A fluid dynamic gauging device for measuring fouling deposit thickness in opaque liquids at elevated temperature and pressure

Experimental Thermal and Fluid Science, Volume 48, July 2013, Pages 19–28
A fluid dynamic gauging device for measuring fouling deposit thickness in opaque liquids at elevated temperature and pressure
A. Ali (a), G.J. Chapman (a), Y.M.J. Chew (a, b), T. Gu (a), W.R. Paterson (a), D.I. Wilson (a)
a Department of Chemical Engineering & Biotechnology, New Museums Site, Pembroke Street, Cambridge CB2 3RA, UK
b Department of Chemical Engineering, University of Bath, Claverton Down, Bath BA2 7AY, UK
Abstract
Reports proof-of-concept results for a fluid dynamic gauging (FDG) device for measuring the thickness and strength of soft solid fouling layers immersed in an opaque liquid in situ and in real time at elevated pressures and temperatures.
The device is configured to make measurements on the inner rod of an annular flow test section. The concept, however, is generic. Authors present data from tests using mineral oil at temperatures and pressures up to 140 °C and 10 bara, respectively. Problems with the prototype hardware prevented testing up to the design limits of 270 °C and 30 bara. The practical working range of the gauge, i.e. 0.05 < h/d_t < 0.25, proved to be unaffected by the pressure and temperature. h is the nozzle-surface clearance and d_t the nozzle throat diameter. At smaller h/d_t values the pressure drop across the nozzle is very high and this can serve as an alarm for close approach. When the Reynolds number at the throat, Re_t, is less than 20 the range of discharge coefficient values (0-C_d^x) is small, with a maximum value dependent on Re_t. A useful range of C_d^x values is obtained when Re_t > 40. Computational fluid dynamics (CFD) simulations of the gauging flow in these quasi-static experiments (no bulk liquid flow) gave good agreement with experimental data for the cases tested. The CFD results showed that the low Re_t regime is related to creeping flow in the nozzle. CFD calculations of the shear stress being imposed on the surface being gauged gave good agreement with an analytical model for flow between parallel discs, indicating that the latter can be used to estimate the maximum shear stress imposed by the gauging flow.
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