Pressure mode fluid dynamic gauging for studying cake build-up in cross-flow microfiltration

Experimental Thermal and Fluid Science

et al. 2013

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 ºC and 30 bara. The practical working range of the gauge, i.e. 0.10 < 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. The range of discharge coefficient, C d, values obtained is sensitive to flow rate when the Reynolds number at the throat, Re t , falls below 20. A useful range of C d 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 flows measurements.

Section: Pressure-mode Fdgmentioning

confidence: 99%

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

Ali

Chapman

Experimental Thermal and Fluid Science

et al. 2013

“…In this work we present the application of pressure mode Fluid Dynamic Gauging (FDG) for estimating the thickness and cohesive strength of cake layers in cross-flow microfiltration of inactive yeast suspensions through a 5 μm nominal pore size cellulosic membrane. Although not strictly considered as non-invasive, this technique has proven an effective non-contact method for measuring cake-layer thickness in both dead-end [18], and cross-flow filtrations [19][20][21].…”

Section: Introductionmentioning

confidence: 99%

The application of fluid dynamic gauging in characterising cake deposition during the cross-flow microfiltration of a yeast suspension

Lewis

Journal of Membrane Science

Bird

2012

Self Cite

Fluid Dynamic Gauging (FDG) has been used to study cake fouling during cross-flow microfiltration of inactive Saccharomyces cerevisiae yeast suspensions through a 5 μm nominal pore size mixed cellulose ester membrane. Cake thickness was measured in-situ and in real-time during fouling, for which an initial growth rate of ca. 0.81 μm•s-1 was observed at TMP = 35 mbar and Re duct = 1000. The thickness increased asymptotically to a terminal value of 130 μm, limited by the FDG process. Although it influences the evolution of the cake thickness, FDG can nevertheless be used to perform strength tests on preformed cakes, by imposing controlled shear stresses to the surface and measuring the thickness following deformation. Cake deformation via incremental increases in shear stress demonstrated that the cake's resilience to tangential fluid shear was inversely proportional to its thickness. It was found that preformed cakes over 250 μm thick were deformed by shear stresses < 10 N•m-2 , indicating very loose cohesion between cells on the cake's surface. The range and accuracy of thickness measurements is subject to the strength of fouling layers and the operating conditions of the apparatus. Measures to enhance the technique's efficacy have been identified and are currently underway.

“…In this study, an enhanced FDG equipment is used to study soft cake fouling layers during cross-flow microfiltra tion of an organic model material, a Kraft lignin, which forms cohesive fouling layers and cakes which exhibit some degree of compressibility. Previous studies have concentrated on ultrafiltration under turbulent conditions (Jones et al, 2012), or microfiltration of near ideal particle suspensions (Lister et al, 2011). The use of lignin in this study demonstrates the complex behaviour of an organic material, which presents problems similar to those seen during the microfiltration of food based materials.…”

Section: Introductionmentioning

confidence: 83%

In situ investigation of soft cake fouling layers using fluid dynamic gauging

Mattsson

Lewis

Food and Bioproducts Processing

et al. 2015

Self Cite

Cake fouling is a phenomenon contributing to flux decline during cross-flow filtration. Its behaviour is also difficult to predict, especially for challenging separations where organic materials often form compressible cakes with a high resistance. In this study Kraft lignin was used as a model material for organic foulants in cross-flow microfiltration experiments, and a non-contact fluid dynamic gauging (FDG) technique in pressure-mode configuration was used to study the cake fouling layers in situ. A new and enhanced FDG equipment was used; enabling an increased accuracy of the fouling layer thickness measurements and capable of producing higher fluid shear stresses on the surface of the cake layer for strength measurements. Using FDG, very thin fouling layers were observed; in addition, FDG was used to investigate their cohesive and adhesive strengths, showing that over a 10-fold increase in fluid shear stress was required to remove foulant closer to the membrane compared with that on the surface of the cake.