Boundary layer control method and boundary layer control system for main chamber of carbon fiber pre-oxidation furnace

Abstract

The invention belongs to the technical field of carbon fiber pre-oxidation, and particularly relates to a boundary layer control method and a boundary layer control system for a main chamber of a carbon fiber pre-oxidation furnace. The method comprises the following steps: acquiring a thickness development formula of the boundary layer of the furnace wall of the pre-oxidation furnace, calculating a key node position of a boundary layer control system, arranging a negative-pressure exhaust system, and timely exhausting detained gas with low oxygen content and high pollutant concentration near the wall surface based on oxygen concentration deviation information of a mainstream area and the boundary layer in the furnace, so as to achieve the purpose of controlling the thickness of the boundary layer. Comprising low-speed gas in a laminar flow boundary layer and rotational flow gas in a turbulent flow boundary layer. The method provides a theoretical basis for an actual process operation process; the uniformity of a flow field in the furnace is obviously improved, and the quality of a carbon fiber product is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of carbon fiber pre-oxidation, and particularly relates to a method for controlling the boundary layer of the main chamber of a carbon fiber pre-oxidation furnace and a boundary layer control system. Background Art

[0002] Carbon fiber has excellent mechanical properties and chemical stability. It has a lower density than aluminum and a higher strength than steel. It is the fiber with the highest specific strength and the highest specific modulus among the high-performance fibers that have been mass-produced at present, and has characteristics such as low density, corrosion resistance, high temperature resistance, wear resistance, fatigue resistance, high vibration attenuation, high electrical and thermal conductivity, low thermal and wet expansion coefficients, high X-ray penetrability, non-magnetic but with electromagnetic shielding effect, etc. It is an important strategic material for the development of national defense and the national economy, and is applied to the national defense industry and high-performance civilian fields, involving military, aerospace, ocean engineering, sports goods, automotive industry, new energy equipment, medical devices, engineering machinery, transportation, construction and its structural reinforcement and other fields.

[0003] In the whole process of preparing high-performance carbon fiber, the pre-oxidation process is a key link affecting the quality of carbon fiber and is a bridge connecting the precursor and carbon fiber. The pre-oxidation process has high requirements for the uniformity of the gas flow field and the oxygen content in the furnace. In traditional pre-oxidation equipment, the wind speed at the furnace inlet is uniform, but due to the existence of the velocity boundary layer, there will be gas retention areas (laminar boundary layer) with higher pollutant concentration and lower oxygen content and swirling areas (turbulent boundary layer) on both side walls. Along the advancing direction of the hot air, the boundary layer thickness increases and gradually invades the oxidation area of the carbon fiber precursor, restricting the product quality.

[0004] Therefore, there is an urgent need to design a method for controlling the boundary layer of the main chamber of a carbon fiber pre-oxidation furnace and a boundary layer control system to solve the technical problems that there will be gas retention areas (laminar boundary layer) with higher pollutant concentration and lower oxygen content and swirling areas (turbulent boundary layer) on both side walls of the furnace, and along the advancing direction of the hot air, the boundary layer thickness increases and gradually invades the oxidation area of the carbon fiber precursor, restricting the product quality.

[0005] It should be noted that the above information disclosed in this background art section is only used to understand the background art of the concept of this application, and therefore, it may include information that does not constitute the prior art. Summary of the Invention

[0006] The embodiments of the present disclosure at least provide a method for controlling the boundary layer of the main chamber of a carbon fiber pre-oxidation furnace and a boundary layer control system.

[0007] In a first aspect, an embodiment of the present disclosure provides a method for controlling the boundary layer of the main chamber of a carbon fiber pre-oxidation furnace. The method includes obtaining the formula for the development of the boundary layer thickness of the furnace wall of the pre-oxidation furnace, calculating the key node positions of the boundary layer control system, and arranging a negative pressure exhaust system to timely remove the stagnant gas with a relatively low oxygen content and a relatively high pollutant concentration near the wall surface, including the low-speed gas in the laminar boundary layer and the swirling gas in the turbulent boundary layer, thereby greatly improving the uniformity of the gas flow field in the furnace. The specific steps are as follows:

[0008] Step A, run the pre-oxidation furnace for trial operation and perform the following analysis and calculations:

[0009] A1, measure the gas flow velocity at the characteristic positions in the oxidation furnace. Based on the above measurement data and in combination with the theory of the development of the boundary layer thickness of a flat plate, obtain the formula for the development of the boundary layer thickness of the furnace wall of the pre-oxidation furnace:

