An ultra-low concentration fast switching dynamic gas distribution system

Abstract

The application discloses a kind of ultra-low concentration fast switching dynamic gas distribution systems, including liquid source or gas source (10), background gas (20, 30), vacuum generator (11), pressure and flow controller (12), microfluidic flow sensor (14), microfluidic chip (15), gasification chamber (40), mixed gas tank (50), mass flow controller (22, 32), detection chamber (60), purging device (61), sensor (63), data acquisition device (70), multiple valves and pipeline for gas transmission between components;Background gas (20) is dilution gas, mixed with gas source or liquid source to become target gas;Background gas (30) is purging gas, and target gas is alternately circulated and switched in detection chamber (60), while, purging device (61) carries out rapid purging to gas;Data acquisition device (70) acquires data, so as to study the response and recovery characteristics of the sensor (63).

Description

TECHNICAL FIELD The present application relates to the field of gas concentration ratio, in particular to a dynamic gas mixing system with ultra-low concentration and fast switching. BACKGROUND

[0001] With the development of science and technology, it is particularly important to configure a certain concentration of gas in the field of sensor research. The most commonly used gas mixing method is to mix two different flow rate range mass flow controllers (MFCs). By selecting a reasonable gas source concentration and mass flow controller (MFC), continuous variable low concentration gas mixing can be achieved. This method can only be used to mix gas sources (such as CO, H2, etc.), and the mixing concentration is mostly in the ppb to ppm level. In order to further reduce the mixing concentration, a secondary dilution method can be used, that is, the configured gas is used as a gas source, and a background gas is added for secondary dilution. This method can further reduce the concentration, but the equilibrium time will be long, and it can only reach about 0.1 ppb level. The above methods cannot configure liquid sources (such as ethanol, methanol, toluene, etc.). If it is necessary to mix low-concentration gas of liquid source, a microcontroller is usually used to push out the liquid at a speed of several microliters per minute, and the needle position is heated and temperature-controlled to evaporate and generate a gas source. This method is limited by the precision of the microcontroller, and the mixing concentration is usually in the ppb level.

[0002] Nowadays, more attention is paid to the research of ultra-low concentration gas, such as respiratory gas and explosive gas, and many other ultra-low concentration gas environments. It is known that there are thousands of VOCs in exhaled gas, most of which are in the picomolar (10 -12 mol / L) or ppt (parts per trillion) level. The existing gas mixing method cannot meet the research of such concentration gas, therefore, it is of great practical significance to provide a dynamic gas mixing system with high precision, ultra-low concentration, fast mixing speed, and fast, efficient and stable dynamic gas mixing system and method. SUMMARY

[0003] In order to solve the problems existing in the prior art, the purpose of the present application is to provide a dynamic gas mixing system with ultra-low concentration and fast switching. Through a complete gas mixing process, the concentration of gas source or liquid source is diluted to ultra-low concentration, i.e. below ppt (10 -12 ) level; by alternatingly controlling the opening and closing of the electromagnetic valves on the two gas inlet paths of the detection chamber, the target gas and the background gas are quickly and circularly switched between the sweeping gas, and the frequency of the sweeping device in the detection chamber is adjusted to control the speed of the gas flow to the sensor.

[0004] The application discloses a kind of ultra-low concentration fast switching dynamic gas distribution systems, including: liquid source or gas source, background gas, background gas purge gas, vacuum generator, pressure and flow controller, microfluidic chip, gasification chamber, mixed gas tank, microfluidic flow sensor, mass flow controller, detection chamber, purging device, sensor, data acquisition device, multiple valves and the pipeline for gas transmission between each component;Microfluidic chip outlet is equipped with gasification chamber;Mixed gas tank is used to mix background gas and gas source gas;Detection chamber is provided with purging device and sensor to be researched inside.The background gas is used as diluent gas, and is used as purge gas, and the flow of the two gases is controlled by mass flow controller;Background gas diluent gas and gas source or liquid source are mixed uniformly in mixed gas tank to become target gas;Detection chamber has two gas inlets and one gas outlet, and is provided with purging device and sensor to be researched inside;Two gas inlets are connected with background gas purge gas and target gas two-way inlet gas flow respectively, and the gas outlet is used to discharge the gas in the detection chamber;By the on-off of electromagnetic valve on two-way inlet gas path by alternating circulation control, the rapid circulation switching between the two gases is realized, the frequency of purging device is adjusted to control the speed of gas flow to sensor;Meanwhile, data acquisition device is used to collect data, so that the response and recovery characteristics of the sensor are researched.

