权利要求：
Claims
1. An electric heating system for heating a fluid flow, the system comprising: a housing having an inlet for a fluid flow to be heated by the electric heating system and an outlet for the fluid flow which has been heated by the electric heating system; and a resistive heater mounted within the housing, the resistive heater comprising:
a fluid input and a fluid output which are fluidically coupled, respectively, to the inlet and the outlet,
a plurality of annular walls composed of an electrically conductive material, the walls being nested to define a plurality of annular flow channels which are serially arranged concentrically about a longitudinal axis, wherein the walls extend between opposite first and second ends of the resistive heater which are mutually separated along the longitudinal axis, and
first and second electrical terminals for connection to a source of electrical energy to heat the walls of the resistive heater, the first and second electrical terminals being electrically connected to respective first and second walls which are mutually adjacent and comprise an outer pair of the walls which are located at a radially outer side of the resistive heater,
wherein the plurality of annular walls are mechanically connected together whereby adjacent flow channels have opposite fluid flow directions and are connected at adjacent ends of the respective channels to define an alternating serpentine flow path which has an input end at the fluid input and an output end at the fluid output, wherein the input and output ends are respectively located at radially outer and radially inner positions relative to the longitudinal axis, and
wherein the plurality of annular walls are electrically connected together to define a continuous electrically conductive path extending between the first and second electrical terminals, the conductive path having a first part which extends from the first wall to a centre of the resistive heater and a second part which extends from the centre of the resistive heater to the second wall.
2. The system according to claim 1, wherein the fluid input and the fluid output are respectively located at the first and second ends of the resistive heater.
3. The system according to claim 1 or claim 2, wherein each annular wall is composed of either a solid layer of the electrically conductive material or a perforated layer of the electrically conductive material.
4. The system according to claim 3, wherein the resistive heater comprises alternating annular walls composed of a solid or perforated layer of the electrically conductive material,
wherein each annular wall composed of the solid layer of the electrically conductive material has adjacent thereto, on at least one or both of a radially outer and a radially inner side thereof, an annular wall composed of the perforated layer of the electrically conductive material, and each annular wall composed of the perforated layer of the electrically conductive material has adjacent thereto, on at least one or both of a radially outer and a radially inner side thereof, an annular wall composed of the solid layer of the electrically conductive material. 3. The system according to claim 3, wherein each annular wall is composed of a solid layer of the electrically conductive material.
6. The system according to any one of claims 1 to 5, wherein the walls comprise » walls which are nested to form a series of the walls, the series having a radially innermost wall having n = 1, a radially outermost wall having » = n, and at least one radially intermediate wall therebetween, each having a respective value of n between 1 and », wherein the walls are electrically connected together by first electrical connections which electrically connect walls having » as an even number to form the first part of the conductive path and by second electrical connections which electrically connect walls having » as an odd number to form the second part of the conductive path.
7. The system according to claim 6, wherein the first and second electrical connections are integral with the walls which are electrically interconnected by the respective electrical connection.
8. The system according to claim 7, wherein each of the first and second electrical connections is either parallel to, or orthogonal to, the longitudinal axis.
9. The system according to any one of claims 6 to 8, wherein at least some walls are provided with openings extending therethrough and at least one of first and second electrical connections extends through a respective opening.
10. The system according to any one of claims 6 to 9, wherein the first and second electrical connections also provide mechanical connections by which the walls are mechanically connected together.
11. The system according to any one of claims 1 to 10, wherein at least one of the walls comprises a cylindrical portion and an adjacent conical portion, wherein a free end part of the cylindrical portion is located at the second end of the resistive heater and the conical portion is oriented towards the first end of the resistive heater.
12. The system according to claim 11, wherein the conical portion which is closest to the first end of the resistive heater comprises a solid layer which defines a closed end part of the plurality of annular walls.
