A water vapor phase change condition calculation method suitable for high-altitude rare gas environment

Abstract

The application belongs to the technical field of phase change, and particularly relates to a water vapor phase change condition calculation method suitable for high-altitude rare gas environment, comprising the following steps: determining the aerodynamic process characteristic length according to the research object; calculating continuity from the water vapor molecule thermal motion velocity distribution; obtaining the actual static pressure of water vapor molecules in the flow field from the continuity; calculating the Gibbs free energy of different phase state water under local working conditions from the actual pressure; and obtaining the phase change condition according to the Gibbs free energy distribution of different phase state water. The water vapor phase change condition calculation method considers the phase change process change rule under the influence of real gas effect, thereby providing a reliable gas component phase change process calculation method in high-altitude exhaust flow, ensuring the reliability of the flow field calculation result, further perfecting the numerical simulation of the engine exhaust flow field distribution, and providing protection for improving the aerospace engine development capability.

Description

Technical Field

[0001] This invention belongs to the field of phase change technology, specifically relating to a method for calculating water vapor phase change conditions applicable to rarefied gas environments at high altitudes. Background Technology

[0002] Infrared radiation calculations for aerospace engines are fundamental to infrared stealth. Both solid and liquid rocket engines produce combustion products in their wakes containing significant amounts of radiation-participating gases such as water vapor and carbon dioxide. While research on the infrared characteristics and infrared radiation transmission of these radiation-participating gases is relatively mature, studies on the infrared radiation of water vapor phase transition products—droplets and ice crystals—are relatively limited. This is because calculating the infrared characteristics of phase transition products requires calculating their distribution, and phase transitions in the rarefied gas environment of high altitudes differ significantly from those in the traditional low-altitude, atmospheric-pressure environment. Therefore, research on the water vapor phase transition process in rarefied gas environments of high altitudes is an important undertaking.

[0003] The foundation for studying the phase change process of water vapor in engine exhaust lies in obtaining the phase change conditions. Phase change conditions are the zoning of operating conditions that drive the phase change of water vapor, and these driving forces are determined by the Gibbs free energy of water in different phases under a given operating condition. The Gibbs free energy is a key parameter of the phase change thermodynamic performance and is directly influenced by the aerodynamic properties of water vapor. The rarefied gas environment at high altitudes introduces irregular aerodynamics and non-equilibrium phenomena, thus affecting the Gibbs free energy and ultimately altering the phase change conditions of water vapor. Therefore, proposing a method for calculating the phase change conditions of water vapor applicable to rarefied gas environments at high altitudes is of paramount importance. Summary of the Invention

[0004] To investigate the phase transition process of water vapor in engine exhaust under a rarefied gas environment at high altitudes, it is necessary to calculate the enthalpy, entropy, and other thermodynamic properties of water in different phases under various operating conditions, and to consider the influence of irregular aerodynamic processes and non-equilibrium on these thermodynamic properties. Traditional phase transition conditions are derived from three-phase diagrams of different substances, primarily through experiments and empirical derivations, but rarely consider the influence of irregular aerodynamics and non-equilibrium on phase transition conditions, thus making it impossible to calculate the phase transition conditions of water vapor in a rarefied environment at high altitudes. To address this problem, this invention provides a method for calculating the phase transition conditions of water vapor in a rarefied gas environment at high altitudes, providing a foundation for calculating the phase transition process of engine exhaust under irregular aerodynamic and non-equilibrium conditions.

