ELECTRIC FLUID FLOW HEATER WITH HEATING ELEMENTS STABILIZATION FINS

Abstract

An electric heater to heat a flow of a fluid having a jacket block comprising a plurality of longitudinal bores to allow the through-flow of a gas phase medium. An elongate heating element extends through each of the bores and is positionally stabilised within the jacket block via a plurality of stabilising fins that project radially inward to at least partially surround the elongate heating element within each of the bores.

Claims

1. An electric heater to heat a flow of a fluid comprising: at least one axially elongate jacket element defining an axially elongate jacket block having first and second lengthwise ends; a plurality of longitudinal bores or channels extending internally through the jacket block and being open at each of the respective first and second lengthwise ends each of the bores or channels defined by an internal facing surface of the at least one jacket element; and at least one heating element extending axially through the bores or channels and having respective bent axial end sections such that the at least one heating element emerges from and returns into adjacent or neighbouring bores or channels at one or both the respective first and second lengthwise ends, the at least one heating element and the jacket block forming a heating assembly, wherein at least three fins project radially inward from the at least one jacket element towards the at least one heating element within each of the bores or channels.

2. The electric heater as claimed in claim 1, wherein in a cross sectional plane through the jacket block, a radial separation distance between the internal facing surface of each bore or channel and an external facing surface of the at least one heating element is at a maximum at a position centrally between adjacent fins in a circumferential direction.

3. The electric heater as claimed in claim 1, wherein a width of each of the fins in a circumferential direction decreases in a direction towards the at least one heating element.

4. The electric heater as claimed in claim 2, wherein in said cross sectional plane the internal facing surface comprises curved regions and linear or planar regions.

5. The electric heater as claimed in claim 4, wherein the curved regions are located at the position centrally between the adjacent fins and flanked at either side by the respective linear of planar regions.

6. The electric heater as claimed in claim 1, wherein the cross-sectional surface area ratio is between 0.12 to 0.72.

7. The electric heater as claimed in claim 2, wherein in said cross sectional plane, a shape of the internal facing surface between the fins in a circumferential direction is non-continuously curved.

8. The electric heater as claimed in claim 2, wherein in said cross sectional plane, a shape of the internal facing surface between the fins in a circumferential direction is not formed exclusively by an arc of a circle having a radius larger than a radius of the at least one heating element.

9. The electric heater as claimed in claim 1, wherein the fins extend over a majority of a length of each bore or channel between the first and second lengthwise ends.

10. The electric heater as claimed in claim 9, wherein the fins extend over a full length of each of the bore or channels between the first and second lengthwise ends.

11. The electric heater as claimed in claim 2, wherein in the cross sectional plane, each of the fins comprise a wedge shape profile with a thinnest part of each wedge positioned radially closest to the at least one heating element.

12. The electric heater as claimed in claim 1, wherein the heating element, wherein a maximum internal spacing between the heating element and the internal facing surface that defines each bore is between 0.5 and 20 mm.

13. The heater as claimed in claim 1, wherein the at least one jacket element comprises a non-electrically conducting material.

14. The heater as claimed in claim 1, further comprising a casing positioned to at least partially surround the heating assembly and the casing comprises an outer sheath and a plurality of spacers extending radially between the outer sheath and the jacket block.

15. The heater as claimed in claim 11, comprising a plurality of the jacket elements assembled together as a unitary body and at least partially surrounded by the spacers.

16. The heater as claimed in claim 1, wherein the elongate jacket block comprises a single elongate jacket element having the plurality of longitudinal bores or channels extending through the jacket block.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0038] A specific implementation of the present invention will now be described, by way of example only, and with reference to the accompanying drawings in which:

[0039] FIG. 1 is a cross sectional side view of a heating assembly within an electric heater according to one aspect of the present invention;

[0040] FIG. 2 is a further cross sectional side view of an electric heater incorporating the heating assembly of FIG. 1;

[0041] FIG. 3 is a cross sectional perspective view of a part of a jacket element surrounding a heating element/wire according to one aspect of the present invention;

[0042] FIG. 4 is a cross sectional perspective view of jacket element of FIG. 3 without the heating element;

[0043] FIG. 5 is an end view of the jacket element of FIG. 4 without the heating element;

[0044] FIG. 6 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 PREFERRED EMBODIMENT OF THE INVENTION

[0045] Referring to FIGS. 1 and 2, an electric heater 1 comprises a casing 2 in the form of a tubular sheath or housing 3 (having internal and external facing surfaces 3b, 3a, respectively) that defines an internal chamber 4 open at both axial ends. The heater 1 comprises a gas feed tube 22, a gas outlet nozzle 16 with inlet tube 15 and a fixing flange 20 mounted to a current feed flange 21. Gas feed tube 22 opens into a cylindrical cavity 19 through which extends parallel current connecting tubes 18 (only one tube shown). The current connecting tubes 18 form a passage for the connection of the ends of an electric heating element 11 mated with electrical connecting flange 21 from which extends external electrical connections 23. A centering extension 17 (that may be part of the heating element) projects into tube 18 to assist stabilisation of the heating assembly 5.

