Electric heating system for heating a fluid stream

Abstract

An electric heating system for heating a fluid stream, the system comprising: a housing having an inlet for a fluid stream to be heated by the electric heating system and an outlet for a fluid stream that has been heated by the electric heating system; and an electric resistance heater mounted within the housing. The electric resistance heater comprises: a fluid input end and a fluid output end fluidly coupled to the inlet and the outlet, respectively; a plurality of annular walls composed of an electrically conductive material, the walls being nested to define a plurality of annular flow channels arranged serially concentrically about a longitudinal axis, with the walls extending between opposite first and second end portions of the electric resistance heater that are spaced apart from one another along the longitudinal axis; and first and second electrical terminals for connecting an electrical energy source to heat the walls of the electric resistance heater, the first and second electrical terminals being electrically connected to respective first and second walls that are adjacent to one another and comprise outer pairs of walls located radially outward of the electric resistance heater. The plurality of annular walls are mechanically connected together whereby adjacent flow channels have opposite fluid flow directions and are connected at adjacent end portions of the respective flow channels to define alternating serpentine flow paths having an input end portion at the fluid input end and an output end portion at the fluid output end, with the input and output end portions being located at radially outer and inner positions, respectively, relative to the longitudinal axis. 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 electrically conductive path having a first portion extending from the first wall to a center of the electric resistance heater and a second portion extending from the center of the electric resistance heater to the second wall. A method of generating a high temperature fluid stream using the electric heating system is also disclosed.

Description

[0001] This invention relates to an electric heating system for heating fluid flows and a method for heating fluid flows using such a system. The invention is particularly applicable to using such electric heating systems to provide heaters or flow heaters, for example, for resistive engines in spacecraft.

[0002] Electrothermal thrusters are a type of electric propulsion system used in satellites that converts electrical energy into heat, thereby increasing the stagnation temperature of the gaseous propellant. Higher stagnation temperatures generally result in higher performance. Resistance engines are another technology within the electrothermal thruster category, heating the gas through Joule (or resistance) heating of solid heating elements. High-temperature resistance engines are attractive because they offer high performance; however, the gas temperature is limited by the operating temperature of the heater.

[0003] Conventional resistance engines use electric heaters to directly or indirectly heat the gaseous propellant. The gas flows through a heat exchanger, which maximizes the thermal efficiency of the resistance engine by limiting the external temperature of the device. High-temperature resistance engine designs have been successfully demonstrated in the past using concentric tubular heat exchangers to directly heat the propellant, showcasing the operational feasibility of this design concept. However, the fabrication of this design involves a combination of two manufacturing techniques: chemical vapor deposition (CVD) and electron beam (EB) welding. Therefore, the assembly process is lengthy and complex.

[0004] Known high-temperature resistance engines include concentric tubular heaters comprising a series of long, thin tubular elements fabricated by chemical vapor deposition, arranged concentrically. The tubes are connected at both ends by small support members attached by electron beam welding. Such tubular heater structures suffer from premature failure due to a combination of significant thermal expansion generated by extreme heating and manufacturing defects stemming from the numerous weld joints required for the heater assembly.

[0005] Such as (1)F.Romei,AN D. Gibbon, “Manufacturing of a High-Temperature Resistojet Heat Exchanger by Selective Laser Melting”, Acta Astronaut, Vol. 138 (2017), pp. 356-368. doi:10.1016 / j.actaastro.2017.05.020, (2) F. Romei and AN The title is “Validation of an additively manufactured resistojet through experimental and computational analysis”, Acta Astronaut (2020). doi:10.1016 / j.actaastro.2019.10.046 and (3) M. Robinson, A. Grubi The paper "Endurance testing of the additively manufactured STAR resistojet" by G. Reempelos, F. Romei, C. Ogunlesi, and S. Ahmed, Mater. Des. (2019) 107907. doi:10.1016 / J.MATDES.2019.107907 discloses the use of metal additive manufacturing to fabricate concentric tubular heaters into a single integral component. However, this tubular heater structure also suffers from premature failure due to thermal expansion generated by the operation of the circulating heater.

[0006] Other aspects and features of additively manufactured resistojet engines were disclosed in the following presentations given at the 36th International Conference on Electric Propulsion held at the University of Vienna in Vienna, Austria, from 15 to 20 September 2019: (i) Romei, F., Robinson, MD, Ogunlesi, C, Gibbon, D. and Grubisic, AN, entitled “The development and qualification of the STAR resistojet system for telecommunications applications”; (2) Robinson, MD, Grubisic, AN, Romei, F. and Ogunlesi, C., entitled “Lifetime investigations of an additively manufactured high-temperature resistojet heat exchanger from tantalum”; and (3) Ogunlesi, C., Romei, F., Robinson, MD, Grubisic, AN and Gibbon, D., entitled “Structural effects on the high-temperature performance of the Super High Temperature Additive Manufactured Resistojet (STAR)”.

[0007] Despite extensive efforts to produce resistance engines with structural designs that overcome the problems of the aforementioned monolithic heater design, there remains a need in the art for an electric heating system for heating fluid flow that can be used as a resistance engine and has a high level of reliability, and preferably can also be additively manufactured, for example, by 3D printing.

[0008] Therefore, the present invention aims to provide an electric heater design that operates reliably at high temperatures such as up to 3500K and achieves enhanced reliability compared to known resistance engines.

