Computer-Controlled Flow Cell for the Study of Particle and Drop Dynamics in Shear Flow Fields

Computer control for flow cells and its application for the study of droplet and particle dynamics in shear flow conditions are presented. In the past, experimental work on single particle motion in flow has been restricted in scope by unsteady flows or by an experimental device that requires the operator to maintain the particle in the flow manually. The aim of this work is to retain particles or droplets within the observation area for arbitrarily long experimental times and to apply higher shear rates than those with other comparable flow cells and control schemes. The control application considered here, using direct image analysis via a CCD camera, allows online control of the position of the particle. A second CCD camera installed at an angle of 90(degree) with respect to the first camera provides additional experimental data for the full spatial observation of, e.g., drop deformation. A digital proportional-integral-differential (PID) controller was implemented to control the flow field. As an example, a device based on a parallel-band design was selected to demonstrate the control scheme and its application. The design of the flow cell, the software implementation including image acquisition and analysis, digital PID control, and the graphical user interface are described. The control scheme is designed in a way that other flow geometries can be utilized by adjusting the PID parameters. Results from experiments on the rotation behavior of rodlike particles (fibers) in a continuous liquid phase as well as on the deformation of a single drop under transient shear flow are presented and discussed.