A joule-thomson effect mass flow measurement and control method

Abstract

The present application belongs to the technical field of gas flow measurement and control, and particularly relates to a novel gas mass flow measurement and control method based on the working principle of Joule-Thomson effect. The measurement method specifically comprises the following steps: throttling step: gas flows through a throttling short hole arranged in a flow channel and occurs throttling expansion, thereby generating Joule-Thomson effect; collecting step: fluid thermodynamics and fluid mechanics parameters upstream and downstream of the throttling short hole are collected in real time; and solving step: according to the collected parameters, the gas mass flow through the throttling short hole is calculated by using a gas state equation and a temperature correction model. The present application solves the high-purity requirement of the original thermal gas mass flow meter and thermal gas mass flow controller on gas, and can be used in industrial grade and food grade, thereby greatly reducing the manufacturing cost of the mass flow meter and mass flow controller based on the method of the present application, and simultaneously having outstanding service performance and long service life.

Description

Technical Field

[0001] This invention belongs to the field of gas flow measurement and control technology, specifically relating to a novel method for measuring and controlling gas mass flow based on the Joule-Thomson effect. Background Technology

[0002] In the field of gas flow meters and flow controllers, the accuracy of common traditional structures on the market is generally not high. For example, the accuracy of worm gear structures can reach ±5%, and the accuracy of Karman vortex street structures can generally be between ±3% and ±5%. Moreover, they all measure volumetric flow rate. To convert volumetric flow rate to mass flow rate, external pressure and temperature sensors must be used for cumbersome temperature and pressure compensation. Conventional turbine or Karman vortex street flow meters often contain mechanical moving parts or complex vortex generator structures, such as turbine bearings that are prone to wear and aging. When dealing with small gas flow rates, such structures will experience significant signal attenuation and a sharp increase in measurement deviation in the low-range section due to mechanical friction torque or excessively low Reynolds number. They are also highly susceptible to interference from pipeline mechanical vibration.

[0003] High-precision mass flow controllers employ thermal mass flow controllers (MFC), also known as capillary metal tube thermoelectric mass flow controllers. These controllers use gas entering a stainless steel capillary tube, and calculate the mass flow rate by sensing the temperature difference through a heating / temperature measuring coil wound around the tube. While the accuracy of such thermal mass flow controllers or thermal mass flow meters can reach ±1%, the inner diameter of the capillary metal tube is only tens of micrometers, making it difficult to manufacture. The small orifice size also makes it prone to clogging, resulting in poor serviceability. Poor serviceability refers to a device or product that is too cumbersome to maintain during daily use, has a high failure rate, is extremely difficult to clean or repair, or has overly demanding requirements for the working environment and supporting facilities.

[0004] The principle of a temperature difference-based mass flow controller is to calculate the mass flow rate based on the temperature difference, power, and specific heat capacity of the gas. Its core formula is: or , Indicates heating power. It is the mass flow rate of the gas. It is the specific heat capacity of the gas. It's the temperature difference.

[0005] Thermoelectric calculations for gas flow rates are extremely sensitive to gas purity, particularly the water vapor content, because nitrogen has a specific heat capacity of 1.04. The specific heat capacity of carbon dioxide is 0.84. The specific heat capacity of water vapor is 1.864. The purity of carbon dioxide is far greater than that of common gases, and the presence of water vapor in the gas will severely affect its accuracy. Furthermore, the heating wire is typically made of precious metals such as platinum, resulting in high costs. Therefore, its application is limited to scenarios requiring extremely high purity gas media and high environmental cleanliness (such as photovoltaics, semiconductors, and chip manufacturing). The semiconductor industry requires gas purity >99.999999%, and the photovoltaic industry requires gas purity >99.9999%. It is difficult to apply to work scenarios with lower purity requirements and harsher operating conditions, such as petroleum, chemical, welding, and cutting industries. The price of gases varies greatly depending on their purity. For example, industrial-grade 99% carbon dioxide costs only 400-700 yuan / ton, food-grade 99.9% costs 800-1200 yuan / ton, 99.9999% costs 45,000-75,000 yuan / ton, and 99.999999% is even more expensive.

[0006] Therefore, there is an urgent need for a gas mass flow controller that can use industrial-grade / food-grade gas purity to achieve precise mass flow control and accurate measurement of mass flow. Summary of the Invention

[0007] To overcome the shortcomings of the prior art, the present invention provides a method for measuring and controlling mass flow rate using the Joule-Thomson effect.

[0008] The technical solution of the present invention is as follows: the measurement method specifically includes the following steps:

[0009] 1) Throttling step: Gas flows through a flow-limiting short orifice set in the flow channel and undergoes throttling expansion, producing the Joule-Thomson effect.

[0010] 2) Data acquisition steps: Real-time acquisition of fluid thermodynamic and hydrodynamic parameters upstream and downstream of the flow-limiting short orifice.

[0011] 3) Calculation steps: Based on the collected parameters, the gas mass flow rate through the flow-limiting orifice is calculated using the gas state equation and temperature correction model.

[0012] Preferably, when the actual pressure ratio satisfies When the fluid is determined to be in a sonic choke flow state, the sonic choke flow flow rate calculation formula is executed.

[0013] When the actual pressure ratio satisfies When the fluid is determined to be in a subsonic flow state, the subsonic flow rate calculation formula is executed.

[0014] in The adiabatic index of the gas is . The absolute pressure before the flow-limiting short orifice. This refers to the absolute pressure after the flow-limiting short orifice.

[0015] Preferably, the formula for calculating the flow rate of the sonic congestion flow is as follows: ,

[0016] The formula for calculating the subsonic flow rate is as follows: ,

[0017] The above formulas for calculating the flow rate of sonic congestion flow and subsonic flow include,

[0018] For quality flow,

[0019] This serves as a comprehensive reference coefficient for the physical structure of the flow-limiting short orifice and the gas properties in the formula for calculating the flow rate of sonic congestion flow.

