Open Access

Till Biedermann, Alexander Felker, Thomas Gandt, Tobias Pohlmann

• It is not uncommon for fans in existing systems to undergo retroactive performance upgrades after many years of operation. Such demands often arise from the addition of new system components or increased production rates. Since completely replacing the fan unit would involve considerable costs and downtime, operators are seeking solutions that enable performance to be increased without having to completely replace the existing machine. However, this requirement significantly limits the available options. If an increase in speed is not possible, moderate pressure increases can be achieved by replacing the impeller or extending the blades. However, these changes are highly system-dependent and restricted by the geometric limitations of the spiral casing. This paper examines an alternative modification of the impeller by subsequently welding deflections to the blade ends, also known as blade tail wedges. Based on a CFD study with experimental validation for a medium-pressure centrifugal fan with backward curved blades, it is shown thatIt is not uncommon for fans in existing systems to undergo retroactive performance upgrades after many years of operation. Such demands often arise from the addition of new system components or increased production rates. Since completely replacing the fan unit would involve considerable costs and downtime, operators are seeking solutions that enable performance to be increased without having to completely replace the existing machine. However, this requirement significantly limits the available options. If an increase in speed is not possible, moderate pressure increases can be achieved by replacing the impeller or extending the blades. However, these changes are highly system-dependent and restricted by the geometric limitations of the spiral casing. This paper examines an alternative modification of the impeller by subsequently welding deflections to the blade ends, also known as blade tail wedges. Based on a CFD study with experimental validation for a medium-pressure centrifugal fan with backward curved blades, it is shown that adding blade tail wedges causes a significant shift in the fan characteristic curve towards higher pressures. The results show that the pressure increase can be attributed to an increase in the swirl component caused by the eflection. The effectiveness depends on the length of the deflection, whereby an increasing loss of efficiency due to increased flow separation can also be observed. For the fan under consideration, pressure increases of 15 – 30% can be achieved with only a slight loss in efficiency of 2 – 3% in the relevant range of the characteristic curve and constant effective impeller diameter. A comparison with the affinity laws shows that, for an equivalent increase in performance, the impeller diameter or rotational speed would have to be increased by about 10 %. Hence, despite the marginal loss of efficiency, blade tail wedges can offer an effective alternative for enhancing fan performance under restrictive boundary conditions for industrial applications on-site.…