Method and device for on-line monitoring of cesium additive concentration in space closed MHD power generation system

Abstract

The application provides a kind of space closed type magnetohydrodynamic power generation system cesium additive concentration on-line monitoring method and device, and the working medium of closed type magnetohydrodynamic circulation system is the helium-cesium binary mixed working medium formed by helium and cesium vapor, wherein the cesium vapor is the additive for enhancing electrical conductivity, and the cesium vapor concentration directly determines the channel conductivity and power generation performance. By using the physical characteristics that the constant volume specific heat capacity of helium and cesium vapor differs by about 31 times, a micro calorimetric sensing unit is connected in parallel on the closed loop magnetohydrodynamic circulation system, the cesium concentration is inverted by micro sampling, constant power heating and accurate measurement of temperature rise rate, which provides the basis for electrical conductivity prediction and adaptive control. Innovatively, the temperature rise rate and steady-state temperature difference are used to invert the double parameters, the total mass of the sensing unit is ≤50g, the power consumption is ≤2W, and the volume is ≤20cm³.

Description

Technical Field

[0001] This invention relates to the field of space power technology, specifically to a method and apparatus for online monitoring of cesium additive concentration in a space closed magnetohydrodynamic power generation system, and more specifically to a method and apparatus for real-time online identification of cesium additive concentration in the circulating working fluid based on calorimetric heating response characteristics for a space closed magnetohydrodynamic thermoelectric conversion device. Background Technology

[0002] The closed-loop magnetohydrodynamic (MHD) power generation system is an important technological route for future space power sources ranging from hundreds of kilowatts to megawatts. Its basic principle is that a high-temperature conductive working gas flows at high speed in a strong magnetic field, generating an induced electromotive force according to Faraday's law of electromagnetic induction, thus achieving a direct conversion of thermal energy into electrical energy. Compared with traditional rotary power generation systems, the closed-loop MHD circulating system has no rotating parts, resulting in a simpler structure, higher reliability, and a theoretical conversion efficiency of over 50%. The main loop of the system consists of a compressor (1), a regenerator (4), a high-temperature heater (5), a closed-loop MHD power generation channel (2), the hot side of the regenerator (3), and a radiator (6) connected in series to form a closed loop. Figure 1 As shown.

[0003] The prerequisite for power generation in a closed-loop magnetohydrodynamic (MHD) system is that the working fluid must have sufficient conductivity. Pure inert gases (such as helium, He) are almost non-conductive below 2000 K (helium has an ionization energy of 24.6 eV, and its ionization degree is extremely low even at 3000 K). Therefore, closed-loop MHD systems must add a small amount of active elements with low ionization potential (such as cesium, Cs) to the inert gas working fluid to provide conductivity.

[0004] Cesium has an ionization energy of only 3.89 eV, the lowest among all metals. Within a temperature range of 2000K to 2500K, only 0.5% to 3% by mass of Cs vapor is required to achieve a working fluid conductivity on the order of 10 to 100 S / m, meeting the requirements for magnetohydrodynamic (MHD) power generation. Therefore, a typical closed-loop MHD system uses a helium-cesium binary mixture as its working fluid, with cesium vapor acting as an additive to enhance conductivity. Helium, due to its excellent thermal conductivity and specific heat capacity, is advantageous for high-temperature heat exchange and compact system design.

[0005] During long-term on-orbit operation, the cesium concentration in the He-Cs mixed working fluid will experience a non-negligible and continuous drift, due to reasons including: 1) High-temperature wall deposition: The wall temperature of the magnetohydrodynamic circulation channel reaches over 2000K, and Cs vapor will condense, deposit and chemically react on the channel wall, continuously consuming Cs.

[0006] 2) Condensation at the cold end of the regenerator: The temperature on the cold side of the regenerator is relatively low. When the temperature is lower than the temperature corresponding to the saturated vapor pressure of Cs, Cs vapor condenses on the surface of the regenerator and is "captured" and removed from the gaseous working fluid. The high heat exchange characteristics of the regenerator actually exacerbate the condensation loss of Cs.

