Electric heating tube with low over-temperature risk

Abstract

The invention relates to the technical field of electric heating tubes, in particular to an electric heating tube with low over-temperature risk, which comprises an outer sleeve and an electric heating tube, and a circulation channel is formed between the electric heating tube and the outer sleeve; the flexible spiral blade is spirally wound on the periphery of the electric heating pipe to form a spiral flow channel, and a first gap D is preset between the outer ring side of the flexible spiral blade and the inner wall of the outer sleeve to form a first transverse flow channel; and the blocking piece is arranged on the outer side of the electric heating pipe, so that the flexible spiral blade deflects by taking the inner ring side as a fulcrum based on the flow velocity change of the incoming flow, and the size of the first gap D is changed. The characteristic that the flexible spiral blade can deform to generate deflection is utilized, so that the flexible spiral blade deflects to different degrees when the flow speed of a heat absorption medium is changed, and the size of the first transverse flow channel is changed; therefore, when necessary, the heat absorption medium flowing through the first transverse flow channel is adaptively utilized to form impact on the boundary layer and the dead zone, and the local overtemperature risk is reduced.

Description

Technical Field

[0001] This invention relates to the field of electric heating element technology, and specifically to an electric heating element with low risk of overheating. Background Technology

[0002] Existing electric heaters typically employ multiple heating elements within a pressure vessel to achieve efficient heating of heat-absorbing media (such as molten salt, heat transfer oil, and liquid metal). Among these, the sheathed electric heating element is a type where the heating element is housed within a sheath. The heat-absorbing medium flows through channels within the sheath, absorbing heat from the heating element. Due to the narrow flow channels within the sheath, the heat-absorbing medium has a small thickness and a high flow velocity, improving heating uniformity and promptly removing heat from the heating element, thus reducing the risk of localized overheating.

[0003] Existing technology incorporates spiral baffles within the flow channels of the casing to increase flow resistance, thereby increasing flow velocity and the heat absorption path of the heat-absorbing medium. This allows for more timely and thorough heat removal, further reducing the risk of localized overheating. However, in actual operation, the flow rate of the heat-absorbing medium varies. Even with a spiral flow channel, it's not possible to achieve a sufficient reduction in localized overheating risk under all flow conditions. Specifically, at higher flow rates, the heat-absorbing medium flows along the spiral flow channel at a higher velocity, resulting in better weakening of dead zones and boundary layers, better temperature uniformity, and a more effective reduction in localized overheating risk. However, if the flow rate decreases, the smaller flow rate of the heat-absorbing medium itself dominates its velocity. Therefore, even though the spiral flow channel can increase the flow velocity of the heat-absorbing medium, its velocity remains relatively low, resulting in insufficient weakening of the boundary layer and dead zones, inability to remove heat in time, and a still relatively high risk of localized overheating. Summary of the Invention

[0004] To address the shortcomings of existing electric heating tubes, this invention provides an electric heating tube with low overheat risk. Flexible helical blades are installed in the flow channel between the outer jacket and the heating tube. The flexible helical blades are fully utilized for their deformability and yaw characteristics, allowing them to yaw to varying degrees when faced with changes in the flow velocity of the heat-absorbing medium. This alters the size of the first gap D, and consequently changes the size of the first transverse flow channel. Thus, while ensuring heat exchange efficiency, when necessary (e.g., when a small flow rate causes a small flow velocity), the heat-absorbing medium flowing through the first transverse flow channel can adaptively impact the boundary layer and dead zones, reducing the risk of localized overheating.

[0005] The technical solution provided by this invention is as follows: an electric heating tube with low overheat risk, comprising: an outer tube; an electric heating tube disposed inside the outer tube, wherein a flow channel is formed between the outer wall of the electric heating tube and the inner wall of the outer tube; a flexible spiral blade disposed within the flow channel and spirally wound around the periphery of the electric heating tube to form a spiral flow channel, wherein a first gap D is pre-set between the outer ring side of the flexible spiral blade and the inner wall of the outer tube to form a first transverse flow channel; and a blocking member disposed outside the electric heating tube and located on the side of the flexible spiral blade away from the incoming flow, blocking the inner ring side of the flexible spiral blade, so that the flexible spiral blade deflects with the inner ring side as the fulcrum based on the change in the velocity of the incoming flow, thereby changing the size of the first gap D.

