective ends 7a, 7b. Such an arrangement is advantageous for maximizing the degree and efficiency of thermal energy transfer within each jacket element 6, as will be described in further detail herein.
[0042] The jacket block 7 is mounted in place (within the casing 2) by a pair of disk-shaped spacers 9a, 9b positioned longitudinally towards each jacket block axial end 7a, 7b. The sheath 3 and spacers 9a, 9b may be formed from metal, whereby the spacers 9a, 9b are fixed to the inwardly facing surface 3b of the sheath 3 by welding. Each spacer 9a, 9b has a rectangular shape profile and is provided with a central aperture 10 that is dimensioned to accommodate the jacket block 7, which is also provided with a substantially cubic external shape profile. The jacket block 7 is thus mounted within each spacer aperture 10 such that it is suspended within the chamber 4 and spatially separated from the sleeve inwardly facing surface 3b.
[0043] The heating assembly, generally designated by reference 11, is formed as an elongated wire (or rod) having respective ends 11d, 11e projecting generally from one of the axial ends of the jacket block 7. For illustrative purposes, ends 11d, 11e are shown in FIGS. 1-3 projecting from the "hot" end 7b of the jacket block 7. Ends 11d, 11e preferably project from the "cool" end 7a of the jacket block 7. The heating element 11 includes a generally circular cross-sectional profile and is sized slightly smaller than the cross-sectional area of each jacket element bore or channel 8. A single heating element 11 is adapted to extend sequentially through each elongated bore or channel 8 of the jacket block 7 via respective bent axial end sections 11a and 11b. In particular, the heating element 11 exits one bore or channel 8 of the first jacket element, bends 180° (heating element end section 11a) and returns into an adjacent or nearby bore or channel 8 at the first axial end 7a of the jacket block. This is repeated at the second axial end 7b of the jacket block via bent end section 11b. The heating element ends 11d, 11e can be coupled to electrical connections (via connectors 23) to allow electrical current to pass through the element 11, as will be appreciated.
[0044] 3, each jacket element 6 comprises four longitudinally extending side surfaces 6a, 6b, 6c, 6d, which are generally planar such that each jacket element has an external, generally square cross-sectional shape profile adapted to allow the jacket elements to be placed together in touching contact to form a rectangular cuboid integral body, with the individual side surfaces of the jacket elements 6 forming the outwardly facing surfaces of the jacket block 7. A small gap is provided between each spacer aperture 10 and the outer surface of the jacket block 7 (defined by the jacket element side surfaces 6a, 6b, 6c, 6d). Such a gap accommodates differential thermal expansion of the spacers 9a, 9b (typically formed from metal) and the jacket elements 6, which are preferably formed from a non-electrically conductive heat-resistant material. However, structural support for at least a portion of the jacket block 7 and the heating elements 11 is provided by the spacers 9a, 9b (through the apertures 7), which are at least partially in contact with the jacket block 7.
[0045] As will be appreciated, the dimensions of the heating element 11 and the bores or channels 8 are carefully controlled to achieve a desired small separation gap between the inwardly facing surface 13 of each bore or channel 8 and the exterior surface 24 of the heating element 11. Such an arrangement is advantageous for maximizing the effectiveness and efficiency of thermal energy transfer from the element 11 to the gas phase medium, which is first introduced into the chamber 4 at location 14a and then flows through each of the bores or channels 8 and exits the heating assembly 5 at location 14b. This effectiveness and efficiency of thermal energy transfer is in turn also provided by the heating element 6 extending longitudinally (axially) in series between each end 7a, 7b. In particular, the heating element 11 is completely and continuously housed, covered and contained by the elongated jacket element 6 between the ends 7a, 7b. When the electric heater 1 is held suspended vertically during use, undesirable contact between the bent end sections 11a, 11b and the end faces 6c, particularly the annular edges defining the inlet and outlet ends of each bore or channel 8, contributes to fatigue and damage to the heating element 11 and a corresponding reduction in the usable life of the heater 1.
