An Experimental Study On The Breakup Of Power Law Liquid Jets

The breakup and atomization of liquid jets are of theoretical importance and have been widely used. In various types of liquid jet, the non-Newtonian fluid especially power law fluid occupies an important place in daily life and practical applications. Due to the complexity and variety of the non-Newtonian liquid, the theoretical explanation of the jet breakup mechanism and experimental understanding are still not satisfactory. In the present work, an investigation has been conducted on the breakup of power law liquid jets.An experimental system mainly consisting of an injecting system, environment control system and photographing system has been designed and established, with which the research on the breakup and spray characteristics of power law liquid jets can be carried out. By applying shadow-graph technique and high speed imaging technique, spray characteristics such as breakup length and spray angle of both types of cylindrical jet and sheet jet are obtained. The effect of parameters such as flow conditions, environmental conditions, fluid properties and nozzle geometries on the spray characteristics has been investigated.The experimental results show that, increasing the jet velocity will reduce the inhibitory effect of liquid viscous force and surface tension, which will lead to a decrease of the jet breakup length and an increase in spray angle, and which promotes the breakup. Both of increasing the backpressure or using SF6 as environment gas will lead to an increase in the gas-liquid density ratio, which will promote the breakup. The temperature of environment has an effect on the liquid evaporation and properties such as power law index and viscosity, the higher the temperature is, the easier the atomization will be observed. Also the nozzle geometries such as diameter, length-diameter ratio and the initial thickness of sheet have effect on the spray characteristics; however it seems that the results are affected by machining accuracy. The results also show the differences between two types of power law fluids, and the consistency index has an inhibiting effect on the breakup of the jet. The experimental results accord well with the theoretical predictions.