Passive heat exchanger induced air cover synergistic structure and optimization design method thereof

Abstract

The invention provides a passive heat exchanger air inducing cover synergistic structure and an optimization design method thereof, relates to the technical field of heat exchanger structure design, and solves the problems that an existing heat exchanger is low in ventilation rate and serious in airflow lateral loss. Wherein the optimal design object is the arrangement angle of the passive heat exchanger air inducing cover and the projection length of the passive heat exchanger air inducing cover on the end face; in the optimization design process, the ventilation rate of the passive heat exchanger under the air inducing covers of various specifications is calculated in a porous medium model simulation mode, the air inducing cover arrangement angle and the projection length meeting the preset engineering requirement are selected according to the ventilation rate, and the corresponding air inducing cover synergistic structure is determined; the induced air cover synergistic structure is a circle of plate-shaped induced air cover arranged around the periphery of the end face of the heat exchanger serving as an airflow inlet. The ventilation rate and the heat dissipation performance of the passive heat exchanger under the natural air cooling condition can be remarkably improved, and an efficient, reliable and low-maintenance heat dissipation solution is provided for a high-power-density wind turbine generator.

Description

Technical Field

[0001] The present invention relates to the technical field of heat exchanger structure design, and in particular to a passive heat exchanger induced draft hood efficiency enhancement structure and an optimization design method thereof. Background Art

[0002] In wind turbine systems, controlling the temperature rise of key electrical components and mechanical transmission units, such as converters, gearboxes, generators, and frequency converters, directly impacts the unit's operational reliability and lifecycle. This type of equipment generally utilizes passive heat exchange structures as its core cooling solution. The efficiency of these heat exchangers directly constrains the compactness and economic efficiency of the overall unit design. Current industry practice demonstrates that these cooling devices experience significant performance bottlenecks under natural convection conditions.

[0003] Due to the lack of a mandatory airflow guidance mechanism, ambient air flows through the heat sink interface in a non-directional manner. A large amount of available air, without fully participating in heat exchange, escapes disorderly from the edges of the heat sink, creating ineffective airflow channels. This phenomenon causes the actual airflow in the core heat exchange area to fall far short of the theoretically available airflow, resulting in high lateral air loss and a significant waste of effective cooling air resources.

[0004] Traditional structures present a dual dilemma under these operating conditions: on the one hand, the heat dissipation surface must maintain a sufficient airflow cross-section to facilitate heat conduction; on the other hand, the open physical boundary makes it difficult to constrain the airflow trajectory. This contradiction prevents the heat dissipation unit from establishing an efficient airflow pattern, resulting in insufficient contact time between the heat exchange medium and the heat dissipation surface, increased boundary layer thermal resistance, and ultimately a decrease in overall heat dissipation power density. Especially in areas with high heat loads, the risk of local overheating increases significantly as the proportion of ineffective airflow outages increases.

[0005] Existing technical solutions often compensate for efficiency losses by increasing the physical size of the heat sink, but this directly leads to an increase in the size of the unit, which not only increases material costs, but also restricts the lightweight and modular design process of wind turbines. In engineering practice, this contradiction has become a key technical obstacle faced in improving the power density of a single machine. In addition, the imbalance between heat dissipation efficiency and space economy objectively restricts the expansion of the performance boundaries of wind power equipment under complex environmental conditions. Especially in low wind speed conditions or high temperature environments, the attenuation of heat dissipation efficiency will directly trigger the derating of equipment and affect power generation revenue. Therefore, it is urgent to develop a new airflow guidance mechanism to optimize the distribution characteristics of the heat dissipation field, break through the bottleneck of airflow control in the natural convection field, and achieve a leap in heat dissipation efficiency while maintaining structural simplicity. This has become a technical direction that the industry continues to explore. Summary of the Invention

[0006] The present invention aims to address the low air permeability and severe lateral airflow losses experienced by traditional passive heat exchangers under natural air cooling conditions. Therefore, a passive heat exchanger induced draft hood efficiency enhancement structure and its optimized design method are proposed. By adding the induced draft hood efficiency enhancement structure, the present invention significantly improves the air permeability and heat dissipation performance of the passive heat exchanger under natural air cooling conditions, providing an efficient, reliable, and low-maintenance heat dissipation solution for high-power density wind turbines.

