A Periodic Transient Method Using Liquid Crystals for the Measurement of Local Heat Transfer Coefficients

A new periodic transient method for the measurement of local heat transfer coefficients is described. In this method, the freestream temperature is periodically heated while the local surface temperature fluctuation is measured. The local heat transfer coefficient can be determined from the frequency, the ratio of the surface temperature fluctuation to the free stream temperature fluctuation and the wall thermal properties. Measurements on a Plexiglas flat plate with a laminar boundary layer are presented as a demonstration of this method. For this demonstration the free stream is electrically heated using a fine wire cloth. The surface temperature fluctuation is measured using liquid crystals with a hue analysis technique. The results show that this is a viable method for measuring local heat transfer coefficients. Its advantages are that it approximates a uniform temperature thermal boundary condition and it is not necessary to control or measure the initial wall temperature.