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.].

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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. @en