Boiling heat transfer runner of segmented variable cross-section steam generator

Abstract

The invention relates to the technical field of steam generators, and discloses a segmented variable-cross-section boiling heat transfer runner of a steam generator, which comprises a primary side runner and a secondary side runner and exchanges heat by sharing a partition wall. The core is that the secondary side runner is divided into at least two functional sections along the flowing direction of a working medium, such as a single-phase heat transfer section, a saturated boiling section and a dry section; the geometric dimension of the circulation cross section and / or the structure of the inner wall surface of each functional section are / is specifically designed according to the main flow pattern and the heat transfer mechanism of the section; the single-phase section can adopt a smaller cross section to improve the flow velocity and strengthen convection; the inner wall surface of the saturated boiling section can be derived into an arc shape, a wave shape and a sawtooth shape or is provided with fins and the like to strengthen boiling; the drying section can adopt a larger section and is provided with rotating fins to delay drying and strengthen heat transfer; and different sections are in smooth transition through continuously changing curved surfaces. The compactness and the comprehensive performance of the steam generator are remarkably improved.

Description

Technical Field

[0001] The invention relates to the technical field of steam generators, in particular to a boiling heat transfer flow channel of a steam generator with segmented variable cross-section. Background Art

[0002] Steam generators are key components in energy conversion systems, particularly in nuclear power, thermal power generation, and various industrial processes. Their primary function is to heat the secondary working fluid (typically water) through heat exchange and convert it into high-temperature, high-pressure steam. Within the steam generator's heat transfer tubes, the secondary working fluid undergoes a complex boiling heat transfer process, during which the fluid morphology and heat transfer mechanism change significantly along the flow path, gradually transitioning from a single-phase liquid at the inlet to bubbly flow, slug flow, annular flow, and potentially drying out.

[0003] However, the currently widely used boiling heat transfer technology for steam generators often utilizes a homogeneous structure with constant or minimally varying geometry and dimensions along its entire length. This traditional design has inherent shortcomings in adapting to the drastically varying physical properties of boiling heat transfer along the entire length. Due to the lack of refined structural optimization tailored to the specific heat transfer mechanisms and flow pattern characteristics of different boiling stages (such as single-phase preheating, nucleate boiling, forced convection evaporation, and near-dryout), the overall heat transfer performance of the heat transfer tubes is difficult to achieve optimal, and heat transfer bottlenecks or low efficiency may occur in certain sections. Furthermore, this lack of targeted design makes it more difficult to effectively suppress or delay flow instabilities and heat transfer deterioration (such as premature dryout), which may in turn affect the operational safety and economic efficiency of the steam generator. Although various heat transfer enhancement technologies have been proposed, most of them focus on universal enhancement of the entire flow channel and fail to provide customized solutions for the stage-specific characteristics of the boiling process. As a result, their performance improvement potential is limited or is accompanied by adverse effects such as a significant increase in flow resistance. At the same time, the limitations of traditional manufacturing processes on the realization of complex internal flow channel structures further hinder the in-depth exploration of boiling heat transfer performance.

[0004] Therefore, developing a new heat transfer channel structure that can adapt to the changes in the characteristics of the entire boiling heat transfer process and achieve efficient coordinated heat exchange in each stage has important theoretical significance and engineering application value for improving the overall performance of the steam generator and achieving compactness and lightweighting of the device. Summary of the Invention

[0005] In response to the problems of existing nuclear steam generator heat transfer elements such as poor adaptability to flow patterns in different stages of boiling heat transfer, large equipment volume and weight, and inflexible distribution of heat transfer area, the present invention aims to provide a new type of steam generator boiling heat transfer flow channel and its application, so as to achieve fine control of the boiling heat transfer process through innovative structural design, thereby improving heat transfer efficiency and contributing to the miniaturization and lightweighting of the steam generator.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0007] In a first aspect, the present invention provides a segmented, variable-section boiling heat transfer channel for a steam generator. The channel is designed for efficient heat exchange between a high-temperature working medium on the primary side and a boiling working medium on the secondary side. The core structural features of the channel are:

[0008] It comprises at least one primary side flow channel for conducting a primary side high temperature working medium and at least one secondary side flow channel for conducting a secondary side boiling working medium. The primary side flow channel and the secondary side flow channel are heat-transferred and physically separated by a common partition wall.

[0009] To achieve a compact arrangement of the flow channel bundle, the secondary side flow channels have a non-circular geometric cross-sectional shape, such as but not limited to a quadrilateral or hexagonal shape. Compared to traditional circular tubes, this cross-sectional shape can more effectively utilize space and reduce the ineffective gaps between flow channels.

[0010] Crucially, the secondary flow channel is intentionally divided into at least two functional sections along its length, i.e., the direction of secondary working fluid flow. This division is based on the different heat transfer stages (such as single-phase heating, nucleate boiling, transition to film boiling, etc.) experienced by the secondary working fluid during boiling and their corresponding characteristic flow patterns (such as bubbly flow, slug flow, annular flow, and dry flow).

[0011] Furthermore, to specifically optimize the heat transfer performance of each heat transfer stage, the secondary channel's cross-sectional geometry, inner wall surface morphology, and the presence and placement of at least one of the flow-regulating or heat-transfer enhancing components within the at least two distinct functional sections are customized according to the specific flow patterns and heat-transfer enhancement mechanisms of the boiling heat transfer stage corresponding to each section. This results in significant differences in these structural features between sections. This differentiated design allows each channel section to better adapt to its internal flow and heat transfer conditions, overcoming the limitations of traditional uniform heat transfer tubes.