[0020] This serves as a comprehensive reference coefficient for the physical structure of the flow-limiting orifice and the gas properties in the subsonic flow rate calculation formula.

[0021] The absolute temperature before the flow-limiting short orifice. The absolute temperature after the flow-limiting short orifice.

[0022] Based on Temperature difference corrected flow coefficient.

[0023] Preferably, the temperature difference corrected flow coefficient Taylor expansion approximation is used;

[0024] use When performing a Taylor expansion, , For the first Temperature correction factor corresponding to the order.

[0025] The formula for calculating the flow rate of the sonic choke flow is as follows: ,

[0026] The formula for calculating the subsonic flow rate is as follows: ;

[0027] , ,

[0028] For flow coefficient, The cross-sectional area of ​​the flow-limiting short orifice is given. For gas molar mass, It is the gas compressibility factor. This is the universal gas constant.

[0029] Preferably, the temperature difference corrected flow coefficient Using a first-order Taylor expansion, the... , This is the temperature correction factor.

[0030] The formula for calculating the sonic choke flow rate is as follows: ,

[0031] The formula for calculating the subsonic flow rate is as follows:

[0032] .

[0033] Designing high-precision gas mass flow controllers and mass flow meters presents additional challenges in terms of both algorithms and hardware when the system operates in the subsonic phase.

[0034] 1. Increase in control variables: High-frequency data acquisition must be performed simultaneously. and The data from the two pressure sensors, any measurement noise or drift from either sensor will be directly added to the error in the flow calculation.

[0035] 2. Computing Power and Hysteresis: Subsonic formulas involve complex nonlinear exponential and square root operations. Performing these floating-point operations in real-time at high frequency in a microcontroller (MCU) consumes a significant number of CPU cycles. This not only lengthens the control cycle's computation time but also easily increases the hysteresis of the entire closed-loop control system, resulting in a slower dynamic response during flow regulation.

[0036] 3. Nonlinear gain: when Very close When the pressure difference and flow rate are extremely small, the effect of pressure ratio change on flow rate change in the formula becomes highly nonlinear. This means that the PID control parameters of the proportional valve are difficult to tune under low opening conditions, and flow rate oscillations are very likely to occur.

[0037] Therefore, this invention tends to use structural design methods such as increasing the gas supply pressure or reducing the flow-limiting orifice diameter to force the gas to remain in a sonic choke flow state in most of the working range, thereby completely shielding the flow. The interference greatly simplifies the algorithm and improves the response speed.

[0038] Preferably, a control switch and a control valve for the switch size are installed at the inlet of the flow channel, and the measurement method includes a zero-point zeroing method.

[0039] The zero-position reset method: the control valve is in a preset micro-opening state, and the intake pressure... Fluctuation, absolute pressure before the flow-limiting short orifice Absolute pressure after the orifice and the flow-limiting short orifice A pressure difference initially exists, and the absolute temperature before the flow-limiting short orifice... Absolute temperature after the orifice and the flow-limiting short orifice A temperature difference begins to exist, at which point the zero point returns to zero.

[0040] Preferably, a control switch and a control valve for controlling the switch size are installed at the inlet of the flow channel. The measurement method includes a maximum range correction method, wherein the control valve opening is gradually increased until the intake pressure... Absolute pressure before the flow-limiting short orifice Absolute pressure after the flow-limiting short orifice Absolute atmospheric pressure The pressure difference between them no longer changes, and the absolute temperature of the ambient atmosphere remains constant. Absolute temperature before the flow-limiting short orifice Absolute temperature after the orifice and the flow-limiting short orifice The temperature difference between the two sides no longer changes, and the flow rate is at its maximum.

[0041] Preferably, a control switch and a control valve for the switch size are installed at the inlet of the flow channel, and the measurement method includes a zero-point zeroing method and a maximum range correction method.

[0042] The zero-position reset method: the control valve is in a preset micro-opening state, and the intake pressure... Fluctuation, absolute pressure before the flow-limiting short orifice Absolute pressure after the orifice and the flow-limiting short orifice A pressure difference initially exists, and the absolute temperature before the flow-limiting short orifice... Absolute temperature after the orifice and the flow-limiting short orifice A temperature difference begins to exist, at which point the zero point returns to zero.

[0043] The maximum range correction method involves gradually increasing the opening of the control valve until the intake pressure... Absolute pressure before the flow-limiting short orifice Absolute pressure after the flow-limiting short orifice Absolute atmospheric pressure The pressure difference between them no longer changes, and the absolute temperature of the ambient atmosphere remains constant. Absolute temperature before the flow-limiting short orifice Absolute temperature after the flow-limiting short orifice The temperature difference between the two sides no longer changes, and the flow rate is at its maximum.

[0044] The system also pre-stores calibration coefficients corresponding to different deviations between the maximum range and the initial maximum range. After the zero-point reset and maximum range correction are completed, the corresponding calibration coefficient is selected based on the current deviation value to correct the mass flow rate calculation formula.

[0045] Preferably, this measurement method can also measure standard volumetric flow rate by converting mass flow rate to standard volumetric flow rate. ,in, Standard volumetric flow rate, For quality flow, This refers to the standard operating density of the gas.

[0046] To overcome the shortcomings of the prior art, this invention provides a flow control method using a Joule-Thomson effect mass flow measurement method. The technical solution of this invention is as follows: a control switch and a control valve for adjusting the switch size are installed at the inlet of the flow channel. The mass flow control method involves: first setting a target flow value, and then dynamically adjusting the opening of the control valve based on the real-time mass flow measured by the mass flow measurement method; the steps for dynamically adjusting the opening of the control valve are as follows:

[0047] 1) If the real-time flow rate is greater than the target flow rate, reduce the opening of the control valve until the real-time flow rate equals the target flow rate.

[0048] 2) If the real-time flow rate is less than the target flow rate, increase the opening of the control valve until the real-time flow rate equals the target flow rate.