[0046] Advantageously, and with reference to Figures 3-5, the present electric heater 1 and in particular each jacket element 6 comprises means for positionally stabilising and centreing the heating element 11 within each bore or channel 8. This centreing and stabilisation is achieved by a set of stabilising fins, generally indicated with reference 25, extending longitudinally along a central region of each bore or channel 8 and projecting radially into and towards the central region. The fins 25 are particularly adapted to maintain the centreing of the heating element 11 in the axial centre of each bore or channel 8, which in turn positionally stabilises the heating element 11 and in particular the bent axial end sections 11a, 11b (projecting axially beyond the respective end faces 7a, 7b of the jacket block 7). As will be recognised, a short circuit of the electric heater 1 will occur if the ends 11a, 11b come into contact with each other, resulting in a total failure of the electric heater 1. Bending and positional distortion of the heating element 11 within the elongated bore or channel 8 may result from localized heat around the heating element 11 in the region between the jacket block ends 7a, 7b. The present fins 25 project radially into the bore or channel 8 and are positioned in very close and almost touching contact with the heating element exterior surface 24. A small radial gap 37 is provided between the radially innermost end face 33 of each fin 25 and the heating element exterior surface 24. If the heating element 11 is radially distorted, surface 24 may contact surface 33 to prevent further radial displacement of the element 11 within the bore or channel 8 and maintain centering, thereby maintaining a predefined separation of each of the bent end sections 11a, 11b.
[0047] According to the particular implementation of Figs. 3-5 and also according to the further embodiment of Fig. 6, each internal bore or channel 8 can be considered to include a substantially square or rectangular cross-sectional shape, with the corners of the square / rectangle being circular. Fins 25 project radially inwardly from each side of the square / rectangle at a central location between the circular corners. In particular, and referring to Fig. 5, each bore or channel 8 is defined by a substantially planar surface 31 (which would otherwise define a square or rectangular cross-sectional shape), each surface 31 extending between respective corners 29. Each internal (bore or channel) corner 29 is positioned radially inwardly from a respective corner 28 provided on the outwardly facing surface of each heating element 6. Each corner 29 comprises an arcuate section bounded on both sides circumferentially around the bore or channel 8 by a proximal surface 31. Fins 25 project inwardly from the proximal surface 31. Each fin 25 has a radially innermost end surface 33 at an innermost tip 35 and tapering sides 32 that project outwardly from the end surface 33 and join to the planar surface 31 by a curved transition surface 34. Thus, each fin 25 is generally wedge-shaped in the cross-sectional plane. The transition surface 34, which marks the area of the wall 38 of each jacket element 6, is positioned at the base 36 of each fin 25. According to each particular embodiment, the four fins 25 project inwardly from the wall 38 towards the axial center of each bore or channel 8. Each fin 25 is positioned approximately midway between each corner 29. Each fin 25 projects an equal distance radially inwardly from the wall 38 such that each of the gaps 37 is the same size. According to one embodiment, the surface area ratio is expressed as the cross-sectional area of the heating element 11 divided by the cross-sectional area of the bore or channel or cavity 8.
[0048] A set of gas flow channels 40 are defined between each fin 25 circumferentially around the heating element. Each channel 40 is defined in part by the tapered sides 32, transition faces 30, flat faces 31, arcuate corner surfaces 30 of each fin 25, and the exterior surface 24 of the heating element 11. The approximately square or rectangular cross-sectional profile of each bore or channel 8 serves to maximize the cross-sectional surface area for through-flow of gas around the heating element 11 (notwithstanding the circular presence of the fins 25 and corners 29). This is important for maximizing the energy transfer between the heating element 11 and the flowing gas. This geometric profile, in addition to the presence of the stabilizing fins 25, is beneficial for controlling and directing the flow of gas around the heating element 11 to avoid undesirable heating differentials that would otherwise result in bending and distortion of the heating element 11 during use. The stabilizing fins 25 also provide a means to prevent large positional shifts of the heating element 11 within each bore or channel 8, as shown. In the cross-sectional plane of FIG. 5, the channel 40 may exhibit lobes 27a, 27b, 27c, 27d with respective enlarged volumes surrounding the element 11 to maximize the throughflow volume of the gas. This improves the heating capacity and efficiency of the electric heater 1. In particular, the inventors have determined that a particular shape profile of the inwardly facing surface 13 of each bore or channel 8 by respective surfaces / faces 31, 30, 34, and 32 contributes to uniform heating of the gas flowing around the heating element 11 and minimizing undesirable temperature gradients of the heating element 11 within the bore or channel 8. In the cross-sectional plane of each bore or channel, each of the lobes 27a, 27b, 27c, 27d may include a petal or leaf shape profile. Thus, in the cross-sectional plane, the separation distance between the heating element surface 24 and the bore or channel surface 13 is non-uniform between each fin 25 in the circumferential direction around the heating element 11. This arrangement is advantageous for providing increased lateral stabilization of the heating element 11 in a direction perpendicular to the longitudinal axis 12 extending through the heater 11 .A heater having positionally centered and stabilized heating elements (within each bore or channel 8) is advantageous for minimizing any movement of the curved axial end sections 11a, 11b, which in turn extends the operational life of the electric heater 1 and in particular the heating assembly 5 including the jacket block 7.
