In a backward-curved fan wheel (backward-curved blades), the energy is largely produced as static pressure present in the fan wheel. With this type of fan wheel higher efficiencies are achieved. They can also be used without fan housing and without any noticable losses in performance, e.g. for roof fan units or for air circulation. To ensure a flow without interruptions in the fan wheel, it is very important to use a suitable fan inlet cone (optimum split flow). In comparison to forward-curved wheels, these wheels make a low frequency humming noise due to the smaller number of blades. The total pressure characteristic curve of backward-curved impellers is steeply inclined. At constant rotational speed, the power requirement for these wheels rises to a given maximum PL max.
Conclusion: For the same application, the backward-curved fan wheel is 10 to 25% larger than a forward-curved wheel, has a higher noise level, but requires less power input.
Comparison of fan wheel types Centrifugal impeller, Mixed Flow impeller, Axial impeller, Backward-curved impeller, Radial impeller, Forward-curved impeller:
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