Digital speckle photography and speckle tomography in heat transfer studies

The line-of-sight speckle photography of transparent media is used for quan titative measurements of the instantaneous temperature fields in 3D unstead y flows. Both electronic and photographic methods are employed for speckleg ram recording. The subsequent specklegram treatment uses the Youngs fringes method as well as cross-correlation analysis of small interrogation areas of the recordings. Experimental data for three different heat transfer conf igurations are obtained and discussed. The first one is natural convection over extended vertical heated plates with forward facing steps, the second is unsteady 3D convective flow around a suddenly heated vertical thin wire, and the third one is a convective plume above a multi-jet flame. Both loca l and global Nusselt numbers are determined via measuring local surface tem perature gradients for these convective flows. The results are compared wit h Ostrach's theory for a single vertical plate and with the data obtained b y Mach-Zehnder interferometry. The 3D temperature fields are reconstructed for axisymmetric convective flows around a suddenly heated vertical wire us ing quasi-double projection measurement and the Radon inversion. 3D tempera ture distributions above the combustion zone are reconstructed using multi- projection speckle photography measurements and computerised tomography. (C ) 2001 Elsevier Science Ltd. All rights reserved.