A cavitation collapse test method using hot water instead of cryogenic fluid

Abstract

The present invention relates to a cavitation collapse test method using hot water instead of a cryogenic fluid. The cavitation collapse test method using hot water instead of a cryogenic fluid of the present invention comprises the following steps: S1, based on the cavitation thermodynamic effect intensity of the cryogenic fluid to be tested, screening out hot water at a certain pressure and temperature with similar cavitation thermodynamic effect intensity. S3, using the hot water as a substitute fluid, to conduct a cavitation collapse experimental test. The cavitation collapse test method using hot water instead of a cryogenic fluid of the present invention has the advantages of safety, low cost, easy operation, and reliable results.

Description

Technical Field

[0001] The invention relates to the technical field of low-temperature cavitation, in particular to a cavitation collapse test method using hot water instead of low-temperature fluid. Background Art

[0002] Liquid rockets generally use liquid hydrogen and liquid oxygen as propellants, which are injected into the reaction chamber by a turbocharger pump for combustion to provide propulsion for the rocket. However, this type of cryogenic fluid is prone to cavitation during transportation. Cavitation bubbles collapse violently under confining pressure, which can release pressure shock waves, produce cavitation noise, vibration, mechanical component failure, etc., which will significantly reduce the working efficiency and service life of the turbocharger pump. Therefore, studying the collapse of cavitation bubbles in cryogenic fluids and quantitatively evaluating the collapse intensity are of great significance for predicting the consequences of cavitation and conducting targeted optimization design of booster pumps.

[0003] However, under existing conditions, it is extremely difficult to conduct experimental research on cavitation collapse in cryogenic fluids. First, the temperature of cryogenic fluids is very low. For example, the temperature of liquid oxygen is below -183°C, while the temperature of liquid hydrogen is as low as -252°C. The cost of preparing such cryogenic fluids is very high. Secondly, in order to simulate the pressure environment under actual working conditions, it is necessary to process special cryogenic insulation containers and seal them to pressurize the fluid. However, sealing materials are prone to failure under ultra-low temperature conditions. Once fluid leakage occurs, it will cause frostbite and other injuries to the experimenters. For liquid hydrogen, the hydrogen formed by evaporation is prone to explosion after leaking into the surrounding air. In order to reduce costs, some researchers use software simulation methods to study the cavitation collapse of cryogenic fluids. However, the cavitation phenomenon involves complex processes such as gas-liquid two-phase flow, phase change, and heat transfer. The reliability of the simulation cannot be guaranteed at this stage. Therefore, it is urgent to develop a safe, low-cost, and easy-to-operate medium to replace this type of fluid for experimental research on cavitation collapse. Summary of the invention

[0004] Based on this, the object of the present invention is to provide a cavitation collapse test method using hot water instead of low-temperature fluid, which has the advantages of safety, low cost, easy operation and reliable results.

[0005] The present invention provides a cavitation collapse test method using hot water instead of low-temperature fluid, comprising:

[0006] S1: According to the cavitation thermodynamic effect intensity of the low-temperature fluid to be tested, hot water at a certain pressure and temperature with similar cavitation thermodynamic effect intensity is selected.

[0007] S2: For the low-temperature fluid to be tested and the selected hot water, the collapse process of cavitation is simulated respectively; the maximum wall motion velocity of cavitation is used as the characterization parameter of collapse intensity, and the simulation results are compared, so as to further adjust the temperature and pressure of the hot water so that the collapse intensity of cavitation therein is consistent with that in the low-temperature fluid.

[0008] S3: Use hot water at this temperature and pressure as a substitute fluid to conduct a cavitation collapse experiment test.

[0009] Step S1 specifically includes the following steps:

[0010] S11: Determine the type, temperature, pressure, and cavitation initial radius of the cryogenic fluid to be tested.

[0011] S12: Calculate the cavitation thermodynamic effect intensity value χ of the cryogenic fluid to be tested at the temperature and pressure,

[0012]

[0013] in,

[0014]

[0015] Where R0 is the initial radius of the cavitation bubble, p ∞ and T ∞ is the fluid pressure and temperature, ρ v and ρ L are the gas density inside the cavitation bubble and the density of the surrounding fluid, respectively, v is the saturated vapor pressure of the fluid, Λ is the latent heat of evaporation, c pL is the specific heat capacity of the fluid at constant pressure, D L is the thermal diffusivity of the fluid.

