Series Fan Connection

In this case the outlet of the first fan is connected to the inlet of the second fan. With this arrangement, the total head developed at a given volume is equal to the sum of the total heads developed by the individual fans. Sometimes more than one fan is used in a duct arrangement. In the series connection (Fig. 9.49), the flow through the fans has the same volume flow, and the leaving flow from the first fan is connected to the suction side of the second fan. 

For the series connection, we indicate by 1 and 2 the suction and leaving sides of the first fan, respectively, and by 3 the leaving side of the second fan. 

The network and fan combination operating point can be obtained from Eq. (9.134). 

In a Ap-q, chart, the characteristic curve of the ducts is drawn. In the same chart is drawn the characteristic curve of both fans. At each volume flow q, the total pressure of each fan is added. In this w ay, we get a new - q  

The regulation of axial fan blade angle also influences the inlet and exit velocity triangles in such a way that the axial velocity and thus the volume flow change. When the relative velocity remains parallel to the blade, the efficiency remains high (Fig. 9.52). 

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