A method of determining the condensation temperature of nitrogen at low vacuum pressure

Abstract

The application discloses a method for determining the condensation temperature of nitrogen under low vacuum pressure, in which, in one test, the total pressure at the inlet of a nozzle is kept unchanged through pressure control, the total temperature at the inlet of the nozzle is first adjusted to a higher total temperature through temperature control, and then the total temperature at the inlet of the nozzle is gradually reduced according to certain temperature intervals, the total pressure at the inlet of the nozzle, the total temperature at the inlet of the nozzle and the pitot pressure at the outlet of the nozzle are monitored in real time during the operation of the wind tunnel, and the condensation temperature of nitrogen under low vacuum pressure is determined through comprehensive analysis of the above data. The method can accurately determine the condensation temperature of nitrogen under low vacuum pressure, and makes up for the deficiencies of the theoretical formula and the traditional test acquisition method. The result can be used to reasonably determine the total temperature of a hypersonic low-density wind tunnel, which can not only reduce the design difficulty of the heater itself, but also reduce the overall energy supporting scale of the wind tunnel.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of hypersonic wind tunnels, and particularly relates to a method for determining the condensation temperature of nitrogen under low vacuum pressure. BACKGROUND

[0002] In a hypersonic wind tunnel, test gas is expanded through a nozzle, and when the test gas reaches the test section, the temperature and pressure of the test gas are sharply reduced. Under a certain pressure, if the static temperature of the test gas is lower than the static saturation temperature (i.e., the condensation temperature) under the pressure, phase change will occur, and the test gas will change from a gaseous state to a liquid state. If liquefaction occurs, it will affect the measurement of the test. In order to prevent the occurrence of liquefaction of the test gas during the operation of the wind tunnel, the test gas usually needs to be heated. At this time, the minimum total temperature of the wind tunnel needs to be determined. At present, the total temperature of the hypersonic wind tunnel is determined by first querying the static saturation temperature of the gas under a certain pressure, and then calculating the minimum operating total temperature from the static saturation temperature according to the operating Mach number and the isentropic relationship. The total temperature should be within a reasonable range and cannot be too low or too high. If the total temperature is too low, condensation will occur, and if the total temperature is too high, it will affect the construction scale and difficulty of the equipment. Since the Mach number of a low-density wind tunnel is high, if the static saturation temperature (i.e., the condensation temperature) is too large, the total temperature will sharply increase, and the required total temperature of the wind tunnel will be too high, which will result in waste of investment and construction difficulties. Therefore, the determination of the condensation temperature of nitrogen under low vacuum pressure is crucial for the operation of the wind tunnel.

[0003] The static saturation temperature of nitrogen under different pressures is given by a theoretical formula. The theoretical formula is used for the case where the pressure is greater than or equal to 100 Pa. When the pressure is greater than 100 Pa, the test value and the theoretical value are in good agreement, and the calculated total temperature is consistent with the actual situation. However, when the pressure is very low, the error of the theoretical formula is large, and the required static saturation temperature is too conservative. If the static saturation temperature is still calculated according to the theoretical formula, the static saturation temperature will be too high, and there will be a large error with the actual situation. Since the operating pressure of a hypersonic low-density wind tunnel is very low, the static pressure of the flow field is less than 10 Pa, and the Mach number is very large (10-25), the static saturation temperature calculated according to the existing theory is too large, and a very high total temperature is required before the gas flow is expanded. This requires the heater to have high-temperature heating capability, which will increase the construction difficulty and investment scale of the equipment. Therefore, the scheme of determining the static saturation temperature of nitrogen under different pressures by the theoretical formula cannot accurately determine the static saturation temperature when the pressure is close to the vacuum environment.

[0004] The static saturation temperature under certain pressure can also be measured by a traditional static test, that is, in a fixed container, vacuumize to a certain pressure, gradually reduce the temperature of the gas, and when the temperature is reduced to a certain temperature, observe the condensation of the gas, and then record the pressure and temperature. Then reduce the pressure of the container, continue to reduce the temperature of the gas, and again observe the condensation of the gas, and again record the pressure and temperature data, and repeat the above process to obtain the pressure and static saturation temperature curve. However, this method relies on manual observation and has large errors. This method is easy to reduce the pressure of the container, but after the temperature of the gas in the container is reduced to-190℃, it is difficult to continue to reduce the temperature by using the traditional liquid nitrogen cooling method or other low-temperature liquefied medium cooling method, that is, it is very difficult to reduce the temperature to near absolute zero. Moreover, this test method has long time, large error and high difficulty in temperature reduction, and is difficult to implement. Since the Mach number of the hypersonic low-density wind tunnel is high and the total pressure is low, the static pressure of the test gas is reduced to below 10 Pa, the static saturation temperature is below 10 K, and is close to absolute zero, so it is very difficult to obtain the saturation relationship under low vacuum pressure and temperature by using the traditional test method, and there is no ready test data.