[0049] When dynamically adjusting the control valve opening, adjustments are made in real time until the real-time flow rate equals the target flow rate value, at which point the control valve opening is no longer adjusted.

[0050] Based on the accurately measured real-time mass flow rate or standard volume flow rate, the system compares the real-time mass flow rate or standard volume flow rate with the set target mass flow rate or target standard volume flow rate, and adjusts the system in real time to ensure that the real-time mass flow rate or standard volume flow rate meets the set flow rate requirements.

[0051] To better control the flow rate, preferably, the control valve is a proportional control valve, such as a proportional solenoid valve. Proportional solenoid valves have near-linear flow characteristics, allowing for better flow rate adjustment by controlling the opening degree of the proportional solenoid valve. The step of dynamically adjusting the control valve opening is as follows:

[0052] 1) Real-time calculation of flow error , For target quality flow rate, This represents the current real-time quality flow rate.

[0053] 2) Obtain the current opening value of the proportional control valve. .

[0054] 3) Calculate the opening adjustment increment using a control closed-loop algorithm. ;in For adjustment coefficients, To prevent the removal of a zero constant, the increment is adjusted according to the opening degree. Update the opening degree of the proportional control valve, if If the value is positive, the valve opening will increase; if... If the value is negative, the valve opening will be reduced.

[0055] This invention addresses the high purity requirements of traditional thermal gas mass flow meters and controllers, enabling their use in industrial and food-grade applications. It significantly reduces the manufacturing cost of mass flow meters and controllers based on this invention, while also offering excellent serviceability and a long service life. Attached Figure Description

[0056] Figure 1 This invention relates to a mass flow rate measurement method.

[0057] Figure 2 This invention relates to a mass flow control method. Detailed Implementation

[0058] The embodiments of the present invention will be further described below with reference to the accompanying drawings:

[0059] Table of key symbols in the instruction manual:

[0060] symbol meaning symbol meaning mass flow adiabatic index of gas Standard volumetric flow rate Flow coefficient Target quality flow Cross-sectional area of ​​the flow-limiting short orifice Flow error gas molar mass Intake absolute pressure Gas compressibility factor Absolute pressure before the flow-limiting short orifice Universal gas constant Absolute pressure after the flow-limiting short orifice Gas standard operating condition density absolute atmospheric pressure Current opening value of proportional control valve Ambient atmospheric absolute temperature Proportional control valve opening adjustment increment Absolute temperature before the flow-limiting short orifice Adjustment coefficient Absolute temperature after the flow-limiting short orifice Preventing zero small constants Temperature difference Heating power Comprehensive reference coefficient under sonic congestion flow conditions Joule-Thomson coefficient Comprehensive reference coefficient under subsonic flow conditions Specific heat capacity of gas Corrected flow coefficient based on temperature difference Thermodynamic enthalpy No. Temperature correction factor corresponding to the order Thermodynamic entropy Temperature correction factor Specific volume of gas

[0061] like Figure 1 As shown, this embodiment provides a method for measuring mass flow rate using the Joule-Thomson effect, the method specifically including the following steps:

[0062] 1) Throttling step: Gas flows through a flow-limiting short orifice set in the flow channel and undergoes throttling expansion, producing the Joule-Thomson effect.

[0063] 2) Data acquisition steps: Real-time acquisition of fluid thermodynamic and hydrodynamic parameters upstream and downstream of the flow-limiting short orifice.

[0064] 3) Calculation steps: Based on the collected parameters, the gas mass flow rate through the flow-limiting orifice is calculated using the gas state equation and temperature correction model.

[0065] This invention innovatively employs the Joule-Thomson Effect principle, utilizing the isenthalpic process phenomenon where an actual gas undergoes a temperature change when flowing through a flow-limiting orifice under adiabatic conditions. The gas spontaneously undergoes throttling expansion as it passes through the orifice, generating a depressurization entropy-changing flow state. By acquiring the pressure and temperature differences before and after the orifice, this invention achieves accurate real-time calculation of the gas's mass flow rate.

[0066] Its flow-limiting orifice diameter is not only tens of times larger than that of the capillary of a thermal gas mass flow meter, but it is also less prone to clogging. It also does not require an active heating device and can basically ignore the purity of the gas. For example, water vapor contained in the gas can cause serious deviations in the accuracy of a thermal gas mass flow meter. This invention ensures accurate gas flow while greatly improving service performance and reducing the manufacturing cost of flow meters based on the measurement method of this invention.

[0067] The Joule-Thomson effect refers to the temperature change of a real gas under adiabatic conditions when it undergoes a pressure reduction process through a throttling valve or orifice. This is a typical isenthalpic process.

[0068] When gas passes through the flow-limiting orifice, due to the pressure difference across it... When a gas expands rapidly, the intermolecular distance increases instantaneously, producing a cooling or heating effect. A cooling effect causes the gas to cool down during expansion, while a heating effect causes it to heat up.

[0069] Cooling effect: At room temperature, the intermolecular attraction of most gases, such as nitrogen, oxygen and air, is dominant. When a gas expands, it does work to overcome the intermolecular attraction, which consumes its own kinetic energy, resulting in a decrease in static temperature.

[0070] Thermal effect: For a very small number of gases, such as hydrogen and helium, the molecular repulsion is dominant at room temperature, and the temperature will rise after throttling.

[0071] The rate of temperature change during the throttling process is determined by the Joule-Thomson coefficient. Decide:

[0072] ,in,

[0073] This is absolute temperature, measured in Kelvin (K).

[0074] Absolute pressure, measured in Pascals (Pa).

[0075] It is the thermodynamic enthalpy, and the unit is joules per kilogram (J / kg).

[0076] This is the specific volume of a gas, expressed in cubic meters (m³). 3 / kg,

[0077] This is the symbol for partial differentials.

[0078] when At that time, the gas is below the reversal temperature: depressurization Caused to cool down Air at room temperature ≈0.22~0.25K / MPa.

