Fireproof performance analysis method for fuel and lubricating oil heat exchanger

Abstract

The invention belongs to the technical field of aviation equipment calculation and analysis, and discloses a fireproof performance analysis method for a fuel and lubricating oil heat exchanger, which comprises the following steps of: firstly, establishing a three-dimensional geometric model of the heat exchanger, then performing standard flame simulation, analyzing flame characteristics, determining a stable section of high-temperature flue gas, and applying a high-temperature flue gas file as a fireproof simulation input boundary; and applying an inner wall surface boundary condition, carrying out heat exchanger transient fireproof simulation calculation to obtain a transient temperature field, and finally carrying out rubber fireproof performance evaluation and metal fireproof performance evaluation. According to the method, the external fire environment of the heat exchanger is equivalent to high-temperature flue gas, the interior of the heat exchanger is equivalent to a third-class heat exchange boundary condition, efficient calculation of fireproof simulation of the heat exchanger is achieved, scientific and comprehensive simulation failure judgment criteria are established, fireproof performance prediction and optimization of the aviation fuel and lubricating oil heat exchanger are supported, and the one-time passing rate of a fireproof performance test is increased.

Description

Technical Field

[0001] The invention belongs to the technical field of aviation equipment calculation and analysis, and relates to an analysis method for the fire protection performance of a fuel and lubricating oil heat exchanger, and specifically to a numerical analysis method for evaluating the fire protection performance of an aviation fuel and lubricating oil heat exchanger. Background Art

[0002] Aircraft engines are the power source of aircraft. Once a fire occurs in the engine, the nearby equipment and accessories must be able to work effectively until the engine stops safely, and the fire will not spread. The fuel and lubricating oil heat exchanger is a large-volume accessory of the engine. According to the fire protection clause requirements of CCAR33.17, it should have a certain fire protection level. At present, the fire protection test conditions of heat exchangers are harsh, the first-time pass rate is low, and because it is a destructive test, the test cost is also high.

[0003] At present, domestic and foreign aircraft engine manufacturers use CFD technology and finite element structural analysis technology to perform numerical simulation on the fire test process of simple engine accessories. The structure of aviation fuel and lubricating oil heat exchanger is usually a shell and tube heat exchanger, which is composed of thousands of heat exchange tubes, heat exchange shells, rubber seals and other non-metallic parts. If the previous simple accessory fire simulation technology is used, the flame combustion, heat exchanger fluid-solid heat transfer and fuel medium phase change heat and mass transfer are coupled with each other to perform non-steady-state simulation calculations. The simulation calculation is large and the efficiency is low. In addition, the failure forms of aviation fuel and lubricating oil heat exchangers under the action of flames are diverse, and each failure form should have a fire performance judgment index. Therefore, the previous fire simulation method cannot be effectively applied to heat exchangers. Summary of the invention

[0004] In order to solve the above problems, the present invention proposes a fire protection performance analysis method for fuel and lubricating oil heat exchangers, which is an experimentally efficient simulation analysis method and also a comprehensive fire protection performance verification method. It can realize the preliminary evaluation of the fire protection performance of large and complex heat exchangers and propose optimization and improvement plans for the fire protection performance of heat exchangers.

[0005] The technical solution of the present invention is as follows:

[0006] A method for analyzing the fire performance of a fuel and lubricating oil heat exchanger is provided. First, a three-dimensional geometric model of the heat exchanger is established, and then the following steps are performed:

[0007] S10: Perform standard flame simulation;

[0008] S20: Analyze flame characteristics;

[0009] S30: Determine the stable cross section of high temperature flue gas;

[0010] S40: Apply high temperature smoke file as fire simulation input boundary;

[0011] S50: Apply inner wall boundary conditions;

[0012] S60: Perform transient fire protection simulation calculation of heat exchanger based on S40 and S50;

[0013] S70: obtaining transient temperature field;

[0014] S80: Evaluate the fire resistance of rubber;

[0015] S90: Evaluate the fire performance of metals;

[0016] Among them, S50 and S40 are in no particular order, and S80 and S90 are in no particular order.

[0017] Furthermore, S10 is specifically as follows: selecting the pressure-based solver in the Fluent software, using transient solving, opening the energy equation and turbulence model, setting the wall function, selecting the radiation model, performing component settings, and using the newly created droplet material to simulate and calculate the gas flow of the standard flame during the combustion process.

[0018] Furthermore, S20 is specifically as follows: selecting cross sections at different distances from the expansion cone outlet in the Fluent software, and analyzing the flame characteristics of each cross section.

[0019] Furthermore, S30 is specifically as follows: a cross-sectional position where both the flame speed and temperature shapes are elliptical rings and the boundary line between the inner and outer rings is obvious is considered as a stable flow heat field distribution, and the velocity distribution file of the combustion products and the temperature distribution file of the flame at the above cross-sectional position is derived, that is, a high-temperature flue gas stable cross-sectional file.

