An online precise calibration method for the volume of a container

Abstract

The present invention discloses an on-line precise calibration method for the volume of a container. This method provides two calibration stages. In stage one, there are two modes, namely the hydrogen-saving mode and the high-pressure mode. Both modes have their respective advantages, and the operator can select one of them according to the requirements. In the first calibration stage, a system of ternary linear equations is established based on the law of conservation of mass, and the method of optimization is used for transformation to solve for three calibrated volume values. In the second calibration stage, a system of equations with reduced elements is established according to the law of conservation of mass, and the remaining calibrated volume values are directly solved using the solve function. The above processes are all completed using a self-made automatic control program based on LabVIEW. This method can calibrate the volumes of multiple cavities at one time. The calibration process is fully automated, the program runs reliably, and the operation process is simple and efficient. The calibration method provided by the present invention has the advantages of low cost, high precision, and high efficiency compared with the previous calibration methods.

Description

Technical Field

[0001] The present invention relates to an on-line accurate calibration method for the volume of a container, belonging to the technical field of gas-solid reaction. Background Art

[0002] With the increasing shortage of energy and the worsening environmental pollution, people are eager to find sustainable clean energy to replace traditional fossil energy. Hydrogen is a good alternative, but one of its main problems is storage. For the storage problem, solid-state hydrogen storage has high volumetric hydrogen storage capacity, high safety, high efficiency and purification function, which encourages people to pursue hydrogen storage materials with excellent performance. High-precision hydrogen storage testing equipment is the key to pursuing high-performance hydrogen storage materials, and the accuracy of the cavity volume calibration of the hydrogen storage testing equipment is the key to the testing accuracy. At present, many volume calibration methods have been proposed, including off-line volume calibration and on-line volume calibration. Even though the accuracy of off-line volume calibration is high, since the equipment uses on-line volume, the volume calibrated off-line still cannot meet the usage requirements of the equipment. Most of the on-line calibration methods are based on the gas expansion method of adding a container with a known volume or the calibration method of adding a mass flowmeter. Most of these volume calibration methods have problems such as high cost, low accuracy, low efficiency and complex operation.

[0003] The patent "A Simple Method for Accurately Calibrating the Volume of a Container" with the Chinese patent number ZL200510046319.9 discloses a simple volume calibration method. This method establishes a binary linear equation according to the MBWR state equation and the law of conservation of mass, and adds a steel ball with a known volume to increase the solution conditions for solving. The final value of the container calibration is selected by averaging or taking the median of the solution results of multiple groups of data.

[0004] This method requires adding a steel ball with a known volume, and only two cavities can be calibrated in one operation, so there are several deficiencies. The accuracy of the steel ball has a great influence on the calibration accuracy. However, the higher the accuracy of the steel ball, the higher the manufacturing cost; and there must be a certain deviation in the volume measurement of the steel ball; the oxidation, rust and low cleanliness of the steel ball will all affect the calibration accuracy; the cumbersome placement process of the steel ball and the calibration of the volumes of multiple cavities will inevitably lead to low calibration efficiency; for containers with special internal structures, this method cannot achieve calibration simply and efficiently; there is also room for further improving the accuracy in the selection of the gas state equation. Summary of the Invention

[0005] The purpose of the present invention is to provide an on-line accurate calibration method for the volume of a container to solve the problems of low efficiency, low accuracy and high cost in the existing technology for volume measurement.

[0006] An on-line accurate calibration method for the volume of a container, the method includes steps,

[0007] Calibration Phase 1:

[0008] Collect the temperature and pressure values of the gas storage chamber, the system composed of the gas storage chamber, cylinder 1, the system composed of the gas storage chamber, cylinder 1 and cylinder 2, and the system composed of cylinder 2 and the gas storage chamber respectively;

[0009] Calculate the molar density of the gas storage chamber, the system composed of the gas storage chamber, cylinder 1, the system composed of the gas storage chamber, cylinder 1 and cylinder 2, and the system composed of cylinder 2 and the gas storage chamber according to the collected temperature and pressure values;

[0010] Construct a quadratic optimization function based on the molar density of each system, and optimize it by the method of finding the minimum value of the quadratic objective function with linear constraints based on the least squares solution program, and solve the volume calibration values of the gas storage chamber, cylinder 1 and cylinder 2;

[0011] Calibration Phase 2:

[0012] Collect the temperature and pressure values of the gas storage chamber, pipeline and sample chamber, and calculate the molar density of the gas storage chamber, pipeline and sample chamber;

[0013] Heat the sample chamber to the preset temperature, collect the temperature and pressure values of the gas storage chamber, pipeline and sample chamber, and calculate the molar density of the gas storage chamber, pipeline and sample chamber according to the collected temperature and pressure values;

[0014] Based on the reducible element equations formed by the molar density of each cavity before and after heating, call the solve function of MATLAB in LabVIEW to solve it, and obtain the volume calibration values of the pipeline and sample chamber.

[0015] Furthermore, in the first calibration phase, the pressure value is obtained by evacuating the gas storage chamber, cylinder 1 and cylinder 2; filling a certain amount of hydrogen into the gas storage chamber and recording the pressure value of the gas storage chamber; opening pneumatic valve 3, the hydrogen in the gas storage chamber flows into cylinder 1 and record the pressure value of the system composed of the gas storage chamber and cylinder 1; opening pneumatic valve 2, the hydrogen in the system composed of the gas storage chamber and cylinder 1 flows into cylinder 2 and record the pressure value of the system composed of the gas storage chamber, cylinder 1 and cylinder 2; evacuating the gas storage chamber, opening pneumatic valve 2, and the hydrogen in cylinder 2 flows into the gas storage chamber and record the pressure value of the system composed of the gas storage chamber and cylinder 2.

[0016] Furthermore, in the second calibration phase, the pressure values of the gas storage chamber, pipeline and sample chamber are obtained by evacuating the gas storage chamber, pipeline and sample chamber; filling a certain amount of hydrogen with a certain pressure into the gas storage chamber and recording the pressure value of the gas storage chamber; opening pneumatic valve 4, the hydrogen in the gas storage chamber flows into the pipeline and sample chamber and record the pressure value of the gas storage chamber, pipeline and sample chamber; heating the heating furnace and record the pressure value of the gas storage chamber, pipeline and sample chamber.

[0017] Furthermore, the temperatures of the gas storage chamber, the system consisting of the gas storage chamber and steel cylinder 1, the system consisting of the gas storage chamber and steel cylinder 1 and steel cylinder 2, the system consisting of steel cylinder 2 and the gas storage chamber, the pipeline and the sample chamber are collected by temperature sensors.

[0018] Furthermore, the gas molar density is based on the actual gas state equation formula (1), specifically the gas molar density is calculated by the Leachman state equation formula (3), and then the hydrogen molar amount of each cavity is calculated:

[0019] PV＝nZRT (1)

[0020] Where P is the gas pressure, V is the cavity volume, n is the molar mass, Z is the gas compressibility factor, R is the gas constant, and T is the absolute temperature. Formula (2) is derived by combining the Leachman state equation, and formula (2) is used to substitute into formula (3);

[0021]

[0022] Furthermore, the method for calculating the gas molar density includes:

[0023] Substitute the temperature and pressure data of the corresponding container to be tested into formula (3) to calculate the gas molar density of the corresponding container to be tested.

