LIQUID-CRYSTAL THERMOGRAPHY ON THE FLUID SOLID INTERFACE OF ROTATING SYSTEMS

Liquid crystal thermography is an effective method widely employed in transient and steady-state heat transfer experiments with excellent sp atial resolution and good accuracy. Most of the past studies in liquid crystal thermography deal with stationary conditions. The present inv estigation deals with the influence of rotation on the color response of encapsulated liquid crystals attached to a flat rotating surface. A general methodology developed for the application of thermochromic li quid crystals in rotating systems is described for the first time. The investigation is performed for a rotational speed range from 0 to 750 0 rpm using two different coatings displaying red at 30 degrees and 45 degrees C, under stationary conditions. Local liquid crystal color on the surface of a rotating disk is correlated with local temperature a s measured by a non-intrusive infrared sensor at various rotational sp eeds. An immediate observation from the present study is that the colo r response (hue) of encapsulated liquid crystals is not altered by eit her the centrifugal acceleration of the rotating environment or the ae rodynamic friction force at the rotating disk-air interface. Present i nvestigation also shows that when a stroboscope light is introduced, t he color response is not significantly altered due to additional perio dic illumination. A complete and general experimental methodology incl uding rotating surfaces with non-axisymmetric temperature distribution is presented. Results from the current liquid crystal technique agree well with the theoretical adiabatic temperature rise of a free rotati ng disk as predicted by an analytical method.