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Figure 1: Components of a centrifugal fan An external motor belt driven inline centrifugal fan discharging inline to the exterior of a building through a duct. Unlike non-inline/non-concentric impeller casing design with a cutoff blade above, the concentrically symetric cylinder casing and impeller geometry of inline type redirects the outflow around so that it is parallel to the inflow of gases.
Ratings found in centrifugal fan performance tables and curves are based on standard cubic feet per minute (SCFM). Fan manufacturers define standard air as clean, dry air with a density of 0.075 pounds mass per cubic foot, with the atmospheric pressure at sea level of 29.92 inches of mercury and a temperature of 70°F.
They apply to pumps, fans, and hydraulic turbines. In these rotary implements, the affinity laws apply both to centrifugal and axial flows. The laws are derived using the Buckingham π theorem. The affinity laws are useful as they allow the prediction of the head discharge characteristic of a pump or fan from a known characteristic measured at ...
The centrifugal fan wheel is typically contained within a scroll-shaped fan housing, resembling the shell of the nautilus sea creature with a central hole. The air or gas inside the spinning fan is thrown off the outside of the wheel, to an outlet at the housing's largest diameter.
Where, is speed of rotation. . is flow rate. . is impeller diameter. . Thus non-dimensional representation is highly advantageous for converging to single performance curve that would otherwise result in multiple curves if plotted dimensionally. Figure 1 shows head characteristics [1] of centrifugal pump versus flow coefficient. Within the normal operating range of this pump, 0.03 <Q/(ND 3 ...
Euler’s pump and turbine equations can be used to predict the effect that changing the impeller geometry has on the head. Qualitative estimations can be made from the impeller geometry about the performance of the turbine/pump. This equation can be written as rothalpy invariance: =
Compressor performance changes, day to day, with changes in the ambient pressure and temperature. Woolenweber [11] shows the change in performance of a turbocharger compressor when the inlet temperature varies between 70 and 100 deg F. In the case of aircraft compressors, inlet pressure and temperature also change with altitude and airspeed.
Actual characteristic curve of the compressor is the modified version of the theoretical characteristic curve. In this we take care of both shock and friction losses as shown in the Figure 4. As seen in the figure the steepness of the curve increases at higher mass flow rates because since there will be higher frictional losses at high flow ...