Supercritical carbon dioxide and liquid gallium dual-working fluid heat exchanger

Abstract

The utility model discloses a supercritical carbon dioxide and liquid gallium double working medium heat exchanger, main include pipe box, cylinder, U type tube bundle, tube sheet, supercritical carbon dioxide import and export and liquid gallium import and export. Super-critical carbon dioxide is as cold fluid and flows through the pipe side of U type tube bundle, and liquid gallium is as hot fluid and flows through the shell side of cylinder, compared with prior art, the utility model discloses the high -efficient heat transfer of supercritical carbon dioxide and the low corrosion characteristic of liquid gallium, realize safe heat exchange.

Description

Technical Field

[0001] This utility model relates to the field of heat exchanger technology for nuclear energy equipment, and in particular to a supercritical carbon dioxide and liquid gallium dual-working-fluid heat exchanger. Background Technology

[0002] As the world's largest producer and consumer of coal, my country has long relied on coal for over 60% of its energy consumption. While this coal-based energy structure has driven industrialization, it has also brought severe environmental pollution and carbon emissions. A shift towards a cleaner, lower-carbon energy structure is imperative. Nuclear energy, with its high energy density, low carbon emissions, and stable power supply, has become one of the alternatives to fossil fuels. However, the efficiency and safety of nuclear energy systems heavily depend on technological breakthroughs in key equipment. Among these, heat exchangers, as the core component of energy conversion, directly affect the operating efficiency, reliability, and safety of nuclear power plants.

[0003] In the nuclear power industry, heat exchangers are widely used in primary loop cooling, secondary loop steam generation, and auxiliary system heat exchange. Currently, mainstream designs mostly employ shell-and-tube or plate structures, with working fluid combinations primarily consisting of water-water, water-steam, or liquid metals (such as sodium or lead-bismuth alloys). For example, steam generators produce steam to drive turbines for power generation through heat exchange between the high-temperature coolant on the tube side and the water on the shell side; liquid metal fast reactors rely on intermediate heat exchangers to isolate the radioactive working fluid from the non-radioactive loop. These heat exchangers need to operate long-term under high temperature, high pressure, and radiation environments, placing high demands on material corrosion resistance, structural sealing, and thermal stress compensation capabilities.

[0004] Researchers at the Xi'an Thermal Power Research Institute, including Ni Yike, investigated the influence of flow channel structure on heat transfer performance in lead-bismuth-supercritical carbon dioxide heat exchangers using numerical simulation. Li Xianwen from the University of Chinese Academy of Sciences studied the heat transfer characteristics of printed circuit board heat exchangers using liquid lead-bismuth and supercritical carbon dioxide as working fluids. Our team, including Chen Ning, simulated the natural circulation heat transfer of liquid potassium-sodium and lead-bismuth metals and analyzed the correlation degree and weight of different parameters using a grey relational analysis algorithm. Team members Liu Mengying and Li Jingjing designed an O-type lead-bismuth heat exchanger and a floating-head lead-bismuth heat exchanger, respectively, using lead-bismuth as the working fluid, and applied for patents. Team member Jiang Yizhen studied the flow heat transfer characteristics of lead-bismuth alloy-supercritical carbon dioxide heat exchangers, combining the flow heat transfer characteristics of printed circuit board heat exchangers. While there is some research on traditional working fluid heat exchangers used in nuclear power plants both domestically and internationally, heat exchangers using gallium and supercritical carbon dioxide as working fluids are still lacking. Existing metal fluid heat exchangers have monotonous structures, insufficient variety, limited applicability, low heat transfer efficiency, and are prone to failure.

