A comparison between transient heat transfer measurements using TLC and IR thermography

Abstract

Narrowband thermochromic liquid crystals (TLCs) and infrared thermography (IRT) are compared in the context of spatially resolved and transient heat transfer measurements. For accurate measurements the TLC coating was calibrated with a stationary method before the experiment. The IRT camera was in-situ calibrated with a surface thermocouple. A good agreement on temperature was achieved for both methods. The TLC data as a single-point-in-time measurement was evaluated for a time-independent heat transfer coefficient hTLC. The surface temperature history measured with the IRT camera enables an additional evaluation for a time-dependent hIR(t). In the case of one-dimensional heat conduction situations and late TLC indications, hTLC and hIR(t) agree well after the first 10 s of the experiment. An investigation of the heat transfer in the wake region of a vortex generator illustrated the influence of lateral conduction. This effect is taken into account by an analytical-empirical correction method for the TLC data. For the IRT data an evaluation method based on an analytical solution of the three-dimensional heat conduction equation is presented. Equally to the one-dimensional case the evaluation methods considering the lateral conduction effects agree well after 10 s while the other methods deliver erroneous results.