[0079] when At that time, the gas is above the reversal temperature: depressurization Caused to rise in temperature .

[0080] Therefore, a temperature difference is generated. The temperature difference between two temperature sensors before and after the decompression entropy change flow-limiting orifice is utilized. The mass flow rate of the gas medium passing through the flow-limiting orifice was calculated. In the Joule-Thomson effect, when gas passes through a flow-limiting orifice of fixed diameter and length, the compressibility and viscous friction of the gas dominate due to the extremely high flow velocity.

[0081] This invention is the first to utilize the Joule-Thomson effect, where a temperature difference is automatically generated when gas passes through a flow-limiting short orifice, eliminating the need for active heating found in commercially available thermal gas mass flow meters, as well as the requirement for high gas purity.

[0082] As gas passes through the flow-limiting orifice, the absolute pressure in front of the orifice increases. As the flow rate increases, the velocity at the outlet of the flow-limiting orifice will reach the speed of sound. The absolute pressure downstream of the flow-limiting orifice at this point... If the flow rate continues to decrease or fluctuate, it will not be able to affect the upstream flow, and the flow will be "blocked". This situation is called sonic blockage flow state, and the opposite is subsonic flow state.

[0083] To enable the flow measurement method of the present invention to adapt to two situations, preferably, when the actual pressure ratio satisfies When the fluid is determined to be in a sonic choke flow state, the sonic choke flow flow calculation formula is executed.

[0084] When the actual pressure ratio satisfies When the fluid is determined to be in a subsonic flow state, the subsonic flow rate calculation formula is executed.

[0085] in The adiabatic index of the gas is . The absolute pressure before the flow-limiting short orifice. This refers to the absolute pressure after the flow-limiting short orifice.

[0086] To accurately calculate the mass flow rate, preferably, the formula for calculating the sonic chokeflow flow rate is as follows: .

[0087] The formula for calculating the subsonic flow rate is as follows: .

[0088] The above formulas for calculating the flow rate of sonic congestion flow and subsonic flow include,

[0089] For quality flow,

[0090] This serves as a comprehensive reference coefficient for the physical structure of the flow-limiting short orifice and the gas properties in the formula for calculating the flow rate of sonic congestion flow.

[0091] This serves as a comprehensive reference coefficient for the physical structure of the flow-limiting orifice and the gas properties in the subsonic flow rate calculation formula.

[0092] The absolute temperature before the flow-limiting short orifice. The absolute temperature after the flow-limiting short orifice.

[0093] Based on Temperature difference corrected flow coefficient.

[0094] The and We recommend using the following method to determine or set:

[0095] In practical industrial applications and embedded computation, the comprehensive benchmark coefficient and The theoretical value is determined by the geometric cross-sectional area of ​​the flow-limiting orifice. Molar mass of gases Insulation index Universal gas constant and compression factor This was decided jointly. However, due to the presence of micron-level tolerances in machining, flow resistance from the roughness of the hole wall edges, and the inherent zero drift of the sensor channel, the aforementioned... and The preferred method for determination is "theoretical preliminary test combined with multi-point least squares experimental calibration".

[0096] The specific recommended solutions are as follows:

[0097] First, based on the nominal cross-sectional area of ​​the flow-limiting orifice... Combined with the physical properties of the gas medium through which it flows, such as air at normal temperature and pressure A molar mass of 1.40 is recommended. Using 28.97 g / mol, the universal gas constant We used 8.314 J / (mol·K) and substituted the initially estimated empirical flow coefficient. , The recommended value range is between 0.85 and 0.98, calculated as follows: and The theoretical initial value, , ,in, For flow coefficient, The cross-sectional area of ​​the flow-limiting short orifice is given. For gas molar mass, It is the gas compressibility factor. This is the universal gas constant.

[0098] Secondly, in order to eliminate the overall manufacturing tolerances of the system and obtain extremely high measurement accuracy, this embodiment recommends placing the initially estimated flow meter in a high-precision sonic nozzle standard device or a high-precision weighing standard gas flow source for multi-point linkage calibration: during system initialization, N sets of preset standard stepped mass flow rates, N ≥ 3, are introduced, and the controller synchronously records the corresponding absolute pressure before the orifice. Absolute pressure after the hole and absolute temperature in front of the hole Absolute temperature after the hole For sonic congestion flow conditions, multiple sets of collected data are substituted into the linear mapping formula, and the least squares method is used to minimize the sum of squared residuals, thereby inversely calculating the most realistic comprehensive benchmark coefficient under the current hardware. The solidified calibration value; similarly, under the subsonic operating condition calibration point, the comprehensive reference coefficient is calculated by inversion. The curing calibration value. Determined by this calibration method. and The coefficient can unify and cancel out the mechanical tolerance and the nonlinear error of the sensor, thereby ensuring that the mass flow measurement accuracy of this invention can still be stably within ±1% in the entire range under harsh working conditions of industrial / food grade low-purity gas.

[0099] To measure mass flow rate more accurately, a temperature difference correction coefficient is preferably introduced. The temperature difference corrected flow coefficient Taylor expansion approximation is used.

[0100] use When performing a Taylor expansion, , For the first The temperature correction factor corresponding to the order.

[0101] The formula for calculating the flow rate of the sonic choke flow is as follows: .

[0102] The formula for calculating the subsonic flow rate is as follows: .

[0103] , .

[0104] For flow coefficient, The cross-sectional area of ​​the flow-limiting short orifice is given. For gas molar mass, It is the gas compressibility factor. This is the universal gas constant.

[0105] Although Higher order results in greater accuracy but also increases computational complexity. Since the invention method is typically used in high-precision flow meters and controllers, the calculations are usually performed using chips installed on these devices. These are mostly inexpensive embedded chips with relatively limited computing power. Because a higher computational load requires more computation time for the same chip with the same computing power, the solution aims to reduce computational load and improve response speed. Preferably, the temperature difference corrected flow coefficient... Using a first-order Taylor expansion, the... , The temperature correction coefficient uses a first-order calculation, which requires significantly less computation. Furthermore, the accuracy of the first-order coefficient is currently comparable to that of a thermal mass flow controller or thermal mass flow meter, i.e., within ±1%.

