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Dew conducted research to reveal the mechanism of internal condensation. And using the idea of ​​fuzzy mathematics, combining various influencing factors to give the possibility of condensation in the system, the detonation of the aerodynamic system, the condensation inside the aerodynamic system, the uniform condensation deposition, the development of the pneumatic system to the miniaturization, the original comparison A new question has arisen in the perfect pneumatic technology, which is the condensation of the pneumatic system. Condensation of pneumatic systems, especially internal condensation, has a great impact on system performance and component life. Therefore, it is an important lesson to correctly discriminate the occurrence of condensation and prevent condensation from occurring. In this paper, the pneumatic filling and deflation system is taken as the research object. Firstly, the mathematical model of the system is established, and the numerical solution is obtained. Secondly, using the uniform condensation theory, the condensation of water vapor in the vessel and pipeline during the deflation process is calculated. Then, using the theory of gas suspension, the method of depositing tiny water droplets in the pneumatic charging and discharging system is proposed, and the amount of water droplets that can be deposited in the system during the deflation process is calculated. Finally, using the idea of ​​fuzzy mathematics, the various influencing factors are combined to give the formula for the possibility of condensation in the system.
1 The mathematical model of the flow field of the pneumatic filling and deflation system abstracts the actual pneumatic charging and discharging system into a system consisting of a fixed volume with a long tube length and two fixed orifices. 1. Establish a mathematical model of the system. At the time, the container adopts the centralized parameter method, and the pipeline adopts the distributed parameter method.
In the study of this section, it is assumed that the National Natural Science Foundation funded project 59375183.200108 received the first draft, and the gas studied in the revised draft was the ideal gas.
The pressure temperature and density within the vessel are evenly distributed.
The pressure temperature and density within each grid in the pipeline are evenly distributed.
The flow of compressed air through the orifice is equal to the flow.
Ignore the effects of gravity.
1.1 Mathematical Model of the Container The following equations are obtained from thermodynamics and fluid mechanics knowledge.
Continuity equation throttle point flow equation accounted for Px orifice low pressure side pressure ideal gas state equation thermodynamics first law cv ratio constant volume heat capacity heat transfer equation 1.2 pipeline mathematical model filling and deflation system in the pipeline compression The flow of air is a compressible unsteady dimensional flow with friction and heat transfer effects. According to the knowledge of gas dynamics, considering the friction heat transfer, omitting the influence of work and gravity, the following equation is obtained. The continuous equation 2 momentum equation Fanning coefficient, the empirical formula gives the water radius of the flow channel 3 energy equation P, the mathematical of the P container The model is an ordinary differential equation and an algebraic equation, which can be solved by the order Runge-Kutta method. The governing equations of the pipeline sections are group-order quasi-linear non-homogeneous partial differential equations, which are hyperbolic, and their solutions can be obtained by the characteristic line method. The connection of the vessel to the pipeline model is handled by the idea that the mass flow of the gas flowing through the same interface is equal, and the boundary conditions on the side of the pipeline vessel are also solved. In this way, the flow field of the charge and discharge system can be obtained.
2 Condensation process of water vapor in the air When the pneumatic system is running, the compressed air will expand violently during the release process, causing its temperature to drop sharply. If the temperature is lower than the dew point of the compressed air, the water vapor will condense. When the gas-liquid interface is infinite, the condensation process takes place according to the saturation curve of water vapor. However, in the pneumatic system, the compressed air is purified by dust removal and water removal, and no liquid phase exists. It can only be tiny particles of impurities or tiny droplets of spontaneous formation, in which case the condensation is uniform. Considering the influence of the surface tension of the water droplets, the condensation does not occur according to the condensation line, but has a certain degree of supersaturation.
According to the theory of uniform condensation, all water droplets that grow up must first reach a critical radius and then continue to grow as a stable water droplet. The critical radius is the water droplet with the current vapor pressure as the saturated vapor pressure. It can be defined as the nuclear formation rate by the number of critical condensation nuclei generated per unit volume per unit time defined by the subscript 7 water vapor subscript drop.
For this nucleation rate, after using Frankel's proposed water droplet to become a stable water droplet, its radius will change with time, and the rate of change is defined as the growth rate of water droplets. A water droplet having a radius r is in a state of a critical radius.
To make the water droplets grow, it is necessary for the water vapor to have a certain degree of supersaturation.
As the density of the compressed air changes during the deflation process, the number density of water droplets in the air also changes. The amount of water droplets generated in the time + time is, during the period of time, the condensation volume per unit volume of water vapor is in the condensation process of water vapor, and new water droplets are continuously generated with the change of time, and the existing water droplets continuously Growth, it is obviously impossible to record the growth process of each water droplet during the calculation process. The solution here is to group the water droplets and think that the water droplets produced during the time of +4; have the same radius. Since the process of generating new water droplets during the coagulation process can be completed in a short time, a limited number of groupings can be used to describe the water droplets generated during the coagulation process, and the same group of water droplets are considered to have the same characteristics.
3 The deposition of tiny water droplets The radius of the water droplets condensed in the pneumatic system is between 7,1051. According to the theory of gas suspension, the deposition methods of these water droplets are kind, namely gravity deposition inertial deposition and diffusion sedimentation. 3.1 Gravity sedimentation gravity deposition is due to The water droplets are subjected to a sinking speed by the action of the gravitational field, and the resulting water droplets are deposited on the solid wall.
When the water droplets sink by gravity, the sinking speed will stabilize at the ultimate speed.
r relaxation time is calculated by the 3 claw correction factor when calculating the ultimate speed of a small water droplet. That is, the pipeline in the 3.2 inertial deposition pneumatic system is inevitably bent, which causes the compressed air to flow in the pipeline. The direction of the airflow will change.