[0005] In summary, the above theoretical method and traditional test method cannot accurately establish the saturation relationship under low vacuum pressure and temperature, so the lowest operating total temperature of the wind tunnel cannot be accurately determined, and only the enlarged margin method can be used for operation, and the condensation temperature of nitrogen gas under low vacuum pressure cannot be accurately determined. SUMMARY

[0006] The technical problem of the present application is to overcome the shortcomings of the prior art and provide a method for determining the condensation temperature of nitrogen gas under low vacuum pressure, which can accurately determine the condensation temperature of nitrogen gas under low vacuum pressure and make up for the shortcomings of the theoretical formula acquisition and traditional test acquisition method. By using the results, the operating total temperature of the hypersonic low-density wind tunnel can be reasonably determined, which not only reduces the design difficulty of the heater itself, but also reduces the overall energy supporting scale of the wind tunnel.

[0007] To solve the above technical problems, the present application discloses a method for determining the condensation temperature of nitrogen gas under low vacuum pressure, comprising:

[0008] Adjusting the total pressure at the inlet of the nozzle to P0 and the total temperature at the inlet of the nozzle to T0, and measuring the pitot pressure at the outlet of the nozzle P 02 ; wherein the values of P0 and T0 satisfy that the gas flow will not condense when the pressure is P0 and the temperature is T0;

[0009] Keeping the total pressure P0 at the inlet of the nozzle stable and unchanged, adjusting the total temperature at the inlet of the nozzle for the first time, and measuring the pitot pressure at the outlet of the nozzle P 02,1 ;

[0010] P 02,1 and P02 By comparison, we obtain P. 02,1 With P 02 The comparison results;

[0011] If P 02,1 With P 02 If the comparison result meets the set criteria, then it is determined that the airflow has condensed, according to P. 02,1 The nozzle outlet static pressure P1 and nozzle outlet static temperature T1 after the first cooling adjustment were calculated.

[0012] If P 02,1 With P 02 If the comparison result does not meet the set criteria, it is determined that no condensation has occurred in the airflow. The total pressure P0 at the nozzle inlet is kept stable, and the total temperature at the nozzle inlet is adjusted for the second time. This process continues until the total temperature at the nozzle inlet is adjusted for the nth time, after which the nozzle outlet Pitot pressure P is measured. 02,n With P 02 The comparison results satisfy the set criteria, determining that condensation occurs in the airflow after the nth cooling adjustment, according to P. 02,n The static pressure P at the nozzle exit after the nth cooling adjustment was calculated. n and nozzle outlet static temperature T n Where n≥2;

[0013] Based on the calculated nozzle outlet static pressure P1 and nozzle outlet static temperature T1 after the first cooling adjustment, or the nozzle outlet static pressure P after the nth cooling adjustment n and nozzle outlet static temperature T n Determine the condensation temperature of nitrogen at pressure P0 as T1, or determine the condensation temperature of nitrogen at pressure P... n The condensation temperature at that time is T n ;

[0014] By changing the total pressure at the nozzle inlet and repeating the above process, the condensation temperature of nitrogen under different low vacuum pressures can be obtained.

[0015] The above method for determining the condensation temperature of nitrogen under low vacuum pressure also includes: selecting a nozzle that meets the Mach number requirement, ensuring that all systems of the wind tunnel are ready, pumping the vacuum pressure to below 5 Pa, and maintaining the operation of the wind tunnel; wherein, the wind tunnel test gas medium is nitrogen.

[0016] In the above method for determining the condensation temperature of nitrogen under low vacuum pressure, if P 02,1 With P 02 The comparison result is: P 02,1 ≥(P 02 +5%P 02 If P is determined, then P is determined. 02,1 With P 02 The comparison result satisfies the set criterion; if P 02,1With P 02 The comparison result is: P 02,n ≥(P 02 +5%P 02 If P is determined, then P is determined. 02,1 With P 02 The comparison result does not meet the established criteria.

[0017] In the above method for determining the condensation temperature of nitrogen under low vacuum pressure, if P 02,n With P 02 The comparison result is: P 02,n ≥(P 02 +5%P 02 If P is determined, then P is determined. 02,n With P 02 The comparison result satisfies the set criteria.

