An underwater dissolved CO2 in-situ sensor based on liquid phase response speed enhancement strategy

Abstract

The present invention relates to the technical field of detection equipment, and specifically to an underwater dissolved CO2 in-situ sensor based on a liquid phase response speed enhancement strategy. The liquid phase response speed enhancement strategy in the system includes designing an optical gas chamber with minimized internal volume and gas resistance, using a deep-sea turbine pump to continuously and quantitatively flush the wet side of the membrane, and using a strategy of high partial pressure difference and high gas pressure difference on both sides of the membrane; the optical gas chamber adopts a hollow-core optical fiber design to serve as a place for light and matter to interact. The underwater dissolved CO2 in-situ sensor with a liquid phase response speed of seconds based on the liquid phase response speed enhancement strategy increases the flux of dissolved gas molecules on the wet side of the membrane, enhances the membrane permeation efficiency, and weakens the memory effect. Based on this strategy, a set of underwater dissolved CO2 in-situ sensors with a liquid phase response speed of seconds is developed. The present invention achieves a large dynamic detection range and high precision by using the method of matching strong and weak absorption lines and carrier gas dilution.

Description

Technical Field

[0001] The present invention relates to the technical field of detection equipment, and in particular to an underwater dissolved CO2 in-situ sensor based on a liquid phase response speed enhancement strategy, specifically an ultrafast response high-precision dissolved CO2 in-situ sensor for underwater mobile detection. Background Art

[0002] In-situ detection of dissolved gases in hydrothermal and cold seep plumes based on underwater vehicles is of great significance in the field of biogeochemistry. At present, the detection of deep-sea cold seeps can only rely on in-situ mobile detection by underwater vehicles or sampling with water samplers and laboratory analysis. The dynamic range of dissolved CO2 concentration in cold seep and hydrothermal areas can be from 10 2 ppmv to 10 4 The concentration of CO2 in the plume is in the ppmv range, and the plume has a drastic concentration boundary with the surrounding seawater. The large concentration variation range, drastic spatial variation, and underwater mobile detection method pose great challenges to the detection performance of the sensor, requiring the sensor to have a fast response capability and a large dynamic measurement range while ensuring high detection accuracy. The in-situ CO2 sensors reported so far are difficult to meet the requirements in terms of response speed, detection accuracy, and dynamic detection range.

[0003] First, the response speed of existing sensors cannot meet the requirements of underwater mobile detection, and cannot effectively characterize the rapid response of the ocean. At present, most of the reported in-situ gas sensors are based on permeable membrane degassing technology, with a liquid phase response speed of several minutes. This is unfavorable in deep-sea in-situ detection based on underwater vehicles, which will result in too low data point density and spatiotemporal resolution of the obtained in-situ data. Moreover, this effect will be more obvious in underwater mobile detection, with the potential risk of undersampling. In general, the low degassing efficiency of the permeable membrane and the insufficient exchange of gas samples in the detection chamber are the decisive reasons for the slow liquid phase response speed of the system.

[0004] On the one hand, the internal volume of the detection gas chamber, the additional "dead zone" volume (which exists but does not participate in the interaction between light and matter, including the inlet and outlet pores and the buffer pool), and the gas resistance of the gas path will hinder the exchange of gas samples in the gas path, causing the exchange efficiency of gas samples in the light path to be too slow and insufficient. The three factors are determined by the gas path structure of the sensor, and together they cause the "memory effect" of the gas path, which has a negative effect on the gas phase response of the sensor.

[0005] On the other hand, the low degassing efficiency of the permeable membrane (between membranes) and the insufficient dissolved gas flux on the wet side of the membrane combined to lead to insufficient sampling capacity of the system, resulting in slow liquid phase response of the sensor.

[0006] The former is determined by the mechanism of membrane degassing technology. Permeable membrane degassing is based on the classic free diffusion membrane mass transfer method (passive transfer of components from high chemical potential to low chemical potential). This method can achieve accurate detection of separated gases in in-situ detection, but at the cost of longer response time (usually on the order of ten minutes, which is difficult to meet the requirements of deep-sea mobile detection). The response speed of all in-situ gas sensors based on permeable membranes is largely restricted by the slow inter-membrane mass transfer process between the gas and liquid phases.

[0007] The latter is determined by the flow rate and working direction of the water sample on the wet side of the membrane. Generally speaking, a higher flow rate means a larger dissolved gas flux on the wet side of the membrane, which means a larger inter-membrane mass transfer coefficient, but in some cases the "concentration polarization phenomenon" on the wet side of the membrane may hinder the rapid transmission of gas molecules. Combining the above two aspects: the degassing capacity of the sampling part occupies a major position in limiting the liquid phase response speed of the system, but after this part is greatly improved, the "memory effect" of the gas path part will gradually replace the limitation of the system degassing capacity and become the main control factor.

[0008] Secondly, for sensors, higher detection sensitivity and larger dynamic measurement range are two contradictory parameters, and it is difficult to achieve both. Under the parameters of ensuring high detection accuracy, the system often experiences absorption saturation when the concentration is high, making it difficult to achieve a larger dynamic detection range. Summary of the invention

[0009] In view of this, in order to solve the limitation of the response speed of the traditional membrane degassing-based sensor, this paper proposes a liquid phase response speed enhancement strategy. Based on this strategy, a set of underwater dissolved CO2 in-situ sensors with a liquid phase response speed of seconds is developed in three aspects: increasing the dissolved gas molecule flux on the wet side of the membrane, enhancing the membrane permeation efficiency, and weakening the memory effect.

