3.5.3. Influence of the Gap Flow

For the optimum performance of a radial fan wheel, the setting of the correct gap dimension is very important. The setting of the correct clearance u (not to be confused with the circumferential speed) can be separated between the backward-curved and forward-curved types. With the backward-curved wheels, the inlet cone dips into the inlet ring of the fan wheel. Performance always depends on the correct (negative) overlap dimension and is communicated by punker with each design.
With forward curved fan wheels, the inlet cone does not dip into the fan wheel. Here, a positive gap dimension must always be maintained for optimum performance.

The different influences of the gap dimension are shown schematically in Figure 3.21a and 3.21b. The larger the dimension a, the higher the efficiency of the fan wheel / fan.

Figure 3.21 b: Influence of the Gap Flow

 

Figure 3.21 b: Influence of the Gap Flow