[0018] In the above method for determining the condensation temperature of nitrogen under low vacuum pressure, the total temperature at the nozzle inlet is reduced by a temperature control system according to a set temperature difference ΔT, thereby achieving temperature regulation of the total temperature at the nozzle inlet.

[0019] In the above method for determining the condensation temperature of nitrogen under low vacuum pressure, the nozzle outlet static pressure P1 and nozzle outlet static temperature T1 during the first cooling are calculated using the following formula:

[0020]

[0021]

[0022] Where γ represents the specific heat ratio of nitrogen; Ma1 represents the Mach number of the nozzle after the first cooling adjustment.

[0023] In the above method for determining the condensation temperature of nitrogen under low vacuum pressure, the nozzle outlet static pressure P after the nth cooling adjustment is calculated using the following formula. n and nozzle outlet static temperature T n :

[0024]

[0025]

[0026] Among them, Ma n This represents the Mach number of the nozzle after the nth cooling adjustment.

[0027] In the above method for determining the condensation temperature of nitrogen under low vacuum pressure, Ma1 and Ma are calculated using the following formula. n :

[0028]

[0029]

[0030] In the method for determining the condensation temperature of nitrogen under low vacuum pressure, ΔT = 10K.

[0031] In the method for determining the condensation temperature of nitrogen under low vacuum pressure, the regulation of the total pressure at the inlet of the nozzle is realized by a pressure regulating system.

[0032] The present application has the following advantages:

[0033] The present application discloses a method for determining the condensation temperature of nitrogen under low vacuum pressure, which overcomes the shortcomings of the existing theoretical method and the traditional test method, and can accurately determine the condensation temperature of nitrogen under low vacuum pressure, so that the lowest operating total temperature of the wind tunnel under different Mach numbers and different total pressures can be accurately determined, accurate temperature input is provided for the design of the heater and the operation of the wind tunnel, the requirements of the anti-condensation of the airflow are met while the operation requirements of the wind tunnel are met, the wind tunnel can be operated at a higher Mach number, and the problems of the existing high total temperature, large design margin and high equipment investment scale are overcome. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 is the implementation principle diagram of the method for determining the condensation temperature of nitrogen under low vacuum pressure in the embodiment of the present application. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical scheme and advantages of the present application more clear, the embodiments disclosed by the present application will be further described in detail below with reference to the drawings.

[0036] One of the core ideas of the present application is that in order to reduce the equipment investment scale and the operation risk, a method for determining the condensation temperature of nitrogen under low vacuum pressure is proposed, accurate temperature input is provided for the design of the heater and the operation of the wind tunnel, the use requirements of the wind tunnel are met, the anti-condensation requirements of the airflow are met at the same time, the wind tunnel can be operated at a higher Mach number, and the problems of the existing high design temperature of the heater, large design margin and high equipment investment scale can be overcome. The method disclosed by the present application utilizes the existing wind tunnel equipment, the total pressure at the inlet of the nozzle, the total temperature at the inlet of the nozzle and the Pitot pressure at the outlet of the nozzle are monitored in real time, the condensation temperature of nitrogen under low vacuum pressure is determined by analyzing the three values. In a test, the total pressure at the inlet of the nozzle is kept stable by the control of the pressure regulating system, the total temperature at the inlet of the nozzle is first adjusted to a higher total temperature by the temperature regulating system, then the total temperature at the inlet of the nozzle is gradually reduced according to a certain temperature interval, the total pressure at the inlet of the nozzle, the total temperature at the inlet of the nozzle and the Pitot pressure at the outlet of the nozzle are monitored in real time during the operation of the wind tunnel, and the condensation temperature of nitrogen under low vacuum pressure is determined by comprehensively analyzing the above data.

[0037] In this embodiment, the method for determining the condensation temperature of nitrogen under low vacuum pressure includes:

[0038] Step 1: Select a nozzle that meets the Mach number requirement, ensure all wind tunnel systems are ready, pump the vacuum pressure to below 5 Pa, and keep the wind tunnel running.

[0039] In this embodiment, a high Mach number nozzle is generally selected; the gas medium for wind tunnel testing is nitrogen.

[0040] Step 2: Adjust the total pressure at the nozzle inlet to P0 and the total temperature at the nozzle inlet to T0, and measure the pressure at the nozzle outlet P0. 02 ,like Figure 1 As shown.