[0005] Specifically, the present invention provides the following technical solutions: A method for calculating water vapor phase transition conditions applicable to rarefied gas environments at high altitudes includes the following steps: Step 1: Obtain local working conditions and, based on the specific circumstances of the research object, determine the structural parameters that affect the local water vapor molecule aerodynamic process, thereby obtaining the characteristic length L of the research object; Step 2: Based on local operating conditions, obtain the thermal velocity distribution of water vapor molecules, and then calculate the mean free path of the water vapor molecules. Then, the continuity parameter of water vapor molecules can be calculated. ; Step 3: Based on local working conditions, calculate the proportion of water vapor molecules actually involved in the collision and their thermal motion state in the research object, thereby obtaining the momentum exchange per unit time, and then calculating the actual static pressure caused by the water vapor. Step 4: Based on local working conditions, substitute the actual static pressure into the thermodynamic calculation to obtain the Gibbs free energy of water under different phases; Step 5: Compare the Gibbs free energy of water under different phase states to obtain the change mode of Gibbs free energy driving force in different phase transition processes, thereby calculating the phase region under different working conditions, and finally obtaining the phase transition conditions of water vapor.

[0006] Preferably, in step one, the local operating conditions include the local water vapor temperature. Water vapor number density And the number density of other gas components Local operating conditions directly affect the aerodynamic / thermal properties of water vapor molecules, thereby influencing the phase change conditions of water vapor.

[0007] Preferably, in step one, if the object of study is a surface of a flow-shaped object, the characteristic length is selected as a structural parameter of the flow-shaped object, such as diameter or length (the selection of the characteristic length is determined by the obstruction process of the thermal motion diffusion of gas molecules in each direction of the flow. For example, for a wall of length L, if the thermal motion amplitude of gas molecules is greater than L, they can bypass the flow through their own thermal motion; otherwise, they cannot bypass it, so the characteristic length is taken as L), serving as the basis for determining the relationship between the structure of the object of study and the thermal motion of water vapor molecules. If the object of study is a flow field space, the characteristic length in the flow field space is the length of the smallest spatial unit that can accurately express the flow characteristics of the flow field, such as the length of a numerical grid. In traditional low-altitude atmospheric pressure environments, even if the water vapor content is extremely low, the thermal motion amplitude is suppressed due to collisions with a large number of other component gas molecules. Therefore, the thermal motion mode of water vapor molecules is regular aerodynamic and is not affected by real gas effects. In regular aerodynamic processes, the thermal motion amplitude of gas molecules is extremely small, and its impact on the aerodynamic process is negligible; therefore, the influence of the real gas effect does not need to be considered. In irregular aerodynamic processes, the thermal motion amplitude of gas molecules is large, and its impact on the aerodynamic process becomes non-negligible. In this case, the irregular aerodynamic phenomenon caused by molecular thermal motion is the real gas effect. The characteristic length L of the research object refers to the length of the structure that reflects the influence of the research object on the thermal motion of water vapor molecules. It is a key factor in calculating the influence of the real gas effect. Different characteristic lengths corresponding to different research objects will lead to different aerodynamic characteristics under the same operating conditions.

[0008] Preferably, in step two, when other gaseous components are absent (i.e., under pure water vapor conditions), the mean free path of the thermal motion of water vapor molecules is... The calculation formula is: ; in, Water vapor number density, in m³ / s. -3 ; Let be the diameter of a water molecule, and take it as . m; When various gaseous components J, including water vapor, are present, the mean free path of the thermal motion of water vapor molecules... The calculation formula is: ; in, This refers to the number density of molecules of other gaseous components excluding water vapor, expressed in m³. -3 ; This represents the average thermal velocity of water vapor molecules, measured in m / s. The average thermal velocity of molecules in other gaseous components, excluding water vapor, is expressed in m / s. Let be the diameter of a water molecule, and take it as . m; The diameter of the molecules of other gaseous components, excluding water vapor, is expressed in meters (m).

[0009] Preferably, in step two, the water vapor molecule continuity quantification parameter The calculation formula is as follows: .