13. The system according to any one of claims 1 to 12, wherein the electric heating system further comprises an annular closure member, which is composed of an electrically insulating material, located at the second end of the resistive heater, wherein the closure member closes ends of the annular flow channels at the second end of the resistive heater to form directional changes in the alternating serpentine flow path at the second end of the resistive heater. 14. The system according to claim 13, wherein the at least one electrically insulating closure member is in contact with, or spaced from, the resistive heater.
15. The system according to any one of claims 1 to 14, wherein one annular wall is configured to form a closed end part of the plurality of annular walls at the first end of the resistive heater, wherein the closed end part closes ends of the annular flow channels at the first end of the resistive heater to form directional changes in the alternating serpentine flow path at the first end of the resistive heater.
16. The system according to any one of claims 1 to 15, wherein the resistive heater further comprises an electrical connector, composed of an electrically conductive material, located at the centre of the resistive heater which electrically connects together an inner pair of the annular walls.
17. The system according to claim 16, wherein the electrical connector comprises a pair of elongate helical elements which are arranged concentrically about the longitudinal axis and are surrounded by the innermost wall, wherein a first end of each helical element is connected to a respective wall of the inner pair of the walls and opposite second ends of the helical elements are connected together by a connection member of the electrical connector. 18. The system according to claim 17, wherein the connection member comprises an annular ring.
19. The system according to claim 17 or claim 18, wherein the first ends of the helical elements are located at the second end of the resistive heater.
20. The system according to any one of claims 1 to 19, wherein the resistive heater comprises an integral monolithic body.
21. The system according to claim 20, wherein the integral monolithic body is fabricated via an additive manufacturing technique, optionally selected from Selective Laser Melting (SLM), Selective Laser Sintering (SLS), Direct Metal Laser Sintering (DMLS), Neutral Beam Melting (NBM), Electron Beam Welding (EBW), Laser Deposition Welding (LDW), Laser Beam Melting (LBM), Laser Metal Deposition (LMD), Electron Beam Melting (EBM), Direct Energy Deposition (DED), Rapid Prototyping (RP), or Rapid Manufacturing (RM).
22. The system according to any one of claims 1 to 21, wherein the housing is electrically connected to one of the first and second electrical terminals of the resistive heater whereby the respective electrical terminal is connectable to the source of electrical energy via the housing. 23. The system according to claim 22, wherein the respective electrical terminal is integral with, or separate from, a mechanical connection between the resistive heater and the housing. 24. The system according to any one of claims 1 to 23, wherein the first and second electrical terminals are configured to be electrically connected by a wired connection to the source of electrical energy.
25. The system according to any one of claims 1 to 24, further comprising a source of electrical energy which is connected to the first and second electrical terminals, wherein the source of electrical energy is configured to supply a direct current, or an alternating current. 26. The system according to any one of claims 1 to 25, wherein a plurality of the resistive heaters are located within the housing, and the resistive heaters are arranged in series or in parallel relative to the inlet and outlet for fluid flow.
27. The system according to any one of claims 1 to 26, wherein the electric heating system is a resistojet and is configured for installation into a spacecraft.
28. A method of producing a high-temperature fluid flow, the method comprising the steps of:
a) providing an electric heating system according to any one of claims 1 to 27;
b) supplying a fluid to be heated to the fluid input of the flow resistor and thereby to flow
along the alternating serpentine flow path to the fluid output of the flow resistor, the
supplied fluid having a pressure greater than an external gas pressure surrounding an
exterior of the housing;
c) applying an electrical potential across the first and second terminals to heat the fluid
flow in the alternating serpentine flow path by the resistive heater; and
d) expelling the heated fluid flow from the outlet of the housing.
29. The method of claim 28, wherein the heated fluid is expelled from the outlet of the housing at a subsonic or sonic velocity via a converging nozzle.
30. The method of claim 28, wherein the heated fluid is expelled from the outlet of the housing at a supersonic or hypersonic velocity via a converging-diverging nozzle. 31. The method according to any one of claims 28 to 30, wherein the electric heating system is a resistojet and installed in a spacecraft, and the method is for moving the spacecraft in space.