[0016] S13: Screen out hot water with a value χ close to the cavitation thermodynamic effect intensity value χ of the low-temperature fluid to be tested, and determine its pressure and temperature.

[0017] In some embodiments, before the test begins, the x values ​​of hot water at different pressures and temperatures can be calculated in advance and the results can be graphed. When it is necessary to find hot water with a x value similar to the cavitation thermodynamic effect intensity value x of the low-temperature fluid to be tested in step S13, the required hot water temperature and pressure can be determined by a table lookup method or a curve comparison method.

[0018] The cavitation collapse test method of the present invention using hot water instead of a low-temperature fluid, in step S2, evaluates the difference in collapse strength, and based on this, further adjusts the hot water temperature and pressure to make the collapse strength of the cavitation in the two media consistent, thereby determining the temperature and pressure of the hot water used as the substitute fluid.

[0019] Step S2 specifically includes the following steps:

[0020] S21: Use the cavitation dynamics model to simulate the cavitation collapse process in the cryogenic fluid to be tested, and obtain the maximum wall motion velocity of the cavitation.

[0021] S22: The cavitation dynamics model is used to simulate the cavitation collapse process in the selected hot water to obtain the maximum wall motion velocity of the cavitation.

[0022] S23: With an error tolerance of 5%, compare the maximum wall movement speed of the cavitation bubbles in the low-temperature fluid to be tested and the screened hot water. When the difference between the two is less than 5%, the screened hot water can be used as a substitute for the low-temperature fluid to be tested; when the difference between the two is greater than 5%, adjust the hot water temperature and pressure, and repeat steps S22 and S23 until the difference between the two is less than 5%.

[0023] Furthermore, in step S21 and step S22, the cavitation dynamics model is specifically described as follows:

[0024] The change in radius of a cavitation bubble when it expands and compresses in a fluid medium at a certain pressure and temperature can be described by the Keller equation:

[0025]

[0026] Where R is the radius of the bubble, c is the speed of sound in the fluid, and ρ L is the fluid density, p ∞ is the confining pressure in the fluid, p B is the pressure on the liquid side of the gas-liquid interface. The black dot above the symbol represents the time derivative.

[0027] Based on the constraint of normal stress equilibrium at the bubble wall, p B The internal pressure p of the cavitation bubble can be expressed by the following relationship:

[0028]

[0029] Where S is the surface tension, μ L is the dynamic viscosity of the fluid.

[0030] At the gas-liquid interface, there are phase changes such as evaporation of liquid and condensation of gas. According to the principle of conservation of mass, the rate of mass change caused by phase change is The relationship between the movement of the gas and liquid phases is as follows:

[0031]

[0032] Among them, v R and u R are the velocity of gas and liquid at the wall, ρ v is the density of the gas inside the cavitation bubble.

[0033] Inside the bubble, the pressure can be considered to be uniformly distributed and the gas can be treated as an ideal gas. Based on these assumptions, the velocity distribution equation inside the bubble can be obtained from the conservation of mass and energy:

[0034]

[0035] Where r is the radial distance from the center of the cavitation bubble, γ is the specific heat ratio of the gas, and k v is the thermal conductivity of the gas, T v is the gas temperature. The right side of the equation takes the value at r = R, and the gas phase velocity at the wall can be obtained.

[0036] By combining the above two equations, we can get the expression of gas phase pressure p:

[0037]

[0038] In the formula is the rate of phase change at the bubble wall, which is related to The relationship is Where M is the molar mass of the substance.

[0039] It can be calculated using the Hertz–Knudsen–Langmuir formula as follows:

[0040]

[0041] Among them, p v is the saturated vapor pressure at the bubble wall, T w is the temperature at the wall, R g is the ideal gas constant, α M is the adjustment coefficient, α M =0.4.

[0042] From the energy equation, the temperature field equations inside and outside the bubble are:

[0043]

[0044]

[0045] Among them, T v and T L are the temperatures in gas and liquid, respectively, c pv is the specific heat of the gas at constant pressure.

[0046] The liquid phase velocity u can be obtained from the mass change rate equation combined with the incompressible fluid characteristics:

[0047]

[0048] The temperature continuity and heat flow conservation at the gas-liquid interface can be expressed as follows:

[0049] T L | r＝R =T v | r＝R

[0050]

[0051] Where Λ is the latent heat of vaporization of the liquid.

