Exhaust Air Control Cone for Outlet Speeds of at Least 7 m/s
G1 New Fan Concepts
According to the guidelines VDI-2280:2005 "Discharge conditions for organic solvents" and VDI-3781:2017 Part 4 "Environmental meteorology, discharge conditions for exhaust gases ...", an exit velocity of at least 7 m/s vertically upwards should be aimed for a better distribution of the corrosive exhaust air, this ensures sufficient dilution and undisturbed removal of the exhaust gases with the free air flow.
The corrosion-resistant speed regulator developed for this purpose is an automatic, purely mechanical regulator for flow speeds that are constantly above a specified minimum speed. The almost maintenance-free speed controller works without external energy. Its smooth-running, centrally mounted inner cone made of polypropylene sets the desired minimum speed at the round gap outlet using minimal aerodynamic forces (pressure and friction) and the spring force.
Initially, purely analytical calculation approaches for the balance of forces between the weight force in relation to the compression spring force and resistance force are shown. Then, using CFD analysis with OpenFoam, the flow in the vertical pipe, the accelerated flow situation between the outer cone and the inner cone and the ejection flow at the outlet are examined. The graphic evaluation shows velocity fields at minimum and maximum volume flow, the pressure fields and streamlines. In addition, an unsteady flow situation is calculated in order to determine the free floating of the inner cone with the resulting height.
By blowing out at a minimum speed of 7 m/s vertically upwards over the roof of the industrial building, the exhaust air regulating cones dilute and discharge any hazardous substances that may be released in the laboratory in order to avoid health hazards via the breathing air. The discharge of laboratory exhaust air is described in DIN 1946 Part 7. Due to the aerodynamically truncated inner cone, there is no need to set an increase in the fan volume flow for lower exhaust air flows. This avoids increased pressure losses and greater drive energy expenditure. In addition, the sound power values of the exhaust air towers are reduced by the insulating inner regulating cone. The rainwater that penetrates less due to the blockage is discharged to the outside via a built-in condensate loop. This technically necessary component is not taken into account in the calculation. The optional side injection into the vertical standpipe is also ignored. Purely stationary considerations are given.