[0010] To achieve the above objectives, the embodiments of the present invention provide the following technical solutions:

[0011] In the first aspect, in an embodiment provided by the present invention, an underwater dissolved CO2 in-situ sensor based on a liquid phase response speed enhancement strategy is provided, wherein the liquid phase response speed enhancement strategy includes designing an optical gas chamber with minimized internal volume and gas resistance, using a deep-sea turbine pump to continuously and quantitatively flush the wet side of the membrane, and using a strategy of high partial pressure difference and high gas pressure difference on both sides of the membrane; the optical gas chamber adopts a hollow core optical fiber design to serve as a place for interaction between light and matter.

[0012] As a further solution of the present invention, in the optical gas chamber, the degassing amount of the Teflon film used is about 1.0-2.0 sccm, and according to the 1:1 carrier gas dilution ratio, the optimal gas chamber internal volume is 33.3-66.7 μL.

[0013] As a further solution of the present invention, in the optical air chamber, the optical air chamber is specially designed based on a hollow-core optical fiber with an inner diameter of 600 μm and a length of 22 cm. It is calculated that the internal volume of the optical air chamber is 46 μL.

[0014] As a further solution of the present invention, a deep-sea turbine pump is used to continuously and quantitatively flush the wet side of the membrane as a method of controlling the direction of water flow to weaken the concentration polarization phenomenon. The water sample flows in a direction parallel to the membrane and flows out in a direction perpendicular to the membrane.

[0015] As a further solution of the present invention, the strategy of adopting high partial pressure difference and high gas pressure difference on both sides of the membrane is:

[0016] The pressure difference on both sides of the membrane is increased by continuous injection detection under low pressure;

[0017] The partial pressure difference on both sides of the membrane is artificially increased by quantitatively and continuously purging the space behind the membrane with carrier gas, and the escaping gas is quantitatively measured.

[0018] As a further solution of the present invention, the underwater dissolved CO2 in-situ sensor is a deep-sea dissolved CO2 in-situ detection sensor device based on tunable infrared laser absorption spectroscopy technology and membrane degassing technology. The sampling and air intake system performs rapid sample collection and quantitative injection, and the gas phase detection part based on tunable infrared laser absorption spectroscopy technology performs quantitative detection of gas samples. A deep-sea turbine pump is used to continuously flush the permeable membrane, and a flow limiting valve is used to obtain a constant seawater flow rate.

[0019] As a further solution of the present invention, the deep-sea dissolved CO2 in-situ detection sensor device includes a gas phase detection part, which is a spectrometer based on TILAS technology. A coaxial optical system is constructed based on a 30mm cage structure. The coaxial optical system consists of a laser, a collimating element containing an aspheric collimating lens and a two-dimensional adjustment frame, an optical gas chamber and a photodetector along the optical axis.

[0020] As a further solution of the present invention, the R18e and R6f absorption line pairs located in the R branch of the mid-infrared band ν1+ν3 are the optimal absorption lines of the coaxial optical system, and the deep-sea dissolved CO2 in-situ detection sensor device also includes a laser with a central wavelength of 2682nm emitted by a continuous waveband cascade laser, which is collimated by an aspheric lens with an effective focal length of 4mm, wherein the collimating lens is mounted on a two-dimensional adjustment frame for XY direction adjustment.

[0021] As a further solution of the present invention, the underwater dissolved CO2 in-situ sensor includes a gas phase detection part, the effective optical path of the gas phase detection part is 22cm; the underwater dissolved CO2 in-situ sensor also includes a Teflon membrane with a thickness of 70μm to extract dissolved gas, and the effective membrane area is 4cm 2 .

[0022] The technical solution provided by the present invention has the following beneficial effects:

[0023] The present invention provides an underwater dissolved CO2 in-situ sensor based on a liquid phase response speed enhancement strategy. The underwater dissolved CO2 in-situ sensor based on the liquid phase response speed enhancement strategy has a liquid phase response speed of seconds. The strategy is used as a basis to develop a set of underwater dissolved CO2 in-situ sensors with a liquid phase response speed of seconds in three aspects: increasing the flux of dissolved gas molecules on the wet side of the membrane, enhancing the membrane permeation efficiency, and weakening the memory effect. The method of using strong and weak absorption lines to match and dilute the carrier gas achieves a large dynamic detection range and high precision. It has been verified that compared with the traditional underwater dissolved CO2 in-situ sensor, the liquid phase response speed of the underwater dissolved CO2 in-situ sensor based on the liquid phase response speed enhancement strategy proposed by the present invention is increased by about 2 orders of magnitude, reaching a response of seconds (τ 100 ); can be achieved from 10 -2 -10 5 Large dynamic detection range of ppmv and detection accuracy less than 1ppmv.

[0024] These and other aspects of the present invention will be more clearly understood in the following description of the embodiments. It should be understood that the above general description and the following detailed description are only exemplary and explanatory and cannot limit the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments or the prior art description. Obviously, the drawings in the following description are only some embodiments of the present invention. In the drawings:

[0026] Figure 1 This is a schematic diagram of a liquid phase response enhancement strategy for an underwater dissolved CO2 in-situ sensor based on a liquid phase response speed enhancement strategy according to an embodiment of the present invention.

[0027] Description of reference numerals:

[0028] 1. Laser beam, 2. Metal pressure plate, 3. Wedge-shaped calcium fluoride optical window, 4. Inlet / outlet holes, 5. Internal volume of hollow-core fiber, 6. Hollow-core fiber, 7. Internal volume of buffer tank, 8. Internal volume of "dead zone", 9. Water inlet direction (perpendicular to the membrane), 10. Water outlet direction, 11. Water inlet direction (parallel to the membrane), 12. Boundary layer, 13. Water sample, 14. Gas sample, 15. Carrier gas, 16. Space behind membrane, 17. Gas-liquid separation membrane, 18. High chemical level, 19. Low chemical level.

