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

We report 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 reported here is configured to make measurements on the inner rod of an annular flow test section but the concept is generic. Data are presented 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/dt < 0.25, proved to be unaffected by the pressure and temperature. h is the nozzle-surface clearance and dt the nozzle throat diameter. At smaller h/dt 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, Ret, is less than 20 the range of discharge coefficient values (0-Cd∞) is small, with a maximum value dependent on Ret. A useful range of Cd∞ values is obtained when Ret > 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 Ret 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.

Plots of dimensionless flow rate against dimensionless distance from surface.Figure optionsDownload as PowerPoint slideHighlights
► Pressure mode FDG developed for measuring soft layers on curved surfaces.
► Prototype gauge demonstrates proof of concept up to 10 bara and 140 °C.
► CFD simulations and experiments show a practical lower limit on flow rate at Ret ∼ 20.
► CFD results confirm analytical estimate of maximum shear stress imposed on surface.