Application of thermochromic liquid crystal to rotating surfaces

Encapsulated thermochromic liquid crystal (TLC) can be used to measure the surface temperature of stationary or rotating bodies. However, some research workers have reported a “rotational shift”: When the temperature of a rotating body is measured by thermocouples and TLC, there is a difference between the two sets of temperatures, and this difference increases with increasing rotational speed. Two research groups (Camci and Glezer in the USA, and Owen, Pilbrow, and Syson in the UK) have independently examined the effect of speed on TLC applied to the surfaces of rotating disks. The USA group used narrow-band TLC on a disk of 305 mm diameter rotating up to 7500 rpm measuring the surface temperature using an infrared (IR) sensor. The UK group used wide-band TLC on a disk of 580 mm diameter rotating up to 7000 rpm, measuring the temperature with an IR thermal imager. Both groups used the so-called hue technique to evaluate the temperature of the TLC and concluded that, even for centripetal accelerations in excess of 104 g, there is no significant effect of rotational speed on either narrow-band or wide-band TLC. It is suggested that the “rotational shift” observed by some researchers was probably caused by thermaldisturbance errors, which affected the thermocouples, rather than by changes in the TLC.