Abstract
In this paper, mixing between the fluid from a primary planar jet and two surrounding secondary planar jets which are pulsated out-of-phase is studied experimentally. Solenoid values are used to control the flow injection into the mixing channel with pulse-width modulation. The experiments are conducted using water at a range of pulsation frequency, two duty cycles (25 and 50%) and a mean Reynolds number between 100 and 250. The flow rate ratio between the primary and secondary flow is kept as unity. Both particle-image velocimetry and planar laser-induced fluorescence techniques are used to visualise the flow patterns and to quantify the mixing degree in the mixing channel. This mixing enhancement method is shown to be effective with a mixing degree as high as 0.9 achieved at a mean Reynolds number of about 166. A combination of different mixing mechanisms is found at play, including sequential segmentation, shearing and stretching, vortex entrainment and breakup. At a given Reynolds number, an optimal frequency exists which scales approximately with a Strouhal number (St = fh/U) of unity. Furthermore, at a given mean Reynolds number a lower duty cycle is found to produce a better mixing due to a resultant higher instantaneous Reynolds number in the jet flow.
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Acknowledgments
The first author of this paper, Qingfeng Xia, would like to acknowledge the financial support from both The University of Manchester and The Universities UK for his PhD studies. He also would like to thank Dr Shanying Zhang for his advice on the use of experimental instrumentations.
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Xia, Q., Zhong, S. Quantification of liquid mixing enhanced by alternatively pulsed injection in a confined jet configuration. J Vis 15, 57–66 (2012). https://doi.org/10.1007/s12650-011-0103-0
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DOI: https://doi.org/10.1007/s12650-011-0103-0