Gas detection device with air flow buffer

Abstract

The application relates to a gas detection device with airflow buffering, which is composed of a buffer (200), a diaphragm pump (300) and a gas-sensitive sensor (400) in series, can eliminate pressure pulse of the diaphragm pump, and can obtain stable flow for gas sampling and gas analysis.

Description

TECHNICAL FIELD

[0001] The device of the present application relates to the field of gas detection, especially the field of breath detection. BACKGROUND

[0002] Gas detection has been applied to various industries, such as toxic and harmful gas detection, environmental emission gas detection, human exhaled gas detection, etc.

[0003] Most of the gas detection applications use gas pumps for gas sampling and gas analysis. The gas-sensitive sensors used in gas detection need to control the flow of gas. In particular, when sampling and analyzing exhaled gas, a gas pump (such as a diaphragm pump or other types of reciprocating pump) is needed to provide stable gas flow. For example, when sampling nitric oxide from nasal air, the sampling concentration is affected by the air flow of 5mL / s or 10mL / s, and the flow fluctuation needs to be controlled within 10%. When analyzing the gas-sensitive sensor, the analysis flow is usually 1mL / s or 2mL / s, and the flow fluctuation needs to be controlled within 10%, otherwise it will affect the detection accuracy.

[0004] The diaphragm pump (or other types of reciprocating pump) of the prior art works by using a crankshaft to drive a piston to cooperate with a one-way valve to periodically change the volume of the pump cavity to form pressure changes. When working, it will inevitably produce a large pulse pressure fluctuation, and the flow is discontinuous. This pulse pressure will damage the pressure and flow sensors if not handled; it will cause severe discomfort to the subjects in human exhaled gas detection; and it will also adversely affect the detection accuracy of the gas-sensitive sensor.

[0005] To solve the above problems, the prior art usually uses the following two methods to smooth the pressure fluctuation of the diaphragm pump.

[0006] The first method is to use a resistance type buffer (such as an elongated micro tube) in series in the gas circuit to reduce the pressure fluctuation by limiting the gas flow, but at the same time it will bring a large pressure and flow loss to the gas pump.

[0007] The other method is to increase the pressure buffer tank. According to Boyle's law, if you want smaller pressure fluctuations, you need a larger volume, which will increase the dead volume in the gas detection circuit and affect the gas analysis results. SUMMARY

[0008] The present application provides a gas detection device with gas flow buffering, which does not affect the pump flow, does not increase the dead volume, can eliminate the pressure pulse of the diaphragm pump, obtain stable flow, is simple to manufacture, small in size, can be integrated with other breath measurement units, and is especially suitable for the fields of breath sampling and breath analysis under normal pressure.

[0009] The gas detection device with airflow buffer comprises a buffer (200), a diaphragm pump (300) and a gas sensitive sensor (400) connected in series, as shown in the figure. The buffer (200) is composed of a rigid support (220) and an elastic diaphragm (210) and is connected in a sealed manner. The rigid support (220) is provided with at least one air vent (230), and the internal cavity is a buffer cavity (240), as shown in the figure. Figure 1 Figure 3

[0010] The diaphragm pump (300) is used to provide power for the airflow movement of the gas detection device and can provide a flow range of 3 mL / min-3000 mL / min.

[0011] The gas sensitive sensor (400) is used for gas detection of the gas detection device, and the detected gas is human exhaled gas, which is a NO, CO, H2S, H2, CH4 or NH3 sensor.

[0012] The volume of the buffer cavity (240) meets the requirement of the maximum reverse stretching of the elastic diaphragm (210).

[0013] The volume of the buffer cavity (240) is adapted to the output flow of the diaphragm pump (300).

[0014] V m =C d ·Q / v·t (1.1)

[0015] V m is the effective volume

[0016] C d is the flow coefficient, which is related to the temperature, density, particle size and the like of the gas

[0017] Q is the output displacement of the diaphragm pump

[0018] v is the rotation speed of the diaphragm pump

[0019] t is the unit time

[0020] When the influence of the pipeline volume is ignored, the fluctuation elimination efficiency is positively correlated

[0021]

[0022] V L is the stretching volume

[0023] C p is the pressure coefficient, which is related to the vacuum degree of the diaphragm pump

[0024] The formula is derived as follows:

[0025] ​​

[0026] According to the actual application, the pulsation elimination rate K can be up to 99.9%, i.e. the residual pulsation is controlled within 0.1%. In the field of gas detection, the residual pulsation is generally controlled within 10%, i.e. the pulsation elimination rate K=90%.

