36D-13 |
|
M. J. FERRUA and R. P. Singh. Dept. of Biological and Agricultural Engineering, Univ. of California, Davis, 1 Shields Ave., Davis, CA 95616-5294 Particle Image Velocimetry (PIV) is a powerful, non-intrusive technique for measuring fluid velocities. PIV can be used to study the airflow pattern during the cooling of packed beds of agricultural produce, in order to improve cooling rate and uniformity. However, since it requires optical access to the flow, its application has been limited mainly to free shear flows or tracing surface motions along black surfaces. In this work, PIV is used to obtain a detailed characterization of the flow field between and around transparent spheres. The influence of the flow rate in the velocity pattern was also investigated. To perform the PIV measurements an optically transparent system was developed. Three Pyrex spheres (0.95 cm radius) were located in a row inside a Pyrex square tube (2.2 x 2.2 x 6.0 cm). In order to eliminate the refraction of the laser sheet as it passes through the system and the distortion of the image, the working fluid was selected to match the refraction index of the Pyrex (Aniseed and Baby Oil mixture 1:5 v/v, η=1.472). Three different flow rates were studied: 2, 5 and 8 cm3/s. Red fluorescent microspheres (10 μm average diameter) were seeded inside the fluid for image acquisition. The particles, capable of tracking the flow, were excited by the PIV's Nd:YAG laser (532 nm) and present a peak in its emission spectra at 612 nm. The camera, which registers the light emitted by the microspheres, was protected with a Schott glass filter that blocked light at wavelengths lower than 560 nm. The PIV measurements were used to elucidate the velocity profile inside and around this packed system as well as the presence of possible separation points from the spheres at higher Reynolds numbers. This study shows how PIV can be used to study flows around complex geometries.
Session 36D, Food Engineering: Rheology
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |