A segmented finned molten salt electric heater and method of zoned power supply thereof
By setting segmented fin areas and zoned power supply on the outside of the U-shaped electric heating rod, and combining this with the rearrangement of the bow-shaped baffle holes, the problem of non-uniform flow around the shell of the U-shaped electric heating rod is solved. This achieves enhanced heat transfer, controllable pressure drop, and suppression of the risk of overheating at the end, thereby improving the operational safety and flow uniformity of the molten salt electric heater.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- BEIJING UNIV OF TECH
- Filing Date
- 2026-03-31
- Publication Date
- 2026-06-23
AI Technical Summary
In the prior art, the non-uniformity of the flow around the shell side of the U-shaped electric heating rod leads to local heat transfer deterioration and thermal fatigue risk. Moreover, the design of the baffle plate is affected by structural strength and processing constraints, making it difficult to simultaneously achieve controllable pressure drop in the inlet section and enhanced heat transfer in the downstream section.
By adopting a segmented fin design and a zoned power supply strategy, a transverse finned area (A section), a longitudinal corrugated finned area (B section), and a finless area (C section) are set on the outside of the U-shaped electric heating rod. The holes are rearranged on the arc-shaped baffle plate. Combined with the zoned power supply method, the heat transfer along the flow path is enhanced, the pressure drop is controllable, and the risk of overheating at the end is suppressed.
It achieves coordination between heat transfer and resistance along the flow path, reduces local pressure drop and hot spot risks, improves operational safety and flow uniformity, and meets the requirements of structural manufacturability and assembly feasibility.
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Abstract
Description
Technical Field
[0001] This invention relates to the fields of molten salt thermal storage, electric heating and enhanced heat exchange technology, and in particular to a U-shaped electric heating rod type molten salt electric heater for heating molten salt by flowing around the outside of an electric heating rod and its zoned power supply method. Background Technology
[0002] Molten salt, as a high-temperature heat transfer and storage medium, is widely used in thermal power generation, industrial heating, and other applications. In shell-side electric heaters, molten salt flows around the outer side of the heating element for heat exchange. Due to the non-uniform flow around the shell and the local backflow / stagnant zone induced by the baffles, heat transfer deterioration and localized overheating may occur on the surface of the heating element. Especially for U-shaped heating elements, a low-velocity zone often forms near the U-shaped bend due to geometric obstruction and flow redistribution, causing the wall temperature in this area to rise and increasing the risk of thermal fatigue. In existing technologies, a single type of fin cannot simultaneously achieve controllable inlet pressure drop and enhanced downstream heat transfer; at the same time, changes in the baffle opening design, such as the aperture or total opening ratio, are often affected by structural strength and manufacturing constraints. To further improve the temperature safety and controllability of the device operation, it is necessary to introduce a zoned power supply strategy to achieve power distribution along the process and suppression of overheating at the end. Summary of the Invention
[0003] The purpose of this invention is to provide an electric heater structure and its power supply strategy suitable for molten salt media, which achieves the comprehensive goals of "enhanced heat exchange, controllable pressure drop, and suppression of terminal overheating risk" while ensuring that the structure is manufacturable and assemblies are feasible.
[0004] To achieve the above objectives, this invention starts from the mechanism of heat transfer around the shell side and proposes the following collaborative design to address the risks of high wall temperature caused by the lagging region behind the baffle, the accumulation of resistance in the inlet section, and the local low velocity at the U-shaped end.
[0005] A molten salt electric heater, characterized in that it comprises: a shell (1), a molten salt inlet (2), a molten salt outlet (3), a head (4), multiple U-shaped electric heating rods (5) and multiple bow-shaped baffles (6); the multiple U-shaped electric heating rods (5) are arranged inside the shell (1) so that the molten salt flows around the outside of the U-shaped electric heating rods (5); the molten salt inlet (2) is located on the upper left side of the shell (1), the molten salt outlet (3) is located on the lower right side of the shell (1), and the right end of the shell (1) is sealed with a circular head (4).
[0006] Multiple bow-shaped baffles (6) are arranged at intervals along the axial direction of the shell and perpendicular to the axial direction of the shell, dividing the space inside the shell (1) into multiple compartments. The transverse fin area (53) of section A is located in the first two compartments on the inlet side. The bow-shaped baffles (6) are provided with electric heating rod shuttle fixing holes (61) and liquid channel micro-holes (62). Multiple U-shaped electric heating rods (5) pass through the electric heating rod shuttle fixing holes (8) and are fixed by the bow-shaped baffles (6). When each U-shaped electric heating rod (5) passes through the corresponding bow-shaped baffle (6), one branch of each U-shaped electric heating rod (5) corresponds to one electric heating rod shuttle fixing hole (8). The bow-shaped baffles (6) have an arc-shaped notch on one side. The circular plate has a notch on the arc surface with a length of 0.2-0.4 times the diameter along the diameter. The arc surface on the other side that is not notched and is symmetrical to the arc surface notch is defined as the high pressure zone (63). The area of the high pressure zone (63) and the arc surface notch paper piece is the ordinary zone (64). The opening ratio of the liquid channel micropores (62) in the high pressure zone (63) is higher than that in the ordinary zone (64) to improve the back flow stagnation and local pressure drop concentration of the baffle.
[0007] Furthermore, the bow-shaped baffle (6) is divided into three equal parts along its width. The area closest to the leftmost 1 / 3 is defined as the high-pressure zone (61), and the remaining 2 / 3 is defined as the non-high-pressure zone. Under the condition that the orifice diameter, total number of orifices, and total opening ratio remain unchanged, the orifice positions in the opening area (62) are rearranged to make the orifices in the high-pressure zone (61) more concentrated and the orifices in the non-high-pressure zone more sparse. This achieves local discharge and redistribution, reducing stagnation on the back of the baffle and local pressure drop concentration.
[0008] The arc-shaped notches of two adjacent bow-shaped baffles (6) are arranged in an alternating manner, so that the fluid flows in a bent bow-shaped flow.
[0009] The U-shaped electric heating rod (5) includes a straight section (51) and a U-shaped connecting bend section (52), and is placed along the length of the shell (1). The open ends of all the U-shaped electric heating rods (5) face the end where the molten salt inlet (2) is located, and the U-shaped connecting bend section (52) is located at the end where the molten salt outlet (3) is located.
[0010] Along the main direction of the molten salt, each branch of the U-shaped electric heating rod (5) is provided with a transverse fin area (53), a longitudinal corrugated fin area (54), and a finless area (55) on its outer side. The transverse fin area (53) is located at the opening end of the U-shaped electric heating rod (5) and is provided with segmented circumferential transverse fins. The first segment is closer to the U-shaped port and is composed of multiple rings of transverse fins evenly distributed along the axial direction. The second segment is relatively far from the U-shaped port and is also composed of multiple rings of circumferential transverse fins evenly distributed along the axial direction. The interval of the first segment is smaller than that of the second segment. The longitudinal corrugated fin area (54) is provided with longitudinal (i.e., the length direction along the axial direction of the branch of the electric heating rod) corrugated fins. Multiple longitudinal corrugated fins are evenly distributed along the circumferential direction. The finless area (55) is not provided with fins.
[0011] The electric heating rod adopts a zoned power supply heating method. The transverse fin area (53) of section A on the inlet side and the longitudinal corrugated fin area (54) of section B downstream are respectively powered by power supply zones with different heat levels. The section corresponding to the finless area (55) of section C is a non-heating section or a low-power section. Section A (53) is a fixed low-power heating section, section B (54) is a fixed high-power heating section and satisfies that the output power PB of section B > the output power PA of section A. Section C (55) is a non-heating section or a low-power section (preferably PC=0). To further achieve the above objectives, the electric heating rods are hollow, and each U-shaped electric heating rod (5) has two sets of independent heating elements inside, corresponding to section A and section B respectively, forming opposing A circuits and independent B circuits respectively; the lead wires of both circuits are led out from the same end of the heating rod and electrically connected to two sets of independent power supply buses outside; when the device contains multiple electric heating rods, the A circuit of each heating rod is uniformly connected to the A bus, and the B circuit is uniformly connected to the B bus, thereby achieving fixed power output for sections A and B and maintaining P B >P A .
[0012] Multiple bow-shaped baffles (6) are arranged at intervals along the axial direction of the shell (1) to divide the space inside the shell (1) into multiple compartments. The two sections of the transverse fin area (53) of section A are located in one compartment respectively, so the transverse fin area (53) of section A corresponds to two compartments.
[0013] Looking from the molten salt outlet (3) inside the shell, multiple U-shaped electric heating rods (5) are arranged in two rings. Each U-shaped electric heating rod (5) forms a certain clockwise or counterclockwise angle with the diameter, and the angles of the two rings are in the same direction (e.g., Figure 4 ).
[0014] The key points of this invention are as follows:
[0015] (1) Strengthen the U-shaped electric heating rod (5) in sections along the flow: Set a transverse fin area (53) in section A on the inlet side, and use transverse fins to periodically disturb and renew the boundary layer of the incoming flow; at the same time, arrange the fins relatively sparsely in the adjacent compartments to reduce the accumulation of blockage effect along the flow and take into account the pressure drop.
[0016] (2) Set up a longitudinal corrugated fin area (54) in the downstream section: The longitudinal corrugated fins are evenly distributed along the circumference, which can increase the near-wall shear and heat transfer area without significantly increasing the lateral blockage, improve the circumferential heat transfer uniformity and reduce the risk of hot spots.
[0017] (3) Set a finless C section near the U-shaped bend end (55): This area is not finned to reduce the risk of local blockage and heat accumulation under complex flow around the bend; and in combination with the zoned power supply strategy, set the corresponding section as a non-heating or low-power section to reduce end overheating from the heat source side.
[0018] (4) Rearrange the opening positions of the baffle (6): Divide the bow-shaped baffle (6) into three equal parts along the width direction. Define the area closest to the leftmost 1 / 3 as the high-pressure zone (61) and the remaining 2 / 3 as the non-high-pressure zone. Under the condition that the orifice diameter, total number of orifices and total opening ratio remain unchanged, rearrange the orifice positions in the opening area (62) to make the openings in the high-pressure zone (61) more concentrated and the openings in the non-high-pressure zone more sparse. This achieves local discharge and redistribution, and reduces the stagnation on the back of the baffle and the concentration of local pressure drop.
[0019] (5) Zoned power supply method: Section A (53) is a fixed low-power heating section, and Section B (54) is a fixed high-power heating section and satisfies P B >P A Section C (55) is a non-heating section or a low-power section (preferably P). C =0). Each U-shaped electric heating rod (5) is equipped with two sets of independent heating elements, corresponding to section A and section B respectively, forming circuit A and circuit B; the lead wires of both circuits are led out from the same end of the heating rod and electrically connected to two sets of independent power supply buses. When the device contains multiple electric heating rods, the A circuit of each heating rod is uniformly connected to bus A and the B circuit is uniformly connected to bus B, thereby realizing fixed power output of sections A and B and maintaining P. B >P A .
[0020] Compared with the prior art, the beneficial effects of the present invention include at least the following: First, the coordination of heat transfer and resistance along the flow path is achieved through "segmented fins"; second, the local pressure drop is reduced and the flow uniformity is improved without changing the aperture and opening ratio by "rearranging the orifice positions in the high-pressure zone"; and third, the risk of overheating at the U-shaped end is reduced and the operational safety is improved by the dual means of "zoned power supply + no fins at the end". Attached Figure Description
[0021] Figure 1 This is a schematic diagram of the overall structure of the molten salt electric heater of the present invention.
[0022] Figure 2 This is a schematic diagram of a single U-shaped electric heating rod.
[0023] Figure 3 This is a schematic diagram of an arc-shaped baffle structure.
[0024] In the figure: shell (1), molten salt inlet (2), molten salt outlet (3), end cap (4), U-shaped electric heating rod (5), straight section (51), U-shaped bent section (52), A-section transverse fin area (53), B-section longitudinal corrugated fin area (54), C-section finless area (55), bow-shaped baffle (6), electric heating rod shuttle fixing hole (61), liquid channel micropore (62), high pressure area (63), ordinary area (64).
[0025] Figure 4 The arrangement of the U-shaped electric heating rods (5) is shown from the end. Detailed Implementation
[0026] The present invention will be further described below with reference to the accompanying drawings, but the scope of protection of the present invention is not limited to the following embodiments.
[0027] like Figure 1 As shown, the molten salt electric heater includes a shell (1), a molten salt inlet (2) on the upper left side of the shell (1), and a molten salt outlet (3) at the end of a circular end cap (4). Multiple U-shaped electric heating rods (5) are arranged inside the shell (1). After the molten salt enters from the inlet (2), it flows around the outside of the U-shaped electric heating rods (5) for heat exchange and is discharged through the outlet (3). In order to guide the molten salt to form a periodic transverse scouring and re-rectification flow inside the shell (1), multiple bow-shaped baffles (6) are arranged at intervals along the axial direction of the shell, dividing the internal space into multiple series chambers.
[0028] In a preferred embodiment, the bow-shaped baffle (6) serves not only as a flow guiding component but also as a means of controlling local pressure drop and dead zones. The pressure difference across the baffle creates a high-pressure zone on the flow-facing side and varying degrees of stagnant flow on the back side. To address this characteristic, this invention, while maintaining the same orifice diameter, total number of orifices, and total opening ratio, achieves the effect of "high-pressure zone venting - back-side flow replenishment - stagnant flow reduction" through orifice rearrangement. The specific implementation is detailed below. Figure 3 Explanation.
[0029] like Figure 2As shown, the U-shaped electric heating rod (5) includes a straight section (51) and a U-shaped bent section (52). Considering the flow characteristics along the shell side and the periodic disturbances caused by the baffle compartments, the present invention divides the U-shaped electric heating rod along the main direction of the molten salt into a transverse finned area (53) in section A, a longitudinal corrugated finned area (54) in section B, and a finless area (55) in section C. Among them, the transverse finned area (53) in section A is located in the first two compartments on the inlet side: the first compartment is used to establish strong disturbances and boundary layer renewal, and the second compartment adopts a relatively sparse segmented annular transverse fin arrangement to reduce the accumulation of transverse fin blockage effect along the flow and take into account pressure drop.
[0030] Section B, with its longitudinal corrugated fins (54), is located in the downstream compartment. The longitudinal corrugated fins extend along the axial direction of the rod and are evenly distributed circumferentially. Compared to pure transverse fins, the longitudinal corrugated fins cause less transverse obstruction to the main flow channel, thereby increasing the heat exchange area while enhancing near-wall shear and fluid mixing, thus improving the heat exchange capacity of the downstream section and improving circumferential temperature uniformity.
[0031] The finless section C (55) is located in the adjacent area near the U-shaped bend end (52). Since flow separation and reattachment are more complex near the bend end, and localized low-velocity zones are prone to occur, this invention does not include fins in this area to avoid additional geometric blockage and heat accumulation. Furthermore, this invention incorporates a zoned power supply strategy to designate the corresponding section of the finless section C (55) as a non-heat-generating section or a low-power section, reducing the risk of the highest wall temperature in the end region from the heat source side.
[0032] The implementation method of the zoned power supply strategy is as follows: Section A (53) is a fixed low-power heating section, and Section B (54) is a fixed high-power heating section that satisfies P B >P A Section C (55) is a non-heating section or a low-power section (preferably P). C =0). Each U-shaped electric heating rod (5) has two sets of independently heated elements that are electrically isolated from each other, corresponding to section A and section B respectively and forming circuit A and circuit B; the lead wires of the two circuits are led out from the same end of the heating rod and electrically connected to two sets of independent power supply buses. When the device contains multiple electric heating rods, the A circuit of each heating rod is uniformly connected to bus A and the B circuit is uniformly connected to bus B, thereby realizing fixed power output of sections A and B and maintaining P. B >P A .
[0033] like Figure 3As shown, the bow-shaped baffle (6) is provided with an opening area (62). The bow-shaped baffle (6) is divided into three equal parts along its width direction. The area closest to the leftmost 1 / 3 is defined as the high-pressure area (61), and the remaining 2 / 3 is defined as the non-high-pressure area. Under the condition that the orifice diameter, total number of orifices and total opening ratio remain unchanged, the orifice positions in the opening area (62) are rearranged to make the orifices in the high-pressure area (61) more concentrated and the orifices in the non-high-pressure area more sparse. This rearrangement of orifice positions can form a more effective local venting channel on the flow-facing side of the baffle and provide a replenishment and redistribution path on the back of the baffle, thereby reducing back stagnation and local pressure drop concentration, and improving the overall flow uniformity and heat transfer performance.
[0034] Looking from the molten salt outlet (3) inside the shell, multiple U-shaped electric heating rods (5) are arranged in two rings. Each U-shaped electric heating rod (5) forms a certain clockwise or counterclockwise angle with the diameter, and the angles of the two rings are in the same direction (e.g., Figure 4 ).
[0035] To verify the flow and heat transfer characteristics of the structure of this invention, steady-state turbulent numerical simulations of the molten salt electric heater were performed using Fluent. The working fluid was solar salt, and its physical properties were input as a function of temperature. The inlet was a mass flow rate boundary with an inlet mass flow rate of 4.3 kg / s and an inlet temperature of 473 K; the outlet was a pressure outlet boundary with an outlet gauge pressure of 0 Pa. The turbulence model used was a Realizable k–ε model, with all fluid-solid walls being no-slip boundaries. The baffle surfaces were set as thermally coupled walls. The total power of the electric heater was 0.192 MW, with a single electric heating tube having a heating power of 8 kW. The tube bundle consisted of 24 U-shaped electric heating tubes arranged in a multi-ring, layered manner; the outer diameter of the heating tubes was 12 mm, and the length was 1335 mm. Simulation results showed that under the above conditions, the outlet temperature was approximately 500 K, the maximum temperature was approximately 590 K, there was no obvious flow dead zone, and no molten salt overheating decomposition occurred, meeting the requirements for safe operation.
Claims
1. A molten salt electric heater, characterized in that, include: The shell (1), molten salt inlet (2), molten salt outlet (3), end cap (4), multiple U-shaped electric heating rods (5) and multiple bow-shaped baffles (6); the multiple U-shaped electric heating rods (5) are arranged inside the shell (1) so that the molten salt flows around the outside of the U-shaped electric heating rods (5); the molten salt inlet (2) is located on the upper left side of the shell (1), the molten salt outlet (3) is located on the lower right side of the shell (1), and the right end of the shell (1) is sealed with a circular end cap (4); Multiple bow-shaped baffles (6) are arranged at intervals along the axial direction of the shell and perpendicular to the axial direction of the shell, dividing the space inside the shell (1) into multiple compartments. The transverse fin area (53) of section A is located in the first two compartments on the inlet side. The bow-shaped baffles (6) are provided with electric heating rod shuttle fixing holes (61) and liquid channel micro-holes (62). Multiple U-shaped electric heating rods (5) pass through the electric heating rod shuttle fixing holes (8) and are fixed by the bow-shaped baffles (6). When each U-shaped electric heating rod (5) passes through the corresponding bow-shaped baffle (6), one branch of each U-shaped electric heating rod (5) corresponds to one electric heating rod shuttle fixing hole (8). The bow-shaped baffles (6) have an arc-shaped notch on one side. The circular plate has an arc-shaped notch with a notch length of 0.2-0.4 times the diameter. The arc-shaped surface on the other side, which is not notched, is defined as the high-pressure zone (63). The area of the high-pressure zone (63) and the arc-shaped notch paper piece is the ordinary zone (64). The opening ratio of the liquid channel micropores (62) in the high-pressure zone (63) is higher than that in the ordinary zone (64) to improve the back flow stagnation and local pressure drop concentration of the baffle. The U-shaped electric heating rod (5) includes a straight section (51) and a U-shaped connecting bend section (52), and is placed along the length of the shell (1). The open ends of all the U-shaped electric heating rods (5) face the end where the molten salt inlet (2) is located, and the U-shaped connecting bend section (52) is located at the end where the molten salt outlet (3) is located. Along the main direction of the molten salt, each branch of the U-shaped electric heating rod (5) is provided with a transverse fin area (53), a longitudinal corrugated fin area (54), and a finless area (55) on its outer side. The transverse fin area (53) is located at the opening end of the U-shaped electric heating rod (5) and is provided with segmented circumferential transverse fins. The first segment is closer to the U-shaped port and is composed of multiple rings of transverse fins evenly distributed along the axial direction. The second segment is relatively far from the U-shaped port and is also composed of multiple rings of circumferential transverse fins evenly distributed along the axial direction. The interval of the first segment is smaller than that of the second segment. The longitudinal corrugated fin area (54) is provided with longitudinal (i.e., the length direction along the axial direction of the branch of the electric heating rod) corrugated fins. Multiple longitudinal corrugated fins are evenly distributed along the circumferential direction. The finless area (55) is not provided with fins. The electric heating rod adopts a zoned power supply heating method. The transverse fin area (53) of section A on the inlet side and the longitudinal corrugated fin area (54) of section B downstream are respectively powered by power supply zones with different heat levels. The section corresponding to the finless area (55) of section C is a non-heating section or a low-power section. Section A (53) is a fixed low-power heating section, section B (54) is a fixed high-power heating section and satisfies that the output power PB of section B > the output power PA of section A. Section C (55) is a non-heating section or a low-power section (preferably PC=0).
2. A molten salt electric heater according to claim 1, characterized in that, The bow-shaped baffle (6) is divided into three equal parts along its width. The leftmost 1 / 3 is defined as the high-pressure zone (61), and the remaining 2 / 3 is defined as the non-high-pressure zone. Under the condition that the orifice diameter, total number of orifices, and total opening ratio remain unchanged, the orifice positions in the opening area (62) are rearranged to make the orifices in the high-pressure zone (61) more concentrated and the orifices in the non-high-pressure zone more sparse. This achieves local discharge and redistribution, reducing stagnation on the back of the baffle and local pressure drop concentration.
3. A molten salt electric heater according to claim 1, characterized in that, The arc-shaped notches of two adjacent bow-shaped baffles (6) are arranged in an alternating manner, so that the fluid flows in a bent bow-shaped flow.
4. A molten salt electric heater according to claim 1, characterized in that, The electric heating rods are hollow, and each U-shaped electric heating rod (5) has two sets of independent heating elements inside, corresponding to section A and section B respectively, forming opposing A circuits and independent B circuits respectively; the lead wires of both circuits are led out from the same end of the heating rod and electrically connected to two sets of independent power supply buses outside; when the device contains multiple electric heating rods, the A circuit of each heating rod is uniformly connected to the A bus, and the B circuit is uniformly connected to the B bus, thereby realizing fixed power output of sections A and B and maintaining P B >P A .
5. A molten salt electric heater according to claim 1, characterized in that, Multiple bow-shaped baffles (6) are arranged at intervals along the axial direction of the shell (1) to divide the space inside the shell (1) into multiple compartments. The two sections of the transverse fin area (53) of section A are located in one compartment respectively, so the transverse fin area (53) of section A corresponds to two compartments.
6. A molten salt electric heater according to claim 1, characterized in that, Looking from the molten salt outlet (3) end inside the shell, multiple U-shaped electric heating rods (5) are arranged in two rings. Each U-shaped electric heating rod (5) forms a certain clockwise or counterclockwise angle with the diameter, and the angles of the two rings are in the same direction.