[0010] The thermal velocity distribution of water vapor molecules follows Maxwell's velocity distribution law, thus possessing a certain molecular free path λ during collisions with other gas molecules. The relationship between the molecular free path and the characteristic length determines the continuity of the aerodynamic process. The key parameter for determining the continuity of water vapor is... When the ratio of the free path of water vapor molecules to the local characteristic length is less than or equal to 0.01, the water vapor can be considered to be in a regular aerodynamic state, and the real gas effect has no effect on the aerodynamic / thermal properties of the water vapor molecules. When the ratio of the free path of water vapor molecules to the local characteristic length is greater than 0.01, the water vapor molecules are considered to be in an irregular aerodynamic state, and the real gas effect affects the aerodynamic / thermal properties of the water vapor molecules. Among all water vapor molecules that satisfy the Maxwell velocity distribution, the velocity distribution can satisfy... Water vapor molecules are continuous molecules, and the average thermal velocity of continuous molecules is... The proportion of molecules is Other water vapor molecules are free molecules, and the average thermal velocity of free molecules is... The proportion of molecules is When other gaseous components are present, the aerodynamic process of water vapor is affected by these other gaseous components.

[0011] Preferably, in step three, the actual static pressure caused by the water vapor... The calculation formula is: ; ; ; in, The continuous water vapor number density is expressed in m³. -3 ; The percentage of continuous water vapor molecules is 100%. The mass of a single water molecule is taken as . ; The average thermal velocity of continuous water vapor molecules is expressed in m / s. Boltzmann's constant is . .

[0012] In step three, the water vapor molecules that actually participate in molecular collisions and generate hydrostatic pressure are continuous molecules, while free molecules do not participate in molecular collisions within the research object, thus demonstrating the real gas effect. The way free molecules exhibit the real gas effect differs for different research objects. Around the surface of a flowing object, continuous molecules, due to their lower molecular mean of freedom, cannot complete flow around it through their own thermal motion, while free molecules, due to their large thermal motion amplitude, complete flow around it through thermal motion, thus avoiding collisions with the surface of the flowing object. In the flow field space, continuous molecules, due to their lower molecular mean of freedom, cannot leave the flow field space through their own thermal motion, while free molecules, due to their large thermal motion amplitude, exchange molecules with the surrounding space through thermal motion, thus avoiding molecular collisions within the flow field space. For objects with temperature... Molecular number density Water vapor, within a flow field of characteristic length L, exhibits a temperature of [temperature value missing] for continuous molecules. The molecular number density is At this point, the actual hydrostatic pressure exhibited by the continuous molecules is Only when the free path of water vapor molecules is relatively low compared to the local characteristic length L, thus making Only when the pressure created by water vapor molecules is sufficient to satisfy the ideal gas law can regular aerodynamic processes occur; when At that time, the presence of free molecules made , This causes the pressure created by water vapor molecules to no longer satisfy the ideal gas law, resulting in irregular aerodynamic processes. The influence of the real gas effect on aerodynamic processes has been verified by molecular distillation, a widely applied engineering practice. In molecular distillation, the high vacuum in the distillation gap makes the time interval between collisions between vapor molecules and the time it takes for molecules to pass through the distillation gap on the same order of magnitude. This results in the aerodynamic process being influenced by the real gas effect, allowing the distilled substance to exist stably in a gaseous state under liquid phase conditions. Although irregular aerodynamic processes occur within the distillation gap due to the real gas effect, the molecular free path of the distilled substance is not on the same order of magnitude as the dimensions of the evaporation and condensation plates, thus exhibiting regular aerodynamics. Consequently, it exists in a liquid state under liquid phase conditions on the evaporation and condensation plates.

[0013] As a preferred option, in step four... The formula for calculating the Gibbs free energy of water vapor is as follows:

[0014] The proportion of continuous gas molecules and the speed of thermal motion directly affect the Gibbs free energy of gaseous water.

[0015] Enthalpy of gaseous water The calculation method is as follows:

[0016] In the formula, This represents the internal energy of gaseous water, expressed in J / kg. Let the mass of a single H2O molecule be . ; Water vapor number density, in m³ / s. -3 ; This represents the actual static pressure caused by water vapor, measured in Pa.