[0020] Furthermore, S60 is specifically as follows: placing the weak position of the heat exchanger at a set position above the cross section applied by S40, performing transient solution in FLUENT, setting the time step and simulation calculation steps, completing the calculation for the previous period of time, and automatically changing the inner wall boundary conditions and the time step by compiling a simulation calculation condition switching program to perform calculations for the next period of time.

[0021] Furthermore, S70 specifically includes: transferring the temperature load calculated by the transient fire protection simulation in S60 from Fluent to Mechanical at the same time step.

[0022] Furthermore, S50 is specifically:

[0023] S51, under the product fire protection condition, compile a file containing fuel and lubricating oil physical property parameters and load it into the Fluent fluid material library;

[0024] S52: Set the performance calculation boundaries of the heat exchanger inlet flow and temperature, outlet pressure and temperature under the fire test state, carry out performance simulation under fire conditions, and output the heat transfer coefficient file of the inner wall of the heat exchanger under fire conditions for a period of time;

[0025] S53: The internal wall temperature of the heat exchanger automatically extracted by compiling the UDF program is used as a criterion for determining whether the working fluid undergoes phase change; if no phase change occurs in the heat exchanger, S54 is executed; if a phase change occurs in the heat exchanger, S55 is executed;

[0026] S54: Use the heat transfer coefficient file output by S52 as the boundary condition of the inner wall of the heat exchanger;

[0027] S55: The Baburajan model is used to calculate the inner wall heat transfer coefficient under phase change conditions as the inner wall boundary condition of the heat exchanger. The calculation formula is as follows:

[0028]

[0029] Where, Bo is the boiling number; Ja is the Jacob number; Pr is the Prandtl number;

[0030] S56, combining the third type of boundary conditions of the above two types of heat transfer coefficients to realize partitioned loading of the internal boundary conditions of the heat exchanger.

[0031] Furthermore, S80 is specifically:

[0032] S81: Mechanical is used to perform nonlinear static simulation on the sealing assembly state of each rubber ring of the heat exchanger, and the Mooney-Rivlin constitutive model is used for the rubber ring to extract the deformation of the rubber ring;

[0033] S82: Reconstruct the three-dimensional model of the radiator sealing ring, eliminate the interference of the geometric model, retain the prestressed field of the rubber material, apply the transient temperature load under the S70 fire protection condition, and set the contact tangent, normal and heat transfer parameters at the rubber ring;

[0034] S83: Carry out thermal-solid coupling simulation of the heat exchanger and output the temperature change curve of the rubber ring;

[0035] S84: The rubber material destruction temperature is used as the criterion for determining the rubber degeneration. If the rubber material degenerates and the rubber ring melts and fails, the process proceeds to S85; if the rubber material does not degenerate and the rubber has elasticity, the process proceeds to S86;

[0036] S85: Calculate the leakage gap at the rubber seal interface under high temperature and high pressure (fire test pressure holding pressure) conditions of the heat exchanger, and then enter S87;

[0037] S86: Input the data of Mooney-Rivlin parameters of rubber materials changing with temperature in Mechanical, and calculate the contact stress at the rubber seal interface under high temperature and high pressure conditions of the heat exchanger;

[0038] S87: Calculate the leakage at the rubber seal interface using the following formula:

[0039]

[0040] Where: is the diameter of the leakage ring; h is the leakage gap; μ is the viscosity of the working fluid; L is the length of the gap; ΔP is the pressure difference at both ends of the gap;

[0041] S88: Conduct fire retardant failure assessments on rubber materials.

[0042] Furthermore, S90 is specifically:

[0043] S91: Set the data of metal material constitutive parameters changing with temperature and pressure load, and output the temperature field and stress field of metal parts;

[0044] S92: Calculate the ablation amount of the metal shell of the heat exchanger with the time when the local temperature of the component reaches the melting point of the metal material as the starting point and the end time of the fire exposure as the end point. The ablation amount is used as the criterion. If the total ablation amount is greater than the shell thickness, the fire protection fails; otherwise, if the indicator is passed, continue to execute S93;

[0045] Calculate the ablation amount D:

[0046]

[0047] Where: ε is the ablation rate;

[0048] S93: Make a stress linearization path along the thickness direction of the structure at the dangerous stress point in the stress field to obtain the primary overall film stress S at the high stress position. I Or the primary local film stress S Ⅱ , and calculate the allowable stress S of the material under high temperature conditions m , the allowable material stress Sm is determined by the minimum value of the following formula:

[0049]

[0050] Where: u : is the tensile strength; σ p0.2 : is the yield strength; σ t p0.2 : is the yield strength at the highest temperature of the component;

[0051] S94: Taking film stress as the criterion, when S I >KSm And S Ⅱ >1.5KS m , the key load-bearing component breaks and fails; otherwise, the indicator passes and it is assessed that the metal component has not failed; K is the safety factor.

