An experimental study of fluid flow and heat transfer in rectangular microchannels

This thesis reports on an experimental study of fluid flow and heat transfer in high aspect ratio, rectangular microchannels. A single channel with width of 10 mm was cut into polycarbonate spacers of various thickness, resulting in channel depths of 128 μm, 263 μm and 521 μm.; Tests conducted in the range of Re = 100–3800 showed friction factors generally larger, and transition to turbulence occurring at lower Reynolds numbers than predicted for macroscale channels. Experimental values of the friction constant were f · Re = 24.2 for an aspect ratio α* = 20:1, f · Re = 26.1 for α* = 40:1, and f · Re = 26.0 for α* = 80:1, compared with classical values of 22.4, 23.2, and 23.6, respectively.; Heat transfer experiments were performed with a constant heat flux boundary condition from the bottom surface of the channel. Experiments conducted for Re = 300–900 and Pr = 3.6–3.8 showed small or no departure from macroscale predictions for channels with hydraulic diameters larger than 500 μm. Results for the 80:1 aspect ratio channel showed a significant departure from theoretical predictions. Experimental values of local Nusselt numbers were approximately 25 percent lower than predicted using macroscale theory. A computer code was developed to model the solution for energy equation in laminar flow, and predict asymptotic values for the laminar Nusselt number.