[0024] Furthermore, the gas storage chamber V ref 、Cylinder-V gb1 And cylinder 2V gb2 The calculation method of the volume calibration value includes: According to the conservation of mass, the equilibrium equation is obtained:

[0025]

[0026] Combining formulas (4), (5) and (6) and sorting them out, we get:

[0027]

[0028] Extract the determinant of equation system (7):

[0029]

[0030] The method of finding an approximate solution to the weighted quadratic objective function based on the least squares solution method is to square and weight the left-hand side of the equation group (7) and then add them to minimize the function to find an approximate solution. After squaring, the right-hand side should also be approximately 0, so f(V) min The function should be 0 + ;

[0031]

[0032] where ω i (i=1,2,3) is the weight coefficient, the default value is 1, and it is selected according to the needs. The container with high volume accuracy requirement corresponds to a large weight, and vice versa. The program based on the least squares solution method solves the weighted quadratic objective function of the linear constraint and automatically solves the function f(V) within the constraint range. min Minimum air chamber V ref 、Cylinder-V gb1 And cylinder 2V gb2 The volume calibration value.

[0033] Furthermore, the pipeline V tube and sample chamber V sc The calculation method of the volume calibration value includes: According to the law of conservation of mass, the equilibrium equation is obtained:

[0034]

[0035] Combining formulas (16) and (17) and sorting them out, we get:

[0036]

[0037] Where V ref The value of has been calibrated in the first stage, so the equation system is reduced to a two-variable linear equation system. Using LabVIEW to call MATLAB's solve function to solve it, the pipeline V tube and sample chamber V sc The volume calibration value.

[0038] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: the present invention does not require the configuration of a high-precision container with a known volume; does not require the configuration of a high-precision steel ball with a known volume; does not require an external mass flow controller; the calibration process is fully automated, no human intervention is required, and the calibration efficiency is high; there are no external containers and steel balls, and the calibration results are highly accurate; the operation process is simple and the cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a structural diagram of the fully automatic hydrogen storage material testing equipment of the present invention;

[0040] Figure 2 It is a first-stage calibration flow chart of the present invention;

[0041] Figure 3 It is a two-stage calibration flow chart of the present invention;

[0042] Figure 4 It is the overall calibration flow chart of the present invention;

[0043] Figure 5 This is a PCT curve diagram of the present invention without sample measurement;

[0044] Figure 6 is the PCT test curve obtained under the calibrated volume in Mode 1 of the present invention;

[0045] Figure 7 is the PCT test curve obtained under the calibrated volume in Mode 2 of the present invention;

[0046] Figure 8 is the Ki test curve obtained under the calibrated volume in Mode 1 of the present invention;

[0047] Figure 9 is the Ki test curve obtained under the calibrated volume in Mode 2 of the present invention;

[0048] In the figure: 1. Temperature sensor 2; 2. Cylinder 1; 3. Cylinder 2; 4. Pressure sensor 2; 5. Computer; 6. Pressure sensor 1; 7. Pneumatic valve 2; 8. Pneumatic valve 3; 9. Pneumatic valve 4; 10. Pneumatic valve 1; 11. Ball valve; 12. Quick connector; 13. Gas cylinder; 14. Sample chamber; 15. Temperature sensor 1; 16. Pneumatic valve 6; 17. Pneumatic valve 5; 18. Vacuum pump; 19. Heating furnace; 20. Temperature sensor 3; 21. Gas storage chamber; 22. Pipeline. Detailed implementation manners

[0049] To make the technical means, creative features, achieved purposes and functions of the present invention easy to understand, the present invention will be further described below in conjunction with specific implementation manners.

[0050] The present invention provides the following technical solution: An on-line accurate calibration method for the volume of a container: This method includes two volume calibration stages. Stage 1 has two modes. Mode 1 is a hydrogen-saving mode with obvious pressure difference change. In this mode, the process of obvious pressure change can be clearly seen during calibration and it has a good function of saving hydrogen; Mode 2 is a high-pressure mode that makes full use of the range of the pressure sensor. In this mode, each pressure sensor is fully utilized during calibration, and the pressure of each reaction is at a position slightly smaller than the maximum range of the pressure sensor. Therefore, the deviation caused by the pressure sensor will be reduced to a certain extent.

[0051] When calibrating the volume V of the gas storage chamber 21 ref , the volume V of cylinder 1 2 gb1 (including the pipeline volume between pneumatic valve 3 8 and cylinder 1 2) and the volume V of cylinder 2 3 gb2 (including the pipeline volume between pneumatic valve 2 7 and pressure sensor 2 4), each mode has its own advantages and disadvantages. The operator can select one of them according to needs, and then the entire process will be automatically controlled by the computer 5. Stage 2 is to calibrate the volume V of the pipeline 22 tube and the volume V of the sample chamber 14 sc .

[0052] Based on the data collected in real time by the temperature sensor and the pressure sensor, as well as the volumes of each part of the cavity, and based on the real gas state equation, the molar amount of gaseous hydrogen in each part can be calculated in real time, and then the molar amount of hydrogen absorption and desorption of the material can be calculated.

[0053] P V = nZR T (1)

[0054] Where P is the gas pressure, V is the cavity volume, n is the molar amount, Z is the gas compressibility factor, R is the gas constant, and T is the absolute temperature. The accuracy of the gas molar amount calculation depends on the accuracy of the real gas state equation. For the selection of the real gas state equation, the present invention selects the Leachman state equation newly recommended by NIST. Because compared with the previous state equations, it has higher accuracy in a larger temperature and pressure range. The uncertainty of the molar density of this state equation is significantly smaller than that of the MBWR state equation.

[0055]

[0056] Where α r is the remainder of the Helmholtz free energy, l = 7, m = 9 and n = 14. Parameters d i , N i , t i , p i , φ i , D i , β i and γ i Specifically, it can refer to the NIST official website or Leachman's graduation thesis (Leachman JW. Fundamental Equations of State for Parahydrogen, Normal Hydrogen, and Orthohydrogen [MScthesis]. Masters Abstracts International: University of Idaho; 2007.).

[0057] Under the condition that the leakage rate of the equipment meets the requirements, the amount of substance of gaseous hydrogen in each part can be calculated by using the above formula with the collected data and the volume of the cavity.

[0058] The following is an elaboration for two stages:

[0059] Phase I, Mode I: includes the following steps

[0060] Select the small molecule hydrogen gas as the calibration gas (the operator can also choose other calibration gases, such as helium), because the gas molecules are extremely small and can fill the container to be calibrated as much as possible; and the calibration gas is consistent with the actual test gas, so that the calibrated volume result can be made closest to the volume size used during actual testing to the greatest extent.

[0061] Conduct a leak rate test to ensure that the hydrogen leak rate of the entire cavity system is < 10 -9 g / s.

[0062] Measure the temperature of the gas storage chamber 21 through the temperature sensor -15; measure the system pressure through the pressure sensor -6, and measure the system pressure of the second cylinder 3 through the second pressure sensor 4.

[0063] First, open the pneumatic valve two 7, pneumatic valve three 8, pneumatic valve five 17 and pneumatic valve six 16 to continuously and rapidly evacuate the entire connected container system for 30 minutes, and then close all valves.

[0064] Manually open the ball valve 11 to prepare for the input of hydrogen.

[0065] Open the pneumatic valve one 10 to fill the gas storage chamber 21 with hydrogen at a certain pressure (the pressure is 9.5 MPa. For test accuracy, make the pressure as close as possible to the maximum value of the range of the pressure sensor one 6), and then close the pneumatic valve one 10. Wait for 10 minutes. After the system stabilizes, record 20 groups of temperature and pressure values of the gas storage chamber 21, and substitute the 20 groups of temperature and pressure data into formula (3) respectively to obtain the corresponding gas molar density (The superscript 1 indicates that the pressure sensor one 6 is used, and the subscript ref corresponds to the gas storage chamber 21).

