Simulation modeling of composite piezotransformer measuring transducer with differential output

The article presents the results of using simulation modeling to study the output characteristics of composite piezotransformer measuring transducers with a differential output. The processes were simulated using the Micro-Cap software. The article presents options for controlling the parameters of the equivalent electrical circuit of the converter. The article presents the results of simulation of composite piezotransformer measuring transducers with two degrees of freedom. Structurally, they can include piezoelectric elements, additional vibrators and communication elements between them. This allows you to expand their functionality, scope of practical application. The advantages are applicable to work in difficult and even extreme conditions. On the basis of such measuring transducers, prototypes of highly sensitive sensors were developed for measuring pressures, forces, temperature and other physical quantities, for monitoring the physical and mechanical characteristics of solids, liquid and gaseous media.

The general directions of development of longitudinally oscillating ultrasonic emitters for gaseous media

The article is devoted to the development of a longitudinally oscillating emitter designed to influence gas-dispersed systems. The main methods and directions of modernization of radiators are proposed in order to increase the area of the radiating surfaces of the radiators, increase the uniformity of vibrations and reduce mechanical stresses.

Picosecond high-current discharge pumping of gaseous media emitting VUV-UV

The possibility of creating small picosecond lasers in the VUV-UV spectral range by pumping by a high-current volume discharge of gaseous media (Xe and N2) at a pressure of 1-3 atm is investigated. Generation of picosecond (200 ps) powerful (1.2 MW) pulses at a wavelength of 337 nm at an N2 pressure of 1–3 atm has been achieved. Based on studies of high-current volume picosecond discharges in xenon, using VUV-UV spectroscopy, the presence of short-lived absorption of VUV radiation by discharge plasma was observed. A mechanism for the suppression of the formation of Xe 2 * dimers due to thermal effects at the stage of recombination of electrons with Xe+ ions at a plasma temperature of 105 K with a pulsed pump of 200 ps duration was suggested.

Evaporation of a liquid sessile droplet subjected to forced convection

Experiments on measuring the rate of evaporation of liquid sessile droplets into air show that the rate of evaporation increases in the presence of forced convection flows. However, data on the effect of convection on evaporation are often contradictory and should be clarified. The paper presents a numerical analysis of evaporation from the surface of a water droplet subjected to forced convection in the gas phase. The drop is located on a smooth horizontal isothermal substrate; the mode with constant contact angle is considered. The shape of the drop has axial symmetry, the same for the velocities and pressure. Forced convection compatible with the symmetry conditions are represented by flows directed downward along the axis of the system and diverging along the sides near the drop and the substrate. The mathematical model is constructed for evaporation controlled by diffusion in the gas phase and takes into account surface tension, gravity, and viscosity in both media, buoyancy and Marangoni convection. The results indicate the existence of the mutual influence of liquid and gaseous media. Thus, a drop vibrates under the influence of movements in the atmosphere, which generates a density wave in the gas: the drop «sounds». The magnitude of the velocity in a liquid is 50 times less than the characteristic velocity in air. It is found that the evaporation rate does not change in the presence of forced convection flows, which contradicts most of the experimental works. The reason for the discrepancies is supposed to be the appearance of nonequilibrium conditions at the boundary of the condensed phase: under these conditions, the evaporation regime ceases to be diffusional.

PROPERTIES OF TUBES FROM Zr-1% Nb ALLOY AFTER THERMOCHEMICAL TREATMENT AND HYDROGENATION

The influence of treatment in controlled gas environments with subsequent hydrogenation on the physical and mechanical characteristics of the Zr-1% Nb zirconium alloy has been investigated. The surface hardness and the size of the diffusion-hardened layer of the ring-samples cut from fuel tubes from the Zr-1% Nb alloy after treatment in oxygen- and nitrogen-containing gaseous media with subsequent saturation with hydrogen have been established. The influence of the parameters of the gaseous medium and the modes of thermochemical treatment (TCT) of specimens-rings on the destructive stresses under static load at temperatures of 20 and 380 °C is shown. It was revealed that treatment in the investigated gas environment increases the resistance to hydrogen saturation and has a positive effect on the long-term strength of ring specimens from the zirconium alloy Zr-1% Nb.

Collisions of Liquid Droplets in a Gaseous Medium under Conditions of Intense Phase Transformations: Review

The article presents the results of theoretical and experimental studies of coalescence, disruption, and fragmentation of liquid droplets in multiphase and multicomponent gas-vapor-droplet media. Highly promising approaches are considered to studying the interaction of liquid droplets in gaseous media with different compositions and parameters. A comparative analysis of promising technologies is carried out for the primary and secondary atomization of liquid droplets using schemes of their collision with each other. The influence of a range of factors and parameters on the collision processes of drops is analyzed, in particular, viscosity, density, surface, and interfacial tension of a liquid, trajectories of droplets in a gaseous medium, droplet velocities and sizes. The processes involved in the interaction of dissimilar droplets with a variable component composition and temperature are described. Fundamental differences are shown in the number and size of droplets formed due to binary collisions and collisions between droplets and particles at different Weber numbers. The conditions are analyzed for the several-fold increase in the number of droplets in the air flow due to their collisions in the disruption mode. A technique is described for generalizing and presenting the research findings on the interaction of drops in the form of theoretical collision regime maps using various approaches.

Pengaruh Waktu Milling Terhadap Sifat Desorpsi Material Penyimpan Hidrogen MgH2-Ni Melalui Teknik Mechanical Alloying

Hydrogen is a renewable energy source that can be used as a fuel and as an alternative to fossil fuels. Solid storage media in solid form are safer to use than liquid (-253 oC) or gaseous media (700 bar) media. To store hydrogen in a solid medium, it requires a metal able to interact with hydrogen . Magnesium is one of the metals which can form metal hybrids based on MgH2 which is capable of absorbing hydrogen up to (7.6wt%). However, the reaction kinetics for magnesium are very slow, it takes at least 60 minutes to absorb hydrogen and the operating temperature is always very high (300 oC). Several attempts have been made to add the catalytic converter and milling time. Hydrogen storage material based on MgH2 with a 10wt%Ni catalyst was successfully synthesized using a mechanical alloy technique with time variations of 2 hours, 5 hours, and 10 hours. From the results of the X-ray diffraction schema at a diffraction angle of 2θ=37.87o, it shows the presence of a MgH2 phase, Ni phase is at a diffraction angle of 61.85o, the diffraction peak also shows that there was a widening of the diffraction peak with increasing milling time, this explains that there was a reduction in the size of the crystal. When calculating with the Schereer method, the crystal size of the material reaches 10 nm. The results of the DSC test indicated a decrease in temperature of 383 oC in 41 minutes with a milling time of 10 hours.

Experimental study of electrostatic fields influencing thermal processes in gaseous methane at its natural convection

The paper shows the history of studying electrostatic fields in various gaseous media, including gaseous methane, and substantiates the necessity to experimentally study electrostatic fields influencing thermal processes in gaseous methane at its natural convection. We describe the experimental base and working areas with the use of electrostatic fields, as well as the method of conducting experimental research. The results of the influence of electrostatic fields on the coefficient of heat transfer to gaseous methane and on the negative process of sedimentation in it — during its natural convection are presented. In our research, we found zones of possible intensification of heat transfer to gaseous methane and zones of saturation with electrostatic fields, in which a further increase in the heat transfer coefficient is impossible. We experimentally established that the boundary of the zone of the beginning of saturation with electrostatic fields is also the beginning of the corona discharge zone. The research results formed the basis for the method of using electrostatic fields in aircraft engines and power plants.