A device and method for measuring gas volume in an open chamber

Abstract

The present invention discloses a device and method for measuring the volume of gas in an open chamber. The device includes a mass flow controller, which is arranged on the air inlet side of the chamber to be measured and is used to detect the flow rate of fresh air flowing into the chamber to be measured; a pressure sensor, a temperature sensor, and a humidity sensor, which are arranged in the chamber to be measured; and a gas analyzer, which is connected to the air outlet side of the chamber to be measured and is used to detect the concentration level of oxygen or carbon dioxide in the air leaving the chamber to be measured. The present invention integrates the data of the gas analyzer and the mass flow controller and draws a fitting exponential curve to find the gas volume of the chamber to be measured under the standard state, and then converts the gas volume under the standard state into the volume of the gas in the chamber to be measured under the current state through the data collected by the pressure sensor, the temperature sensor, and the humidity sensor. Since the changing parameter is the gas concentration, it can be applied to the measurement of the gas volume in the open chamber under the condition that the gas in the chamber is evenly mixed.

Description

Technical Field

[0001] The present invention relates to the field of volume detection technology, and in particular to a device and method for measuring the volume of gas in an open chamber. Background Art

[0002] For volume measurement, the commonly used methods currently include geometric dimension measurement method, volume comparison method, weighing measurement method, mass flow controller measurement method, gas calibration method, etc.; the geometric dimension measurement method uses three-coordinate measuring tools to measure the actual dimensions of the part or chamber to be measured, and calculates the volume of the part to be measured based on the dimensions; the weighing measurement method uses a balance to weigh the mass of the part to be measured when it is not filled with a medium, and at the same time weighs the mass of the part to be measured when it is filled with a medium, and calculates the volume of the part to be measured by the mass difference and the density of the medium; and the mass flow controller measurement method is to connect the mass flow controller and the part to be measured, first record the initial value of the mass flow controller, fill the part to be measured with liquid, and record the mass The cumulative value of the flow controller, the volume of the measured component is equal to the cumulative value minus the initial value; for the above measurement methods: the weighing measurement method and the mass flow controller measurement method both use liquid as the medium. When the internal shape of the measured component is complex, it cannot be guaranteed that the liquid fills the entire space. At the same time, it cannot be guaranteed that the liquid is completely discharged after cleaning, which will greatly affect the accurate measurement of the volume; and the use of liquid will often affect the future performance of the original components in the chamber. The geometric dimension measurement method can only be used for chambers with not very complex regular shapes. At the same time, an unmeasurable "dead point" position is often formed between other components of the chamber and the chamber. The application scenarios of this measurement method are limited.

[0003] In gas experiment systems, precise control of the gas volume is often required, with an error of no more than 1%. Furthermore, in metabolic experiment systems, precise measurement of the metabolic chamber volume is often required, as this measurement often plays a decisive role in the final metabolic assessment. In metabolic chamber modeling, the chamber is often treated as a low-pass filter, a large gas tank that dilutes subtle input signals (small amounts of VO2 and VCO2 produced by the subject). In metabolic experiment systems, the inputs (VO2 and VCO2 concentrations) are hidden variables, while the outputs (VO2 and VCO2 concentrations in the air within the chamber) are directly measured. This creates an inverse system. To solve this inverse problem, the MR signal is modeled as a linear combination of the recorded gas concentration data and their derivatives, transforming the inverse problem into a direct problem. This method differs from traditional open-circuit calorimetry in that the metabolic chamber volume is introduced to mitigate the measurement error of the respiratory quotient (RQ) in open-circuit calorimetry involving a mixing chamber. The importance of accurate compartment volume to the overall system is self-evident.

