Search

To quantitatively study the pressure fluctuations induced by the process of droplet formation in a T-junction microdroplet generator, the mathematical model which can accurately predict the amplitude and the frequency of the pressure fluctuations is demonstrated. Different geometries of the T-junction microchannels are designed for the experiments of droplet formation, and the time-varying pressure difference between the upstream and downstream of each droplet is measured during the droplet production progress. From both theoretical and experimental study, it can be observed the pressure difference is a periodic function of time for the whole process of droplet generation. In particular, the frequency of the pressure fluctuations coincides with the production rate of droplets, and the amplitude of the pressure fluctuations varies with the geometrical parameters of the T-junctions. Additionally, good agreements are shown between the theoretical calculations and the experimental measurements of the magnitude of the pressure fluctuations. Therefore, our mathematical model is validated experimentally, and the magnitude of the pressure fluctuations can be drastically reduced by optimization of the geometrical parameters of the T-junction. [ABSTRACT FROM AUTHOR]

To precisely control the size of the droplets is quite important for the application of the droplet microfluidic systems. To date, the size of monodisperse droplets is usually measured by the method of image processing for droplet microfluidics, which requires expensive detection devices such as microscope and high-speed camera. In this paper, an electrical-detection droplet microfluidic closed-loop control system is demonstrated, where the flow rates of fluids are controlled by the pressure-driven microfluidic device and the droplet size can be obtained from the method of electrical detection. The mathematical model of the closed-loop control system is established. Compared with the method of image processing, both the measuring efficiency and accuracy of the droplet size are increased significantly by the electrical-detection method, which can improve the dynamic characteristics of the droplet microfluidic closed-loop control system. In particular, a PI controller is integrated into the closed-loop control system to improve the control precision of the droplet size. By varying the flow rates of the fluids, the effects of the droplet production rates on the dynamic characteristics of the closed-loop control system are studied, and the control precision and stability of the system can be obtained from the experimental measurements. [ABSTRACT FROM AUTHOR]

Novel gas sensors with high sensing properties, simultaneously operating at room temperature are considerably more attractive owing to their low power consumption, high security and long-term stability. Till date, zinc oxide (ZnO) as semiconducting metal oxide is considered as the promising resistive-type gas sensing material, but elevated operating temperature becomes the bottleneck of its extensive applications in the field of real-time gas monitoring, especially in flammable and explosive gas atmosphere. In this respect, worldwide efforts have been devoted to reducing the operating temperature by means of multiple methods In this communication, room-temperature gas sensing properties of ZnO based gas sensors are comprehensively reviewed. Much more attention is particularly paid to the effective strategies that create room-temperature gas sensing of ZnO based gas sensors, mainly including surface modification, additive doping and light activation. Finally, some perspectives for future investigation on room-temperature gas-sensing materials are discussed as well. [ABSTRACT FROM AUTHOR]

VOC has brought a lot of troubles to human life. They are the main factors that cause smog and photochemical pollution. SnO 2 -based gas sensors have many good qualities, such as good sensitivity, good response/recovery time, and good stability. Therefore, in this review, we will focus on detecting SnO 2 -based chemical sensors for indoor formaldehyde, ethanol related to road traffic safety, acetone that can detect human health and other significant VOC. The sensing mechanism, performance, etc., of the SnO 2 -based gas sensor, which can selectively detect these gases, are discussed in detail. [Display omitted] [ABSTRACT FROM AUTHOR]

To precisely control the size of monodisperse droplets for droplet microfluidics, we here establish a closed-loop control system with real-time feedback of droplet length during droplet generation. Particularly, the microvalves are integrated into the system to control the flow rates of the two immiscible fluids. From experimental measurements, we observe that the droplet length is a linear function of the flow-rate ratio for low capillary numbers ( C a ≤ 0.1). More importantly, the coefficients of the linear relation are determined by the geometry of the microchannel, and independent of the viscosity of the fluids. Based on MATLAB Simulink, the deviation between the predicted and measured droplet length is quantitatively studied. By using a PI controller, both the response speed and control accuracy of the droplet length can be greatly improved for the closed-loop control system. As a result, high monodispersity and uniformity of droplet generation can be achieved in a T-junction microdroplet generator. [ABSTRACT FROM AUTHOR]

New energy resources applied in electricity generation have attracted great attention nowadays, especially in the auto industry. Because of the high energy density and enduring use life, the lithium-ion battery has been considered an appropriate electrical power resource for electric vehicles. However, cells with high energy density are more inclined to have thermal runaway problems, which can cause severe damage to battery performance. Sensors based on pressure and temperature have been applied in safety early warning and monitoring of thermal runaway, which do not perfectly meet the requirement of global technical regulation that passengers need to be warned before serious accidents. Therefore, gas detection for early safety warning of lithium-ion batteries can be an effective method to control and prevent thermal runaway problems. This review aims to summarize the recent progress in gas sensing of thermal runaway gases. We discuss the advantages and disadvantages of different types of sensors. Gas evolution mechanism in lithium-ion batteries is also proposed. It is expected that this review will inspire the development of battery safety early warning. More stable conditions for high energy density systems could be provided with such gas detection strategies and devices. [Display omitted] [ABSTRACT FROM AUTHOR]