[0010] δ(x) = k1x / Re x 1 / 2 , Re x ≤Re cr , laminar boundary layer;

[0011] δ(x) = k2x / Re x 1 / 5 , Re x >Re cr , turbulent boundary layer;

[0012] Among them, δ(x) is the thickness of the flat plate velocity boundary layer, and the Reynolds number Re x = ux / v is the ratio of the fluid inertial force to the viscous force, v is the kinematic viscosity of air, u is the set air supply wind speed of the pre-oxidation furnace, Re cr is the critical Reynolds number for the transition between laminar and turbulent flows, k1 and k2 are correction coefficients, and x is the position of the leading edge of the flat plate;

[0013] A2, obtain the minimum distance d between the carbon fiber tow and the wall surface in the actual process, calculate the position x0 where the velocity boundary layer invades the tow running area, and let δ(x) = d to solve for x = x0;

[0014] A3, let Re x = ux / v = Re cr , obtain x = x1, and calculate the target exhaust air volume Q of the system and the target negative pressure setting value P of the exhaust port;

[0015] When x0 < x1,

[0016]

[0017] When x0 ≥ x1,

[0018]

[0019] Wherein, L is the length of the preoxidation furnace, W is the width of the preoxidation furnace, H is the height of the preoxidation furnace, x1 is the position where the laminar boundary layer transforms into the turbulent boundary layer, τ is the set exhaust time, P0 is the measured pressure value of the boundary layer gas, u1 is the exhaust wind speed, and ρ is the air density;

[0020] Step B, based on the above analysis data, arrange the boundary layer control system, operate the pre-oxidation furnace, when the deviation between the measured oxygen concentration F0 and the target oxygen concentration F is a1=│F-F0│ / F>a0, feed back the first signal to the control system, the control system sends a signal to the fresh air fan, adjusts the fresh air volume, when a1≤a0, the fresh air fan maintains the current air volume and continues to operate, wherein a0 is the allowable deviation of the oxygen concentration in the pre-oxidation furnace;

[0021] Step C, the detector collects the measured oxygen concentration values ​​F1 and F2 of the wall boundary layer and the mainstream area at the position x=x0 in the pre-oxidation furnace, and sends them to the control system, and the control system calculates the relative deviation a2=│F1-F2│ / F;

[0022] When a2>a0, it is judged that the oxygen concentration in the boundary layer is too low, the flow field non-uniformity increases, and it cannot meet the process requirements. The second signal is fed back to the control system, and the control system controls the negative pressure exhaust system to start the negative pressure exhaust. At the same time, the control system controls the circulating fan to adjust the return air volume to maintain the air supply flow at Q0;

[0023] When a2≤a0, it is determined that the oxygen concentration in the furnace is uniform, and a third signal is fed back to the control system, and the control system controls the negative pressure exhaust system to stop exhausting.

[0024] In an optional implementation, in step B, the target oxygen concentration F is in the range of 5% to 20%, and the allowable deviation a0 of oxygen concentration is in the range of 1% to 2%.

[0025] In an optional embodiment, in step A, the critical Reynolds number Re cr The value range is: 3.5×10 5 ≤Re cr ≤5×10 5 .

[0026] In step A, the target exhaust air volume Q does not exceed 30% of the target air supply volume Q0 of the pre-oxidation furnace.

[0027] In an optional embodiment, the arrangement range of the negative pressure system is from x2 to L, wherein 0.85x0≤x2≤x0.

[0028] In an optional implementation, the deviation ΔT=|T0-T1| between the actual supply air temperature T1 and the target supply air temperature T0 is monitored, and ΔT≤1°C is maintained.

[0029] In an alternative embodiment, the value range of the exhaust air velocity u1 is from 1 m / s to 3 m / s.

[0030] In a second aspect, an embodiment of the present disclosure further provides a pre-oxidation furnace boundary layer control system, which is applied to execute the boundary layer control method as shown above. The pre-oxidation furnace boundary layer control system includes:

[0031] A main chamber having at least one negative pressure exhaust mechanism. The negative pressure exhaust mechanism includes a negative pressure generator and an exhaust chamber. The negative pressure generator is connected to the exhaust chamber, and the negative pressure generator is used to provide the power required for exhaust.

[0032] An exhaust flowmeter is arranged at the outlet of the exhaust chamber, and the exhaust flowmeter is used to feedback the actual exhaust air volume.