[0017] Entropy of gaseous water The calculation method is as follows:

[0018] In the formula, Let be the entropy of liquid water under triple point conditions, which is set to 0 in the calculation. ; The latent heat of vaporization of liquid water under triple point conditions is expressed in J / kg. The triple point temperature is 273.16 K; This is the isochoric specific heat of gaseous water, in units of . ; Boltzmann's constant, ; Let the mass of a single H2O molecule be . ; This represents the actual static pressure caused by water vapor, expressed in Pa. This refers to the number density of water molecules in gas under triple point conditions, expressed in m³. -3 .

[0019] The formula for calculating the Gibbs free energy of solid water is as follows:

[0020] The formula for calculating the Gibbs free energy of liquid water is as follows:

[0021] in, , , These are the Gibbs free energies of gaseous, liquid, and solid water, respectively, expressed in J / kg. , , These are the enthalpies of water in gaseous, liquid, and solid states, respectively, expressed in J / kg. , , These are the entropy values ​​for gaseous, liquid, and solid water, respectively, in units of... ; , , These represent the temperatures of gaseous, liquid, and solid water, respectively, in Kelvin (K). Under thermal equilibrium conditions, all three are equal.

[0022] In step four, the Gibbs free energy is a crucial parameter for determining thermodynamic properties. Since thermodynamic properties are directly influenced by aerodynamic characteristics, the phase transition conditions, which are directly related to thermodynamic properties, are also affected by aerodynamic characteristics. The Gibbs free energy is determined by both enthalpy (h) and entropy (s), i.e. The Gibbs free energies of water in different phases are obtained by calculating the enthalpy and entropy of each phase. Furthermore, the enthalpy and entropy of solid and liquid water are determined solely by temperature and are unrelated to the number density of water vapor; the enthalpy and entropy of gaseous water, i.e., water vapor, are related to both the water vapor temperature and partial pressure. The insufficient collisions of gas molecules due to the real gas effect lead to a non-equilibrium state. In this state, due to insufficient exchange of molecular kinetic energy, the translational temperature of the gas molecules increases. Temperature of gas molecule rotation Existing droplet ice crystal temperature The time intervals are no longer necessarily the same. The enthalpy and entropy of solid water and liquid water are determined by the existing temperature of the ice crystal droplets. The enthalpy and entropy of gaseous water are determined directly by the thermodynamic temperature of water vapor. It is determined that, for water molecules, the thermodynamic temperature satisfies The aerodynamic properties of water vapor molecules are determined by translational temperature. The distribution of the thermal motion velocity of water vapor molecules is determined by translational temperature. Therefore, the translational temperature of water vapor molecules is determined. It can directly affect the actual static pressure of water vapor molecules, and thus affect the Gibbs free energy of water vapor.

[0023] In step five, the Gibbs free energy is a key parameter determining the phase transition process. Phase transitions tend to occur in the direction of decreasing Gibbs free energy. Therefore, under a given operating condition, if the Gibbs free energy of solid water is the lowest, the condition is in the solid phase region, and water vapor tends to transform into a solid state. If the Gibbs free energy of liquid water is the lowest, the condition is in the liquid phase region, and water vapor tends to transform into a liquid state. If the Gibbs free energy of gaseous water (i.e., water vapor) is the lowest, then water vapor does not exhibit a phase transition tendency. The operating conditions encompassing the gas, liquid, and solid phases are collectively referred to as phase transition conditions. The curves formed by the operating points where the Gibbs free energies of gas / liquid, gas / solid, and liquid / solid are the calculated results of the gas / liquid, gas / solid, and liquid / solid boundary lines, respectively. The operating point where the Gibbs free energies of gas, liquid, and solid are all the same is the calculated result of the three-phase point.

