Improving Coating Processes

Researchers at the von Karman Institute (VKI) used both FLUENT and NEKTON to study annular jet wiping, a precise technique used to control the thickness of the liquid coating on a moving wire. In this technique, a gas jet is used to meter the coating thickness by exerting pressure and shear forces on the liquid film. This approach is widely used in several coating processes, such as hot-dip galvanization of metal strips and wires, and deposition of photographic emulsions.

Figure 1. FLUENT's prediction of the impinging gas flow from the nozzle yielded the pressure and shear stress distribution on the substrate in this prediction of annular jet wiping. NEKTON predicted the resulting coating thickness. Courtesy of von Karman Institute for Fluid Dynamics

FLUENT was used to simulate the gas jet from the nozzle impinging on the substrate. The pressure and shear stress on the wire were determined for various nozzle-slot sizes, nozzle-wire distances, wire diameters, etc. The computed pressure and shear stress were then imposed as boundary conditions for the simulation of the moving liquid film in NEKTON and the final coating thickness on the wire was calculated. The data obtained from the simulations were used to create an analytical model that can predict the final coating thickness with a given set of operating parameters, and can be implemented on a feedback loop to control the continuous coating line. The simulations have also increased understanding of the effect of the various operating parameters on the final coating thickness.

Water Treatment Process Optimization

ALand availability, limited funds, and strict regulatory standards require water treatment plant designers to minimize process tank size without compromising the effectiveness of the treatment process. Engineers from Hazen and Sawyer presented the results of several successful CFD projects that have contributed to this goal of equipment optimization.

In one study, Hazen and Sawyer created a CFD model of a chlorine contact tank used in an existing drinking water treatment plant. Chlorine contact tanks are required to provide sufficient contact time for disinfection, and the flow hydraulics and detention time within the contact tanks are critical to the effectiveness of the process. Hazen and Sawyer computed the residence time for chlorine contact and the results from the CFD model were compared to the results of a tracer study performed on the existing tank. The CFD model came within 5% of the tracer study results, helping to validate CFD in the environmental industry. Upon achieving validation, CFD modeling was used to aid in the design of a new chlorine contact tank for the facility.

Figure 2. FLUENT's prediction of residence time in this chlorine contact tank was within 5% of the field measurements. Courtesy of Hazen and Sawyer

FluentNEWS