[0066] Open the pneumatic valve three 8. The hydrogen in the gas storage chamber 21 enters the first cylinder 2. Wait for 10 minutes. After the system stabilizes, close the pneumatic valve three 8. Wait for the system to stabilize again, record 20 groups of temperature and pressure values of the system composed of the gas storage chamber 21 and the first cylinder 2, and substitute the 20 groups of temperature and pressure data into formula (3) respectively to obtain the corresponding gas molar density (The superscript 1 indicates that the pressure sensor one 6 is used, and the subscript ref&gb1 corresponds to the system composed of the gas storage chamber 21 and the first cylinder 2). According to the law of conservation of mass, the equilibrium equation is obtained Open the pneumatic valve three 8 and the pneumatic valve two 7. The hydrogen in the system enters the second cylinder 3. Wait for 10 minutes. After the system stabilizes, close the pneumatic valve three 8 and the pneumatic valve two 7. Wait for the system to stabilize again, record 20 groups of temperature and pressure values of the system composed of the gas storage chamber 21, the first cylinder 2 and the second cylinder 3, and substitute the 20 groups of temperature and pressure data into formula (3) respectively to obtain the corresponding gas molar density (The superscript 2 indicates the use of pressure sensor 4, and the subscripts ref&gb1&gb2 correspond to the system composed of the gas storage chamber 21, cylinder 1 2, and cylinder 2 3).

[0067] According to the law of conservation of mass, the equilibrium equation is obtained Open pneumatic valve 5 17 and pneumatic valve 6 16 to perform rapid vacuum pumping for 10 minutes, and then close pneumatic valve 5 17 and pneumatic valve 6 16.

[0068] Open pneumatic valve 2 7, and the hydrogen in cylinder 2 3 enters the gas storage chamber 21. Wait for 10 minutes. After the system stabilizes, close pneumatic valve 2 7. After the system stabilizes again, record 20 sets of temperature and pressure values of the system composed of cylinder 2 3 and the gas storage chamber 21. Substitute the 20 sets of temperature and pressure data into formula (3) respectively to obtain the corresponding gas molar density (The superscript 2 indicates the use of pressure sensor 4, and the subscripts gb2&ref correspond to the system composed of cylinder 2 3 and the gas storage chamber 21).

[0069] According to the law of conservation of mass, the equilibrium equation is obtained Combine formulas (4), (5), and (6) and organize to get:

[0070]

[0071] Extract the determinant of the system of equations (7)

[0072]

[0073] The system of equations (7) is a homogeneous system of three equations with three unknowns, and there must be an analytical solution. If the determinant (8) is not equal to 0, the system of equations has only the 0 solution, and this solution has no practical guiding significance. Only when the determinant is equal to 0, the system of equations has infinitely many solutions, and there may be a practical solution. However, for the actual situation, both the sensor and the system have certain deviations, and the determinant is basically impossible to be equal to 0. The MATLAB simulation experimental data proves that the determinant (8) cannot be equal to 0, so there is no available analytical solution.

[0074] Since there is no available analytical solution, the present invention proposes a method for obtaining an approximate solution by using a weighted quadratic objective function based on the least squares method. Square and weight the left side terms of the system of equations (7) and then sum them to obtain an approximate solution. After squaring, the right side terms should also be approximately 0, so f(V) min The function should be 0+.

[0075]

[0076] Where ω i(i = 1, 2, 3) is the weight coefficient, with a default value of 1. The operator can select according to requirements. Containers with high volumetric accuracy correspond to large weight values, and vice versa.

[0077] Finally, define the volume V of the gas storage chamber 21 ref , the volume V of cylinder 1 2 gb1 and the volume V of cylinder 2 3 gb2 constraint ranges, and use LabVIEW to call a self-developed program based on the least squares method in the laboratory to solve the weighted quadratic objective function of linear constraints, and automatically solve the volume V of the gas storage chamber 21 that makes the function f(V) min minimum ref , the volume V of cylinder 1 2 gb1 and the volume V of cylinder 2 3 gb2 three volume calibration values, take the median of 20 groups of volume data and output the median result of the calibrated volume.

[0078] Open pneumatic valve 2 7 and pneumatic valve 3 8, then open pneumatic valve 5 17 and pneumatic valve 6 16 to evacuate the system to near atmospheric pressure, and then close pneumatic valve 2 7, pneumatic valve 3 8, pneumatic valve 5 17 and pneumatic valve 6 16 to end the volume calibration of mode 1 in the first stage.

[0079] Stage 1, mode 2: includes the following steps

[0080] Select hydrogen as the calibration gas.

[0081] Conduct a leak rate test to ensure that the hydrogen leak rate of the entire volume system < 10 -9 g / s.

[0082] Measure the temperature of the gas storage chamber 21 through temperature sensor 1 15; measure the system pressure through pressure sensor 1 6, and measure the system pressure of the system with cylinder 2 3 through pressure sensor 2 4.

[0083] First, open pneumatic valve 2 7, pneumatic valve 3 8, pneumatic valve 5 17 and pneumatic valve 6 16 to continuously and rapidly evacuate the entire connected container system for 30 minutes, and then close all valves.

[0084] Manually open ball valve 11 to prepare for hydrogen input.

[0085] Open the pneumatic valve three 8 and the pneumatic valve one 10 in sequence, and fill the system composed of the gas storage chamber 21 and the first cylinder 2 with hydrogen at a certain pressure (the pressure is 9.5 MPa. For the test accuracy, make the pressure as close as possible to the maximum range of the first pressure sensor 6). Close the pneumatic valve one 10 and wait for 10 minutes. After the system is stable, close the pneumatic valve three 8. After the system is stable again, record 20 groups of temperature and pressure values of the system composed of the gas storage chamber 21 and the first cylinder 2, and substitute the 20 groups of temperature and pressure data into formula (3) respectively to obtain the corresponding gas molar density of the first cylinder 2 (The superscript 1 indicates that the first pressure sensor 6 is used, and the subscript gb1 corresponds to the first cylinder 2).

[0086] Open the pneumatic valve five 17 to slowly evacuate the air until the system pressure drops to <0.32 MPa, open the pneumatic valve six 16 to quickly evacuate the air for 10 minutes, and then close the pneumatic valve five 17 and the pneumatic valve six 16

[0087] Open the pneumatic valve three 8, and the hydrogen in the first cylinder 2 enters the gas storage chamber 21. Wait for 10 minutes. After the system is stable, close the pneumatic valve three 8. After the system is stable again, record 20 groups of temperature and pressure values of the system composed of the first cylinder 2 and the gas storage chamber 21, and substitute the 20 groups of temperature and pressure data into formula (3) respectively to obtain the gas molar density of the system composed of the first cylinder 2 and the gas storage chamber 21 (The superscript 1 indicates that the first pressure sensor 6 is used, and the subscript gb1&ref corresponds to the system composed of the first cylinder 2 and the gas storage chamber 21).

[0088] According to the law of conservation of mass, the equilibrium equation is obtained For this embodiment, open the pneumatic valve three 8 and the pneumatic valve five 17, and evacuate the system composed of the first cylinder 2 and the gas storage chamber 21 to 4 MPa, and then close the pneumatic valve five 17. (Before opening the pneumatic valve two 7, the program will automatically determine that if opening the pneumatic valve two 7 will cause the system pressure to exceed the maximum range of the second pressure sensor 4, then open the pneumatic valve five 17 to first perform a slow evacuation process on the system).