[0024] The beneficial effects of this invention are at least as follows: (1) The research of this invention will directly solve the problem of calculating the conditions for the occurrence of phase change process of engine tail jet under the rarefied gas conditions at high altitude. It takes into account the change law of phase change process under the influence of real gas effect, thus providing a reliable calculation method for phase change process of gas components in high altitude tail jet and ensuring the reliability of flow field calculation results. (2) The research of this invention provides a basis for the calculation of the phase change process of engine exhaust under irregular aerodynamic and non-equilibrium conditions, thereby improving the numerical simulation of the flow field distribution of engine exhaust and providing a guarantee for improving the research and development capabilities of aerospace engines. (3) Due to the influence of the real gas effect, the phase transition conditions under irregular aerodynamic non-equilibrium conditions are significantly different from the traditional three-phase diagram under normal atmospheric pressure conditions at low altitudes. According to the calculation results of the method of this invention, the existence of the real gas effect reduces the gas phase region and decreases the tendency of water vapor to transform into other phase states. When water vapor is in the liquid phase region or solid phase region, it will not necessarily transform into droplets or ice crystals. Meeting the phase transition conditions only means that it has the driving force for phase transition. Only on the surface of hydrophilic adhering materials can it be approximately considered that water vapor directly begins phase transition after reaching the phase transition conditions. Attached Figure Description

[0025] Figure 1 This is a flowchart of a method for calculating water vapor phase change conditions applicable to high-altitude rarefied gas environments, according to the present invention.

[0026] Figure 2 It is a schematic diagram of irregular aerodynamic processes under the influence of real gas effects around the object.

[0027] Figure 3 This is a schematic diagram of irregular aerodynamic processes under the influence of real gas effects in the flow field space.

[0028] Figure 4 This is a schematic diagram illustrating the division of gas molecules into continuous molecules and free molecules based on the molecular path of freedom.

[0029] Figure 5 This is a schematic diagram illustrating the influence of different characteristic lengths on phase transition conditions under the same operating conditions.

[0030] Figure 6 This is a schematic diagram of the actual static pressure generated by continuous molecular collisions.

[0031] Figure 7 This is a schematic diagram of how the real gas effect alters the phase transition conditions; curve 1 is the gas-liquid boundary line of the traditional distilled substance, curve 2 is the gas-liquid boundary line under the influence of the real gas effect, and point set 3 represents the actual operating parameters of the gas in the distillation gap.

[0032] Figure 8This is a schematic diagram illustrating the influence of the real gas effect on the phase change conditions of water vapor under thermal equilibrium conditions. Curve 1 is the gas-solid boundary line in the traditional three-phase diagram of water, curve 2 is the gas-liquid boundary line in the traditional three-phase diagram of water, curve 3 is the solid-liquid boundary line in the traditional three-phase diagram of water, curve 4 is the gas-solid boundary line of water under the influence of the real gas effect, curve 5 is the gas-liquid boundary line of water under the influence of the real gas effect, and curve 6 is the solid-liquid boundary line under the influence of the real gas effect.

[0033] Figure 9 This is a schematic diagram showing the variation of water vapor phase change conditions with characteristic length; curve 1 shows the variation of phase change conditions under pure water vapor conditions, and curve 2 shows the variation of phase change conditions under the influence of other gas components.

[0034] Figure 10 This is a schematic diagram illustrating the influence of real gas effects on water vapor phase transition conditions under non-equilibrium conditions; curves 1, 2, and 3 represent... The gas / solid, gas / liquid, and liquid / solid boundary lines at the time; curves 4, 5, and 6 are respectively The boundary lines between gas / solid, gas / liquid, and liquid / solid at that time.

[0035] Figure 11 This is a schematic diagram showing the influence of other gas components on the phase change conditions of water vapor; curve 1 shows the change law of phase change conditions under pure water vapor conditions, and curve 2 shows the change law of phase change conditions under the influence of other gas components. Detailed Implementation