[0004] In order to accurately detect the volume of the chamber, the existing technology generally adopts a gas calibration method with a relatively complex test system, which often uses high-purity gases, such as Figure 5 As shown, it consists of a standard container, a control valve, two sets of temperature and pressure sensors, as well as supporting systems and connecting pipes. When measuring volume, the chamber to be measured is first filled with gas at an appropriate pressure through the valve, the control valve is closed, and the temperature T1, T2 and pressure P1, P2 of the standard container and the chamber to be measured are recorded after the system is balanced. Then, the control valve is opened to fill the chamber to be measured with an appropriate amount of gas, the control valve is closed, and the temperature T1', T2' and pressure P1', P2' of the standard container and the chamber to be measured are recorded after the system is rebalanced. Since the entire test system is sealed to the outside world, the mass of the system is conserved before and after the gas is injected, and thus , where P is the gas pressure, V is the gas volume, Z is the gas compressibility coefficient, M is the gas mass, T is the gas temperature, and R is the gas constant; according to the law of conservation of mass, the calculation formula for the measured chamber volume can be obtained as follows;

[0005] ;

[0006] in, is the volume of the cavity to be measured, is the volume of the standard container, , is the gas compressibility coefficient after the first system equilibrium, , ′ is the gas compression coefficient after the second system equilibrium. When the gas pressure is constant and the pressure in the standard container and the measured chamber is close, the gas compression system can be approximately considered to be the same. When the ambient temperature fluctuates slightly, the control valve opens slowly, and the flow injection rate is low, the temperature change of the entire system is small, and the above formula can be simplified to:

[0007] ;

[0008] Relying on the simplified formula, a Chinese patent (CN112903058A) discloses a volume detection device and method, which estimates the volume of the chamber by setting a standard container with measurable volume and further simplifying the formula (making the temperature of the same measurement approximately the same).

[0009] It is foreseeable that the following problems will arise when using the above-mentioned gas calibration method to measure the volume of the chamber: (1) Since the gas calibration method uses the ideal gas formula for calculation, it is necessary to ensure the airtightness of the system, and it is not applicable to open or semi-open chambers; (2) Each parameter is an actual direct measurement value, and in order to obtain the accurate volume of the gas in the chamber, multiple measurements are required to obtain the average value. Summary of the Invention

[0010] The purpose of the present invention is to provide a device and method for measuring the volume of gas in an open chamber in order to solve the above problems, thereby improving the measurement accuracy by using data fitting.

[0011] In order to achieve the above object, the present invention is implemented through the following technical solutions:

[0012] A device for measuring the volume of gas in an open chamber, comprising an air inlet and an air outlet of the chamber to be measured, comprising:

[0013] A mass flow controller, which is arranged on the air inlet side of the chamber to be tested and is used to detect the flow rate of fresh air flowing into the chamber to be tested;

[0014] A pressure sensor, a temperature sensor, and a humidity sensor are arranged in the chamber to be tested and are used to detect the pressure, temperature, and relative humidity in the chamber to be tested;

[0015] A gas analyzer connected to the gas outlet of the chamber to be tested, used to detect the concentration level of oxygen or carbon dioxide in the air leaving the chamber to be tested;

[0016] A fully mixing mechanism includes multiple groups of tangential fans; the tangential fans are vertically arranged between the air inlet and the air outlet of the chamber to be tested, and the gas blown by the tangential fans collides with the fresh air entering the chamber, and the fresh air and the air in the chamber to be tested are fully mixed before entering the air outlet of the chamber to be tested;

[0017] The control unit receives signals from the gas analyzer, pressure sensor, temperature sensor, and humidity sensor, samples them in real time, and then controls the tangential blower and mass flow controller in real time;

[0018] The computer stores and displays the data collected and uploaded by the control unit, integrates the data from the gas analyzer and the mass flow controller, and draws a fitting exponential curve to find the gas volume of the chamber to be tested under standard conditions. Then, the gas volume under standard conditions is converted into the volume of the chamber to be tested under the current state through the data collected by the pressure sensor, temperature sensor, and humidity sensor.

[0019] Furthermore, a T-type valve is provided at the air inlet pipe on the air inlet side of the chamber to be tested, and one side of the T-type valve is connected to the mass flow controller through the first blower, so that the real-time flow rate of the fresh air entering is measured by the mass flow controller while the first blower delivers fresh air.

[0020] Furthermore, it also includes a gas collection system, one side of which is connected to the chamber to be tested, and the other side is connected to the gas analyzer through an outlet pipe; the gas collection system includes a gas outlet composed of multiple groups of flexible Tygon tubes with the same geometric shape, which is arranged on the gas outlet side of the chamber to be tested. The other side of the gas outlet is connected to a polyvinyl chloride tube, and the other end of the polyvinyl chloride tube is connected to the gas analyzer to ensure that the air in the chamber to be tested is evenly transported to the gas analyzer.