[0029] Figure 2 This is a schematic diagram of the structure of an optical path system in an underwater dissolved CO2 in-situ sensor based on a liquid phase response speed enhancement strategy according to an embodiment of the present invention.

[0030] Description of reference numerals:

[0031] 20. Water outlet, 21. Metal pressure plate outside the membrane, 22. Sintered metal plate, 23. Pressure cabin cover, 24. Air pressure sensor, 25. Water vapor filter, 26. Metering valve, 27. Optical detection part, 28. Mass flow meter (total flow), 29. Pressure controller, 30. Vacuum pump, 31. Water inlet, 32. Water flow valve, 33. Seawater filter, 34. Deep sea turbine water pump, 35. Gas line stop valve, 36. Mass flow controller (carrier gas), 37. Carrier gas, 38. Nitrogen or calibration gas, 39. Laser, 40. Collimating lens and two-dimensional adjustment frame, 41. Air inlet, 42. Air outlet, 43. Fiber optic connector, 44. Photodetector, 45. Cage structure optical support rod, 46. Metal sleeve, 47. Laser controller, 48. Adder, 49. Signal generator, 50. Phase-locked amplifier, 51. Data acquisition card.

[0032] Figure 3 This is a schematic diagram of an optical fiber connector in an ultrafast response in-situ sensor for underwater motion detection according to an embodiment of the present invention.

[0033] Description of reference numerals:

[0034] In the figure, 52. buffer tank, 53. screws, 54. connecting flange, 55. ceramic bushing, 56. cage structure fastening screws, and 57. O-ring. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0036] In some of the processes described in the specification and claims of the present invention and the above-mentioned figures, multiple operations that appear in a specific order are included, but it should be clearly understood that these operations may not be executed in the order in which they appear in the present invention or executed in parallel, and the sequence numbers of the operations, such as 101, 102, etc., are only used to distinguish between different operations, and the sequence numbers themselves do not represent any execution order. In addition, these processes may include more or fewer operations, and these operations may be executed in sequence or in parallel. It should be noted that the descriptions of "first", "second", etc. in the present invention are used to distinguish different messages, devices, modules, etc., do not represent the order of precedence, and do not limit the "first" and "second" to be different types.

[0037] The following will be combined with the drawings in the exemplary embodiments of the present invention to clearly and completely describe the technical solutions in the exemplary embodiments of the present invention. Obviously, the exemplary embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0038] Firstly, the low degassing efficiency of the permeable membrane and the insufficient exchange of gas samples in the detection chamber are the decisive reasons for the slow liquid phase response of the system.

[0039] On the one hand, the internal volume of the detection gas chamber, the additional "dead zone" volume (which exists but does not participate in the interaction between light and matter, the inlet and outlet pores and the buffer pool) and the gas resistance of the gas path will hinder the exchange of gas samples in the gas path, resulting in too slow and insufficient exchange efficiency of gas samples in the optical path. The three factors are determined by the gas path structure of the sensor, and together they cause the "memory effect" of the gas path, which has a negative effect on the gas phase response speed of the sensor.

[0040] On the other hand, the low degassing efficiency of the permeable membrane (inter-membrane) and the insufficient dissolved gas flux on the wet side of the membrane lead to insufficient sampling capacity of the system, resulting in slow liquid phase response of the sensor. The former is determined by the mechanism of membrane degassing technology. Permeable membrane degassing is based on the classic free diffusion membrane mass transfer mode (passive transfer of components from high chemical potential to low chemical potential). This method can achieve accurate detection of separated gases in in-situ sensor detection, but at the cost of longer response time (usually on the order of ten minutes, which is difficult to meet the requirements of deep-sea mobile detection). The response speed of all in-situ gas sensors based on permeable membranes is largely subject to the slow inter-membrane mass transfer process between the gas and liquid phases. The latter is determined by the flow rate and working direction of the water sample on the wet side of the membrane. Generally speaking, a higher flow rate means a larger dissolved gas flux on the wet side of the membrane, which means a larger inter-membrane mass transfer coefficient, but in some cases, the "concentration polarization phenomenon" on the wet side of the membrane may hinder the rapid transmission of gas molecules. Combining the above two aspects: the degassing capacity of the sampling part plays a major role in limiting the liquid phase response speed of the system. However, after this part is greatly improved, the "memory effect" of the gas path part will gradually replace the limitation of the system degassing capacity and become the main controlling factor.

[0041] Secondly, for sensors, higher detection sensitivity and larger dynamic measurement range are two contradictory parameters, and it is difficult to achieve both. Under the parameters of ensuring high detection accuracy, the system often experiences absorption saturation when the concentration is high, making it difficult to achieve a larger dynamic detection range.

[0042] In view of the common problems of in-situ CO2 sensors, such as slow response speed, low detection accuracy and small dynamic range, the present invention provides an ultra-fast response high-precision dissolved CO2 in-situ sensor system for underwater mobile detection. Regarding the "slow response speed", a solution that can improve the response speed of the system is proposed based on the mechanism of membrane mass transfer. The specific response speed increase strategy is to artificially increase the chemical potential energy on both sides of the membrane (i.e., increase the average driving force of molecular transmission and quantitatively release gas), reduce the gas demand (i.e., weaken the memory effect and prevent insufficient degassing), and control the flow rate and direction of the water sample (i.e., increase the mass transfer coefficient and weaken the concentration polarization phenomenon) to improve the gas transmission rate on both sides of the membrane.

[0043] In view of this, the present invention provides an underwater dissolved CO2 in-situ sensor with a liquid phase response speed of seconds based on a liquid phase response speed enhancement strategy. The strategy is used to increase the dissolved gas molecule flux on the wet side of the membrane, enhance the membrane permeation efficiency and weaken the memory effect. A set of underwater dissolved CO2 in-situ sensors with a liquid phase response speed of seconds is developed based on this strategy.

