Multi-hole steam injection device of non-uniform gradient hole array and Laval pipeline

Abstract

The invention discloses a multi-hole steam injection device of a non-uniform gradient hole array and a Laval pipeline. The device comprises the Laval pipeline, a hole plate and a flange. The Laval pipeline is composed of a contraction section, a throat part and an expansion section and is designed based on the isentropic flow theory, steam is accelerated to the supersonic speed, and the kinetic energy conversion efficiency is improved. The pore plate adopts a hexagonal densely-arranged non-uniform gradient pore array and is divided into a core area, a transition area and an edge area along the radial direction, and the permeability distribution is optimized and the interference effect of steam plume is reduced by adjusting the proportion of the pore diameter to the pore pitch of each area. The penetration length and the heat exchange area of the steam jet flow are remarkably increased through the synergistic effect of the two pore plates, the heat transfer performance is improved, and through optimization of the pore diameter and the distance in the pore plate, the flow resistance surge and the blocking risk caused by mismatching of the flow speed and the pore diameter are avoided. The invention solves the problems of turbulent flow superposition, strong structural coupling, fast kinetic energy attenuation and the like of the traditional uniform hole array, and is suitable for high-efficiency vapor-liquid two-phase heat exchange of the nuclear power station containment.

Description

Technical Field

[0001] The present invention relates to the technical field of heat removal from the containment of nuclear power plants, and particularly to a porous steam injection device with a non-uniform gradient hole array and a Laval pipe for the steam immersion jet process. Background Art

[0002] Due to its excellent heat and mass transfer characteristics, the steam immersion jet condensation process is widely used in various industrial fields, such as the waste heat discharge systems of nuclear reactors and ships. Under severe accident conditions in nuclear power plants, steam in the containment is injected into cooling water through a porous sprinkler to form a steam immersion jet for rapid heat removal. Traditional devices mostly adopt the design of round pipes and uniformly distributed straight hole arrays, which have the following defects in practical applications:

[0003] 1. Steam plume interference effect: The steam plumes generated by the uniform hole array interfere severely with each other, forming a turbulent superposition, which hinders effective heat transfer. The measured fluctuation range of the heat transfer coefficient reaches ±35%;

[0004] 2. Strong structural coupling: The sprinkler adopts an integrated design, and local damage requires the whole to be replaced, resulting in high maintenance costs;

[0005] 3. Jet kinetic energy attenuation: The length of the jet core area of the circular straight hole structure is usually 5-8 times the hole diameter, and the steam kinetic energy decays prematurely, affecting the penetration length and limiting the effective heat transfer area.

[0006] Existing improvement technologies often optimize the flow field by adding a flow guiding structure, but the flow guiding system has problems such as increased pressure loss, complex structure, and difficult maintenance. Therefore, it is of great significance for related industrial applications to find a porous injection structure with simple and efficient heat transfer. Summary of the Invention

[0007] In order to solve the problems existing in the above-mentioned prior art, the present invention aims to provide a porous steam injection device with a non-uniform gradient hole array and a Laval pipe. The steam flows through the Laval acceleration pipe and the non-uniform gradient hole array in sequence, and through the synergistic effect of the two, the deficiencies existing in the prior art are overcome, and efficient gas-liquid two-phase heat transfer is achieved.

[0008] To achieve the above object, the present invention is realized by the following solutions:

[0009] The device includes: a Laval pipe (101), an orifice plate (102), and a flange (103);

[0010] A porous steam injection device with a non-uniform gradient hole array and a Laval pipe, the device includes: a Laval pipe 101, flanges 103 connected to both ends of the Laval pipe 101, and an orifice plate 102 connected to the flange 103;

[0011] The Laval nozzle 101 is of a convergent-divergent configuration, including a convergent section 201, a throat 202, and a divergent section 203. It is designed based on the isentropic flow theory. The cross-sectional area of the throat meets the critical flow condition, and the cross-sectional area at the outlet of the divergent section is determined by iteratively solving for the Mach number.

[0012] The surface of the orifice plate 102 is provided with a non-uniform gradient hole array arranged in a hexagonal close-packed pattern. It is radially divided into a core area A, a transition area B, an edge area C, and bolt holes D. The ratio of the hole pitch to the hole diameter in each area is 1.2, 1.5 - 2.4, and 3.

[0013] Preferably, the throat 202 of the Laval nozzle 101 is designed as follows:

[0014] Based on the isentropic flow theory, the flow velocity v at the outlet of the nozzle is determined 出口 and the pressure P 出口 ;

[0015] When the throat of the nozzle reaches the critical state, Ma 喉部 = 1, A 喉部 = m / (ρ * c * ), where ρ * and c * are the critical density and the speed of sound of the steam at the throat, calculated from the steam physical properties, m is the mass flow rate of the steam, Ma 喉部 is the Mach number at the throat of the nozzle, and A 喉部 is the area of the throat of the nozzle;

[0016] At the outlet of the divergent section of the nozzle, there is The Mach number Ma 出口 at the outlet of the divergent section of the Laval nozzle is determined by iterative solution to obtain the outlet cross-sectional area and the divergence angle of the divergent section, where γ is the ratio of the specific heat at constant pressure to the specific heat at constant volume of the steam.

