Losses due to the Flow Through Conduit Components in Mini- and Micro- Systems Accounted for by Head Loss/Change Coefficients

The definition of head loss/change coefficients should be based on the dissipation in the flow field or, in a more general sense, on the entropy generation due to a conduit component. When, in the simplest case, unbranched flow is considered, an entropy based approach is straight forward since the flow rate can be used as the general reference quantity. If, however, one mass flow rate is split or two partial flow rates are united like in junctions, a new aspect appears: There is an energy transfer between the single branches that has to be accounted for appropriately. It turns out that this energy transfer changes the total head in each flow branch in addition to the loss of total head due to entropy generation. Therefore, appropriate coefficients for junctions should be named head change coefficients. As an example, head change coefficients for dividing and combining flows due to T-shape micro-junctions are investigated and discussed with respect to their physical meaning. For combining flows, the special case of engulfment, leading to enhanced mixing in micro mixers, is considered in detail.