[0044] Specifically, the embodiments of the present application are further described below in conjunction with the accompanying drawings.

[0045] See also Figure 1 As shown, one embodiment of the present invention provides an underwater dissolved CO2 in-situ sensor based on a liquid phase response speed enhancement strategy, wherein the liquid phase response speed enhancement strategy in the system includes designing an optical gas chamber with minimized internal volume and gas resistance, using a deep-sea turbine pump to continuously and quantitatively flush the wet side of the membrane, and using a strategy of high partial pressure difference and high gas pressure difference on both sides of the membrane; the optical gas chamber adopts a hollow core optical fiber design to serve as a place for interaction between light and matter.

[0046] The "memory effect" of the gas path and the insufficient degassing capacity of the sampling part lead to the low efficiency of gas sample exchange and gas-liquid separation in the optical gas chamber, which together limit the liquid phase response speed of the system. In view of the above two aspects, the present invention proposes a liquid phase response speed efficient enhancement strategy, which improves the liquid phase response speed of the sensor based on membrane degassing and TILAS technology through the combined coupling of three aspects, see Figure 1 shown.

[0047] In some embodiments, the optical gas chamber is specially designed based on a hollow-core optical fiber with an inner diameter of 600 μm and a length of 22 cm, and the internal volume is calculated to be 46 μL.

[0048] In some embodiments, a deep-sea turbine pump is used to continuously and quantitatively flush the wet side of the membrane as a method to control the direction of water flow to weaken the concentration polarization phenomenon. The water sample flows in a direction parallel to the membrane and flows out in a direction perpendicular to the membrane.

[0049] In some embodiments, the strategy of using high partial pressure difference and high gas pressure difference across the membrane is:

[0050] The pressure difference ΔP on both sides of the membrane is increased by continuous injection detection under low pressure;

[0051] The partial pressure difference Δx on both sides of the membrane is artificially increased by quantitatively and continuously purging the space behind the membrane with carrier gas, and the escaping gas is quantitatively measured.

[0052] In some embodiments, the degassing amount of the Teflon film used in the optical gas chamber is about 1.0-2.0 sccm, and according to the 1:1 carrier gas dilution ratio, the optimal gas chamber internal volume is 33.3-66.7 μL.

[0053] Among them, in terms of weakening the "memory effect": In order to reduce the "memory effect" of the gas path, the strategy adopted by the present invention is to design an optical gas chamber with minimized internal volume and gas resistance, that is, minimized gas chamber volume, "dead zone" volume and gas resistance. To this end, the present invention uses hollow-core fiber (Hollow-core fiber, HCF) to specially design an optical gas chamber as a place for light to interact with matter. However, filling gas into hollow-core fiber is usually challenging because the smaller core diameter and longer length of hollow-core fiber means greater gas resistance, so it is necessary to determine the appropriate inner diameter and length. Generally speaking, when the total amount of gas entering the gas chamber is in a ratio of 1:1 to the internal volume of the gas chamber, the gas exchange efficiency in the gas chamber is better. Although a higher ratio can bring higher gas exchange efficiency, this will pose a challenge to the design of the internal volume of the gas chamber. According to the investigation, the degassing amount of the Teflon membrane used is about 1.0-2.0sccm. According to the calculation of the carrier gas dilution ratio of 1:1 (the gas inlet system partially introduces the assistance of the carrier gas), the optimal internal volume of the gas chamber is 33.3-66.7μL. Finally, the present invention specially designed an optical gas chamber based on the HCF with an inner diameter of 600μm and a length of 22cm. The internal volume is calculated to be 46μL. At the same time, compared with the hollow-core photonic crystal fiber, the HCF with an inner diameter of 600μm and a length of 22cm selected by the present invention will not introduce excessive gas resistance, and the buffer tank and the inlet and outlet holes with minimized design inside the optical gas chamber together ensure the micro-liter internal volume of the optical gas chamber.

[0054] Among them, in terms of increasing the dissolved gas flux on the wet side of the membrane: in order to increase the dissolved gas molecule flux on the wet side of the membrane, the present invention adopts a method of continuous quantitative flushing of the wet side of the membrane by a deep-sea turbine pump. The effect of liquid flow rate on the gas molecule transmission flux is reflected in the mass transfer coefficient, and the mass transfer coefficient increases with the increase of flow rate. When the water flow continuously flushes the wet side of the membrane, the "concentration polarization phenomenon" that may occur on the wet side of the membrane will cause the flux to decrease. In this regard, the present invention adopts a method of controlling the direction of water flow to weaken the concentration polarization phenomenon, that is, the water sample flows in in a direction parallel to the membrane and flows out in a direction perpendicular to the membrane.

[0055] Among them, in terms of improving membrane mass transfer efficiency: the reported membrane degassing technology is based on the classic free diffusion membrane mass transfer method, that is, the passive transfer of components from high chemical potential to low chemical potential. The transfer rate of gas molecules between membranes depends on the average driving force W during the transfer process. mean In the special case described in the present invention, according to the membrane mass transfer mechanism, the chemical potential difference Δμ composed of pressure difference, concentration difference and temperature is meanIt occupies a major position in the composition. The average driving force exerted on the molecules between the membranes is positively correlated with the concentration difference, pressure difference and temperature. According to the membrane mass transfer mechanism, the average driving force of molecular transfer can be positively correlated by changing the pressure difference and concentration difference on both sides of the membrane, which provides theoretical support for the optimization of the diffusion rate of dissolved gas molecules in seawater on both sides of the membrane in the present invention. Therefore, in order to improve the permeation efficiency of gas molecules on both sides of the membrane, the present invention adopts a strategy of high partial pressure difference and high gas pressure difference on both sides of the membrane, namely: increasing the gas pressure difference ΔP on both sides of the membrane by continuous injection detection under low pressure; artificially increasing the partial pressure difference Δx on both sides of the membrane by quantitatively and continuously sweeping the space behind the membrane with carrier gas (relative to the zero gas of CO2), and realizing the quantification of the degassed gas.

