Laser speckle photography in heat transfer studies

Laser speckle photography, as a technique making use of the displacement of optical speckle by refraction as an information carrier, has recently been used to measure fluid density, temperature, and heat transfer. The concept of laser speckle photography and the principles of measuring the temperature gradient field are briefly described, including the formation of laser speckle and its displacement, six kinds of recording systems, and two methods for reconstructing a specklegram. The major advantages of the laser speckle photography method for heat transfer study in comparison with interferometric methods are listed and discussed. Finally, many applications of laser speckle photography in the study of heat transfer are given, including cases of natural convection along a vertical plate, measurements of the axisymmetric temperature field of a flame, heat tranfser in channel natural convection and verification of thermal drag phenomena, and heat transfer of small-scale objects.