Heat exchanger temperature regulation and heat exchange deterioration recovery method based on liquid nitrogen working medium

Abstract

The invention discloses a heat exchanger temperature adjustment and heat exchange deterioration recovery method based on a liquid nitrogen working medium. Constructing test conditions; 2, air state adjustment: adjusting the air flow and temperature of the air inlet of the precooler according to the test working condition of the test engine; 3, initial supply of liquid nitrogen; 4, liquid nitrogen flow adjustment is conducted, specifically, the air flow and temperature of an air inlet of the precooler are changed respectively, and the liquid nitrogen supply flow is adjusted at the same time in the process; 5, liquid nitrogen heat exchange failure judgment is conducted, and when the temperature of liquid nitrogen at a medium outlet is decreased, but the temperature of an air outlet is almost unchanged or continuously increased, heat exchange deterioration occurs; sixthly, liquid nitrogen heat exchange failure recovery is conducted, the liquid nitrogen supply pressure is kept, and it is ensured that liquid nitrogen in a medium pipeline in the precooler is in a supercritical state; and 7, liquid nitrogen heat exchange failure recovery is judged, the liquid nitrogen supply flow is adjusted, and when the air temperature of an air outlet is decreased and the nitrogen discharge temperature is increased, it is indicated that heat exchange deterioration is recovered.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of aero-engine test, and particularly relates to a method for regulating temperature and recovering heat exchange deterioration of a heat exchanger based on a liquid nitrogen working medium. BACKGROUND

[0002] With the increase of the flight speed of an airplane, the engine inlet temperature gradually increases, and in order to improve the engine flight envelope and enhance the engine flight performance, the problem of thermal protection needs to be solved by using an advanced thermal management technology, which can cool the engine inlet air by installing a pre-cooler with large flow and high heat exchange at the engine inlet. This method has outstanding cooling capacity, but also has certain shortcomings, such as large system weight, refrigerant storage, etc.

[0003] In the combined operation test of the pre-cooler and the engine, the risk is still high, and in the test, when and how to accurately regulate the liquid nitrogen supply can meet the engine inlet air temperature requirement. At the same time, the heat exchange deterioration of the pre-cooler is prone to occur in the test, and at this time, the heat exchange deterioration state needs to be quickly exited, otherwise the engine inlet air temperature will sharply increase, which will cause the engine to flame out and even damage the engine. At present, the method adopted is to stop the engine in emergency, close the high-temperature inlet, and gradually close the liquid nitrogen supply. On the one hand, the time is long, which will affect the service life of the engine, and on the other hand, the efficiency is low, which will cause great waste of energy.

[0004] Therefore, how to provide a method for regulating temperature and recovering heat exchange deterioration of a heat exchanger based on a liquid nitrogen working medium is a problem to be solved by those skilled in the art. SUMMARY

[0005] Therefore, the application provides a method for regulating temperature and recovering heat exchange deterioration of a heat exchanger based on a liquid nitrogen working medium, which can not only guarantee the regulation accuracy of the engine inlet air temperature to meet the test requirement, but also guarantee the quick exit of the engine protection in the heat exchange deterioration, and truly support the development of the project.

[0006] In order to achieve the above purpose, the application adopts the following technical scheme: a method for regulating temperature and recovering heat exchange deterioration of a heat exchanger based on a liquid nitrogen working medium, comprising the following steps: step one; constructing a test condition, arranging a pre-cooler in front of the inlet of a test engine, and connecting the outlet of the pre-cooler to the inlet of the test engine through a pipeline; Step two: air state regulation, adjusting the air flow and temperature at the inlet of the pre-cooler according to the test condition of the test engine; Step three: initial supply of liquid nitrogen, introducing the liquid nitrogen into the medium inlet of the pre-cooler and into the medium pipeline inside the pre-cooler; Step four: liquid nitrogen flow regulation, respectively change the air flow and temperature of the pre-cooler inlet, while adjusting the liquid nitrogen supply flow to ensure that the temperature fluctuation of the pre-cooler outlet is within 15 DEG C; Step five: liquid nitrogen heat exchange failure judgment, when the liquid nitrogen flow increases or the pre-cooler medium outlet liquid nitrogen temperature drops, but the outlet air temperature hardly changes or continuously rises, it indicates that the heat exchange deterioration occurs; Step six: liquid nitrogen heat exchange failure recovery, maintain the liquid nitrogen supply pressure to ensure that the liquid nitrogen in the pre-cooler internal medium pipeline is in a supercritical state; Step seven: liquid nitrogen heat exchange failure recovery judgment, adjust the liquid nitrogen supply flow to ensure heat exchange, observe the nitrogen discharge temperature after heat exchange and the air temperature at the outlet, when the air temperature at the outlet drops and the nitrogen discharge temperature rises, it indicates that the heat exchange deterioration is recovered.