[0052] The above equations constitute a complete closed set of equations. Solving them can obtain the dynamic characteristics of cavitation that can fully reflect the thermodynamic characteristics, including the cavitation radius R, the wall motion velocity Internal pressure p, gas temperature T v , liquid temperature T L The instantaneous quantity of other parameters.

[0053] In step S3, hot water is used as a substitute liquid to perform the cavitation collapse test, which effectively reduces the difficulty of the experiment and the requirements for low temperature and high pressure in the experimental environment. In addition, the influence of cavitation collapse on mechanical components can be observed intuitively, which improves the reliability of the test results.

[0054] For better understanding and implementation, the present invention is described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 A flow chart of a cavitation collapse test method using hot water instead of a cryogenic fluid in the present application;

[0056] Figure 2 This is a diagram showing the changes in cavitation radius and wall motion velocity during the cavitation collapse process of an embodiment of the present application. DETAILED DESCRIPTION

[0057] In the prior art, cavitation collapse experiments are usually conducted directly using the cryogenic fluid to be tested or simulated using software. When the cryogenic fluid to be tested is directly used for the experiment, the refrigeration cost is high and the safety risk is high due to the extremely low temperature of the cryogenic fluid. If software is used for simulation testing, the impact of cavitation collapse on the components cannot be observed intuitively, and the reliability of the simulation results cannot be guaranteed.

[0058] In order to solve the above problems, it is necessary to find a suitable cryogenic fluid substitute medium. The most important feature of cryogenic fluid cavitation is its strong thermodynamic effect. Compared with water at room temperature, cryogenic fluid vapor density is large, thermal conductivity and specific heat capacity are small, and saturated vapor pressure changes dramatically with temperature. These properties determine that when cavitation occurs, the temperature of the fluid surrounding the cavitation bubble is significantly reduced and the growth of the cavitation bubble is limited; on the other hand, when the cavitation bubble is compressed, the surrounding fluid heats up rapidly and the internal gas pressure rises sharply. Therefore, a suitable cryogenic fluid substitute medium should have similar cavitation thermodynamic effects.

[0059] After research, the inventors found that, similar to cryogenic fluids, the cavitation effect in hot water also has a strong thermodynamic effect, and the safety and operating performance are significantly improved when using it to conduct experiments. Therefore, hot water is a more ideal substitute for cryogenic fluids. However, in order to apply the experimental results of cavitation collapse in hot water at a certain temperature and pressure to cryogenic fluids, it is necessary to establish a matching relationship between the two based on certain collapse strength evaluation standards. To this end, the present invention proposes a design method to replace cryogenic fluids with hot water and conduct cavitation collapse tests.

[0060] Example

[0061] See also Figure 1 , an embodiment of the present application provides a cavitation collapse test method using hot water instead of low-temperature fluid.

[0062] This example tests the collapse of cavitation bubbles in liquid oxygen at a certain temperature and pressure. The specific steps are as follows:

[0063] SA11: Determine that the temperature of the liquid oxygen to be tested is 80K, the pressure is 10 bar, and the initial radius of the cavitation bubble is R0 = 1 mm.

[0064] SA12: The cavitation thermodynamic effect intensity value of the cavitation bubble in the liquid oxygen is obtained as χ=2.067.

[0065] SA13: Based on the above χ value, hot water with a temperature of 343.2K (70℃) and a pressure of 1.28bar was preliminarily screened out.

[0066] SA21: Based on the cavitation dynamics model, simulate the cavitation collapse process in liquid oxygen, obtain the radius of cavitation collapse and the change of wall velocity, and determine the maximum wall velocity

[0067] SA22: Based on the cavitation dynamics model, simulate the cavitation collapse process in the selected hot water, obtain the change of cavitation collapse radius and wall velocity, and determine the maximum wall velocity

[0068] SA23: Comparison of the maximum wall velocity of liquid oxygen and hot water and If the difference between the two is greater than 5%, change the hot water temperature and pressure, and repeat steps S22 and S23 until the difference between the two maximum wall movement velocities is less than 5%.

[0069] SA24: When the hot water temperature is adjusted to 343.2K and the pressure is 1.9 bar, the maximum wall velocity of the hot water is simulated. At this time, the maximum wall velocity of liquid oxygen The difference is 2.7%, so hot water under this condition can be used as a substitute for liquid oxygen.