[0009] The present invention also aims to provide an electric heater design that is compact and can be manufactured at low cost, for example, using an additive manufacturing process also known in the art as "3D printing," which can produce a monolithic electric heater. The preferred additive manufacturing process used in the present invention is known in the art as selective laser melting (SLM).

[0010] The present invention also aims to provide an electric heater design that exhibits high thermal efficiency.

[0011] The present invention also aims to provide an electric heater design that can be used in other applications besides resistance engines to provide a heated fluid flow.

[0012] This invention provides an electric heating system for heating a fluid flow, the system comprising:

[0013] A housing having an inlet for a fluid flow heated by an electric heating system and an outlet for a fluid flow already heated by the electric heating system; and

[0014] A resistance heater installed inside a housing, the resistance heater comprising:

[0015] The fluid inlet and fluid outlet are fluidly coupled to the inlet and outlet, respectively.

[0016] Multiple annular walls made of conductive material are nested to define multiple annular flow channels, which are arranged concentrically in series about a longitudinal axis. The walls extend between opposing first and second ends of the resistance heater, separated from each other along the longitudinal axis.

[0017] First and second electrical terminals are used to connect electrical energy to heat the walls of the resistance heater. The first and second electrical terminals are electrically connected to corresponding first and second walls, which are adjacent to each other and include paired outer walls located radially outside the resistance heater.

[0018] The plurality of annular walls are mechanically connected together, such that adjacent flow channels have opposite fluid flow directions and are connected at adjacent ends of the respective channels to define alternating serpentine flow paths. The flow paths have an input end at the fluid inlet and an output end at the fluid outlet, wherein the input end and output end are located radially outward and radially inward relative to the longitudinal axis, respectively.

[0019] The plurality of annular walls are electrically connected together to define a continuous conductive path extending between a first electrical terminal and a second electrical terminal. The conductive path has a first portion extending from the first wall to the center of the resistance heater and a second portion extending from the center of the resistance heater to the second wall.

[0020] The present invention also provides a method for heating a fluid flow using a system that generates a high-temperature fluid flow, the method comprising the following steps:

[0021] a) Provide an electric heating system according to the invention;

[0022] b) The fluid to be heated is supplied to the fluid inlet of the resistance heater, thereby flowing along an alternating serpentine flow path to the fluid outlet of the resistance heater. The supplied fluid has a pressure greater than that of the external gas surrounding the exterior of the housing.

[0023] c) Applying a potential across the first and second terminals to heat the fluid flow in the alternating serpentine flow path via the resistance heater; and

[0024] d) The heated fluid flow is discharged from the outlet of the housing.

[0025] Preferred features of the system and method of the invention are defined in each of the dependent claims.

[0026] The systems and methods of the present invention can be used in any application that requires heating fluids to high temperatures, such as up to 3500K.

[0027] A preferred embodiment of the present invention can provide an electric heating system for heating a fluid flow, the electric heating system including a resistance heater that is compact and can be manufactured at low cost, particularly by means of an additive manufacturing process such as selective laser melting (SLM), which can produce an integral resistance heater.

[0028] A preferred embodiment of the present invention provides a resistance heater design that allows the high-temperature components of the resistance heater to expand and contract freely under thermal loads. This improvement is fundamental for electric heater systems capable of meeting the typical lifespan requirements of space missions when the resistance heater is used as a resistance engine in a spacecraft. Laboratory environmental life testing demonstrates that the preferred embodiment of the present invention can provide a resistance heater design exhibiting a heater lifespan exceeding 6000 heating / cooling cycles, surpassing typical mission requirements of spacecraft such as satellites.

[0029] A preferred embodiment of the invention provides a resistance heater composed of a heat-resistant metal in pure or alloy form, enabling the heating of fluids to temperatures up to 3500 K. Alternatively, non-heat-resistant metals such as nickel alloys or steel can be used to manufacture resistance heaters for applications where the highest temperature is not the only requirement, such as applications where corrosion or oxidation is a potentially significant problem. The resistance heater of the preferred embodiment of the invention can be designed to achieve any given outlet temperature within this range while maintaining high thermal efficiency and exhibiting heater integrity over thousands of heating cycles. Furthermore, when the resistance heater has an integrated, monolithic design, it offers greater design freedom and faster, cheaper production compared to conventional assembly methods using multiple components and materials. Moreover, manufacturing an integrated, monolithic resistance heater using additive manufacturing technology has the advantage of anticipated future cost reductions in additive manufacturing (AM) technology, while simultaneously anticipated increases in print quality and material selection, thereby enhancing the benefits and advantages of the resistance heater according to the preferred embodiment of the invention.

[0030] A preferred embodiment of the invention can provide improved heat transfer to the fluid by using a wall structure in which a first set of walls defines an annular flow path and a second set of walls is located within the annular flow path created by the first set of walls.

[0031] A preferred embodiment of the invention may provide electrical terminals positioned outside the resistance heater where the temperature is low. This simplifies the mechanical connection of the electrical terminals and reduces heat conduction losses in the resistance heater, thereby improving thermal efficiency.

[0032] A preferred embodiment of the invention provides that the resistance heater does not form part of the housing of the electric heater system, which serves as a pressure seal for the electric heater system during use. Therefore, the resistance heater can be manufactured without welding.

[0033] A preferred embodiment of the invention provides that the resistance heater can be manufactured by an additive manufacturing process such as selective laser melting (SLM), which can produce an integral electric heater. Using such a process, a large number of resistance heaters can be produced in a single printing process, and the resistance heaters can be manufactured using high-melting-point materials, such as nickel alloys and heat-resistant alloys known to those skilled in the art, for example, from the publications described above.