[0007] The present invention adopts the following technical solutions to achieve the purpose: A passive heat exchanger induced draft hood efficiency enhancement structure, wherein the passive heat exchanger has a first end face and a second end face arranged opposite to each other; the first end face is an air flow inlet or an air flow outlet, and the second end face is correspondingly an air flow outlet or an air flow inlet; the first end face and the second end face are a flow path of the air flow inside the passive heat exchanger, and multiple layers of fins are arranged between the first end face and the second end face; the induced draft hood efficiency enhancement structure is a circle of plate-shaped induced draft hood arranged around the first end face or the second end face serving as the air flow inlet; the induced draft hood is arranged at an angle of 0° to 90° relative to the first end face or the second end face, wherein the 0° arrangement means that the induced draft hood and the first end face or the second end face are in the same plane, and the 90° arrangement means that the induced draft hood is perpendicular to the first end face or the second end face where it is located, and extends in the direction away from the air flow outlet.

[0008] Preferably, the air induced hood is arranged at an angle of 0° relative to the first end face or the second end face, that is, the air induced hood and the first end face or the second end face where it is located are in the same plane.

[0009] The present invention also provides an optimization design method for the induced draft hood efficiency enhancement structure of a passive heat exchanger. The optimization design objects are the arrangement angle of the induced draft hood and the projected length of the induced draft hood on the first end face or the second end face thereof in claim 1. By adopting a porous medium model simulation method, the air permeability of the passive heat exchanger under induced draft hoods of various specifications is calculated. According to the air permeability, the arrangement angle and projected length of the induced draft hood that meet the preset engineering requirements are selected, and the corresponding induced draft hood efficiency enhancement structure is determined to achieve optimized design.

[0010] Specifically, the calculation of the air permeability of passive heat exchangers under induced draft hoods of various specifications includes the following steps: S1. Through simulation analysis of the natural convection characteristics of a single-layer fin in a passive heat exchanger, a pressure loss model is established between the incoming air velocity and the pressure loss per unit length of the fin. S2. Based on the pressure loss model, the fins and airflow path of the passive heat exchanger are simplified into an isotropic porous medium model with equivalent flow resistance; S3. Applying the porous medium model simplified in step S2, performing overall simulation calculations on passive heat exchangers equipped with induced draft hoods of different specifications, and obtaining the pressure loss between the air inlet and air outlet of the passive heat exchanger for each specification; S4. Using a pre-established pressure loss and wind speed behind the plate relationship model, the pressure loss value obtained in step S3 is converted into an actual wind speed value corresponding to the wind speed behind the passive heat exchanger plate; S5. For each specification of the hood, based on the conversion result of step S4, calculate the ratio of the wind speed behind the hood to the incoming wind speed to obtain the air permeability, which is used as an indicator to evaluate the effect of the hood's efficiency-enhancing structure, and complete the optimized design of the hood's efficiency-enhancing structure.

[0011] Specifically, in step S1, natural convection simulation is performed on a single-layer fin in a passive heat exchanger to calculate the pressure loss value between the front and rear inlets and outlets of the fin in the airflow path, thereby establishing a dynamic correlation equation between the incoming wind speed and the pressure loss value as a pressure loss model.

[0012] Furthermore, in step S2, the porous media model is constructed by adding a momentum source to the standard fluid flow equation. After modeling, the momentum source is obtained It consists of viscous loss term and inertial loss term, as shown below:

[0013] Where, Representative The momentum source in the momentum equation is Represents the direction index of the momentum equation, which takes values ​​of 1, 2, or 3, corresponding to the x, y, or z direction, respectively; represents the first specified matrix, which is used to represent the coefficients related to viscous losses; Represents the viscosity of the fluid; Represents the speed The direction of the component, Represents the direction index of the velocity component, with a value of 1, 2, or 3, corresponding to the x, y, or z direction, respectively; represents the second specified matrix, which is used to represent the coefficients related to inertia loss; represents the density of the fluid; Represents the velocity modulus, that is, the velocity of the fluid; By adding a momentum source , which affects the pressure gradient in the porous unit and produces a pressure loss that is proportional to the fluid velocity or the square of the velocity in the unit; then based on the momentum source The modeling principle of is applied to the case of simple homogeneous porous media as follows:

[0014] Where, represents the permeability; Represents the inertia loss coefficient; this formula comes from the first specified matrix and the second specified matrix After specifying them as diagonal matrices, the first specified matrix The diagonal elements after being designated as a diagonal matrix are , the second specified matrix The diagonal elements after being designated as a diagonal matrix are ; While applying to simple homogeneous porous media, the momentum source Modeled as a power law function of velocity, as follows:

[0015] Where, Represents the coefficient related to the medium characteristics; Representative decision Momentum Source The coefficient of the degree of influence.

[0016] Furthermore, the modeling process of the porous media model also includes the modeling of the packed bed, and the modeling of the packed bed also applies the permeability and inertia loss coefficient ; First, use the Ergun equation to derive the relevant constants as follows:

[0017] When simulating the laminar flow of a packed bed based on the above equation, the second term is omitted, resulting in the Blake-Kozeny equation, as follows:

[0018] In the above two equations, represents pressure loss; represents the bed depth, i.e. the vertical distance between the first end face and the second end face in a passive heat exchanger; represents the average particle diameter; represents the void fraction, which is defined as the ratio of the void volume of the airflow flow path to the volume of the packed bed area of ​​the fin; Represents the apparent velocity of a fluid as it passes through a porous medium; based on a momentum source The definitions of the formulas and the Ergun equation are used to determine the permeability of the porous media model that characterizes the passive heat exchanger. and inertia loss coefficient The definition of is as follows:

[0019]

[0020] The isotropic porous medium model is obtained and used for the subsequent overall simulation calculation of the passive heat exchanger.

[0021] Specifically, in step S3, the input condition for the simulation calculation is the incoming wind speed and the fin simulation model of the passive heat exchanger; the simulation output is the first pressure loss of the first and second end faces of the passive heat exchanger and wind speed behind the board ; Based on the first pressure loss Calculate the pressure loss per unit length, that is, use the first pressure loss Divide by the perpendicular distance between the first end face and the second end face ; Thus, the pressure loss simulation data between the air flow inlet and outlet of the passive heat exchanger is obtained.

[0022] Specifically, in step S4, based on the pressure loss simulation data of the passive heat exchanger, the incoming wind speed is constructed. The first relationship model between the pressure loss per unit length and the first pressure loss is constructed Wind speed behind the board The first relationship model is used to set the medium characteristic correlation coefficient and velocity influence coefficient of the porous medium model during the simulation process, and the second relationship model is used to set the second pressure loss of the passive heat exchanger with different specifications of induced draft hoods installed. , calculate the corresponding wind speed behind the board .

[0023] Specifically, in step S5, the air permeability of the passive heat exchanger under the induced draft hood of each specification is determined, which is the corresponding wind speed behind the plate. and incoming wind speed The ratio is used as an indicator to evaluate the effect of the hood efficiency-enhancing structure, and then the hood layout angle and projection length that meet the preset engineering requirements are obtained.

[0024] In summary, due to the adoption of this technical solution, the beneficial effects of the present invention are as follows: This invention improves the airflow distribution characteristics in natural convection fields through a high-efficiency structural design. The induced draft hood effectively suppresses the disordered lateral escape of airflow, directing the available airflow toward the core heat exchange area and substantially improving air permeability. As a result, the contact efficiency between the heat dissipation medium and the heat exchange surface of the passive heat exchanger is optimized, significantly reducing boundary layer thermal resistance and achieving a significant increase in overall heat dissipation power density.

[0025] This invention resolves the inherent conflict between heat dissipation efficiency and space usage while maintaining structural simplicity. The efficiency-enhancing structure meets the temperature control requirements of high-heat-load areas without relying on external forced air ducts or additional energy-consuming devices, creating the foundation for increasing the equipment's power density. The heat exchanger itself, coupled with the induced draft hood, is also a relatively compact structure, maintaining cabin space utilization and reducing the material consumption and manufacturing costs required for complex improvements, thus promoting lightweight and modular design of the unit.