[0033] The negative pressure exhaust mechanism further includes an air outlet, and the air outlet is arranged on the side wall of the main chamber of the pre-oxidation furnace and is connected to the exhaust chamber.

[0034] An exhaust solenoid valve is further provided between the negative pressure generator and the exhaust chamber.

[0035] In an alternative embodiment, an exhaust outlet pressure sensor is installed at the outlet of the exhaust chamber for feedback of the exhaust pressure P.

[0036] A boundary layer pressure sensor is installed on the side wall of the main chamber for feedback of the air flow pressure P0 in the boundary layer.

[0037] In an alternative embodiment, a first oxygen concentration sensor and a second oxygen concentration sensor are respectively arranged in the wall boundary layer and the mainstream region at the position x = x0 of the main chamber.

[0038] In an alternative embodiment, the boundary layer control system further includes a fresh air fan, a circulating air fan and an electric heater. The fresh air fan and the circulating air fan are respectively connected to the inlet of the electric heater. The outlet of the electric heater is connected to the inlet of the main chamber through an air supply pipe. The outlet of the main chamber is connected to the inlet of the circulating air fan through a circulating pipe.

[0039] The fresh air fan is used to provide the oxygen required for the pre-oxidation process, the circulating air fan is used to provide the power for the return air circulation, and the electric heater is used to provide the heat required for the pre-oxidation process.

[0040] An air supply temperature sensor, an air supply flowmeter and an inlet oxygen concentration sensor are further arranged on the air supply pipe for feedback of the air supply temperature, the air supply flow rate and the oxygen concentration in the air supply pipe.

[0041] The beneficial effects of the present invention are as follows: 1. The present invention obtains the development parameters of the velocity boundary layer of the pre-oxidation furnace wall, calculates the target exhaust air volume and pressure of the boundary layer, and provides a theoretical basis for the actual process operation; 2. Based on the oxygen concentration deviation information between the mainstream area and the boundary layer in the furnace, the present invention timely removes the stagnant gas and swirling gas with a high pollutant concentration and a low oxygen concentration in the boundary layer through the exhaust system, thereby significantly improving the uniformity of the flow field in the furnace.

[0042] Other features and advantages of the present invention will be described in the following specification, and in part, will be obvious from the specification, or will be understood by implementing the present invention. The objectives and other advantages of the present invention are achieved and obtained by the structures specifically pointed out in the specification, claims, and drawings.

[0043] To make the above objectives, features, and advantages of the present invention more obvious and understandable, the following specifically provides preferred embodiments and, in conjunction with the accompanying drawings, the detailed description is as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0045] Figure 1 It is a schematic flow chart of a method for controlling the boundary layer of the main chamber of a carbon fiber pre-oxidation furnace provided by an embodiment of the present disclosure;

[0046] Figure 2 It is a schematic structural diagram of a boundary layer control system for a pre-oxidation furnace provided by an embodiment of the present disclosure;

[0047] Figure 3 It is a schematic diagram of the distribution of the internal laminar boundary layer and turbulent boundary layer of the main chamber provided by an embodiment of the present disclosure.

[0048] In the figure:

[0049] 1. Main chamber; 11. Exhaust port; 12. Exhaust chamber; 2. Exhaust solenoid valve; 3. Exhaust flowmeter; 4. Negative pressure generator; 50. Exhaust outlet pressure sensor; 51. Boundary layer pressure sensor; 60. Inlet oxygen concentration sensor; 61. First oxygen concentration sensor; 62. Second oxygen concentration sensor; 7. Air supply temperature sensor; 8. Air supply flowmeter; 9. Electric heater; 10. Fresh air fan; 13. Recirculating air fan;

[0050] C1. First control center; C2. Second control center. Detailed implementation manners

[0051] To make the objectives, technical solutions, and advantages of the embodiments of the present disclosure clearer, the technical solutions of the embodiments of the present disclosure will be clearly and completely described below with reference to the accompanying drawings. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0052] Through research, it is found that the pre-oxidation process has high requirements for the uniformity of the gas flow field and the oxygen content in the furnace. In traditional pre-oxidation equipment, the air velocity at the furnace inlet is uniform. However, due to the existence of the velocity boundary layer, there will be gas retention zones (laminar boundary layers) with high pollutant concentrations and low oxygen contents and swirl zones (turbulent boundary layers) on both side walls. Along the advancing direction of the hot air, the boundary layer thickness increases and gradually invades the oxidation zone of the carbon fiber roving, restricting the product quality.

