Liquid crystal thermography and image processing in heat and fluid flow experiments
Liquid crystal techniques, combined with sophisticated software in increasingly powerful personal computers, are now permitting fairly comprehensive full-field studies of velocity, temperature and heat transfer coefficent-distributions, with their accompanying automatic analysis. Liquid crystals and true-colour image processing have opened some new approaches for heat transfer research and offer satisfactory accuracy and resolution. New and more incisive experiments are being designed for conventional situations, and other problems can now be studied which were previously not practical to consider. The history of these techniques is reviewed and the principal methods are described using illustrative examples from the literature and work of the author. A new liquid crystal thermometry method is described to determine quantitatively two-dimensional temperature distributions on a surface and in a fluid, from colour records obtained using a thermosensitive chiral-nematic material combined with image processing. Application type experiments have been carried out both to visualise the complex distribution of temperature and local heat transfer coefficient over a cooled surface disturbed by different solid obstacles, and also to investigate temperature and flow patterns in a rectangular cavity for natural convection. A new experimental method (optical and non-invasive) has been established to measure simultaneously both flow and thermal fields - this method may be described as particle image velocimetry and thermometry (PIVT). Some of the experimental results presented are applied to an important Industrial improvement in heat exchanger design and could result in substantial reductions in energy costs.