Abstract
The grainy appearance of a diffusing object illuminated by a monochromatic source such as laser light is known as ‘laser speckle’. This paper presents an optical method for measuring temperature gradients in liquids, based on this phenomena. Double exposure speckle photography is used to measure temperature gradients in liquids heated from below, in the Rayleigh number range 1.5–276 where the heat transfer is by conduction. Comparison with thermocouple measurements yields reasonable agreement. A few experiments illustrating the feasibility of using ‘speckle’ to study convection problems in the Rayleigh number range 4600–8957 are included.
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