[0053] Regarding the defects existing in the above solutions, they are all the results obtained by the inventors through practice and careful research. Therefore, the discovery process of the above problems and the solutions proposed by the present disclosure for the above problems in the following text should all be the contributions made by the inventors to the present disclosure during the process of the present disclosure.

[0054] The following will describe in detail some embodiments of the present invention with reference to the accompanying drawings. Without conflict, the following embodiments and the features in the embodiments can be combined with each other. In addition, in the drawings, to effectively describe the technical content, the thickness of the components can be exaggerated or reduced.

[0055] It should be noted that similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0056] Based on the above research, referring to Figure 1 , the embodiments of the present disclosure provide a method for controlling the boundary layer of the main chamber of a carbon fiber pre-oxidation furnace, obtaining the development formula of the boundary layer thickness of the furnace wall of the pre-oxidation furnace, calculating the key node positions of the boundary layer control system, and arranging a negative pressure exhaust system to timely remove the retained gas with low oxygen content and high pollutant concentration near the wall surface, including the low-speed gas in the laminar boundary layer and the swirl gas in the turbulent boundary layer, thereby greatly improving the uniformity of the gas flow field in the furnace. The specific steps are as follows:

[0057] Step A, run the pre-oxidation furnace in trial operation and perform the following analysis and calculation:

[0058] A1. Measure the air flow velocity at the characteristic position in the oxidation furnace. Based on the above measurement data and combined with the theory of the development of the flat plate boundary layer thickness, obtain the formula for the development of the boundary layer thickness of the pre-oxidation furnace wall:

[0059] δ(x) = k1x / Re x 1 / 2 , Re x ≤Re cr , laminar boundary layer;

[0060] δ(x) = k2x / Re x 1 / 5 , Re x >Re cr , turbulent boundary layer;

[0061] Among them, δ(x) is the thickness of the flat plate velocity boundary layer, and the Reynolds number Re x = ux / v is the ratio of the fluid inertial force to the viscous force, v is the kinematic viscosity of the air, u is the set air supply wind speed of the pre-oxidation furnace, Re cr is the critical Reynolds number for the transition between laminar and turbulent flows, k1 and k2 are correction coefficients, and x is the position of the leading edge of the flat plate;

[0062] A2. Obtain the minimum distance d between the carbon fiber tow and the wall surface in the actual process, calculate the position x0 where the velocity boundary layer invades the tow running area, let δ(x) = d, and solve for x = x0;

[0063] A3. Let Re x = ux / v = Re cr , obtain x = x1, and calculate the system target exhaust air volume Q and the target negative pressure setting value P of the exhaust port;

[0064] When x0 < x1,

[0065]

[0066] When x0 ≥ x1,

[0067]

[0068] Among them, L is the length of the pre-oxidation furnace, W is the width of the pre-oxidation furnace, H is the height of the pre-oxidation furnace, x1 is the position where the laminar boundary layer transitions to the turbulent boundary layer, τ is the set exhaust time, P0 is the measured pressure value of the boundary layer gas, u1 is the exhaust wind speed, and ρ is the air density;

[0069] Step B: Based on the above analysis data, arrange the boundary layer control system and operate the pre-oxidation furnace. When the deviation a1 = │F - F0│ / F between the measured oxygen concentration F0 and the target oxygen concentration F is greater than a0, feedback the first signal to the control system. The control system sends a signal to the fresh air fan to adjust the fresh air volume. When a1 ≤ a0, the fresh air fan maintains the current air volume and continues to operate, where a0 is the allowable deviation of the oxygen concentration in the pre-oxidation furnace.

[0070] Step C: The detector collects the measured oxygen concentration values F1 and F2 at the wall boundary layer and the mainstream area at the position x = x0 inside the pre-oxidation furnace and sends them to the control system. The control system calculates the relative deviation a2 = │F1 - F2│ / F.

[0071] When a2 > a0, it is determined that the oxygen concentration in the boundary layer is too low, the flow field non-uniformity increases, and the process requirements cannot be met. Feedback the second signal to the control system. The control system controls the negative pressure exhaust system to start negative pressure exhaust. At the same time, the control system controls the circulation fan to adjust the return air volume so that the supply air flow rate is maintained at Q0.

[0072] When a2 ≤ a0, it is determined that the oxygen concentration in the furnace is uniform, and feedback the third signal to the control system. The control system controls the negative pressure exhaust system to stop exhausting.

