Daniel Gubler writes "Optimal local ventilation systems
by Daniel Gubler, ETH Zurich
The "Air&Climate" group of the Institute of Building Technology at the Swiss Federal Institute of Technology in Zurich has been working with CFX-5 for two years now. The group is using CFD for building technology-related research, in areas including airflow in office buildings, spread of smoke during fires and particulates transport.
The latest project deals with new systems for local ventilation, which are frequently used in industry in environments such as welding workplaces. Within a European COST project, CFX has been chosen to optimize a new system, the REEXS (REinforced EXhaust System). This system provides local ventilation with an extended suction range by blowing several fine clean-air jets normal to the exhaust, these jets serving to closely channel the contaminant to the exhaust hood.
CFX-5 was used to optimize the design of both the exhaust hood and the air-jet nozzles as well as to find the right operating parameters for specific hood designs. With CFX-5ís unstructured mesher, systematic analyses of design variations, such as nozzle details or jet exit angles, could all be carried out with less effort than with conventional meshing methods.
After initial simulations showed very close agreement with experimental data, CFX was used to evaluate the performance of the design under realistic operating conditions. The simulations considered the removal of welding fumes (accounting for the buoyant flow and heat source) in specific environments such as a draughty workplace. The capture efficiency was calculated automatically from the mass balance provided in the output files of the simulations.
These calculations have allowed the capture efficiency of the local exhaust system to be estimated within the real working environment. Based on these results a prototype has been built and is now undergoing final testing in the wind tunnel. CFX-5 has proved to be a useful tool with which to optimise the REEXS design and will be used in further research for dimensioning of specific REEXS systems."