[0106] Of course, as the computing power of embedded chips develops rapidly and becomes more energy-efficient, in the future, chips with greater computing power and higher energy efficiency will be available at the same price. At that time, second-order or third-order Taylor expansions can also be used to approximate the temperature difference correction flow coefficient. Of course, for gas mass flow meters and gas mass controllers that require an accuracy of ±0.5%, the cost of the embedded chip can be increased by directly using a high-performance chip, thereby improving the accuracy.

[0107] The formula for calculating the sonic choke flow rate is as follows: .

[0108] The formula for calculating the subsonic flow rate is as follows:

[0109] .

[0110] If the temperature sensor is not an absolute temperature sensor and the pressure sensor is not an absolute pressure sensor, then conversion is required. For example, convert Celsius to absolute temperature (K), and convert standard gauge pressure to absolute pressure. Kelvin temperature = Celsius + 273.15, and absolute pressure = gauge pressure + 101.325 kPa.

[0111] Designing high-precision gas mass flow controllers or high-precision gas flow meters presents additional challenges in terms of algorithms and hardware if the system operates in the subsonic phase.

[0112] 1. Increase in control variables: High-frequency data acquisition must be performed simultaneously. and The data from the two pressure sensors, any measurement noise or drift from either sensor will be directly added to the error in the flow calculation.

[0113] 2. Computing Power and Hysteresis: Subsonic formulas involve complex nonlinear exponential and square root operations. Real-time, high-frequency execution of these floating-point operations in microcontrollers (MCUs) consumes a significant number of CPU cycles. This not only lengthens the control cycle's computation time but also significantly increases the hysteresis of the entire closed-loop control system, resulting in a slower dynamic response during flow regulation.

[0114] 3. Nonlinear gain: when Very close When the pressure difference and flow rate are extremely small, the effect of pressure ratio change on flow rate change in the formula becomes highly nonlinear. This means that the PID control parameters of the proportional valve are difficult to tune under low opening conditions, and flow rate oscillations are very likely to occur.

[0115] Therefore, the design of high-precision gas mass flow controllers or high-precision gas flow meters tends to utilize structural design techniques such as increasing the gas supply pressure or reducing the flow-limiting orifice diameter to force the gas to remain in a sonic choke flow state for most of the operating range, thereby completely shielding the flow. The interference greatly simplifies the algorithm and improves the response speed.

[0116] In order to eliminate the "false temperature difference and false pressure difference signals" caused by the inherent manufacturing discreteness of the sensor hardware, the zero-point drift due to long-term use and environmental thermal disturbances, and to prevent the phenomenon of zero-point "flow leakage" when the system is static and not ventilated, this invention method can use gas with a purity of only 99% to 99.9%, which will result in a small amount of impurities in the gas. During long-term operation, these impurities will cause wear and tear on the hardware.

[0117] In actual industrial settings, high-precision temperature and pressure sensors inevitably suffer from interference after leaving the factory due to factors such as mechanical installation stress in pipelines, inherent residual voltage drift in microcontroller hardware (A / D conversion zero drift), and weak environmental thermal radiation. This invention innovatively utilizes the extremely small Joule-Thomson effect temperature difference spontaneously generated when gas passes through a flow-limiting short orifice. With pressure difference To inversely calculate mass flow rate, when the system is in a static, non-flowing state with the control valve closed or slightly open, the aforementioned hardware and environmental interferences can cause the sensor array to continuously output non-zero, small false temperature differences, such as 0.01℃~0.05℃, or false pressure differences. If this state is not dynamically processed, the mass flow rate calculation model will misjudge, resulting in a serious "static flow leakage" phenomenon in cumulative measurement. By executing the zero-point zeroing function of this invention, the controller can capture the sensor reference residual quantity under this static boundary online and forcibly define it as the physical origin at the mathematical solution level, establishing a rigid zero-point convergence boundary. This provides an extremely clean and accurate starting point for subsequent high-dynamic, high-precision flow measurement.

[0118] Preferably, a control switch and a control valve for the switch size are installed at the inlet of the flow channel, and the measurement method includes a zero-point zeroing method.

[0119] The zero-position reset method: the control valve is in a preset micro-opening state, and the intake pressure... Fluctuation, absolute pressure before the flow-limiting short orifice Absolute pressure after the orifice and the flow-limiting short orifice A pressure difference initially exists, and the absolute temperature before the flow-limiting short orifice... Absolute temperature after the flow-limiting short orifice A temperature difference begins to exist, at which point the zero point returns to zero.

[0120] The zero-point zeroing method included in the method has the core technical function of eliminating hardware zero-point drift of the sensor array and pseudo-flow interference caused by environmental thermal disturbances.

[0121] During actual production or on-site operation initialization, when the control valve is in a closed or slightly open non-flow static boundary, if the sensor array collects non-zero small temperature and pressure difference signals due to inherent hardware residual voltage or ambient temperature and pressure fluctuations, the control center will forcibly define the solution result at this time as a physical zero point by executing the zero-point zeroing method and establish a mathematical convergence boundary.

[0122] This step ensures that the system output is absolutely zero when the flow rate is zero, effectively eliminating the superposition of errors in subsequent flow accumulation measurement caused by minute sensor noise, and guaranteeing the starting reference accuracy of the entire system's measurement loop. In this way, flow meters and flow controllers made based on the method of this invention can be frequently zeroed, avoiding accuracy degradation.

[0123] Preferably, a control switch and a control valve for controlling the switch size are installed at the inlet of the flow channel. The measurement method includes a maximum range correction method, wherein the control valve opening is gradually increased until the intake pressure... Absolute pressure before the flow-limiting short orifice Absolute pressure after the flow-limiting short orifice Absolute atmospheric pressure The pressure difference between them no longer changes, and the absolute temperature of the ambient atmosphere remains constant. Absolute temperature before the flow-limiting short orifice Absolute temperature after the flow-limiting short orifice The temperature difference between the two sides no longer changes, and the flow rate is at its maximum.