[0005] Further, the bottom of the gasification chamber has a temperature control chip and a temperature sensor, and the surrounding has a heat preservation and insulation layer, and the liquid is vaporized by controlling the heating temperature.

[0006] Further, the pressure and flow controller and the microfluidic flow sensor form a closed loop PID control flow, to realize the continuous gas distribution of pL / min small flow.

[0007] Further, the microfluidic chip is sealed and assembled by a polydimethylsiloxane (PDMS) layer, a top frame and a bottom frame, a Y-shaped channel is processed on the polydimethylsiloxane (PDMS) profile, and the channel can pass liquid and gas.

[0008] Further, the PDMS layer of the microfluidic chip is prepared by soft etching technology and replication molding technology, a customized master plate, a PDMS elastomer and a curing agent are mixed, then the mixture is poured on a patterned mold and baked, and finally, the cured PDMS is peeled off from the master mold.

[0009] Further, the Y-shaped channel of the PDMS layer of the microfluidic chip can control the volume of 10 -9 ~10 -18 L gas or liquid in and out, the channel of inlet and outlet is formed by Y-shaped channel punched in the PDMS layer by hand puncher and polydimethylbenzene layer covered on the PDMS layer.

[0010] Further, the microfluidic chip is assembled by sealing the PDMS layer with a customized top frame and bottom frame, the top frame has inlet / outlet holes, small steel pipes are inserted into the inlet / outlet holes to connect the Y-shaped channels of the PDMS layer, the small steel pipes exposed outside the top frame are connected with polyethylene plastic pipes, and the polyethylene plastic pipes can be connected with gas or liquid.

[0011] Further, the detection chamber has two gas inlets and one gas outlet, and is internally provided with a purging device and a sensor to be studied, the on-off of electromagnetic valves on the two gas inlet channels is adjusted in an alternating cycle, the rapid cycle switching between the target gas and the background gas purging gas is realized, and the frequency of the purging device is adjusted to control the speed of the gas flow to the sensor.

[0012] The application also provides a dynamic gas mixing method for ultra-low concentration and rapid switching, which is composed of a gas source channel and a background gas channel; wherein the background gas channel is divided into two channels, one of which is used as a dilution gas, and the other is used as a purging gas; during gas mixing, a vacuum generator is used to vacuumize the gas source channel, a liquid source or a gas source is connected to the gas source channel, and a pressure and flow controller is used to control the flow of the liquid source or the gas source; the liquid gas source flows out of the microfluidic chip and enters the gasification chamber, and after being vaporized in the gasification chamber, it enters the gas mixing tank to mix with the background gas dilution gas to become the target gas; the gas gas source directly enters the gas mixing tank to mix with the background gas dilution gas to become the target gas; the detection chamber has two gas inlets and one gas outlet, and is internally provided with a purging device and a sensor to be studied, the two gas inlets are respectively connected with the background gas purging gas flow and the target gas flow, the gas outlet is used to discharge the gas in the detection chamber, the on-off of electromagnetic valves on the two gas inlet channels is adjusted in an alternating cycle, the rapid cycle switching between the target gas and the background gas purging gas is realized, and the frequency of the purging device is adjusted to control the speed of the gas flow to the sensor; at the same time, data is collected through a data acquisition device, so as to study the response and recovery characteristics of the sensor. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 A schematic diagram of a dynamic gas mixing system for ultra-low concentration and rapid switching according to the present application is shown;

[0014] Figure 2 A schematic diagram of a microfluidic chip structure according to the present application is shown;

[0015] Figure 3 A schematic diagram of a background gas purging gas and target gas switching channel according to the present application is shown. DETAILED DESCRIPTION

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0017] The purpose of this invention is to provide a dynamic gas mixing system for rapid switching at ultra-low concentrations, which dilutes the concentration of a gas or liquid source to an ultra-low concentration (ppt, 10) through a single complete gas mixing process. -12 (Level) and below; by alternately and cyclically controlling the on / off state of the solenoid valves on the two intake air lines of the detection chamber, the target gas and background gas purge gas can be rapidly switched in a cycle, and the frequency of the purging device can be adjusted to control the speed of the airflow towards the sensor.