[0026] This invention, by introducing physical models to simplify complex flow field simulations at the R&D and design level, significantly reduces computing resource requirements and simulation time, thereby improving the efficiency of optimizing heat dissipation structure parameters. This significantly shortens the design verification cycle, providing technical support for rapidly responding to customized requirements under diverse environmental conditions and enhancing the environmental adaptability of various types of passive heat exchangers and their induced draft hood enhancement structures.

[0027] The present invention improves heat dissipation reliability while reducing the operation and maintenance costs throughout the entire life cycle. Through an economical and convenient design optimization method, it avoids the energy consumption requirements and failure risks of the heat dissipation system to a certain extent. It is suitable for unmanned scenarios of wind farms in remote areas, and provides a basic guarantee for the continuous and efficient power generation of wind turbines. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention further illustrates its implementation and technical solutions in detail through the following drawings, which specifically include 6 drawings as follows: Figure 1 This is a schematic diagram of the overall structure of the induced draft hood efficiency enhancement structure of the present invention; Figure 2 Schematic diagram of the angle arrangement range of the induced draft hood in the present invention; Figure 3 Schematic diagram of the angle arrangement and projected length of the induced draft hood in the present invention; Figure 4 Schematic diagram of the overall process of the method of the present invention for calculating air permeability; Figure 5 is the incoming wind speed in the method of the present invention And the fitting diagram of pressure loss per unit length; Figure 6 The first pressure loss in the method of the present invention Wind speed behind the board Schematic diagram of the fitting.

[0029] The meanings of the symbols in the accompanying drawings are as follows: 1- Passive heat exchanger, 2- induced draft hood. DETAILED DESCRIPTION

[0030] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0031] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0032] Example 1 like Figure 1 The figure shows a passive heat exchanger induced draft hood efficiency enhancement structure, wherein the passive heat exchanger has a first end face and a second end face arranged opposite each other; the first end face is an airflow inlet or outlet, and the second end face is an airflow outlet or inlet accordingly; the airflow path within the passive heat exchanger is between the first and second end faces, and multiple layers of fins are arranged between the first and second end faces. The induced draft hood efficiency enhancement structure is a plate-shaped induced draft hood arranged around the first or second end face, which serves as the airflow inlet. Figure 1 Only the plate-shaped induced draft hoods outside two adjacent sides in the plane of the rectangular heat exchanger are shown, and the induced draft hood structures of the remaining two sides are omitted in the figure.

[0033] like Figure 2 As shown, the induced draft hood is arranged at an angle of 0° to 90° relative to the first end face or the second end face, wherein the 0° arrangement means that the induced draft hood and the first end face or the second end face on which it is located are in the same plane, and the 90° arrangement means that the induced draft hood is perpendicular to the first end face or the second end face on which it is located and extends in the direction away from the air flow outlet.

[0034] As a preference of this embodiment, the induced draft hood is arranged at an angle of 0° relative to the first end face or the second end face, that is, the induced draft hood and the first end face or the second end face where it is located are in the same plane.

[0035] Example 2 Based on the hardware structural features of the induced draft hood in Example 1, this embodiment provides an optimization design method for the induced draft hood efficiency enhancement structure of a passive heat exchanger. Figure 3 As shown, the optimized design object is the layout angle of the induced draft hood in Example 1. and the projected length of the hood on the first or second end face thereof .

[0036] The core of the method of this embodiment is: by using a porous medium model simulation method, the air permeability of passive heat exchangers under induced draft hoods of various specifications is calculated, and the induced draft hood layout angle and projection length that meet the preset engineering requirements are selected according to the air permeability, and the corresponding induced draft hood efficiency enhancement structure is determined to achieve optimized design.