[0006] Optionally, the flexible helical blade includes a plurality of continuously spliced ​​helical baffles, and adjacent helical baffles are movably connected.

[0007] Optionally, the spiral baffle is provided with a slot and a plug on both sides, the width of the slot being greater than the width of the plug; both the slot and the plug are provided with a through waist-shaped hole, the length direction of the waist-shaped hole being consistent with the extension direction of the slot, and also include a connecting pin, the length of the connecting pin being less than the length of the waist-shaped hole; the slots on adjacent spiral baffles are plugged into the plugs to form a first sliding gap, and the connecting pin passes through the waist-shaped hole to form a second sliding gap.

[0008] Optionally, a plurality of the blocking members are evenly distributed along the spiral extension direction of the flexible spiral blade, and the blocking members are arranged in a one-to-one correspondence with the spiral baffle.

[0009] Optionally, the radial dimension of the first gap D accounts for 10%–20% of the radial dimension of the flow channel.

[0010] Optionally, a second gap is provided between the inner ring of the flexible helical blade and the heating tube to form a second transverse flow channel.

[0011] Optionally, the device further includes several limiting components, which are disposed on the inner wall of the outer sleeve and evenly distributed along the outer ring of the flexible helical blade. Each limiting component includes a first support and a second support. The first support is provided with a first limiting pin, and the second support is provided with a second limiting pin. The first limiting pin and the second limiting pin are disposed opposite to each other and form a limiting space. At least a portion of the flexible helical blade is located in the limiting space so that the limiting space restricts the sway stroke of the flexible helical blade.

[0012] Optionally, both the ends of the first limiting pin and the second limiting pin are provided with flexible damping.

[0013] Optionally, the limiting component further includes an elastic reset member, one end of which is fixedly connected to the first bracket, and the other end of which is fixedly connected to the flexible helical blade; the elastic reset member is located on the side of the flexible helical blade facing the incoming flow, so that the elastic reset member provides an external force for resetting the flexible helical blade.

[0014] Optionally, the lower limit of the yaw angle of the flexible helical blade relative to the horizontal axis is 30-45°, and the upper limit of the yaw angle of the flexible helical blade relative to the horizontal axis is 60-75°.

[0015] Compared with the prior art, the technical solution provided by this invention has the following advantages: The electric heating tube with low overheat risk proposed by this invention is provided with flexible spiral blades in the flow channel between the outer tube and the electric heating tube. The flexible spiral blades are fully utilized to generate swaying due to their deformability. This allows the flexible spiral blades to sway to different degrees when facing changes in the flow velocity of the heat-absorbing medium, thereby changing the size of the first gap D and thus changing the size of the first transverse flow channel. When necessary (such as when a small flow rate causes a small flow velocity), the heat-absorbing medium flowing through the first transverse flow channel is used adaptively to impact the boundary layer and dead zone, reducing the risk of local overheating.

[0016] Specifically, when the medium flow rate is high, the outer ring of the flexible spiral blades deflects more towards the outlet direction, and the preset gap D continuously decreases, even almost closing. This allows the medium to flow mainly through the spiral channel under high flow conditions. At this time, the medium flows at a higher velocity, and the medium itself can weaken the dead zone and boundary layer. It can also allow the medium to pass through the heating tube along the spiral channel, thus improving the heat exchange effect.

[0017] When the medium flow velocity is low, the outer ring of the flexible helical blade deflects little or almost no towards the outlet. At this time, the preset gap D decreases slightly or almost not at all. Therefore, this preset gap D constitutes the first transverse flow channel for the medium flow, allowing some of the medium to bypass through this gap D. Because the first transverse flow channel is narrow, the medium flowing through it has a high velocity and strong impact force. This high-speed flow of the medium can reduce the flow dead zone present in traditional structures, significantly improving the uniformity of velocity distribution. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of the electric heating tube with low overheat risk during deformation, as proposed in an embodiment of the present invention.