[0005] The heat exchangers widely used in the nuclear power field currently face significant challenges in the selection of working fluids and performance matching. Among liquid metal working fluids, sodium reacts violently with water, requiring strict sealing; lead-bismuth alloys are highly corrosive to carbon steel, necessitating expensive coatings or regular maintenance, resulting in high costs for radioactive leakage control. Liquid gallium, however, exhibits unique advantages: its low melting point of 29.8°C, strong chemical inertness, and corrosiveness to stainless steel only 1 / 10 that of sodium, coupled with no radioactive risk, significantly improve operational safety. Furthermore, traditional gaseous working fluids, such as helium, suffer from insufficient heat exchange efficiency due to their low thermal conductivity, while liquid gallium has a thermal conductivity nearly twice that of lead-bismuth alloys and also possesses low viscosity, allowing for optimized flow field distribution. While water-based systems are technically mature, supercritical water is prone to pipe wall oxidation and scaling under high temperature and pressure. Water's critical pressure is 22.1 MPa, requiring high pressure resistance and posing a significant risk of leakage. In contrast, supercritical carbon dioxide (SCO2) is chemically stable, with no risk of phase transformation corrosion. Its critical pressure is 7.38 MPa, significantly lower than water, greatly reducing the design complexity of high-pressure systems. However, currently, there is no heat exchanger that combines the high heat transfer efficiency of SCO2 with the low corrosion resistance of liquid gallium, while also maintaining structural compactness and material durability under extreme conditions.

[0006] Therefore, it is necessary to design a new type of heat exchanger using supercritical carbon dioxide and liquid gallium as working fluids to solve the above problems and provide a safer, more efficient and economical heat exchange solution for nuclear energy systems. Utility Model Content

[0007] The purpose of this invention is to address the problems existing in the background technology by proposing a supercritical carbon dioxide and liquid gallium dual-working-fluid heat exchanger. To achieve the above objective, the technical solution adopted by this invention is as follows: A supercritical carbon dioxide and liquid gallium dual-fluid heat exchanger mainly includes a tube box, a shell, a U-shaped tube bundle, a tube sheet, supercritical carbon dioxide inlet and outlet, and liquid gallium inlet and outlet. Supercritical carbon dioxide flows as a cold fluid through the tube side of the U-shaped tube bundle, while liquid gallium flows as a hot fluid through the shell side of the shell. The tube bundle, as the core heat transfer element, adopts various structural designs, combining the heat transfer principle of a printed circuit board heat exchanger with that of a traditional U-shaped tube heat exchanger. The tube bundle is manufactured using a one-piece molding technology, and its internal tube wall is no longer a smooth or simply ribbed flow channel, but rather forms a continuous, integrated microchannel. The structure of these channels includes, but is not limited to, serrated channels based on PCHE technology, or biomimetic channels based on fractal geometry such as canine tongue blood vessels or leaf vein patterns. The novel tube bundle material uses shape memory alloy to achieve self-healing function, and the tube bundle can be equipped with two types of fins to enhance heat transfer, thereby strengthening fluid turbulence and achieving efficient heat transfer.

[0008] Preferably, the U-shaped tube bundle uses nickel-based alloy Inconel 625, titanium alloy TA10, or shape memory alloy; its bending radius is not less than 5 times the tube diameter, and the tube bundle can be completely disassembled and extracted from the cylinder for easy cleaning and maintenance.

[0009] Preferably, the microchannel structure inside the U-shaped tube bundle is a continuous, uninterrupted biomimetic fractal and / or sawtooth microchannel; the ribs on the outer wall of the tube are straight ribs or threaded ribs.

[0010] Preferably, when the U-shaped tube bundle is made of shape memory alloy, it can self-repair by compressing the cracks through the contraction or expansion of the material when cracks occur on the inner wall of the pipe. When microcracks occur on the inner wall of the pipe due to erosion or corrosion, the shape memory alloy can undergo a phase transformation under the triggering of local stress or temperature changes, producing a "compression" effect on the cracks, thereby achieving self-repair of the material and improving the lifespan and reliability of the equipment under extreme conditions such as nuclear irradiation.

[0011] Preferably, the tube box includes a tube box gasket and a tube sheet; the partition plate inside the tube box is horizontally installed and arranged at the tube box axis, located between the supercritical carbon dioxide inlet and outlet, and extends to the tube box flange connection surface at both ends to ensure complete isolation of the inlet and outlet flow channels; the partition plate divides the inner cavity of the tube box, forcing the supercritical carbon dioxide to form a double-pass reversible flow in the inner core U-shaped tube bundle; balancing the flow distribution and reducing pressure loss; the tube sheet is arranged between the tube box and the shell body to fix the U-shaped tube bundle and separate the tube side and shell side, and to withstand the impact loads on the tube side and shell side.