[0089] Open the pneumatic valve two 7, and hydrogen enters the second cylinder 3. After the system is stable, close the pneumatic valve three 8 in sequence, open the pneumatic valve one 10 to fill hydrogen until the second pressure sensor 4 shows a pressure of 0.45 MPa, and then close the pneumatic valve one 10

[0090] After the system is stable, close the pneumatic valve two 7 and wait for 10 minutes. After the system is stable again, record 20 groups of temperature and pressure values of the second cylinder 3, and substitute the 20 groups of temperature and pressure data into formula (3) respectively to obtain the corresponding gas molar density of the second cylinder 3 (The superscript 2 indicates that the second pressure sensor 4 is used, and the subscript gb2 corresponds to the second cylinder 3).

[0091] Open pneumatic valve five 17 to conduct slow vacuum pumping until the pressure in the gas storage chamber 21 drops to <0.32 MPa. Open pneumatic valve six 16 to conduct rapid vacuum pumping for 10 minutes, and then close pneumatic valve five 17 and pneumatic valve six 16.

[0092] Open pneumatic valve two 7, and hydrogen in cylinder two 3 enters the gas storage chamber 21. Wait for 10 minutes. After the system stabilizes, close pneumatic valve two 7. After the system stabilizes again, record the temperature and pressure values of the system composed of cylinder two 3 and the gas storage chamber 21 for 20 groups. Substitute the 20 groups of temperature and pressure data into formula (3) respectively to obtain the corresponding gas molar density (The superscript 2 indicates that pressure sensor two 4 is used, and the subscript gb2&ref corresponds to the system composed of cylinder two 3 and the gas storage chamber 21).

[0093] According to the law of conservation of mass, the equilibrium equation is obtained Open pneumatic valve three 8 and pneumatic valve five 17 in sequence to conduct slow vacuum pumping until the system pressure drops to <0.32 MPa. Open pneumatic valve six 16 to conduct rapid vacuum pumping for 10 minutes, and then close pneumatic valve five 17 and pneumatic valve six 16.

[0094] Close pneumatic valve three 8, open pneumatic valve two 7. After the system stabilizes, open pneumatic valve one 10 to fill hydrogen into the system until the pressure sensor two 4 shows a pressure of 0.45 MPa, and then close pneumatic valve one 10. Wait for 10 minutes, close pneumatic valve two 7. After the system stabilizes again, record the temperature and pressure values of the system composed of cylinder two 3 and the gas storage chamber 21 for 20 groups. Substitute the temperature and pressure data into formula (3) respectively to obtain the corresponding gas molar density (The superscript 2 indicates that pressure sensor two 4 is used, and the subscript gb2&ref corresponds to the system composed of cylinder two 3 and the gas storage chamber 21).

[0095] Open pneumatic valve two 7 and pneumatic valve three 8. Hydrogen in the system composed of cylinder two 3 and the gas storage chamber 21 enters cylinder one 2. Wait for 10 minutes, close pneumatic valve three 8. After the system stabilizes, then close pneumatic valve two 7. After the system stabilizes again, record the temperature and pressure values of the system composed of cylinder two 3, the gas storage chamber 21 and cylinder one 2 for 20 groups. Substitute the temperature and pressure data into formula (3) respectively to obtain the corresponding gas molar density (The superscript 2 indicates that pressure sensor two 4 is used, and the subscript gb2&ref&gb1 corresponds to the system composed of cylinder two 3, the gas storage chamber 21 and cylinder one 2).

[0096] According to the law of conservation of mass, the following equilibrium equation is obtained

[0097]

[0098] Simultaneously solve formulas (10), (11) and (12) and organize to get:

[0099]

[0100] The system of equations (13) is a homogeneous system of three equations with three unknowns, and there must be an analytical solution. For the actual situation, both the sensor and the system have certain deviations. Similarly, it is almost impossible for its determinant to be equal to 0. The MATLAB simulation experimental data also proves that its determinant cannot be equal to 0, so there is no analytical solution with practical guiding significance.

[0101] Since there is no available analytical solution, the present invention proposes a method for obtaining an approximate solution. The left - hand terms of the system of equations (13) are weighted and squared and then added together to obtain an approximate solution. After squaring, the right - hand terms should also be approximated to 0, so the function f(V) min should be 0 +.

[0102]

[0103] where ω i (i = 1, 2, 3) are weight coefficients, with a default value of 1. The operator can select according to requirements. Containers with high volume accuracy requirements correspond to large weight values, and vice versa.

[0104] Finally, define the constraint ranges of the volume V ref of the gas storage chamber 21, the volume V gb1 of the first cylinder 2, and the volume V gb2 of the second cylinder 3. And use LabVIEW to call a self - made program based on the least - squares method to solve the weighted quadratic objective function of the linear constraint, and automatically solve the volume V min of the gas storage chamber 21, the volume V ref of the first cylinder 2, and the volume V gb1 of the second cylinder 3 that minimize the function f(V) within the constraint range. Take the median of 20 groups of volume data and output the median result of the calibrated volume. gb2 Open the second pneumatic valve 7, the third pneumatic valve 8, and the fifth pneumatic valve 17 to slowly evacuate until the system pressure drops to <0.32 MPa. Open the sixth pneumatic valve 16 to quickly evacuate until the system pressure is near one atmosphere. Then close the second pneumatic valve 7, the third pneumatic valve 8, the fifth pneumatic valve 17, and the sixth pneumatic valve 16 to end the volume calibration of the first - stage mode two.

[0105] Open the second pneumatic valve 7, the third pneumatic valve 8, and the fifth pneumatic valve 17 to slowly evacuate until the system pressure drops to <0.32 MPa. Open the sixth pneumatic valve 16 to quickly evacuate until the system pressure is near one atmosphere. Close the second pneumatic valve 7, the third pneumatic valve 8, the fifth pneumatic valve 17, and the sixth pneumatic valve 16 to end the volume calibration of the first - stage mode two.

