A test facility with simplified flow geometry is used, which provide optical access, but with boundary conditions matching those found in the real devices by similarity laws. Micro sized tubes of different cross sections can be connected to stagnation chambers equipped with k-thermocouples and pressure transducers to measure the temperature rise and pressure drop, respectively. The liquid flow is imposed by a syringe pump Green Stream SY P Argus 600 with Syringe B-D Perfusion 50/60mL, through a micro sized channel. The volume fluxes can be set from 0.1 to 999.9mL.h-1 with increments of 0.1mL.h-1 (deviation ▒2%), at a maximum working pressure of 120kPa.
Test facility for a) momentum transfer and b) heat transfer characterization
The tubes are covered with a transparent homogeneous InOX thin film to provide a constant heat flux at the surface. Precise control of the film thickness allows setting the proper electrical current to heat the tube up to a maximum temperature around 140║C. Surface thermocouples located along the tube length allow measure the rate of heat removal.
The microchannels used are made of very smooth borosilicate glass from Vitrocom«, USA, with inner and outer diameters shown on the representative photos of the tubes below obtained with the Hitachi S_2400 scanning electronic microscope. Multi Image V2.1 software and Matlab« were used to assess and correct the inner and outer diameters of the channels.
EDS (energy dispersive spectroscopy) elemental analysis showed that all the tubes used in the experiments have similar chemical composition. Also, the InOx thin film deposition is presented as homogeneous along the channel wall.
EDS elemental analysis prepared with a Jeol JSM-7001F FEG-SEM InOx thin film deposit at the outer wall and corresponding surface SEM image. Magnification of 45000x.