[0007] 3) Selective leakage of helium: He molecules have a very small diameter (about 0.26 nm) and can leak into outer space through pipe joints, sealing interfaces and other locations, resulting in a reduction in the total amount of carrier gas and indirectly affecting the relative concentration of Cs.

[0008] Changes in cesium concentration have a severe impact on system performance. Conductivity σ The relationship between Cs concentration and conductivity is non-linear (approximately exponentially dependent). When the Cs concentration drops from the design value of 2% to 1%, the conductivity may decrease by more than an order of magnitude, directly leading to a sharp drop in the power generation of the magnetohydrodynamic (MHD) circulation channel. Simultaneously, changes in Cs concentration also alter the gas constant, specific heat capacity, and thermal conductivity of the mixture, affecting the regenerator efficiency and compressor operating condition matching. Therefore, real-time and accurate monitoring of Cs concentration is crucial for the performance evaluation and lifespan management of MHD circulation systems.

[0009] Existing gas component detection methods (mass spectrometers, gas chromatographs, spectrometers, etc.) are bulky, heavy (>5kg), and power-consuming (>20W), making them unsuitable for the stringent mass and power consumption constraints of space missions. Furthermore, in high-temperature magnetohydrodynamic (MHD) circulation systems, the optical windows are susceptible to Cs deposition contamination, reducing the reliability of spectroscopic methods. Therefore, a lightweight, low-power, and highly reliable online monitoring method is urgently needed. Summary of the Invention

[0010] To address the shortcomings of existing technologies, the purpose of this invention is to provide a method and apparatus for online monitoring of cesium additive concentration in a closed-loop magnetohydrodynamic power generation system.

[0011] According to the present invention, an online monitoring device for cesium additive concentration in a closed-loop magnetohydrodynamic power generation system includes: a closed-loop magnetohydrodynamic circulation system, a calorimetric component sensing unit 8, a gas intake bypass pipeline 10 and an exhaust bypass pipeline 15, and a sensing and control module 17. The closed-loop magnetohydrodynamic circulation system includes: a compressor 1, a regenerator 4, a heater 5, a magnetohydrodynamic circulation power generation channel 2, a regenerator hot side 3, and a radiator 6 connected in series to form a closed loop; The calorimetric component sensing unit 8 is connected in parallel through the gas intake bypass pipe 10 and the exhaust bypass pipe 15 on the pipeline between the outlet of the compressor 1 and the cold side inlet of the cooler 4. The calorimetric component sensing unit 8 is used to heat the gas to be measured by a heating element and simultaneously measure the gas temperature by a temperature measuring element, thereby calculating the specific heat capacity of the gas to be measured. The sensing control module 17 is connected to the calorimetric component sensing unit 8 and is used to control the micro-mixing mass introduced into the calorimetric component sensing unit 8.

[0012] Preferably, the closed-loop magnetohydrodynamic circulation system includes: After the working fluid is compressed and heated in the compressor 1, it is preheated by the cold side of the regenerator 4, and then heated to the preset temperature by the heater 5. It then flows at high speed through the magnetohydrodynamic circulation power generation channel 2, where it generates an induced electromotive force under the action of a strong magnetic field to generate electricity. After the regenerator hot side 3 recovers the waste heat and the radiator 6 cools it down by radiation, it returns to the compressor 1.

[0013] Preferably, the calorimetric component sensing unit 8 includes: a microchannel gas intake valve 9, a constant volume sealed cavity 11, and an exhaust valve 14; The microchannel gas intake valve 9 and the exhaust valve 14 are both piezoelectrically driven microvalves. The microchannel gas intake valve 9 is used to periodically fill the constant volume sealed cavity 11 with gas from the closed-loop magnetohydrodynamic circulation system. The constant-volume sealed cavity 11 is used for heating and measuring the gas to be measured; The exhaust valve 14 is used to discharge the gas inside the constant volume sealed cavity 11 to the outside after the measurement is completed.

[0014] Preferably, the constant-volume sealed cavity 11 has a cylindrical structure with a volume of 0.5mL to 5mL. The cavity is made of AlN ceramic with a wall thickness of ≤0.3mm. The high thermal conductivity of about 170W / (m·K) is used to make the wall temperature uniform, and the low heat capacity design reduces the interference of wall surface thermal effect on calorimetry.