[0036] This invention provides a method for calculating water vapor phase transition conditions applicable to high-altitude rarefied gas environments. The specific implementation follows... Figure 1 The process is divided into 5 steps: S1: Based on the way the research object affects the aerodynamic process, determine the dimensions of the structure or space affecting the aerodynamic process, thus providing the characteristic length for calculating the aerodynamic process and laying the foundation for calculating the influence of real gas effects. The characteristic length of the research object is a key parameter for determining the influence of real gas effects. Under the same operating conditions, different characteristic lengths will lead to different real gas effect effects. The real gas effect refers to the influence of gas molecule thermal motion on the aerodynamic process when it is on the same order of magnitude as the characteristic length, resulting in irregular aerodynamic processes and non-equilibrium phenomena. Therefore, the characteristic length is obtained and compared with the free path of water vapor molecules. During the flow around the object, obtain the structural parameters such as the diameter and length of the object, which serve as the basis for determining whether water vapor molecules can complete the flow around the object through their own thermal motion. Figure 2 As shown, water vapor molecules flow around an object of characteristic length L, due to the molecular path of freedom... Being on the same order of magnitude as L, it can directly complete the flow around itself through thermal motion without the need for mechanical motion. In the flow field space, the minimum spatial size that ensures uniform flow parameters is obtained, which serves as the basis for whether water vapor molecules can leave the space through their own thermal motion and exchange molecules with the surrounding space. Figure 3 The water vapor molecules shown are in a flow field with a characteristic length of L, due to the molecular path of freedom Being on the same order of magnitude as L, it can leave the flow field space through its own thermal motion, thus constantly exchanging molecules with the surrounding space.

[0037] S2: Operating conditions for obtaining gas molecules: temperature Water vapor number density Other gaseous component molecular number density The Maxwell velocity distribution of water vapor molecules is obtained by solving for the operating conditions, and the mean free path of the thermal motion of water vapor molecules is then calculated. The continuity parameters of water vapor molecules were compared with the characteristic length of the research object. .like If so, it can be determined that the real gas effect has no effect on aerodynamic / thermal performance; if At this point, it can be determined that the real gas effect influences the aerodynamic / thermal process. When the real gas effect influences the aerodynamic / thermal process, water vapor molecules can be classified into continuous molecules and free molecules. Figure 4 The diagram illustrates the methods for classifying continuous and free molecules. For the research object, continuous molecules all satisfy... Because of their low thermal motion amplitude, free molecules cannot complete their own flow around an object through thermal motion, thus colliding with the object's molecules. Furthermore, they cannot leave the flow field space through thermal motion, thus colliding with molecules within the flow field space. All free molecules satisfy... Due to its high thermal motion amplitude, it can complete the flow around an object through its own thermal motion, thus avoiding molecular collisions with the object. Within the flow field, it can leave the flow field space through its own thermal motion, constantly exchanging molecules with the surrounding space without molecular collisions. By analyzing the molecular distillation process, which has been widely implemented in engineering, the influence of real gas effects on aerodynamic / thermal processes can be obtained. Figure 5The diagram illustrates the thermal motion of gas molecules during molecular distillation. The substance being distilled, at a temperature significantly below its boiling point, releases gas molecules from the evaporator plate EP. These gas molecules then leave the distillation gap DG through their own thermal motion, reaching the condenser plate CP, where they re-condense into a liquid. Under vacuum conditions, the free path of gas molecules is on the same order of magnitude as the length of the distillation gap. This allows a large number of free molecules to exchange molecules with EP and CP through their own thermal motion. However, because the free path of gas molecules is less than the width of EP and CP, they can only collide with EP and CP, thus maintaining their liquid state.

[0038] S3: Calculated percentage of continuous water vapor molecules Continuous average thermal motion speed of water vapor molecules Temperature as a continuous molecule . Figure 6 The diagram illustrates the thermal motion of water vapor molecules within a flow field of characteristic length L. Free molecules in the diagram constantly exchange molecules with their surroundings, while continuous molecules that cannot leave the flow field through their own thermal motion continuously collide with the surrounding fluid, thus generating the actual pressure within the flow field. Among them, the continuous water vapor molecule number density The temperature embodied by continuous water vapor molecules The thermal motion amplitude of gas molecules is on the same order of magnitude as the distillation gap, and the resulting real gas effect alters the phase transition conditions, such as... Figure 7 As shown, under the influence of the real gas effect, the tendency of vapor to undergo phase change into liquid and solid states is reduced, thus allowing the distilled substance to exist in the gas phase in the traditional liquid phase region.