[0012] Preferably, the cylinder includes a tube box side gasket, an anti-impact plate, a baffle plate, and a liquid gallium inlet and outlet; The cylinder has a double-layer composite structure. The inner layer is a plasma-sprayed tantalum coating with a thickness of 0.2mm–0.5mm, and the outer layer is 316L stainless steel.

[0013] Preferably, the shell side of the cylinder is provided with an anti-impact plate and multiple baffles; An anti-impact plate is installed at the liquid gallium inlet and covers the surface of the U-shaped tube bundle to disperse the impact energy of the liquid gallium jet and reduce the impact corrosion of the tube bundle by the liquid gallium. The impact protection plate is made of 316L stainless steel and has a surface coating made of tungsten carbide, aluminum oxide or chromium oxide. The baffles are arranged alternately up and down along the axis of the cylinder, running through the entire liquid gallium flow channel on the shell side, guiding the liquid gallium to form baffles, increasing the flow path of the liquid gallium, improving the heat exchange opportunities between the liquid gallium and the U-shaped tube bundle, and improving the heat transfer efficiency. The baffle plate is made of 316L stainless steel sheet with a polished surface.

[0014] Preferably, the supercritical carbon dioxide inlet and outlet are located on the tube box and cooperate with the partition plate to realize the two-pass flow of supercritical carbon dioxide. The liquid gallium inlet and outlet are located on the cylinder, and their interfaces employ diffusion or tapering structures to reduce pressure loss and improve flow uniformity. The liquid gallium inlet and outlet have conical diffusion sections at the inlet and tapering sections at the outlet to optimize the flow field distribution on the shell side and reduce pressure loss. A gasket on the tube sheet side is located between the cylinder and the tube sheet to compensate for thermal expansion differences and isolate the working fluid to prevent cross-leakage.

[0015] The heat exchanger can be arranged in a counter-current or co-current manner.

[0016] Preferably, the gasket is located inside the tube box and is used to seal the connection gap between the partition plate and the tube sheet; The shell-side gasket is located between the shell and the tube sheet to compensate for thermal expansion differences and to isolate the shell-side and tube-side working fluids.

[0017] Preferably, the device also includes supports symmetrically distributed at the bottom of the cylinder. The supports are arranged along the axis of the cylinder and connected to the ground by anchor bolts. They bear the overall weight of the heat exchanger and transmit it to the base. A rubber shock-absorbing buffer layer is installed at the bottom of the supports to limit the vibration and displacement of the heat exchanger.

[0018] Compared with the prior art, the present invention has the following beneficial technical effects: The most significant advantage of the heat exchanger provided by this invention lies in combining the structure of a U-tube heat exchanger with the high-efficiency heat transfer characteristics of a printed circuit board heat exchanger. The novel PCHE inner core U-tube bundle, through its internal microchannel design and external finned structure, provides an excellent heat transfer path for the heat exchange medium. Simultaneously, the introduced biomimetic fractal design and self-healing material concept provide support for the safe and efficient operation of next-generation nuclear energy systems.