[0018] Figure 1 The present invention discloses a schematic diagram of a dynamic gas mixing system for rapid switching of ultra-low concentration. The dynamic gas mixing system for rapid switching of ultra-low concentration includes a liquid source or gas source (10), a vacuum generator (11), a pressure and flow controller (12), a background gas (20), a background gas purge gas (30), a microfluidic flow sensor (14), a microfluidic chip (15), a vaporization chamber (40), a mixing tank (50), a first mass flow controller (22), a second mass flow controller (32), solenoid valves (13, 16, 17, 21, 31, 33, 51, 62), a detection chamber (60), a purging device (61), a sensor (63), a data acquisition device (70), and gas pipelines for connecting the components.

[0019] Figure 2 The diagram shows the structure of a microfluidic chip (15), which is assembled from a polydimethylsiloxane (PDMS) layer, a top frame, and a bottom frame. Y-shaped channels are fabricated on the PDMS profile, allowing the passage of liquids and gases. The PDMS layer is fabricated using soft etching and replication molding techniques. A customized master mold, PDMS elastomer, and curing agent are mixed, and the mixture is poured onto a patterned mold and baked. Finally, the cured PDMS is peeled off from the master mold. The PDMS layer of the microfluidic chip (15) has Y-shaped channels (optionally, for example, 2 mm wide and 1 mm deep), enabling 10... -9 ~10 -18L. Gas or liquid enters and flows out. In order to form a channel with an inlet and an outlet, a Y-shaped channel is punched in the PDMS layer with a handheld punch and a polyxylene layer is covered on the PDMS layer. The assembly of the microfluidic chip (15) uses a customized top and bottom frame to seal the PDMS layer. The top frame has inlet / outlet holes. A small steel tube is inserted at the inlet / outlet holes to connect it to the Y-shaped channel of the PDMS layer. The part of the small steel tube exposed outside the top frame is connected to a polyethylene plastic tube. Gas or liquid flows into the microfluidic chip from the inlet and then flows out from the outlet.

[0020] During gas mixing, the vacuum generator (11) evacuates the gas path containing the gas source or liquid source (10). The liquid source or gas source (10) is connected to the pressure and flow controller (12), and there is a closed-loop PID control between the pressure and flow controller (12) and the microfluidic flow sensor (14). A constant fluid flow rate or a predefined fluid flow rate is set in the software, and the pressure and flow controller (12) automatically adjusts according to the output pressure value to maintain the set fluid flow rate. When pressure is applied to the fluid, the fluid passes through the first solenoid valve (13) and the microfluidic flow sensor (14) into the microfluidic chip (15), and then flows out from the outlet of the microfluidic chip (15). If it is a liquid source, it flows out from the outlet of the microfluidic chip (15) and enters the vaporization chamber (40) through the fourth solenoid valve (16). After being rapidly vaporized in the vaporization chamber (40), it enters the mixing tank (50) and mixes with the background gas (20) to become the target gas. If it is a gas source, it flows out from the outlet of the microfluidic chip (15) and enters the mixing tank (40) directly through the fifth solenoid valve (17) to mix with the background gas (20) to become the target gas.

[0021] The vaporization chamber (40) contains a temperature control chip and a temperature sensor, and is surrounded by a heat insulation layer. To accelerate the rapid evaporation and vaporization of the liquid, the chip is heated to a specific temperature to speed up the liquid's evaporation process. The liquid flows out from the microfluidic chip (15) and immediately enters the vaporization chamber (40) through the fourth solenoid valve (16). When the sample is injected into the hot zone, it vaporizes instantly and quickly enters the mixing tank. The requirements for the vaporization chamber are that it should have a large heat capacity, a sufficiently high temperature, and a small volume with no dead corners to prevent sample diffusion, reduce dead volume, and improve efficiency.