[0027] According to the Boyle's law V=C / P, the volume of gas is inversely proportional to the pressure of gas, and the volume of the elastic diaphragm and the buffer cavity can offset the corresponding pressure change.

[0028] K=ΔP max1 / ΔP max2 (1.4)

[0029] K is the pulsation elimination rate

[0030] ΔP max1 is the residual peak pressure, i.e. the maximum pressure and the minimum pressure difference after the gas flow through the buffer device

[0031] ΔP max2 is the pulsation peak pressure, i.e. the maximum pressure and the minimum pressure difference of the original gas flow

[0032] In order to achieve a higher pulsation elimination rate, the stretching volume can be taken as 0.1-10 times the effective volume of the pump according to the hardness of the elastic diaphragm.

[0033] Under the given working pressure and the elastic diaphragm area, the maximum stretching volume will reduce the pulsation elimination efficiency.

[0034] The calculation diagram of the deformation of the elastic diaphragm is shown in Figure 5 The thickness of the elastic diaphragm used in the buffer is relatively thin, and the rigidity of the elastic diaphragm when bending can be ignored, that is, the bending does not have any effect on the balance of the elastic diaphragm when the elastic diaphragm is subjected to elastic deformation. The external load of the elastic diaphragm is balanced by the tension in the circular surface, just like a thin film, which is usually called absolutely flexible. The absolutely flexible diaphragm can be regarded as a special case of the general solution of the large deflection shell calculation problem, and the approximate curved surface equation is:

[0035]

[0036] In the formula, W0 is the central deflection of the elastic diaphragm, mm;

[0037] W is the ordinate value of the elastic diaphragm, mm;

[0038] R is the radius of the elastic diaphragm, mm;

[0039] r is the distance from the symmetry axis to the calculation point on the elastic diaphragm, mm.

[0040] The relationship between the pressure difference and the maximum deflection is:

[0041]

[0042] It can be obtained that:

[0043]

[0044] In the formula, Δp is the pressure difference on both sides of the elastic diaphragm, MPa;

[0045] μ is the Poisson's ratio;

[0046] E is the elastic modulus of the material, GPa;

[0047] h is the thickness of the elastic diaphragm, mm.

[0048] The volume surrounded by the elastic diaphragm bending away from the middle position in two directions is:

[0049] V L = πR 2 W0 (1.8)

[0050] The thickness and diameter of the elastic diaphragm are selected, and the pressure value Δp that can be offset is calculated.

[0051] The elastic diaphragm (210) used in the application is used as a pressure damping device, and the elastic diaphragm (210) is used to absorb pressure fluctuations by stretching and shrinking. When the pressure in the gas pipeline rises, the elastic diaphragm (210) on the device is stretched under force, which can weaken the positive pressure pulse; when the pressure in the gas pipeline drops, the elastic diaphragm (210) shrinks or is reversely stretched, which can weaken the negative pressure pulse. When the diaphragm size and hardness are reasonably designed, a better buffering effect can be achieved.

[0052] The elastic diaphragm (210) is made of an elastic polymer material, which can be selected from silicone, fluororubber, PE film, PVC film, etc.

[0053] The elastic diaphragm (210) can be sealed by ultrasonic welding, hot melting, a sealing ring, or pressure bonding according to the material.

[0054] Further, the buffer (200) and the diaphragm pump (300) can also exchange positions, and the buffer (200) is arranged at the rear end of the diaphragm pump (300). The buffer (200) can also be connected to the front end or the rear end of the diaphragm pump (300) in parallel flow.

[0055] The prior art diaphragm pump (or other type of reciprocating pump) works by using a crankshaft to drive a piston to cooperate with a one-way valve to periodically change the volume of the pump cavity to form pressure changes, so there are pressure pulses at the gas inlet and gas outlet, and there are large fluctuations in flow. The buffer device of the present application is arranged at the front end or rear end of the diaphragm pump, which can effectively solve the pressure pulse and obtain stable flow, thereby improving the accuracy of gas detection.

[0056] These and other features will become more apparent from the following detailed description in conjunction with the accompanying drawings and claims. BRIEF DESCRIPTION OF DRAWINGS

[0057] Figure 1 . Device block diagram of the present application.

[0058] Figure 2 . Side flow type gas flow buffer device block diagram of the present application.

[0059] Figure 3 . Main flow type buffer structure schematic diagram of the present application.

[0060] Figure 4 . Side flow type buffer structure schematic diagram of the present application.

[0061] Figure 5 . Elastic diaphragm deformation calculation diagram of the buffer of the present application.

