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