ABSTRACT
Understanding the flow in the entrance region of a microchannel is very important because the transport properties of the flow, such as the pressure gradient and the heat transfer coefficient, depend strongly on the flow region. Planar microfabrication techniques generally constrain the reservoir upstream of the microchannel to be the same height as the channel — a marked departure from the geometries used at macroscopic-length scales to study entrance length. Advanced optical diagnostics for microscale flows are essential in acquiring a spatially resolved view of the flow in the small entrance region of microchannel flows. This chapter will describe the entrance length problem in microchannels, outline several microscale fluid diagnostic techniques, and use those techniques to analyze the entrance length in a microchannel.