[0034] The preferred embodiment of the present invention utilizes a hybrid of different heat exchanger and heater concepts, particularly when manufactured as a single component in an additive manufacturing (AM) process. The resistance heater has two main functions: it generates heat using resistance when an electric current passes through it, and it convectively heats the fluid flowing through it. The resistance heater of the preferred embodiment of the present invention can be easily configured to achieve high fluid temperatures with high thermal efficiency in a compact and low-cost package. High temperatures are achieved through a circulating flow geometry, whereby the fluid continuously passes through the resistance heater, thereby extending the fluid heating time.

[0035] Using additive manufacturing processes, the resistance heater of the preferred embodiment of the present invention can be easily incorporated with features such as meshes to improve heat transfer efficiency, which can maximize the fluid temperature for a given structure temperature. The circulating flow geometry achieves high thermal efficiency by introducing cold fluid to be heated at the outer diameter of the resistance heater, whereby the cold fluid captures radiant heat lost from the resistance heater as it circulates inward toward the center, which is in fluid communication with the fluid outlet of the resistance heater.

[0036] Embodiments of the invention will now be described by way of example only with reference to the following accompanying drawings, in which:

[0037] Figure 1 This is a schematic diagram showing the general structure of an electric heater system including a resistance heater according to the present invention;

[0038] Figure 2 This is according to one embodiment of the present invention. Figure 1 The schematic diagram is of an electric heater system, but the electric heater system is modified to provide a housing or pressure encapsulation that causes the fluid heated by the resistance heater to expand and remain in a subsonic / sonic flow state, and the discharged fluid to maintain a high static temperature.

[0039] Figure 3 This is according to another embodiment of the present invention. Figure 1 The schematic diagram is of an electric heater system, but the electric heater system is modified to provide a housing or pressure encapsulation that causes the fluid heated by the resistance heater to expand and be accelerated to a supersonic / hypersonic flow state, and the discharged fluid has a low static temperature.

[0040] Figure 4 This is a perspective side view of an integral resistance heater according to another embodiment of the present invention, viewed from the outlet end and partially cut off.

[0041] Figure 5 It is as a passage Figure 4A schematic diagram of half a longitudinal section of an integral resistance heater, and schematically showing fluid flow and electrical connections within the integral resistance heater; and

[0042] Figure 6 This is a perspective side view of an integral resistance heater according to another embodiment of the present invention, viewed from the outlet end and partially cut off.

[0043] Referring to the illustration, a general arrangement of an electric heating system according to a preferred embodiment of the present invention is shown. Figure 1 The present invention provides an electrically heated system, generally designated 100, for heating a fluid flow. The fluid flow is supplied from a fluid source 101 by a feed system 102. The fluid may comprise a single fluid component or a mixture of multiple fluid components. System 100 includes a housing 104, also referred to in the art as a pressure envelope, having an inlet 110 for a fluid inflow 103 to be heated by the electrically heated system 100 and an outlet 111 for a fluid outflow 105 already heated by the electrically heated system 100. A resistance heater 108 is mounted within the housing 104 via a mounting mechanism (not shown). The resistance heater 108 includes a fluid inlet 112 and a fluid outlet 113, which are fluidly coupled to the inlet 110 and outlet 111, respectively. Fluid is supplied by the feed system 102 to the inflow 103 at a desired pressure and flow rate.

[0044] System 100 also includes a power electronic device 107 located outside housing 104 for supplying electrical energy from electrical energy source 106 to resistance heater 108. In the illustrated embodiment of the invention, resistance heater 108 is configured to be electrically connected to electrical energy source 106 via a wire.

[0045] The electrical energy source 106 is configured to supply alternating current or direct current of any desired frequency for heating the resistance heater 108.

[0046] The fluid flows through the resistance heater 108, which releases heat energy and heats the fluid, and the total enthalpy of the outflow 105 increases relative to the enthalpy of the inflow 103.

[0047] In the illustrated embodiment of the invention, a single resistance heater 108 is located within the housing 104. However, in an alternative embodiment of the invention, multiple resistance heaters 108 are located within the housing 104, and the resistance heaters 104 may be arranged in series or in parallel with respect to the inflow 103 and the outflow 105. Furthermore, the multiple resistance heaters 104 may be arranged electrically in series or electrically in parallel.

[0048] In a preferred embodiment of the invention, the electric heating system 100 is a resistance engine and is configured to be installed in a spacecraft for moving the spacecraft in space.

[0049] Figure 2 A first preferred embodiment of the invention is shown, wherein the outlet 211 for the fluid effluent 205 has a constricted shape defined by the truncated conical wall 201 of the housing 204. In use, such an outlet 211 discharges heated fluid through one or more orifices 202 at a velocity less than or equal to the speed of sound in the fluid, thereby maintaining a high static temperature in the fluid. The degree of constriction of the truncated conical wall 201 can be varied to change the outflow velocity and static temperature.

[0050] Figure 3 A second preferred embodiment of the invention is shown, wherein the outlet 311 for fluid outflow 305 is integrated with the housing 304, or implemented using additional components. The outlet 311 consists of a constriction portion 301, a throat portion 302, and an expansion portion 303. When operating under conditions where the back pressure within the housing is sufficiently higher than the downstream pressure or ambient pressure, such an outlet 305 discharges heated fluid at a speed greater than the speed of sound in the fluid. This results in a cooler, high-speed flow. The degree of expansion of the conduit can be varied to alter the outflow velocity and static temperature.