[0007] The technical effects generated by the application are: according to the engine working condition, the corresponding air temperature and flow can be provided to support the related test, and when the heat exchange fails, the heat exchange deterioration state can be quickly controlled and exited, in specific implementation, by adjusting the initial liquid nitrogen supply amount, the situation that the air side temperature sharply decreases is prevented, and the heat exchange efficiency is ensured by quickly processing the heat exchange deterioration in the test, the application can provide the supply process for the pre-cooler and the solution measure when the heat exchange deterioration occurs, and the operation of the pre-cooled engine is ensured. Preferably, in step three, the liquid nitrogen is provided by a liquid nitrogen supply device, a medium pipeline is arranged between the liquid nitrogen supply device and the pre-cooler medium inlet, and a liquid nitrogen regulating valve is arranged on the medium pipeline, and when the liquid nitrogen is initially supplied, the opening degree of the liquid nitrogen regulating valve is below 10%.

[0008] The technical effects generated thereby are: the liquid nitrogen is provided by the liquid nitrogen supply device to ensure the liquid nitrogen supply demand and the supply safety, and the liquid nitrogen amount needs to be controlled to prevent the heat exchange from being too intense to cause the air side temperature to sharply decrease.

[0009] Preferably, in step three, the liquid nitrogen supply device and the liquid nitrogen pipeline need to be pre-cooled before the liquid nitrogen is initially supplied, so that the temperature before entering the liquid nitrogen regulating valve reaches 90K.

[0010] The technical effects generated thereby are: the liquid nitrogen needs to be pre-cooled before being supplied to ensure the accuracy of the test parameters and the influence of the cooling.

[0011] Preferably, in step four, the air temperature at the pre-cooler outlet is taken as a control target, and a switch control mode or a closed-loop control mode is adopted to control the liquid nitrogen supply flow of the medium inlet.

[0012] The technical effect produced thereby is that the liquid nitrogen supply is feedback controlled with the air temperature at the outlet of the pre-cooler as the result value, so as to ensure that the air parameters entering the intake port of the test engine meet the requirements.

[0013] Preferably, in the step five, when the liquid nitrogen flow increases but the outlet temperature remains almost unchanged or continues to rise, it indicates that heat exchange deterioration occurs. Normally, the state of the liquid nitrogen changes after absorbing heat, and the temperature gradually rises to a supercritical state inside the pre-cooler. Once the supercritical state changes, the heat exchange efficiency will rapidly decrease, and the air temperature at the outlet will rise, requiring the intake temperature and flow to remain unchanged.

[0014] The technical effect produced thereby is that the heat exchange deterioration judgment is based on the refrigeration effect of the liquid nitrogen and the temperature change of the air. When heat exchange deterioration occurs, the engine will be damaged if not treated, and the liquid nitrogen system needs to be adjusted to maintain the air temperature and flow unchanged.

[0015] Preferably, in the step six, the pre-cooler medium outlet is connected with a nitrogen medium discharge pipeline, and a medium outlet regulating valve is connected to the nitrogen medium discharge pipeline. By adjusting the opening of the medium outlet regulating valve, the liquid nitrogen supply pressure is kept not lower than 4.5 MPa to ensure that the liquid nitrogen is in a supercritical state, improve the heat exchange efficiency, gradually reduce the air temperature at the intake port, and restore it completely.

[0016] Preferably, in the step seven, the liquid nitrogen supply flow is adjusted, and the discharge nitrogen temperature after heat exchange and the outlet temperature of the heat exchanger are observed. After 3-5 minutes, if the air temperature decreases and the discharge nitrogen temperature rises, it indicates that the heat exchange deterioration has been restored.