[0070] SA3: Use hot water with a temperature of 343.2K and a pressure of 1.9bar as a substitute liquid to conduct cavitation collapse experimental tests.

[0071] See also Figure 2 , the horizontal axis in the figure is the normalized time, where t c is the Rayleigh collapse time; the vertical axis is the normalized radius of the cavitation bubble and the wall motion velocity. The changes in the cavitation radius and wall motion velocity during the collapse process of the cavitation bubble in liquid oxygen at a temperature of 80K and a pressure of 10 bar and in hot water at a temperature of 343.2K and a pressure of 1.9 bar are compared. It can be seen that in the first three cycles, the dynamic changes of the cavitation bubble in the two liquids are very similar, which further confirms the rationality of using hot water as a substitute liquid.

[0072] The present invention discloses a cavitation collapse test method that uses hot water instead of cryogenic fluid, which reduces the difficulty of the test, improves the safety and operability of the test, and saves costs compared to the prior art. The test results can be observed intuitively, and compared with the pure numerical simulation method, the test results have higher reliability and can provide guidance for engineering practice.

[0073] The above-mentioned embodiments only express several implementation methods of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, and the present invention is also intended to include these modifications and modifications.

Claims

1. A cavitation collapse test method using hot water instead of low-temperature fluid, characterized in that: The following steps are involved: S1. According to the cavitation thermodynamic effect intensity of the low-temperature fluid to be tested, hot water at a certain pressure and temperature with similar cavitation thermodynamic effect intensity is selected; S2 takes the maximum wall movement speed in the cavitation collapse process as a reference, compares the maximum wall movement speed of the cavitation in the low-temperature fluid and the screened hot water, adjusts the temperature and pressure of the screened hot water, and thus determines the temperature and pressure of the hot water as the replacement fluid; S3 uses the hot water as a substitute liquid to perform a cavitation collapse experiment test.

2. The cavitation collapse test method using hot water instead of low-temperature fluid according to claim 1, characterized in that: The step S1 comprises: Step S11: determining the type, temperature, pressure, and cavitation initial radius of the cryogenic fluid to be tested; Step S12: calculating the cavitation thermodynamic effect intensity value of the cryogenic fluid to be tested at the temperature and pressure; Step S13: Screen out hot water with a cavitation thermodynamic effect similar to that of the low-temperature fluid to be tested, and determine its pressure and temperature.

3. The cavitation collapse test method using hot water instead of low-temperature fluid according to claim 2, characterized in that: In step S12, the cavitation thermodynamic effect intensity value is , in, ; is the initial radius of the cavitation bubble, and are the fluid pressure and temperature, and are the density of the gas inside the cavitation bubble and the density of the surrounding fluid, respectively. is the saturated vapor pressure of the fluid, is the latent heat of evaporation, is the specific heat capacity of the fluid at constant pressure, is the thermal diffusivity of the fluid.

4. The cavitation collapse test method using hot water instead of low-temperature fluid according to claim 3, characterized in that: In the step S13, the cavitation thermodynamic effect intensity value of the hot water is obtained by a table lookup method.

5. The cavitation collapse test method using hot water instead of low-temperature fluid according to claim 4, characterized in that: The step S2 comprises: Step S21: simulating and calculating to obtain the maximum wall movement velocity of the cavitation bubble in the cryogenic fluid to be tested; Step S22: simulating and calculating the maximum wall movement velocity of the cavitation bubble during the cavitation bubble collapse process in the hot water; Step S23 sets the error tolerance; compare the maximum wall movement speeds in steps S21 and S22, and when the difference between the two is less than the error tolerance, the screened hot water can be used as a substitute for the low-temperature fluid to be tested; when the difference between the two is greater than the error tolerance, adjust the temperature and pressure of the hot water, and repeat steps S22 and S23 until the difference between the maximum wall movement speeds is less than the error tolerance.

6. The cavitation collapse test method using hot water instead of low-temperature fluid according to claim 5, characterized in that: The error tolerance is 5%.

7. The cavitation collapse test method using hot water instead of low-temperature fluid according to claim 6, characterized in that: In the step S21 and the step S22, the collapse process of the cavitation in the low-temperature fluid to be tested and the hot water is simulated by a cavitation dynamics model.

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