[0012] Specifically, the secondary side flow channel can be divided into a single-phase heat transfer section, a saturated boiling section and a drying section along its length, corresponding to the main physical process of the secondary side working medium from liquid phase heating to complete evaporation.

[0013] 1. In the single-phase heat transfer stage, the secondary fluid is primarily liquid. To enhance convective heat transfer and improve flow stability in this phase, the cross-sectional geometry (e.g., hydraulic diameter or flow area) of the secondary flow passages in this section is designed to be relatively smaller than the corresponding dimensions in the subsequent saturated boiling stage. This smaller cross-sectional area helps increase the fluid's flow rate, thereby enhancing turbulence, improving the wall heat transfer coefficient, and potentially suppressing undesirable premature boiling.

[0014] 2. In the saturated boiling section, the secondary side working fluid undergoes a drastic phase change, experiencing a variety of complex flow patterns from bubbly flow to annular flow. The secondary side flow channel of this section can adopt the aforementioned quadrilateral or hexagonal basic cross-sectional shape. In order to further enhance the boiling heat transfer in this area, the surface morphology characteristics of its inner wall can be specially designed. For example, the side wall of the flow channel can be evolved into an arc, a wave, a serrated shape, or longitudinal fin-like protrusions can be provided along the length of the flow channel; or, the longitudinal section of the flow channel along the flow direction itself can be designed into a wavy, periodic transverse rib or a serrated profile. These changes in surface morphology are intended to significantly improve the boiling heat transfer efficiency by increasing the number of vaporization cores, promoting bubble detachment, enhancing liquid film disturbance, and expanding the effective heat exchange area.

[0015] 3. In the drying section, the liquid film may tend to break, and the heat transfer is at risk of deterioration. To address this problem, the geometric dimensions of the flow cross-section of the secondary side flow channel in this section are designed to be relatively larger than the corresponding dimensions of the saturated boiling section, which helps to reduce the vapor phase flow rate and reduce the pressure drop. More importantly, specific flow adjustment or heat transfer enhancement components, such as rotating fins, are provided inside the secondary side flow channel in this section. These rotating fins are designed to guide the secondary side working fluid to produce a strong rotation or vortex flow. The working principle is that the centrifugal force generated by the rotating flow can effectively throw the unevaporated droplets entrained in the air flow to the heated partition wall surface and re-wet it, thereby delaying or reducing the occurrence of drying, and enhancing the convection and evaporation heat transfer in this area. At the same time, the fins themselves also serve as an extended surface to increase the heat transfer area.

[0016] To ensure smooth flow of the secondary working fluid through functional sections with different structural features and to reduce additional flow resistance and localized overheating that may be caused by sudden changes in cross-section or internal structure, the single-phase heat transfer section, saturated boiling section, and dry-up section are preferably connected by a smooth transition using a continuously changing curved surface. This gradual transition design helps maintain flow field stability and reduce energy loss.

[0017] Considering the segmented, variable-section flow channel and the possible fine surface features and geometric complexity of its internal components (such as rotating fins), traditional subtractive manufacturing or tube bending assembly processes are difficult to achieve accurately and integrally. Therefore, this flow channel structure is particularly suitable for advanced additive manufacturing technologies, such as laser powder bed fusion (L-PBF), which uses metal powder materials for layer-by-layer printing and integral molding. This manufacturing method provides technical feasibility for realizing heat transfer flow channels with highly optimized and complex internal geometries, ensuring the precise realization of design intent.

[0018] The second aspect of the present invention provides a steam generator comprising the above-mentioned segmented variable cross-section boiling heat transfer flow channel:

[0019] The core heat transfer area of the steam generator is composed of one or more arrays of segmented, variable-section boiling heat transfer channels, as described above. By employing this novel channel design, the steam generator is expected to achieve a more compact and lightweight overall structure while maintaining or even improving heat transfer capacity. This, in turn, may improve adaptability to diverse operating conditions and operational stability.

[0020] In summary, the present invention provides an effective new approach to improving the comprehensive performance of nuclear steam generators through the innovative segmented and variable-section design of the boiling heat transfer flow channel on the secondary side of the steam generator, refined structural optimization based on the characteristics of each heat transfer stage, and combined with advanced manufacturing technology.

[0021] The present invention provides a segmented variable cross-section boiling heat transfer flow channel for a steam generator. It has the following beneficial effects:

[0022] 1. The present invention divides the secondary side flow channel into a single-phase heat transfer section, a saturated boiling section, and a dry-down section along the flow direction of the working fluid. The cross-sectional geometry and internal structure design are customized according to the flow pattern and heat transfer characteristics of each section (such as reducing the cross-section to increase the flow rate in the single-phase section, optimizing the wall morphology to increase the vaporization core in the saturated boiling section, and providing rotating fins in the dry-down section to enhance droplet wall wetting). This allows each heat transfer stage to operate under more optimal heat exchange conditions, thereby significantly improving the boiling heat transfer coefficient of the secondary side working fluid and the overall energy transfer efficiency.

[0023] 2. The present invention adopts a segmented design. For example, in the saturated boiling section, an optimized basic flow channel and surface derivative structure are used to adapt to the transition from bubbly flow to annular flow. In the dry-up section, the flow channel size is increased and internal rotating fins are used to manage the diffuse flow with high gas content, thereby improving the heat transfer performance in the flow transition area, suppressing flow instability, and improving the operating stability and safety of the steam generator under different operating conditions.

[0024] 3. The present invention's use of non-circular base cross-sections (e.g., quadrilateral or hexagonal) allows for tighter arrangement of flow channel bundles, reducing the dead space between conventional tube bundles. Furthermore, targeted heat transfer enhancement in each section reduces the required total heat transfer area while maintaining the same heat transfer output. These factors work together to reduce the overall size and weight of the steam generator, meeting the growing demand for compact and lightweight equipment in nuclear power plants.