[0051] exist Figure 2 and 3 In some embodiments, outlets 211 and 311 may be integrated with the main bodies 220 and 230 of housings 204 and 304, or may include additional components fitted to the main bodies 220 and 230 of housings 204 and 304. Using such additional components improves the thermal stress robustness of the electric heating system compared to using an integrated housing including outlets for high-temperature fluid effluents, thereby allowing for longer periods of operation at higher temperatures.

[0052] In another alternative embodiment not shown, the outlet for fluid outflow can be straight, without any contraction or expansion shape, and its orifice has a diameter smaller than that of the body of the housing.

[0053] Now refer to Figure 4 and Figure 5 The structure of a resistance heater 108 according to a preferred embodiment of the present invention is described, the structure of which can be... Figures 1 to 3 Used in the arrangement of any diagram.

[0054] The resistance heater 108 includes a plurality of annular walls 120 made of conductive material. In this specification, the term "annular" means "generally annular" and is not limited to a geometrically circular shape, but includes shapes that may be circular or other than circular, such as ellipses, polygons, etc. In the illustrated embodiment, the annular walls 120 have a circular cross-section. However, the annular walls can have any desired cross-sectional shape, which can be any polygonal shape, such as a square, rectangle, triangle, hexagon, etc., or can be a curved or arcuate shape, such as a circle, ellipse, etc.

[0055] An annular wall 120 is nested to define a plurality of annular flow channels 122, which are arranged concentrically in series about a longitudinal axis LL. The annular wall 120 extends between opposing first ends 124 and second ends 126 of the resistance heater 108, which are separated from each other along the longitudinal axis LL.

[0056] Multiple annular walls 120 are mechanically connected together, such that adjacent flow channels 122 have opposite fluid flow directions and are connected at adjacent ends 128 of the respective channels 122 to define alternating serpentine flow paths 130, which have an input end 132 at a fluid input end 112 and an output end 134 at a fluid output end 113. The input end 132 and the output end 134 are located at radially outer and radially inner positions relative to the longitudinal axis LL, respectively. The fluid input end 112 and the fluid output end 113 are located at a first end 124 and a second end 126 of the resistance heater 108, respectively. The alternating serpentine flow path 130 has a first annular closing edge 131 and a second annular closing edge 133 located at the first end 124 and the second end 126 of the resistance heater 108, respectively. At the closing edges 131 and 133, bends 137 and 139 connecting adjacent flow channels 122 are respectively provided.

[0057] In the illustrated embodiment, the outermost wall 120f is cylindrical, and each of the other walls 120a to 120e, inwardly in addition to the outermost wall 120f, includes a cylindrical portion 136 and an adjacent tapered portion 138. The free end portion 140 of the cylindrical portion 136 is located at the second end portion 126 of the resistance heater 108, and the tapered portion 138 is oriented toward the first end portion 124 of the resistance heater 108. The tapered portion 138 closest to the first end portion 124 of the resistance heater 108 includes a solid layer 142 defining a closed end portion 144 of a plurality of annular walls 120.

[0058] Therefore, an annular wall 120e adjacent to the outermost wall 120f is configured to form a closed end portion 144 of a plurality of annular walls 120 at the first end 124 of the resistance heater 108. The closed end portion 144 closes the end 128 of the annular flow channel 122 at the first end 124 of the resistance heater 108 to form an alternating directional change of the serpentine flow path 130 at the first end 124 of the resistance heater 108.

[0059] Each annular wall 120 is composed of a non-porous layer of conductive material (in... Figure 5 (shown schematically in solid lines) or a perforated layer of conductive material (in) Figure 5 (The text is schematically shown in dashed lines.)

[0060] exist Figure 4 and Figure 5 In one embodiment, the resistance heater 108 includes alternating annular walls 120 composed of a void-free layer or a perforated layer of conductive material. The innermost wall 120a is composed of a void-free layer 125 of conductive material, the adjacent wall 120b is composed of a perforated layer 127 of conductive material, the next wall 120c is composed of a void-free layer 125 of conductive material, the next wall 120d is composed of a perforated layer 127 of conductive material, the next wall 120e is composed of a void-free layer 125 of conductive material, and the outermost wall 120f is composed of a perforated layer 127 of conductive material.

[0061] Therefore, each annular wall 120a, 120c, 120e composed of a void-free layer 125 of conductive material has an adjacent annular wall 120b, 120d, 120f composed of a perforated layer 127 of conductive material on at least one or two of its radially outer and radially inner sides, and each annular wall 120b, 120d, 120f composed of a perforated layer 127 of conductive material has an adjacent annular wall 120a, 120c, 120e composed of a void-free layer 125 of conductive material on at least one or two of its radially outer and radially inner sides. The perforated layer 127 includes a perforated mesh, but may also include any other type of perforation.

[0062] In such Figure 6 In the alternative embodiment shown, each annular wall 120a to 120f is composed of a void-free layer 125 of conductive material.

[0063] The annular walls 120a to 120f comprise n walls nested together to form a series of annular walls 120a to 120f. This series includes a radially innermost wall 120a having n = 1 and a radially outermost wall 120f having n = n. The series also includes at least one radially intermediate wall 120b to 120e between the radially innermost wall 120a and the radially outermost wall 120f. Each radially intermediate wall 120b to 120e has a corresponding value n between 1 and n.