[0073] In at least one embodiment, in Step B, the value range of the target oxygen concentration F is 5% to 20%, and the value range of the allowable deviation a0 of the oxygen concentration is 1% to 2%.

[0074] In at least one embodiment, in Step A, the critical Reynolds number Re cr has a value range of:

[0075] 3.5×10 5 ≤ Re cr ≤ 5×10 5 .

[0076] In Step A, the target exhaust air volume Q does not exceed 30% of the target supply air volume Q0 of the pre-oxidation furnace.

[0077] Referring to Figure 3 , in at least one embodiment, the arrangement range of the negative pressure system is from x2 to L, where 0.85x0 ≤ x2 ≤ x0.

[0078] In at least one embodiment, monitor the deviation ΔT = |T0 - T1| between the actual supply air temperature T1 and the target supply air temperature T0, and keep ΔT ≤ 1°C.

[0079] In at least one embodiment, the value range of the exhaust air velocity u1 is 1 m / s to 3 m / s.

[0080] In addition, an embodiment of the present disclosure also provides a pre-oxidation furnace boundary layer control system, which is applied to execute the boundary layer control method as shown above. Refer to Figure 2 , the pre-oxidation furnace boundary layer control system includes: a main chamber 1, which is a square cavity and has process parameters according to the square structure, a length L, a width W, and a height H. The inside of the main chamber 1 is suitable for performing the carbon fiber pre-oxidation process. At least one negative pressure exhaust mechanism is installed on the side wall of the main chamber 1. The negative pressure exhaust mechanism includes a negative pressure generator 4 and an exhaust chamber 12. The air outlet of the exhaust chamber 12 is connected to the negative pressure generator 4 through an exhaust pipe. The negative pressure generator 4 is used to provide the power required for exhaust. The negative pressure exhaust mechanism also includes an exhaust port 11. A plurality of exhaust ports 11 are evenly arranged on the side wall of the pre-oxidation furnace main chamber 1, and the exhaust port 11 is connected to the exhaust chamber 12. The exhaust port 11 is used to guide the gas in the main chamber 1 to be discharged. The exhaust chamber 12 is used to collect the gas discharged from each exhaust port 11 and transmit it to the negative pressure generator 4.

[0081] Refer to Figure 1 , in at least one embodiment, an exhaust flow meter 3 is provided at the outlet of the exhaust chamber 12. The exhaust flow meter 3 is used to feedback the actual exhaust air volume.

[0082] Refer to Figure 1 , in at least one embodiment, an exhaust solenoid valve 2 is further provided between the negative pressure generator 4 and the exhaust chamber 12. The exhaust solenoid valve 2 is used to adjust the opening degree of the exhaust pipe, where the minimum opening degree means closing the exhaust pipe, and the maximum opening degree means the exhaust pipe is fully open.

[0083] Refer to Figure 1 , in at least one embodiment, an exhaust outlet pressure sensor 50 is installed at the outlet of the exhaust chamber 12 to feedback the exhaust pressure P. A boundary layer pressure sensor 51 is installed on the side wall of the main chamber 1 to feedback the air flow pressure P0 in the boundary layer.

[0084] Refer to Figure 1 , in at least one embodiment, two negative pressure exhaust mechanisms are provided, and the two negative pressure exhaust mechanisms are respectively arranged on both sides of the main chamber 1, so that the two negative pressure exhaust mechanisms can evenly discharge the gas in the main chamber 1 from both sides.

[0085] Refer to Figure 1 , in at least one embodiment, a first oxygen concentration sensor 61 and a second oxygen concentration sensor 62 are respectively arranged in the wall boundary layer and the mainstream area at the position x = x0 of the main chamber 1 to monitor the oxygen concentration in the main chamber 1. Preferably, the first oxygen concentration sensor 61 and the second oxygen concentration sensor 62 are ZrO2 sensors.

[0086] Refer to Figure 1, in at least one embodiment, the boundary layer control system further includes a fresh air fan 10, a recirculating air fan 13 and an electric heater 9. The fresh air fan 10 and the recirculating air fan 13 are respectively connected to the inlet of the electric heater 9. The outlet of the electric heater 9 is connected to the inlet of the main chamber 1 through a supply air duct. The outlet of the main chamber 1 is connected to the inlet of the recirculating air fan 13 through a circulation duct. The fresh air fan 10 is used to provide the oxygen required for the pre-oxidation process, the recirculating air fan 13 is used to provide the power for the return air circulation, and the electric heater 9 is used to provide the heat required for the pre-oxidation process. A supply air temperature sensor 7, a supply air flow meter 8 and an inlet oxygen concentration sensor 60 are also provided on the supply air duct to feedback the supply air temperature, supply air flow and oxygen concentration in the supply air duct.