[0019] Figure 2 This is a schematic diagram of the initial structure of the electric heating tube with low overheat risk proposed in an embodiment of the present invention.

[0020] Figure 3 This is a schematic diagram of the structure of the flexible helical blade proposed in an embodiment of the present invention.

[0021] Figure 4 This is one of the connection diagrams of the flexible helical blade proposed in the embodiments of the present invention.

[0022] Figure 5 This is the second schematic diagram of the connection of the flexible helical blade proposed in the embodiment of the present invention. Detailed Implementation

[0023] To further understand the content of this invention, a detailed description of the invention will be provided in conjunction with the accompanying drawings and embodiments.

[0024] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It is understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings. The terms "first," "second," etc., used in this invention are for the convenience of describing the technical solutions of the invention and have no specific limiting effect; they are all general terms and do not constitute a limitation on the technical solutions of the invention. It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of this application can be combined with each other. In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, not to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. In addition, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances. Multiple technical solutions in the same embodiment, as well as multiple technical solutions in different embodiments, can be arranged and combined to form new technical solutions that do not contradict or conflict, all of which are within the scope of protection claimed by this invention.

[0025] Example 1 Combined with appendix Figure 1 To be continued Figure 5This embodiment proposes an electric heating tube with low overheat risk, including an outer tube 1, an electric heating tube 2, flexible spiral blades 3, and a blocking member 6. The outer tube 1 has an inlet 101 and an outlet 102 at its two ends. The electric heating tube 2 is located inside the outer tube 1, and a flow channel 100 is formed between the outer wall of the electric heating tube and the inner wall of the outer tube. The flexible spiral blades 3 are located within the flow channel 100 and spirally wound around the outer periphery of the electric heating tube 2, forming a spiral flow channel. A first gap D is pre-set between the outer ring side of the flexible spiral blades 3 and the inner wall of the outer tube 1, forming a first transverse flow channel. The blocking member 6 is located outside the electric heating tube 2 and on the side of the flexible spiral blades 3 opposite to the incoming flow, blocking the inner ring side of the flexible spiral blades 3. This causes the flexible spiral blades 3 to deflect based on the velocity change of the incoming flow, using the inner ring side as a fulcrum, thereby changing the size of the first gap D.

[0026] For the electric heating tube with low overheat risk in this embodiment, the outer tube 1 is a cylindrical pressure-resistant container, and the electric heating tube 2 is arranged inside it for heating the molten salt medium.

[0027] The flexible helical blade 3 is used to guide the fluid along the helical flow channel to form a helical flow, thereby enhancing the turbulent mixing effect. The inner ring of the flexible helical blade 3 needs to be fixed and limited with the heating tube 2 to prevent relative displacement between the inner ring of the flexible helical blade 3 and the heating tube 2.

[0028] The flexible helical blade 3 possesses a certain degree of deformability. Molten salt medium flows in from the inlet 101 of the outer casing 1 and flows out from the outlet 102, forming a unidirectional flow. During the flow, the medium exerts a force on the flexible helical blade 3, causing the outer ring of the flexible helical blade 3 to oscillate with the inner ring side as the fulcrum based on the velocity change of the medium flow. Generally, the flexible helical blade 3 can be made flexible by setting a thinner thickness, setting a larger blade size, or using a metal with strong elastic deformation capability.

[0029] Here is an example of an implementable flexible helical blade 3, with the following parameters: a base thickness of 0.8mm–2.0mm, a gradient design for the blade section, and the root thickness of the blade section being approximately 30%–50% thicker than the edge. This ensures both the installation stability of the flexible helical blade 3 and enhances the flexible rotation performance of the middle and edges of the blade section. The fan-shaped chord length of the blade section is set to 1 / 3–1 / 2 of the inner diameter of the outer casing 1, and the material is selected as 316 stainless steel.