[0041] In this embodiment, the total pressure at the nozzle inlet can be adjusted to P0 and kept stable using a pressure regulating system; the total temperature at the nozzle inlet can be adjusted to a higher temperature using a temperature regulating system to ensure that the airflow does not condense at this temperature. That is, the values ​​of P0 and T0 satisfy the condition that the airflow will not condense when the pressure is P0 and the temperature is T0.

[0042] Step 3: Keep the total pressure P0 at the nozzle inlet constant, perform the first cooling adjustment on the total temperature at the nozzle inlet, and measure the pressure P at the nozzle outlet after the first cooling adjustment. 02,1 .

[0043] In this embodiment, the total temperature at the nozzle inlet can be reduced by a temperature control system according to a set temperature difference ΔT, thereby achieving temperature regulation of the total temperature at the nozzle inlet. Generally, ΔT = 10K.

[0044] Step 4, P 02,1 With P 02 By comparison, we obtain P. 02,1 With P 02 The comparison results.

[0045] Step 5, if P 02,1 With P 02 If the comparison result meets the set criteria, then it is determined that the airflow has condensed, according to P. 02,1 The static pressure P1 and static temperature T1 at the nozzle exit were calculated after the first cooling adjustment.

[0046] In this embodiment, if P 02,1 With P 02 The comparison result is: P 02,1 ≥(P 02 +5%P 02 If P is determined, then P is determined. 02,1 With P 02The comparison result of P and P satisfies the set criterion. The nozzle outlet static pressure P1 and the nozzle outlet static temperature T1 at the first time of temperature reduction can be calculated by the following formula:

[0047]

[0048]

[0049] wherein γ represents the specific heat ratio of nitrogen; Ma1 represents the Mach number of the nozzle after the first time of temperature reduction adjustment,

[0050] Further, the condensation temperature of nitrogen at the pressure P0 can be determined as T1.

[0051] Step 6, if P 02,1 and P 02 The comparison result of P and P does not satisfy the set criterion, and it is determined that the gas flow does not condense, the nozzle inlet total pressure P0 is kept stable, and the second time of temperature reduction adjustment is performed on the nozzle inlet total temperature; until the nozzle outlet pitot pressure P 02,n and P 02 The comparison result of P and P satisfies the set criterion, and it is determined that the gas flow condenses after the n times of temperature reduction adjustment, and the nozzle outlet static pressure P n and the nozzle outlet static temperature T n after the n times of temperature reduction adjustment are calculated according to P 02,n ; wherein n≥2.

[0052] In this embodiment, if the comparison result of P 02,1 and P 02 is: P 02,n ≥(P 02 +5%P 02 ), it is determined that the comparison result of P 02,1 and P 02 does not satisfy the set criterion, which indicates that the gas flow does not condense at this time, and the condensation point of the gas flow has not been found.

[0053] Further, if the comparison result of P 02,n and P 02 is: P 02,n ≥(P 02 +5%P 02 ), it is determined that the comparison result of P 02,n and P 02 satisfies the set criterion, which indicates that the condensation has occurred. Because when the gas condenses, the Mach number of the nozzle outlet will decrease, and the pitot pressure value of the nozzle outlet will increase.

[0054] Further, the nozzle outlet static pressure P nand the nozzle exit static temperature T n :

[0055]

[0056]

[0057] wherein Ma n n represents the Mach number of the nozzle after the nth temperature adjustment,

[0058] Further, the condensation temperature of nitrogen at a pressure P n may be determined as T n .

[0059] At this time, the calculated (P n , T n ) is a state point.

[0060] Step 7, change the nozzle inlet total pressure, repeat the above process to obtain the condensation temperature of nitrogen at different low vacuum pressures.

[0061] Although the present application has been disclosed with the preferred embodiments as above, it is not intended to limit the present application, and any person skilled in the art can make possible changes and modifications to the technical solutions of the present application by using the disclosed methods and technical contents without departing from the spirit and scope of the present application. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present application, which does not depart from the technical solutions of the present application, shall fall within the protection scope of the technical solutions of the present application.

[0062] The contents not described in detail in the specification of the present application are the known technology of the person skilled in the art.

