Optical Methods for Data Processing in Heat and Fluid Flow

24

Automated Fringe Analysis for Profilometric Mass-transfer Experiments

J J Nebrensky

Abstract

A new approach has been proposed for the automated analysis of fringe patterns obtained in mass transfer experiments, where the rate at which live fringes cross a given point (and hence the local mass flux) is identified by finding the first-order peak in a time-domain Fourier transform of that point's intensity history during the experiment. A software implementation of this approach has been tested on synthetic data to evaluate the precision of the data produced; several peak frequency interpolation schemes are also compared.

24.1 Introduction

Profilometric mass-transfer techniques, such as naphthalene sublimation, have an important place in the investigation of transfer processes. Their use, however, is hampered by the difficulty of the data reduction process: e.g. co-ordinate measuring machines measure at only a selection of points over the test surface and can suffer from errors due to natural convection, whereas optical interferometric methods can quickly and easily record the surface deformation but the conventional manual analysis of the resulting fringe patterns is time consuming.

Two major difficulties are that mass transfer coefficient distributions may have multiple maxima or minima and that it is necessary to find absolute, rather than just relative, fringe order values, meaning that the zero-order fringe must be identified. Button et al. (1) and Paler et al. (2) describe ...