[0015] Preferably, the constant-volume sealed cavity 11 includes: a thin-film resistance heater 12, a temperature sensor 13, and a miniature pressure sensor 16; The temperature sensor 13 is used to obtain the temperature of the gas in the cavity; The miniature pressure sensor 16 is used to calculate the pressure of the sampled gas; The thin-film resistance heater 12 uses a platinum thin-film resistor for heating and temperature self-detection.

[0016] According to the present invention, a method for online monitoring of cesium additive concentration in a closed-loop magnetohydrodynamic (MHD) power generation system is provided, which, based on the aforementioned online monitoring device for cesium additive concentration in a closed-loop magnetohydrodynamic (MHD) power generation system, performs the following steps: Step S1: Draw out a small amount of mixed working fluid from the closed-loop magnetohydrodynamic circulation system and fill it into the constant-volume sealed cavity; Step S2: After closing the valve, the gas in the constant-volume sealed cavity is heated at a constant power by the thin-film resistance heater 12, and the temperature change curve over time is recorded by the temperature sensor 13 at a preset frequency. T ( t ); Step S3: From T ( t Extract the initial heating rate from the sample. Step S4: Invert the equivalent isochoric specific heat capacity of the working fluid from the initial heating rate. c v ; Step S5: According to c v Calculate cesium concentration x _Cs; Step S6: Open the vent valve to discharge the working fluid back into the main circuit, completing one measurement; Step S7: The identified cesium concentration x The _Cs signal is fed back to the power generation system controller, which then predicts the magnetohydrodynamic channel conductivity. σ Adjust the heater power or compressor speed to maintain optimal power generation conditions; if the cesium concentration is lower than the preset threshold, send an alarm for insufficient additives to the ground via telemetry.

[0017] Preferably, step S1 includes: controlling the microchannel gas intake valve 9 through the sensing control module 17 to draw out a small amount of working fluid from the pipeline between the compressor 1 outlet and the cold side of the regenerator 4 in the closed-loop magnetohydrodynamic circulation system and fill it into the constant volume sealed cavity 11. The pressure P0 and temperature T0 inside the constant-volume sealed cavity 11 are obtained by the miniature pressure sensor 16 and temperature sensor 13 in the constant-volume sealed cavity 11.

[0018] Preferably, step S3 includes: performing least-squares linear fitting on T(t) to obtain the initial heating rate dT / dt.

[0019] Preferably, step S4 includes: based on d T / d t = P / (m· c v Inversion c v ,in, P The pressure inside the measuring chamber is denoted by m, and the mass of the gas inside the measuring chamber is denoted by m.

[0020] Preferably, step S5 includes: c v = x _Cs× c v_Cs+(1-x _Cs)× c v_He solution x _Cs; in, c v_Cs is cesium vapor, which is also a monatomic gas. c v_He represents helium, a monatomic gas.

[0021] Compared with the prior art, the present invention has the following beneficial effects: 1. The sensing unit in this invention is reduced by several orders of magnitude compared to traditional instruments; 2. He and Cs c v The difference is 31 times, which provides extremely high sensitivity for Cs concentration detection; a component change of 0.1% can be reliably detected. 3. This invention does not depend on the state of rotating machinery and can work under any operating condition of the system, including the standby state of the magnetohydrodynamic circulation channel.

[0022] 4. The dual-parameter joint inversion of heating rate and steady-state temperature difference provides high robustness; 5. Micro-sampling does not disturb the closed-loop magnetohydrodynamic circulation system, the working fluid is returned without being consumed, and the measurement cycle is 2-5 minutes; 6. This invention can directly predict the conductivity of the magnetohydrodynamic circulation channel through Cs concentration, providing a key input for adaptive control of power generation and system lifetime assessment—this is the unique value of applying calorimetry to magnetohydrodynamic circulation systems.

[0023] 7. The present invention sets up a calorimetric component sensing unit in parallel on a closed-loop magnetohydrodynamic circulation system. It utilizes the significant difference in the constant-volume specific heat capacity between helium and cesium vapor to achieve online identification of cesium concentration through micro-sampling, constant-power heating, and measurement of the heating rate. Attached Figure Description

[0024] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a schematic diagram of the overall layout of the calorimetric component sensing unit in a space-closed magnetohydrodynamic power generation system.