[0106] As Figure 2As shown, the specific process of this one-stage calibration method includes that there are two calibration modes available in this stage. The calibration procedure of Mode 1 includes: First, a certain amount of hydrogen is filled into the gas storage chamber 21. After the air pressure stabilizes, 20 groups of temperature and pressure values of the gas storage chamber 21 are recorded, and the corresponding values are substituted into formula (3) to obtain the molar density of the gas storage chamber 21. Then, the hydrogen in the gas storage chamber 21 flows into the first steel cylinder 2. After the system stabilizes, 20 groups of temperature and pressure values of the system composed of the gas storage chamber 21 and the first steel cylinder 2 are recorded, and they are substituted into formula (3) to obtain the molar density of the system composed of the gas storage chamber 21 and the first steel cylinder 2. According to the law of conservation of mass, the equilibrium equation formula (4) is obtained. Then, the hydrogen in the system composed of the gas storage chamber 21 and the first steel cylinder 2 flows into the second steel cylinder 3. After the system stabilizes, 20 groups of temperature and pressure values of the system composed of the gas storage chamber 21, the first steel cylinder 2, and the second steel cylinder 3 are recorded, and they are substituted into formula (3) to obtain the molar density of the system composed of the gas storage chamber 21, the first steel cylinder 2, and the second steel cylinder 3. According to the law of conservation of mass, the equilibrium equation formula (5) is obtained. Finally, the gas storage chamber 21 is evacuated, and the hydrogen in the second steel cylinder 3 flows into the gas storage chamber 21. After the system stabilizes, 20 groups of temperature and pressure values of the system composed of the second steel cylinder 3 and the gas storage chamber 21 are recorded, and they are substituted into formula (3) to obtain the molar density of the system composed of the second steel cylinder 3 and the gas storage chamber 21. According to the law of conservation of mass, the equilibrium equation formula (6) is obtained. Equations (4), (5), and (6) form a system of equations (7). This system of equations has no available solutions. Another function is constructed, and a self-made program based on the least squares method is called by LabVIEW to solve the quadratic objective function with linear constraints, and the optimal solution within the constraint range is automatically solved. The volume data is output. Finally, the system is evacuated to atmospheric pressure to protect the equipment, and the calibration of Mode 1 ends. The calibration process of Mode 2 includes: First, a certain amount of hydrogen is filled into the gas storage chamber 21 and the first steel cylinder 2. After the system stabilizes, 20 groups of temperature and pressure values of the system composed of the gas storage chamber 21 and the first steel cylinder 2 are recorded, and the corresponding values are substituted into formula (3) to obtain the molar density of the first steel cylinder 2. Then, the gas storage chamber 21 is evacuated. Subsequently, the hydrogen in the first steel cylinder 2 flows into the gas storage chamber 21. After the system stabilizes, 20 groups of temperature and pressure values of the system composed of the first steel cylinder 2 and the gas storage chamber 21 are recorded, and they are substituted into formula (3) to obtain the molar density of the system composed of the first steel cylinder 2 and the gas storage chamber 21. According to the law of conservation of mass, the equilibrium equation formula (10) is obtained. Then, hydrogen is allowed to flow into the second steel cylinder 3, and a certain amount of hydrogen is additionally filled into the second steel cylinder 3. After the system stabilizes, 20 groups of temperature and pressure values of the system are recorded, and they are substituted into formula (3) to obtain the molar density of the second steel cylinder 3. After that, the gas storage chamber 21 is evacuated. Then, the hydrogen in the second steel cylinder 3 flows into the gas storage chamber 21. After the system stabilizes, 20 groups of temperature and pressure values of the system composed of the second steel cylinder 3 and the gas storage chamber 21 are recorded, and they are substituted into formula (3) to obtain the molar density of the system composed of the second steel cylinder 3 and the gas storage chamber 21. According to the law of conservation of mass, the equilibrium equation formula (11) is obtained.Evacuate cylinder 1 - 2, then fill cylinder 2 - 3 and the gas storage chamber 21 with a certain amount of hydrogen. After the system stabilizes, record 20 sets of temperature and pressure values of the system composed of cylinder 2 - 3 and the gas storage chamber 21. Substitute them into formula (3) to obtain the molar density of the system composed of cylinder 2 - 3 and the gas storage chamber 21. Finally, let the hydrogen in cylinder 2 - 3 and the gas storage chamber 21 flow into cylinder 1 - 2. After the system stabilizes, record 20 sets of temperature and pressure values of the system composed of cylinder 2 - 3, the gas storage chamber 21 and cylinder 1 - 2. Substitute them into formula (3) to obtain the molar density of the system composed of cylinder 2 - 3, the gas storage chamber 21 and cylinder 1 - 2. According to the law of conservation of mass, obtain the equilibrium equation formula (12). Equations (10), (11) and (12) construct the equation set (13). This equation set has no available solution. Another function is constructed, and LabVIEW is used to call the self - developed program based on the least - squares method in the laboratory to solve the quadratic objective function with linear constraints, and automatically solve the optimal solution within the constraint range. Output the volume data. Finally, evacuate the system to atmospheric pressure to protect the equipment, and the calibration of mode two ends.

[0107] Stage two: includes the following steps

[0108] Obtain the volume calibration value V of the gas storage chamber 21 calibrated in stage one rev , and the volume calibration in the second stage can be carried out only under the conditions of completing the first - stage calibration.

[0109] Select the type of calibration gas to be the same as that in stage one. In this embodiment, small - molecule hydrogen is selected as the calibration gas.

[0110] Conduct a leak rate test to ensure that the hydrogen leak rate of the entire cavity system < 10 -9 g / s.

[0111] Measure the temperature of the gas storage chamber 21 through temperature sensor 1 - 15, the temperature of the pipeline 22 through temperature sensor 2 - 1, and the temperature of the sample chamber 14 through temperature sensor 3 - 20; measure the system pressure through pressure sensor 1 - 6.

[0112] First, open pneumatic valve 4 - 9, pneumatic valve 5 - 17 and pneumatic valve 6 - 16 to continuously and rapidly evacuate the entire connected container system for 30 minutes, and then close all valves.

[0113] Open pneumatic valve 1 - 10 to fill the gas storage chamber 21 with hydrogen at a certain pressure (the pressure is 9.5 MPa. For test accuracy, make the pressure as close as possible to the maximum range of pressure sensor 1 - 6). Close pneumatic valve 1 - 10 and wait for 10 minutes. After the system stabilizes, record 20 sets of temperature and pressure values of the gas storage chamber 21. Substitute the 20 sets of temperature and pressure data into formula (3) respectively to obtain the corresponding gas molar density of the gas storage chamber 21 (The superscript 1 indicates that pressure sensor 1 - 6 is used; the subscript V cref corresponds to the gas storage chamber 21; Tcref The temperature indicated is the temperature of the gas storage chamber 21 before the pneumatic valve 29 is opened and the hydrogen has not yet flowed into the sample chamber 14).

[0114] Open the pneumatic valve 29, and the hydrogen in the gas storage chamber 21 flows into the pipeline 22 and the sample chamber 14. Wait for 10 minutes until the system is stable, then close the pneumatic valve 29. Wait until the system is stable again, and record 20 sets of temperature and pressure values ​​of the gas storage chamber 21, pipeline 22 and sample chamber 14. Substitute the 20 sets of temperature and pressure data into formula (3) to obtain the corresponding gas molar density:

[0115] and (The superscript 1 indicates that a pressure sensor 6 is used, and the subscript V oref 、V otube and V osc Corresponding to the gas storage chamber 21, the pipeline 22 and the sample chamber 14; T oref , T otube and T osc respectively represent the temperatures of the gas storage chamber 21, pipeline 22 and sample chamber 14 when the pneumatic valve 29 is opened).

[0116] According to the law of conservation of mass, the equilibrium equation is

[0117] Open the pneumatic valve 9, turn on the heating furnace 19, and raise the temperature to 400°C (considering the influence of the temperature gradient, the temperature frequently used is the best according to the actual test situation. The present invention selects the middle temperature of the heating furnace 19 to be 400°C.)

[0118] After 30 minutes of constant temperature at 400°C, the system is stabilized and the pneumatic valve 9 is closed. After the system is stabilized again, 20 sets of temperature and pressure values ​​of the gas storage chamber 21, pipeline 22 and sample chamber 14 are recorded. The 20 sets of temperature and pressure data are respectively substituted into formula (3) to obtain the corresponding gas molar density: and (The superscript 1 indicates that a pressure sensor 6 is used, and the subscript V sref 、V stube and V ssc Corresponding to the gas storage chamber 21, the pipeline 22 and the sample chamber 14 respectively; T sref , T stube and T ssc respectively correspond to the temperatures of the gas storage chamber 21, pipeline 22 and sample chamber 14 after the temperature is increased).

[0119] According to the law of conservation of mass, the equilibrium equation is

[0120] Combining formulas (15) and (16) and sorting them out, we get:

[0121]

[0122] Among which V ref has been calibrated and obtained in the first stage, then the system of equations (17) is reduced to a system of binary linear equations, and the solve function of MATLAB is called by LabVIEW to solve it, and the calibration values of pipeline 22V tube and sample chamber 14V sc can be obtained. Take the median of 20 groups of volume data and output the median result of the calibrated volume.

[0123] Close the heating furnace 19, open pneumatic valve four 9 and pneumatic valve five 17 to slowly evacuate until the system pressure drops to <0.32 MPa, open pneumatic valve six 16 to quickly evacuate until the system pressure is near one atmosphere, and then close pneumatic valve four 9, pneumatic valve five 17 and pneumatic valve six 16 to end the second-stage volume calibration.