[0021] Furthermore, a connecting pipe is provided on one side of the polyvinyl chloride tube to connect to one end of the chamber to be tested, for balancing the pressure of fresh air flowing out of the chamber and the air in the chamber. A second blower is provided in the connecting pipe to control the airflow returning to the chamber to be tested.

[0022] The present invention also provides a method for measuring the gas volume in an open chamber, comprising the following steps:

[0023] S001, first, a certain amount of carbon dioxide is filled into the chamber to be tested, so that the concentration levels of oxygen and carbon dioxide in the chamber to be tested are different from those of fresh air;

[0024] S002, continuously filling the chamber to be tested with fresh air through a mass flow controller, and continuously detecting the concentration of oxygen or carbon dioxide flowing out of the chamber through a gas analyzer; the difference between the concentration of oxygen or carbon dioxide flowing out of the chamber to be tested and the concentration of the corresponding gas in the fresh air decreases as the detection duration continues, until the concentration of oxygen or carbon dioxide flowing out of the chamber to be tested is consistent with the concentration in the fresh air;

[0025] S003, by collecting the flow rate of fresh air flowing into the chamber to be tested and the concentration of oxygen or carbon dioxide flowing out of the chamber to be tested, solving the zero-input differential equation to invert the gas volume of the chamber to be tested, and then converting the gas volume under standard conditions into the volume of the chamber to be tested under current conditions through the data collected by the pressure sensor, temperature sensor, and humidity sensor.

[0026] Furthermore, in step S003, the zero-input differential equation is:

[0027] ;

[0028] in, It is the outflow rate of a single gas, measured by a gas analyzer. is the inflow rate of fresh air, which is set by the mass flow controller. It is the gas flow rate under standard conditions. A and C are fitting exponents, V is the gas volume in the chamber under standard conditions, and t is the time constant.

[0029] Furthermore, in step S003, the pressure P, temperature T, and relative humidity RH measured by the pressure sensor, temperature sensor, and humidity sensor are used to correct the above-calculated volume V of the gas in the chamber under the standard state. The correction formula is:

[0030] ;

[0031] in, is the gas volume in the chamber at the current state, 、 are the temperature and pressure under standard conditions, is the water vapor partial pressure.

[0032] Furthermore, the water vapor partial pressure Equal to RH ,in is the partial pressure of saturated water vapor.

[0033] Compared with the existing technology, the beneficial effects of the present invention are embodied in:

[0034] (1) The present invention does not require the use of a standard container to calibrate the gas in the chamber to be measured, and can more accurately measure the gas volume in the chamber;

[0035] (2) Since the variable parameter of the present invention is gas concentration, under the condition that the gas in the chamber is uniformly mixed, there is no need to worry about the airtightness of the chamber to be measured, and the method is applicable to the measurement of gas volume in an open chamber;

[0036] (3) The present invention uses data fitting to correct it and can improve the measurement accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic diagram of the structure of the gas volume measuring device in an open chamber of the present invention;

[0038] Figure 2 This is a schematic structural diagram of another embodiment of the device for measuring the volume of gas in an open chamber according to the present invention;

[0039] Figure 3 It is a schematic diagram of the principle of the present invention;

[0040] Figure 4 This is an example of fitting an exponential curve in the present invention;

[0041] Figure 5 Schematic diagram of the measurement principle of the gas calibration method. DETAILED DESCRIPTION

[0042] The present invention will be further described in detail below with reference to the embodiments in the accompanying drawings, but this does not constitute any limitation to the present invention.

