LASER SPECKLE PHOTOGRAPHY IN HEAT-TRANSFER STUDIES

Laser speckle photography, as a technique making use of the displaceme nt of optical speckle by refraction as an information carrier, has rec ently been used to measure fluid density, temperature, and heat transf er. The concept of laser speckle photography and the principles of mea suring the temperature gradient field are briefly described, including the formation of laser speckle and its displacement, six kinds of rec ording systems, and two methods for reconstructing a specklegram. The major advantages of the laser speckle photography method for heat tran sfer study in comparison with interferometric methods are listed and d iscussed. Finally, many applications of laser speckle photography in t he study of heat transfer are given, including cases of natural convec tion along a vertical plate, measurements of the axisymmetric temperat ure field of a flame, heat transfer in channel natural convection and verification of thermal drag phenomena, and heat transfer of small-sca le objects.