[0124] The method includes a maximum range correction step, the core technology of which is to dynamically lock the upper limit of the physical flow rate under the current operating conditions and adaptively correct the gain slope of the entire range.

[0125] Due to the discrete differences in total intake pressure, environmental boundaries, and the actual purity of the gas medium under different industrial application scenarios, such as the presence of water vapor impurities, the comprehensive reference coefficient in the theoretical calculation formula will deviate from the actual flow field gain. By gradually increasing the control valve opening until the various thermodynamic and hydrodynamic parameters tend to stabilize, the control center can capture online the limit of blocked flow that the hardware can achieve under the current specific operating condition.

[0126] Marking this limit flow rate as the maximum range allows for the establishment of a rigid absolute amplitude lock-in boundary for the flow calculation model. This boundary is used to absorb and compensate for the cumulative inaccuracy of the full-scale gain caused by gradual changes in gas properties and discrete measurement errors, thereby significantly improving the system's service performance and control robustness under harsh operating conditions and high flow rates.

[0127] The core technical purpose of introducing a maximum range correction step in the measurement and control method described in this invention is to enable the solution algorithm to adapt to changes in harsh industrial operating conditions, dynamically adjust the "gain slope" across the entire range, and eliminate cumulative inaccuracies in the high-flow-rate section. Although in the theoretical formula, the comprehensive reference coefficient... and It can be based on the nominal adiabatic index of the gas. molar mass While physical constants are initially estimated, the total intake pressure of the upstream gas source varies under harsh industrial conditions such as petroleum, chemical, and welding processes. Frequent and drastic fluctuations in the purity of the gas medium, such as trace amounts of moisture and other gaseous impurities mixed in with industrial-grade gases, can cause the actual microscopic physical properties of the gas to deviate from theoretical constants. This leads to a deviation in the overall gain slope of the flow calculation equation, ultimately resulting in severe linear gain inaccuracies between measured values ​​and actual flow rates, especially under sonic choke conditions, at high flow rates. By implementing the maximum range correction function, the control valve opening is gradually increased, allowing the system to dynamically sense and capture the limit of physical choke flow field data achievable by the hardware under specific field conditions. Marking this limit of stable state as the maximum range is equivalent to drawing the most accurate highest point tangent line online for the entire nonlinear flow calculation model, thus solidifying a rigid absolute amplitude lock-in boundary. This greatly absorbs and compensates for the full-scale gain inaccuracies caused by gradual changes in gas properties and discrete measurement errors, ensuring the robustness and control response quality of this invention during operation across the entire flow range (especially at high flow rates).

[0128] Preferably, a control switch and a control valve for the switch size are installed at the inlet of the flow channel, and the measurement method includes a zero-point zeroing method and a maximum range correction method.

[0129] The zero-position reset method: the control valve is in a preset micro-opening state, and the intake pressure... Fluctuation, absolute pressure before the flow-limiting short orifice Absolute pressure after the orifice and the flow-limiting short orifice A pressure difference initially exists, and the absolute temperature before the flow-limiting short orifice... Absolute temperature after the flow-limiting short orifice A temperature difference begins to exist, at which point the zero point returns to zero.

[0130] The maximum range correction method involves gradually increasing the opening of the control valve until the intake pressure... Absolute pressure before the flow-limiting short orifice Absolute pressure after the flow-limiting short orifice Absolute atmospheric pressure The pressure difference between them no longer changes, and the absolute temperature of the ambient atmosphere remains constant. Absolute temperature before the flow-limiting short orifice Absolute temperature after the flow-limiting short orifice The temperature difference between the two sides no longer changes, and the flow rate is at its maximum.

[0131] The system also pre-stores calibration coefficients corresponding to different deviations between the maximum range and the initial maximum range. After the zero-point reset and maximum range correction are completed, the corresponding calibration coefficient is selected based on the current deviation value to correct the mass flow rate calculation formula.

[0132] Over time, impurities such as particles in the gas can cause wear and dust accumulation on hardware such as the flow-limiting orifice, leading to deviations in the coefficients of the flow calculation formula. Since wear and dust accumulation affect the accuracy of flow measurement, in order to improve the service life of products manufactured based on the method of this invention, coefficients for different deviation values ​​have been pre-stored. Thus, different deviation values ​​can select the corresponding coefficients, or the corresponding coefficients can be calculated using methods such as the least squares method based on different deviation values ​​and coefficient tables. This ensures that the invention can still accurately measure flow after long-term use.

[0133] Since some users are accustomed to using standard volumetric flow rate, preferably, this measurement method can also measure standard volumetric flow rate by converting mass flow rate to standard volumetric flow rate. ,in, Standard volumetric flow rate, For quality flow, The density is the standard operating condition density of the gas. Mass flow rate can be easily converted to standard volumetric flow rate (SLM) using a formula, thus enabling this invention to measure not only mass flow rate but also standard volumetric flow rate.

[0134] like Figure 2 As shown, this invention provides a flow control method using a Joule-Thomson effect mass flow measurement method. The technical solution of this invention is as follows: a control switch and a control valve for adjusting the switch size are installed at the inlet of the flow channel. The mass flow control method involves: first setting a target flow value, and then dynamically adjusting the opening of the control valve based on the real-time mass flow measured by the mass flow measurement method; the steps for dynamically adjusting the opening of the control valve are as follows:

[0135] 1) If the real-time flow rate is greater than the target flow rate, reduce the opening of the control valve until the real-time flow rate equals the target flow rate.

[0136] 2) If the real-time flow rate is less than the target flow rate, increase the opening of the control valve until the real-time flow rate equals the target flow rate.

[0137] When dynamically adjusting the control valve opening, adjustments are made in real time until the real-time flow rate equals the target flow rate value, at which point the control valve opening is no longer adjusted.