[0025] 4. The present invention uses a partition wall to directly separate the primary and secondary flow channels, and performs fine variable cross-section and internal structure design on the secondary flow channel, which can more flexibly allocate and optimize the heat transfer interface on demand, improve the effective utilization rate of materials, and avoid potential waste of heat transfer area.

[0026] 5. The complex segmented, variable-cross-section flow channel structure proposed in this invention, particularly its refined internal surface features and reinforcement elements, is achieved through additive manufacturing technologies such as laser powder bed fusion. This not only overcomes the limitations of traditional manufacturing processes but also opens up new ideas and technical paths for the future design of complex flow channel heat exchange equipment with higher integration and improved performance, thereby promoting advancements in heat exchange equipment design and manufacturing technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of a typical boiling heat transfer fluid flow pattern;

[0028] Figure 2 Schematic diagram of the basic heat transfer channel; a) is a quadrilateral basic heat transfer channel, b) is a hexagonal basic heat transfer channel;

[0029] Figure 3 Schematic diagram of the derived structure of the basic heat transfer channel; a) is the cross section of the channel, b) is the longitudinal section of the channel;

[0030] Figure 4 A two-dimensional view of the segmented flow passage of the steam generator of the present invention;

[0031] Figure 5 A three-dimensional view of the segmented flow passage of the steam generator of the present invention;

[0032] Figure 6 This is a picture of the principle prototype of the present invention;

[0033] Figure 7 This is a test picture of the heat transfer performance of the principle prototype of the present invention.

[0034] Among them, 1. The edge of the flow channel; 2. The partition wall; 3. The primary side flow channel; 4. The secondary side flow channel; 5. The rounded corners at the connection of the flow channel; 6. The beveled corners at the connection of the edge of the flow channel; 7. The arc; 8. The first wave shape; 9. The first serrated shape; 10. The longitudinal fin; 11. The second wave shape; 12. The transverse fin structure; 13. The second serrated shape. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Unless the context clearly dictates otherwise, the singular form appearing herein also includes the plural form. Similarly, unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention belongs.

[0036] For clarity, certain terms are used in the drawings and the following description. These terms should be understood broadly and not in a limiting sense. For example, "primary" and "secondary" refer to relative areas of fluid flow, while "upstream" and "downstream" refer to relative positions along the direction of fluid flow.

[0037] An embodiment of the present invention provides a segmented variable cross-section steam generator boiling heat transfer channel (hereinafter referred to as "heat transfer channel"), the structure and layout of its basic unit are described as follows.

[0038] In a preferred embodiment, Figure 2 As shown, the basic unit of the heat transfer channel comprises at least one primary channel 3 for conducting a high-temperature working medium on the primary side, and at least one secondary channel 4 for conducting a boiling working medium on the secondary side. The primary channel 3 and the secondary channel 4 are arranged adjacent to each other and physically separated and heat-transferred by a shared partition wall 2. The partition wall 2 serves as the primary heat transfer interface, transferring heat from the high-temperature working medium in the primary channel 3 to the working medium in the secondary channel 4, causing the secondary working medium to boil.

[0039] The cross section of the secondary side flow channel 4 in the embodiment of the present invention is designed to be a non-circular basic cross section shape that can achieve efficient space utilization and close arrangement. Figure 2 As shown in a, this non-circular basic cross-sectional shape can be specifically a quadrilateral. In another embodiment, as shown in Figure 2As shown in b, the basic cross-sectional shape can be a hexagon. Compared with the traditional circular pipe, the main advantage of using a non-circular cross-section such as a quadrilateral or hexagon is that when multiple such flow channel units are arranged side by side to form a flow channel bundle, the ineffective gap between the flow channel units can be significantly reduced, achieving a higher space filling rate. The side 1 ( Figure 2 1) constitutes the outer boundary of the flow channel or shares part of the partition wall with the adjacent flow channel.

[0040] This compact arrangement not only helps reduce the volume of the entire steam generator heat exchange core, but also helps reduce the overall weight of the equipment. This is of great significance for applications with limited space or strict weight requirements, such as steam generators in small modular reactors (SMRs).

[0041] Multiple such basic flow channel units can be arranged in a regular array to form a core heat transfer component with large-scale heat exchange capabilities. By sharing the partition wall 2, adjacent flow channel units can effectively share the heat transfer surface, further optimizing structural compactness and material utilization efficiency. The primary and secondary flow channels 3 and 4 can be designed with different flow cross-sectional areas and geometries to match the physical properties and flow characteristics of the working fluids on either side, depending on specific heat transfer requirements.

[0042] In the embodiment of the present invention, a key segmentation strategy is adopted in the design of the secondary side flow channel 4. This segmentation design is proposed based on an in-depth analysis of the complex physical phenomena and variable fluid flow patterns experienced by the secondary side working fluid during the heated boiling process.

[0043] Reference Figure 1 , the figure schematically shows the various fluid flow patterns that may appear when the secondary side working fluid (such as water) flows along the heating channel during a typical boiling heat transfer process. Starting from the single-phase liquid water at the inlet, as heat is continuously added, the working fluid temperature rises and reaches a saturated state, and then begins to boil. During the boiling process, the gas phase gradually increases, and the fluid exhibits bubbly flow (bubbles are dispersed in the continuous liquid phase), slug flow (large bubbles occupy most of the channel cross-section, forming slug-shaped gas masses), confined bubbles, elongated bubbles, mixing-annular flow, annular flow (the liquid phase adheres to the wall in the form of a thin film, and the gas phase flows at high speed in the center) until the final possible dry flow (the liquid film ruptures, dry spots appear on the wall, and liquid droplets are entrained in the gas phase). Each flow pattern corresponds to a specific gas-liquid two-phase distribution morphology and heat transfer mechanism.