[0017] The technical effect produced thereby is that by changing the liquid nitrogen supply flow, under normal circumstances, the discharge nitrogen temperature will rise due to heat exchange, and the air outlet temperature will decrease due to heat exchange. If the above conditions are met, it indicates that the heat exchange deterioration has been restored.

[0018] Preferably, in the step one, an air regulating valve, an air detection pressure gauge, and an air detection temperature gauge are connected to the pipeline between the outlet of the pre-cooler and the intake port of the test engine. When the air state is adjusted, the intake port temperature and flow are calculated according to the engine flight height and Mach number, and then the flow entering the intake port of the engine is adjusted through the air regulating valve.

[0019] The technical effect produced thereby is that the air flow entering the intake port of the engine is directly controlled through the air regulating valve, and the air detection pressure gauge and the air detection temperature gauge can detect the temperature and pressure at the outlet, facilitating the understanding of the heat exchange condition.

[0020] Preferably, in the step one, the air inlet of the pre-cooler is connected with a gas supply pipeline, the air supply pipeline is connected with an air adjusting valve and an air heater, and the upstream of the air supply pipeline is connected with an air compression system and can provide a compressed air source.

[0021] The technical effect thus generated is that the compressed air source is provided by the air compression system, and the initial air supply amount and the initial air supply temperature can be changed through the air adjusting valve and the air heater. BRIEF DESCRIPTION OF DRAWINGS

[0022] Fig. 1 The flow chart of the method for adjusting the temperature of a heat exchanger and recovering heat exchange deterioration based on a liquid nitrogen working medium according to the present application; Fig. 2 The system configuration diagram of the method for adjusting the temperature of a heat exchanger and recovering heat exchange deterioration based on a liquid nitrogen working medium according to the present application.

[0023] 1 air compression system, 2 air adjusting valve, 3 air heater, 4 liquid nitrogen supply device, 5 liquid nitrogen adjusting valve, 6 pre-cooler, 7 outlet air pressure, 8 nitrogen discharge pressure, 9 outlet air temperature, 10 nitrogen discharge temperature, 11 outlet air adjusting valve, 12 medium outlet adjusting valve. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0025] Reference is made to the drawings of the present application Figs. 1-2 According to the method for adjusting the temperature of a heat exchanger and recovering heat exchange deterioration based on a liquid nitrogen working medium according to the embodiment of the present application, the following steps are included. Step one: air state adjustment, the air parameters are estimated according to the engine speed, and the air flow and temperature at the inlet of the pre-cooler are adjusted; Step two: liquid nitrogen supply system pipeline cooling, until the temperature before the supply valve (liquid nitrogen adjusting valve 5) reaches 90K; Step three: initial liquid nitrogen supply, the liquid nitrogen adjusting valve 5 is opened, and the liquid nitrogen enters the internal pipeline of the pre-cooler according to the flow; Step four: liquid nitrogen flow adjustment, the air flow and temperature at the inlet of the pre-cooler are changed respectively, and the liquid nitrogen supply flow is adjusted in the process to ensure that the air temperature fluctuation at the outlet of the pre-cooler does not exceed 15℃; Step five: liquid nitrogen heat exchange failure judgment, when the pre-cooler medium outlet liquid nitrogen temperature drops, but the air side outlet temperature hardly changes or continues to rise, it means that heat exchange deterioration has occurred. Because under normal circumstances, after passing through the pre-cooler, the state of liquid nitrogen changes after absorbing heat, it becomes supercritical state inside the pre-cooler, and after the pre-cooler, it becomes gaseous state with gradually increasing temperature, while the air temperature gradually decreases. Once the supercritical state changes, it will cause the heat exchange efficiency to decrease rapidly, at this time the pre-cooler outlet air temperature will rise, if not handled, it will damage the engine, the liquid nitrogen system needs to be adjusted to keep the air side temperature and flow unchanged; Step six: liquid nitrogen heat exchange failure recovery, adjust the liquid nitrogen system medium outlet regulating valve 12, keep the liquid nitrogen supply pressure not less than 4.5MPa, ensure that the liquid nitrogen is in supercritical state; Step seven: liquid nitrogen heat exchange failure recovery judgment, adjust the liquid nitrogen supply flow to ensure heat exchange, observe the nitrogen discharge temperature after heat exchange and the air temperature at the outlet, after 3-5 minutes, the air side temperature decreases and the nitrogen discharge temperature rises, indicating that the heat exchange deterioration has basically recovered; The specific application implementation is as follows: During the combined operation test of a certain type of pre-cooled engine, the engine operating condition is slow running state, the maximum air inlet temperature is 900K, the air temperature at the outlet is 300K, and the air flow is 2kg / s. During the test, the liquid nitrogen supply flow and pressure are gradually changed according to the change of the engine air inlet temperature to keep the pre-cooler outlet air temperature constant at about 300K.