[0138] Based on precise flow measurement, this flow control method can achieve precise flow control.

[0139] To reduce the computational load on the flow controller and more quickly limit the flow to the set target value, preferably, the control valve is a proportional control valve, and the step of dynamically adjusting the opening of the control valve is as follows:

[0140] 1) Real-time calculation of flow error , For target quality flow rate, This represents the current real-time quality flow rate.

[0141] 2) Obtain the current opening value of the proportional control valve. .

[0142] 3) Calculate the opening adjustment increment using a control closed-loop algorithm. ;in For adjustment coefficients, To prevent the removal of a zero constant, the increment is adjusted according to the opening degree. Update the opening degree of the proportional control valve, if If the value is positive, the valve opening will increase; if... If the value is negative, the valve opening will be reduced.

[0143] Preventing zero small constants This closed-loop algorithm avoids calculation problems where the denominator is zero, and can more quickly control the traffic within the target range, achieving a rapid response. With conventional low-end chips on the market, a response time of less than 500ms can be achieved, while with higher-performance chips, the response time can be less than 100ms.

[0144] Due to mass flow Compared with standard volumetric flow rate They can be converted to each other, so the method of this invention can also accurately control the standard volumetric flow rate.

[0145] The specific method of using this invention is as follows:

[0146] 1. Operating in the mode of a gas mass flow meter (displaying real-time output flow rate)

[0147] 1. Before starting: Constant pipeline gas or gas from a cylinder after being depressurized by a pressure reducing valve enters the gas inlet. At this time, the proportional solenoid valve is in the normally closed state.

[0148] 2. Power-on self-test: Turn on the power, set the gas medium type on the display screen or via the communication protocol, set the operating mode to "flowmeter" mode on the display screen or via the communication protocol, open the output control valve to its maximum opening, and the system will perform a self-test. Is it greater than And within the detection range. If If the input air pressure is abnormal, a warning will be issued.

[0149] 3. The microcontroller will automatically input a small current or voltage into the proportional solenoid valve, causing the valve to open slightly. Pressure fluctuations, , There is a slight differential pressure. , With a slight temperature difference, the zero point returns to zero, thus preventing zero-point drift.

[0150] 4. The microcontroller inputs a large current or voltage to the proportional solenoid valve, causing the valve opening to continue to increase until... , , , Pressure difference and , , The temperature difference no longer changes; and , , , When the value no longer changes, the flow rate is at its maximum range, which helps prevent maximum range drift.

[0151] 5. Define the flow range by zeroing the zero point and the maximum range, and calculate the flow values ​​of each flow within the allocated flow range through the program.

[0152] 6. The program will compensate based on parameters such as medium, pressure, and temperature to obtain the actual mass flow rate and standard volumetric flow rate, and then display or output them.

[0153] The zero-point reset and maximum range correction in steps 3 and 4 do not need to be performed every time.

[0154] II. Operating in the mode of a gas mass flow controller (output flow rate set according to input signal).

[0155] 1. Before starting: Constant pipeline gas or gas from a cylinder after being depressurized by a pressure reducing valve enters the gas inlet. At this time, the proportional solenoid valve is in the normally closed state.

[0156] 2. Power-on self-test: Turn on the power, set the gas medium type on the display screen or via the communication protocol, and set the operating mode to "flow controller" mode on the display screen or via the communication protocol. The system will then perform a self-test. Is it greater than And within the detection range. If If the input air pressure is abnormal, a warning will be issued.

[0157] 3. The microcontroller will automatically input a small current or voltage into the proportional solenoid valve, causing the valve to open slightly. Pressure fluctuations, , There is a slight differential pressure. , With a slight temperature difference, the zero point returns to zero, thus preventing zero-point drift.

[0158] 4. The microcontroller inputs a large current or voltage to the proportional solenoid valve, causing the valve opening to continue to increase until... , , , Pressure difference and , , The temperature difference no longer changes; and , , , When the value no longer changes, the flow rate is at its maximum range, which helps prevent maximum range drift.

[0159] 5. Define the flow range by zeroing the zero point and the maximum range, and calculate the flow values ​​of each flow within the allocated flow range through the program;

[0160] 6. Input the set flow rate through the display screen or communication protocol, and the program will compensate according to parameters such as medium, pressure, and temperature to obtain the actual mass flow rate and standard volumetric flow rate.

[0161] 7. Adjust the opening of the proportional solenoid valve in real time until the actual mass flow rate or standard volume flow rate reaches the set flow target value.

[0162] The zero-point reset and maximum range correction in steps 3 and 4 do not need to be performed every time.

[0163] This embodiment should not be considered as a limitation of the invention, but any improvements made based on the spirit of the invention should be within the protection scope of the invention.

Claims

1. A method for measuring mass flow rate using the Joule-Thomson effect, characterized in that: The measurement method specifically includes the following steps: 1) Throttling step: Gas flows through a flow-limiting short orifice set in the flow channel and undergoes throttling expansion, producing the Joule-Thomson effect; 2) Data Acquisition Steps: Real-time acquisition of fluid thermodynamic and hydrodynamic parameters upstream and downstream of the flow-limiting orifice; 3) Calculation steps: Based on the collected parameters, the gas mass flow rate through the flow-limiting orifice is calculated using the gas state equation and temperature correction model.

2. The method for measuring mass flow rate using the Joule-Thomson effect according to claim 1, characterized in that: When the actual pressure ratio satisfies When the fluid is determined to be in a sonic choke flow state, the sonic choke flow flow rate calculation formula is executed. When the actual pressure ratio satisfies When the fluid is determined to be in a subsonic flow state, the subsonic flow rate calculation formula is executed. in The adiabatic index of the gas is . The absolute pressure before the flow-limiting short orifice. This refers to the absolute pressure after the flow-limiting short orifice.

