Highly gas permeable, ultrathin Teflon AF2400/γ-alumina composite hollow fiber membranes for dissolved gas analysis

Improving Anti-Humidity Property of a SnO2-Based Chemiresistive Hydrogen Sensor by a Breathable and Hydrophobic Fluoropolymer Coating

Metal-oxide-based chemiresistive hydrogen sensors exhibit high sensitivity, long-term stability, and low cost and have been extensively applied in safety monitoring of H₂. However, the sensing performances are dramatically affected by the water vapor, resulting in reduced response value and increased response/recovery time. To improve the anti-humidity property of sensors, coating the breathable and hydrophobic membrane on the surface of the sensing film is an effective strategy. In this work, the poly[4,5-difluoro-2,2-bis(trifluoromethyl)-1,3-dioxole-co-tetrafluoroethylene] (Teflon AF-2400) was dip-coated on the surface of SnO₂ in a commercial hydrogen sensor (TGS2615) as a breathable and hydrophobic membrane. For safety, He instead of H₂ was used to test the gas permeability of membranes. The Teflon membrane shows a high He permeability of up to 40,700 Barrer and an excellent He/H₂O selectivity of 99. Moreover, Teflon shows high processability to form a defect-free coating on the rough surface of the sensing film and high chemical stability under the operando condition of the sensor. Thus, the Teflon-modified sensor possesses excellent selectivity with a value of 5, and the resistance is stable at 10,554 ± 3% Ω for 20 days in 80% RH. The modified sensor shows an improved anti-humidity property with a 75% response to 200 ppm H₂ at 80% RH and has a low coefficient of variation value of 7.23% that shows advances than other reported sensors modified by coatings. The commercially available Teflon and the simple coating technology make the strategy easily scale up and show promising applications.

Influence of Oil Status on Membrane-Based Gas-Oil Separation in DGA

Gas-oil separation by membrane stands for a promising technique in dissolved gas analysis (DGA). Since the accuracy of DGA relies on the results of gas-oil separation to a great extent, it is necessary to study the influence factor of membrane for better performance. Although plentiful studies have been conducted aiming at membrane modification to obtain better separation performance, it cannot be ignored that the conditions of oil also affect the performance of membrane much. In this work, a photoacoustic spectroscopy-based sensor for DGA, which employed membrane for gas-oil separation, was established first. By detecting the photoacoustic signal, the performance of membrane could be evaluated. Furthermore, the influences of feed velocity and pressure have on the performance of membrane were analyzed. Both simulation and experiment were employed in this work to evaluate the influences by collecting the equilibrium time of membrane under different conditions. As a result, the simulation and experiment agreed with each other well. Moreover, it was reasonable to draw the conclusion that the equilibrium time was evidently reduced with the raise of feed velocity but remained with a minimum change when pressure changed. The conclusion may serve as a reference for the application of membrane in optical sensor and DGA.

Development of an Online Detection Setup for Dissolved Gas in Transformer Insulating Oil

The type and concentration of dissolved gases in transformer insulating oil are used to assess transformer conditions. In this paper, an online detection setup for measuring the concentration of multicomponent gases dissolved in transformer insulating oil is developed, which consists of an oil-gas separation system and an optical system for acquiring the transformer status in real time. The oil-gas separation system uses low pressure, constant temperature, and low-frequency stirring as working conditions for degassing large-volume oil samples based on modified headspace degassing. The optical system uses tunable diode laser absorption spectroscopy (TDLAS) to determine the gas concentration. Six target gases (methane, ethylene, ethane, acetylene, carbon monoxide, and carbon dioxide) were detected by three near-infrared lasers (1569, 1684, and 1532 nm). The stability of the optical system was improved by the common optical path formed by time-division multiplexing (TDM) technology. The calibration experiments show that the second harmonics and the concentrations of the six gases are linear. A comparison experiment with gas chromatography (GC) demonstrates that the error of acetylene reaches the nL/L level, while the other gases reach the μL/L level. The data conforms to the power industry testing standards, and the state of the transformer is analyzed by the detected six characteristic gases. The setup provides an effective basis for the online detection of dissolved gas in transformer insulating oil.