[0025] Figure 2 This is a schematic cross-sectional view of the calorimetric component sensing unit.

[0026] Figure 3 This is a schematic diagram of the principle and calibration curve of calorimetric component monitoring. The left side shows the temperature-time curve of constant volume heating at different Cs concentrations, and the right side shows the Cs concentration-calorimetric response calibration curve.

[0027] Figures 4a to 4bThis paper shows the effect of Cs additive concentration on the conductivity of the magnetohydrodynamic circulation channel and the system performance. The left side shows the change in conductivity with Cs concentration, and the right side shows the comparison of system performance with and without component monitoring during on-orbit operation.

[0028] Among them, 1—compressor; 2—magnetic fluid circulation power generation channel; 3—hot side of regenerator; 4—regenerator; 5—heater; 6—radiator; 8—calorimetric component sensing unit; 9—microchannel gas intake valve; 10—gas intake bypass pipeline; 11—constant volume sealed cavity; 12—thin film resistance heater; 13—temperature sensor; 14—exhaust valve; 15—exhaust bypass pipeline; 16—miniature pressure sensor; 17—sensor control module. Detailed Implementation

[0029] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0030] Example 1 According to the present invention, an online monitoring device for cesium additive concentration in a closed-loop magnetohydrodynamic power generation system is provided, such as... Figure 1-2 As shown, it includes: a closed-loop magnetohydrodynamic circulation system, a calorimetric component sensing unit 8, an intake bypass pipeline 10 and an exhaust bypass pipeline 15, and a sensing control module 17. The closed-loop magnetohydrodynamic circulation system includes: a compressor 1, a regenerator 4, a heater 5, a magnetohydrodynamic circulation power generation channel 2, a regenerator hot side 3, and a radiator 6 connected in series to form a closed loop; The calorimetric component sensing unit 8 is connected in parallel through the gas intake bypass pipe 10 and the exhaust bypass pipe 15 on the pipeline between the outlet of the compressor 1 and the cold side inlet of the cooler 4 (where the temperature is moderate at about 400K~600K, the pressure is stable, and it is far away from the high temperature area to avoid Cs condensation interference). The calorimetric component sensing unit 8 is used to heat the gas to be measured by a heating element and simultaneously measure the gas temperature by a temperature measuring element, thereby calculating the specific heat capacity of the gas to be measured. The sensing control module 17 is connected to the calorimetric component sensing unit 8 and is used to control the micro-mixing mass introduced into the calorimetric component sensing unit 8.

[0031] The closed-loop magnetohydrodynamic circulation system includes: After the working fluid is compressed and heated in the compressor 1, it is preheated on the cold side of the regenerator 4, and then heated to 2000K~2500K by the heater 5 (at which point Cs is fully ionized and the working fluid has high electrical conductivity). It then flows at high speed through the magnetohydrodynamic circulation power generation channel 2, where it generates an induced electromotive force under the action of a strong magnetic field, thus generating electricity. After the working fluid recovers waste heat through the hot side of the regenerator 3 and is cooled by radiation by the radiator 6, it returns to the compressor 1.

[0032] The calorimetric component sensing unit 8 includes: a microchannel gas intake valve 9, a constant volume sealed cavity 11, and an exhaust valve 14. The microchannel gas intake valve 9 and exhaust valve 14 are both piezoelectrically driven microvalves with a mass ≤5g, response ≤10ms, and diameter ≤0.5mm. The microchannel gas intake valve 9 is used to periodically fill the constant volume sealed cavity 11 with gas from the closed-loop magnetohydrodynamic circulation system. The calorimetric component sensing unit 8 has a total mass ≤50g, power consumption ≤2W, and volume ≤20cm³.

[0033] The constant-volume sealed cavity 11 is used for heating and measuring the gas to be measured; The exhaust valve 14 is used to discharge the gas inside the constant volume sealed cavity 11 to the outside after the measurement is completed.