[0044] Traditional homogeneous heat transfer tubes have a geometry and dimensions that remain constant or vary minimally throughout their entire length, making them difficult to optimize for the specific heat transfer characteristics of the various flow patterns described above. Therefore, the present invention proposes that the secondary flow channel 4 be divided along its length, i.e., the direction of secondary working fluid flow, into at least two, and in this preferred embodiment, three, primary functional sections.

[0045] like Figure 4 and Figure 5 As shown in the figure, the three functional sections are: a single-phase heat transfer section at the working fluid inlet, a saturated boiling section immediately following it, and a dry-down section at the working fluid outlet. This division allows the structural design of each section to match the prevailing flow pattern and dominant heat transfer mechanism within that region, thereby maximizing heat transfer performance at each stage and improving flow stability.

[0046] The purpose of dividing these functional sections is to achieve refined management and enhancement of the boiling heat transfer process. By adopting different flow channel geometric parameters or internal structural features in different sections, heat transfer bottlenecks or flow problems that may arise in each stage can be specifically addressed. For example, convective heat transfer enhancement in the single-phase zone, bubble management in the nucleate boiling zone, and liquid film maintenance and heat transfer degradation suppression in the dry zone can be achieved. This segmented design, based on the physical characteristics of the boiling process, is one of the core technical means of achieving efficient heat transfer and a compact structure.

[0047] In the embodiment of the present invention, the single-phase heat transfer section, saturated boiling section and drying section divided by the secondary side flow channel 4 are each designed with unique structural features to adapt to and enhance the physical process of its corresponding heat transfer stage.

[0048] First, let’s consider the design of the single-phase heat transfer section. Figure 4 and Figure 5 As shown, this section is located in the upstream part where the secondary side working medium enters the heat transfer channel. In this embodiment, the flow cross-sectional geometric dimensions of the secondary side flow channel 4 of the single-phase heat transfer section, such as its hydraulic diameter or effective flow area, are designed to be relatively smaller than the corresponding dimensions of the saturated boiling section downstream. The purpose of this design is to achieve a higher flow rate when the secondary side working medium (usually liquid water) flows through this smaller cross-section. A higher flow rate helps to increase the turbulence of the fluid and destroy the laminar bottom layer near the tube wall, thereby enhancing the single-phase counter-current heat transfer effect, so that the liquid working medium can quickly and effectively absorb heat from the partition wall 2, preparing for the subsequent boiling process. At the same time, a higher flow rate and a regular flow channel (complex internal components are usually not set in this section) also help to improve flow stability and suppress undesirable early boiling or uneven flow that may be caused by local overheating.

[0049] Next, the design of the saturated boiling section is carried out. This section is the core area where the secondary side working medium undergoes a drastic phase change, and undergoes a variety of complex flow patterns such as bubbly flow and annular flow. In this embodiment, Figure 4 and Figure 5 As shown, the secondary side flow channel 4 of the saturated boiling section can adopt the aforementioned non-circular basic cross-sectional shape such as a quadrilateral or hexagon. In order to further enhance the boiling heat transfer in this area, its inner wall surface, that is, the surface of the partition wall 2 facing the secondary side flow channel 4 and the inner surface of the edge 1 of the flow channel, can be subjected to specific geometric modifications or integrated heat transfer enhancement structures. These modifications or structures are intended to significantly improve the boiling heat transfer coefficient in one or more ways, such as by increasing the density of effective vaporization core points, promoting the effective generation and timely separation of bubbles, enhancing the turbulent disturbance and macroscopic mixing of the fluid in the near-wall area, increasing the effective heat exchange area, or improving the wetting characteristics of the wall to maintain effective liquid film coverage. The specific inner wall surface geometric derivation and the selection and design of the enhancement structure.

[0050] Finally, let’s talk about the design of the dry section. This section is located at the downstream end of the secondary side flow channel. At this time, the gas phase fraction of the working fluid is very high, and the liquid film may become very thin or even rupture, resulting in deterioration of heat transfer. To address this problem, Figure 4 and Figure 5 As shown, in this embodiment, the cross-sectional geometry of the secondary side flow channel 4 of the dry section is designed to be relatively larger than the corresponding dimensions of the upstream saturated boiling section. This increase in cross-sectional size helps to reduce the flow rate of the high-speed steam flow, reducing flow resistance and the associated pressure drop.

[0051] More importantly, inside the secondary side flow channel 4 of the dry section, fins are provided for generating a rotating flow and directing the droplets to the heat transfer wall. In this preferred embodiment, these fins are rotating fins (such as Figure 5 (As shown inside the drying section in the three-dimensional view). These rotating fins are usually spiral-shaped or arranged uniformly or unevenly in the flow channel at a specific inclination angle along the circumference. Its working mechanism is that when a high-speed gas-liquid two-phase fluid flows through these rotating fins, the guiding effect of the fins causes the fluid to produce a strong rotation or vortex motion. In this rotating flow field, the droplets with higher density will be thrown to and reattached to the heat transfer wall surface with higher temperature (i.e., the inner surface of the partition wall 2 and the inner surface of the flow channel edge 1) due to the action of centrifugal force. This forced wall rewetting effect can effectively delay or alleviate the occurrence of drying, improve heat transfer conditions, and enable the wall surface to continue to transfer heat through evaporating droplets, thereby significantly improving the heat transfer efficiency and critical heat flux density of the drying section and even the entire flow channel. At the same time, the rotating fins themselves also serve as an extended surface, which increases the heat transfer area to a certain extent.

