Wiener filtering technique applied to thermographic data reduction intended for the estimation of plate fins performance

The present work deals with the optimization of a data processing technique aimed to the estimation of local heat transfer coefficient in plate fin commonly used in compact heat exchangers. When the assumption of uniform heat flux boundary condition cannot be made, the convective heat transfer coefficient distribution on thin fins may be recovered by solving the inverse heat conduction problem. The ill-posed nature of this problem has here been handled by pre-processing the raw temperature map, recorded with a high resolution infrared camera, with a filtering technique based on the Wiener filter. In order to increase the data processing efficiency, in the present work the algorithm by which the filter is usually implemented, has been modified. Basically, the filtering function here tested has been defined in such a way that only the pixels belonging to the measured temperature map are used, without any fictitious extrapolation of the signal. Besides, for the regions close to the boundaries, a variable size of the window used to perform the local statistical processing of the signal, has been used. This feature makes the filtering technique more suitable for processing low resolution images containing signal discontinuities. The estimation procedure has-been validated throughout its application to experimental data regarding the usual plate fin and tube configuration subject to parallel air flow. (C) 2003 Elsevier Inc. All rights reserved.