[0046] A heating assembly indicated generally by reference 5 is mounted within chamber 4 and is formed from a plurality of lengthwise elongate jacket elements 6 assembled and held together to form a lengthwise elongate jacket block 7. Each elongate jacket element 6 comprises a lengthwise extending longitudinal internal bore or channel 8 extending the full length of each jacket element 6 so as to be open at a first and second axial end 7a, 7b of the jacket block 7. The jacket element 6 and jacket block 7 are formed as hollow bodies in which the solid mass and volume extends continuously between the first and second axial ends 7a, 7b. That is, the jacket elements 6 and jacket blocks 7 are not discontinuous between respective ends 7a, 7b. Such an arrangement is advantageous to maximise the extent and efficiency of thermal energy transfer within the respective jacket elements 6 as explained in further detail herein.

[0047] Jacket block 7 is mounted in position (within casing 2) via a pair of disc-shaped spacers 9a, 9b positioned in a lengthwise direction towards each jacket block axial end 7a, 7b. Sheath 3 and spacers 9a, 9b may be formed from metal such that spacers 9a, 9b are secured to an internal facing surface 3b of sheath 3 via welding. Each spacer 9a, 9b comprises a central aperture 10 having a rectangular shape profile and dimensioned to accommodate jacket block 7 that also comprises an external generally cuboidal shape profile. Accordingly, jacket block 7 is mounted within each spacer aperture 10 so as to be suspended within chamber 4 and spatially separated from sleeve internal facing surface 3b.

[0048] A heating element indicated generally by reference 11 is formed as an elongate wire (or rod) having respective ends 11d, 11e projecting generally from one of the axial ends of jacket block 7. Ends 11d, 11e are illustrated in FIGS. 1 to 3 projecting from the ‘hot’ end 7b of the jacket block 7 for illustrative purposes. Ends 11d, 11e, preferably extend from the ‘cool’ end 7a of jacket block 7. Heating element 11 comprises a generally circular cross sectional profile and is dimensioned slightly smaller than the cross-sectional area of each jacket element bore or channel 8. The single heating element 11 is adapted to extend sequentially through each elongate bore or channel 8 of the jacket block 7 via respective bent axial end sections 11a and 11b. In particular, heating element 11 emerges from one bore or channel 8 of a first jacket element 6 is bent through 180° (heating element end section 11a) so as to return into an adjacent or neighbouring bore or channel 8 at the jacket block first axial end 7a. This is repeated at the jacket block second axial end 7b via bent end sections 11b. Heating element ends 11d, 11e are capable of being coupled to electrical connections (via connector 23) to enable a current to be passed through element 11 as will be appreciated.

[0049] Referring to FIG. 3, each jacket element 6 comprises four longitudinal extending side faces 6a, 6b, 6e and 6h that are generally planar such that each jacket element comprises an external generally square cross sectional shape profile adapted to enable the jacket elements to sit together in touching contact to form a rectangular cuboidal unitary body in which the individual side faces of the jacket elements 6 form the external facing surfaces of the jacket block 7. A small gap is provided between each spacer aperture 10 and the external surfaces of jacket block 7 (defined by jacket element side faces 6a, 6b, 6e, 6h). Such gaps accommodated differential thermal expansion of the spacers 9a, 9b (typically formed from metal) and the jacket elements 6 that are preferably formed from a non-electrically conducting refractory material. However, at least some structural support of the jacket block 7 and heating element 11 is provided by spacers 9a, 9b (via apertures 10) that are at least partially in contact with jacket block 7.

[0050] As will be appreciated, the dimensions of the heating element 11 and bores or channels 8 are carefully controlled to achieve a desired small separation gap between an inward facing surface 13 of each bore or channel 8 and an external surface 24 of heating element 11. Such an arrangement is advantageous to maximise the effectiveness and efficiency of heat energy transfer from element 11 to a gas phase medium initially introduced into the chamber 4 at position 14a to then flow through each of the bore or channel 8 and exit from the heating assembly 5 at position 14b. This effectiveness and efficiency of heat energy transfer is also provided, in turn, by the heating elements 6 extending continuously lengthwise (axially) between respective ends 7a, 7b. In particular, heating element 11 is entirely and continuously housed, covered and contained by the elongate jacket elements 6 between ends 7a, 7b. When the electric heater 1 is suspended vertically in use, undesirable contact between the bent end sections 11a, 11b and the end faces 6c, and in particular the annular edges that define the entry and exit end of each bore or channel 8, contribute to fatigue and damage to the heating element 11 and a corresponding reduction in the service lifetime of the heater 1.