[0037] In this embodiment, the air permeability of the passive heat exchanger under the induced draft hood of various specifications is calculated. Figure 4 The process is briefly described as follows: S1. Through simulation analysis of the natural convection characteristics of a single-layer fin in a passive heat exchanger, a pressure loss model is established between the incoming air velocity and the pressure loss per unit length of the fin. S2. Based on the pressure loss model, the fins and airflow path of the passive heat exchanger are simplified into an isotropic porous medium model with equivalent flow resistance; S3. Applying the porous medium model simplified in step S2, performing overall simulation calculations on passive heat exchangers equipped with induced draft hoods of different specifications, and obtaining the pressure loss between the air inlet and air outlet of the passive heat exchanger for each specification; S4. Using a pre-established pressure loss and wind speed behind the plate relationship model, the pressure loss value obtained in step S3 is converted into an actual wind speed value corresponding to the wind speed behind the passive heat exchanger plate; S5. For each specification of the hood, based on the conversion result of step S4, calculate the ratio of the wind speed behind the hood to the incoming wind speed to obtain the air permeability, which is used as an indicator to evaluate the effect of the hood's efficiency-enhancing structure, and complete the optimized design of the hood's efficiency-enhancing structure.

[0038] First, in step S1, natural convection simulation is performed on a single-layer fin in a passive heat exchanger to calculate the pressure loss between the front and rear inlets and outlets of the fin in the airflow path. This establishes a dynamic correlation equation between the incoming wind speed and the pressure loss value, which serves as the principle of the pressure loss model and guides subsequent steps.

[0039] In step S2 of this embodiment, the porous medium model is constructed by adding a momentum source to the standard fluid flow equation. After modeling, the momentum source is obtained It consists of viscous loss term and inertial loss term, as shown below:

[0040] Where, Representative The momentum source in the momentum equation is Represents the direction index of the momentum equation, which takes values ​​of 1, 2, or 3, corresponding to the x, y, or z direction, respectively; represents the first specified matrix, which is used to represent the coefficients related to viscous loss, which describes the resistance caused by viscosity when the fluid flows in porous media; Represents the viscosity of the fluid; Represents the speed The direction of the component, Represents the direction index of the velocity component, with a value of 1, 2, or 3, corresponding to the x, y, or z direction, respectively; represents the second specified matrix, which is used to express the coefficients related to inertial loss, which describes the resistance caused by inertia when the fluid flows in the porous medium; represents the density of the fluid; Represents the velocity modulus, that is, the velocity of the fluid.

[0041] In this embodiment, by adding a momentum source , which affects the pressure gradient in the porous unit and produces a pressure loss that is proportional to the fluid velocity or the square of the velocity in the unit; by adjusting the first specified matrix and the second specified matrix , can simulate the flow characteristics of different porous media, that is, applied to passive heat exchangers with different fin layouts. The modeling principle of is applied to the case of simple homogeneous porous media as follows:

[0042] Where, represents the permeability; Represents the inertia loss coefficient; this formula comes from the first specified matrix and the second specified matrix After specifying them as diagonal matrices, the first specified matrix The diagonal elements after being designated as a diagonal matrix are , the second specified matrix The diagonal elements after being designated as a diagonal matrix are .

[0043] While applying to simple homogeneous porous media, the momentum source Modeled as a power law function of velocity, as follows:

[0044] Where, Represents the coefficient related to the medium characteristics; Representative decision Momentum Source The coefficient of the degree of influence.

[0045] In this embodiment, It usually represents the resistance of porous media to fluid flow, which may include factors such as the geometric structure of the material and surface roughness; As an index, it determines the influence of velocity on momentum source. When , the formula degenerates into a linear relationship, similar to the viscous loss term; when When , the formula is more similar to the inertia loss term; if other values ​​are used, it represents a more complex nonlinear relationship, which can better fit the experimental data or the flow characteristics of a specific medium during the simulation process.

[0046] In this embodiment, the modeling process of the porous media model also includes the modeling of the packed bed, and the modeling of the packed bed also applies the permeability and inertia loss coefficient ; First, use the Ergun equation to derive the relevant constants as follows:

[0047] When simulating laminar flow in a packed bed based on the above equation, the second term can be omitted due to the small Reynolds number, resulting in the Blake-Kozeny equation, as shown below:

[0048] At this time, only the influence of viscosity loss is considered. In the above two equations, represents pressure loss; represents the bed depth, i.e. the vertical distance between the first end face and the second end face in a passive heat exchanger; represents the average particle diameter; represents the void fraction, which is defined as the ratio of the void volume of the airflow path to the volume of the packed bed area of ​​the fin; Represents the superficial velocity of the fluid when it passes through a porous medium. The definition of is the velocity of the fluid at the same flow rate when the entire packed bed or porous medium is completely void. It is equal to the total flow rate divided by the cross-sectional area of ​​the packed bed or porous medium, and does not take into account the space occupied by the particles. The actual velocity It is the average velocity of the fluid in the real void, that is, the velocity after taking into account the space occupied by particles; due to the space occupied by particles, the actual velocity will be faster than the apparent velocity, and the relationship between the two can be obtained through the void ratio Make an association.