[0052] Through the above-mentioned refined structural design for each functional section, the heat transfer channel of the present invention can more effectively adapt to the complex changes in the boiling heat transfer process and achieve an improvement in the overall heat exchange performance.

[0053] As mentioned above, in order to achieve heat transfer enhancement in a specific section of the secondary side flow channel (especially the saturated boiling section), or to improve the overall fluid dynamics performance of the flow channel, the embodiments of the present invention provide a variety of derivations and optimization schemes for the flow channel geometric features. Figure 3 , which shows in detail the basic heat transfer flow path (e.g. Figure 2 Various specific geometric derivative structures of the quadrilateral or hexagonal flow channel shown in FIG. These derivative structures can be used alone or in combination according to actual heat transfer requirements and fluid properties.

[0054] In terms of optimization of the geometric features of the flow channel cross section, such as Figure 3 As shown in a, the shape of the flow channel connection and the flow channel edge can be finely adjusted.

[0055] One aspect is the transition design at the corners of the flow channel. For example, the connection between the edge 1 of the flow channel and the partition wall 2 (or the edge of the adjacent flow channel) that constitutes the secondary side flow channel 4 can no longer be a sharp right angle, but can be designed as a smooth rounded transition 5 at the flow channel connection. This rounded transition helps to reduce the local pressure loss when the fluid flows through the corner, avoids the formation of flow dead zones or excessive turbulence, thereby making the flow field more uniform and possibly reducing the risk of deposition or corrosion. Similarly, an oblique angle transition 6 at the edge connection of the flow channel can also be used to achieve a smooth transition according to specific design requirements.

[0056] Another important aspect is to perform morphological evolution on the edge 1 of the flow channel itself to actively influence the flow and heat transfer in the near-wall region.

[0057] One variant is to design the side 1 of the flow channel into an arc 7 that bends inward or outward. This arc-shaped side wall can change the perimeter and area distribution of the flow channel cross section, affecting the development of the boundary layer.

[0058] Another approach is to design the channel edge 1 into a periodically undulating first wave shape 8. This undulating wall surface effectively disturbs the near-wall fluid, promoting mixing between the main flow and the fluid near the wall, disrupting the thermal boundary layer, and thus enhancing convective heat transfer. The amplitude and wavelength of the waves are important design parameters.

[0059] Another approach is to design the edge 1 of the flow channel into a repeating first sawtooth shape 9. The tips and valleys of the sawtooth can act as vortex generators, similarly strongly disturbing the boundary layer and enhancing heat transfer. The shape, angle, and depth of the sawtooth also affect its effectiveness.

[0060] Furthermore, longitudinal fins 10 can be provided on the side 1 of the flow channel, along the flow direction of the secondary working medium. These fins extend directly into the fluid, serving as an extended heat transfer surface, significantly increasing the effective heat exchange area on the secondary side. Furthermore, the longitudinal fins can also regulate and guide the fluid, or, under specific designs, be used to separate different flow zones within the flow channel.

[0061] In terms of the derivation of the geometric characteristics of the longitudinal section of the flow channel, that is, the flow channel profile along the flow direction of the secondary side working medium, such as Figure 3 As shown in b, various optimization designs can also be performed to enhance heat transfer.

[0062] One approach is to design the inner wall surface of the flow channel (e.g., the side of the partition wall 2 facing the secondary flow channel 4, or the inner surface of the side 1 of the flow channel) in the longitudinal direction into a second wave shape 11 with continuous and smooth undulations. When the fluid flows over this wavy surface, it experiences periodic acceleration and deceleration, as well as streamline bending. This can induce secondary flow and vortex streets, enhance macroscopic mixing of the fluid, effectively destroy and rebuild the thermal boundary layer, and thus improve the overall heat transfer coefficient.

[0063] Another approach is to install transverse fin structures 12 in the longitudinal cross-section of the flow channel. These transverse fins (also known as ribs or flow ribs) can be arranged perpendicular to the main flow direction or at a certain angle. They act as obstacles to forcibly change the main flow path of the fluid, forming recirculation and reattachment zones downstream of the fins. These areas typically have higher local heat transfer coefficients. Transverse fins also increase the heat transfer surface area.

[0064] Similarly, the longitudinal section of the flow channel can also be designed into a second sawtooth profile 13. This sawtooth wall also generates strong fluid disturbance and vortex by introducing periodic geometric mutations in the flow direction, thereby enhancing gas-liquid two-phase mixing and wall heat transfer.

[0065] These are Figure 3 The geometrically derived features shown in the example provide designers with a range of structural elements and configurations for optimized design. Designers can flexibly select and combine these features based on the specific heat transfer requirements of different sections of the secondary channel (e.g., promoting bubble nucleation, enhancing liquid film turbulence, increasing turbulence intensity, and expanding heat transfer area) to achieve optimal heat transfer performance and fluid dynamics.

[0066] In an embodiment of the present invention, since the secondary side flow channel 4 is divided into multiple functional sections with different geometric characteristics and internal structures (such as a single-phase heat transfer section, a saturated boiling section, and a drying section), how to achieve a smooth transition between these different sections is an important design consideration.

[0067] Reference Figure 5A three-dimensional schematic diagram clearly demonstrates that in a preferred embodiment of the present invention, the single-phase heat transfer section, saturated boiling section, and dry-up section are smoothly connected by a continuously changing curved surface. This means that at the junction of different functional sections, the geometry of the flow channel inner wall (such as the flow cross-sectional area, hydraulic diameter, or internal features such as fins) does not change abruptly, but instead is achieved through a transition area with a gradually changing profile.

