Liquid mixing enhanced by pulse width modulation in a Y-shaped jet configuration

Abstract

In this paper, mixing between two fluid streams, which are injected into a planar mixing channel via a Y-shaped confluence section at the same volume flow rate, is studied experimentally. The injection of the two fluid streams is controlled by two separate solenoid valves, which are operated with a phase difference of 180 • , using pulse width modulation. The experiments are conducted using water at a mean Reynolds number between 83 and 250, a range of pulsation frequencies and two duty cycles (25 and 50%). Both particle-image velocimetry and planar laser-induced fluorescence technique are used to visualize the flow patterns and to quantify the mixing degree in the mixing channel. This experiment shows that the pulsation of each jet produces vortical structures, which promotes mixing via vortex entrainment and vortex breakup, and at the same time the mixing is also greatly enhanced by sequential segmentation produced by a 180 • out-of-phase pulsation of the two jets. This mixing enhancement method is effective at a Reynolds number greater than 125 with a mixing degree of 0.9 being achieved. For the Reynolds numbers studied in the present experiments, an optimal frequency exists, which corresponds to a Strouhal number in the range of 0.5-2. Furthermore, at a given mean Reynolds number a lower duty cycle is found to produce a better mixing due to the resultant higher instantaneous Reynolds number in the jet flow. It is also found that pulsation of only one jet can produce a similar mixing effect.

A Review on Micromixers

“…The typical pressure field driven micromixer is based on alternate perturbation, which was first reported by Deshmukh et al [ 67 ] using the pulsatile flow micropumps to induce alternate perturbation on fluids in 2000. Some similar micromixers were then reported for mixing two fluids with different flow characteristics and hydrodynamic instability [ 15 , 16 , 68 ]. One common design of the pulsatile pressure driven micromixer uses two micropumps and a typical T-type channel [ 16 ].…”

“…Active micromixers depend on different external energy sources to disturb the fluids, increase the contact area, or induce the chaotic advection, thus enhancing the mixing effect. Based on the types of external energy sources, the active micromixers can be further categorized as pressure field driven [ 7 , 13 , 14 , 15 , 16 ], electrical field driven [ 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 ], sound field driven [ 6 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 ], magnetic field driven [ 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 ], and thermal field driven [ 58 ,…”

Effect of pulsation on the near flow field of a submerged water jet

“…For a particular Reynolds number, as the pulsation frequency increases, the number of vortex structure increases in the flow field. Whereas after a certain frequency of pulsation both the size and strength of vortices decrease due to reduced time interval between successive vortex formation [19]. However as the Reynolds number increases the velocity of jet increases, which pulls the surrounding fluid at a faster rate, and the optimum frequency of pulsation shifts towards the higher frequency.…”

Rapid AC Electrokinetic Micromixer with Electrically Conductive Sidewalls

“…In contrast, active mixers usually employ external energy to introduce disturbances on the flow to enhance fluid mixing. Several types of active micromixers with flow disturbances generated in terms of temperature [6], pressure [7], electrohydrodynamics [8,9], acoustics [10], as well as magnetics [11], have already been reported to effectively enhance fluid mixing in microchannels.…”