[0030] The outer tube 1 and the heating element 2 form a flow channel 100. In the initial state, when the flexible spiral blade 3 has not deformed, there is a first gap D between the outer ring of the flexible spiral blade 3 and the outer tube 1. Generally, the radial dimension of the first gap D is set to account for 10%-20% of the radial dimension of the flow channel 100. Within this range, on the one hand, it ensures that the flexible spiral blade 3 has an initial adjustment margin, and on the other hand, it ensures that the flexible spiral blade 3 can form a sufficient spiral flow channel as the main medium flow path.

[0031] For the electric heating element in this embodiment, the flow pattern of the molten salt medium inside is as follows: the molten salt medium flows from the inlet 101 into the flow channel 100 formed between the outer casing 1 and the electric heating element 2, and then flows out through the outlet 102. Based on this flow pattern, the principle of adaptive adjustment of the electric heating element in this embodiment based on the medium flow rate is as follows: When the medium flow velocity is high, the fluid impact force on the facing side of the flexible helical blade 3 is large. The resulting torque overcomes the elastic force of the flexible helical blade 3 itself, causing the flexible helical blade 3 to deflect. The deflection occurs as follows: under the action of the blocking member 6, the outer ring of the flexible helical blade 3 deflects relative to the inner ring towards the side where the outlet 102 is located, thereby reducing the first gap D. As a result, the first gap D between the outer ring of the flexible helical blade 3 and the outer sleeve 1 gradually decreases with the deflection of the flexible helical blade 3, and even tends to close, thereby reducing the size of the first transverse flow channel and increasing the flow resistance. This allows the medium to flow mainly through the helical flow channel under high flow conditions. At this time, the medium flows at a higher velocity, which weakens the dead zone and boundary layer on its own. It also allows the medium to pass through the heating tube entirely through the helical flow channel, improving the heat exchange effect.

[0032] When the medium velocity is low, the fluid impact force on the facing side of the flexible helical blade 3 is small, and the generated torque is insufficient to overcome the elastic force of the flexible helical blade 3 itself. It can hardly, or only slightly, push the flexible helical blade 3 to deflect. At this time, the flexible helical blade 3 is in a state where the outer ring of the flexible helical blade 3 slightly deflects relative to the inner ring towards the side where the outlet 102 is located, the first gap D slightly decreases, and the size of the first transverse flow channel slightly decreases; or the outer ring of the flexible helical blade 3 hardly deflects relative to the inner ring, and the corresponding first gap D hardly decreases, and the size of the first transverse flow channel hardly decreases. In this case, the first transverse flow channel, formed by the slightly reduced or almost unchanged first gap D, allows approximately 5%–8% of the medium to pass through, thus forming bypass flow. Because the first transverse flow channel is narrow, the medium flowing through it has a high velocity and strong impact force. The medium in the first transverse flow channel can reduce the flow dead zone present in the traditional structure, significantly improving the uniformity of the velocity distribution.

[0033] Therefore, when the medium velocity is high, the first gap D is significantly reduced or even closed. At this time, the medium mainly flows along the spiral channel formed by the flexible spiral blades 3. The high-flow-rate medium itself has the advantage of strong impact force, thus solving or reducing the dead zone problem. Moreover, the medium flows fully along the spiral channel, which can obtain more heat exchange time and improve the heat exchange effect.

[0034] When the medium velocity is relatively low, the impact force is small, and the first gap D decreases slightly or even remains almost unchanged. While most of the medium flows along the spiral channel, a small portion of the medium flows through the first transverse channel formed by the first gap D. The first transverse channel is relatively narrow, so the medium flowing through it naturally has a higher velocity and stronger impact force. This high-velocity, high-impact medium continuously crosses the outer edge of the flexible spiral blade 3 axially, which can intensify the turbulence and mitigate the dead zone problem.

