Related to nuclear reactor safety problems, such as the loss of coolant accident caused by some small crevasses in nuclear reactor, choked flows after postulated breaks of hot and cold legs of pressurized water reactors and the boiling flow instability in parallel channels, the characteristics of pressure wave propagation were investigated experimentally for the air-water bubbly and slug two-phase flow in a vertical pipe. Pressure wave was generated from the small pressure disturbance by the up-and-down movement of piston in the test section. Air void fraction was up to 0.7 and superficial liquid velocity was up to 1.5 m/s as experimental conditions. The experimental results show that the pressure wave propagation velocity in bubbly flow decreases acutely with the increase of air void fraction from 0 to 0.05. In slug flow, it is constant when the air void fraction is less than 0.5 but increases gradually when the void fraction increases beyond 0.5. The attenuation coefficient of pressure wave increases with the increase of air void fraction in bubbly flow. The dependency of pressure wave propagation velocity on angle frequency ω in air-water flow shows the dispersion characteristic. The propagation velocity and attenuation coefficient increases gradually with the increase of angle frequency. However, the increase vanishes slowly as the angle frequency reaches 250 Hz in bubbly flow. The propagation of pressure wave in bubbly flow is independent of the superficial velocity of fluids in the range of experiment. 相似文献
The transport and dosage of granular materials are an important part of Process Engineering. Thereby, the food, chemical, pharmaceutical and coating industries set high demands on the transport and dosage performances of the used plants. In this context, Ultrasound Process Technology in the past years has developed itself into an attractive alternative compared to presently used classical technologies.
This paper describes the application of ultrasonic progressive waves in a powder-feeding device. The use of a specific pipe material with appropriate damping characteristics allows to generate a progressive wave using a single piezoelectric actuator. Small objects can be carried along the surface of a pipe by the elliptic motion at the surface, which is the result of a flexural progressive wave. The operational principle is the same as in travelling wave ultrasonic motors.
It was experimentally confirmed that the device can be used for feeding and supplying small amounts of powder. The powder-fed performance, however, strongly depends on environmental conditions, so that a control of the system is required. Construction and characteristics of a trial device are shown. 相似文献
Measurements of boundary parameters and their fluctuations have been performed in ohmic (OH) plasma and Ion Bernstein Wave (IBW) and Lower Hybrid Current Drive (LHCD) enhanced confinement plasma using a pneumatically driven Langmuir probe array on HT-7 toka-maX. In the enhanced confinement plasma~ the gradients of electron density and temperature become higher and a transport barrier comes into being in the vicinity of the limiter. The boundary potential shows a clear modification in the same region. The fluctuation levels are significantly depressed and the coherences between fluctuations are reduced evidently in the enhanced plasma.Meanwhile, we obtained the spectral features and the poloidal phase velocity of fluctuations us-ing a two-point correlation technique and found obvious modifications of the turbulence and the poloidal flow. The results suggest that the improved confinement in the IBW and LHCD enhanced plasma is at least partially due to the modification of the boundary parameters and the suppression of the boundary fluctuations and fluctuation induced fluxes. 相似文献
In this paper, the calculated results about the propagation properties of electromag-netic wave in a plasma slab are described. The relationship of the propagation properties with frequencies of electromagnetic wave, and parameters of plasma (electron temperature, electron density, dimensionless collision frequency and the size of the plasma slab) is analyzed. 相似文献