When the airflow changes the direction of motion, the water droplets entrained in the airflow tend to have a tendency to separate from the air to varying degrees due to the inertial force. Set a diameter of water droplets around the point to make a circular motion, the radius is the ruler, the angular velocity is the angle at which the heart water droplet turns around the point. When water droplets move in the air, their Reynolds number is small, the movement will be affected, 3 resistance, and the resistance received by the water droplets.
In the heart time, the radial displacement of the water droplets is needed because the radius of the water droplets in the pneumatic system is small, and its relaxation time is also small, so it can be considered that the tangential velocity of the water droplets and the airflow are as the heart if the angle of the bending of the pipeline is the heart. The radial displacement as the airflow flows through the elbow is 3.3. Diffusion deposition The phenomenon of water droplets deposited by diffusion is called diffusion deposition. Diffusion deposition occurs in water droplets suspended in laminar and turbulent flow, but the mechanism is different. According to calculations and analysis, the amount of deposition caused by diffusion deposition is much smaller than that caused by the first two methods, and can be ignored here.
4 The fuzzy criterion of internal condensation According to experience, the factors affecting the condensation of the pneumatic system, in addition to the amount of water droplet deposition, are the cycle of system charging and discharging, the cumulative effect of charging and discharging, and the influence of impurities in the air on condensation. Taking these factors into consideration, the fuzzy idea is used to give the possibility that condensation will occur in a pneumatic system. For the convenience of discussion, the factors affecting the condensation of the system are called the image of the system. According to the actual situation, there is a deposition amount of water droplets. The charge and discharge cycle is longer. The accumulation effect of charge and discharge gas is larger and the impurity particles in the air are larger. .
Let only the real axis, look at the subset of only 4 of the Violet space, Y = iXIX = xi, x2, J, 3, xa, 23 degree from the perspective of judging whether the system is condensation, the vector has no =, especially All the images of a system. The value of the work reflects the extent of the seventh item of the system. The vector fork is defined as an image group, and the subset is called an image space.
Taking the image space as the domain of the study, the internal condensation is regarded as whether the previous system makes internal condensation. The question is how much the determined element belongs to this for a long time.
The extent to which water droplets are deposited. The value is in the closed interval, which is specifically defined as the internal dew point. The external dew point is especially determinable for a given pneumatic charge and discharge system. Therefore, the membership degree can be calculated according to Equation 30. This membership is the possibility of internal condensation in the system.
Through the analysis of the previous calculation results, the essential reason that the system parameters affect the condensation is the difference of the system parameters, which makes the diameter of the water droplets generated by the system during the deflation process different, the volume ratio and the charge and discharge cycle are different, thus determining Whether there are excess water droplets deposited in the system determines whether condensation will occur in the system.
5 Test Verification of the Criterion In order to verify the correctness of the previous theoretical results, the system consisting of different volume containers and different lengths of gas tubes is subjected to gas and gas venting test under defined conditions, and internal dew condensation results are obtained. There are 3 possibilities for internal condensation. It can be seen from this that the calculated boundary of the internal condensation and the experimental results basically indicate that the theory in this paper is basically correct, and the viewpoint can explain the essential cause of internal condensation.
In the case of 1 mmcr, the amount of water droplets deposited at 7 o'clock is 8 TTlct critical deposition amount. When the sediment amount is greater than that, the degree of membership of the water droplet deposition is considered to be 1. Here = 0.05.
The degree of system charge and discharge cycle is long in the closed interval, specifically defined as the Tcr critical period. 3 When the charge and discharge cycle is greater than D, the system is considered to have a longer degree of charge and discharge cycle. Based on the results of experimental studies and other researchers, it is believed that the effect on the cumulative effect of charge and discharge is mainly the ratio of the volume of the vessel to the volume of the pipeline. The degree to which the system cumulative effect is large 13 is defined as the closed interval, which is defined as the volume of the pipeline. The impurity particles in the compressed air have a certain influence on the condensation of the system, and vary with the size and number of the particles. In the actual pneumatic system, the compressed air needs to be purified before entering the system. Taking the common air purification equipment as an example, the compressed air purified by different air purification equipment can be divided into several grades, namely compressed air. The maximum diameter of the particles contained is 5, 0.3, and 0.01 claws. It can be considered that the higher the filtration precision, the smaller the diameter of the impurity particles and the smaller the number. According to experience, the extent to which the impurity particles in the compressed air are much larger is defined as the effect of the various aspects on internal dew condensation, and their weights are also different. The corresponding weights are as follows 5,3 5, xl defines the degree of membership of the fork to the internal condensation is 6 Conclusion A mathematical model of the aerodynamic steady-flow flow of the pneumatic charge and discharge system is established and solved.
The uniform condensation theory is used to calculate the condensation of water vapor in the system during deflation, and the distribution of the diameter and diameter of the water droplets with time and position.
The theory of gas suspension is used to derive the deposition methods of tiny water droplets in pneumatic systems, and their calculation methods are given.
Using the idea of ​​fuzzy mathematics, the various factors affecting condensation are given to give a formula for the possibility of internal condensation of the system. Through theoretical analysis, the mechanism of internal condensation of the pneumatic system is revealed.
1 left Crook Hoffmann gas dynamics. Beijing National Defence Industry Press, 1984, on page 53 Deposition author Li Jun, born in 1972, lecturer. Engaged in pneumatic technology research, published more than 20 papers, participated in the National Natural Science Foundation and other courses, and won one national defense science and technology award.
Research on burning and emission control technologies.
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