[0087] Referring to Figure 1 , in at least one embodiment, the boundary layer control system further includes a control module. The control module further includes a first control center C1 and a second control center C2. Among them, the negative pressure generator 4, the exhaust air flow meter 3, the exhaust air solenoid valve 2, the first oxygen concentration sensor 61 and the second oxygen concentration sensor 62, the exhaust air outlet pressure sensor 50 and the boundary layer pressure sensor 51 are all electrically connected to the first control center C1. The first control center C1 can control the opening and closing of the negative pressure generator 4 and the opening degree of the exhaust air solenoid valve 2. The data collected by the exhaust air flow meter 3, the exhaust air outlet pressure sensor 50 and the boundary layer pressure sensor 51 are all fed back to the first control center C1; the inlet oxygen concentration sensor 60, the supply air temperature sensor 7, the supply air flow meter 8, the electric heater 9, the fresh air fan 10, the recirculating air fan 13 are all electrically connected to the second control center C2. The second control center C2 can control the opening and closing of the electric heater 9, the fresh air fan 10 and the recirculating air fan 13. The data collected by the inlet oxygen concentration sensor 60, the supply air temperature sensor 7 and the supply air flow meter 8 are all fed back to the first control center C2.

[0088] Referring to Figure 1 , in at least one embodiment, the specific process of the pre-oxidation furnace boundary layer control system executing the carbon fiber pre-oxidation furnace main chamber boundary layer control method shown above is as follows:

[0089] Step S1, commission the pre-oxidation furnace;

[0090] Step S11, measure the air flow velocity at the characteristic positions in the oxidation furnace. Based on the above measurement data and combined with the flat plate boundary layer thickness development theory, obtain the pre-oxidation furnace wall boundary layer thickness development formula:

[0091] δ(x) = k1x / Re x 1 / 2 , Re x ≤Re cr , laminar boundary layer;

[0092] δ(x) = k2x / Re x 1 / 5 , Re x > Re cr , turbulent boundary layer;

[0093] where δ(x) is the thickness of the flat plate velocity boundary layer, and the Reynolds number Re x = ux / v is the ratio of the fluid inertial force to the viscous force, v is the kinematic viscosity of air, u is the set air supply velocity of the pre-oxidation furnace, and Re cr is the critical Reynolds number for the transition between laminar and turbulent flows, k1 and k2 are correction factors, and x is the position of the leading edge of the flat plate;

[0094] Step S12: Obtain the minimum distance d between the carbon fiber tow and the wall surface in the actual process, calculate the position x0 where the velocity boundary layer invades the tow running area, let δ(x) = d, and solve for x = x0;

[0095] Step S13: Let Re x = ux / v = Re cr , obtain x = x1, and calculate the system target exhaust air volume Q and the target negative pressure setting value P of the exhaust port;

[0096] When x0 < x1,

[0097]

[0098] When x0 ≥ x1,

[0099]

[0100] where L is the length of the pre-oxidation furnace, W is the width of the pre-oxidation furnace, H is the height of the pre-oxidation furnace, x1 is the position where the laminar boundary layer transitions to the turbulent boundary layer, τ is the set exhaust time, P0 is the measured pressure value of the boundary layer gas, u1 is the exhaust air velocity, and ρ is the air density;

[0101] Step S2: Based on the above analysis data, arrange the boundary layer control system, operate the pre-oxidation furnace, monitor the measured oxygen concentration F0 through the intake oxygen concentration sensor 60 and feedback it to the second control center C2. The second control center C2 feeds back a signal to the control module. When the control module calculates that the deviation a1 = │F - F0│ / F > a0 between F0 and the target oxygen concentration F, the control module feeds back the first signal to the second control center C2. The second control center C2 sends a signal to the fresh air fan 13 to adjust the fresh air volume. When a1 ≤ a0, the fresh air fan 13 continues to operate at the current air volume, where a0 is the allowable deviation of the oxygen concentration in the pre-oxidation furnace;