[0049] In this embodiment, based on the momentum source The definitions of the formulas and the Ergun equation can be used to determine the permeability of the porous media model that characterizes the passive heat exchanger. and inertia loss coefficient The definition of is as follows:

[0050]

[0051] The isotropic porous medium model is obtained and used for the subsequent overall simulation calculation of the passive heat exchanger.

[0052] In step S3 of this embodiment, the input condition for the simulation calculation is the incoming wind speed and the fin simulation model of the passive heat exchanger; the simulation output is the first pressure loss of the first and second end faces of the passive heat exchanger and wind speed behind the board ; Based on the first pressure loss Calculate the pressure loss per unit length, that is, use the first pressure loss Divide by the perpendicular distance between the first end face and the second end face ; Thus, the pressure loss simulation data between the air flow inlet and outlet of the passive heat exchanger is obtained.

[0053] In step S4 of this embodiment, based on the pressure loss simulation data of the passive heat exchanger, the pressure loss simulation data of the single-layer fin shown in Table 1 below can be used to construct the incoming wind speed. The first relationship model between and pressure loss per unit length can be found in Figure 5 At the same time, the first pressure loss is also constructed Wind speed behind the board The second relational model can be found in Figure 6 's hint.

[0054] Table 1 Schematic diagram of pressure loss simulation data of single-layer fin

[0055] The first relationship model and the second relationship model can be understood as the basic model for further simulation and comparative analysis of the passive heat exchanger, because they involve various key parameters for calculating the air permeability. The first relationship model is used to calculate the medium characteristic correlation coefficient of the porous medium model during the simulation process. and speed influence coefficient The second relationship model is used to calculate the second pressure loss of the passive heat exchanger with different specifications of induced draft hoods installed. , calculate the corresponding wind speed behind the board .

[0056] Finally, in step S5, the air permeability of the passive heat exchanger under the induced draft hood of each specification is determined, which is the corresponding wind speed behind the plate. and incoming wind speed The ratio is used as an indicator to evaluate the effect of the hood efficiency-enhancing structure, and then the hood layout angle and projection length that meet the preset engineering requirements are obtained.

[0057] This example uses this method to simulate and analyze the effect of the air permeability of the same passive heat exchanger under hoods of different specifications. After exploring the variation pattern, the key points of the optimal design of the hood are as follows: First, the passive heat exchanger with an induced draft hood efficiency enhancement structure has a higher air permeability than the same passive heat exchanger without an induced draft hood, and the natural air cooling and heat dissipation effect is better.

[0058] For the arrangement angle of the hood From 0° to 90°, the air permeability at 0° is optimal. At 0°, the hood inlet plane is parallel to the passive heat exchanger surface, effectively aligning with it. Airflow enters the heat exchanger primarily through suction generated by the negative pressure zone behind the heat exchanger. Because the inlet and heat exchanger surface are coplanar or nearly so, and the airflow and suction directions are essentially aligned, there's virtually no significant airflow separation at the inlet. This increases the air permeability in this scenario, and simulations have verified that this is the maximum air permeability.

[0059] As the angle increases from 0°, the hood inlet no longer adheres closely to the heat exchanger surface, instead forming a "flared" shape with a large, angled, outward-flapping shape. This leads to increased inlet losses and flow separation, leading to a decrease in air permeability, as shown in simulations. Flow separation primarily occurs at the outer edge of the hood inlet, away from the heat exchanger, creating a large external vortex zone. Separation, however, decreases on the inner side, closer to the heat exchanger.