[0064] A first electrical terminal 150 and a second electrical terminal 152 are provided for connection to an electrical energy source 106 to heat the wall 120 of the resistance heater 108. The first electrical terminal 150 and the second electrical terminal 152 are electrically connected to corresponding first walls 120f and second walls 120e, which are adjacent to each other and include outer paired walls 120f, 120e located radially outward of the resistance heater 108. Therefore, the electrical terminals 150, 152 are connected to the outermost wall 120f and the wall 120e adjacent inwardly to the outermost wall 120f. In a preferred embodiment, the walls 120 to which the terminals 150, 152 are connected include the outer paired walls 120f, 120e; however, the terminals 150, 152 themselves do not need to be located radially outward of or towards the resistance heater 108. The first terminal 150 may be located radially outward of or toward the resistance heater 108, while the second terminal 152 may be located elsewhere, separate from the first terminal 150, such as at the center of the resistance heater 108 below the closed end portion 144 of the wall 120. However, terminals 150 and 152 may be located at any desired location. As described above, the first electrical terminal 150 and the second electrical terminal 152 are configured to be electrically connected to the electrical energy source 106 via a wired connection.

[0065] Multiple annular walls 120 are electrically connected together to define a continuous conductive path 156 extending between a first electrical terminal 150 and a second electrical terminal 152. The conductive path 156 has a first portion 158 and a second portion 160, the first portion 158 extending from the first wall, i.e., the outermost wall 120f, to the center C of the resistance heater 108, and the second portion 160 extending from the center C of the resistance heater to a second wall, i.e., the wall 120e adjacent to the outermost wall 120f inward.

[0066] The annular walls 120a to 120f are electrically connected together by a first electrical connector 162 and a second electrical connector 164. The first electrical connector 162 is electrically connected to the wall 120 having an even number of n to form a first portion 158 of the conductive path 156, and the second electrical connector 164 is electrically connected to the wall 120 having an odd number of n to form a second portion 160 of the conductive path 156.

[0067] In a preferred embodiment, the first electrical connector 162 and the second electrical connector 164 are integral with the wall 120, which is electrically interconnected by the respective electrical connectors 162 and 164. Each of the first electrical connector 162 and the second electrical connector 164 is parallel to or orthogonal to the longitudinal axis LL. At least some of the walls 120 are provided with openings 168 extending through the walls, and at least one of the first electrical connectors 162 and the second electrical connector 164 extends through a corresponding opening 168. The first electrical connector 162 and the second electrical connector 164 are also provided with mechanical connectors 170 by which the walls 120 are mechanically connected together.

[0068] In a preferred embodiment, the first electrical connector 162 and the second electrical connector 164, which are orthogonal to the longitudinal axis LL, of the mechanical connector 170 also include radially oriented transverse supports 172, and a plurality of circumferentially spaced radially oriented transverse supports 172 are provided around the periphery of the wall 120 for interconnecting the walls 120 (where n is an even number or an odd number). The supports 172 are positioned toward the first end 124 and the second end 126 of the resistance heater 108. The supports 172 electrically and mechanically connect the annular walls 120, thereby providing structural rigidity and current path.

[0069] In a preferred embodiment, the mechanical connector 170 is also provided with a first electrical connector 162 and a second electrical connector 164 parallel to the longitudinal axis LL, each comprising a longitudinally oriented wall portion 174, and a plurality of circumferentially spaced longitudinally oriented wall portions 164 are provided around the periphery of the wall 120 for interconnecting the walls 120 (where n is an even number or an odd number) to provide an opening 168; or a single longitudinally oriented wall portion 174 is provided around the periphery of the wall 120 for interconnecting the walls 120 (where n is an even number or an odd number), and one or more 168s are provided in the single longitudinally oriented wall portion 174.

[0070] The resistance heater 108 also includes an electrical connector 176 made of conductive material located at the center C of the resistance heater 108, which electrically connects the internal paired annular walls 120a, 120b together. Figure 4 Electrical connector 176 is shown, but for clarity, in Figure 5 Electrical connector 176 is not shown in the diagram; instead, it is represented by a shaded area.

[0071] In the illustrated embodiment, the electrical connector 176 takes the form of the internal coil 177 of the resistance heater 108. However, in alternative embodiments of the invention, electrical connectors of any other shape and configuration can be used to electrically connect the internal paired annular walls 120a, 120b. For example, in... Figure 6 In the alternative embodiment shown, the electrical connector 276 is in the form of an annular member 278 made of conductive material, which has a central aperture 280 through which heated fluid is discharged.

[0072] In each embodiment, electrical connectors 176, 276 are preferably integrated with the annular wall 120 of the resistance heater 108, and the resistance heater 108 is formed as an integral body, for example by an additive manufacturing process such as selective laser melting (SLM).

[0073] Electrical connector 176 includes a pair of elongated helical elements 178a, 178b, concentrically arranged about a longitudinal axis LL and surrounded by an innermost sidewall 120a. A first end 180a, 180b of each helical element 178a, 178b is connected to a corresponding wall in the inner pair of walls 120a, 120b, and opposing second ends 182a, 182b of the helical elements 178a, 178b are connected together by a connecting member 184 of electrical connector 176. Connecting member 184 includes an annular ring. The first ends 180a, 180b of the helical elements 178a, 178b are located at the second end 126 of the resistance heater 108.