[0043] This invention aims to solve the problem of low measurement accuracy and inapplicability of existing gas calibration methods to open chambers by redesigning the gas calibration method to expand its application to chambers with smaller openings. By calibrating the concentration level of a single gas after thorough mixing, the problem of the existing gas calibration method requiring a large number of measurement parameters is circumvented. The principle of the solution is as follows:

[0044] Larger chambers have inherently slow response times that are related to the size of the chamber and its ventilation rate. The single concentration in the chamber at time t after a unit step change in gas production can be inverted from the general solution of the zero-input response differential equation to determine the volume of gas in the chamber under test:

[0045] ;

[0046] in, It is the outflow rate of a single gas, measured by a gas analyzer. is the inflow rate of fresh air, set by a mass flow controller. It is the gas flow rate under standard conditions (stp). A and C are fitting exponents, V is the gas volume in the chamber under standard conditions, and t is the time constant. The gas volume V in the chamber is found by fitting the curve, and then the precise value of the gas volume in the chamber is obtained by correcting for temperature, humidity, and pressure.

[0047] So far, a method for measuring the gas volume in the chamber can be designed. In this method, there are only two directly measured parameters, namely and At the same time, after the filled gas and the air in the cavity are fully mixed, since the concentration of each single gas remains unchanged during gas diffusion, the measurement method of the present invention can be used to detect some smaller open cavities. In this way, a gas volume measurement device in an open cavity will be designed, and its specific structure is as follows: Figure 1 、 2 , 3, and 4:

[0048] First, it is necessary to set up connectable air ports according to the structure of the chamber 100 to be tested: an air inlet 101 and an air outlet 102. A T-valve 103 is also provided on the air inlet pipe on the air inlet 101 side of the chamber 100 to be tested. One side of the T-valve 103 is connected to a mass flow controller 200 through a first blower 104. Fresh air is delivered through the first blower 104, and the real-time flow rate of the incoming fresh air is measured by the mass flow controller 200.

[0049] The measuring device specifically includes a mass flow controller 200, which is arranged on the air inlet 101 side of the chamber to be measured 100 and is used to detect the flow rate of fresh air flowing into the chamber to be measured 100;

[0050] The pressure sensor 301, the temperature sensor 302, and the humidity sensor 303 are disposed in the chamber 100 to detect the pressure P, the temperature T, and the relative humidity RH in the chamber 100;

[0051] A gas analyzer 400 connected to the gas outlet 102 of the chamber 100 to be tested and used to detect the concentration level of oxygen or carbon dioxide in the air leaving the chamber 100 to be tested;

[0052] In order to meet the requirement of the system assumption that the mixed gas should be fully mixed with the gas in the chamber before flowing out of the chamber to be tested 100, Figure 1 A full mixing mechanism is provided, which includes multiple groups of tangential fans 500; the tangential fans 500 are vertically arranged between the air inlet 101 and the air outlet 102 of the chamber to be tested 100, and the gas blown out by the tangential fans 500 collides with the fresh air entering the chamber, so that the fresh air and the air in the chamber to be tested 100 are fully mixed and then enter the air outlet 102 of the chamber to be tested 100. It is worth mentioning that in order to reduce the impact of the tangential fans 500 on the system, the tangential fans 500 should be arranged as a whole inside the chamber to be tested 100, and the gas circulated therein is limited to the gas in the chamber to be tested 100.

[0053] In order to meet another requirement of the system assumption that the pressure of the mixed gas flowing out of the chamber is consistent with the pressure of the gas in the chamber, Figure 2 In another embodiment shown in FIG, a connecting pipe 700 is provided on one side of the polyvinyl chloride tube 602 to connect to one end of the chamber to be tested 100, for balancing the pressure of fresh air flowing out of the chamber and the air inside the chamber. A second blower 701 is provided in the connecting pipe 700 to control the airflow returning to the chamber to be tested 100, thereby controlling the pressure difference between the two ends by balancing the airflow.

[0054] The PVC tube 602 is provided to achieve multi-point sampling. A gas collection system is also provided, one side of which is connected to the chamber 100 to be tested and the other side is connected to the gas analyzer 400 via an outlet pipe. The system includes a gas outlet composed of multiple sets of geometrically identical flexible Tygon tubes 601, located on the gas outlet 102 side of the chamber 100 to be tested. The other side of the gas outlet is connected to a PVC tube 602. The other end of the PVC tube 602 is connected to the gas analyzer 400 to ensure that the air in the chamber 100 to be tested is evenly transported to the gas analyzer 400.