[0026] Implementation step one: air state adjustment, adjust the air inlet valve (air regulating valve 2) to keep the air flow unchanged at 2kg / s, and change the air heater 3 (air electric heating furnace) power to gradually increase the air temperature to 900K; Implementation step two: liquid nitrogen supply device pre-cooling, the internal liquid nitrogen temperature is reduced until the temperature before the liquid nitrogen regulating valve 5 reaches 90K; Implementation step three: liquid nitrogen initial supply, open the liquid nitrogen regulating valve 5 (the opening degree is not more than 5% to prevent the air side temperature from dropping sharply due to excessive heat exchange), and supply liquid nitrogen; Implementation step four: liquid nitrogen flow adjustment, adjust the liquid nitrogen supply flow (change the opening degree of the liquid nitrogen regulating valve 5) synchronously with the increase of the air inlet temperature to ensure that the pre-cooler outlet temperature fluctuates within 15℃; Implementation step five: liquid nitrogen heat exchange failure judgment, when the liquid nitrogen flow increases, but the nitrogen discharge temperature does not rise but drops, and the air side outlet temperature hardly changes, it means that heat exchange deterioration has occurred, at this time the air side temperature and flow need to be kept, and the engine speed needs to be maintained unchanged; Step 6: liquid nitrogen heat exchange failure recovery, adjust the medium outlet regulating valve 12, so that the liquid nitrogen supply pressure is maintained at 4.5MPa, ensure that the liquid nitrogen is in supercritical state, in the process, maintain the air regulating valve 2 opening degree and the power of the air heater 3; Step 7: liquid nitrogen heat exchange failure recovery judgment, adjust the liquid nitrogen supply flow, ensure the heat exchange capacity, observe the nitrogen discharge temperature 10 and the air outlet temperature 9 after heat exchange, estimate 3-5min, the air outlet temperature 9 decreases, the nitrogen discharge temperature 10 rises, indicating that the heat exchange deterioration is basically recovered.

[0027] The supercritical state of the application refers to the state that the temperature and pressure are higher than the critical point.

[0028] The application uses a kind of heat exchanger temperature regulation and heat exchange deterioration recovery method based on liquid nitrogen working medium, guarantees the efficient implementation of test.

[0029] For the device and use method disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple, and the relevant part can be referred to the method part.

[0030] The above description of the disclosed embodiments enables those skilled in the art to implement or use the application. Various modifications to the embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the application. Therefore, the application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for temperature regulation and heat transfer degradation recovery of a heat exchanger based on liquid nitrogen working fluid, characterized in that, Includes the following steps: Step 1: Construct test conditions by placing a precooler in front of the air inlet of the test engine, with the outlet of the precooler connected to the air inlet of the test engine via a pipeline. Step 2: Air condition adjustment. Adjust the airflow and temperature at the precooler inlet according to the test conditions of the test engine. Step 3: Initial supply of liquid nitrogen. Liquid nitrogen is introduced into the medium inlet of the precooler and into the internal medium pipeline of the precooler. Step 4: Liquid nitrogen flow rate adjustment. Change the air flow rate and temperature at the precooler inlet, while simultaneously adjusting the liquid nitrogen supply flow rate to ensure that the temperature fluctuation at the precooler outlet is within 15°C. Step 5: Liquid nitrogen heat exchange failure judgment. When the liquid nitrogen flow rate increases or the liquid nitrogen temperature at the precooler medium outlet decreases, but the outlet temperature remains almost unchanged or continues to rise, it indicates that the heat exchange has deteriorated. Step 6: Recover from liquid nitrogen heat exchange failure, maintain liquid nitrogen supply pressure, and ensure that the liquid nitrogen in the medium pipeline inside the precooler is in a supercritical state; Step 7: Judgment of recovery of liquid nitrogen heat exchange failure. Adjust the liquid nitrogen supply flow rate to ensure heat exchange. Observe the nitrogen discharge temperature and the air temperature at the outlet after heat exchange. When the air temperature at the outlet decreases and the nitrogen discharge temperature increases, it indicates that the heat exchange deterioration has been recovered.

