A re-evaluation of a pulsed laser technique for measuring surface heat transfer coefficients

Data from a previously reported experimental technique, for measuring wall shear stress using a pulsed laser, is re-evaluated using a new numerically based data reduction technique in order to determine surface heat transfer coefficients. This new technique was suggested by recent experimental studies into the use of uncalibrated liquid crystals and periodic heat fluxes to measure absolute values of the local heat transfer coefficient and wall shear stress. These studies, which were initially based upon a one-dimensional analytical conduction model, demonstrated that the shape of the temperature-time response, to an instantaneous deposition of energy on a surface, is a function of the thermophysical properties of the surface and the value of the local heat transfer coefficient. In order to account for situations where two-dimensional effects are important a new numerical model has been developed. It is possible, using this new model, to extend the previous phase delay technique to measure heat transfer coefficients to the case whereby a pulsed laser is used to initiate a temperature transient. The new results using the old data show reasonable agreement with those predicted by a standard correlation. Suggestions are made on how the technique can be significantly improved.