[0074] Therefore, the outermost annular wall 120f is connected to the helical element 178a of the inner coil 177, and the adjacent annular wall 120e is connected to the helical element 178b of the inner coil 177. The helical elements 178a and 178b are connected to the bottom end 179 of the inner coil 177 by the connecting member 184.

[0075] In the illustrated embodiment, the gapless annular walls 120a, 120c, and 120e generate heat and create flow channels for the fluid. A support member 172 passes through an opening 168 in the annular wall 120, allowing current from the electrical terminal 150 to sequentially pass through all the perforated annular walls 120f, 120d, and 120b, then through the central heating coil 177, and subsequently through all the gapless annular walls 120a, 120c, and 120e to the electrical terminal 152 (or vice versa). Terminal 150 includes both an electrical terminal (positive or negative) and means for mechanically connecting the resistance heater 108 to the housing. Terminal 152 includes an electrical terminal (positive or negative) connected to an electrical conductor that passes through the wall of the housing 104 forming the boundary of the pressure encapsulation and is sealed to the housing by an electrically insulating seal (not shown).

[0076] In a preferred embodiment of the invention, the resistance heater 108 includes an integrated body 186. In other words, the annular wall 120, the first electrical connector 162 and the second electrical connector 164, the mechanical connector 170, the electrical connector 176, and the first electrical terminal 150 and the second electrical terminal 152 are all included in a single integrated body 186.

[0077] The integrated monolithic body 186 can be manufactured using additive manufacturing technology, 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), and rapid manufacturing (RM). Preferably, the integrated monolithic body 186 is manufactured by selective laser melting (SLM) to produce continuous horizontal slices or layers starting from the second end 126 of the resistance heater 108 and gradually forming the resistance heater 108 to terminate at the first end 124 of the resistance heater 108.

[0078] The electric heating system 100 also includes an annular closure member 188 located at the second end 126 of the resistance heater 108. Figure 5 The annular closure member 188 is shown schematically at a medium height, but for clarity, it is shown in [the remaining text]. Figure 4 Not shown in the image.

[0079] The annular closure member 188 is composed of an electrically insulating material such as ceramic. The closure member 188 is typically an electrically insulating perforated disc that includes one or more holes 190 corresponding to the fluid outlet 113 and covers the second end 126 of the resistance heater 108 to close one side of the alternating serpentine flow path 130. The closure member 188 closes the end of the annular flow channel 122 at the second end 126 of the resistance heater 108 to form a change in direction of the alternating serpentine flow path 130 at the second end 126 of the resistance heater 108. The closure member 188 may be in contact with the resistance heater 108 or spaced apart from it, for example, by a small distance.

[0080] In some embodiments of the invention, the housing 104 is not electrically connected to the resistance heater 108. However, in alternative embodiments of the invention, the housing 104 may be electrically connected to one of the first electrical terminals 150 and the second electrical terminal 152 of the resistance heater 108, thereby allowing the respective electrical terminals 150, 152 to be connected to the electrical power source 106 via the housing 104. The respective electrical terminals 50, 52 may be integrated with or separate from a mechanical connection (not shown) between the resistance heater 108 and the housing 104.

[0081] The present invention also provides a method for generating a high-temperature fluid flow. In a preferred embodiment of the invention, the electric heating system 100 is a resistance engine and is installed in a spacecraft, and the method is used to move the spacecraft in space.

[0082] The method includes providing an electric heating system 100 as described above. A fluid to be heated is supplied to a fluid inlet 112 of a flow resistor 108, thereby flowing along a serpentine flow path 130 to a fluid outlet 113 of the flow resistor 108. The supplied fluid has a density greater than that surrounding the exterior 192 of the housing 104 (see [reference]). Figure 1 The external gas pressure is high.

[0083] A potential is applied across the first terminal 150 and the second terminal 152 to heat the fluid flow in the alternating serpentine flow path 130 via the resistance heater 108. The fluid flows from the bottom and continuously circulates through the flow channel 122 via the upper bend 139 and the lower bend 137, ultimately reaching the inner coil 177 and the outlet. The heated fluid flow is then discharged from the outlet 112 of the housing 104. Figure 2 In this embodiment, the heated fluid is discharged from the outlet of the shell via a contraction diffuser at subsonic or sonic speeds. Figure 3 In one embodiment, the heated fluid is discharged from the outlet of the housing via a contraction-expansion nozzle at supersonic or hypersonic speeds.

[0084] The gapless annular walls 120 define flow channels 122 between the gapless annular walls 120. Compared to a gapless annular wall of the same size, the perforated annular walls 120, which are typically in the form of a perforated mesh, have increased resistance and increased surface area. Therefore, providing alternating perforated annular walls 120 adjacent to the gapless annular walls 120—particularly providing alternating perforated annular walls 120 within the flow channels 122—can achieve enhanced heat transfer to the fluid for a given current.

[0085] Furthermore, in the illustrated embodiment, the gapless annular wall 120 has a smooth inner cylindrical surface and an outer cylindrical surface. Alternatively, however, either or both of the inner and outer cylindrical surfaces may be provided with uneven surfaces, which can increase the surface area and enable enhanced heat transfer. Such surface features can be readily achieved using additive manufacturing processes such as selective laser melting (SLM). The annular wall 120 can also vary in thickness and cross-sectional shape and size.

[0086] The primary application of the electric heater system of the preferred embodiment of the present invention is in high-temperature resistive engines for space applications. Such high-temperature resistive engines can be used on platforms ranging from small to large, where the resistive engine can be used as a thruster to provide either primary or auxiliary propulsion.