[0039] S4: The actual static pressure caused by the real gas effect on the research object is substituted into the calculation of the Gibbs free energy of water vapor and compared with the Gibbs free energies of liquid and solid water to obtain the driving force of the phase change Gibbs free energy of water vapor. Simultaneously, the influence of the real gas effect on thermal properties is quantified. During the calculation, the non-equilibrium problem caused by insufficient molecular collisions needs to be considered, including the translational temperature of water vapor at this point. Rotation temperature Existing droplet ice crystal temperature There may be discrepancies between them, where the Maxwell velocity distribution of water vapor molecules is affected by translational temperature. The decision was made.

[0040] S5: Based on the calculated Gibbs free energies of water vapor, liquid water, and solid water, the phases with the lowest Gibbs free energy under different operating conditions are compared to determine the corresponding phase regions. At a given operating point, if water vapor has the lowest Gibbs free energy, the operating point is in the gas phase region; if liquid water has the lowest Gibbs free energy, the operating point is in the liquid phase region; and if solid water has the lowest Gibbs free energy, the operating point is in the solid phase region.

[0041] After completing the calculation steps, the calculation result should be as follows: Under thermal equilibrium conditions, when the real gas effect affects the phase change conditions of water vapor, the gas phase region expands, thereby reducing the tendency of water vapor to undergo phase change and transform into other phase states. Figure 8 This demonstrates the impact of the real gas effect on phase transition conditions. The real gas effect causes the gas-solid and gas-liquid boundaries in the phase transition conditions to shift to the left, and also alters the triple point of water.

[0042] The water vapor number density at the gas / solid or gas / liquid boundary is used as an important research parameter. Figure 9 The study shows the variation of phase transition conditions with characteristic length. The presence of other gas components and the increase in the characteristic length of the research object will reduce the number density of water vapor under the condition of irregular gas movement, thus making the water vapor phase transition more inclined to follow the traditional three-phase diagram.

[0043] Under non-equilibrium conditions, Figure 10 The vapor-liquid boundary line of water shown corresponds to a saturated water vapor number density that varies with the temperature of the existing droplets / ice crystals. The increase gradually decreases, while the saturated water vapor number density corresponding to the gas / solid ratio will change with the temperature of the existing droplets / ice crystals. The vapor density gradually decreases with increasing gas temperature, with 273.15 K serving as the boundary between the solid and liquid phases. When the water vapor number density decreases to a certain level, the gas / liquid and gas / solid boundaries will also be deflected due to the real gas effect. The saturated water vapor number density increases with increasing gas temperature, consistent with the conditions under thermal equilibrium.

[0044] Under non-equilibrium conditions, the number density of water vapor at the triple point varies with the thermodynamic temperature of the gas. The pattern of change is as follows Figure 11 As shown in the figure, even under non-equilibrium conditions, the saturation number density still increases with increasing gas temperature. In the presence of other gas components, the real gas effect leads to a decrease in the corresponding water vapor number density. As the gas temperature increases, the corresponding triple-point water vapor number density gradually increases until the free path of water vapor molecules is much smaller than the characteristic size of the object under study. At this point, the real gas effect no longer affects the phase transition conditions, and the presence of other gas components no longer influences the water vapor phase transition conditions.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for calculating water vapor phase transition conditions applicable to rarefied gas environments at high altitudes, characterized in that, Includes the following steps: Step 1: Obtain local working conditions and, based on the specific circumstances of the research object, determine the structural parameters that affect the local water vapor molecule aerodynamic process, thereby obtaining the characteristic length L of the research object; Step 2: Based on local operating conditions, obtain the thermal velocity distribution of water vapor molecules, and then calculate the mean free path of the water vapor molecules. Then, the continuity parameter of water vapor molecules can be calculated. ; Step 3: Based on local working conditions, calculate the proportion of water vapor molecules actually involved in the collision and their thermal motion state in the research object, thereby obtaining the momentum exchange per unit time, and then calculating the actual static pressure caused by the water vapor. Step 4: Based on local working conditions, substitute the actual static pressure into the thermodynamic calculation to obtain the Gibbs free energy of water under different phases; Step 5: Compare the Gibbs free energy of water under different phase states to obtain the change mode of Gibbs free energy driving force in different phase transition processes, thereby calculating the phase region under different working conditions, and finally obtaining the phase transition conditions of water vapor.

