Droplet Generation with Controllable Diameter using PID Controller: Experimental Study

Droplet generation with controllable precise size is the target of this research. For this purpose, a flow focusing micro-channel is constructed using photolithography. Then, by injecting two incompatible fluids to the channel, micro-droplets are generated. Two syringe pumps are used. The Meros high speed camera is used for recording the image of droplets, and a fast image processing algorithm is used to calculate the size of the droplets. The feedback loop is completed by connecting the camera, microscope, syringe pumps and PC computer. To regulate the size of the droplet, the PID controller is used due to its ease of implementation and robustness. The flow rate of the continuous phase is the control input and the size of the droplets is the output of the closed-loop system. Experimental tests are done by considering three desired droplet diameter, i.e. 100, 140 and 160 μm. In all cases, the controller shows good performance. To show the disturbance rejection characteristic of the designed system, the flow rate of the discrete phase is changed stepwise. Due to this disturbance the transient response of the system changed, but the controller attenuates this disturbance, and regulates the system to the desired size. The experimental tests show that the designed closed-loop microfluidic system is able to generate droplets with desired precise size.