This study investigates the flow behaviors of the microflow in a sudden expansion microfluidic channel with a rectangular block structure. 2D and 3D numerical simulations are used to predict the vortex formation behavior and experimental approaches are adopted to confirm the simulated results. A novel microfluidic rectifier is proposed by operating the designed microfluidic device under opposite flow conditions. The performance of the flow rectifier is also evaluated under difference flow velocities. There are three parts finished in this thesis. Firstly, the vortex formation behavior is investigated for the microchannel with the block at different distances downstream the sudden expansion channel. The size of the fully developed vortices is measured and analyzed. Results show that the size of the vortex reaches stable while the distance between the block and sudden expansion channel is longer than 1000 £gm. Secondly, this study also investigates the sequence of the vortex formation under different flow velocity (Reynolds number). Results indicate that there are four stages for the vortex formation in the microfluidic channel. Vortices are formed firstly at the sudden expansion channel and then behind the block. Two small vortices are then formed once beside the block and then merge with the two big vortices behind the block under increasing velocity conditions. The flow becomes instable once the Reynolds number higher than 555, two symmetrical shedding flows are observed behind the block structure. This flow behavior is rarely observed in a microfluidic channel due to the big viscous force of the flow in the microchannel. Thirdly, this study measures the pressure drops for the forward and backward flows under different flow speeds. Results show that the vortex formation behavior in backward flow is different from it is in forward conditions. Two symmetric vortexes are formed beside the channel while the Reynolds number higher than 416. The squeezed vortices form a virtual valve structure and increase the flow resistance of the microflow, resulting in a high performance valve structure. The calculated results indicate that the diodicity (Di) of the designed microchannel is as high as 1.76 and 1.5 for the numerical result and experimental result, respectively. The rectifying performance of the developed microchip device is higher than the reported devices fabricated using delicate processes and designed. The results of this research will give valuable knowledge for the flow behavior in a microchannel and the design of microfluidic chips.

Tesla valve applications for passive flow enhancement in micro fluidic applications are promising, because of its design of no-moving-parts. The effectiveness of the valve (measured via its pressure and thermal diodicity) can be increased by creating a multi-staged Tesla valve. Present study investigates the effect of varying Reynolds number (25-200) on flow rectification and thermal enhancement capability of a Tesla valve. Gamboa Morris Forster (GMF) design with a cross-section of 1mm2 and constant valve-to-valve distance (1mm) was utilized for this research. An arbitrary fluid with constant properties at a reference temperature was used as the working fluid. Periodicity in flow and thermal distribution are noticed in the latter part of MSTV. Average friction factor and pressure diodicity decreased with increasing Reynolds number whereas average Nusselt number and thermal diodicity increased. Correlations for friction factor, pressure diodicity, Nusselt number, and thermal diodicity were derived by fitting a non-linear curve fit model.