Uncertainties in transient heat transfer measurements with liquid crystal

Thermochromic liquid crystal (TLC) is used extensively as an experimental tool to determine heat transfer coefficients. In a transient experiment, if the time at which the TLC changes colour is known, then h, the heat transfer coefficient, can be found from the solution of the so-called semi-infinite-plate problem. If T-aw, the adiabatic-wall temperature, is unknown, then two narrow-band TLCs can be used to determine both h and T-aw. In this paper, an uncertainty analysis is used to calculate P-h, the uncertainty in h, and P-T aw the uncertainty in T-aw (when T-aw is unknown), in terms of the random uncertainties in the measured temperatures. Computed values, obtained using a Monte Carlo method, are in good agreement with the uncertainties obtained from the analysis. It is also shown how the uncertainties P-h, and P-T aw can be minimised by selecting the appropriate ranges of TLC. Conversely, a poor choice of TLC can result in large values of these uncertainties. (C) 2002 Published by Elsevier Science Inc.