Computer Simulation Helps Solve Challenging Airflow Problem in Paint Booth
Engineers at Technicon Engineering Inc. and Flomerics Inc. worked together to solve a challenging airflow problem in a paint booth at Robins Air Force Base, Warner-Robins, Georgia. The air is supposed to flow smoothly across the 40x85X70 feet paint booth in order to move the fumes out of the painters' faces. Instead, the air swirled around the room. Flomerics used FloVENT computational fluid dynamics (CFD) software to analyze the airflow conditions in the air supply ductwork and plenum and paint booth. The models showed that the relationship of the holes in the ducts in the plenum that supplies the paint booth to the duct's wall thickness needed to be carefully controlled in order to get the air to turn 90 degrees so it could be delivered evenly across the length of the plenum. "Without computer simulation, it could have taken months of very expensive experiments to understand what was causing the turbulence," said Clint Hardie, Principal with Technicon Engineering. "With the simulation results in hand, we were quickly able to specify a duct material that solved the problem."
The paint booth is primarily used on large ground support equipment. Technicon engineers were quickly able to determine that the problem was that air was entering the plenum at too high a velocity to approach uniform distribution of air out of the supply grills. They set a goal of approaching an even cross-sectional velocity of 65 FPM across the paint bay. Experiments showed that the delivered flow rate of 58,000 CFM, which is roughly a one-quarter of the total flow, produced a duct velocity of roughly 567 FPM, far too high to achieve uniform distribution in the paint booth. Technicon made the decision to utilize the services of Flomerics to create a CFD model of the airflow through the plenum and paint booth. CFD graphically calculates and displays flow velocity and direction, pressure and temperature throughout the computational domain, which helps engineers understand the root cause of flow problems and what is needed to fix them. CFD also provides the ability to model a variety of options on the computer so that the most economical solutions can be pursued with a high degree of confidence in their validity.
Flomerics engineers modeled the ductwork with small holes of ¼ to ½ inch in diameter with FloVENT software in an effort to deliver the air evenly across the length of the plenum. FloVENT's automatic sequential optimization capability adjusts the values of all design variables intelligently to optimize the value of a design aim specified by the user. The models showed that in order to get the air to turn 90 degrees, the relationship of hole size to wall thickness needed to be 4 to 1 or greater. Technicon engineers found a material that met these requirements, Microbe-X LT fabric from Ductsox. The fabric contains hundreds of thousands of holes and the relationship of hole size to wall thickness ranges from 10-12 to 1. Flomerics modeled this material and discovered that it delivered the required performance. In addition, exit velocities from the fabric approach 50 FPM, lowering the effect of stray eddy currents.
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