[0035] In summary, the electric heating tube of this embodiment, which has a low risk of overheating, can achieve the technical effect of reducing dead zones and avoiding the risk of local overheating under all flow conditions.

[0036] In a preferred embodiment, the flexible helical blade 3 is composed of several helical baffles 300 continuously spliced ​​together, with adjacent helical baffles 300 being movably connected. Thus, the continuous connection of the helical baffles 300 constitutes a multi-segment modular design, which allows for convenient and efficient assembly of the overall flexible helical blade 3, while the movable connection ensures the overall deformation capability of the flexible helical blade 3.

[0037] In a further embodiment, slots 301 and inserts 302 are respectively provided on both sides of the spiral baffle 300, with the width of the slot 301 being greater than the width of the insert 302. Both the slot 301 and the insert 302 have through-holes 303, the length direction of which is consistent with the extension direction of the slot 301. A connecting pin 304 is also included, the length of which is less than the length of the slit 303. The slots 301 and inserts 302 on adjacent spiral baffles 300 are inserted into each other to form a first sliding gap 310, and the connecting pin 304 passes through the slit 303 to form a second sliding gap 320. Thus, this movable connection method, through the cooperation of the slit 303 and the connecting pin 304, ensures the connection stability of adjacent baffles.

[0038] Furthermore, this embodiment further incorporates a first sliding gap 310 and a second sliding gap 320. This ensures sufficient dynamic adjustment space for the flexible helical blade 3 during deformation, guaranteeing its ability to deflect the outer ring. The gap fit also effectively prevents the flexible helical blade 3 from detaching or undergoing abnormal displacement during deformation, thereby significantly improving the overall operational stability and structural reliability of the electric heating tube.

[0039] As can be seen from the aforementioned embodiments, the inner ring of the flexible spiral blade 3 needs to be connected to the heating element 2 for limiting, so that the outer ring of the flexible spiral blade 3 can deflect relative to the inner ring. Therefore, in this embodiment, the heating element with low overheat risk also includes a blocking element 6 to provide a fulcrum. Based on the aforementioned form in which the flexible spiral blade 3 is continuously spliced ​​from several spiral baffles 300, for the blocking element 6, a preferred embodiment is that several blocking elements 6 are evenly distributed along the spiral extension direction of the flexible spiral blade 3, and the blocking elements 6 are arranged in a one-to-one correspondence with the spiral baffles (300).

[0040] Several blocking elements 6 are fixedly disposed on the heating element 2, and are evenly distributed along the spiral extension direction of the flexible spiral blade 3. The blocking elements 6 abut against the flexible spiral blade 3 to form a limiting connection between the inner ring of the flexible spiral blade 3 and the heating element 2; at each point of contact between the blocking element 6 and the flexible spiral blade 3, the blocking element 6 is located on the side of the flexible spiral blade 3 facing the outlet 102. Thus, the relative displacement between the inner ring of the flexible spiral blade 3 and the heating element 2 can be limited by the blocking elements 6. This limiting connection structure is simple, reliable, and low-cost, without increasing production costs or assembly burden excessively.

[0041] Furthermore, in another preferred embodiment, a second gap is provided between the inner ring of the flexible helical blade 3 and the heating element 2 to form a second transverse flow channel. On one hand, since the flexible helical blade 3 can be cantilevered and fixedly connected to a stable frame or structure such as the housing or junction box of the electric heater without needing to connect to the heating element, the second gap between the inner ring of the flexible helical blade 3 and the heating element 2 ensures that the flexible helical blade 3 does not directly contact the heating element 2, thereby improving the service life of both the heating element 2 and the flexible helical blade 3. On the other hand, the second transverse flow channel formed by this second gap can also further serve as a channel for medium flow.

[0042] The flow of the medium in the second transverse channel is similar to that in the first transverse channel (i.e., the first gap D). Because the second transverse channel is also narrower, the medium flowing through it has a high velocity and strong impact force. The medium in this second transverse channel can reduce the flow dead zones present in traditional structures, significantly improving the uniformity of velocity distribution. The aforementioned implementation of the blocking member 6 also facilitates the implementation of the second gap, without creating unnecessary structural constraints.

