Numerical study of cavitating flow in orifices and its effect on spray characteristics

The bubbly flow regime inside orifices has significant effects on several applications, and studying its trend along an orifice could be helpful in identifying the flow mechanism in various situations. The flow regime inside an orifice depends on the situation which has been specified for the orifice. Orifice geometry has a considerable effect on bubbly flow in injectors. Meanwhile, spray characteristics are influenced by the fuel flow inside an orifice, which has strong effects on the mixture of fuel-air. In this study, spray characteristics are studied for different values of the orifice angle. The cavitation phenomenon which occurs inside an orifice varies in intensity and patterns at different angles of the orifice and consequently has diverse effects on spray characteristics. The governing equations are solved by the SIMPLE algorithm. The spray flow is modeled by the discrete droplet method（DDM）, the droplet breakup is modeled by the WAVE model, and the primary breakup is modeled by the DIESEL BREAK UP model. In order to generate cavitation phenomenon inside orifices and investigate its effect on spray characteristics, the angle of orifice with respect to the injector body is varied and the problem is studied for different angles of orifice.

Active power based distance protection scheme in the presence of series compensators

Flexible ac transmission system(FACTS)controllers,especially the series-FACTS controllers,affect the operation of distance relays and can lead to the relays under/over-reaching.This paper aims to demonstrate the effects of static synchronous series compensator(SSSC)and series capacitive compensation(SCC),as two important series compensators,on the distance protection using theoretical and computational methods.The results of the investigation are used to develop a feasible and adequate method for eliminating the negative effects of these devices on the distance relays.The developed method measures the voltages at terminals of the SSSC and SCC by phasor measurement units(PMUs)which are then transmitted to the relay location by communication channels.The transmitted signals are used to modify the voltage measured by the relay.Different operation types and conditions of SSSC and SCC,and different faults such as phase-to-phase and phase-to-ground faults are investigated in simulations.Since the modeled distance relay can measure the fault resistance,trip boundaries are used to show the performance of the presented method.Results show that the presented method properly eliminates the negative effects on the distance relays and prevents them from mal-operation under all fault resistance conditions.

Design and fabrication of a vigorous“cavitation-on-a-chip”device with a multiple microchannel configuration

Hydrodynamic cavitation is one of the major phase change phenomena and occurs with a sudden decrease in the local static pressure within a fluid.With the emergence of microelectromechanical systems(MEMS),high-speed microfluidic devices have attracted considerable attention and been implemented in many fields,including cavitation applications.In this study,a new generation of‘cavitation-on-a-chip’devices with eight parallel structured microchannels is proposed.This new device is designed with the motivation of decreasing the upstream pressure(input energy)required for facile hydrodynamic cavitation inception.Water and a poly(vinyl alcohol)(PVA)microbubble(MB)suspension are used as the working fluids.The results show that the cavitation inception upstream pressure can be reduced with the proposed device in comparison with previous studies with a single flow restrictive element.Furthermore,using PVA MBs further results in a reduction in the upstream pressure required for cavitation inception.In this new device,different cavitating flow patterns with various intensities can be observed at a constant cavitation number and fixed upstream pressure within the same device.Moreover,cavitating flows intensify faster in the proposed device for both water and the water–PVA MB suspension in comparison to previous studies.Due to these features,this next-generation‘cavitation-on-a-chip’device has a high potential for implementation in applications involving microfluidic/organ-on-a-chip devices,such as integrated drug release and tissue engineering.