[0052] The technical effects of the present invention are as follows:

[0053] The fire protection simulation analysis of the above-mentioned fuel and lubricating oil heat exchanger equates the external fire environment of the heat exchanger to high-temperature flue gas, and the interior of the heat exchanger to the third-type heat exchange boundary condition, thereby achieving efficient calculation of the heat exchanger fire protection simulation, establishing scientific and comprehensive simulation failure judgment criteria, supporting the prediction and optimization of the fire protection performance of aviation fuel and lubricating oil heat exchangers, and improving the first-time pass rate of fire protection performance tests. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for describing the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative work.

[0055] Figure 1 The figure is a flow chart of the fire protection performance analysis method for heat exchangers.

[0056] Figure 2 This is the flow chart for heat transfer calculation on the inner wall of the heat exchanger.

[0057] Figure 3 This is the flow chart of the fire protection simulation calculation of rubber sealing ring.

[0058] Figure 4 This is the flow chart of fire protection simulation calculation for metal parts. DETAILED DESCRIPTION

[0059] This section is an embodiment of the present invention, which is used to explain and illustrate the technical solution of the present invention. In the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

[0060] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate directions or positional relationships based on the orientations or positional relationships in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or case referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", etc. are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance or implying the number of technical features indicated. Thus, features defined as "first", "second", etc. may explicitly or implicitly include more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0061] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected" and "connected" should be interpreted in a broad sense, for example, it can be a fixed connection, a detachable connection or an integrated connection; it can be a mechanical connection or a point connection; it can be a direct connection or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0062] Embodiment 1:

[0063] A method for analyzing the fire performance of a fuel and lubricating oil heat exchanger is provided. First, a three-dimensional geometric model of the heat exchanger is established, and then the following steps are performed:

[0064] S10: Perform standard flame simulation;

[0065] S20: Analyze flame characteristics;

[0066] S30: Determine the stable cross section of high temperature flue gas;

[0067] S40: Apply high temperature smoke file as fire simulation input boundary;

[0068] S50: Apply inner wall boundary conditions;

[0069] S60: Perform transient fire protection simulation calculation of heat exchanger based on S40 and S50;

[0070] S70: obtaining transient temperature field;

[0071] S80: Evaluate the fire resistance of rubber;

[0072] S90: Evaluate the fire performance of metals;

[0073] Among them, S50 and S40 are in no particular order, and S80 and S90 are in no particular order.

[0074] S10 is specifically as follows: select the pressure-based solver in the Fluent software, use transient solution, open the energy equation and turbulence model, set the wall function, select the radiation model, perform component settings, and use the newly created droplet material to simulate and calculate the gas flow of the standard flame during the combustion process.

[0075] S20 is specifically as follows: In the Fluent software, sections at different distances from the expansion cone outlet are selected to analyze the flame characteristics of each section.

[0076] S30 is specifically as follows: a cross-sectional position characterized by the flame velocity and temperature being both elliptical in shape and the inner and outer rings having a distinct boundary is regarded as a stable flow heat field distribution, and a velocity distribution file of the combustion products and a temperature distribution file of the flame at the cross-sectional position is derived, i.e., a high-temperature flue gas stable cross-sectional file.

[0077] S60 is specifically as follows: the weak position of the heat exchanger is placed at a set position above the cross section applied by S40, transient solution is carried out in FLUENT, the time step and simulation calculation steps are set, calculations for the previous period of time are completed, and the inner wall boundary conditions and time step are automatically changed by compiling a simulation calculation condition switching program to carry out calculations for the next period of time.

[0078] S70 is specifically as follows: the temperature load calculated by the transient fire protection simulation in S60 is transferred from Fluent to Mechanical at the same time step.

[0079] S50 is specifically:

[0080] S51, under the product fire protection condition, compile a file containing fuel and lubricating oil physical property parameters and load it into the Fluent fluid material library;

[0081] S52: Set the performance calculation boundaries of the heat exchanger inlet flow and temperature, outlet pressure and temperature under the fire test state, carry out performance simulation under fire conditions, and output the heat transfer coefficient file of the inner wall of the heat exchanger under fire conditions for a period of time;

[0082] S53: The internal wall temperature of the heat exchanger automatically extracted by compiling the UDF program is used as a criterion for determining whether the working fluid undergoes phase change; if no phase change occurs in the heat exchanger, S54 is executed; if a phase change occurs in the heat exchanger, S55 is executed;

[0083] S54: Use the heat transfer coefficient file output by S52 as the boundary condition of the inner wall of the heat exchanger;

[0084] S55: The Baburajan model is used to calculate the inner wall heat transfer coefficient under phase change conditions as the inner wall boundary condition of the heat exchanger. The calculation formula is as follows:

[0085]

[0086] Where, Bo is the boiling number; Ja is the Jacob number; Pr is the Prandtl number;

[0087] S56, combining the third type of boundary conditions of the above two types of heat transfer coefficients to realize partitioned loading of the internal boundary conditions of the heat exchanger.

