PIV investigation of the flow features of double and single 45° up-pumping pitched blade turbines in a square tank

Past and current components-based detailing of particle image velocimetry: A comprehensive review

Particle image velocimetry has been widely used in various sectors from the automotive to aviation, research, and development, energy, medical, turbines, reactors, electronics, education, refrigeration for flow characterization and investigation. In this study, articles examined in open literature containing the particle image velocimetry techniques are reviewed in terms of components, lasers, cameras, lenses, tracers, computers, synchronizers, and seeders. The results of the evaluation are categorized and explained within the tables and figures. It is anticipated that this paper will be a starting point for researchers willing to study in this area and industrial companies willing to include PIV experimenting in their portfolios. In addition, the study shows in detail the advantages and disadvantages of past and current technologies, which technologies in existing PIV laboratories can be renewed, and which components are used in the PIV laboratories to be installed.

Infection control measures for public transportation derived from the flow dynamics of obstructed cough jet

During the COVID-19 pandemic, WHO and CDC suggest people stay 1 m and 1.8 m away from others, respectively. Keeping social distance can avoid close contact and mitigate infection spread. Many researchers suspect that suggested distances are not enough because aerosols can spread up to 7-8 m away. Despite the debate on social distance, these social distances rely on unobstructed respiratory activities such as coughing and sneezing. Differently, in this work, we focused on the most common but less studied aerosol spread from an obstructed cough. The flow dynamics of a cough jet blocked by the backrest and gasper jet in a cabin environment was characterized by the particle image velocimetry (PIV) technique. It was proved that the backrest and the gasper jet can prevent the front passenger from droplet spray in public transportation where maintaining social distance was difficult. A model was developed to describe the cough jet trajectory due to the gasper jet, which matched well with PIV results. It was found that buoyancy and inside droplets almost do not affect the short-range cough jet trajectory. Infection control measures were suggested for public transportation, including using backrest/gasper jet, installing localized exhaust, and surface cleaning of the backrest.

Investigation on the Flow Field and Mixing Efficiency of a Stirred Tank Equipped with Improved Intermig Impellers

The flow field in a transparent stirred tank with a diameter of D = 0.42 m equipped with dual-layer improved Intermig impellers was numerically investigated using a multi-reference frame method based on the computational fluid dynamics (CFD) simulation code: Fluent. The simulation results were validated by experiments based on a stirred tank testing platform and a Particle Image Velocimetry (PIV) testing instrument. The effects on the flow field arising from the diameter of impellers, the installation height of impellers (C1), the rotational speed as well as the distance between two impellers (C2) were investigated. It was revealed that the distance between two impellers and the installation height has obvious influences on the local flow field around impellers. Appropriately increasing the two parameters can enhance the axial flow and achieve a better mass transfer effect. For the tank model rescaled for experiments, the optimized geometrical parameters are C1 = 0.36D and C2 = 0.49D that can result in full occupation of large eddies in the entire volume. The mixing process simulation indicates that the mixing efficiency is the best in the region near the impellers while it is the worst in the bottom of the tank. An appropriate increase in the diameter of the lower impellers and a reduction in the distance from the lower impellers to the tank bottom can improve the mixing efficiency in the central region near the tank bottom.