Papers by Keyword: Laser Doppler Velocimeter

Abstract: Gas velocity in cyclone separator is measured by testing with laser Doppler velocimeter in this paper. The measuring results indicates that tangential velocity, axial velocity, radial velocity of air distribute following some certain rules, reasonable selected structure parameters can improve separating efficiency

Abstract: Using a semiconductor laser as a lightsource of a laser Doppler velocimeter (LDV) is desirable to reduce the size and the cost of velocity measurement equipment. However, typical inexpensive semiconductor lasers suffer from the problem of instability in lasing wavelength. In this paper, LDVs with small wavelength sensitivity are reviewed. The wavelength sensitivity can be reduced by using arrayed waveguide gratings (AWGs), Mach-Zehnder interferometers (MZIs) or cascaded MZIs. These structures can be formed by planar lightwave circuit (PLC) technology. The principles and the possibility for realizing wavelength-insensitive operation are discussed.

Abstract: Integrated laser Doppler velocimeters (LDVs) using integrated waveguide technology are reviewed. LDVs have been widely used to measure the velocity of a fluid flow or rigid object in various research and industries. However, bulk optical systems used in conventional measurement need special care from temperature change and vibration, which become the expected sources of uncertainty in measurement, due to large optical path length. Therefore, the optical system should be more compact. The LDV can be drastically reduced by using a planar lightwave circuit (PLC). The possibility for realizing several types of novel integrated LDVs, including a wavelength-insensitive LDV, a scanning LDV and a multi-point LDV, is discussed.

Abstract: The turbo air classifier is one of the most widely used equipment in powder classification. The complex flow behaviour inside it, however, prevents material experiments from providing information about its internal separation mechanisms. A study of the interaction of structural variables is therefore undertaken examining air flow behaviour, specifically the air flow between the blades of the rotor cage. The investigation of these flow field characteristics made use of the computational fluid dynamics (CFD) to simulate the air flow in the classifier. It was found that the inlet velocity of the turbo air classifier and the rotary speed of the rotor cage are two of the dominating, non-structural factors that affect velocity distributions in the region between the rotor cage blades. Once the inlet velocity settles, a critical rotary speed must be present to smoothen the flow field between the blades, resulting in an excellent classification performance. Three-dimensional velocity measurements of the region between the blades by laser Doppler velocimeter (LDV) were performed to test the results of the flow field simulation. This revealed that when inlet velocity is invariable, the velocity distributions in the region between the blades are at its most symmetric with the critical rotary speed of the rotor cage making it more favourable for classification. The velocity measurement results are likewise in good agreement with the results of the flow field simulation. Newly structured rotor cages are also simulated and compared with a conventional turbo air classifier, air flow in the newly structured model is smoother. The distributions of radial and tangential velocities are more symmetric and the trend of the rotating vortex between the blades attenuates, particularly when the rotary speed is high. The newly structured rotor cages can therefore achieve higher classification performances.