[0022] The background gas is divided into two paths: one is dilution gas, and the other is purge gas. The background gas dilution gas (20) is used as dilution gas. It passes through the second solenoid valve (21) and the first mass flow controller (22) and is mixed with the gas source or liquid source (10) in the mixing tank (40) to become the target gas. The first mass flow controller (21) controls the flow rate of the background gas dilution gas (20). The background gas purge gas (30) is used as purge gas. There is a third solenoid valve (31) and a second mass flow controller (32) in the gas path. This gas is used to purge the target gas out of the detection chamber. The first and second mass flow controllers (22, 32) in the dilution gas path and the purge gas path are connected to the intelligent control device, which can accurately control the gas flow rate according to the user settings and display the flow rate value in real time.

[0023] Figure 3 The diagram shows the rapid switching between background purge gas (30) and target gas. The detection chamber (60) has two air inlets and one air outlet, and contains a gas purging device (61) and a sensor (63). The two air inlets are located above the gas purging device (61). Optionally, the two air inlets are symmetrically distributed on both sides of the central axis of the purging device (61), and the purging device (61) is placed above the sensor (63). The purging device (61) is an AC-controlled frequency-adjustable miniature fan. When the fan rotates, it generates pressure on the gas in the detection chamber, causing the airflow to flow towards the sensor. The frequency range is 1 to 80 Hz, and the speed at which the gas flows towards the sensor (63) is controlled by adjusting the frequency. Two air inlets are connected to the background purge gas (30) and the target gas, respectively. The sixth and seventh solenoid valves (33, 51) are installed on the two air inlets, and the eighth solenoid valve (62) is installed at the air outlet. By alternately controlling the opening and closing of the solenoid valves on the two air inlets, the two air inlets flow into the detection chamber (60) continuously and stably according to the time sequence. The frequency of the purge device (61) is adjusted to control the speed of the airflow to the sensor (63). The opening and closing of the eighth solenoid valve (62) is controlled to discharge the gas in the detection chamber. At the same time, the sensor values ​​are collected by the data acquisition device (70) to study the response and recovery characteristics of the sensor (63).

[0024] A dynamic gas mixing method for rapid switching at ultra-low concentrations includes the following steps:

[0025] In the first step, when mixing the gas, the vacuum generator (11) is used to evacuate the gas path through which the source gas passes. According to the gas mixing concentration, the flow rate value is input in the software. The microfluidic flow sensor (14) monitors the actual flow rate value and feeds back the monitoring value to the pressure and flow controller (12). The pressure and flow controller (12) maintains the flow rate of the gas source or liquid source through closed-loop PID control with the microfluidic flow sensor (14).

[0026] The second step is to configure target gases of different concentrations of the same gas, and then configure the order of dilution gas concentrations according to user requirements, and set the flow rate of the gas source or liquid source.

[0027] In the third step, the gas source or liquid source (10) enters the microfluidic chip (15) through the first solenoid valve (13) and the microfluidic flow sensor (14), and enters the mixing tank (50) through the gas pipeline or vaporization chamber (40) to be fully mixed with the background gas dilution gas (20). The target gas after mixing is discharged from the outlet of the mixing tank (50) and enters the detection chamber (60) through the solenoid valve (51) to react with the gas sensor (62).

[0028] In the fourth step, within the detection chamber (60), the sixth and seventh solenoid valves (33, 51) on the two intake air paths are alternately and cyclically adjusted to achieve rapid cyclic switching between the target gas and the background purge gas (30). The speed of the airflow to the sensor (63) is controlled by adjusting the frequency of the purging device (61), and the gas in the detection chamber is discharged by controlling the opening and closing of the eighth solenoid valve (62). At the same time, the data of the sensor is collected by the data acquisition device (70) to study the response and recovery characteristics of the sensor (61).