[0062] Figure 6 . Specific embodiment 1 schematic diagram of the present application.

[0063] Figure 7 . Pressure comparison curve change diagram of the buffer installed in specific embodiment 1 of the present application.

[0064] Figure 8 . Flow comparison curve change diagram of the buffer installed in specific embodiment 1 of the present application.

[0065] Figure 9 . Specific embodiment 2 schematic diagram of the present application. DETAILED DESCRIPTION Specific embodiment one:

[0067] This embodiment uses Figure 1 The device structure shown is composed of a buffer (200), a diaphragm pump (300), and a gas sensitive sensor (400) in series, adopts a main flow type buffer scheme, and the buffer structure is as shown in Figure 3 , which is composed of a rigid support body (220) and an elastic diaphragm (210), wherein the rigid support body (220) is provided with two air vents, and the internal cavity is a buffer cavity (240). The elastic diaphragm (210) is tightly sealed by a sealing ring (250), as shown in Figure 6The rigid support (220) is made of PC which has good rigidity and toughness, the elastic diaphragm (210) is made of silica gel, and the diaphragm pump (300) is selected from the 2002 series of Thomas.

[0068] μ is Poisson's ratio, 0.48;

[0069] E is the elastic modulus of the material, 1.2 GPa;

[0070] h is the diaphragm thickness, 0.15 mm;

[0071] R is the diaphragm radius, 10 mm;

[0072] Q is the output displacement of the diaphragm pump, 0.1 mL / r;

[0073] v is the diaphragm pump speed, 3000 r / min;

[0074] t is the unit time, 1 min;

[0075] The vacuum degree of the diaphragm pump is 36%;

[0076] The gas involved in the device is the ideal gas under the conventional pressure, and it is assumed that the pipeline is a smooth circular inlet flow coefficient C d =1.0, and the pressure coefficient is C p =0.36;

[0077] According to the above formula, the calculation can be carried out:

[0078]

[0079] V L =πR 2 W0

[0080] The equation set can be calculated to obtain W0, and then substituted into the formula of the pressure value Δp to calculate:

[0081]

[0082] As can be calculated above, the pressure difference that can be eliminated is 193 Pa.

[0083] According to the above design, the device model is processed, and the actual measurement of the output flow and pressure of the diaphragm pump without buffer and with buffer is compared, and the actual test results are shown in Figure 8 and Figure 9 .

[0084] ΔP max1 The residual peak pressure average is 29 Pa, and ΔP max2The average of the fluctuation peak pressure is 198 Pa, the measured result is that the elimination of Δp is 169 Pa, and after the buffer of the device is used, the pressure pulse of the diaphragm pump can be effectively reduced, and stable flow is obtained. Specific embodiment two:

[0086] This embodiment uses Figure 2 The device structure is composed of a buffer (200), a diaphragm pump (300) and a gas-sensitive sensor (400), the buffer adopts a bypass flow buffer scheme, the buffer structure is as shown in Figure 4 The buffer (200) is sealed and connected by ultrasonic welding, and the rigid support body (220) is provided with an air vent connected with the front end of the diaphragm pump (300), and the internal cavity is a buffer cavity (240). The buffer (200) is used as a bypass flow buffer, and the buffer cavity structure is designed to be appropriate, so that the volume of the buffer cavity (240) meets the requirement of the maximum reverse stretching of the elastic diaphragm (210), and is adapted to the output flow of the diaphragm pump (300), so that the pressure pulse of the diaphragm pump (300) can be buffered, and stable flow can be obtained.

[0087] Compared with the mainstream buffer, the calculation method of the bypass flow buffer is the same as that of the mainstream buffer. Since the bypass flow buffer needs to pass through the pipeline to reach the buffer cavity of the buffer, there is a temporary deviation between the device and the main gas path, so a stable time is needed when the device is started. The stable time required in this embodiment is 2s.

[0088] The rigid support body (220) is made of a high polymer material PC with good rigidity and toughness, the elastic diaphragm (210) is made of PE material, and the diaphragm pump (300) is selected from the 3003 series of Thomas.

[0089] μ is the Poisson ratio, 0.377;

[0090] E is the elastic modulus of the material, 1.07 GPa;

[0091] h is the diaphragm thickness, 0.1 mm;

[0092] R is the diaphragm radius, 10 mm;

[0093] Q is the output displacement of the diaphragm pump, 1 mL / r;

[0094] v is the diaphragm pump speed, 3000 r / min;

[0095] t is the unit time, 1 min;

[0096] The vacuum degree of the diaphragm pump is 38%;

[0097] The gas involved in the device is the ideal gas under normal pressure, and it is assumed that the pipeline is a smooth circular inlet flow coefficient C d = 1.0, and the pressure coefficient is C p = 0.38.

