| A spiral-shaped volute is used in many applications of compressors to collect the rotating flow, which discharges from a diffuser downstream of the impeller, and to deliver it into a single discharge pipe. The performance and design of volutes has not received the detailed study given to the other components of compressors. This can be attributed to the fact that the volute is a simple collecting device and all the necessary diffusion has been achieved in the vaned or vaneless diffuser upstream of the volute. The volute is usually designed through the application of one-dimensional analysis. A design objective is to achieve a uniform pressure distribution at the volute inlet. This is usually attained at the design flow rate only; at off-design conditions the volute is either too small or too large and pressure distortion develops circumferentially around the volute passage. The static pressure distortions are transmitted to the diffuser exit, the impeller discharge, and even through the inducer. Therefore, these pressure distortions reduce the stage performance and have a direct impact on diffuser and impeller stability.; In the present study, a Trane CVHF 1280 two-stage centrifugal compressor, which is used in air-conditioning applications, was modified to a single stage. Air replaced the refrigerant gas and a new motor replaced the old driving system. The compressor's inlet and outlet components were modified to accommodate the performance evaluation experiments. The data acquisition system was developed to measure static, total temperatures and pressures at diffuser, volute casings, inlet and outlet pipes. Measurements have been performed at three speeds of 2000, 3000 and 3497 RPM in order to evaluate the performance of this compressor and its volute.; In addition, Fluent 5.0 was utilized to simulate the flow in this compressor utilizing the experimental and meanline analysis data as the boundary conditions. An unstructured grid was generated in GAMBIT for the region of vaneless diffuser inlet to the volute cone outlet. The simulations were performed for adiabatic flow in this flow path to extract the flow structure and calculate the performance of the components. The numerical results are in a good agreement with the experimental ones, which validates the simulations. Furthermore, the flow properties were extracted for various cross sections of the volute and vaneless diffuser from the simulation results in order to investigate the flow structure inside these components at off design condition. These results revealed the deviation of the volute flow from the free vortex design methodology in all cases. In addition the compressor performance improved as speeds and mass flow rates increases because the losses decrease for those conditions. The losses corresponding to tongue region were inevitable and design modifications were discussed to reduce the effect of the tongue and improve the compressor performance. |