[0102] Step S3: The first oxygen concentration sensor 61 and the second oxygen concentration sensor 62 respectively collect the measured oxygen concentration values F1 and F2 at the wall boundary layer and the mainstream area at the position of x = x0 in the pre-oxidation furnace, and feedback them to the first control center C1. The first control center C1 feeds back a signal to the control module, and the control module calculates the relative deviation a2 = │F1 - F2│ / F;

[0103] When a2 > a0, it is determined that the oxygen concentration in the boundary layer is too low, the flow field non-uniformity increases, and the process requirements cannot be met. The control module feeds back a second signal to the first control center C1, and the control system controls the negative pressure generator to adjust the negative pressure value P of the air outlet 11 and increases the opening degree of the exhaust air solenoid valve 2 to turn on the negative pressure exhaust. At the same time, the second control center C2 controls the circulation air fan 13 to adjust the return air volume so that the value of the gas flowmeter 8 still maintains the set air supply flow rate Q0.

[0104] When a2 ≤ a0, it is determined that the oxygen concentration in the furnace is uniform. The control module feeds back a third signal to the first control center C1, and the first control center C1 controls the opening degree of the exhaust air solenoid valve 2 to the minimum and stops the exhaust.

[0105] In several embodiments provided in the present application, it should be understood that the disclosed systems, devices, and methods can be implemented in other ways. The device embodiments described above are merely illustrative. For example, the division of the units is only a logical function division, and there can be other division methods in actual implementation. For another example, multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Based on the above inspiration from the ideal embodiments of the present invention, through the above description, relevant workers can make various changes and modifications completely within the scope of the technical idea of this disclosed embodiment without departing from it. The technical scope of this disclosed embodiment is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A method for controlling the boundary layer of the main chamber of a carbon fiber preoxidation furnace, characterized in that: Obtain the formula for the thickness development of the boundary layer of the pre-oxidation furnace wall, calculate the key node positions of the boundary layer control system, and arrange a negative pressure exhaust system to promptly remove the trapped gas with low oxygen content and high pollutant concentration near the wall, including the low-speed gas in the laminar boundary layer and the swirling gas in the turbulent boundary layer, thereby greatly improving the uniformity of the air flow field in the furnace. The specific steps include the following: Step A, test run the pre-oxidation furnace, and make the following analysis and calculation: A1, measure the air flow velocity at the characteristic position in the oxidation furnace. Based on the above measurement data and the flat plate boundary layer thickness development theory, the boundary layer thickness development formula of the pre-oxidation furnace wall is obtained: δ(x)=k1x / Rex1 / 2, Rex≤Recr, laminar boundary layer; δ(x)=k2x / Rex1 / 5, Rex>Recr, turbulent boundary layer; Where δ(x) is the thickness of the flat plate velocity boundary layer, and the Reynolds number Re x =ux / v is the ratio of fluid inertia force to viscous force, v is the kinematic viscosity of air, u is the set air supply speed of the pre-oxidation furnace, Re cr is the critical Reynolds number for transition between laminar flow and turbulent flow, k1 and k2 are correction coefficients, and x is the position of the leading edge of the flat plate; A2, obtain the minimum distance d between the carbon fiber tow and the wall in the actual process, calculate the position x0 where the velocity boundary layer invades the tow running area, set δ(x) = d, and solve x = x0; A3, let Re x =ux / v=Re cr , obtain x=x1, calculate the system target exhaust volume Q and the exhaust port target negative pressure setting value P; When x0<x1, When x0 ≥ x1, Wherein, L is the length of the preoxidation furnace, W is the width of the preoxidation furnace, H is the height of the preoxidation furnace, x1 is the position where the laminar boundary layer transforms into the turbulent boundary layer, τ is the set exhaust time, P0 is the measured pressure value of the boundary layer gas, u1 is the exhaust wind speed, and ρ is the air density; Step B, based on the above analysis data, arrange the boundary layer control system, operate the pre-oxidation furnace, when the deviation between the measured oxygen concentration F0 and the target oxygen concentration F is a1=│F-F0│ / F>a0, feed back the first signal to the control system, the control system sends a signal to the fresh air fan, adjusts the fresh air volume, when a1≤a0, the fresh air fan maintains the current air volume and continues to operate, wherein a0 is the allowable deviation of the oxygen concentration in the pre-oxidation furnace; Step C, the detector collects the measured oxygen concentration values ​​F1 and F2 of the wall boundary layer and the mainstream area at the position x=x0 in the pre-oxidation furnace, and sends them to the control system, and the control system calculates the relative deviation a2=│F1-F2│ / F; When a2>a0, it is judged that the oxygen concentration in the boundary layer is too low, the flow field non-uniformity increases, and it cannot meet the process requirements. The second signal is fed back to the control system, and the control system controls the negative pressure exhaust system to start the negative pressure exhaust. At the same time, the control system controls the circulating fan to adjust the return air volume to maintain the air supply flow at Q0; When a2≤a0, it is determined that the oxygen concentration in the furnace is uniform, and the third signal is fed back to the control system, and the control system controls the negative pressure exhaust system to stop exhausting.