Claims

1. A method of determining the condensation temperature of nitrogen at low vacuum pressure, characterized in that, Comprise: The total pressure at the inlet of the nozzle is adjusted to P0, and the total temperature at the inlet of the nozzle is adjusted to T0. The Pitot pressure at the outlet of the nozzle is measured to be P 02 ; Wherein, the value of P0 and T0 meet: when the pressure is P0, the temperature is T0, the gas flow will not condense; Keeping the total pressure P0 of the inlet of the nozzle stable and unchangeable, the total temperature of the inlet of the nozzle is adjusted for the first time, and the Pitot pressure P 02,1 of the outlet of the nozzle after the first time of temperature adjustment is measured. P 02,1 compared with P 02 , resulting in P 02,1 compared with P 02 ; If the comparison result of P 02,1 and P 02 satisfies a set criterion, it is determined that the airflow condenses, and the first reduced static pressure P1 and the first reduced static temperature T1 at the nozzle outlet are calculated according to P 02,1 . If the comparison result of P 02,1 and P 02 does not satisfy the set criterion, it is determined that the airflow does not condense, the total pressure P0 of the nozzle inlet is kept stable, and the total temperature of the nozzle inlet is adjusted for the second time; until the total temperature of the nozzle inlet is adjusted for the nth time, the pitot pressure P 02,n of the nozzle outlet is measured, and the comparison result of P 02 and P 02,n satisfies the set criterion, it is determined that the airflow condenses after the nth time of temperature adjustment, the static pressure P n and the static temperature T n of the nozzle outlet after the nth time of temperature adjustment are calculated according to P 02,n ; wherein n≥2. According to the calculated first temperature-adjusted nozzle outlet static pressure P1 and nozzle outlet static temperature T1, or the n-th temperature-adjusted nozzle outlet static pressure Pn and nozzle outlet static temperature Tn, the condensation temperature of nitrogen at a pressure of P0 is determined as T1, or the condensation temperature of nitrogen at a pressure of Pn is determined as Tn n and nozzle outlet static temperature T n , the condensation temperature of nitrogen at a pressure of P0 is determined as T1, or the condensation temperature of nitrogen at a pressure of Pn is determined as Tn n n ;​ Change the nozzle inlet total pressure, repeat the above process, get the condensation temperature of nitrogen at different low vacuum pressure.

2. The method of determining the condensation temperature of nitrogen at low vacuum pressure according to claim 1, wherein, Also include: Select the nozzle that meets the Mach number requirements, the wind tunnel system is ready, the vacuum pressure is extracted to below 5 Pa, and the wind tunnel is kept running; wherein, the wind tunnel test gas medium is nitrogen.

3. The method of determining the condensation temperature of nitrogen at low vacuum pressure according to claim 1, wherein, If P 02,1 With P 02 The comparison result is: P 02,1 ≥(P 02 +5%P 02 If P is determined, then P is determined. 02,1 With P 02 The comparison result satisfies the set criterion; if P 02,1 With P 02 The comparison result is: P 02,n ≥(P 02 +5%P 02 If P is determined, then P is determined. 02,1 With P 02 The comparison result does not meet the established criteria.

4. The method of determining the condensation temperature of nitrogen at low vacuum pressure according to claim 1, wherein, If the comparison result of P 02 ,n and P 02 is: P 02,n ≥(P 02 +5%P 02 ), it is determined that the comparison result of P 02 ,n and P 02 meets the set criterion.

5. The method of determining the condensation temperature of nitrogen at low vacuum pressure according to claim 1, wherein, Through the temperature control system, the nozzle inlet total temperature is reduced according to the set temperature difference ΔT, and the temperature reduction regulation of the nozzle inlet total temperature is realized.

6. The method of determining the condensation temperature of nitrogen at low vacuum pressure according to claim 5, wherein, The nozzle outlet static pressure P1 and the nozzle outlet static temperature T1 at the first temperature reduction are calculated by the following formula: Wherein, γ represents the specific heat ratio of nitrogen; Ma1 represents the Mach number of the nozzle after the first temperature reduction regulation.

7. The method of determining the condensation temperature of nitrogen at low vacuum pressure according to claim 6, wherein, The static pressure P at the nozzle exit after the nth temperature adjustment is calculated by the following equation n and the static temperature T at the nozzle exit n : where Ma n represents the Mach number of the nozzle after the nth temperature adjustment.

8. The method of determining the condensation temperature of nitrogen at low vacuum pressure according to claim 7, wherein, Ma1 and Ma are calculated by the following formula n :

9. The method of determining the condensation temperature of nitrogen at low vacuum pressure according to claim 5, wherein, ΔT = 10 K.

10. The method of determining the condensation temperature of nitrogen at low vacuum pressure according to claim 1, wherein, The adjustment of the nozzle inlet total pressure is realized through the pressure regulating system.

Images