[0087] Compared to any other current resistive propulsion engine, the electric heater system of the preferred embodiment of the present invention can provide a greater propellant utilization efficiency (specific impulse Isp). Therefore, the electric heater system of the preferred embodiment of the present invention can provide a very cost-effective propulsion system for small satellites (including constellations).

[0088] The resistance heater in the electric heater system of the preferred embodiment of the present invention can convert electrical energy into heat energy with extremely high efficiency, and the heat energy is transferred to the fluid. The resistance heater both releases energy directly to the fluid and forms a recirculation path, resulting in the highest temperature being generated at the center of the resistance heater, thus achieving a thermal efficiency of up to 95%. When the resistance heater is composed of heat-resistant metal, it can heat the fluid to temperatures up to 3500K without relying on combustion or any other chemical reaction. Furthermore, the resistance heater in the electric heater system of the preferred embodiment of the present invention can be manufactured by an additive manufacturing process such as selective laser melting (SLM) to provide a one-piece, monolithic resistance heater. This additive manufacturing process not only serves as a single manufacturing process, reducing costs and complexity during manufacturing, but also provides resistance heaters with high service reliability because thermal expansion stress can be minimized or eliminated. This additive manufacturing process can also produce compact, low-cost monolithic resistance heaters.

[0089] Furthermore, electrical terminals can be located on or connected to the outside of the resistance heater and to the radially outermost paired annular walls of the resistance heater. This allows the outermost annular walls of the resistance heater to remain cooled, and the increasing thermal gradient typically extends from the outer periphery of the resistance heater outwards towards the center. This increasing thermal gradient also typically extends from the fluid flow inlet through the resistance heater to the outlet. This improves thermal efficiency and enables the achievement of high fluid outlet temperatures.

[0090] In the satellite industry, the electric heater system of the preferred embodiment of the present invention can be used to replace chemical propulsion systems that use hazardous propellants, which can significantly reduce the cost of satellite assembly, integration and testing activities, and can simplify spacecraft design.

[0091] Furthermore, the electric heater system of the preferred embodiment of the present invention can be used in a variety of other heat flow applications besides satellite propulsion. For example, the present invention can be used for: generators of superheated steam for antibacterial sterilization of biofilms and hard surfaces; food processing; epoxy resin curing; and stripping or cleaning applications in refining and hydrocarbon industries; as an electric alternative to gas torches for localized heat treatment; high-precision glass and jewelry processing; equipment preheating in metal foundry workshops; and start-up heating for solid oxide fuel cells; ignition of internal combustion engines; electric heating sources for hot gas welding of plastics and most metal alloys; generators of high-energy non-ionizing currents in hypersonic wind tunnels to test the flight characteristics of aircraft, launchers, and satellite reentry; and hot air guns with an enhanced temperature range above typical 600°C airflow temperatures for wire harnesses, soldering, and desoldering of circuit boards in electronic devices.

[0092] Various improvements and modifications to the preferred embodiments of the invention will be apparent to those skilled in the art, and such improvements and modifications are covered by the invention as defined in the appended claims.

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 a fluid flow that has already been heated by the electric heating system; as well as A resistance heater installed within the housing, the resistance heater comprising: The fluid inlet and fluid outlet are respectively connected to the fluid inlet and the fluid outlet. Multiple annular walls made of conductive material are nested to define multiple annular flow channels arranged concentrically in series about a longitudinal axis. The annular walls extend between opposing first and second ends of the resistance heater, the first and second ends being separated from each other along the longitudinal axis. A first electrical terminal and a second electrical terminal are used to connect to an electrical energy source to heat the plurality of annular walls of the resistance heater. The first electrical terminal and the second electrical terminal are electrically connected to a corresponding first wall and a second wall among the plurality of annular walls. The first wall and the second wall are adjacent to each other and located radially outside the resistance heater, forming an outer paired wall among the plurality of annular walls. The plurality of annular walls are mechanically connected together, such that adjacent flow channels have opposite fluid flow directions and are connected at adjacent ends of the respective flow channels to define alternating serpentine flow paths. These alternating serpentine flow paths have an input end at the fluid input end and an output end at the fluid output end, wherein the input end and the output end are located radially outward and radially inward relative to the longitudinal axis, respectively. The plurality of annular walls are electrically connected together to define a continuous conductive path extending between the first electrical terminal and the second electrical terminal, the conductive path having a first portion extending from the first wall to the center of the resistance heater and a second portion extending from the center of the resistance heater to the second wall.

2. The system according to claim 1, wherein, The fluid input end and the fluid output end are located at the first end and the second end of the resistance heater, respectively.

3. The system according to claim 1, wherein, Each of the plurality of annular walls consists of a void-free layer of the conductive material or a perforated layer of the conductive material.

4. The system according to claim 3, wherein, The resistance heater includes alternating annular walls composed of a void-free layer or a perforated layer of the conductive material, wherein each annular wall composed of a void-free layer of the conductive material has an annular wall composed of a perforated layer of the conductive material adjacent to it on at least one or both of its radially outer and radially inner sides, and each annular wall composed of a perforated layer of the conductive material has an annular wall composed of a void-free layer of the conductive material adjacent to it on at least one or both of its radially outer and radially inner sides.

