Investigation of the Effect of Multiple Centrifugal Fans Close to Each Other in Operation- A Numerical Study to Improve Fan Efficiency in an Air Handling Unit
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Typ
Examensarbete för masterexamen
Master Thesis
Master Thesis
Program
Sustainable energy systems (MPSES), MSc
Publicerad
2019
Författare
Stankic, Sylvester Serban
Ploesteanu, Radu-Cristian
Modellbyggare
Tidskriftstitel
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Volymtitel
Utgivare
Sammanfattning
Centrifugal fans are commonly utilized in applications for treatment and ventilation of air, given their excellent ability to induce pressure and drive this flow medium. In manufacturing of compact Air Handling Units (AHU) where lower areal footprints are a necessity, several centrifugal fans (in parallel) are often use for each flow direction. It has been shown that there is a risk of decreased individual fan efficiency when multiple fans are introduced next to each other in operation. This is problematic in cases where single, larger fans cannot be used due to mentioned space constraints. The aims of this study were therefore to investigate the reasons as to why this happens and what potential measurements that could be implemented in order to improve fan performance. Numerical simulations using the commercial Computational Fluid Dynamics (CFD) software STAR CCM+ have been performed on a scaled down version of the supply side down in an AHU, consisting of two centrifugal fans positioned next to each other. Steady state conditions and turbulence modelling (k-epsilon realizable) have been applied for simulating four different airflow rates. Modifications to the initial design of the AHU have also been tested in order to evaluate impact on fan efficiency for the same conditions. The attempted modifications were based on the principle of adding additional geometry in between the centrifugal fans like a wall or guiding vanes (and combination of those). Another principally different design that was investigated was by offsetting on the fans further downstream from its original position. By evaluating obtained results in could be concluded that the poor fan performance in the initial design happens due to the open interaction area in between the centrifugal fans, where airstreams from each of the fans will collide and interfere with each other (which adds an extra resistance to the system). Fan performance could be improved by implementing most of above mentioned modifications, and the most promising results were accomplished through the separation of the two centrifugal with a straight wall, that covers half of the distance of the outlet chamber, in which the two fans are located. The would theoretically increase the averaged fan efficiency with 3.8-7.3%, relative to that observed in the initial design. The collected data has to be validated in experimental settings, and this lack of comparison at this stage can be seen as one of the main drawbacks with the study.
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Ämne/nyckelord
Energi , Hållbar utveckling , Strömningsmekanik och akustik , Energy , Sustainable Development , Fluid Mechanics and Acoustics