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 According
to Hagen-Poiseuille´s law, the fully developed stationary
flow through a microchannel with constant cross section is directly
proportional to the pressure drop across the channel. In particular,
the flow rate at a certain pressure drop depends on the micro
channel cross section, the length and the viscosity of the fluid
(which is usually influenced by temperature). Thus, the direction
and flow rate of a liquid medium can be determined by measuring
the difference in pressure across a given micro channel, provided
the medium's viscosity and its temperature dependence are known
and compensated. The flow sensor consists of a micro channel
and two piezo resistive pressure sensors. The micro channel
can be a pitot tube or orifice plate. An external temperature
compensation may be necessary to eliminate the effect of a varying
fluid viscosity.
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