F-16 High Temperature Fouling Unit Redesign - Part I: Annular Test Section
Our ongoing analysis of the HTRI crude oil fouling data revealed an unacceptably high degree of scatter. A computational fluid dynamics (CFD) model of the High Temperature Fouling Unit (HTFU) test section demonstrated that the flow over the heated portion was undeveloped and asymmetrical, resulting in wall shear stress variations of up to ± 200 percent. This degree of variation, along with other factors such as changes in the fouling rod calibration constant, made it impossible to study the effects of shear stress and temperature on crude oil fouling. Consequently, the test sections were redesigned with 22 diameters of turbulent mixing volume, 132 hydraulic diameters for flow development, and a 101.6-mm heated section to minimize axial duty losses.
A CFD model of flow in the Reynolds number range of 41.7 to 41700 confirmed that the new test section design resulted in fully developed symmetrical flow with an even distribution of suspended particulate matter and shear stress variation of less than five percent. The pump outlet manifold and the reservoir were also redesigned to provide an even distribution of particulate matter throughout the rig. Crude oil experiments revealed that the data scatter was improved from a linear fit weighted average R2 value of 0.615 to 0.959 for the Arrhenius data. This initial testing also showed that improvements in the manufacturing and quality control of the heater rods are needed to maintain low experimental scatter.