2. The method for calculating water vapor phase transition conditions applicable to high-altitude rarefied gas environments according to claim 1, characterized in that, In step one, the local operating conditions include the local water vapor temperature. Water vapor number density And the number density of other gas components .

3. A method for calculating water vapor phase transition conditions applicable to high-altitude rarefied gas environments according to claim 1 or 2, characterized in that, In step one, if the object of study is a surface of a flow-shaped object, the characteristic length is selected as a structural parameter of the flow-shaped object, which serves as the basis for determining the relationship between the structure of the object and the thermal motion of water vapor molecules; if the object of study is a flow field space, the characteristic length in the flow field space is the length of the smallest spatial unit that can accurately express the flow characteristics of the flow field.

4. A method for calculating water vapor phase transition conditions applicable to high-altitude rarefied gas environments according to claim 1 or 2, characterized in that, In step two, when other gaseous components are absent, the mean free path of the thermal motion of water vapor molecules is... The calculation formula is: ； in, Water vapor number density, in m³. -3 ; Let be the diameter of a water molecule, and take it as . m; When various gaseous components J, including water vapor, are present, the mean free path of the thermal motion of water vapor molecules... The calculation formula is: ； in, The number density of other gas components is expressed in m³. -3 ; This represents the average thermal velocity of water vapor molecules, measured in m / s. The average thermal velocity of molecules in other gas components is expressed in m / s. Let be the diameter of a water molecule, and take it as . m; The diameter of the molecules of other gas components is in meters (m). The water vapor molecule continuity quantification parameter The calculation formula is as follows: 。 5. A method for calculating water vapor phase transition conditions applicable to high-altitude rarefied gas environments according to claim 1 or 2, characterized in that, In step three, the actual static pressure caused by the water vapor The calculation formula is: ； ； ； in, The continuous water vapor number density is expressed in m³. -3 ; The percentage of continuous water vapor molecules is 100%. The mass of a single water molecule is taken as . ; The average thermal velocity of continuous water vapor molecules is expressed in m / s. Boltzmann's constant is . .

6. A method for calculating water vapor phase transition conditions applicable to high-altitude rarefied gas environments according to claim 1 or 2, characterized in that, In step four, the formula for calculating the Gibbs free energy of water vapor is as follows: Enthalpy of gaseous water The calculation method is as follows: In the formula, This represents the internal energy of gaseous water, expressed in J / kg. Let the mass of a single H2O molecule be . ; Water vapor number density, in m³. -3 ; This represents the actual static pressure caused by water vapor, expressed in Pa. Entropy of gaseous water The calculation method is as follows: In the formula, Let be the entropy of liquid water under triple point conditions, which is set to 0 in the calculation. ; The latent heat of vaporization of liquid water under triple point conditions is expressed in J / kg. The triple point temperature is 273.16 K; This is the isochoric specific heat of gaseous water, in units of . ; Boltzmann's constant, ; Let the mass of a single H2O molecule be . ; This represents the actual static pressure caused by water vapor, expressed in Pa. This refers to the number density of water molecules in gas under triple point conditions, expressed in m³. -3 ; The formula for calculating the Gibbs free energy of solid water is as follows: The formula for calculating the Gibbs free energy of liquid water is as follows: in, , , These are the Gibbs free energies of gaseous water, liquid water, and solid water, respectively, in J / kg; , , These are the enthalpies of gaseous water, liquid water, and solid water, respectively, in J / kg; , , These are the entropy values ​​for gaseous water, liquid water, and solid water, respectively, in units of... ; , , These are the temperatures of gaseous water, liquid water, and solid water, respectively, in K. Under thermal equilibrium conditions, the three are equal.

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