[0098] According to the above formula, the calculation can be carried out:

[0099]

[0100] V Ｌ = πR 2 W0

[0101] The simultaneous equations can be calculated to obtain W0, and then substituted into the formula of the pressure value Δp to calculate:

[0102]

[0103] As can be calculated above, the pressure difference that can be eliminated is 124 Pa.

[0104] The gas sensitive sensor (400) of the embodiment is a NO sensor. The response results of the NO sensor to a 60 ppb NO standard gas bag are compared by repeated tests when no buffer is added and when the buffer is added, and the comparison results are as follows:

[0105] 60 ppb NO test results / ppb No buffer Increased buffer 1# 58.5 59.5 2# 59.1 60.1 3# 57.8 59.3 4# 60.1 59 5# 62.8 60.3 6# 60.8 60.1 7# 63.2 61.1 8# 58.9 59.3 9# 57.9 59.9 10# 56.6 58.9 Mean 59.6 59.8 Relative standard deviation 3.6％ 1.1％

[0106] The actual measurement results show that after the buffer of the device is used, the pressure pulse of the diaphragm pump can be effectively reduced, and stable flow can be obtained, thereby improving the accuracy of gas detection. Specific embodiment three:

[0108] The device of the application can be further integrated, as shown in Figure 9 In the gas analysis device, an elastic diaphragm (210) is used to seal one side of the buffer (200), a diaphragm pump (300) is installed on the left side of the buffer (200), a one-way valve (500) and a gas sensitive sensor (400) are installed on the gas outlet on the right side of the buffer (200), and a flow sensor (100) can be installed at the exhalation inlet on the top for detecting the flow of exhaled gas; during exhalation test, gas is blown into the buffer (200) and is exhausted through the one-way valve, the buffer (200) has two functions, namely, gas storage and flow buffering; the flow sensor monitors the flow during the entire exhalation process; after sampling is completed, the analysis mode is entered, the diaphragm pump (300) is started to draw the gas in the buffer (200) into the gas sensitive sensor (400) for analysis; during the entire analysis process, the elastic diaphragm (210) can eliminate the pressure pulse of the diaphragm pump and obtain stable flow.

[0109] The invention is not limited to the embodiments shown and described, but any variations and modifications are within the scope of the appended claims.

Claims

1. A gas detection device with air flow buffering, comprising a buffer (200), a diaphragm pump (300) and a gas sensitive sensor (400) connected in series, characterized in that: The buffer (200) is composed of a rigid support (220) and an elastic diaphragm (210) and is sealedly connected, the rigid support (220) is provided with at least one air vent (230), and the internal cavity is a buffer cavity (240); The volume of the buffer cavity (240) meets the requirement of the maximum reverse stretching of the elastic diaphragm (210) and is adapted to the output flow of the diaphragm pump (300); V L = πR 2 W0 (2) V m effective volume C d for the flow coefficient Q is the output displacement of the diaphragm pump V is the rotating speed of the diaphragm pump T is the unit time V L to stretch the volume C P For the pressure coefficient W0 is the central deflection of the elastic diaphragm The value of W0 is obtained by bringing (2) into (1) In the formula, ΔP is the pressure difference between the two sides of the elastic diaphragm, MPa; μ is the Poisson's ratio; E is the elastic modulus of the material, GPa; h is the thickness of the elastic diaphragm, mm, The value of ΔP is calculated by bringing W0 into (3).

2. The gas detection device with airflow buffering of claim 1, wherein: The material of the elastic diaphragm (210) is an elastic polymer material, which is silicone, fluororubber, PE film or PVC film.

3. The gas detection device with airflow buffering of claim 1, wherein: The elastic diaphragm (210) and the rigid support (220) are sealed by pressure bonding, glue sealing, sealing ring or ultrasonic process.

4. The gas detection device with airflow buffering of claim 1, wherein: The diaphragm pump (300) is used for providing airflow movement power for the gas detection device and can provide a flow range of 3 mL / min-3000 mL / min.

5. The gas detection device with airflow buffering of claim 1, wherein: The gas sensitive sensor (400) is used for gas detection and can detect the exhaled gas of a human body and is a NO, CO, H2S, H2, CH4 or NH3 sensor.

6. The gas detection device with airflow buffering of claim 1, wherein: The buffer (200) has two structures of a main flow type buffer and a side flow type buffer.

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