[0049] As will be appreciated, although the subject invention is described with reference to a collection of heating elements 6 assembled together as a unitary body, the jacket block 7 may comprise a unitary body having a plurality of internal bores or channels 8 each with the described geometric profile and stabilizing fins 25. The unitary jacket block 7 according to any such further implementation may be positionally stabilized within the casing 2 by corresponding stabilizing spaces 9a, 9b having appropriately sized apertures 10.
Claims
1. 2. An electric heater for heating a flow of fluid, comprising: at least one axially elongated jacket element (6) defining an axially elongated jacket block (7) having a first longitudinal end (7a) and a second longitudinal end (7b); a plurality of longitudinal bores or channels (8) extending internally through said jacket block (7) and opening at each of said respective first and second longitudinal ends (7a, 7b), each of said bores or channels being defined by an inwardly facing surface (13) of said at least one jacket element (6); at least one heating element (11) extending axially through said bore or channel (8) and having a respective bent axial end section (11a), whereby at least one heating element (11) exits an adjacent or nearby bore or channel (8) and returns into said adjacent or nearby bore or channel (8) at one or both of said respective first and second longitudinal ends (7a, 7b), said at least one heating element (11) and said jacket block (7) forming a heating assembly (5), 1. An electric heater characterized by at least three fins (25) projecting radially inwardly from said at least one jacket element (6) towards said at least one heating element (11) within each of said bores or channels (8).
2. 2. The electric heater of claim 1, wherein, in a cross-sectional plane through the jacket block, the radial separation distance between the inwardly facing surface (13) of each bore or channel (8) and the outwardly facing surface (24) of the at least one heating element (11) is greatest at a central position between adjacent fins (25) in the circumferential direction.
3. 3. An electric heater according to claim 1 or 2, wherein the width of each of the fins (25) in the circumferential direction decreases in a direction towards the at least one heating element (11).
4. 4. An electric heater according to claim 2 or 3, wherein in the cross-sectional plane, the inwardly facing surface (13) comprises curved regions (30) and straight or flat regions (31).
5. 5. An electric heater as claimed in claim 4 when dependent on claim 2, wherein the curved region (30) is located at the location centrally between adjacent fins (25) and is flanked on either side by the respective straight or flat regions (31).
6. The electric heater according to any one of claims 1 to 5, wherein the cross-sectional surface area ratio is between 0.12 and 0.
72.
7. 7. An electric heater according to any one of claims 1 to 6, wherein in the cross-sectional plane, the shape of the inwardly facing surface (13) between the circumferential fins (25) is discontinuously curved.
8. 8. An electric heater as claimed in any one of claims 1 to 7, wherein, within the cross-sectional plane, the shape of the inwardly facing surface (13) between the circumferential fins (25) is not exclusively formed by an arc of a circle having a radius greater than the radius of the at least one heating element (11).
9. 9. An electric heater as claimed in any one of claims 1 to 8, wherein the fins (25) extend over the majority of the length of each bore or channel (8) between the first and second longitudinal ends (7a, 7b).
10. 10. An electric heater as claimed in claim 9, wherein the fins (25) extend over the entire length of each of the bores or channels (8) between the first and second longitudinal ends (7a, 7b).
11. 11. An electric heater as claimed in any one of claims 1 to 10, wherein within the cross-sectional plane, each of the fins (25) comprises a wedge-shaped profile, the thinnest portion (35) of each wedge being positioned radially closest to the at least one heating element (11).
12. 12. An electric heater according to any one of claims 1 to 11, comprising the heating element (11), the maximum internal spacing between the heating element and the inwardly facing surface defining each bore being between 0.5mm and 20mm.
13. 13. Electric heater according to any one of the preceding claims, wherein the at least one jacket element (6) comprises an electrically non-conductive material.
14. 14. The electric heater of claim 1, further comprising a casing (2) positioned to at least partially surround the heating assembly (5), the casing comprising an outer sheath (3) and a number of spacers (9a, 9b) extending radially between the outer sheath (3) and the jacket block (7).
15. 15. Electric heater according to any one of claims 11 to 14, comprising a number of said jacket elements (6) assembled together as an integral body and at least partially surrounded by said spacers (9a, 9b).
16. 16. An electric heater according to any one of claims 1 to 15, wherein the elongated jacket block (7) comprises a single elongated jacket element (6) having the plurality of longitudinal bores or channels (8) extending through the jacket block (7).