Analysis and Design of Centrifugal Blowers for the Pressure Ratio Range 1.2 - 1.8

Centrifugal/centrifugal compressor designs within pressure ratio range of 2.0–4.0 have well-established guidelines for most common gases, and it is possible to determine optimum compressor geometry for numerous applications as characterized by specific speed or flow coefficient. Specific speed can be correlated to various combinations of inlet tip-exit diameter ratio, inlet hub-tip diameter ratio, blade exit back-sweep, and inlet-tip absolute tangential velocity for solid body pre-whirl. For centrifugal compressors in the pressure ratio range of 1.2–1.8, commonly known as blowers, there lacks organized and systematic optimum design procedures. Blowers, among many others uses, are widely used in HVAC, and provide air for ventilation and industrial process requirements. Due to broad applications in industry, blowers comprise an important sub-group of turbomachinery. This paper provides analysis and design data for blowers in the pressure ratio range of 1.2–1.8. Specific speed is determined from the data provided, and accurate correlations to possible achievable maximum efficiencies are established within a good operational range. Furthermore, plots of impeller exit flow angle, inlet tip-exit diameter ratio, inlet hub-tip diameter ratio, head coefficient, and blade exit back-sweep are provided over a range of specific speeds for various tip speeds to permit rapid selection of optimum blower size and shape for a variety of applications. The design procedure follows a method that enables efficient blade passage sizing. When the blower inlet and outlet velocities, diameters, blade widths, and blade angles are determined and fixed, the blade passage and profile will be sized by applying an energy, momentum, and continuity balance analysis. The application of these equations equates the proper pressure and velocity distribution throughout the blower impeller. Generally, the passage is designed to accommodate an optimum prescribed diffusion rate.