Flow pattern measurement by PIV in the microchannels of a heat exchanger and associated problems due to fouling

This paper presents preliminary experimental results of measuring velocity fields of a transparent liquid flow in a closed circuit, through a 100 mum, 200 mum and 500 mum depth flat cell with and without included 200 mum x 200 mum heat exchanger microchannel elements. A microscopic particle image velocimetry system has been developed which consists of a 5 ns pulsed Nd:YAG laser, an epi-fluorescent microscope and a cooled interline transfer CCD camera to record high-resolution 0.7 mum diameter fluorescent particle image fields. The development of the optical micro-flow measuring instrument for the present application took into consideration the fact that the test object is aimed to be exposed to pressures up to 0.6 MPa leading to flow velocities up to 15 m/s, as well as temperatures up to 100degreesC. Particle fouling phenomenon proved to be the main difficulty in performing velocity field measurements in microchannels and techniques to avoid or limit it are proposed.