Inverse Method Applied for the Determination of the Wall Shear Rate in a Scraped Surface Heat Exchanger using the Electrochemical Technique

In this study, an inverse method is presented so as to determine the wall shear rate in a scraped surface heat exchanger using polarography technique. Based on a numerical sequential estimation, this method which enables the inversion of the convection diffusion equation, is applied to measured mass transfer temporal signals. Other solutions, mostly used in polarograghy, are also presented in order to compare them with this inverse technique; they are the quasi-steady (Levêque) and the Sobolik et al. methods. The objective of this study is to understand the validity limits of these classical methods, and to frame their uses in mass transfer studies. The experimental device used is an industrial scraped surface heat exchanger with a high viscous of an isotherm Newtonian or non Newtonian liquid, normally utilized in food engineering. Three liquid solutions have been in main used in this test setup: Emkarox HV45 (which is a mixture of polypropylene glycol and polyethylene glycol), a low viscous Newtonian solution of polyethylene glycol 35000 (PEG), and a shear-thinning guar gum solution (where the rheological behaviour was modelled by two different power-laws according to the shear rate domains)