[0019] This invention provides a novel heat exchanger using supercritical carbon dioxide and liquid gallium as working fluids, featuring a simple structure and high heat exchange efficiency. Compared to existing technologies, this invention combines the high heat transfer efficiency of supercritical carbon dioxide with the low corrosiveness of liquid gallium to achieve safe heat exchange. Supercritical carbon dioxide has a low critical temperature, making it easy to maintain a supercritical state under the high-temperature conditions of nuclear reactors. Its high thermal conductivity and low viscosity significantly improve heat transfer efficiency, while its critical pressure is much lower than that of supercritical water, greatly reducing the design difficulty and leakage risk of high-pressure systems. Liquid gallium, as a thermal fluid, has a low melting point and a wide liquid temperature range, maintaining stable flow even at high temperatures. Its chemical inertness significantly weakens the penetration and corrosion of metallic materials, avoiding the safety hazards caused by violent reactions or radioactive contamination of traditional liquid metal working fluids. Furthermore, if the heat exchanger adopts a counter-current layout, the heat transfer temperature difference is maximized, improving heat exchange efficiency. This invention, with working fluid compatibility as its core, combined with material and structural innovations, provides a reliable guarantee for efficient heat exchange and safe operation of nuclear reactors, promoting the development of nuclear energy systems. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the overall structure of the novel heat exchanger of this invention, which uses supercritical carbon dioxide and liquid gallium as working fluids.

[0021] Figure 2 This is a schematic diagram of a composite U-shaped tube bundle.

[0022] Reference numerals: 1. Tube box; 2. Cylinder; 3. U-shaped tube bundle; 4. Tube box gasket; 5. Tube sheet; 6. Tube box side gasket; 7. Anti-impact plate; 8. Baffle plate; 9. Divider plate; 10a. Supercritical carbon dioxide inlet; 10b. Supercritical carbon dioxide outlet; 11a. Liquid gallium inlet; 11b. Liquid gallium outlet; 12. Support; 3a. Straight rib; 3b. Threaded rib; 3c. Bionic topology; 3d. Serrated microchannel. Detailed Implementation Example 1

[0023] like Figure 1As shown, this embodiment provides a novel heat exchanger using supercritical carbon dioxide and liquid gallium as working fluids. The device includes a tube box 1, a cylinder 2, a novel PCHE inner core U-shaped tube bundle 3, tube box gaskets 4, a tube sheet 5, tube box side gaskets 6, an anti-impact plate 7, a baffle plate 8, a partition plate 9, supercritical carbon dioxide inlet and outlet 10a, 10b, liquid gallium inlet and outlet 11a, 11b, a support 12, straight ribs 3a, threaded ribs 3b, a biomimetic topology structure 3c, and serrated microchannels 3d. The design of the novel PCHE inner core U-shaped tube bundle 3 includes serrated channels based on PCHE technology, or biomimetic channels based on fractal geometry such as canine tongue blood vessels and leaf vein patterns. The tube bundle can be externally equipped with two types of ribs to enhance heat exchange. The following details its operation process and structural synergy: If a counter-flow arrangement is adopted, supercritical carbon dioxide enters from the inlet 10a at the bottom of tube box 1 and first contacts the horizontally installed partition 9. The partition 9 is arranged along the tube box axis, extending to both ends of the tube box and tube sheet, dividing the inner cavity of the tube box into two independent flow channels. Under the forced guidance of the partition 9, the supercritical carbon dioxide achieves upward reversal flow, forming a two-pass path, flowing sequentially through the lower and upper halves of the new PCHE inner core U-shaped tube bundle 3, and finally exiting from the tube box outlet 10b. If a co-flow arrangement is adopted, supercritical carbon dioxide enters from the top of tube box 1, flows through the upper and lower halves of the U-shaped tube bundle, and finally exits from the bottom of the tube box.

[0024] In this invention, the design of the baffle plate 9 not only balances the flow distribution but also improves heat exchange efficiency by extending the flow path. The tube sheet 5, located between the tube box 1 and the shell 2, is used to fix the novel PCHE inner core U-shaped tube bundle 3. This structure separates the tube-side and shell-side working fluid channels and withstands the impact of the supercritical carbon dioxide working fluid on the tube side. The tube box gasket 4, located at the sealing connection between the tube box 1 and the tube sheet 5, compensates for thermal deformation through the thermophysical properties of the metal, preventing supercritical carbon dioxide leakage.

