A method for processing transient heat transfer measurements in the presence of nonuniform initial wall temperature

This paper presents a method to consider the influence of nonuniform initial temperature that always exists in the transient heat transfer measurements. The core of this technique is an equation derived from one-dimensional unsteady conduction equation with nonuniform initial wall temperature through Laplace transformation. Numerical simulation method is used to compute the conduction process of transient heat transfer measurement of film cooling with imposed heat transfer coefficient (HTC) and film cooling effectiveness (FCE). The comparison between calculated values of (HTC, FCE) and the imposed values shows that when the initial temperature is nonuniform and the measurement duration is short, HTC and FCE calculated by the equation derived from constant initial temperature deviate from the true values significantly. If the nonuniform initial temperature distribution in the region where conduction exercises more influence on the wall surface temperature change than convection is well fitted by power series, accurate heat transfer coefficient and film cooling effectiveness can be calculated by the newly derived equation. When the initial temperature distribution is difficult to obtain and the equation derived from constant initial temperature has to be employed, some methods are suggested to reduce the influence of nonuniform initial temperature, such as using low heat conductivity material as the test plate or/and performing the transient measurements in a high heat transfer coefficient condition and properly increasing the duration of transient heat transfer measurements.