FLUID DYNAMIC GAUGING IN DUCT FLOWS – EXPERIMENTS AND CFD SIMULATIONS

The technique of fluid dynamic gauging (FDG) has been developed to measure the thickness of deformable foulant deposits on solid immersed in liquid, in real time and in situ, with a precision of ± 10 micron. Suction is imposed across a gauging nozzle; the flow rate of liquid through the nozzle allows calculation of the proximity of the nozzle to the surface of the deposit. The technique has been demonstrated by Tuladhar et al. (2000) to work well in quasi-static situations, where the bulk liquid is not moving apart from the gauging flow, and in duct flows. FDG in the quasi-static mode has recently been extended by Chew and co-workers (2004a) using computational fluid dynamics (CFD) simulations of the gauging flow fields to allow the forces imposed on the foulant to be estimated, and thereby test its mechanical strength. We term this technique ‘enhanced FDG’. This paper describes the extension of enhanced FDG to simple duct flows, which requires numerical solution of the governing fluid flow equations in the geometries under consideration. The geometry is that employed by Tuladhar et al. (2003), namely a long duct of square cross-section. The experimental results of the present study are compared with the experimental results from Tuladhar et al. (2003) and Chew et al. (2004b). The CFD results of the study are mainly compared with the present experimental results and with the numerical results from Chew et al. (2004a)