[0056] See also Figure 1 As shown, Figure 1 Schematic diagram of the proposed liquid phase response enhancement strategy. Figure 1 Schematic diagram of a single-path optical gas cell. Figure 1 In the liquid phase response enhancement strategy, the laser beam 1, metal pressure plate 2, wedge-shaped calcium fluoride optical window 3, inlet / outlet holes 4, hollow core fiber internal volume 5, hollow core fiber 6, buffer tank internal volume 7, "dead zone" internal volume 8, water inlet direction (perpendicular to the membrane) 9, water outlet direction 10, water inlet direction (parallel to the membrane) 11, boundary layer 12, water sample 13, gas sample 14, carrier gas 15, membrane back space 16, gas-liquid separation membrane 17, high chemical potential 18, low chemical potential 19. Its internal volume includes the buffer tank volume, gas inlet and outlet volume, hollow core fiber internal volume and "dead zone" volume. In the proposed strategy, all of these should be designed to minimize and smaller gas resistance.

[0057] In order to increase the flux of dissolved gas molecules on the wet side of the membrane, this embodiment uses a submersible pump to increase the water sample flow rate on the wet side of the membrane, which can significantly increase the flux of dissolved gas on the wet side of the membrane. Figure 1 As shown by the arrow in the middle, a dense boundary layer may appear on the wet side of the membrane, preventing the dissolved gas molecules from being transported to the dry side, which is called "concentration polarization phenomenon". In order to weaken it, this embodiment uses a deep-sea turbine pump to continuously and quantitatively flush the wet side of the membrane to control the direction of water flow to weaken the concentration polarization phenomenon. The water sample flows in parallel to the membrane and flows out perpendicular to the membrane.

[0058] The effect of the partial pressure difference on both sides of the membrane on the molecular movement speed. μ0, initialization degree of the wet side of the membrane; μ1, chemical potential of the dry side of the membrane without carrier gas; μ2, chemical potential of the dry side of the membrane with carrier gas; Δμ1, chemical potential difference between the two sides of the membrane without carrier gas; Δμ2, chemical potential difference between the two sides of the membrane with carrier gas. Compared with no carrier gas, injecting carrier gas (zero gas) into the space behind the membrane will enhance the chemical potential difference between the two sides of the membrane, thereby enhancing the driving force for gas molecule transport.

[0059] See also Figure 2 As shown, Figure 2 It is a deep-sea dissolved CO2 in-situ detection sensor device based on TILAS technology and membrane degassing technology. Figure 2 It includes a water outlet 20, a metal pressure plate outside the membrane 21, a sintered metal plate 22, a pressure cabin hatch 23, an air pressure sensor 24, a water vapor filter 25, a metering valve 26, an optical detection part 27, a mass flow meter (total flow) 28, a pressure controller 29, a vacuum pump 30, a water inlet 31, a water flow valve 32, a seawater filter 33, a deep-sea turbine water pump 34, a gas circuit stop valve 35, a mass flow controller (carrier gas) 36, a carrier gas 37, nitrogen or calibration gas 38, a laser 39, a collimating lens and a two-dimensional adjustment frame 40, an air inlet 41, an air outlet 42, a fiber optic connector 43, a photodetector 44, a cage-type optical support rod 45, a metal sleeve 46, a laser controller 47, an adder 48, a signal generator 49, a phase-locked amplifier 50, and a data acquisition card 51. The rapid quantitative analysis of dissolved gas requires efficient and stable extraction of dissolved gas in seawater and quantitative injection of it into the optical detection part. The rapid collection and quantitative injection of samples are completed by the sampling and air intake system, and the quantitative detection of gas samples is completed by the gas phase detection part.

[0060] The sampling system uses a 70μm thick Teflon membrane to extract dissolved gases. In order to increase the flux of dissolved gas molecules on the wet side of the membrane, a deep-sea turbine pump is used to continuously flush the permeable membrane, and a flow-limiting valve is used to obtain a constant seawater flow. In order to prevent the "concentration polarization phenomenon" that may occur on the wet side of the membrane during the continuous flushing of the membrane by water flow, the present invention adopts Figure 2 The water flow direction shown in the figure is "parallel to the membrane inflow and perpendicular to the membrane outflow".

[0061] In order to improve the permeation efficiency of gas molecules on both sides of the membrane, the present invention adopts the strategy of high partial pressure difference and high gas pressure difference on both sides of the membrane as described in the liquid phase response enhancement strategy. A low-pressure working environment is created by a vacuum pump and the gas path pressure is controlled at 30 torr by a pressure controller, and nitrogen is used as a carrier gas to perform quantitative and continuous purge of the dry side of the membrane at a fixed flow rate. The gas released from the permeable membrane is mixed with the carrier gas and coupled with the gas phase detection part in a manner of continuous sample injection under low pressure for detection. At the same time, the introduction of the carrier gas also solves the risks of insufficient degassing and instability that may occur during in-situ detection of the ocean. In order to quantify the gas sample delivered to the optical gas chamber, the carrier gas flow rate is controlled and quantified by a mass flow controller (carrier gas), and the total gas flow rate υ entering the optical gas chamber is measured by a mass flowmeter. tol , which represents the escape gas flow rate and carrier gas flow rate υ CG sum.