[0068] For example, when transitioning from a single-phase heat transfer section with a relatively small flow cross-section to a saturated boiling section with a relatively large flow cross-section and potentially complex internal wall morphology, the flow channel walls are connected by a smoothly expanding curved section. Similarly, when transitioning from the saturated boiling section to the dry-down section with a larger flow cross-section and internally arranged rotating fins, a similar gradual transition design is adopted, with the starting ends of the fins also designed to gradually merge into the flow channel.

[0069] The main benefits of using this continuous surface for smooth transition connections are:

[0070] First, it reduces the additional flow resistance caused by abrupt changes in flow channel geometry. Dramatic cross-sectional expansion or contraction, or the sudden appearance of internal structure, can lead to separation of the fluid boundary layer, the generation of vortices, and large fluctuations in local pressure, all of which increase energy loss and, in other words, pressure drop. Smooth transitions help maintain flow field stability and reduce unnecessary energy dissipation.

[0071] Secondly, smooth transitions help avoid localized stress concentrations or hot spots at points of structural change. Sharp changes in geometry can lead to uneven heat flux distribution or create weak links in the mechanical structure where stress concentrations occur. The continuous curved transition design results in more uniform wall temperature and structural stress distribution, which helps improve the operational reliability and service life of the heat transfer channel.

[0072] Furthermore, for the secondary side working fluid, especially when it is in a two-phase flow state, a smooth transition helps to maintain the stable development of the flow pattern and avoid drastic flow pattern conversion or unstable flow phenomena caused by geometric mutations, such as flow stratification, backflow or pulsation.

[0073] Therefore, in the specific implementation of the present invention, although the characteristic structures of each functional segment are optimized for its specific heat transfer stage and are different, the connection between these segments is preferably gradual and smooth to ensure that the entire heat transfer channel has good fluid dynamics performance and structural integrity while achieving efficient heat transfer.

[0074] In an embodiment of the present invention, the structure of the segmented, variable-section steam generator boiling heat transfer flow channel is significantly complex. This complexity is reflected in the following aspects: the secondary side flow channel has variable flow cross-sectional geometry along the flow direction; each functional section may contain finely modified internal wall surface geometry (such as curved edges, wavy shapes, serrated shapes, longitudinal or transverse fins, etc.); and complex flow adjustment or heat transfer enhancement components (such as rotating fins) are installed within specific sections (such as the dry section). In addition, the different functional sections need to be smoothly transitioned through continuously changing curved surfaces.

[0075] Traditional manufacturing processes, such as subtractive or combined methods based on tube bending, welding, and machining (e.g., drilling and milling), face significant challenges in accurately and integrally creating these complex internal geometries and fine structures. In some cases, these processes are simply not feasible. For example, traditional processes struggle to achieve the required precision and integrity required to create precisely shaped rotating fins or fine wall corrugations within elongated, non-circular channels while ensuring smooth transitions between sections.

[0076] Therefore, the complex structure of the flow channel in the embodiment of the present invention is particularly suitable for its manufacture using additive manufacturing (AM) technology, also commonly known as 3D printing technology. Among various AM technologies, laser powder bed fusion (L-PBF) technology is a preferred solution for realizing the heat transfer flow channel described in the present invention because it can produce dense metal parts with excellent mechanical properties and has a high degree of flexibility in forming complex geometric shapes.

[0077] When using L-PBF technology to manufacture the heat transfer flow channel described in the present invention, its basic process includes: first, the detailed 3D CAD model of the heat transfer flow channel is sliced to generate cross-sectional data for each layer; then, a thin layer of metal powder material (such as high-temperature and corrosion-resistant nickel-based alloys, stainless steel, and other materials suitable for steam generator operating conditions) is laid in a molding cavity filled with a protective atmosphere (such as argon or nitrogen); then, a high-energy laser beam selectively melts the metal powder based on the cross-sectional data of the current layer, causing it to solidify and combine with the previous layer; the powder laying and laser melting process is repeated, layer by layer, until the entire heat transfer flow channel component (or its key parts) is formed in an integrated manner.

[0078] Additive manufacturing technology, especially L-PBF, brings the following key advantages to the design and implementation of the heat transfer channel of the present invention:

[0079] High geometric freedom: Flow channel structures with arbitrarily complex internal channels, fine surface features (such as tiny fins and corrugations), and internal components (such as integrally molded rotating fins) can be manufactured directly from CAD models without the need for traditional molds or complex assembly processes.

[0080] Integrated molding: Functional structures that originally required the combination of multiple parts to achieve (such as a variable-section channel with internal ribs) can be printed as a whole at one time, reducing the connection interface, improving the integrity and sealing of the structure, and possibly reducing the risk of potential defects introduced by connection processes such as welding.

[0081] Flexibility in material selection: L-PBF technology is applicable to a variety of metal materials, making it easy to select the most suitable material based on the specific operating requirements of the steam generator (such as temperature, pressure, and corrosive environment).

[0082] Rapid prototyping and iterative optimization: Prototypes can be quickly manufactured for testing and verification, and the design can be easily modified and iterated based on the test results, accelerating the development of new high-performance heat exchangers.

[0083] By adopting additive manufacturing technology, the complex and sophisticated design concept contained in the segmented variable-section boiling heat transfer flow channel proposed in this invention can be accurately realized, providing strong technical support for breaking through the limitations of traditional manufacturing processes on heat exchanger structure optimization and developing advanced steam generators with higher heat transfer efficiency and more compact structure.

[0084] In an embodiment of the present invention, the aforementioned segmented variable cross-section steam generator boiling heat transfer flow channel is intended to be used as a core heat exchange element in the steam generator to improve its overall performance.

