White-light speckle photography technique applied for free convection heat transfer problems

White light speckle photography, as its laser counterpart, measures light beam deflection through a phase object, that is a transparent medium with non uniform refractive index. As the beam deflection at the solid surface is connected to the wall-temperature gradient, a convection heat transfer coefficient can be obtained. In this work, the advantages and disadvantages of using a white light speckle photography technique are evaluated using both simulation and experimental comparison with a different optical technique, namely holographic interferometry. The simulation study is proposed to analyze the sensitivity of the technique to different data reduction algorithms. Sensitivity problems, when the working fluid is air, are considered and suggestive discussions are made to further improve the sensitivity, such as modifying the experimental setup and/or introducing an image offset. Finally, some selected experimental results and a brief discussion are presented for several free convection heat transfer problems.