SF 6 is widely used in insulation and arc extinguishing due to its excellent insulation performance. The detection of its decomposed gases can help us to effectively identify the types of internal malfunctions in gas-insulated switchgear (GIS). Based on the Density functional theory (DFT), the adsorption performance of intrinsic MoTe 2 and Sc-doped MoTe 2 (Sc-MoTe 2) on four gases (SO 2 , H 2 S, SO 2 F 2 , SOF 2) from SF 6 decomposition were studied in this paper. The calculation results indicate that the intrinsic MoTe 2 monolayers have weak adsorption capacity and low adsorption energy (E ad) for SF 6 decomposition gas products, which are all physical adsorption and with small transfer charge. However, the adsorption ability of MoTe 2 monolayer film to SF 6 decomposition gas products is significantly enhanced after doping the Sc atom. The adsorption energy is changed into chemical adsorption, and the amount of transferred charge in the adsorption process is significantly increased. Therefore, the adsorption performance of Sc-MoTe 2 for four gas products (SO 2 , H 2 S, SO 2 F 2 , SOF 2) from SF 6 decomposition are obviously superior to intrinsic MoTe 2. The results are helpful to further explain the sensing mechanism of gases in MoTe 2 , and establish a foundation for the sensor based on MoTe 2 to detect SF 6 decomposition gases. [Display omitted] • The effect of Sc dopant on structural and electronic properties of MoTe 2 monolayer were discussed. • The adsorption performances of intrinsic MoTe 2 monolayer to SF 6 decompositions SO 2 , H 2 S, SO 2 F 2 , SOF 2 are discussed. • The excellent adsorption performances of Sc-doped MoTe 2 monolayer to SO 2 , H 2 S, SO 2 F 2 , SOF 2 are discussed in detail. [ABSTRACT FROM AUTHOR]

In this paper, the adsorption performances for HCN upon pure and metal (Fe, Ag, Au, As and Mo) doped WSe 2 monolayers are analyzed on the ground of the density functional theory (DFT) and the best sites of doping are assumed. The adsorption performance of intrinsic WSe 2 , Fe-WSe 2 , Ag-WSe 2 , Au-WSe 2 and Mo-WSe 2 to HCN molecule were simulated according to the charge transfer, DOS and molecular orbital. The results manifest that all metal (Fe, Ag, Au, As and Mo) doped WSe 2 monolayers have better adsorption properties for HCN. Nevertheless, occurrence of chemisorption only exists in HCN/Mo-WSe 2 system, indicating this system might be candidate materials for the adsorption of HCN. Besides, after adsorption, the conductivity of all systems changes a lot, meaning that monitoring conductivity change of all systems above could be a method to sensing HCN. Thus, all metal (Fe, Ag, Au, As and Mo) doped WSe 2 could be favorable materials for HCN detection. [Display omitted] • The structural and electronic properties of Ag, As, Au, Fe and Mo doped WSe 2 monolayer were discussed in detail. • The adsorption properties of HCN on intrinsic and doped WSe2 monolayers were explored. [ABSTRACT FROM AUTHOR]

The adsorption performances of Cr atoms doped InN and GaN monolayers to SF 6 decomposed species were investigated based on density functional theory (DFT). We found that Cr-InN and Cr-GaN monolayers have excellent adsorption performance for SO 2 and SO 2 F 2 gas. Besides, for SOF 2 gas, the adsorption capacity of Cr-GaN monolayer is significantly stronger than Cr-InN. [Display omitted] • The effect of Cr dopant on structural and electronic properties of InN and GaN monolayer were discussed in detail. • The adsorption performances of the monolayers to three SF6 decomposition gases were discussed and compared in detail. • The changes in conductivity of Cr doped InN and GaN monolayers after adsorption were discussed in detail. In this paper, the adsorption properties of Cr modified InN (Cr-InN) and GaN (Cr-GaN) monolayers to SF 6 decomposed components were investigated based on the density functional theory (DFT). Results reveal that these two graphene-like materials exhibit strong adsorption capacity for the three decomposed species SO 2 , SOF 2 and SO 2 F 2. Remarkable adsorption energy, significant charge transfer and molecular deformation indicate the occurrence of chemisorption. The hybridization of atomic electron orbitals in the density of states calculation verifies the strong chemical interaction between the gases and two monolayers. According to this strong adsorption capacity, Cr-InN and Cr-GaN monolayers demonstrate their potential as gas Scavenger for removing SF 6 decomposition products in the insulation equipment. Besides, the significant change in conductivity of the monolayer caused by gas adsorption makes it possible to explore gas sensors based on Cr-InN and Cr-GaN monolayer. This paper indicates that Cr-doped InN and GaN monolayers can be used as adsorbents and sensors to guard the operation status of SF 6 insulation devices by detecting and scavenging SF 6 decomposed components. [ABSTRACT FROM AUTHOR]