[0124] As Figure 3 shown, the specific process of this second-stage calibration method includes first evacuating the connected system, then filling a certain amount of hydrogen into the gas storage chamber 21. After the system stabilizes, record the temperature and pressure values of 20 groups of the gas storage chamber 21, and substitute the corresponding values into formula (3) to obtain the molar density of the gas storage chamber 21. Let the hydrogen in the gas storage chamber 21 flow into the sample chamber 14 through pipeline 22. After the system stabilizes, record the temperature and pressure values of 20 groups of the gas storage chamber 21, pipeline 22 and sample chamber 14 respectively, and substitute the corresponding values into formula (3) to obtain the molar density of the gas storage chamber 21, pipeline 22 and sample chamber 14 respectively. According to the law of conservation of mass, the equilibrium equation formula (15) is obtained. Then heat up the sample chamber 14 until the temperature rises to the preset temperature value. After the system stabilizes, record the temperature and pressure values of 20 groups of the gas storage chamber 21, pipeline 22 and sample chamber 14 respectively, and substitute the corresponding values into formula (3) to obtain the molar density of the gas storage chamber 21, pipeline 22 and sample chamber 14 respectively, and then close the heating furnace 19. According to the law of conservation of mass, the equilibrium equation formula (16) is obtained. Equations (15) and (16) are constructed into a system of equations formula (17). This system of equations is a system of binary linear equations with two volume unknowns and two equations. Use the solve function of MATLAB to solve it, and then output the volume data. Evacuate the system to atmospheric pressure to protect the equipment, and the second-stage calibration ends.

[0125] As Figure 4As shown, the overall process of this calibration method specifically includes: First, select the calibration gas (taking hydrogen as an example for the description of the embodiment), and then enter the first stage of calibration. Before calibration, first perform a leak rate test. After the leak rate test is completed, evacuate the system. The above steps ensure the smooth progress of the calibration procedure. To facilitate the rapid and accurate calibration of the volume, first define the volume constraint range of the container to be calibrated, and this constraint range is obtained by simple estimation. Next, select the calibration mode for the first stage, which can be selected according to the operator's needs, and the default is the hydrogen-saving mode. The three volume calibration values obtained from the first stage of calibration, the volume V of the gas storage chamber 21 ref , the volume V of cylinder 1 2 gb1 , and the volume V of cylinder 2 3 gb2 are output to the second stage of calibration. After the first stage ends, enter the second stage of calibration. After all volume calibrations are completed, output and store the volume data.

[0126] The specific process of this calibration method, the acquisition, processing, display, and storage of data are automatically realized through a program based on LabVIEW. This calibration program includes multiple modules: pneumatic valve on / off control and sensor data acquisition, experimental parameter configuration, leak rate test, temperature control program, temperature and pressure curve display, MATLAB function call, and display and storage of experimental data tables. Through the pneumatic valve on / off control and sensor data acquisition module, the current on / off status of each pneumatic valve can be observed in real time, and the real-time values of the pressure and temperature detected by the sensors can be viewed. Through the experimental parameter configuration module, the user can complete the setting of all volume calibration parameters. The parameter configuration includes: 1. The volume constraint range of the container to be calibrated. Configuring the constraint range facilitates the rapid solution of the function; 2. The range of the pressure sensor. The configuration of the sensor range and the container volume range allows the computer to calculate the appropriate amount of hydrogen charging and discharging gas, eliminating the need for manual control of the valves and realizing the full automation of calibration; 3. The setting of the equilibrium waiting time, which is the time to wait for the pressure to stabilize after each gas flow; 4. The setting of the number of records of temperature and pressure data, with the default setting being 20 times. The higher the number of times, the smaller the deviation and the better the stability; 5. The setting of the evacuation time. The longer the time, the more thorough the evacuation and the more accurate the calibration result; 6. The setting of the storage path for the calibration data results, which is used to store the data during the calibration process. The data is continuously updated and stored as the calibration progresses, avoiding the loss of calibration data caused by unpredictable power outages during the process.

[0127] For the above method, as Figure 1 shown, the present invention discloses an on-line precise calibration device for container volume (fully automatic hydrogen storage material testing equipment), including:

[0128] A gas cylinder 13, the output end of the gas cylinder 13 is connected with a ball valve 11, the output end of the ball valve 11 is connected with a gas storage chamber 21 through a pneumatic valve 10, and the gas storage chamber 21 is provided with a first pressure sensor 6 and a first temperature sensor 15;

[0129] A vacuum pump 18, the vacuum pump 18 is connected with the gas storage chamber 21 through a fifth pneumatic valve 17 and is connected with the gas storage chamber 21 through a sixth pneumatic valve 16;

[0130] A pipeline 22, the pipeline 22 is connected with a sample chamber 14 through a fourth pneumatic valve 9, the sample chamber 14 is provided with a heating furnace 19, and the heating furnace 19 is provided with a third temperature sensor 20; a second temperature sensor 1 is arranged on the pipeline 22;

[0131] A first steel cylinder 2, the first steel cylinder 2 is connected with the gas storage chamber 21 through a third pneumatic valve 8;

[0132] A second steel cylinder 3, the second steel cylinder 3 is connected with the gas storage chamber 21 through a second pneumatic valve 7, and the second steel cylinder 3 is provided with a second pressure sensor 4;

[0133] A computer 5, the computer 5 is used for collecting data of the first pressure sensor 6, the first temperature sensor 15, the second pressure sensor 4, the second temperature sensor 1 and the third temperature sensor 20, and controlling the opening and closing of the pneumatic valves according to the data.

[0134] The pneumatic valve 1 (10), pneumatic valve 2 (7), pneumatic valve 3 (8), pneumatic valve 4 (9), pneumatic valve 5 (17), and pneumatic valve 6 (16) are all normally closed types and are driven by compressed air. When the computer 5 sends a signal command, compressed air will be introduced into the inlet of the pneumatic valve cylinder to open the valve, and the valve will close when the compressed air is exhausted. The pressure range of the compressed air is 0.3 - 0.8 MPa. The pneumatic valve 1 (10) is used for the controllable charging of hydrogen in the hydrogen storage test equipment; the pneumatic valve 2 (7) is used to open during hydrogen release for using cylinder 2 (3) and pressure sensor 2 (4); the pneumatic valve 3 (8) is used to facilitate the use of cylinder 1 (2) during hydrogen absorption and release tests; the pneumatic valve 4 (9) is used for the closing and opening operations during the hydrogen absorption and release process to control the reaction of the gas with the sample; the pneumatic valve 5 (17) is used for the slow and controllable extraction of hydrogen in the test device. The slow extraction is to avoid damaging the vacuum pump 18 by high-pressure gas and is used when the hydrogen pressure in the system ≥ 0.32 MPa; the pneumatic valve 6 (16) is used for the fast and controllable extraction of hydrogen in the test device. The fast extraction can shorten the vacuum pumping time and improve the test efficiency and is used when the hydrogen pressure in the system < 0.40 MPa. The ball valve 11 is used for manual control of gas input to further improve the safety of the system. The sample chamber 14 is in the constant temperature environment of the heating furnace 19, and the constant temperature range of the heating furnace 19 is 0 - 800 °C. The other parts are in the room temperature environment. The computer 5 is used for sensor data acquisition, data processing, and logical on-off control of the valves. The volume formed by the pipelines between the pneumatic valve 1 (10), pneumatic valve 2 (7), pneumatic valve 3 (8), pneumatic valve 4 (9), pneumatic valve 5 (17), pneumatic valve 6 (16), and pressure sensor 1 (6) is V rev , which is called the volume of the gas storage chamber 21 ( Figure 1 the volume included in the right dotted line box). The volume formed by the pipeline between the pneumatic valve 4 (9) and the quick connector 12 is V tube , which is called the volume of the pipeline 22 ( Figure 1 the volume included in the left dotted line box). A pressure sensor 1 (6) and a temperature sensor 1 (15) are installed on the gas storage chamber 21, and a pressure sensor 2 (4) is installed on the cylinder 2 (3). The temperature sensor 2 (1) is installed on the pipeline 22 between the pneumatic valve 4 (9) and the quick connector 12. A temperature sensor 3 (20) is installed at the bottom of the sample chamber 14. Among them, the temperature measurement ranges of the temperature sensor 1 (15) and the temperature sensor 2 (1) are 0 - 50 °C, and the temperature measurement range of the temperature sensor 3 (20) is 0 - 600 °C. The pressure measurement range of the pressure sensor 1 (6) is 0 - 10 MPa, the pressure measurement range of the pressure sensor 2 (4) is 0 - 0.5 MPa, and the test accuracy of the pressure sensor 1 (6) and the pressure sensor 2 (4) ≥ 0.04% FS. Using the data collected in real time by these temperature and pressure sensors, as well as the volumes of each part of the cavity, based on the real gas state equation, the molar amount of gaseous hydrogen in each part can be calculated in real time, and then the molar amount of hydrogen absorption and release of the material can be calculated.