[0062] As the gas phase detection part of the sensor - TILAS-Based Spectrometer based on TILAS technology, the optical gas cell specially designed based on the selected inner diameter and length of HCF and TILAS technology is designed as follows Figure 2 The optical path system shown. In some embodiments, the deep-sea dissolved CO2 in-situ detection sensor device includes a gas phase detection part, which is a spectrometer based on TILAS technology, and a coaxial optical system is constructed based on a 30mm cage structure, and the coaxial optical system is composed of a laser, a collimating element containing an aspheric collimating lens and a two-dimensional adjustment frame, an optical gas chamber, and a photodetector along the optical axis. Therefore, this part constructs a coaxial optical system based on a 30mm cage structure, which is composed of a laser, a collimating element containing an aspheric collimating lens and a two-dimensional adjustment frame, an optical gas chamber, and a photodetector along the optical axis.

[0063] In some embodiments, the R18e and R6f absorption line pairs located in the R branch of the mid-infrared band ν1+ν3 are the optimal absorption lines of the coaxial optical system, and the deep-sea dissolved CO2 in-situ detection sensor device also includes a laser with a central wavelength of 2682nm emitted by a continuous waveband cascade laser, which is collimated by an aspheric lens with an effective focal length of 4mm, wherein the collimating lens is mounted on a two-dimensional adjustment frame for XY direction adjustment.

[0064] It is worth noting that the present invention selects R18e and R6f located in the R branch of the mid-infrared band ν1+ν3 as the optimal absorption lines, and realizes a large dynamic detection range while ensuring detection accuracy by means of primary and secondary absorption peaks and carrier gas dilution. The selected absorption peak has a good isolation effect on CH4, H2O, nitrogen oxides and sulfur oxides. The laser with a central wavelength of 2682nm emitted by the continuous waveband cascade laser is collimated by an aspherical lens (CL) with an effective focal length of 4mm.

[0065] The collimating lens is mounted on a two-dimensional adjustment frame that can be adjusted in the XY direction to facilitate the adjustment of the laser emission direction. The two-dimensional adjustment frame is suitable for a cage structure. The collimated laser beam is coupled into the optical gas cell to interact with the internal gas sample. The laser emitted from the optical gas cell carries the CO2 concentration information and is eventually captured by the MCT detector. After demodulation by the phase-locked amplifier, a second harmonic (2f) signal that is positively correlated with the concentration is obtained.

[0066] In addition, the existence of the extracavity optical path will increase the detection uncertainty of the system. Since the detector is fixed on the cage structure through the diode mount, there is no extracavity optical path between the detector and the optical chamber light exit hole. The only extracavity optical path exists between the collimating lens and the optical chamber light entrance hole (length is about 10mm). In order to avoid the additional measurement uncertainty caused by the ambient CO2, the optical path length outside the optical chamber of the system is designed to be minimized, and this part of the extracavity optical path is sealed.

[0067] See also Figure 2 As shown, Figure 2 Figure 2 is a schematic diagram of a dissolved CO2 sensor based on a permeable membrane and TILAS technology, including a sampling system, a sample injection system, and a TILAS spectrometer. The spectrometer based on TILAS technology uses a tunable interband cascade laser (ICL, Nanoplus GmbH, Germany) with a central wavelength of 2682 nm and a maximum optical power output of 5.7 mW. A satellite laser controller (LDTC 0520, Wavelength, US) is used to control the temperature and current of the laser. The wavelength is sinusoidally modulated at 31 kHz by the internal signal generator of the customized FPGA controller, and the R18e and R6f absorption lines of CO2 are scanned at a frequency of 2 Hz. The second harmonic of the absorption signal is demodulated by a digital phase-locked amplifier circuit in the FPGA controller and transmitted to a computer through a data acquisition card for further processing.

[0068] Figure 2 In MFC CG , mass flow controller for controlling the carrier gas flow; OGC, optical gas cell; MFM TG , mass flow meter to monitor the total gas flow; PC, gas pressure controller; V # , solenoid valve. V # Indicates three solenoid valves, which are used to control the on and off of gas flow during system calibration. The needle valve and water vapor filter are used for coarse adjustment of gas flow and removal of water vapor, respectively. Illustration: Schematic diagram of optical spectrometer developed based on TILAS. ICL, interband cascade laser; CL, collimating lens; FC, fiber connector; PD, photodetector; LD, laser driver; SG, signal generator; LIA, lock-in amplifier; DAQ, 16-bit data acquisition card; sig., detection signal; Ref., reference signal; temp.mod., temperature modulation; cur.mod. current modulation.

[0069] In some embodiments, the underwater dissolved CO2 in-situ sensor is a deep-sea dissolved CO2 in-situ detection sensor device based on tunable infrared laser absorption spectroscopy technology and membrane degassing technology. The sampling and air intake system performs rapid sample collection and quantitative injection, and the gas phase detection part based on tunable infrared laser absorption spectroscopy technology performs quantitative detection of gas samples. A deep-sea turbine pump is used to continuously flush the permeable membrane, and a flow limiting valve is used to obtain a constant seawater flow rate.

[0070] In some embodiments, the underwater dissolved CO2 in-situ sensor includes a gas phase detection part, the effective optical path of the gas phase detection part is 22cm; the underwater dissolved CO2 in-situ sensor also includes a Teflon membrane with a thickness of 70μm to extract dissolved gas, and the effective membrane area is 4cm 2 .

[0071] In some embodiments of the present invention, the effective optical path of the gas phase detection part is only 22 cm, so it is necessary to select a suitable absorption line strength to ensure detection sensitivity. In this regard, the selection criteria for the CO2 absorption line in this work are as follows:

[0072] (1) The intrinsic absorption line strength must be strong enough to obtain excellent detection sensitivity under limited absorption pathlength.

[0073] (2) A larger dynamic detection range can be obtained.

[0074] (3) Clearly isolated from other potentially interfering gas absorption lines to avoid spectral line overlap and mutual interference.