[0088] S80 is specifically:

[0089] S81: Mechanical is used to perform nonlinear static simulation on the sealing assembly state of each rubber ring of the heat exchanger, and the Mooney-Rivlin constitutive model is used for the rubber ring to extract the deformation of the rubber ring;

[0090] S82: Reconstruct the three-dimensional model of the radiator sealing ring, eliminate the interference of the geometric model, retain the prestressed field of the rubber material, apply the transient temperature load under the S70 fire protection condition, and set the contact tangent, normal and heat transfer parameters at the rubber ring;

[0091] S83: Carry out thermal-solid coupling simulation of the heat exchanger and output the temperature change curve of the rubber ring;

[0092] S84: The rubber material destruction temperature is used as the criterion for determining the rubber degeneration. If the rubber material degenerates and the rubber ring melts and fails, the process proceeds to S85; if the rubber material does not degenerate and the rubber has elasticity, the process proceeds to S86;

[0093] S85: Calculate the leakage gap at the rubber seal interface under high temperature and high pressure (fire test pressure holding pressure) conditions of the heat exchanger, and then enter S87;

[0094] S86: Input the data of Mooney-Rivlin parameters of rubber materials changing with temperature in Mechanical, and calculate the contact stress at the rubber seal interface under high temperature and high pressure conditions of the heat exchanger;

[0095] S87: Calculate the leakage at the rubber seal interface using the following formula:

[0096]

[0097] Where: is the diameter of the leakage ring; h is the leakage gap; μ is the viscosity of the working fluid; L is the length of the gap; ΔP is the pressure difference at both ends of the gap;

[0098] S88: Conduct fire retardant failure assessments on rubber materials.

[0099] S90 is specifically:

[0100] S91: Set the data of metal material constitutive parameters changing with temperature and pressure load, and output the temperature field and stress field of metal parts;

[0101] S92: Calculate the ablation amount of the metal shell of the heat exchanger with the time when the local temperature of the component reaches the melting point of the metal material as the starting point and the end time of the fire exposure as the end point. The ablation amount is used as the criterion. If the total ablation amount is greater than the shell thickness, the fire protection fails; otherwise, if the indicator is passed, continue to execute S93;

[0102] Calculate the ablation amount D:

[0103]

[0104] Where: ε is the ablation rate;

[0105] S93: Make a stress linearization path along the thickness direction of the structure at the dangerous stress point in the stress field to obtain the primary overall film stress S at the high stress position. I Or the primary local film stress S Ⅱ , and calculate the allowable stress S of the material under high temperature conditions m , the allowable material stress Sm is determined by the minimum value of the following formula:

[0106]

[0107] Where: u : is the tensile strength; σ p0.2 : is the yield strength; σ t p0.2 : is the yield strength at the highest temperature of the component;

[0108] S94: Taking film stress as the criterion, when S I >KS m And S Ⅱ >1.5KS m , the key load-bearing component breaks and fails; otherwise, the indicator passes and it is assessed that the metal component has not failed; K is the safety factor.

[0109] Embodiment 2:

[0110] The present invention proposes an efficient simulation analysis method and a comprehensive fire performance verification method for a fuel and lubricating oil heat exchanger fire protection test, thereby improving the calculation speed of the fire protection test simulation, reducing the requirements for computer performance, realizing efficient evaluation and calculation of the fire protection performance of the heat exchanger, and providing an optimized design scheme for the fuel and lubricating oil heat exchanger.

[0111] The fireproof performance simulation and analysis method of the fuel and lubricating oil heat exchanger performs the following steps: obtaining the state of the rubber sealing ring after assembly through static simulation, and reconstructing the three-dimensional model of the heat exchanger; analyzing the standard flame characteristics of the fire simulation test, obtaining the appropriate cross-sectional heat distribution as the high-temperature flue gas inlet boundary, and equating the external fire environment of the heat exchanger to the high-temperature flue gas; writing a UDF program to judge the internal phase change state of the heat exchanger, and equating the inside of the heat exchanger to the third type of heat exchange boundary conditions to realize automatic loading of the boundary conditions; performing non-steady-state calculation of the temperature field and thermal deformation calculation of the heat exchanger to obtain four indicators of the ablation amount, stress damage, contact stress of the sealing ring and leakage of the heat exchanger, so as to comprehensively judge the fireproof performance of the fuel and lubricating oil heat exchanger.