[0025] Liquid gallium enters the shell side through inlet 11a at the top of cylinder 2. A conical diffuser section is provided at the inlet, which gradually widens the cross-section to reduce the flow velocity and distribute the flow evenly. The liquid gallium first impacts the anti-impact plate 7, an arc-shaped plate covering the surface of the U-shaped tube bundle 3. The surface is coated with a variety of materials to disperse the impact energy of the flow and prevent local corrosion of the tube bundle. Subsequently, guided by baffle 8, the liquid gallium flows up and down along the cylinder axis, making full contact with the surface of the U-shaped tube bundle 3. The surface of baffle 8 is polished to reduce flow resistance and extend the liquid gallium flow path, improving heat exchange efficiency. After heat exchange, the liquid gallium flows through the tapered section of outlet 11b, where the tapered cross-section reduces pressure loss and maintains flow stability.

[0026] In this invention, the inner layer of the cylinder 2 is covered with a tantalum coating with a thickness of 0.2mm–0.5mm, and the outer layer is made of 316L stainless steel, forming a liquid gallium flow channel. The gasket 6 on the tube box side is located between the cylinder 2 and the tube sheet 5, and compensates for the difference in thermal expansion through the thermophysical properties of the metal, thereby isolating the risk of cross-leakage between the liquid gallium on the shell side and the supercritical carbon dioxide on the tube side.

[0027] In this invention, the novel PCHE inner core U-shaped tube bundle 3 is made of nickel-based alloy Inconel 625, titanium alloy TA10 or shape memory alloy material, with a tube wall thickness of 4mm-6mm, a bending radius of not less than 5 times the tube diameter, and the tube bundle can be disassembled and pulled out as a whole for easy cleaning and maintenance.

[0028] In this invention, the novel PCHE inner core U-shaped tube bundle 3 adopts an integral molding technology, which enables the realization of a complex internal microchannel structure.

[0029] In one embodiment, the inner wall of the tube bundle 3 is etched with continuous sawtooth-shaped microchannels 3d. This structure incorporates the technical features of PCHE, where eddies are generated at each sawtooth corner when supercritical carbon dioxide flows through, increasing disturbance and effectively disrupting the flow boundary layer and thermal boundary layer, thereby achieving a high tube-side heat transfer coefficient while maintaining a compact structure.

[0030] In another embodiment, the internal microchannels of the tube bundle 3 are a biomimetic fractal structure 3c. This structure mimics the efficient vascular network in a canine tongue or the vein distribution of a leaf, forming a multi-branched, flow-resistance-optimized microchannel network. This design not only achieves uniform fluid distribution but also increases the heat transfer area.

[0031] Furthermore, in terms of material selection, alloys with shape memory function can be used to manufacture the U-shaped tube bundle. During operation, if a micro-crack occurs at a certain point, the change in the stress field of the crack will trigger a phase transformation of the surrounding shape memory alloy, generating recovery strain and applying compressive stress to the crack surface, thereby closing the crack or slowing its propagation, that is, realizing the "self-repair" capability of the heat exchanger pipe.

[0032] In this utility model, the supports 12 are symmetrically distributed at the bottom of the cylinder. The bottom of the saddle structure integrates a rubber shock-absorbing buffer layer, which is fixed to the base by anchor bolts to absorb operating vibration and prevent displacement.

[0033] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited thereto. Various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention.

Claims

1. A supercritical carbon dioxide and liquid gallium dual-working-fluid heat exchanger, characterized in that, Includes tube box, cylinder, U-shaped tube bundle, supercritical carbon dioxide inlet and outlet, and liquid gallium inlet and outlet; The heat exchanger has a shell-and-tube structure; the tube box is located on one side of the shell; the U-shaped tube bundle is installed inside the shell; a partition plate is installed inside the tube box to divide the inner cavity of the tube box into two independent flow channels; the upper and lower flow channels are respectively connected to the inlet and outlet ends of the U-shaped tube bundle. Supercritical carbon dioxide flows as a cold fluid through the tube side of the U-shaped tube bundle, while liquid gallium flows as a hot fluid through the shell side of the cylinder. The U-shaped tube bundle is manufactured in one piece, with a PCHE inner core microchannel structure to enhance heat transfer inside the tube, and a biomimetic, memory and rib structure on the outer wall of the tube.

