Micro-flow metering and viscosity measurement of low viscosity Newtonian fluids using a fibreoptical spatial filter technique

The paper describes an experimental method that is capable of measuring liquid flows of the order of millilitres per hour. Volume flow of laminar flows of Newtonian liquids in pipes or channels can be determined by measurement of the centreline velocity and application of the equation of Hagen-Poiseuille. Micro-flow meters with double fibre-array sensor were developed for the measurements of liquid volume flow in capillaries and micro-channels. The main units of the micro-flow meters are a laser-diode system, a double fibre-array sensor and different transparent capillaries or micro-channels. The accuracy of the measured water volume flow was tested with a balance and a syringe pump with given volume flow. Furthermore, the influence of the size of tracer particles on the volume flow results was also determined. This method of flow metering of Newtonian liquids needs no calibration and the results are not influenced by changes in temperature, pressure or nature of Newtonian liquid. An additional measuring result is the determination of the viscosity function by the application of a stripe model of the two-dimensional micro-channel flow. Possible applications of the fibreoptical micro-flow meter lie in micro- volume flow measurements of different Newtonian liquids and in viscosity measurements of Newtonian and non-Newtonian liquids.