[0043] With the second gap in place, when the medium velocity is high, the sway of the outer ring of the flexible helical blade 3 will also be transmitted to the inner ring, so that the second gap will also be reduced to a certain extent. At this time, the velocity of the medium in the second transverse flow channel will be further increased and the impact force will be stronger. The turbulence generated by this part of the medium during the flow process can further weaken the dead zone problem.

[0044] In a preferred embodiment, a plurality of limiting components are further included. These limiting components are disposed on the inner wall of the outer sleeve 1 and evenly distributed along the outer ring of the flexible helical blade 3. Each limiting component includes a first support 701 and a second support 702. A first limiting pin 703 is disposed on the first support 701, and a second limiting pin 704 is disposed on the second support 702. The first limiting pin 703 and the second limiting pin 704 are disposed opposite to each other and form a limiting space. At least a portion of the flexible helical blade 3 is located within the limiting space, thereby restricting the swaying stroke of the flexible helical blade 3. Both the first limiting pin 703 and the second limiting pin 704 point towards the flexible helical blade 3 and are used to abut against it. In this embodiment, the limiting components ensure that all parts of the flexible helical blade 3 are restricted, preventing excessive swaying that could damage its structure. The limitation of the swing amplitude of the flexible spiral blade 3 by the limiting component is achieved by designing the distance between the first limiting pin 703 and the second limiting pin 704, i.e. the size of the limiting space, which can be adjusted according to the actual situation.

[0045] Furthermore, under actual operating conditions, high-frequency oscillations may occur at the outer edge of the flexible helical blade 3 during media flow. By designing the distance between the first limiting pin 703 and the second limiting pin 704, the limiting assembly can also suppress such high-frequency oscillations.

[0046] Furthermore, dampers 705 can be provided at the ends of the first limiting pin 703 and the second limiting pin 704 to effectively prevent fatigue damage to the structure caused by collisions between the flexible helical blade 3 and the first limiting pin 703 and the second limiting pin 704, especially high-frequency collisions. Specifically, the dampers 705 can be made of 316 stainless steel, which has good rigidity and wear resistance, and can withstand the impact of collisions with the flexible helical blade 3.

[0047] In other embodiments, an elastic reset member 706 is also included. One end of the elastic reset member 706 is fixedly connected to the first bracket 701, and the other end of the elastic reset member 706 is fixedly connected to the flexible helical blade 3. The elastic reset member 706 is located on the side of the flexible helical blade 3 facing the incoming flow, so that the elastic reset member 706 provides an external force for resetting the flexible helical blade 3.

[0048] For each interconnected first support 701 and elastic reset member 706, the first support 701 and elastic reset member 706 are located on the side of the flexible helical blade 3 facing the inlet 101 at the corresponding position. In this embodiment, the elastic reset member 706 is used to ensure that the outer ring of the flexible helical blade 3 can return to its original shape after deflection. Furthermore, the elastic reset member 706 can serve as a structure to resist the impact of the molten salt medium. It is understood that without the elastic reset member 706, the molten salt medium only needs to overcome the elastic force of the flexible helical blade 3 itself to cause the flexible helical blade 3 to deflect. If the flexibility characteristics of the flexible helical blade 3 are poorly designed, even a small molten salt impact force may cause the flexible helical blade 3 to deflect. However, in this case, the risk of dead zones in the edge region of the flexible helical blade 3 is still relatively large. However, when the elastic reset element 706 is provided, the molten salt medium still needs to overcome the elastic force of the elastic reset element 706. Therefore, through the design of the elastic force of the elastic reset element 706, it can be ensured that the outer ring of the flexible spiral blade 3 can only deflect under the medium flow conditions with sufficient flow velocity and impact force, thereby further reducing the dead zone problem in a targeted manner.

