A miniature high strain rate device

Presented here are micro-PIV measurements of velocity and strain rate in a cross-slot region of a micro-cross channel. A micro-cross channel produces a homogeneous two-dimensional extensional flow with hyperbolic streamlines similar to Taylor’s four-roll mill at larger scale. Due to the existence of the moving elements in four-roll mills, manufacturing a micron-sized four-roll mill is extremely challenging and consequently their applications are limited to the study of millimetre-scaled objects. Moreover, the natural instability of the flow in four-roll mills, caused by growing vortices at high rotational speed, limits the study of objects at high strain rates. Thanks to advances in micro-fluidics, the micro-cross channel is an alternative device for the four-roll mill without its restrictions. However, no systematic study has been carried out to measure the strain rate of the flow field in these devices. Apart from presenting a detailed procedure for the construction of micro-cross-channels, our micro-PIV results illustrate that high strain rates up to 24 s^-1 can be reached, whereas 6 s^-1 was the highest reported strain rate in a four-roll mill to date.