[0055] In order to realize automated measurement, a control unit is also provided, which receives signals from the gas analyzer 400, the pressure sensor 301, the temperature sensor 302, and the humidity sensor 303, samples them in real time through the control unit, and then controls the tangential blower 500 and the mass flow controller 200 in real time, with the concentration change of a single gas detected by the gas analyzer 400 as the independent variable. When the concentration change is very small or close to the concentration in fresh air, the operation of the tangential blower 500 and the mass flow controller 200 is stopped, and the T-type valve 103 is closed at the same time; the computer stores and displays the data collected and uploaded by the control unit, integrates the data from the gas analyzer 400 and the mass flow controller 200, and draws a fitting exponential curve to find the gas volume of the chamber to be tested 100 under the standard state, and then converts the gas volume under the standard state into the volume of the gas in the chamber to be tested 100 under the current state through the data collected by the pressure sensor 301, the temperature sensor 302, and the humidity sensor 303.

[0056] like Figure 3 As shown, a method applicable to the volume measurement device can be proposed based on the above-mentioned volume measurement device, including the following steps:

[0057] S001: First, a certain amount of carbon dioxide is filled into the chamber 100 to be tested, so that the concentration levels of oxygen and carbon dioxide in the chamber 100 are different from those in fresh air. Before measuring the volume of the chamber, the concentration of each single gas in the mixed gas in the chamber needs to be different from the concentration of the single gas in the filled mixed gas. The concentration difference can be a single gas or a combination of gases. The difference between the concentration of the multiple single gases flowing out of the chamber 100 and the concentration of the corresponding gases in fresh air decreases as the test continues until the concentration of the single gas flowing out of the chamber 100 is consistent with the concentration in fresh air.

[0058] S002, continuously filling fresh air into the chamber to be tested 100 through the mass flow controller 200, and continuously detecting the concentration of oxygen or carbon dioxide flowing out of the chamber through the gas analyzer 400;

[0059] S003, by collecting the flow rate of fresh air flowing into the test chamber 100 and the concentration of oxygen or carbon dioxide flowing out of the test chamber 100, solving the zero-input differential equation to invert the gas volume of the test chamber 100, and then converting the gas volume under the standard state into the volume of the gas in the test chamber 100 under the current state through the data collected by the pressure sensor 301, the temperature sensor 302, and the humidity sensor 303.

[0060] The gas volume in the chamber 100 to be tested is tested using the device of the present invention. The results are as follows: Figure 4 shown; from Figure 4The fitting curve equation is used to obtain the fitting parameters A and C and the chamber gas volume V under the standard state. Then, the gas volume under the standard state is converted into the volume of the gas in the chamber 100 under the current state through the data collected by the pressure sensor 301, the temperature sensor 302, and the humidity sensor 303. The conversion formula is as follows:

[0061]

[0062] in, is the gas volume in the chamber at the current state, 、 are the temperature and pressure of the standard state, and is the water vapor partial pressure, which is equal to RH ,in is the partial pressure of saturated water vapor, which in turn is determined by the volume of gas in the chamber. About the chamber gas volume under standard conditions The formula gives the exact value of the gas volume in the chamber.

[0063] The above embodiments are preferred implementation modes of the present invention and are only used to facilitate the explanation of the present invention. They are not intended to limit the present invention in any form. Any person with ordinary knowledge in the technical field can, without departing from the scope of the technical features of the present invention, make partial changes or modifications to the technical contents disclosed in the present invention and make equivalent embodiments without departing from the technical features of the present invention. Such modifications still fall within the scope of the technical features of the present invention.