[0049] The present invention and its embodiments have been described above illustratively. This description is not restrictive, and the figures shown are only one embodiment of the present invention; the actual structure is not limited thereto. Therefore, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the invention, such designs should fall within the protection scope of the present invention.

Claims

1. An electric heating element with low risk of overheating, characterized in that, include: Outer tube (1); An electric heating element (2) is disposed inside the outer casing (1), and a flow channel (100) is formed between the outer wall of the electric heating element and the inner wall of the outer casing. Flexible spiral blades (3) are disposed in the flow channel (100) and spirally wound around the periphery of the electric heating tube (2) to form a spiral flow channel. A first gap D is preset between the outer ring side of the flexible spiral blades (3) and the inner wall of the outer sleeve (1) to form a first transverse flow channel. The blocking element (6) is located outside the heating tube (2) and on the side of the flexible spiral blade (3) away from the incoming flow. It blocks the inner ring side of the flexible spiral blade (3) so that the flexible spiral blade (3) can swing based on the velocity change of the incoming flow with the inner ring side as the fulcrum, thereby changing the size of the first gap D.

2. The electric heating element with low overheat risk according to claim 1, characterized in that, The flexible helical blade (3) includes several continuously spliced ​​helical baffles (300), and adjacent helical baffles (300) are movably connected.

3. The electric heating element with low overheat risk according to claim 2, characterized in that, The spiral baffle (300) has a slot (301) and a plug (302) on both sides, respectively, and the width of the slot (301) is greater than the width of the plug (302); Both the slot (301) and the insert (302) are provided with through waist-shaped holes (303), the length direction of the waist-shaped holes (303) is consistent with the extension direction of the slot (301), and a connecting pin (304) is also provided, the length of the connecting pin (304) is less than the length of the waist-shaped holes (303); The slot (301) on the adjacent spiral baffle (300) is inserted into the plug (302) to form a first sliding gap (310), and the connecting pin (304) passes through the waist-shaped hole (303) to form a second sliding gap (320).

4. The electric heating element with low overheat risk according to claim 2, characterized in that, Several of the blocking members (6) are evenly distributed along the spiral extension direction of the flexible spiral blade (3), and the blocking members (6) are arranged in a one-to-one correspondence with the spiral baffle (300).

5. The electric heating element with low overheat risk according to claim 1, characterized in that, The radial dimension of the first gap D accounts for 10%–20% of the radial dimension of the flow channel (100).

6. The electric heating element with low overheat risk according to claim 1, characterized in that, A second gap is provided between the inner ring of the flexible spiral blade (3) and the electric heating tube (2) to form a second transverse flow channel.

7. The electric heating element with low overheat risk according to claim 1, characterized in that, It also includes several limiting components, which are disposed on the inner wall of the outer sleeve (1) and are evenly distributed along the outer ring of the flexible spiral blade (3); The limiting component includes a first bracket (701) and a second bracket (702). The first bracket (701) is provided with a first limiting pin (703), and the second bracket (702) is provided with a second limiting pin (704). The first limiting pin (703) and the second limiting pin (704) are arranged opposite to each other and form a limiting space. At least a portion of the flexible helical blade (3) is located in the limiting space so that the limiting space restricts the yaw stroke of the flexible helical blade (3).

8. An electric heating element with low overheat risk according to claim 7, characterized in that, The ends of the first limiting pin (703) and the second limiting pin (704) are both provided with damping (705).

9. An electric heating element with low overheat risk according to claim 7, characterized in that, The limiting component also includes an elastic reset member (706), one end of which is fixedly connected to the first bracket (701), and the other end of which is fixedly connected to the flexible spiral blade (3). The elastic reset member (706) is located on the side of the flexible helical blade (3) facing the incoming flow, so that the elastic reset member (706) provides an external force for resetting the flexible helical blade (3).

10. An electric heating tube with low overheat risk according to claim 7, characterized in that, The lower limit of the sway angle of the flexible helical blade (3) relative to the horizontal axis is 30-45°, and the upper limit of the sway angle of the flexible helical blade (3) relative to the horizontal axis is 60-75°.

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