[0135] Specifically, the full-automatic hydrogen storage material test equipment has passed the leak rate detection, and its structural distribution is as Figure 1As shown, the specific components used are as described above. Using the previous volume calibration technology, it can be known that the volume V of the gas storage chamber 21 ref is about 12 ml, the pipeline 22 is V tube is about 8 ml, the sample chamber 14 V sc is about 3 ml, the cylinder 1 2V gb1 is about 100 ml (the specification of cylinder 1 is 100 ml, with a deviation of ±5%), and the cylinder 2 3V gb2 is about 1000 ml (the specification of cylinder 2 is 1000 ml, with a deviation of ±5%).

[0136] In this embodiment, calibrations of two modes are carried out respectively and corresponding evaluations are made. The calibration gas is hydrogen. According to the above estimated volume, the volume V of the gas storage chamber 21 ref , the volume V of the cylinder 1 2 gb1 and the volume V of the cylinder 2 3 gb2 are respectively (1 - 30 ml), (80 - 120 ml) and (800 - 1200 ml). In the following steps, it is necessary to wait for a certain time for the system to reach stability. In the first - stage mode one, first, the entire system is evacuated for 30 minutes; hydrogen at 9.8025 MPa is filled into the gas storage chamber 21. After the system is stable, 20 groups of data are recorded; the hydrogen in the gas storage chamber 21 is made to flow into the cylinder 1 2. After the system is stable, 20 groups of data are recorded; then the hydrogen is made to flow into the cylinder 2 3. After the system is stable, 20 groups of data are recorded; finally, the gas storage chamber 21 is evacuated; the gas in the cylinder 2 3 is made to flow into the gas storage chamber 21. After the system is stable, 20 groups of data are recorded. In the first - stage mode two, first, the entire system is evacuated for 30 minutes; hydrogen at 9.5298 MPa is filled into the cylinder 1 2. After the system is stable, 20 groups of data are recorded; the gas storage chamber 21 is evacuated to vacuum; the hydrogen in the cylinder 1 2 is made to flow into the gas storage chamber 21. After the system is stable, 20 groups of data are recorded; hydrogen at 0.4523 MPa is filled into the cylinder 2 3. After the system is stable, 20 groups of data are recorded; the gas storage chamber 21 is evacuated to vacuum; the hydrogen in the cylinder 2 3 is made to flow into the gas storage chamber 21. After the system is stable, 20 groups of data are recorded; the cylinder 1 2 is evacuated to vacuum; hydrogen at 0.4492 MPa is filled into the system composed of the cylinder 2 3 and the gas storage chamber 21. After the system is stable, 20 groups of data are recorded; the hydrogen in the system is made to flow into the cylinder 1 2. After the system is stable, 20 groups of data are recorded. In the calibration second - stage, the entire system is evacuated for 30 minutes, and hydrogen at 9.7832 MPa is filled into the gas storage chamber 21. After the system is stable, 20 groups of data are recorded; the gas in the gas storage chamber 21 is made to flow into the sample chamber 14. After the system is stable, 20 groups of data are recorded; the sample chamber 14 is heated to 400 °C. After the system is stable, 20 groups of data are recorded. When the data of both stages are collected, the program automatically processes the data, and the specific calibration results are output as shown in Table 1. The f(V) output by mode one min= 0.000732430 is larger than f(V) of Mode 2 min by nearly 28.5 percentage points. Although f(V) of Mode 1 min is larger, just based on the output f(V) min value, it cannot be used as the criterion for accuracy. Multiple tests need to be carried out for verification.

[0137] Table 1 Calibration Volume and Its Function Minimum Value

[0138]

[0139] Verification of volume accuracy: The volume values calibrated by Mode 1 and Mode 2 are respectively used to conduct air PCT tests at room temperature and 400 °C to verify the accuracy of volume calibration. The results of the two air tests are very close. Figure 5 The shown is only the air-side PCT curve using the volume calibrated by Mode 1. It can be seen that whether in the low-pressure area or in the high-pressure area, the air-side test effect is very good. The maximum deviation of the air test at room temperature is only -0.007205 wt.% at 8.992259 MPa, while the maximum deviation of the 400 °C test is only -0.005143 wt.% at 9.202071 MPa. If the hydrogen storage capacity of the test sample is greater than 1 wt.%, the deviation of the hydrogen storage capacity caused by the volume in this test is less than 0.72%. Furthermore, we use the commercially available classic alloy La 0.5 Ce 0.5 Ni 4 Co to conduct PCT and kinetic tests at test temperatures of 40 °C, 60 °C and 80 °C respectively. The test PCT and Ki results are as Figure 6 and Figure 7 shown. By comparing with the world-recognized authoritative data, it can be seen that the PCT curve results of the La 0.5 Ce 0.5 Ni 4 Co alloy tested by using the test equipment with this calibrated volume are very consistent with the internationally recognized PCT curve test results. International literature reports La 0.5 Ce 0.5 Ni 4The maximum hydrogen absorption atomic ratio H / f.u. on the PCT test curve of the Co alloy at 40 °C is 6.44, while the maximum hydrogen absorption atomic ratios H / f.u. of Mode 1 and Mode 2 of this embodiment tested under the same conditions are 6.66 and 6.56 respectively, both of which are very close to the results in the international literature. Just looking at the PCT curve, the test result of Mode 2 is closer to the international literature. However, considering the Ki curves and PCT curves at their respective temperatures comprehensively, the test result of Mode 1 is better than that of Mode 2. Through the comparative analysis with the data reported in the international literature and the comparative analysis of the Ki curves and PCT curves under the same test conditions, it can be known that the volume calibration result of this test system is accurate, the test results reflect the objective reality, and the calibration result meets the usage requirements of this type of hydrogen storage material testing equipment.

[0140] Figure 5 PCT curves of the empty side without samples at different temperatures under the calibrated volume of Mode 1.

[0141] Figure 6 La tested under the calibrated volume of Mode 1 0.5 Ce 0.5 Ni 4 PCT curves of the Co alloy at different temperatures.

[0142] Figure 7 La tested under the calibrated volume of Mode 2 0.5 Ce 0.5 Ni 4 PCT curves of the Co alloy at different temperatures.

[0143] Figure 8 La tested under the calibrated volume of Mode 1 0.5 Ce 0.5 Ni 4 Ki curves of the Co alloy at different temperatures.

[0144] Figure 9 La tested under the calibrated volume of Mode 2 0.5 Ce 0.5 Ni 4 Ki curves of the Co alloy at different temperatures.