[0034] The constant-volume sealed cavity 11 is a cylindrical structure with an inner diameter of 5mm~10mm, a length of 10mm~30mm, and a volume of 0.5mL~5mL. The cavity is made of AlN ceramic with a wall thickness of ≤0.3mm. The high thermal conductivity of about 170W / (m·K) is used to make the wall temperature uniform, and the low heat capacity design reduces the interference of wall surface thermal effect on calorimetry.

[0035] Specifically, the constant-volume sealed cavity 11 includes: a thin-film resistance heater 12, a temperature sensor 13, and a miniature pressure sensor 16; A platinum thin-film resistance heater 12 is arranged along the axis inside the cavity, serving both heating and temperature self-detection functions. A Pt1000 temperature sensor 13, with an accuracy of ±0.01K and a sampling frequency of ≥10Hz, is located at the center to obtain the temperature of the gas in the cavity. A miniature pressure sensor 16 is located on one side to accurately calculate the pressure of the sampled gas.

[0036] Example 2 There is a very significant difference in the specific heat capacity at constant volume between helium and cesium vapor—helium is a monatomic gas. c v He = 3116 J / (kg·K); Cesium vapor is also a monatomic gas. c vCs≈100 J / (kg·K) (estimated based on a monatomic ideal gas) R Cs = 64.0 J / (kg·K), c v = R / ( γ -1)=64.0 / 0.667≈96 J / (kg·K)). The difference between the two is about 31 times.

[0037] Under constant-volume heating conditions, according to the first law of thermodynamics: d T / d t = P _heat / ( m · c v The heating rate is strictly inversely proportional to the specific heat capacity. The equivalent specific heat capacity of the He-Cs mixture satisfies a linear superposition relationship: c v = x _Cs× c v _Cs+(1- x _Cs)× c v He. Because c v _Hehe c v The Cs concentration differs by a factor of 31, meaning even a small change in Cs concentration (such as from 2% to 1.5%) can cause [a significant difference]. c v The significant change in heating rate provides extremely high sensitivity for group-based identification.

[0038] Based on this, a miniature calorimetric sensing unit was designed. Through this miniature calorimetric sensing unit (i.e., a calorimetric component sensing unit 8), micro-sampling, constant-power heating, and precise measurement of the heating rate are performed, the Cs concentration can be inverted. Figure 3 As shown.

[0039] According to the present invention, a method for online monitoring of cesium additive concentration in a closed-loop magnetohydrodynamic (MHD) power generation system comprises the following steps based on the aforementioned online monitoring device for cesium additive concentration in a closed-loop magnetohydrodynamic (MHD) power generation system: Step S1: Draw out a small amount of mixed working fluid from the closed-loop magnetohydrodynamic circulation system and fill it into the constant-volume sealed cavity; Step S2: After closing the valve, the gas in the constant-volume sealed cavity is heated at a constant power by the thin-film resistance heater 12, and the temperature change curve over time is recorded by the temperature sensor 13 at a preset frequency. T ( t ); Step S3: From T ( tExtract the initial heating rate from the sample. Step S4: Invert the equivalent isochoric specific heat capacity of the working fluid from the initial heating rate. c v ; Step S5: Based on c v Calculate cesium concentration x _Cs; Step S6: Open the vent valve to discharge the working fluid back into the main circuit, completing one measurement; Step S7: The identified cesium concentration x The _Cs signal is fed back to the power generation system controller, which then predicts the magnetohydrodynamic channel conductivity. σ Adjust the heater power or compressor speed to maintain optimal power generation conditions; if the cesium concentration is lower than the preset threshold, send an alarm for insufficient additives to the ground via telemetry.

[0040] like Figure 4a As shown, the conductivity of the magnetohydrodynamic (MHD) circulation channel is highly sensitive to Cs concentration. A 50% reduction in Cs concentration from the design value can cause a decrease in conductivity of more than an order of magnitude, directly leading to a sharp drop in power generation. Figure 4b As shown, during on-orbit operation, without component monitoring and adaptive control, the continuous deposition of Cs will lead to irreversible degradation of system performance. However, with the online monitoring device of this invention, the trend of Cs concentration changes can be grasped in real time, and compensatory measures can be taken in advance (such as adjusting the heating power to increase the wall temperature to reduce Cs condensation, or supplementing Cs in a timely manner), which can significantly extend the on-orbit life of the system.