[0060] From its lowest point after 0°, the air permeability begins to recover as the angle increases. At this point, as the hood angle increases, the hood shape becomes more like a slowly expanding tube. While inlet losses still exist, the internal flow path is smoother. After entering the hood, the airflow needs to turn at a smaller angle, avoiding the severe separation and secondary flow that can occur on the inner wall of the hood at small angles. However, even after the final tilt angle is increased to 90 degrees, the recovered air permeability remains below the 0° level, because 0° minimizes inlet losses and maximizes suction efficiency.

[0061] As for the projection length of the hood on its first end face or second end face Through simulation experiments with different specifications, it was found that, taking the layout angle of 0° as an example, as the projection length With the extension of the ventilation rate, the ventilation rate will be further significantly improved, but the growth rate here will increase with the The extension shows a decreasing trend.

[0062] Through the above-mentioned simulation method, this embodiment can determine specific design parameter indicators that meet the air permeability requirements when optimizing the design of the induced draft hood efficiency enhancement structure for a passive heat exchanger by simulating air permeability data under different specifications. After considering factors such as material costs, actual engineering manufacturing and application are carried out. This not only improves the air permeability of the heat exchanger with a simple structure, but also significantly reduces the resources and time costs required for the design process, allowing for rapid application in engineering practice.

Claims

1. A passive heat exchanger induced draft hood efficiency enhancement structure, wherein the passive heat exchanger has a first end face and a second end face disposed opposite each other; the first end face serves as an airflow inlet or outlet, and the second end face serves as an airflow outlet or inlet, respectively; a flow path within the passive heat exchanger is defined between the first and second end faces, and multiple layers of fins are disposed between the first and second end faces; and characterized in that: The air induced hood enhancement structure is a plate-shaped air induced hood arranged around the first end face or the second end face serving as the air flow inlet; the air induced hood is arranged at an angle of 0° to 90° relative to the first end face or the second end face, wherein the 0° arrangement means that the air induced hood and the first end face or the second end face are in the same plane, and the 90° arrangement means that the air induced hood is perpendicular to the first end face or the second end face where it is located, and extends in the direction away from the air flow outlet.

2. The passive heat exchanger induced draft hood efficiency enhancement structure according to claim 1, characterized in that: The induced draft hood is arranged at an angle of 0° relative to the first end face or the second end face, that is, the induced draft hood and the first end face or the second end face where it is located are in the same plane.

3. A method for optimizing the design of a passive heat exchanger induced draft hood efficiency enhancement structure, characterized by: The objects of optimized design are the arrangement angle of the induced draft hood and the projected length of the induced draft hood on the first end face or the second end face thereof in claim 1; by adopting the method of porous medium model simulation, the air permeability of the passive heat exchanger under the induced draft hoods of various specifications is calculated, and the arrangement angle and projected length of the induced draft hood that meet the preset engineering requirements are selected according to the air permeability, and the corresponding induced draft hood efficiency enhancement structure is determined to achieve optimized design.

4. The optimization design method according to claim 3, characterized in that: Calculating the air permeability of passive heat exchangers under various sizes of induced draft hoods involves the following steps: S1. Through simulation analysis of the natural convection characteristics of a single-layer fin in a passive heat exchanger, a pressure loss model is established between the incoming air velocity and the pressure loss per unit length of the fin. S2. Based on the pressure loss model, the fins and airflow path of the passive heat exchanger are simplified into an isotropic porous medium model with equivalent flow resistance; S3. Applying the porous medium model simplified in step S2, performing overall simulation calculations on passive heat exchangers equipped with induced draft hoods of different specifications, and obtaining the pressure loss between the air inlet and air outlet of the passive heat exchanger for each specification; S4. Using a pre-established pressure loss and wind speed model, convert the pressure loss value obtained in step S3 into the actual wind speed value corresponding to the wind speed behind the passive heat exchanger plate; S5. For each specification of the hood, based on the conversion result of step S4, calculate the ratio of the wind speed behind the hood to the incoming wind speed to obtain the air permeability, which is used as an indicator to evaluate the effect of the hood's efficiency-enhancing structure, and complete the optimized design of the hood's efficiency-enhancing structure.

5. The optimization design method according to claim 4, characterized in that: In step S1, natural convection simulation is performed on a single-layer fin in a passive heat exchanger to calculate the pressure loss between the front and rear inlets and outlets of the fin in the airflow path, thereby establishing a dynamic correlation equation between the incoming wind speed and the pressure loss value as a pressure loss model.