2. The method for temperature regulation and heat exchange deterioration recovery of a heat exchanger based on liquid nitrogen working fluid according to claim 1, characterized in that, In step three, liquid nitrogen is supplied by a liquid nitrogen supply device. A medium pipeline is installed between the liquid nitrogen supply device and the medium inlet of the precooler, and a liquid nitrogen regulating valve is installed on the medium pipeline. When liquid nitrogen is initially supplied, the opening of the liquid nitrogen regulating valve is less than 10%.

3. The method for temperature regulation and heat exchange deterioration recovery of a heat exchanger based on liquid nitrogen working fluid according to claim 2, characterized in that, In step three, the liquid nitrogen supply device and liquid nitrogen pipeline need to be pre-cooled before the initial liquid nitrogen supply to ensure that the temperature reaches 90K before entering the liquid nitrogen regulating valve.

4. The method for temperature regulation and heat exchange deterioration recovery of a heat exchanger based on liquid nitrogen working fluid according to claim 1, characterized in that, In step four, the air temperature at the precooler outlet is used as the control target, and the liquid nitrogen supply flow rate at the medium inlet is controlled by either a switch control method or a closed-loop control method.

5. The method for temperature regulation and heat exchange deterioration recovery of a heat exchanger based on liquid nitrogen working fluid according to claim 1, characterized in that, In step five, if the liquid nitrogen flow rate increases but the outlet temperature remains almost unchanged or continues to rise, it indicates that the heat exchange has deteriorated. Under normal circumstances, after liquid nitrogen absorbs heat, its state changes and its temperature gradually increases. It is in a supercritical state inside the precooler. Once the supercritical state changes, the heat exchange efficiency will decrease rapidly. At this time, the air temperature at the outlet will rise, and it is necessary to keep the inlet temperature and flow rate constant.

6. The method for temperature regulation and heat exchange deterioration recovery of a heat exchanger based on liquid nitrogen working fluid according to claim 1, characterized in that, In step six, the precooler medium outlet is connected to a nitrogen venting medium pipeline, and a medium outlet regulating valve is connected to the nitrogen venting medium pipeline. By adjusting the opening of the medium outlet regulating valve, the liquid nitrogen supply pressure is maintained at no less than 4.5 MPa, ensuring that the liquid nitrogen is in a supercritical state, improving heat exchange efficiency, and gradually reducing the air temperature at the inlet until it is fully restored.

7. The method for temperature regulation and heat exchange deterioration recovery of a heat exchanger based on liquid nitrogen working fluid according to claim 1, characterized in that, In step seven, the liquid nitrogen supply flow rate is adjusted, and the nitrogen discharge temperature and heat exchanger outlet temperature after heat exchange are observed. If the air side temperature decreases and the nitrogen discharge temperature increases after 3-5 minutes, it indicates that the heat exchange deterioration has been recovered.

8. The method for temperature regulation and heat exchange deterioration recovery of a heat exchanger based on liquid nitrogen working fluid according to claim 1, characterized in that, In step one, an outlet air regulating valve, an air pressure sensor, and an air temperature sensor are connected to the pipeline between the outlet of the precooler and the inlet of the test engine. When adjusting the air condition, the inlet temperature and flow rate are calculated based on the engine's flight altitude and Mach number, and then the flow rate entering the engine inlet is adjusted through the outlet air regulating valve.

9. The method for temperature regulation and heat exchange deterioration recovery of a heat exchanger based on liquid nitrogen working fluid according to claim 1, characterized in that, In step one, the air inlet of the precooler is connected to an air supply pipeline, which is connected to an air regulating valve and an air heater. An air compression system is connected upstream of the air supply pipeline and can provide compressed air.

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