[0041] Example 3 Example 3 is a preferred example of Example 1 and / or Example 2. Taking a 50kW space magnetohydrodynamic (MHD) power generation system as an example: He-Cs mixed working fluid, Cs design mass fraction x _Cs=2%, compressor speed 45000rpm, pressure ratio 2.50, inlet temperature of magnetofluid circulation channel 2200K, total amount of working fluid in main circuit about 1.0kg, operating pressure about 0.8MPa.

[0042] Sensing unit parameters: cavity volume 2.0mL, AlN ceramic wall thickness 0.2mm, Pt heater rated power 0.5W, Pt1000 temperature sensor, piezoelectric microvalve diameter 0.4mm. Total weight approximately 35g, volume approximately 12cm³, peak power consumption approximately 0.8W.

[0043] Ground calibration: In 15 standard gas mixtures with different Cs concentrations (0.5%~3.5%), when x_Cs=2% (design value), d T / d t ≈2.85 K / s, Δ T_ss≈18.2K. When x When _Cs drops to 1%, d T / d t ≈4.52 K / s (increase of 58.6%), Δ T _ss≈14.8K. Calibration data show that a 0.1% change in Cs concentration can cause d T / d t The change is approximately 3%, and the sensitivity meets engineering requirements.

[0044] In-orbit example: After two years of operation, the concentration of Cs decreased to [a level not specified in the original text] due to deposition on the channel walls and condensation at the cold end of the regenerator. x Cs≈1.2%. The sensing unit performs one measurement: after gas sampling. P 0 = 0.78 MPa T 0 = 423.6K, measured heating temperature d T / d t =3.95 K / s, inversion x _Cs=1.18%. Δ T The _ss auxiliary verification deviation is <0.05%, confirming the reliability of the results. Based on this, the system increases the heater power by 5%, raises the channel wall temperature to reduce Cs condensation, and adjusts the inlet temperature of the magnetofluid circulation channel to 2280K to maintain conductivity, restoring optimal power generation conditions.

[0045] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. An online monitoring device for cesium additive concentration in a closed-loop magnetohydrodynamic power generation system, characterized in that, include: Closed-loop magnetohydrodynamic circulation system, calorimetric component sensing unit (8), intake bypass pipeline (10) and exhaust bypass pipeline (15), sensing control module (17). The closed-loop magnetohydrodynamic circulation system includes: a compressor (1), a regenerator (4), a heater (5), a magnetohydrodynamic circulation power generation channel (2), a regenerator hot side (3), and a radiator (6) connected in series to form a closed loop; The calorimetric component sensing unit (8) is connected in parallel through the gas intake bypass pipe (10) and the exhaust bypass pipe (15) on the pipeline between the outlet of the compressor (1) and the cold side inlet of the cooler (4). The calorimetric component sensing unit (8) is used to heat the gas to be measured by heating the heating element and at the same time to measure the gas temperature by using the temperature measuring element, thereby calculating the specific heat capacity of the gas to be measured. The sensing control module (17) is connected to the calorimetric component sensing unit (8) and is used to control the micro-mixing mass introduced into the calorimetric component sensing unit (8).

2. The online monitoring device for cesium additive concentration in a closed-loop magnetohydrodynamic power generation system according to claim 1, characterized in that, The closed-loop magnetohydrodynamic circulation system includes: After the working fluid is compressed and heated in the compressor (1), it is preheated on the cold side of the regenerator (4), and then heated to the preset temperature by the heater (5). It then flows at high speed through the magnetohydrodynamic circulation power generation channel (2) under the action of the strong magnetic field in the magnetohydrodynamic circulation power generation channel (2) to generate induced electromotive force and generate electricity. After the waste heat is recovered by the hot side of the regenerator (3) and cooled by radiation by the radiator (6), it returns to the compressor (1).

3. The online monitoring device for cesium additive concentration in a closed-loop magnetohydrodynamic power generation system according to claim 1, characterized in that, The calorimetric component sensing unit (8) includes: a microchannel gas intake valve (9), a constant volume sealed cavity (11), and an exhaust valve (14). Among them, the microchannel gas intake valve (9) and the exhaust valve (14) are both piezoelectrically driven microvalves; The microchannel gas intake valve (9) is used to periodically fill the gas in the closed-loop magnetohydrodynamic circulation system into the constant volume sealed cavity (11). The constant-volume sealed cavity (11) is used for heating and measuring the gas to be measured; The exhaust valve (14) is used to discharge the gas inside the constant volume sealed cavity (11) to the outside after the measurement is completed.

