![]() Results are similar to computational fluid dynamics, i.e. With sequences of velocity vector maps, statistics, spatial correlations and other relevant data are available.All three components may be obtained with the use of a stereoscopic arrangement.Instantaneous velocity vector maps in a cross-section of the flow.Velocity range from zero to supersonic.The technique is non-intrusive and measures the velocities of micron-sized particles following the flow.Image Credits : Dantec Dynamics Advantages : The use of modern digital cameras and dedicated computing hardware, results in real-time velocity maps. Two velocity components are measured, but use of a stereoscopic approach permits all three velocity components to be recorded, resulting in instantaneous 3D velocity vectors for the whole area. Particle Image Velocimetry (PIV) is a whole-flow-field technique providing instantaneous velocity vector measurements in a cross-section of a flow. PIV software is used to post-process the optical images. Typical PIV apparatus consists of a camera (normally a digital camera with a CCD chip in modern systems), a strobe or laser with an optical arrangement to limit the physical region illuminated (normally a cylindrical lens to convert a light beam to a line), a synchronizer to act as an external trigger for control of the camera and laser, the seeding particles and the fluid under investigation.Ī fiber optic cable or liquid light guide may connect the laser to the lens setup. When the particle concentration is so low that it is possible to follow an individual particle it is called Particle tracking velocimetry, while Laser speckle velocimetry is used for cases where the particle concentration is so high that it is difficult to observe individual particles in an image. ![]() The main difference between PIV and those techniques is that PIV produces two-dimensional or even three-dimensional vector fields, while the other techniques measure the velocity at a point.ĭuring PIV, the particle concentration is such that it is possible to identify individual particles in an image, but not with certainty to track it between images. Other techniques used to measure flows are laser Doppler velocimetry and hot-wire anemometry. The motion of the seeding particles is used to calculate speed and direction (the velocity field) of the flow being studied. ![]() The fluid with entrained particles is illuminated so that particles are visible. The fluid is seeded with tracer particles which, for sufficiently small particles, are assumed to faithfully follow the flow dynamics (the degree to which the particles faithfully follow the flow is represented by the Stokes number). It is used to obtain instantaneous velocity measurements and related properties in fluids. A scaling analysis shows the importance of thermocapillary convection in evaporating menisci.Particle image velocimetry (PIV) is an optical method of flow visualization used in education and research. Particle streaks and micro-particle image velocimetry images obtained in multiple horizontal and vertical planes provide an understanding of this three-dimensional flow behavior. The high mass fluxes in smaller-diameter tubes drive stronger vortices. For larger tubes, buoyancy effects become apparent as they dominate the flow field. For the 75 μ m tube, a symmetrical toroidal vortex is observed near the meniscus. A transition from a pure two-dimensional thermocapillary flow to a 3D buoyant-thermocapillary flow is observed with an increase in tube diameter. The relative influence of buoyancy and thermocapillarity on the flow was investigated for tube diameters ranging from 75 to 1575 μ m. This results in a surface tension gradient which, coupled with buoyancy effects, causes buoyant-thermocapillary convection in the liquid film. Analysis of the vapor diffusion away from the meniscus reveals a zone of intense heat flux near the solid-liquid-vapor junction that creates a temperature gradient along the meniscus. Micro-particle image velocimetry measurements of the three-dimensional (3D) convection patterns generated near an evaporating meniscus in horizontally oriented capillary tubes are presented.
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