[0145] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and deformations can be made, and these improvements and deformations should also be regarded as the protection scope of the present invention.

Claims

1. An on-line precise calibration method for the volume of a container, characterized in that, the method comprises the steps of, Calibration stage one: Collect the temperature and pressure values of the gas storage chamber, the system composed of the gas storage chamber and cylinder one, the system composed of the gas storage chamber, cylinder one and cylinder two, and the system composed of cylinder two and the gas storage chamber respectively; Calculate the molar density of the gas storage chamber, the system composed of the gas storage chamber and cylinder one, the system composed of the gas storage chamber, cylinder one and cylinder two, and the system composed of cylinder two and the gas storage chamber according to the collected temperature and pressure values; Construct a quadratic optimization function according to the molar density of each system, and optimize by the method of finding the minimum value of the quadratic objective function with linear constraints based on the least squares solution program, and solve the volume calibration values of the gas storage chamber, cylinder one and cylinder two; Calibration stage two: Collect the temperature and pressure values of the gas storage chamber, pipeline and sample chamber, and calculate the molar density of the gas storage chamber, pipeline and sample chamber; Heat the sample chamber to a preset temperature, collect the temperature and pressure values of the gas storage chamber, pipeline and sample chamber, and calculate the molar density of the gas storage chamber, pipeline and sample chamber according to the collected temperature and pressure values; Based on the reducible element equations formed by the molar density of each cavity before and after heating, call the solve function of MATLAB in LabVIEW to solve it, and obtain the volume calibration values of the pipeline and sample chamber; In the first calibration stage, the pressure value is obtained by evacuating the gas storage chamber, cylinder one and cylinder two; filling a certain amount of hydrogen into the gas storage chamber and recording the pressure value of the gas storage chamber; opening pneumatic valve three, the hydrogen in the gas storage chamber flows into cylinder one, and record the pressure value of the system composed of the gas storage chamber and cylinder one; opening pneumatic valve two, the hydrogen in the system composed of the gas storage chamber and cylinder one flows into cylinder two, and record the pressure value of the system composed of the gas storage chamber, cylinder one and cylinder two; evacuating the gas storage chamber, opening pneumatic valve two, and the hydrogen in cylinder two flows into the gas storage chamber, and record the pressure value of the system composed of the gas storage chamber and cylinder two; In the second calibration stage, the pressure values of the gas storage chamber, pipeline and sample chamber are obtained by evacuating the gas storage chamber, pipeline and sample chamber; filling a certain amount of pressured hydrogen into the gas storage chamber and recording the pressure value of the gas storage chamber; opening pneumatic valve four, the hydrogen in the gas storage chamber flows into the pipeline and sample chamber, and record the pressure value of the gas storage chamber, pipeline and sample chamber; heating the heating furnace and recording the pressure value of the gas storage chamber, pipeline and sample chamber; The temperature of the gas storage chamber, the system composed of the gas storage chamber and cylinder one, the system composed of the gas storage chamber, cylinder one and cylinder two, the system composed of cylinder two and the gas storage chamber, the pipeline and the sample chamber is collected by a temperature sensor; The gas molar density is based on the real gas state equation formula (1), specifically, the gas molar density is calculated by the Leachman state equation formula (3), and then the hydrogen molar amount of each cavity is calculated: PV = nZR T (1) Where P is the gas pressure, V is the cavity volume, n is the molar amount, Z is the gas compressibility factor, R is the gas constant, T is the absolute temperature, and formula (2) is deduced by combining the Leachman state equation, and formula (2) is used to substitute into formula (3); 2. The on-line precise calibration method for the volume of a container according to claim 1, characterized in that, the calculation method of the gas molar density includes: Substitute the temperature and pressure data corresponding to the container to be measured into formula (3) to calculate the gas molar density corresponding to the container to be measured.

3. The on-line precise calibration method for container volume according to claim 1, characterized in that The gas storage chamber V ref , the first cylinder V gb1 and the second cylinder V gb2 The calculation method of the volume calibration value includes: According to the law of conservation of mass, the equilibrium equation is obtained: Combining formulas (4), (5) and (6) and arranging them gives: Extract the determinant of the system of equations (7): Based on the method of finding the approximate solution of the weighted quadratic objective function by the least squares method, the method of squaring and weighting the left side terms of the system of equations (7) and then summing them to minimize the function to find the approximate solution. After squaring, the right side terms should also be approximately 0, so f(V) min The function should be 0 + ; where ω i is the weight coefficient, i = 1, 2, 3, with a default value of 1 and is selected according to requirements. Containers with high volume accuracy requirements correspond to large weight values, and vice versa; the weighted quadratic objective function with linear constraints is solved based on the least squares solution procedure, and the storage chamber V min that minimizes the function f(V) ref , the calibration value of the volume of cylinder 1 V gb1 and the calibration value of the volume of cylinder 2 V gb2 are obtained. corresponds to the gas molar density of the storage chamber. The superscript 1 indicates that pressure sensor 1 is used, and the subscript ref corresponds to the storage chamber. corresponds to the gas molar density of the system composed of cylinder 1 and the storage chamber. The superscript 1 indicates that pressure sensor 1 is used, and the subscript ref&gb1 corresponds to the system composed of cylinder 1 and the storage chamber. corresponds to the gas molar density of the system composed of cylinder 2 and the storage chamber. The superscript 2 indicates that pressure sensor 2 is used, and the subscript gb2&ref corresponds to the system composed of cylinder 2 and the storage chamber. corresponds to the gas molar density of the system composed of cylinder 2, the storage chamber, and cylinder 1. The superscript 2 indicates that pressure sensor 2 is used, and the subscript gb2&ref&gb1 corresponds to the system composed of cylinder 2, the storage chamber, and cylinder 1.

4. The on-line precise calibration method for container volume according to claim 1, characterized in that The pipeline V tube and the sample chamber V sc The calculation method of the volume calibration value includes: according to the law of conservation of mass, obtaining the equilibrium equation: Combining formulas (15) and (16) and arranging them gives: Among which V ref The value of has been calibrated in the first stage. Then the system of equations is reduced to a system of binary linear equations, and the solve function of MATLAB can be called by LabVIEW to solve it to obtain the volume calibration values of pipeline V tube and sample chamber V sc . represents the molar density of the gas in the gas storage chamber. The superscript 1 indicates that pressure sensor 1 is used; the subscript V cref corresponds to the gas storage chamber, T cref represents the temperature before pneumatic valve 4 is opened, which is the temperature of the gas storage chamber when hydrogen has not flowed into the sample chamber represents the gas molar density of the gas storage chamber, represents the gas molar density of the pipeline, represents the gas molar density of the sample chamber, where the superscript 1 indicates the use of pressure sensor one, and the subscript V oref 、V otube and V osc correspond to the gas storage chamber, the pipeline, and the sample chamber; T oref 、T otube and T osc respectively represent the temperatures of the air storage chamber, pipeline and sample chamber when the pneumatic valve four is opened; represents the molar density of the gas in the gas storage chamber. The superscript 1 indicates that pressure sensor 1 is used; the subscript V cref corresponds to the gas storage chamber; T cref represents the temperature before pneumatic valve 4 is opened, which is the temperature of the gas storage chamber when hydrogen has not flowed into the sample chamber represents the gas molar density of the pipeline and represents the gas molar density of the sample chamber, where the superscript 1 indicates the use of pressure sensor 1, and the subscript V sref 、V stube and V ssc correspond to the gas storage chamber, the pipeline, and the sample chamber respectively; T sref 、T stube and T ssc correspond to the temperatures of the gas storage chamber, the pipeline, and the sample chamber after heating respectively.

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