4. The online monitoring device for cesium additive concentration in a closed-loop magnetohydrodynamic power generation system according to claim 3, characterized in that, The constant-volume sealed cavity (11) is a cylindrical structure with a volume of 0.5mL~5mL. The cavity is made of AlN ceramic with a wall thickness of ≤0.3mm. The high thermal conductivity of about 170W / (m·K) is used to make the wall temperature uniform. The low heat capacity design reduces the interference of wall surface thermal effect on calorimetry.

5. The online monitoring device for cesium additive concentration in a closed-loop magnetohydrodynamic power generation system according to claim 3, characterized in that, The constant-volume sealed cavity (11) includes: a thin-film resistance heater (12), a temperature sensor (13), and a miniature pressure sensor (16). The temperature sensor (13) is used to obtain the temperature of the gas in the cavity; The miniature pressure sensor (16) is used to calculate the pressure of the sampled gas; The thin-film resistance heater (12) uses a platinum thin-film resistor for heating and temperature self-detection.

6. A method for online monitoring of cesium additive concentration in a closed-loop magnetohydrodynamic power generation system, characterized in that, The online monitoring device for cesium additive concentration in a closed-loop magnetohydrodynamic power generation system according to any one of claims 1 to 5 performs the following steps: Step S1: Draw out a small amount of mixed working fluid from the closed-loop magnetohydrodynamic circulation system and fill it into the constant-volume sealed cavity; Step S2: After closing the valve, the gas in the constant-volume sealed cavity is heated at a constant power by a thin-film resistance heater (12), and the temperature change curve over time is recorded by a temperature sensor (13) at a preset frequency. T ( t ); Step S3: From T ( t Extract the initial heating rate from the sample. Step S4: Invert the equivalent isochoric specific heat capacity of the working fluid from the initial heating rate. c v ; Step S5: Based on c v Calculate cesium concentration x _Cs; Step S6: Open the vent valve to discharge the working fluid back into the main circuit, completing one measurement; Step S7: The identified cesium concentration x The _Cs signal is fed back to the power generation system controller, which then predicts the magnetohydrodynamic channel conductivity. σ Adjust the heater power or compressor speed to maintain optimal power generation conditions; if the cesium concentration is lower than the preset threshold, send an alarm for insufficient additives to the ground via telemetry.

7. The method for online monitoring of cesium additive concentration in a closed-loop magnetohydrodynamic power generation system according to claim 6, characterized in that, Step S1 includes: controlling the microchannel gas intake valve (9) through the sensing control module (17) to draw out a small amount of working fluid from the pipeline between the compressor (1) outlet and the cold side of the regenerator (4) in the closed-loop magnetohydrodynamic circulation system and fill it into the constant volume sealed cavity (11). The pressure P0 and temperature T0 inside the constant-volume sealed cavity (11) are obtained by using the miniature pressure sensor (16) and temperature sensor (13) in the constant-volume sealed cavity (11).

8. The method for online monitoring of cesium additive concentration in a closed-loop magnetohydrodynamic power generation system according to claim 6, characterized in that, Step S3 includes: performing least-squares linear fitting on T(t) to obtain the initial heating rate dT / dt.

9. The method for online monitoring of cesium additive concentration in a closed-loop magnetohydrodynamic power generation system according to claim 8, characterized in that, Step S4 includes: based on d T / d t = P / (m· c v Inversion c v ,in, P To measure the internal pressure of the cavity ， m represents the mass of the gas inside the measuring chamber.

10. The method for online monitoring of cesium additive concentration in a closed-loop magnetohydrodynamic power generation system according to claim 6, characterized in that, Step S5 includes: c v = x _Cs× c v_Cs+(1- x _Cs)× c v_He solution x _Cs; in, c v_Cs is cesium vapor, which is also a monatomic gas. c v_He represents helium, a monatomic gas.

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