[0051] Advantageously and referring to FIGS. 3 to 5, the present electric heater 1 and in particular each jacket element 6 is provided with means to positionally stabilise and centre heating element 11 within each bore or channel 8. This centering and stabilisation is achieved via a set of stabilising fins indicated generally by reference 25, that extend longitudinally along and project radially into and towards a central region of each bore or channel 8. Fins 25 are adapted specifically to maintain centering of heating element 11 at the axial centre of each bore or channel 8 which in turn positionally stabilises heating element 11 and in particular the bent axial end sections 11a, 11b (that project axially beyond the respective end faces 7a, 7b of the jacket block 7). As will be appreciated, short circuiting of the electric heater 1 would occur if ends 11a, 11b were to contact one another resulting in complete failure of the electric heater 1. Bending and positional distortion of the heating element 11 within the elongate bore or channel 8 may result from localised heating around heating element 11 at regions between 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 external surface 24. A small radial gap 37 is provided between a radially innermost end face 33 of each fin 25 and heating element external surface 24. Should heating element 11 distort radially, surface 24 may contact surface 33 to prevent further radial displacement and maintain centering of element 11 within bore or channel 8 to maintain the pre-defined separation of each of bent end sections 11a, 11b.

[0052] According to the specific implementation of FIGS. 3 to 5 and also the further embodiment of FIG. 6, each internal bore or channel 8 may be considered to comprise a general square or rectangular cross sectional shape with the corners of the square/rectangle being rounded. The fins 25 project radially inward from each side face of the square/rectangle at a mid-position between the rounded corners. In particular, and referring to FIG. 5, each bore or channel 8 is defined by generally planar faces 31 (that would otherwise define the square or rectangular cross sectional shape) with each face 31 extending between the respective corners 29. Each internal (bore or channel) corner 29 is positioned radially inward from respective corners 28 provided at the external facing surface of each heating element 6. Each corner 29 comprises an arcuate section, bordered at each side in a circumferential direction around bore or channel 8 by neighbouring surfaces 31. Fins 25 project inwardly from neighbouring surfaces 31. Each fin 25 comprises a radially innermost end face 33 provided at an innermost tip 35 and tapering side faces 32 that projects outwardly from end surface 33 and mate with planar surfaces 31 via curved transition faces 34. Accordingly, each fin 25 is generally wedge shaped in the cross sectional plane. Transition faces 34 are positioned at a base 36 of each fin 25 that represent a region of a wall 38 of each jacket element 6. According to each specific embodiment, four fins 25 project inwardly from wall 38 towards an axial centre of each bore or channel 8. Each fin 25 is positioned approximately mid-way between each corner 29. Each fin 25 projects radially inward from wall 38 by an equal distance so 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.

[0053] A set of gas-flow channels 40 are defined between each fin 25 in the circumferential direction around heating element. Each channel 40 is defined, in part, by the tapered side faces 32 of each fin 25, the transition faces 30, the planar faces 31, the arcuate corner surfaces 30 and the external surface 24 of heating element 11. The generally square or rectangular cross sectional profile of each bore or channel 8 (notwithstanding the presence of fins 25 and the rounding of the corners 29) serves to maximise the cross sectional surface area for the through flow of gas around heating element 11. This is important to maximise the energy transfer between heating element 11 and the flowing gas. This shape profile in addition to the presence of stabilising fins 25 is beneficial to control and direct the flow of the gas around the heating element 11 to avoid undesirable differential heating that would otherwise lead to bending and distortion of the heating element 11 in use. Stabilising fins 25 also provide a means of preventing large positional shifts of the heating element 11 within each bore or channel 8 as indicated. In the cross sectional plane of FIG. 5, the channels 40 may represent lobes 27a, 27b, 27c, 27d surrounding element 11 and having respective enlarged volumes to maximise the volume of the through flow of gas. This improves the heating capacity and efficiency of the electric heater 1. In particular, the inventors have identified that the specific shape profile of the inward facing surface 13 of each bore or channel 8 via the respective surfaces/faces 31, 30, 34 and 32 contribute to the uniform heating of the gas flowing around the heating element 11 and a minimising of undesirable temperature gradients of the heating element 11 within the bore or channel 8. In a cross sectional plane of each bore or channel, each of the lobes 27a, 27b, 27c, 27d may comprise a petal or leaf shape profile. As such, in the cross sectional plane, a separation distance between heating element surface 24 and bore or channel surface 13 and is non-uniform between each fin 25 in a circumferential direction around the heating element 11. The present arrangement is advantageous to provide an increased lateral stabilisation of the heating element 11 in a direction perpendicular to longitudinal axis 12 extending through heater 11. The heater having a positionally centred and stabilised heating element (within each bore or channel 8) is advantageous to minimise any movement in the bent axial end sections 11a, 11b and in turn extend the operational lifetime of the electric heater 1 and in particular the heating assembly 5 including jacket block 7.

[0054] As will be appreciated, whilst 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 single body having a plurality of internal bores or channels 8 each provided with a shape profile and stabilisation fins 25 as described. The single jacket block 7 according to any such further implementations may be positionally stabilised within casing 2 via corresponding stabilising spaces 9a, 9b having appropriately sized apertures 10.