This dissertation is an experimental investigation of the flow organization and performance enhancement of the micro-hydrocyclone by the means of Dean vortices. Micro-hydrocyclones are compact, passive microfluidic devices designed for the continuous separation of particles. While they hold strong potential for high-throughput applications, their internal flow organization and overall performance remain poorly characterized. Miniaturization can lead to fundamental changes in the flow regime. Yet, the nature of these changes has not been experimentally explored. On the performance side, most prior investigations rely on simplified test cases involving two particles or cell sizes evaluated at a small number of flow rates, offering only a narrow view of device capabilities. As a result, the flow behavior and device performance remain largely unknown. Dean vortices are known as secondary flow form in both macro and micro-curved channels which has significant role in conventional microfluidic devices employing micro-curved channel for particle separation and mixing. In this dissertation it is hypothesized that inducing Dean vortices at the inlet of the micro-hydrocyclone can enhance the performance of the device. Dean vortices play an important role in particle lateral migration separation techniques but have often been discussed in literature without consistency. A thorough review revealed that the Dean number, a dimensionless parameter used to characterize the onset and strength of Dean vortices, was defined inconsistently across studies, with variations in geometric parameters and reference velocities. This lack of standardization has led to inconsistencies in reported thresholds and made it difficult to develop generalized design criteria. To resolve this, a comprehensive analysis of existing definitions was conducted, and a unified and physically consistent definition of the Dean number, for the microscale flow, was formulated. This new formulation provides a baseline for comparing results and guiding future microfluidic designs involving curved geometries. To validate the presence and behavior of Dean vortices in microscale geometries, a series of experiments were conducted using curved microchannels. The goal was to directly observe the formation of secondary flows and assess their influence on larger, deformable objects. Through a combination three-dimensional scanning Particle Image Velocimetry (PIV), and two-phase flow studies, it was experimentally confirmed that Dean vortices consistently form in the curved microchannel geometry when the Reynolds number is high enough. Moreover, these vortices were shown to interact with suspended deformable structures, affecting their shape and trajectory. These findings established a physical basis for manipulating flow fields within a micro-hydrocyclone by integrating a curved inlet geometry. To investigate whether the flow within a micro-hydrocyclone can be effectively visualized and measured under realistic operating conditions, optical diagnostics were applied to capture both the structure and dynamics of the internal flow. Using planar PIV and Particle Tracking Velocimetry (PTV), flow field was measured in configurations with and without Dean vortex induction. Experiments were also conducted with and without the presence of cell clusters to assess the influence of them on flow organization and measurement feasibility. Additionally, stereoscopic microscopy was employed to resolve the three-component velocity field at the midplane of the micro-hydrocyclone, providing deeper insight into the three-dimensional nature of the flow structures. These techniques together enabled clear visualization and flow measurement of swirling motion and vortex asymmetries inside the device, demonstrating that the internal flow can be captured even in complex, multiphase scenarios. This multi-modal approach established the feasibility of using optical diagnostics to evaluate and compare the flow organization without the existence of the cell clusters. Building on the flow characterization, the performance of the micro-hydrocyclone was evaluated across a wide range of operating conditions using both particles and biological cell clusters. To support this extensive analysis, a dedicated software tool was developed to automate image processing, particle detection, size classification, and statistical quantification. This enabled high-throughput assessment of separation efficiency and repeatability. The results showed that Dean vortex induction significantly improved separation performance. In experiments using cell clusters, it was demonstrated that the modified configuration maintained the clusters intact while still enhancing separation efficiency. This confirmed that inducing secondary flows through geometric design not only boosts performance but also allows for gentler operation suitable for biological applications