5. The system according to claim 3, wherein, Each annular wall consists of a void-free layer of the conductive material.

6. The system according to any one of claims 1 to 5, wherein, The plurality of annular walls include n The wall, the n Each wall is nested to form a series of annular walls, the series including having n =1 radial innermost sidewall, having n = n radial outermost wall and at least one radial intermediate wall between the radial innermost wall and the radial outermost wall, each radial intermediate wall having a corresponding value between 1 and n. n The plurality of annular walls are electrically connected together by a first electrical connector and a second electrical connector, wherein the first electrical connector has an even number of... n The wall electrical connections form the first portion of the conductive path, and the second electrical connection will have an odd number of... n The wall is electrically connected to form the second part of the conductive path.

7. The system according to claim 6, wherein, The first electrical connector and the second electrical connector are integral with the plurality of annular walls electrically interconnected through the respective electrical connectors.

8. The system according to claim 7, wherein, Each of the first electrical connector and the second electrical connector is parallel to or orthogonal to the longitudinal axis.

9. The system according to claim 6, wherein, At least some of the annular walls are provided with openings extending through the at least some of the annular walls, and at least one of the first electrical connector and the second electrical connector extends through the respective opening.

10. The system according to claim 6, wherein, The first electrical connector and the second electrical connector also provide mechanical connectors through which the plurality of annular walls are mechanically connected together.

11. The system according to any one of claims 1 to 5, wherein, At least one of the plurality of annular walls includes a cylindrical portion and an adjacent conical portion, wherein the free end portion of the cylindrical portion is located at a second end of the resistance heater, and the conical portion is oriented toward a first end of the resistance heater.

12. The system according to claim 11, wherein, The tapered portion closest to the first end of the resistance heater includes a void-free layer that defines the closed end portions of the plurality of annular walls.

13. The system according to any one of claims 1 to 5, wherein, The electric heating system further includes an annular sealing member composed of an electrically insulating material, located at the second end of the resistance heater, wherein the sealing member closes the end of the annular flow channel at the second end of the resistance heater to form the direction change of the alternating serpentine flow path at the second end of the resistance heater.

14. The system according to claim 13, wherein, At least one electrically insulating enclosure is in contact with or spaced apart from the resistance heater.

15. The system according to any one of claims 1 to 5, wherein, An annular wall is configured to form a closed end portion of the plurality of annular walls at a first end of the resistance heater, wherein the closed end portion closes the end of the annular flow channel at the first end of the resistance heater to form a change in the direction of the alternating serpentine flow path at the first end of the resistance heater.

16. The system according to any one of claims 1 to 5, wherein, The resistance heater also includes an electrical connector made of conductive material, located at the center of the resistance heater, which electrically connects the internal pairs of annular walls together.

17. The system according to claim 16, wherein, The electrical connector includes a pair of elongated helical elements arranged concentrically about the longitudinal axis and surrounded by an innermost sidewall, wherein a first end of each helical element is connected to a corresponding wall in the inner pair of inner walls of the plurality of annular walls, and opposite second ends of the helical elements are connected together by a connecting member of the electrical connector.

18. The system according to claim 17, wherein, The connecting component includes an annular ring.

19. The system according to claim 17, wherein, The first end of the spiral element is located at the second end of the resistance heater.

20. The system according to any one of claims 1 to 5, wherein, The resistance heater comprises an integrated, one-piece body.

21. The system according to claim 20, wherein, The integrated monolithic body is manufactured using additive manufacturing technology.

22. The system according to claim 21, wherein, The additive manufacturing technology includes any one or more of the following: 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).

23. The system according to any one of claims 1 to 5, wherein, The housing is electrically connected to one of the first and second electrical terminals of the resistance heater, thereby enabling the corresponding electrical terminal to be connected to the electrical energy source via the housing.

24. The system according to claim 23, wherein, The corresponding electrical terminals and the mechanical connection between the resistance heater and the housing are either integrated or separate from the mechanical connection.

25. The system according to any one of claims 1 to 5, wherein, The first electrical terminal and the second electrical terminal are configured to be electrically connected to the electrical energy source via a wired connection.

26. The system according to any one of claims 1 to 5, further comprising an electrical power source connected to the first electrical terminal and the second electrical terminal, wherein, The electrical energy source is configured to supply direct current or alternating current.

27. The system according to any one of claims 1 to 5, wherein, Multiple resistance heaters are located within the housing, and the resistance heaters are arranged in series or in parallel with respect to the inlet and outlet of the fluid flow.

28. The system according to any one of claims 1 to 5, wherein, The electric heating system is a resistance engine and is configured to be installed in a spacecraft.

29. A method for generating a high-temperature fluid flow, the method comprising the following steps: a) Provide an electric heating system according to any one of claims 1 to 5; b) The fluid to be heated is supplied to the fluid inlet of the resistance heater and flows thereto along an alternating serpentine flow path to the fluid outlet of the resistance heater, the supplied fluid having a pressure greater than the external gas pressure surrounding the exterior of the housing; c) Applying a potential across the first and second terminals to heat the fluid flow in the alternating serpentine flow path via a resistance heater; and d) The heated fluid flow is discharged from the outlet of the housing.

30. The method according to claim 29, wherein, The heated fluid is discharged from the outlet of the housing via a constricting nozzle at subsonic or sonic speeds.

31. The method according to claim 29, wherein, The heated fluid is discharged from the outlet of the housing via a contraction-expansion nozzle at supersonic or hypersonic speeds.

32. The method according to claim 29, wherein, The electric heating system is a resistance engine and is installed in the spacecraft, and the method is used to move the spacecraft in space.

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