Claims

1. A dynamic gas distribution system for rapid switching at ultra-low concentrations, comprising: The system includes a liquid or gas source, background gas, a vacuum generator, pressure and flow controllers, a microfluidic chip, a vaporization chamber, a mixing tank, a microfluidic flow sensor, a mass flow controller, a detection chamber, a purging device, a sensor, a data collection device, multiple valves, and piping for gas transfer between components. A vaporization chamber is located at the outlet of the microfluidic chip. The background gas is simultaneously connected to two gas paths: one for dilution and the other for purging, with both flow rates controlled by the mass flow controller. The background gas and dilution gas are uniformly mixed with the gas or liquid source in the mixing tank to form the target gas. The detection chamber has two inlets and one outlet, and houses the purging device and the sensor under study. The two inlets are connected to the background gas source and the vacuum generator. The system employs two intake airflows: a purge gas and a target gas. Data is collected via a data acquisition device while the two gases are alternately switched and the purge speed is controlled. This allows for the study of the sensor's response and recovery characteristics. The vaporization chamber has a temperature control chip and a temperature sensor at its bottom, surrounded by a thermal insulation layer. Liquid vaporization is achieved by controlling the heating temperature. A closed-loop PID control flow is formed between the pressure and flow controller and the microfluidic flow sensor, enabling continuous gas distribution at a low flow rate of pL / min. The microfluidic chip is assembled from a polydimethylsiloxane (PDMS) layer, a top frame, and a sealed bottom frame. Y-shaped channels are machined into the PDMS profile, allowing both liquid and gas to pass through.

2. The ultra-low concentration rapid switching dynamic gas distribution system as described in claim 1, wherein the PDMS layer of the microfluidic chip is prepared using soft etching technology and replication molding technology, wherein a customized master board, PDMS elastomer and curing agent are mixed, the mixture is then poured onto a patterned mold and baked, and finally, the cured PDMS is peeled off from the master mold.

3. The ultra-low concentration rapid switching dynamic gas distribution system as described in claim 2, wherein the Y-shaped channel of the PDMS layer of the microfluidic chip can control a volume of 10 -9 ~10 -18 A channel for gas or liquid to enter and exit, an inlet and an outlet, is formed by punching Y-shaped channels in the PDMS layer with a handheld punch and covering the PDMS layer with a polyxylene layer.

4. The ultra-low concentration rapid switching dynamic gas distribution system as described in claim 2, wherein the microfluidic chip is assembled by sealing the PDMS layer with a customized top and bottom frame, the top frame has inlet / outlet holes, a small steel tube is inserted at the inlet / outlet holes to connect it to the Y-shaped channel of the PDMS layer, the part of the small steel tube exposed outside the top frame is connected to a polyethylene plastic tube, which can allow gas or liquid to pass through.

5. The dynamic gas distribution system for rapid switching at ultra-low concentrations as described in claim 1, characterized in that, The rapid switching between the target gas and the background gas purge gas is achieved by alternately adjusting the on / off state of the solenoid valves on the two intake gas lines, and adjusting the frequency of the purging device to control the speed of the airflow towards the sensor.

6. The dynamic gas distribution method for a dynamic gas distribution system with rapid switching at ultra-low concentrations as described in any one of claims 1-5, comprising a gas source gas path and a background gas path; wherein, The background gas path is divided into two paths: one is used as dilution gas, and the other is used as purge gas. During gas mixing, a vacuum generator is used to evacuate the gas source path, and a liquid or gas source is connected to the gas source path. Pressure and flow controllers control the flow rate of the liquid or gas source. The liquid gas source flows out of the microfluidic chip and into the vaporization chamber. After being vaporized in the vaporization chamber, it enters the mixing tank and mixes with the background gas dilution gas to become the target gas. The gas source flows out of the microfluidic chip directly into the mixing tank and mixes with the background gas dilution gas to become the target gas. The detection chamber has two air inlets and one air outlet. It is equipped with a purging device and the sensor to be studied. The two air inlets are connected to the background gas purge gas flow and the target gas flow, respectively. By rapidly switching between the target gas and the background gas purge gas and controlling the airflow rate, data is collected through a data acquisition device to study the response and recovery characteristics of the sensor.

7. In the dynamic gas distribution method as described in claim 6, the rapid cyclic switching between the target gas and the background gas purge gas is achieved by alternately and cyclically adjusting the on / off state of the solenoid valves on the two intake gas paths, and adjusting the frequency of the purge device to control the speed of the airflow towards the sensor.

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