2. The method for controlling the boundary layer of the main chamber of the carbon fiber preoxidation furnace according to claim 1, characterized in that: In step B, the target oxygen concentration F is in the range of 5% to 20%, and the allowable deviation a0 of the oxygen concentration is in the range of 1% to 2%.

3. The method for controlling the boundary layer of the main chamber of the carbon fiber preoxidation furnace according to claim 1, characterized in that: In step A, the critical Reynolds number Re cr The value range is: 3.5×10 5 ≤Re cr ≤5×10 5 . In step A, the target exhaust air volume Q does not exceed 30% of the target air supply volume Q0 of the pre-oxidation furnace.

4. The method for controlling the boundary layer of the main chamber of the carbon fiber preoxidation furnace according to claim 1, characterized in that: The arrangement range of the negative pressure system is from x2 to L, where 0.85x0≤x2≤x0.

5. The method for controlling the boundary layer of the main chamber of the carbon fiber preoxidation furnace according to claim 1, characterized in that: Monitor the deviation ΔT=|T0-T1| between the actual supply air temperature T1 and the target supply air temperature T0, and keep ΔT≤1°C.

6. The method for controlling the boundary layer of the main chamber of the carbon fiber preoxidation furnace according to claim 1, characterized in that: The exhaust wind speed u1 ranges from 1 m / s to 3 m / s.

7. A boundary layer control system for a pre-oxidation furnace, characterized in that: Applied to executing the boundary layer control method according to any one of claims 1 to 6, the pre-oxidation furnace boundary layer control system comprises: A main chamber (1) having at least one negative pressure exhaust mechanism, the negative pressure exhaust mechanism comprising a negative pressure generator (4) and an exhaust chamber (12), the negative pressure generator (4) being connected to the exhaust chamber (12), the negative pressure generator (4) being used to provide power required for exhaust; An exhaust flow meter (3) is provided at the outlet of the exhaust chamber (12), and the exhaust flow meter (3) is used to feed back the actual exhaust volume; The negative pressure exhaust mechanism further comprises an exhaust port (11), the exhaust port (11) being arranged on the side wall of the main chamber (1) of the pre-oxidation furnace, and the exhaust port (11) being connected to an exhaust chamber (12); An exhaust solenoid valve (2) is also provided between the negative pressure generator (4) and the exhaust chamber (12).

8. The boundary layer control system of the pre-oxidation furnace according to claim 7, characterized in that: An exhaust outlet pressure sensor (50) is installed at the outlet of the exhaust chamber (12) to provide feedback of the exhaust pressure P; A boundary layer pressure sensor (51) is installed on the side wall of the main chamber (1) for feeding back the airflow pressure P0 in the boundary layer.

9. The boundary layer control system of the pre-oxidation furnace according to claim 7, characterized in that: A first oxygen concentration sensor (61) and a second oxygen concentration sensor (62) are respectively arranged in the wall boundary layer and the mainstream region of the main chamber (1) at the position x=x0.

10. The boundary layer control system of the pre-oxidation furnace according to claim 7, characterized in that: The boundary layer control system further comprises a fresh air fan (10), a circulating air fan (13) and an electric heater (9); the fresh air fan (10) and the circulating air fan (13) are respectively connected to the inlet of the electric heater (9); the outlet of the electric heater (9) is connected to the inlet of the main chamber (1) via an air supply pipe; and the outlet of the main chamber (1) is connected to the inlet of the circulating air fan (13) via a circulation pipe; The fresh air fan (10) is used to provide oxygen required for the pre-oxidation process, the circulating air fan (13) is used to provide return air circulation power, and the electric heater (9) is used to provide heat required for the pre-oxidation process; The air supply pipe is also provided with an air supply temperature sensor (7), an air supply flow meter (8) and an intake oxygen concentration sensor (60) for feeding back the air supply temperature, air supply flow rate and oxygen concentration in the air supply pipe.

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