Impact of Improved Design on Knudsen Force for Micro Gas Sensor

Knudsen force generated by thermally driven gas flow in a microscale structure has been used for gas detection and has shown immeasurable potential in the field of microelectromechanical system (MEMS) gas sensors due to its novel sensing characteristics. In this article, the performances of three kinds of Knudsen force gas sensors with improved isosceles triangular shuttle arm structures were studied. In the first design, the top side and right side lengths were equal; in the second, the top side and bottom side lengths were equal; and for the third, the bottom side and right side lengths were equal. A detailed investigation including gas flow, thermal characteristics, Knudsen force, and coupling effects between the shuttle-heater pairs was conducted using the direct simulation Monte Carlo (DSMC) method and the main mechanisms for gas flow presented were almost the same in this work. However, the second design returned the highest Knudsen force performance. The value increased by 42.9% (P = 387 Pa) compared to the Knudsen force of the original square shuttle arm. The results also demonstrate that the coupling effects become weak toward the right with an increase in the number of shuttle-heater pairs.

Development of Knudsen thermal force for mass analysis of CH4/He gas mixture

Natural gas is known as the main source of energy and also contains significant and noble gases. Numerous researches have been performed to present novel methods for the detection and analysis of natural gas. In this study, Direct Simulation Monte Carlo (DSMC) method is used to evaluate the performance of a new micro gas sensor (MIKRA) for detection of helium in CH4/He gas mixture. In this sensor, the temperature difference of two arms inside a rectangular domain at low-pressure condition induces a Knudsen force which is proportional to physical properties of the gas. In order to define flow feature of a low-pressure gas inside the micro gas actuator, high order equation of Boltzmann is used to attain high precision results. To solve these equations, DSMC approach is used as a robust method for the non-equilibrium flow field. The effects of main factors such as length and gap of arms are comprehensively investigated in different ambient pressures. Furthermore, the effect of various concentrations of the CH4/He gas mixture on force generation is comprehensively studied. Our findings show that value of generated Knudsen force significantly different when the fraction of He in CH4/He gas mixture is varied. This indicates that this micro gas sensor could precisely detect the concentration of Helium gas inside a low-pressure CH4/He gas mixture.

Catalytic Micro Gas Sensor with Excellent Homogeneous Temperature Distribution and Low Power Consumption for Long-Term Stable Operation

This paper presents a long-term stable thermoelectric micro gas sensor with ligand linked Pt nanoparticles as catalyst. The sensor design gives an excellent homogeneous temperature distribution over the catalytic layer, an important factor for long-term stability. The sensor consumes very low power, 18 mW at 100 °C heater temperature. Another thermoresistive sensor is also fabricated with same material for comparative analysis. The thermoelectric sensor gives better temperature homogeneity and consumes 23% less power than thermoresistive sensor for same average temperature on the membrane. The sensor shows linear characteristics with temperature change and has significantly high Seebeck coefficient of 6.5 mV/K. The output of the sensor remains completely constant under 15,000 ppm continuous H2 gas flow for 24 h. No degradation of sensor signal for 24 h indicates no deactivation of catalytic layer over the time. The sensor is tested with 3 different amount of catalyst at 2 different operating temperatures under 6000 ppm and 15,000 ppm continuous H2 gas flow for 4 h. Sensor output is completely stable for 3 different amount of catalyst.

Real Time In-situ Detection System Research for Methane in Offshore Shallow Gas based on Thin Film Interface

In order to get ridded of the non real-time detection methods of artificial site sampled and laboratory instrument analyzed in the field of methane detection in the offshore shallow gas, real-time in-situ detection system for methane in offshore shallow gas was designed by the film interface.The methane in the offshore shallow gas through the gas-liquid separation membrane of polymer permeation into the system internal detection probe, analog infrared micro gas sensor sensed the methane concentration and the corresponded output value, data acquisition and communication node fitted into standard gas concentration.Based on the experimental data compared with the traditional detection method, and further analyzed the causes of error produced by the case experiment. The application results show that the system can achieve a single borehole layout, long-term on-line in-situ on-line detection, and improve the detection efficiency and the timeliness of the detection data.