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This study numerically investigates the effects of changing vaned diffuser angles and vaneless diffuser widths of a twostage centrifugal refrigerant compressor on the reduction of surge flow rate and the improvement of part-load performance. The first stage has a low-solidity vaned diffuser, while the second stage has a vaneless diffuser. The analysis results show that adjusting the angle of low-solidity vaned diffuser in the first stage can lower the surge flow rate and keeps high efficiencies at low flow rates. The inlet guide vane of the first stage can also lower the surge flow rate; however, their simultaneous actuation cannot lower the surge flow rate further. Reducing the vaneless diffuser width of the second stage can lower the surge flow rate. Meanwhile, simultaneously adjusting the individual inlet guide vanes of the second stage can also effectively lower the surge flow rate. If the diffuser width of the first stage is reduced while the low-solidity vaned diffuser blade angle is fixed, the surge flow rate will be lowered obviously as the inlet guide vane is adjusted. However, reduction in diffuser width decreases the efficiency at low flow rate. Controlling the inlet guide vane and diffuser width well can lower the surge flow rate to 30% of the design flow.

This study numerically investigated the influence of using the second row of a double-row deswirl vane as the inlet guide vane of the second stage on the performance of the first stage in a two-stage refrigeration centrifugal compressor. The working fluid was R134a, and the turbulence model was the Spalart-Allmaras model. The parameters discussed included the cutting position of the deswirl vane, the staggered angle of two rows of vane, and the rotation angle of the second row. The results showed that the performance of staggered angle 7.5 ∘ was better than that of 15 ∘ or 22.5 ∘ . When the staggered angle was 7.5 ∘ , the performance of cutting at 1/3 and 1/2 of the original deswirl vane length was slightly different from that of the original vane but obviously better than that of cutting at 2/3. When the staggered angle was 15 ∘ , the cutting position influenced the performance slightly. At a low flow rate prone to surge, when the second row at a staggered angle 7.5 ∘ cutting at the half of vane rotated 10 ∘ , the efficiency was reduced by only about 0.6%, and 10% of the swirl remained as the preswirl of the second stage, which is generally better than other designs.