[0017] Preferably, the orifice plate 102 is designed as follows to cooperate with the Laval nozzle 101:

[0018] The permeability of the orifice plate is defined as where ΔP is the pressure drop across the orifice plate, and A 孔板 is the effective flow area of the orifice plate;

[0019] The local permeability K i in the core area A, the transition area B, and the edge area C i is related to the hole diameter d i and the hole pitch S

[0020]

[0021] By adjusting d i / S iA ratio such that K matches the mass flow rate of the Laval duct;

[0022] The steam flow velocity in the small holes in the core area is It should be within a preset outlet flow velocity range and be adjusted by the number of holes N in the core area, where m is the mass flow rate of the steam, ρ is the density of the steam, and d is the hole diameter; A Adjustment is made, where m is the mass flow rate of the steam, ρ is the density of the steam, and d is the hole diameter;

[0023] The pressure drop in the large holes in the edge area is It should be within a preset orifice plate pressure drop range;

[0024] The empirical formula for the orifice plate hole pitch S and the hole diameter d is:

[0025] S = k·d (k 核心区 = 1.2, k 过渡区 = 1.5 - 2.4, k 边缘区 = 3), where k is the proportionality coefficient, and the hole pitch is determined by the hole diameter.

[0026] Preferably, the Laval duct 101 and the flange 103 are connected by welding.

[0027] Preferably, the flange 103 and the orifice plate 102 are connected by 6 M10 bolts, with a sealing gasket in the middle to prevent steam leakage.

[0028] The porous steam injection device with a non-uniform gradient hole array and a Laval duct provided by the present invention can significantly increase the heat transfer area of the steam plume by optimizing the hole array layout and the duct structure, thereby improving the heat transfer performance. By optimizing the hole diameter and pitch in the orifice plate, the risk of a sharp increase in flow resistance and blockage caused by the mismatch between the flow velocity and the hole diameter is avoided. At the same time, the device structure is compact, facilitating installation and subsequent maintenance, and effectively reducing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the overall device of the embodiment of the present invention;

[0030] Figure 2 It is a schematic cross-sectional view of the Laval duct structure of the embodiment of the present invention;

[0031] Figure 3 It is a non-uniform gradient hole array distribution diagram;

[0032] Wherein: 101 - Laval duct; 102 - orifice plate; 103 - flange; 201 - contraction section; 202 - throat; 203 - expansion section; A - core area; B - transition area; C - edge area; D - bolt hole. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0033] In order to make the above objects, features, and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with 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 do not limit the present invention.

[0034] Refer to Figure 1 FIG. is a schematic diagram of a steam injection device with a non-uniform gradient orifice array and a Laval duct provided by the present invention, which mainly includes a Laval duct 101, an orifice plate 102, and a flange 103. The Laval duct 101 is connected to the flange 103 by welding, and the flange 103 is connected to the orifice plate 102 by six M10 bolts with a sealing gasket in between. The injection device is usually arranged in the normal temperature water tank of the containment vessel and immersed underwater. The inlet pipe of the injection device is connected to the pipe of the pressure relief system. When there is no steam discharge during normal operation, the injection device is filled with water; when the pressure relief system discharges steam, the high-pressure steam squeezes out the normal temperature water in the pipe, the velocity increases after passing through the Laval duct, and then it is dispersed into the water tank through the orifice plate to form a stable steam jet, which is absorbed efficiently at high speed in the way of direct contact condensation.

[0035] Refer to Figure 2 FIG. is a schematic cross-sectional view of the structure of the Laval duct 101 in the device provided by the present invention. The Laval duct 101 mainly consists of a converging section 201, a throat 202, and a diverging section 203. The Laval duct 101 realizes the acceleration of steam from subsonic to supersonic through a converging-diverging configuration. In this process, the steam first enters the converging section 201, the cross-sectional area decreases, and according to the continuity equation (ρAv) 进口 =(ρAv) 喉部 it can be known that the flow velocity ν increases and the pressure gradually decreases, and the pressure energy is converted into kinetic energy. When reaching the throat, the critical sonic speed is achieved. According to the ideal gas hypothesis, the flow relationship is obtained:

[0036]

[0037] where γ is the specific heat ratio of steam and ρ is the density of steam. Further calculation gives the throat diameter Combined with the steam flow rate and the physical property parameters of steam, when flowing through the diverging section, according to the characteristics of supersonic flow, the steam continues to expand to supersonic speed, the kinetic energy further increases, compared with a circular pipe, the kinetic energy of steam injection is increased, the jet penetration length is increased, and the condensation heat transfer area is enlarged.