[0112] Fluent was used to calibrate the standard flame of the fire protection test, analyze the flame heat transfer characteristics, and select the high-temperature flue gas distribution field at the stable cross-section position of the combustion product flow field at the front end of the expansion cone as the inlet boundary of the flow-solid thermal coupling of the external environment of the heat exchanger.

[0113] By compiling a UDF program, the internal wall temperature of the heat exchanger is automatically extracted as the criterion for determining whether the working fluid has undergone phase change. If no phase change occurs in the heat exchanger, the steady-state flow thermal field inside the heat exchanger is simulated and calculated, and the calculation results of the steady-state flow thermal field are used as the third-class boundary conditions inside the heat exchanger shell; if a phase change occurs in the heat exchanger, the phase change theoretical solution is loaded as the third-class boundary condition inside the heat exchanger shell.

[0114] The temperature variation law of the heat exchanger shell surface is obtained by calculating the non-steady-state temperature field. The ablation amount of the heat exchanger metal shell is calculated with the melting point time of the metal material as the starting point and the end time of the fire as the end point. The ablation amount is used as the criterion. If the total ablation amount is greater than the shell thickness, the fire protection fails, otherwise the indicator passes.

[0115] The overall membrane stress S of the heat exchanger shell is obtained by thermal deformation calculation. I , primary local film stress S Ⅱ And the allowable stress S of the material at high temperature m , taking the film stress as the criterion, when S I >KS m And S Ⅱ >1.5KS m If the key load-bearing parts break and fail, otherwise the indicator will pass.

[0116] When the temperature of the sealing ring is higher than the destruction temperature of the rubber material, the rubber ring melts and fails. Taking the temperature and pressure loads into consideration, the leakage gap at the sealing interface is calculated. The leakage amount is calculated theoretically based on the leakage gap. The total leakage amount is used as the criterion. If the total leakage amount is greater than the allowable value, the leakage fails. Otherwise, the indicator passes.

[0117] When the sealing ring temperature is lower than the destruction temperature of the rubber material, the temperature and pressure loads must be comprehensively considered to calculate the contact stress at the sealing interface. The contact stress is used as the criterion. If the maximum contact stress is greater than the pressure in the cavity, the rubber ring seal fails. Otherwise, the indicator passes.

[0118] Embodiment 3:

[0119] According to the structure and material of each component of the fuel and lubricating oil heat exchanger, Catia 3D software is used to create a 3D geometric model of the fuel and lubricating oil heat exchanger.

[0120] After the above modeling process is completed, the fire protection performance analysis and evaluation method of the fuel and lubricating oil heat exchanger is carried out in the simulation environment. Figures 1 to 4 Steps shown.

[0121] Step 10 In Fluent software, select the pressure-based solver, use transient solution, open the energy equation and turbulence model, set the wall function, select the DO model for the radiation model, set the component to non-premixed combustion, and consider the interaction between the discrete phase and the continuous phase. Create a new material in the droplet material under the material, select diesel-liquid from the fluent database, and change its evaporation / boiling model to convection / diffusion-controlled, then change the material in the jet source to diesel-liquid, and simulate and calculate the gas flow of the standard flame during the combustion process.

[0122] Step 20: In the Fluent software, select sections at different distances from the expansion cone outlet, analyze the flame characteristics of each section, and consider the section position where the flame speed and temperature are both elliptical rings and the boundary between the inner and outer rings is obvious as a stable flow heat field distribution.

[0123] Step 30 exports the velocity distribution of the combustion products and the temperature distribution Profile file of the flame at the above cross-sectional position.

[0124] In step 40, the cross section of the external calculation domain of the fire simulation is loaded with the profile file output in step 30, and it is used as the external equivalent boundary of the high-temperature smoke in step 60.

[0125] The weak position of the heat exchanger is placed at a set position above the section, and the simulation boundary of the inner wall of the heat exchanger obtained in step 50 is applied (including: the first 5 minutes and the last 10 minutes of the fire test conditions), and the transient flow thermal field simulation of the heat exchanger is performed in step 60. The transient solution is carried out in FLUENT, the time step is set to 0.5s, the number of simulation calculation steps is 600, and the calculation of the first 5 minutes is completed. By compiling a simulation calculation condition switching program, the inner wall boundary conditions are automatically changed, and the step size is changed to 1200 steps, and the calculation of the last 10 minutes is performed.

[0126] In step 70, the temperature load calculated by the 15-minute transient fire simulation in step 60 is transferred from Fluent to Mechanical with the same time step of 0.5 seconds. In step 80, the fire performance evaluation of the rubber material of the heat exchanger is carried out. In step 90, the fire performance evaluation of the metal material of the heat exchanger is carried out.

