Turbo Compressors

Thermal turbo compressors are turbo machines which concentrate a compressible gas with the help of dynamic principles.

In doing so the gas continuously enters the rotating impeller. Mechanical shaft power is transferred to the fluid with the help of the blades and resulting in a significant pressure and temperature increase. The remaining kinetic flow energy is afterwards mostly converted into pressure in the diffusor. The compressed gas is then either collected in a volute or transferred to a second compressor stage with the help of a return channel. In Figure 1, the components of a one-stage, centrifugal turbo compressor are shown, where Figure 2 shows the close-up of an impeller including blades.

Components of a one-stage centrifugal compressor
Figure 1: Components of a one-stage centrifugal compressor
Close-up of an impeller with blades
Figure 2: Close-up of an impeller with blades

In general, different types of turbo compressors can be defined based on their design:

  • Centrifugal turbo compressors: the flow enters the turbo compressor in axial direction and exits the impeller in the centrifugal direction. Both 2D- or 3D-impeller blades are possible.
  • Mixed flow turbo compressors: the flow enters the turbo compressor in axial direction and exits the impeller neither in a pure centrifugal nor in a pure axial direction, and the exit has a larger radius.
  • Axial turbo compressors: the flow enters the turbo compressor in axial direction and exits the impeller in axial direction with a similar radius.

The following figures illustrate the different compressors-types:

Centrifugal compressor
Figure 3: Centrifugal compressor
Mixed flow compressor
Figure 4: Mixed flow compressor
Axial compressor
Figure 5: Axial compressor

The capability of a turbo compressor is best illustrated in a compressor performance and a power map (see Figures 6 and 7), where the pressure ratio (outlet pressure p2 to inlet pressure p1) versus the mass flow at a constant speed n is shown. Dots with the same efficiency η on different characteristic curves are joined to provide efficiency curves. In general, the compressor map is defined by the maximum speed of the compressor (to the right) and by the surge line (to the left). Surging is defined as the unpreventable aerodynamic instability. Operating the compressor left of the surge line is not allowed. The performance of the Celeroton products is presented in this visual form and to see more specific details please view the product datasheet.

Compressor performance map with efficiency shell curves
Figure 6: Compressor performance map with efficiency shell curves
Power map
Figure 7: Power map

Advantages and disadvantages

The pros and cons of a turbo compressor can be summarised as follows:

Advantages of turbo compressors

  • High power density and therefore small physical dimensions and low weight

  • High reliability, due to only one rotating partin and proven technology

  • High efficiency of the energy conversion

  • Low noise level


Disadvantages of turbo compressors

  • Dynamic operating principle limits the operating area (see compressor map)

  • High power density leads to a more challenging thermal management system

  • Limited pressure ratios can be achieved for each stage. Higher pressure ratios can be achieved by the series connection of several turbo compressors



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