[0085] A steam generator incorporating the heat transfer channels described herein will have its core heat exchange region (i.e., the evaporator core or heat transfer tube bundle region) comprised of one or more segmented, variable-section boiling heat transfer channel units, as described in detail above, or a channel bundle formed by a regular array of these channel units. The arrangement of these heat transfer channel units within the steam generator can be flexibly adjusted based on factors such as the overall steam generator design (e.g., vertical, horizontal, or integrated for a specific compact reactor), the design of the primary and secondary working fluid inlet and outlet manifolds, and the required total heat exchange power.

[0086] Specifically, in the steam generator design, the primary high-temperature working fluid (e.g., coolant from a nuclear reactor core) is introduced and distributed to each primary channel 3 that constitutes the heat transfer channel array. Simultaneously, secondary feedwater (e.g., preheated liquid water) is introduced and distributed to the inlet end (i.e., the beginning of the single-phase heat transfer section) of the corresponding secondary channel 4. The primary high-temperature working fluid flows downward or upward (depending on the specific design) in the primary channel 3, transferring its heat to the secondary working fluid in the secondary channel 4 through the shared partition wall 2.

[0087] When the secondary side working fluid flows in the secondary side flow channel 4, it will sequentially undergo the aforementioned single-phase heating, saturated boiling, and possible superheating (if a superheating section is designed). Since the secondary side flow channel 4 adopts a segmented variable cross-section design and has been structurally optimized according to the characteristics of each heat transfer stage (such as the small cross-section of the single-phase section, the wall reinforcement of the saturated boiling section, the rotating fins of the drying section, etc.), the heat transfer efficiency of the secondary side working fluid in the entire boiling and evaporation process is significantly improved. Ultimately, at the outlet end of the secondary side flow channel 4, high-temperature and high-pressure steam (or a high-dryness steam-water mixture, depending on whether it is a superheated steam generator) will be generated. These steam are then collected and exported to the steam generator to drive the steam turbine for power generation or for other industrial processes.

[0088] By adopting the segmented variable cross-section boiling heat transfer flow channel of the present invention, the steam generator constructed is expected to achieve performance improvements in one or more of the following aspects:

[0089] Higher heat transfer efficiency: Since each heat transfer stage is specifically enhanced, the heat transfer capacity per unit heat transfer area is improved, so that more heat can be transferred under the same temperature difference and flow conditions, or a smaller temperature difference is required to transfer the same amount of heat.

[0090] More compact structure and lighter weight: The use of non-circular basic cross-sections (such as quadrilaterals and hexagons) and improved heat transfer efficiency can reduce the total heat transfer area and number of flow channels required to meet the same heat transfer power requirements, or make the flow channels more densely arranged, thereby significantly reducing the size and weight of the steam generator's core heat exchange components and even the entire equipment. This is particularly important for the miniaturization and modularization of nuclear power plants.

[0091] Improved operational stability and safety: By better adapting to and managing the flow patterns at different stages of boiling heat transfer (e.g., by rotating fins to delay dry-out), the operational stability of the steam generator under different operating conditions can be improved, the safe operating margin can be widened, and the risks of local overheating or flow instability caused by deteriorated heat transfer may be reduced.

[0092] Potential material savings: Improved heat transfer efficiency and compact structure may lead to a reduction in the amount of high-performance materials required to manufacture steam generators, thereby reducing costs.

[0093] In summary, the application of the segmented, variable-section boiling heat transfer flow channel proposed in this invention to steam generator design, through its innovative structure and resulting performance advantages, can provide an effective technical approach for improving the economic efficiency, safety, and adaptability of nuclear power plants to future development needs. The specific structural parameters of this new steam generator, such as the number of flow channel units, their arrangement, overall length, and the length ratio of each segment, can be carefully designed and optimized based on specific application scenarios and performance indicators.

[0094] To further verify the beneficial effects of the segmented variable cross-section boiling heat transfer flow channel described in the present invention when applied to a steam generator, a prototype based on the principles of the present invention was developed and its heat transfer characteristics were experimentally studied. The design power of the prototype is approximately 1 / 30 of the power of a certain type of steam generator in the prior art (hereinafter referred to as "prior art SG"). Figure 6 As shown in the figure, the physical picture of the principle prototype is shown, and the main design parameters of the principle prototype are shown in Table 1.

[0095] Table 1 Principle prototype parameters

[0096] Power (MW) 0.8 Weight (kg) 29 Length (mm) 200 Width (mm) 100 Height(mm) 1200 <![CDATA[Primary side heat transfer area (m 2 )]]> 0.747 <![CDATA[Secondary side heat transfer area (m 2 )]]> 3.9 Material AM-316LN

[0097] For this prototype, performance tests were carried out under specific working conditions, such as Figure 7 As shown in Figure 2, the heat transfer performance test pictures of the prototype are shown. The target values of the test, the measured values of some key parameters, and the converted values (such as heat transfer power) obtained by further processing based on the measured values are summarized in Table 2.

[0098] Table 2 Experimental results

[0099] parameter Target value Measurements Conversion value Primary side inlet temperature (℃) 319.5 319.3 / Primary side outlet temperature (℃) / 286.6 / <![CDATA[Primary side flow rate (m 3 / h)]]> 20.83 21.3 / Heat exchange power (MW) 0.8 / 0.813 Secondary side inlet temperature (℃) 140 139 / Secondary side outlet temperature (℃) 290 291 / Secondary side outlet pressure (MPa) 4.5 4.6 / Primary side resistance (kPa) / 29 /

[0100] The experimental results in Table 2 show that, under experimental conditions, the prototype of the present invention achieved a heat exchange power of 0.813 MW, meeting and slightly exceeding the design target power of 0.8 MW. Furthermore, the secondary outlet steam temperature reached 291°C and the outlet pressure reached 4.6 MPa, both meeting design requirements. This demonstrates that the steam generator employing the flow channel design of the present invention can effectively achieve the intended energy conversion and steam generation functions. The measured flow resistance on the primary side was 29 kPa.

