A Single Blow Transient Test Technique With Volume Averaging Theory Modeling for Random Fiber Matrices

Measurements of the internal heat transfer coefficient in complex surfaces such as random fiber matrices are difficult and often done using the so-called single blow transient test method. In such a method the inlet fluid temperature is perturbed, and measurement of the transient fluid temperature response at the outlet allows the heat transfer coefficient to be determined. Obtaining an accurate heat transfer coefficient for a sample, using this method, relies on developing an accurate model for the thermal phenomena taking place. Existing models employed appear to be too simple and lack rigor in their derivation. A model based on Volume Averaging Theory (VAT) is believed to alleviate such problems. A precise expression for the local heat transfer coefficient has previously been rigorously derived from the microscale governing equations. This expression provides a clear definition of the transport coefficient that is being measured. Nusselt number results for several random fiber matrices are obtained for Reynolds numbers between 5 and 70, and are compared to existing correlations. The dimensionless numbers used are scaled with the simple “universal” porous media length scale. It is found that this new combined experimental and computational method is effective in determining the local convective heat transfer coefficient in complex porous structures. Moreover, the experimental apparatus and VAT-based model may be used in other samples of complex morphology provided the porosity and specific surface area can be determined.