Liquid flow through converging microchannels and a comparison with diverging microchannels

Diverging and converging microchannels are becoming an important part of microdevices. In this work, an experimental study of liquid flow through converging microchannels is performed and analyzed using results from 3D numerical simulations. Converging microchannels of various configurations: hydraulic diameter (118-177 mu m), length (10-30 mm) and convergence angle (4 degrees-12 degrees) are used to measure the pressure drop for a volume flow rate range of 0.5-5 ml min(-1) (8.33 x 10(-6)-8.33 x 10(-5) kg s(-1)) using deionised water as the working fluid. It is observed that the pressure drop in a converging microchannel varies non-linearly with the volume flow rate, and inversely with the convergence angle and hydraulic diameter. An equivalent hydraulic diameter is introduced in order to predict the overall pressure drop through the converging microchannel using the established theory for straight microchannels. The equivalent hydraulic diameter of the converging microchannel lies at 1/3.6th of the total length from the narrowest width of the microchannel; compared with 1/3rd for the diverging microchannel. A comparative analysis of flow through diverging and converging microchannels is also performed. It is shown that fluidic diodicity varies asymptotically with the angle and length of microchannels, whereas it increases with the volume flow rate. A theoretical expression for diodicity is also derived. The maximum fluidic diodicity is found to lie between 1.2 and 1.3. The data presented in this work is of fundamental importance and can help in optimizing the design of various microdevices.