3. The method for measuring mass flow rate using the Joule-Thomson effect according to claim 2, characterized in that: The formula for calculating the flow rate of the sonic choke flow is as follows: , The formula for calculating the subsonic flow rate is as follows: , The above formulas for calculating the flow rate of sonic congestion flow and subsonic flow include, For quality flow, This serves as a comprehensive reference coefficient for the physical structure of the flow-limiting short orifice and the gas properties in the formula for calculating the flow rate of sonic congestion flow. This serves as a comprehensive reference coefficient for the physical structure of the flow-limiting orifice and the gas properties in the subsonic flow rate calculation formula. The absolute temperature before the flow-limiting short orifice. The absolute temperature after the flow-limiting short orifice. Based on Temperature difference corrected flow coefficient.

4. The method for measuring mass flow rate using the Joule-Thomson effect according to claim 3, characterized in that: The temperature difference correction flow coefficient Taylor expansion approximation is used; use When performing a Taylor expansion, , For the first Temperature correction factor corresponding to the order. The formula for calculating the flow rate of the sonic choke flow is as follows: , The formula for calculating the subsonic flow rate is as follows: ; ， ， For flow coefficient, The cross-sectional area of ​​the flow-limiting short orifice is given. For gas molar mass, It is the gas compressibility factor. This is the universal gas constant.

5. The method for measuring mass flow rate using the Joule-Thomson effect according to claim 4, characterized in that: The temperature difference correction flow coefficient Using a first-order Taylor expansion, the... , This is the temperature correction factor. The formula for calculating the sonic choke flow rate is as follows: , The formula for calculating the subsonic flow rate is as follows: 。 6. The method for measuring mass flow rate using the Joule-Thomson effect according to claim 2, characterized in that: A control switch and a control valve for the switch position are installed at the inlet of the flow channel. The measurement method includes a zero-point reset method. The zero-position reset method: the control valve is in a preset micro-opening state, and the intake pressure... Fluctuation, absolute pressure before the flow-limiting short orifice Absolute pressure after the orifice and the flow-limiting short orifice A pressure difference initially exists, and the absolute temperature before the flow-limiting short orifice... Absolute temperature after the flow-limiting short orifice A temperature difference begins to exist, at which point the zero point returns to zero.

7. The method for measuring mass flow rate using the Joule-Thomson effect according to claim 2, characterized in that: A control switch and a control valve for the switch size are installed at the inlet of the flow channel. The measurement method includes a maximum range correction method. The maximum range correction method involves gradually increasing the opening of the control valve until the intake pressure... Absolute pressure before the flow-limiting short orifice Absolute pressure after the flow-limiting short orifice Absolute atmospheric pressure The pressure difference between them no longer changes, and the absolute temperature of the ambient atmosphere remains constant. Absolute temperature before the flow-limiting short orifice Absolute temperature after the flow-limiting short orifice The temperature difference between the two sides no longer changes, and the flow rate is at its maximum.

8. The method for measuring mass flow rate using the Joule-Thomson effect according to claim 2, characterized in that: A control switch and a control valve for the switch size are installed at the inlet of the flow channel. The measurement methods include a zero-point calibration method and a maximum range correction method. The zero-position reset method: the control valve is in a preset micro-opening state, and the intake pressure... Fluctuation, absolute pressure before the flow-limiting short orifice Absolute pressure after the orifice and the flow-limiting short orifice A pressure difference initially exists, and the absolute temperature before the flow-limiting short orifice... Absolute temperature after the flow-limiting short orifice A temperature difference begins to exist, at which point the zero point returns to zero. The maximum range correction method involves gradually increasing the opening of the control valve until the intake pressure... Absolute pressure before the flow-limiting short orifice Absolute pressure after the flow-limiting short orifice Absolute atmospheric pressure The pressure difference between them no longer changes, and the absolute temperature of the ambient atmosphere remains constant. Absolute temperature before the flow-limiting short orifice Absolute temperature after the flow-limiting short orifice The temperature difference between the two parts no longer changes, and the flow rate is at its maximum range at this time. The system also pre-stores calibration coefficients corresponding to different deviations between the maximum range and the initial maximum range. After the zero-point reset and maximum range correction are completed, the corresponding calibration coefficient is selected based on the current deviation value to correct the mass flow rate calculation formula.

9. A method for measuring mass flow rate using the Joule-Thomson effect according to any one of claims 1-8, characterized in that: This measurement method can also measure standard volumetric flow rate by converting mass flow rate to standard volumetric flow rate. ,in, Standard volumetric flow rate, For quality flow, This refers to the standard operating density of the gas.

10. A flow control method based on the Joule-Thomson effect mass flow measurement method according to any one of claims 1-8, characterized in that: A control switch and a control valve for the switch size are installed at the inlet of the flow channel. The mass flow control method is as follows: first, set the target flow value, and then dynamically adjust the opening of the control valve according to the real-time mass flow measured by the mass flow measurement method. The steps for dynamically adjusting the opening of the control valve are as follows: 1) If the real-time flow rate is greater than the target flow rate, reduce the opening of the control valve until the real-time flow rate equals the target flow rate. 2) If the real-time flow rate is less than the target flow rate, increase the opening of the control valve until the real-time flow rate equals the target flow rate. When dynamically adjusting the control valve opening, adjustments are made in real time until the real-time flow rate equals the target flow rate value, at which point the control valve opening is no longer adjusted.

11. The flow control method according to any one of claims 10, characterized in that: The control valve is a proportional control valve, and the step of dynamically adjusting the opening of the control valve is as follows: 1) Real-time calculation of flow error , For target quality flow rate, This represents the current real-time quality flow rate; 2) Obtain the current opening value of the proportional control valve. ; 3) Calculate the opening adjustment increment using a control closed-loop algorithm. ;in For adjustment coefficients, To prevent the removal of a zero constant, the increment is adjusted according to the opening degree. Update the opening degree of the proportional control valve, if If the value is positive, the valve opening will increase; if... If the value is negative, the valve opening will be reduced.

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