[0038] Refer to Figure 3The non-uniform gradient hole array distribution diagram in the injection device provided by the present invention. The hole array is a hexagonal close-packed non-uniform gradient layout, which is radially divided into a core area A, a transition area B, an edge area C, and a bolt hole D. During this process, steam enters the water pool through the hole array with different hole diameters and spacings, and the flow field is optimized through the partition gradient layout. The core area A has the smallest hole diameter and the smallest spacing, generating more fine droplets, increasing the contact area between the vapor and the liquid, and at the same time reducing the local Reynolds number, which has a certain inhibitory effect on the turbulence intensity; the gradual change design in the transition area B makes the velocity gradient smoother, preventing flow separation caused by the sudden change from the core area A to the edge area C, and helping the steam to gradually diffuse; the edge area C has the largest hole diameter and the largest spacing, forming a high-speed drainage channel, reducing the steam plume interference effect and at the same time reducing the intensity of the eddy current. At the same time, the velocity limit and pressure drop limit for the core area A and the edge area C are ensured to match the acceleration characteristics of the Laval pipe with the permeability distribution of the non-uniform hole array jet, avoiding local high-pressure areas, sudden increase in flow resistance, and blockage risks caused by the mismatch between the flow velocity and the hole diameter.

[0039] A steam injection device with a non-uniform gradient hole array and a Laval pipe provided by the present invention optimizes the hole array layout and the pipe structure, and produces the following beneficial effects: the non-uniform gradient hole array layout reduces the steam plume interference area and improves the heat transfer performance; the Laval pipe structure accelerates the steam to supersonic speed, improves the kinetic energy conversion efficiency, and increases the steam plume penetration depth; the block design shortens the component replacement time and reduces the manufacturing cost; the above effects achieve the purpose of improving reliability and economy.

[0040] The above embodiments are only the preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A porous steam injection device with a non-uniform gradient hole array and a Laval pipeline, characterized in that: The device comprises: A Laval pipe (101), flanges (103) connected to both ends of the Laval pipe (101), and an orifice plate (102) connected to the flanges (103); The Laval pipe (101) is of a contraction-expansion configuration, comprising a contraction section (201), a throat (202) and an expansion section (203), and is designed based on isentropic flow theory, wherein the cross-sectional area of ​​the throat satisfies the critical flow condition, and the cross-sectional area of ​​the expansion section outlet is determined by iteratively solving the Mach number; The surface of the orifice plate (102) is provided with a hexagonal closely packed non-uniform gradient hole array, which is radially divided into a core area (A), a transition area (B) and an edge area (C), and the ratio coefficients of the hole spacing to the hole diameter in each area are 1.2, 1.5-2.4 and 3.

2. The porous steam injection device according to claim 1, characterized in that: The throat cross-sectional area of ​​the Laval pipeline (101) is given by the formula A 喉部 =m / (ρ * c * ) is determined, where ρ * and c * is the critical density and sound velocity of steam in the throat, and m is the mass flow rate of steam.

3. The porous steam injection device according to claim 1, characterized in that: The permeability of the orifice plate (102) satisfies K=∑(K i ·A i / A 总 ), where K i is the permeability of each area, A i is the flow area of ​​the hole array in each area, A 总 is the flow area of ​​all holes, and by adjusting each area d i / S i The ratio matches the mass flow rate of the Laval pipeline, where d i is the aperture of each area, S i is the hole spacing of the orifice plate in each area.

4. The porous steam injection device according to claim 1, characterized in that: The core area (A) has the smallest pore size and the smallest pore spacing, the edge area (C) has the largest pore size and the largest pore spacing, and the pore size and pore spacing of the transition area (B) are in a gradient transition.

5. The porous steam injection device according to claim 4, characterized in that: The steam flow rate in the small holes in the core area (A) is It should be within the preset outlet flow rate range and pass through the core area holes N A Adjust, m is the mass flow rate of steam, ρ is the density of steam, and d is the pore size.

6. The porous steam injection device according to claim 4, characterized in that: The pressure drop in the macropores of the edge region (C) is It should be within the preset orifice pressure drop range.

7. The porous steam injection device according to claim 1, characterized in that: The throat (202) of the Laval pipeline (101) reaches a critical point, Ma 喉部 =1,Ma 喉部 is the Mach number at the pipe throat.

8. The porous steam injection device according to claim 1, characterized in that: The outlet pipe cross-sectional area A of the expansion section (203) of the Laval pipe (101) is 出口 Cross-sectional area of ​​the pipe at the throat A 喉部 The ratio is The Mach number Ma at the outlet of the Laval pipe expansion section is solved by iteration 出口 Determine the outlet cross-sectional area and the inclination angle of the expansion section, where γ is the ratio of the specific heat of steam at constant pressure to the specific heat of steam at constant volume.

9. The porous steam injection device according to claim 1, characterized in that: The Laval pipe (101) is connected to the flange (103) by welding.

10. The porous steam injection device according to claim 1, characterized in that: The flange (103) is connected to the orifice plate (102) by means of 6 M10 bolts, with a sealing gasket in between to prevent steam leakage.

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