[0127] The simulation boundary of the inner wall of the heat exchanger is calculated by step 50. To complete step 50, refer to Figure 2 First, perform step 51. Under the product fire protection condition, compile a UDF file containing the physical property parameters of fuel RP-3 and lubricant HY-4050 and load it into the Fluent fluid material library. Then, in step 52, set the performance calculation boundaries of the heat exchanger inlet flow and temperature, outlet pressure and temperature under the fire protection test state, and carry out performance simulation under the fire protection condition, and output the heat transfer coefficient Profile file of the inner wall of the heat exchanger before 5 minutes and after 10 minutes under the fire protection condition.

[0128] By compiling the UDF program, execute step 53, and the automatically extracted internal wall temperature of the heat exchanger is used as the criterion for determining whether the working fluid undergoes phase change. If no phase change occurs in the heat exchanger, execute step 54, and use the heat transfer coefficient Profile file output in step 52 as the boundary condition of the inner wall of the heat exchanger; if a phase change occurs in the heat exchanger, execute step 55, and use the Baburajan model to calculate the inner wall heat transfer coefficient under the phase change condition as the boundary condition of the inner wall of the heat exchanger. The calculation formula is as follows:

[0129]

[0130] Where Bo is the boiling number, Ja is the Jacob number, and Pr is the Prandtl number.

[0131] Finally, step 56 is executed to combine the third type of boundary conditions of the above two types of heat transfer coefficients to realize the partition loading of the internal boundary conditions of the heat exchanger.

[0132] The fire performance evaluation of the heat exchanger rubber material is calculated by step 80. To complete step 80, refer to Figure 3, first proceed to step 81, use Mechanical to perform nonlinear static simulation on the sealing assembly state of each rubber ring of the heat exchanger, use the Mooney-Rivlin constitutive model for the rubber ring, and extract the deformation of the rubber ring. Secondly, in step 82, reconstruct the three-dimensional model of the radiator sealing ring, eliminate the interference of the geometric model, retain the prestressed field of the rubber material, and apply the transient temperature load under the fire protection condition of step 70 at the same time, set the contact tangential, normal and heat transfer parameters of the rubber ring, and carry out the thermo-solid coupling simulation of the heat exchanger in step 83, and output the temperature change curve of the rubber ring. Step 84 uses the destruction temperature of the rubber material as the criterion for judging the degeneration of the rubber. If the rubber material degenerates and the rubber ring melts and fails, step 85 is used to calculate the leakage gap at the rubber sealing interface under the conditions of high temperature and high pressure (fire protection test holding pressure) of the heat exchanger. Further, in step 87, the leakage of the rubber sealing interface is calculated, and the calculation formula is as follows:

[0133]

[0134] Where: is the diameter of the leakage ring; h is the leakage gap; μ is the viscosity of the working fluid; L is the length of the flow through the gap; ΔP is the pressure difference at both ends of the gap.

[0135] If the rubber material has not been denatured and has elasticity, step 86 is used to input the data of the Mooney-Rivlin parameter of the rubber material changing with temperature in Mechanical to calculate the contact stress at the rubber sealing interface under the conditions of high temperature and high pressure (fire test holding pressure) of the heat exchanger.

[0136] Finally, step 88 is executed to carry out the evaluation of the failure of the fireproof performance of the rubber material. When the total leakage is used as the criterion, if it is higher than the test allowable leakage, the fuel oil heat exchanger will fail due to leakage, otherwise the indicator passes; when the contact stress is used as the criterion, if the maximum contact stress is greater than the cavity pressure, the rubber ring seal fails, otherwise the indicator passes.

[0137] The fire failure assessment of the heat exchanger metal material is calculated by step 90. To complete step 90, refer to Figure 4 , retain the key load-bearing components of the heat exchanger, load the transient temperature load under the fire protection condition in step 70, set the data of the constitutive parameters of the metal material changing with temperature and the pressure load in step 91, and output the temperature field and stress field of the metal component. Step 92 calculates the ablation amount of the heat exchanger metal shell with the time when the local temperature of the component reaches the melting point of the metal material as the starting point and the end time of the fire as the end point. The ablation amount is used as the criterion. If the total ablation amount is greater than the shell thickness, the fire protection fails. Execute step 96 and the process ends. Otherwise, the indicator passes and continue to execute step 93. The ablation amount calculation formula is as follows:

[0138]

[0139] Where: ε is the ablation rate.

[0140] Step 93 performs stress linearization path along the thickness direction of the structure at the dangerous stress point in the stress field to obtain

[0141] Take the primary overall film stress S at the high stress position I Or the primary local film stress S Ⅱ , and calculate the allowable stress S of the material under high temperature conditions m , the allowable material stress Sm is determined by the minimum value of the following formula:

[0142]

[0143] Where: u : is the tensile strength; σ p0.2 : is the yield strength; σ t p0.2 : Yield strength at the highest temperature of the component.