Claims

1. A device for measuring the volume of gas in an open chamber, comprising an air inlet and an air outlet of the chamber to be measured, characterized in that: include: A mass flow controller, which is arranged on the air inlet side of the chamber to be tested and is used to detect the flow rate of fresh air flowing into the chamber to be tested; A pressure sensor, a temperature sensor, and a humidity sensor are arranged in the chamber to be tested and are used to detect the pressure, temperature, and relative humidity in the chamber to be tested; A gas analyzer connected to the gas outlet of the chamber to be tested, used to detect the concentration level of oxygen or carbon dioxide in the air leaving the chamber to be tested; A fully mixing mechanism includes multiple groups of tangential fans; the tangential fans are vertically arranged between the air inlet and the air outlet of the chamber to be tested, and the gas blown by the tangential fans collides with the fresh air entering the chamber, and the fresh air and the air in the chamber to be tested are fully mixed before entering the air outlet of the chamber to be tested; The control unit receives signals from the gas analyzer, pressure sensor, temperature sensor, and humidity sensor, samples them in real time, and then controls the tangential blower and mass flow controller in real time; The computer stores and displays the data collected and uploaded by the control unit, integrates the data from the gas analyzer and the mass flow controller, and draws a fitting exponential curve to find the gas volume of the chamber to be tested under the standard state. Then, the gas volume under the standard state is converted into the volume of the gas in the chamber to be tested under the current state through the data collected by the pressure sensor, temperature sensor, and humidity sensor.

2. The device for measuring the volume of gas in an open chamber according to claim 1, wherein: A T-type valve is also provided at the air inlet pipe on the air inlet side of the chamber to be tested. One side of the T-type valve is connected to the mass flow controller through the first blower, so that the real-time flow rate of the fresh air entering is measured by the mass flow controller while the first blower delivers fresh air.

3. The device for measuring the volume of gas in an open chamber according to claim 2, wherein: The device also includes a gas collection system, one side of which is connected to the chamber to be tested and the other side is connected to the gas analyzer through an outlet pipe. The gas collection system includes a gas outlet arranged on the gas outlet side of the chamber to be tested and composed of multiple groups of flexible Tygon tubes with the same geometric shape. The other side of the gas outlet is connected to a polyvinyl chloride tube, and the other end of the polyvinyl chloride tube is connected to the gas analyzer to ensure that the air in the chamber to be tested is evenly transported to the gas analyzer.

4. The device for measuring the volume of gas in an open chamber according to claim 3, wherein: A connecting pipe is also provided on one side of the polyvinyl chloride tube to connect to one end of the chamber to be tested, which is used to balance the pressure of fresh air flowing out of the chamber and the air in the chamber. A second blower is provided in the connecting pipe to control the airflow returning to the chamber to be tested.

5. A method for measuring the volume of gas in an open chamber according to any one of claims 1 to 4, characterized in that: The following steps are involved: S001, first, a certain amount of carbon dioxide is filled into the chamber to be tested, so that the concentration levels of oxygen and carbon dioxide in the chamber to be tested are different from those of fresh air; S002, continuously filling the chamber to be tested with fresh air through a mass flow controller, and continuously detecting the concentration of oxygen or carbon dioxide flowing out of the chamber through a gas analyzer; the difference between the concentration of oxygen or carbon dioxide flowing out of the chamber to be tested and the concentration of the corresponding gas in the fresh air decreases as the detection duration continues, until the concentration of oxygen or carbon dioxide flowing out of the chamber to be tested is consistent with the concentration in the fresh air; S003, by collecting the flow rate of fresh air flowing into the chamber to be tested and the concentration of oxygen or carbon dioxide flowing out of the chamber to be tested, solving the zero-input differential equation to invert the gas volume of the chamber to be tested, and then converting the gas volume under standard conditions into the volume of the gas in the chamber to be tested under current conditions through the data collected by the pressure sensor, temperature sensor, and humidity sensor.

6. The method for measuring the gas volume in an open chamber according to claim 5, characterized in that: In step S003, the zero-input differential equation is: ； in, It is the outflow rate of a single gas, measured by a gas analyzer. is the inflow rate of fresh air, which is set by the mass flow controller. It is the gas flow rate under standard conditions. A and C are fitting exponents, V is the gas volume in the chamber under standard conditions, and t is the time constant.

7. The method for measuring the gas volume in an open chamber according to claim 5, wherein: In step S003, the pressure P, temperature T, and relative humidity RH measured by the pressure sensor, temperature sensor, and humidity sensor are used to correct the above-calculated volume V of the gas in the chamber under the standard state. The correction formula is: ； in, is the gas volume in the chamber at the current state, 、 are the temperature and pressure under standard conditions, is the water vapor partial pressure.

8. The method for measuring the gas volume in an open chamber according to claim 7, characterized in that: Water vapor partial pressure Equal to RH ,in is the partial pressure of saturated water vapor.

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