2. The supercritical carbon dioxide and liquid gallium dual-working-fluid heat exchanger according to claim 1, characterized in that, The bending radius of the U-shaped tube bundle is not less than 5 times the tube diameter, and the tube bundle can be completely disassembled and extracted from the cylinder.

3. A supercritical carbon dioxide and liquid gallium dual-fluid heat exchanger according to claim 1, characterized in that, The microchannel structure inside the U-shaped tube bundle is a continuous, uninterrupted biomimetic fractal and / or sawtooth microchannel; the ribs on the outer wall of the tube are straight ribs or threaded ribs.

4. A supercritical carbon dioxide and liquid gallium dual-fluid heat exchanger according to claim 1, characterized in that, When U-shaped tube bundles are made of shape memory alloys, they can self-repair when cracks occur on the inner wall of the tube by compressing the cracks through the contraction or expansion of the material.

5. A supercritical carbon dioxide and liquid gallium dual-fluid heat exchanger according to claim 1, characterized in that, The tube box includes a tube box gasket and a tube sheet; the partition plate inside the tube box is horizontally installed and arranged at the tube box axis, located between the supercritical carbon dioxide inlet and outlet, and extends to the tube box flange connection surface at both ends to ensure complete isolation of the inlet and outlet flow channels; the partition plate divides the inner cavity of the tube box, forcing the supercritical carbon dioxide to form a double-pass reversible flow in the inner core U-shaped tube bundle; The tube sheet is placed between the tube box and the shell to fix the U-shaped tube bundle and separate the tube side from the shell side, and to withstand the impact loads on the tube side and the shell side.

6. A supercritical carbon dioxide and liquid gallium dual-fluid heat exchanger according to claim 5, characterized in that, The cylinder body includes a side gasket, a shock absorber, a baffle, and liquid gallium inlet and outlet; The cylinder has a double-layer composite structure. The inner layer is a plasma-sprayed tantalum coating with a thickness of 0.2mm–0.5mm, and the outer layer is 316L stainless steel.

7. A supercritical carbon dioxide and liquid gallium dual-fluid heat exchanger according to claim 6, characterized in that, The shell side of the cylinder is provided with an anti-impact plate and multiple baffles; An anti-impact plate is installed at the liquid gallium inlet and covers the surface of the U-shaped tube bundle to disperse the impact energy of the liquid gallium jet and reduce the impact corrosion of the tube bundle by the liquid gallium. The impact protection plate is made of 316L stainless steel and has a surface coating made of tungsten carbide, aluminum oxide or chromium oxide. The baffles are arranged alternately up and down along the axis of the cylinder, running through the entire liquid gallium flow channel on the shell side, and are used to guide the flow path of the working fluid to enhance heat transfer; The baffle plate is made of 316L stainless steel sheet with a polished surface.

8. A supercritical carbon dioxide and liquid gallium dual-working-fluid heat exchanger according to claim 1, characterized in that, The inlet and outlet of supercritical carbon dioxide are located on the tube box and cooperate with the partition plate to realize the two-pass flow of supercritical carbon dioxide. The liquid gallium inlet and outlet are located on the cylinder, and the interface adopts a diffusion or tapering structure to reduce pressure loss and improve flow uniformity. The heat exchanger can be arranged in a counter-current or co-current manner.

9. A supercritical carbon dioxide and liquid gallium dual-fluid heat exchanger according to claim 6, characterized in that, The tube box gasket is located inside the tube box and is used to seal the connection gap between the partition plate and the tube sheet; The shell-side gasket is located between the shell and the tube sheet to compensate for thermal expansion differences and to isolate the shell-side and tube-side working fluids.

10. A supercritical carbon dioxide and liquid gallium dual-working-fluid heat exchanger according to claim 1, characterized in that, It also includes supports symmetrically distributed at the bottom of the cylinder. The supports are arranged along the axis of the cylinder and connected to the ground by anchor bolts. They bear the overall weight of the heat exchanger and transmit it to the base. A rubber shock-absorbing buffer layer is installed at the bottom of the supports to limit the vibration and displacement of the heat exchanger.

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