[0075] In the embodiment of the present invention, the effective optical path of the gas phase detection part is only 22cm, so it is necessary to select a suitable absorption line strength to ensure both detection sensitivity and dynamic detection range. Carbon dioxide has a wide range of absorption lines from near infrared to mid-infrared, and the main absorption band is ν 2， The center wavelengths of the ν1+ν3 and ν3 bands are 1.5μm, 2.7μm and 4.3μm respectively. Compared with the ν1+ν3 band, the CO2 absorption line intensity near 1.5μm is about two orders of magnitude weaker, so sufficient sensitivity cannot be achieved under limited optical path. Similarly, the absorption line intensity of the ν3 band is too large, resulting in a narrow dynamic detection range of the sensor.

[0076] The present invention is based on the HITRAN database to analyze the 3575-3775cm -1 The CO2 absorption lines in the spectral range were simulated, and the gas resistance, internal volume, detection sensitivity and dynamic detection range were comprehensively considered. Finally, R18e and R6f in the R branch of the mid-infrared band ν1+ν3 were selected as the optimal absorption lines, with the central wavelengths at 3728.41cm -1 and 3728.56cm-1 The two serve as the main absorption line and secondary absorption line of this sensor, respectively, and the corresponding spectral line intensity is 5.792e -20 cm / molecule and 1.467e -21 cm / molecule. The two selected absorption lines have a significant isolation effect on CH4 and H2O. It also has a similar isolation effect on potential interfering substances such as nitrogen oxides and sulfur oxides. The selected primary and secondary absorption peaks can be detected simultaneously in one laser scanning cycle without the need for laser mode hopping.

[0077] The sampling system uses a 70 μm thick Teflon membrane to extract dissolved gases, with an effective membrane area of ​​4 cm 2 . The back of the membrane is supported by a sintered metal plate to resist the high-pressure environment of the deep sea. The space behind the membrane is designed to be as small as possible to weaken the "memory effect" of this part. Based on the diameter of 2cm, the thickness is designed to be 1mm, and the corresponding total volume of the space behind the membrane is 0.4ml. The gas released from the membrane enters the spectrometer for detection through a 1 / 16" stainless steel tube under the push of the carrier gas to reduce the consumption of the released gas; and the gas path after OGC is changed to a 1 / 8" metal tube transmission to reduce gas resistance. In order to increase the flux of dissolved gas molecules on the wet side of the membrane, a deep-sea turbine pump is used to continuously flush the permeable membrane. However, the complexity of the marine environment determines that the flow rate of the liquid sample is difficult to maintain constant, resulting in unstable degassing efficiency, which is not allowed. The present invention uses a flow limiting valve to obtain a constant seawater flow rate, and the water sample flow rate after control is about 2.6L / min. In the process of continuous flushing of the membrane by water flow, the "concentration polarization phenomenon" that may occur on the wet side of the membrane will cause the driving force of the membrane process to decrease, thereby reducing the flux. In the present invention, the concentration polarization phenomenon is weakened by adopting a method in which the flow flows in a direction parallel to the membrane and flows out in a direction perpendicular to the membrane.

[0078] Quantitative analysis of dissolved gas requires that the gas sample quickly extracted from the membrane enters the OGC in a constant state, so the present invention deploys a gas injection system. As mentioned above, the internal volume of the OGC is less than 50 microliters, with a small internal volume and gas resistance, which weakens the gas path memory effect, thereby providing hardware support for improving the liquid phase response speed of the system. In order to improve the permeation efficiency of gas molecules on both sides of the membrane, the present invention adopts a strategy of high partial pressure difference and high gas pressure difference on both sides of the membrane. The gas injection system is coupled with the above-mentioned optical gas phase detection part in a continuous sample injection manner at low pressure. Two pressure gauges are used to monitor the pressure of the OGC and the space behind the membrane, respectively. A diaphragm vacuum pump is used to create a low-pressure environment, and a pressure controller based on a PID algorithm is combined to maintain the internal pressure of the OGC at 30 torr. Compared with the standard atmospheric pressure (760 torr), the working gas pressure of 30 torr significantly increases the pressure difference ΔP on both sides of the membrane, which is beneficial to increase the average driving force Wmean In order to increase the partial pressure difference of dissolved gas on both sides of the membrane, the present invention uses an inert gas (nitrogen) as a carrier gas and performs quantitative continuous purge on the dry side of the membrane at a fixed flow rate. In this way, the chemical potential difference of gas molecules on both sides of the membrane is artificially increased, thereby increasing the average driving force W of gas molecules transferred between the membranes. mean . At the same time, it also solves the risk of insufficient degassing that may occur during in-situ marine detection. Because the in-situ marine detection environment is very complex, unstable water mass movement, changing water temperature and water pressure will interfere with the degassing efficiency of the degassing membrane, resulting in the degassing volume no longer being constant. In addition, the solubility of the gas in different detection environments will also change greatly, and the continuous injection working mode will face the risk of unstable or even insufficient degassing, which has a fatal impact on the accuracy of the detection results. Therefore, it is necessary to quantify the gas volume and assist the flow of carrier gas for accurate detection of gas concentration. Although this increases the complexity of the system, it is undoubtedly worthwhile. Generally, a larger carrier gas flow rate can bring a higher partial pressure difference on both sides of the membrane, which also means that the membrane separation gas is dynamically diluted by a larger multiple, resulting in the negative result that the detection limit and detection accuracy will deviate from the optimal position, and the difficulty of detecting exhaust gas treatment will increase (a problem that in-situ sensors must consider). Therefore, it is necessary to balance the response speed, exhaust gas volume and detection performance according to the actual situation and select a suitable carrier gas flow rate.

