| Summary: | The ventilation of industrial areas and tunnels is a safety requirement and
characterizes the quality of a working environment. Low speed fans are used to
achieve the required ventilation level. An attempt to design a low speed
vaneaxial fan, meeting the specifications of a given fan that is already in the
market takes place in this Thesis. The project was conducted with the support of
the Fläkt-Woods Company and the main target is to design a ventilation fan,
meeting the requirements for pressure rise, volume flow and size, of an existing
model. The efficiency improvement is driven in part by the new national and
international legislation concerning the operation of electrical equipment.
Companies require higher efficiencies without compromising safety features of
the fan and the fan capability to operate at high temperatures.
A low speed fan design procedure is established based on the available
literature and design tools. The free vortex approach is employed, which provides
acceptable efficiency and relatively simpler design. The design procedure can be
used to design a fan given a set of customer requirements. Many software tools
are used to design the fan. A Matlab code for the blade design is developed and
other codes are used to establish the final fan design. The effectiveness of the
design procedure is verified with CFD simulations carried out as part of this
project. Three new designs that are developed with the established design
procedure are presented in this Thesis. The new designs differ in the hub to tip
ratio, the rotational speed and the number of the blades and the vanes. The
experience acquired from the analysis of the performance of the first new design
is used to improve the performance of the following designs in order to achieve
the best efficiency possible. The effect of tip clearance is investigated thoroughly
in the new designs because the tip clearance has a major impact on the fan
performance and safe operation of the fan at high temperatures. The mechanical
integrity of the fan is examined last to verify that the fan can operate in high
temperature.
The target of improved efficiency (higher than 79%) is achieved in one of
the fan designs attempted and it was calculated 82%. The off design
performance of the new fan is satisfactory as well. This new design can be
further optimized, since the modification of minor design features is in itself a
methodology that can incrementally improve the efficiency of a low speed fan.
The new fan can operate at high temperatures (400°C), however the safety factor
at this temperature is 1.25 for combined steady mechanical and thermal loading
and it can be further improved either through the use of materials with better
resistance in thermal loading or with an increased tip clearance.
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