6. The optimization design method according to claim 4, characterized in that: In step S2, the porous media model is constructed by adding a momentum source to the standard fluid flow equation After modeling, the momentum source is obtained It consists of viscous loss term and inertial loss term, as shown below: Where, Representative The momentum source in the momentum equation is Represents the direction index of the momentum equation, which takes values ​​of 1, 2, or 3, corresponding to the x, y, or z direction, respectively; represents the first specified matrix, which is used to represent the coefficients related to viscous losses; Represents the viscosity of the fluid; Represents the speed The direction of the component, Represents the direction index of the velocity component, with a value of 1, 2, or 3, corresponding to the x, y, or z direction, respectively; represents the second specified matrix, which is used to represent the coefficients related to inertia loss; represents the density of the fluid; Represents the velocity modulus, that is, the velocity of the fluid; By adding a momentum source , which affects the pressure gradient in the porous unit and produces a pressure loss that is proportional to the fluid velocity or the square of the velocity in the unit; then based on the momentum source The modeling principle of , which is applied to the case of simple homogeneous porous media, is as follows: Where, represents the permeability; Represents the inertia loss coefficient; this formula comes from the first specified matrix and the second specified matrix After specifying them as diagonal matrices, the first specified matrix The diagonal elements after being designated as a diagonal matrix are , the second specified matrix The diagonal elements after being designated as a diagonal matrix are ; While applying to simple homogeneous porous media, the momentum source Modeled as a power law function of velocity, as follows: Where, Represents the coefficient related to the medium characteristics; Representative decision Momentum Source The coefficient of the degree of influence.

7. The optimization design method according to claim 6, characterized in that: The modeling process of the porous media model also includes the modeling of the packed bed, and the modeling of the packed bed also applies the permeability and inertia loss coefficient ; First, use the Ergun equation to derive the relevant constants as follows: When simulating the laminar flow of a packed bed based on the above equation, the second term is omitted, resulting in the Blake-Kozeny equation, as follows: In the above two equations, represents pressure loss; represents the bed depth, i.e. the vertical distance between the first end face and the second end face in a passive heat exchanger; represents the average particle diameter; represents the void fraction, which is defined as the ratio of the void volume of the airflow flow path to the volume of the packed bed area of ​​the fin; Represents the apparent velocity of a fluid as it passes through a porous medium; based on a momentum source The definitions of the formulas and the Ergun equation are used to determine the permeability of the porous media model that characterizes the passive heat exchanger. and inertia loss coefficient The definition of is as follows: The isotropic porous medium model is obtained and used for the subsequent overall simulation calculation of the passive heat exchanger.

8. The optimization design method according to claim 4, characterized in that: In step S3, the input condition for the simulation calculation is the incoming wind speed and the fin simulation model of the passive heat exchanger; the simulation output is the first pressure loss of the first and second end faces of the passive heat exchanger and wind speed behind the board ; Based on the first pressure loss Calculate the pressure loss per unit length, that is, use the first pressure loss Divide by the perpendicular distance between the first end face and the second end face ; Thus, the pressure loss simulation data between the air flow inlet and outlet of the passive heat exchanger is obtained.

9. The optimization design method according to claim 8, characterized in that: In step S4, based on the pressure loss simulation data of the passive heat exchanger, the incoming wind speed is constructed. The first relationship model between the pressure loss per unit length and the first pressure loss is constructed Wind speed behind the board The first relationship model is used to set the medium characteristic correlation coefficient and velocity influence coefficient of the porous medium model during the simulation process, and the second relationship model is used to set the second pressure loss of the passive heat exchanger with different specifications of induced draft hoods installed. , calculate the corresponding wind speed behind the board .

10. The optimization design method according to claim 9, characterized in that: In step S5, the air permeability of the passive heat exchanger under the induced draft hood of each specification is determined, which is the corresponding wind speed behind the plate. and incoming wind speed The ratio is used as an indicator to evaluate the effect of the hood efficiency-enhancing structure, and then the hood layout angle and projection length that meet the preset engineering requirements are obtained.

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