[0144] Further proceed to step 94, using the film stress as a criterion, when S I >KS m And S Ⅱ >1.5KS m (where K is the safety factor) if the key load-bearing component breaks and fails, execute step 96 and the process ends. Otherwise, if the indicator passes, execute step 95.

[0145] The following are examples:

[0146] Here, the titanium alloy shell-and-tube heat exchanger with a typical structure is used as an example to introduce the above-mentioned fire prevention simulation and evaluation analysis method. First, simulate the standard flame according to step 10, analyze the flame characteristics in step 20, execute step 30, obtain the thermal field distribution of high-temperature flue gas flow, load the external boundary and the inner wall boundary respectively in steps 40 and 60, carry out transient simulation analysis in step 50, and output the transient temperature load under the fire prevention condition in step 70. In steps 80 and 90, the internal pressure of the head, that is, the internal pressure on the fuel oil side, is set to 4.0MPa in the first 5 minutes and 2.5MPa in the next 10 minutes; the internal pressure of the shell side, that is, the internal pressure on the lubricating oil side, is maintained at a constant value of 1.0MPa. The simulation obtains that the maximum surface temperature of the No. 1 heat exchanger is 1017℃, which is lower than the long-term ablation temperature of titanium alloy TC4, so it will not fail due to ablation. Use Mechanical to calculate its stress damage. The stress level in the dangerous area does not exceed the allowable stress during the entire calculation cycle, and no failure will occur. Abaqus was used to calculate the contact stress of the unmodified rubber seal ring. The minimum contact stress of the rubber seal ring at the inlet and outlet nozzles of the heat exchanger was 4.3MPa, which was much greater than the working pressure of 1.0MPa, and no failure occurred. Mechanical was used to calculate the gap near the modified rubber seal ring, and the leakage was calculated using the formula. The leakage of the modified bypass valve rubber seal ring after standing for 15 minutes was 4.003L, which was much greater than the 0.25L required by the fire test. Therefore, it was judged that the heat exchanger did not meet the fire protection requirements.

[0147] Based on the above-mentioned shell-and-tube heat exchanger fire protection simulation analysis method, after a comprehensive evaluation of the fire resistance of the shell-and-tube heat exchanger, a comparative analysis was carried out in combination with the actual fire protection test, and finally a fire protection performance design optimization scheme for the shell-and-tube heat exchanger can be given. This is of great significance for optimizing the fire protection performance of the fuel and lubricating oil heat exchanger and improving the first-time pass rate of the fire protection test.

[0148] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the field can easily think of various equivalent modifications or substitutions within the technical scope disclosed by the present invention, and these modifications or substitutions should all be covered within the protection scope of the present invention.

Claims

1. A method for analyzing the fire protection performance of a fuel oil heat exchanger, characterized in that: First, establish the 3D geometric model of the heat exchanger, and then perform the following steps: S10: Perform standard flame simulation; S20: analyzing flame characteristics; S30: Determine the stable cross section of high temperature flue gas; S40: Apply high temperature smoke file as fire simulation input boundary; S50: Apply inner wall boundary conditions; S60: Perform transient fire protection simulation calculation of heat exchanger based on S40 and S50; S70: Obtaining transient temperature field; S80: Evaluate the fire resistance of rubber; S90: Evaluate the fire performance of metals; Among them, S50 and S40 are in no particular order, and S80 and S90 are in no particular order.

2. The method for analyzing the fire protection performance of a fuel and lubricating oil heat exchanger according to claim 1, characterized in that: S10 is specifically as follows: select the pressure-based solver in the Fluent software, use transient solution, open the energy equation and turbulence model, set the wall function, select the radiation model, perform component settings, and use the newly created droplet material to simulate and calculate the gas flow of the standard flame during the combustion process.

3. The method for analyzing the fire protection performance of a fuel and lubricating oil heat exchanger according to claim 1, characterized in that: S20 is specifically as follows: In the Fluent software, sections at different distances from the expansion cone outlet are selected to analyze the flame characteristics of each section.

4. The method for analyzing the fire protection performance of a fuel and lubricating oil heat exchanger according to claim 1, characterized in that: S30 is specifically as follows: a cross-sectional position characterized by the flame velocity and temperature being both elliptical in shape and the inner and outer rings having a distinct boundary is regarded as a stable flow heat field distribution, and a velocity distribution file of the combustion products and a temperature distribution file of the flame at the cross-sectional position is derived, i.e., a high-temperature flue gas stable cross-sectional file.