[0101] To more intuitively demonstrate the advancements brought about by the present invention's technical solution, the experimental results of the prototype were compared with the performance parameters of the prior art SG. Since the prototype's design functionality is 1 / 30 of that of the prior art SG, the corresponding parameters of the prior art SG were converted to a 1:30 ratio for comparison. A detailed performance comparison is shown in Table 3.

[0102] Table 3 Performance comparison table

[0103]

[0104] According to the comparative data in Table 3, it can be clearly seen that, under the premise of achieving similar power output (converted at 1:30), the principle prototype using the segmented variable cross-section boiling heat transfer flow channel of the present invention is:

[0105] Its weight has been significantly reduced from 59.2kg to 29kg, a reduction of 50.9%.

[0106] Its outer volume is from 0.076m 3 Significantly reduced to 0.024m 3 , the reduction reached 68.4%.

[0107] The primary side flow resistance was significantly reduced from the converted 81kPa to 29kPa, a reduction of 64.0%.

[0108] At the same time, the volumetric heat transfer area of the prototype (area efficiency, defined as total heat transfer area / external volume) reached 464.7m 2 / m 3 , much higher than the 320m of the existing technology SG 2 / m 3 (This area efficiency comparison is based on the original parameters of the prior art SG. Since the outer volume and heat exchange area of the comparison base are proportionally reduced, its area efficiency remains unchanged in theory), which further demonstrates the significant advantages of the design of the present invention in terms of structural compactness and space utilization.

[0109] These experimental data and comparative results fully demonstrate that the proposed segmented variable cross-section steam generator boiling heat transfer flow channel technology can effectively maintain or even improve heat transfer performance while significantly reducing the weight and volume of the steam generator and significantly reducing primary-side flow resistance. This has important practical significance and application value for improving the overall economy, compactness, and operational efficiency of nuclear power plants.

[0110] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A boiling heat transfer channel of a segmented variable cross-section steam generator, characterized in that: include: at least one primary flow channel and at least one secondary flow channel, the primary flow channel and the secondary flow channel being separated by a common partition wall, the secondary flow channel having a non-circular basic cross-sectional shape that enables close arrangement; The secondary side flow channel is divided into at least two sections along its length direction, that is, the flow direction of the secondary side working medium, and the at least two sections correspond to different boiling heat transfer stages of the secondary side working medium respectively; Moreover, in the at least two sections of the secondary side flow channel, the geometric dimensions of its flow cross section, the surface features of the inner wall, or at least one of the flow disturbances or heat transfer enhancement elements arranged inside it are specifically configured according to the flow pattern and heat transfer characteristics of the boiling heat transfer stage corresponding to each section, so that the at least one feature of each section is different from each other.

2. The boiling heat transfer channel of the segmented variable cross-section steam generator according to claim 1, characterized in that: The basic cross-sectional shape of the secondary side flow channel is a quadrilateral or a hexagon.

3. The boiling heat transfer channel of the segmented variable cross-section steam generator according to claim 2, characterized in that: The secondary side flow channel is divided into a single-phase heat transfer section, a saturated boiling section and a drying section along its length direction.

4. The boiling heat transfer channel of the segmented variable cross-section steam generator according to claim 3, characterized in that: The characteristics of the single-phase heat transfer section are: Compared with the saturated boiling section, the flow cross-sectional area of the secondary side flow channel is relatively reduced, so as to improve the flow velocity and flow stability of the secondary side working medium.

5. The boiling heat transfer channel of the segmented variable cross-section steam generator according to claim 3, characterized in that: The characteristics of the saturated boiling section are: The quadrilateral or hexagonal basic cross-sectional shape is adopted, and at least one of the following heat transfer enhancement structures is provided on its inner wall surface: The flow channel edge has arc-shaped derivation, wave-shaped derivation, zigzag-shaped derivation, and longitudinal fin derivation; Or the wavy derivation of the longitudinal section of the flow channel, the transverse fin structure derivation, and the serrated derivation.

6. The boiling heat transfer channel of a segmented variable cross-section steam generator according to claim 3, characterized in that: The characteristics of the dry section are: Compared with the saturated boiling section, the flow cross-sectional area of the secondary side flow channel is relatively larger, and fins are arranged inside the secondary side flow channel for generating a rotating flow and guiding the droplets to the heat transfer wall surface.

7. The boiling heat transfer channel of a steam generator with segmented variable cross-section according to claim 6, characterized in that: The fins are rotating fins, and their structure can guide the fluid to generate a rotating flow, thereby using centrifugal force to separate the droplets entrained in the secondary side working fluid and guide them to the heat transfer wall of the secondary side flow channel to delay drying and enhance heat transfer.

8. The boiling heat transfer channel of a steam generator with segmented variable cross-section according to claim 3, characterized in that: The single-phase heat transfer section, the saturated boiling section and the drying section are smoothly transitionally connected via a continuously changing curved surface.

9. The boiling heat transfer channel of a steam generator with segmented variable cross-section according to claim 1, characterized in that: The flow channel is made of metal material and is suitable for being integrally manufactured by additive manufacturing technologies such as laser powder bed melting.

10. A steam generator, characterized in that: The core heat transfer component thereof comprises a plurality of boiling heat transfer flow channels of the segmented variable cross-section steam generator as described in any one of claims 1 to 9.

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