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Abstract: In microscopic particle image velocimetry (micro-PIV), correlation averaging over multiple frames is often required, leading to a loss in temporal resolution, therefore limiting the measurement accuracy for unsteady flows. Here, we present a new PIV method suitable to study steady and unsteady laminar flows between parallel plates (i.e., Hele-Shaw flow), which is a common flow configuration in microfluidic applications. Our method reduces the effective seeding density and yields similar if not higher signal-to-noise ratio (SNR) compared to conventional micro-PIV. We call this algorithm Ψ -PIV. Ψ -PIV requires a much smaller number of frames to reach the same SNR compared to the widely used correlation averaging method. This leads to a significant improvement of the temporal resolution. The Ψ -PIV algorithm is used in an experimental investigation of steady and unsteady flows in a Hele-Shaw cell. Our experiment shows that Ψ -PIV reduces the number of required frames by 8 times and 30 times compared to the frames required by conventional PIV for steady and unsteady laminar flow, respectively. In this study, PIV and Ψ -PIV use a single-pass cross-correlation to present the underlying difference between the two approaches. Graphic abstract: [Figure not available: see fulltext.]., With Correction: https://doi.org/10.1007/s00348-020-2913-0, Fluid Mechanics

In micro-PIV, reaching the optimum image density has always been difficult due to high displacement gradient, coagulation of particles at the inlet and due to particles adhering to the surface to name a few. The most widely used method is to take ensemble correlation average of multiple PIV images to extract the velocity field. However, this leads to low temporal resolution. Hence, a method with high temporal resolution is pivotal to study unsteady laminar flow in microfluidic application. This work aims at developing a new PIV algorithm which reduces the effective seeding density and at the same time yield similar if not higher SNR compared to conventional PIV. We call this algorithm Ψ-PIV. This method is suitable for steady and unsteady laminar flows which are generally found in microfluidic applications. The reliability and the precision of the new method as a function of particle image pairs is investigated by synthetic image analysis. The main advantage of Ψ-PIV is its ability to achieve higher temporal resolution from the typical micro-PIV raw images. The experimental investigation for the flow around a 2D cylinder in a Hele-Shaw cell showed that the Ψ-PIV results in a reduction by approximately a factor of 25 in the number of frames required compared to conventional PIV., Fluid Mechanics

The interest in manipulating particles, droplets and bubbles have garnered significant attention in recent years, owing to the advantages offered by micro-fluidics and the advancement in micro-fabrication technologies. These manipulation activities have found its applications in myriad fields of engineering, ranging from medical diagnostics to chemical industry to drug discovery. This has increased demand for the development of devices such as 'Lab on a chip', which performs laboratory-sized experiments and analysis on a single small chip, with the same speed and accuracy as its room-sized counterpart. However, manipulation activities carried out in these devices has fixed channels, designed to serve purpose for specific manipulation tasks. This makes the device suitable for a specific application. Addressing this aspect, a device designed without having any real channels would give an opportunity to integrate multiple functionalities onto a single-chip in the long run. As a first step towards reaching this 'bigger picture', it is necessary to explore the feasibility of manipulating particles, droplets and bubbles by generating so called 'virtual channels'. The present thesis focuses on an attempt to manipulate particles without the use of any real channels or external field. Although such manipulation is desired in the micro-scale, a top down approach is preferred and hence, the manipulation is carried out in a scaled up model. First, a Hele-Shaw flow cell is designed with sources and sinks in the millimeter scale to deviate streamlines in the same range. Thereafter, four different velocity fields are studied under different combination of sources and sinks, which are then compared to the computational ones. The property of a Hele-Shaw cell that the averaged velocity over the height of the channel is irrotational, makes it possible to compute velocity fields by the use of potential flow theory. The same velocity fields are hence, computed using a discrete sourc, Mechanical Engineering

The interest in manipulating particles, droplets and bubbles have garnered significant attention in recent years, owing to the advantages offered by micro-fluidics and the advancement in micro-fabrication technologies. These manipulation activities have found its applications in myriad fields of engineering, ranging from medical diagnostics to chemical industry to drug discovery. This has increased demand for the development of devices such as 'Lab on a chip', which performs laboratory-sized experiments and analysis on a single small chip, with the same speed and accuracy as its room-sized counterpart. However, manipulation activities carried out in these devices has fixed channels, designed to serve purpose for specific manipulation tasks. This makes the device suitable for a specific application. Addressing this aspect, a device designed without having any real channels would give an opportunity to integrate multiple functionalities onto a single-chip in the long run. As a first step towards reaching this 'bigger picture', it is necessary to explore the feasibility of manipulating particles, droplets and bubbles by generating so called 'virtual channels'. The present thesis focuses on an attempt to manipulate particles without the use of any real channels or external field. Although such manipulation is desired in the micro-scale, a top down approach is preferred and hence, the manipulation is carried out in a scaled up model. First, a Hele-Shaw flow cell is designed with sources and sinks in the millimeter scale to deviate streamlines in the same range. Thereafter, four different velocity fields are studied under different combination of sources and sinks, which are then compared to the computational ones. The property of a Hele-Shaw cell that the averaged velocity over the height of the channel is irrotational, makes it possible to compute velocity fields by the use of potential flow theory. The same velocity fields are hence, computed using a discrete sourc, Mechanical Engineering