5. The method for analyzing the fire protection performance of a fuel and lubricating oil heat exchanger according to claim 1, characterized in that: S60 is specifically as follows: the weak position of the heat exchanger is placed at a set position above the cross section applied by S40, transient solution is carried out in FLUENT, the time step and simulation calculation steps are set, calculations for the previous period of time are completed, and the inner wall boundary conditions and time step are automatically changed by compiling a simulation calculation condition switching program to carry out calculations for the next period of time.

6. The method for analyzing the fire protection performance of a fuel and lubricating oil heat exchanger according to claim 1, characterized in that: S70 is specifically as follows: the temperature load calculated by the transient fire protection simulation in S60 is transferred from Fluent to Mechanical at the same time step.

7. The method for analyzing the fire protection performance of a fuel and lubricating oil heat exchanger according to claim 1, characterized in that: S50 is specifically: S51, under the product fire protection condition, compile a file containing fuel and lubricating oil physical property parameters and load it into the Fluent fluid material library; S52: Set the performance calculation boundaries of the heat exchanger inlet flow and temperature, outlet pressure and temperature under the fire test state, carry out performance simulation under fire conditions, and output the heat transfer coefficient file of the inner wall of the heat exchanger under fire conditions for a period of time; S53: The internal wall temperature of the heat exchanger automatically extracted by compiling the UDF program is used as a criterion for determining whether the working fluid undergoes phase change; if no phase change occurs in the heat exchanger, S54 is executed; if a phase change occurs in the heat exchanger, S55 is executed; S54: Use the heat transfer coefficient file output by S52 as the boundary condition of the inner wall of the heat exchanger; S55: The Baburajan model is used to calculate the inner wall heat transfer coefficient under phase change conditions as the inner wall boundary condition of the heat exchanger. The calculation formula is as follows: Where, Bo is the boiling number; Ja is the Jacob number; Pr is the Prandtl number; S56, combining the third type of boundary conditions of the above two types of heat transfer coefficients to realize partitioned loading of the internal boundary conditions of the heat exchanger.

8. The method for analyzing the fire protection performance of a fuel and lubricating oil heat exchanger according to claim 1, characterized in that: S80 is specifically: S81: Mechanical is used to perform nonlinear static simulation on the sealing assembly state of each rubber ring of the heat exchanger, and the Mooney-Rivlin constitutive model is used for the rubber ring to extract the deformation of the rubber ring; S82: Reconstruct the three-dimensional model of the radiator sealing ring, eliminate the interference of the geometric model, retain the prestressed field of the rubber material, apply the transient temperature load under the S70 fire protection condition, and set the contact tangent, normal and heat transfer parameters at the rubber ring; S83: Carry out thermal-solid coupling simulation of the heat exchanger and output the temperature change curve of the rubber ring; S84: The rubber material destruction temperature is used as the criterion for determining the rubber degeneration. If the rubber material degenerates and the rubber ring melts and fails, the process proceeds to S85; if the rubber material does not degenerate and the rubber has elasticity, the process proceeds to S86; S85: Calculate the leakage gap at the rubber seal interface under high temperature and high pressure conditions of the heat exchanger, and then enter S87; S86: Input the data of Mooney-Rivlin parameters of rubber materials changing with temperature in Mechanical, and calculate the contact stress at the rubber seal interface under high temperature and high pressure conditions of the heat exchanger; S87: Calculate the leakage at the rubber seal interface using the following formula: Where: is the diameter of the leakage ring; h is the leakage gap; μ is the viscosity of the working fluid; L is the length of the gap; ΔP is the pressure difference at both ends of the gap; S88: Conduct fire retardant failure assessments on rubber materials.

9. The method for analyzing the fire protection performance of a fuel and lubricating oil heat exchanger according to claim 1, characterized in that: S90 is specifically: S91: Set the data of metal material constitutive parameters changing with temperature and pressure load, and output the temperature field and stress field of metal parts; S92: Calculate the ablation amount of the metal shell of the heat exchanger with the time when the local temperature of the component reaches the melting point of the metal material as the starting point and the end time of the fire exposure as the end point. The ablation amount is used as the criterion. If the total ablation amount is greater than the shell thickness, the fire protection fails; otherwise, if the indicator is passed, continue to execute S93; Calculate the ablation amount D: Where: ε is the ablation rate; S93: Make a stress linearization path along the thickness direction of the structure at the dangerous stress point in the stress field to obtain the primary overall film stress S at the high stress position. I Or the primary local film stress S Ⅱ , and calculate the allowable stress S of the material under high temperature conditions m , the allowable material stress Sm is determined by the minimum value of the following formula: Where: u : is the tensile strength; σ p0.2 : is the yield strength; σ t p0.2 : is the yield strength at the highest temperature of the component; S94: Taking film stress as the criterion, when S I >KS m And S Ⅱ >1.5KS m , the key load-bearing component breaks and fails; otherwise, the indicator passes and it is assessed that the metal component has not failed; K is the safety factor.

Images