Liquid Crystal Thermography on the Fluid Solid Interface of Rotating Systems

Abstract

Liquid crystal thermography is an effective method widely employed in transient and steady-state heat transfer experiments with excellent spatial resolution and good accuracy. Most of the past studies in liquid crystal thermography deal with stationary conditions. The present investigation 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 liquid crystals in rotating systems is described for the first time. The investigation is performed for a rotational speed range from 0 to 7500 rpm using two different coatings displaying red at 30° and 45°C, under stationary conditions. Local liquid crystal color on the surface of a rotating disk is correlated with local temperature as measured by a non-intrusive infrared sensor at various rotational speeds. An immediate observation from the present study is that the color response (hue) of encapsulated liquid crystals is not altered by either the centrifugal acceleration of the rotating environment or the aerodynamic friction force at the rotating disk-air interface. Present investigation also shows that when a stroboscope light is introduced, the color response is not significantly altered due to additional periodic illumination. A complete and general experimental methodology including 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 rotating disk as predicted by an analytical method.