[0079] As mentioned above, an optical air chamber is specially designed based on HCF. The hollow core fiber is sealed in a metal sleeve to fix and protect the fiber. The metal tube is filled with thermal conductive silicone grease to reduce fiber vibration and facilitate subsequent temperature control. Both ends of the HCF are fixed to the fiber connector through a ceramic ferrule. Figure 3 As shown, Figure 3 The detailed design of the fiber optic connector is shown, including: buffer pool 52, screws 53, connecting flange 54, ceramic bushing 55, cage structure fastening screws 56, and O-ring 57. Sapphire (Al2O3) windows are used to isolate the optical air chamber from the atmosphere, and are sealed on the optical connector with an O-ring at a wedge angle of 10° to reduce or avoid the influence of the "etalon effect". The fiber optic connector is also designed to be suitable for a cage structure. The inclined inlet and outlet design effectively shortens the length of the gas path between the inlet and outlet to the hollow-core optical fiber, and reduces the "dead zone" volume inside the fiber optic connector. In order to minimize the internal volume of the optical air chamber, many special designs are adopted, such as: using a hollow-core optical fiber with a limited length, shortening the diameter and length of the gas path between the inlet and outlet and the buffer pool, and minimizing the buffer pool design. After the minimized design, the internal volume of the entire optical air chamber reaches 46μL.

[0080] The present invention provides an underwater dissolved CO2 in-situ sensor based on a liquid phase response speed enhancement strategy. The underwater dissolved CO2 in-situ sensor based on the liquid phase response speed enhancement strategy has a liquid phase response speed of seconds. The underwater dissolved CO2 in-situ sensor increases the dissolved gas molecule flux on the wet side of the membrane, enhances the membrane permeation efficiency and weakens the memory effect. Based on the strategy, a set of underwater dissolved CO2 in-situ sensors with a liquid phase response speed of seconds is developed, and a large dynamic detection range and high precision are achieved by using the method of matching strong and weak absorption lines and carrier gas dilution.

[0081] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A liquid phase response rate enhancement strategy for underwater dissolved CO 2 In-situ sensor, It is characterized in that The underwater dissolved CO 2 The liquid phase response speed enhancement strategy of the in-situ sensor includes designing an optical gas chamber with minimized internal volume and gas resistance, using a deep-sea turbine pump to continuously and quantitatively flush the wet side of the membrane, and using a strategy of high partial pressure difference and high gas pressure difference on both sides of the membrane; the optical gas chamber is designed with a hollow core optical fiber as a place for light to interact with matter; In the optical gas chamber, the degassing amount of the Teflon membrane used is 1.0-2.0 sccm, and according to the 1:1 carrier gas dilution ratio, the optimal gas chamber internal volume is 33.3-66.7 μL; The concentration polarization phenomenon is weakened by using a deep-sea turbine pump to continuously and quantitatively flush the wet side of the membrane to control the direction of water flow. The water sample flows in parallel to the membrane and flows out perpendicular to the membrane. The strategy of using high partial pressure difference and high gas pressure difference on both sides of the membrane is: The pressure difference on both sides of the membrane is increased by continuous injection detection under low pressure; The partial pressure difference on both sides of the membrane is artificially increased by quantitatively and continuously purging the space behind the membrane with carrier gas, and the escaping gas is quantitatively measured.

2. The underwater dissolved CO based on the liquid phase response speed enhancement strategy according to claim 1 2 In-situ sensor, It is characterized in that In the optical air chamber, the optical air chamber is specially designed based on a hollow-core optical fiber with an inner diameter of 600 μm and a length of 22 cm. The internal volume of the optical air chamber is calculated to be 46 μL.

3. The underwater dissolved CO based on the liquid phase response speed enhancement strategy according to claim 2 2 In-situ sensor, It is characterized in that The underwater dissolved CO 2 In situ sensor for deep-sea dissolved CO based on tunable infrared laser absorption spectroscopy and membrane degassing technology 2 The in-situ detection sensor device is equipped with a sampling and air intake system for rapid sample collection and quantitative injection, a gas phase detection part based on tunable infrared laser absorption spectroscopy technology for quantitative detection of gas samples, a deep-sea turbine pump for continuous flushing of the permeable membrane, and a flow limiting valve to obtain a constant seawater flow rate.

4. The underwater dissolved CO based on the liquid phase response speed enhancement strategy according to claim 3 2 In-situ sensor, It is characterized in that The deep-sea dissolved CO 2 The in-situ detection sensor device includes a gas phase detection part, which is a spectrometer based on TILAS technology. A coaxial optical system is constructed based on a 30mm cage structure. The coaxial optical system consists of a laser, a collimating element containing an aspheric collimating lens and a two-dimensional adjustment frame, an optical gas chamber and a photodetector along the optical axis.

5. The underwater dissolved CO based on the liquid phase response speed enhancement strategy according to claim 4 2 In-situ sensor, It is characterized in that Located in the mid-infrared band ν 1 +ν 3 The R18e and R6f absorption line pairs with R branches are the optimal absorption lines of the coaxial optical system. 2 The in-situ detection sensor device also includes a laser with a central wavelength of 2682nm emitted by a continuous waveband inter-cascade laser, which is collimated by an aspheric lens with an effective focal length of 4mm, wherein the collimating lens is mounted on a two-dimensional adjustment frame for XY direction adjustment.

6. The underwater dissolved CO based on the liquid phase response speed enhancement strategy according to claim 1 2 In-situ sensor, It is characterized in that The underwater dissolved CO 2 The in-situ sensor includes a gas phase detection part, the effective optical path of the gas phase detection part is 22 cm; the underwater dissolved CO 2 The in-situ sensor also includes a 70 μm thick Teflon membrane to extract dissolved gases, with an effective membrane area of ​​4 cm 2 .

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