The effect of variable inlet guide vanes in the multistage centrifugal compressor for the turbo chiller on the part load efficiency improvement was analyzed by using CFD (computational fluid dynamics). The area we analyzed targeted two stages including the first and second variable inlet guide vanes arranged upstream of each compressor. The numerical simulation involved three-dimensional, steady, and compressible flow analysis with ANSYS-CFX. The flash gas injected from the intermediate inlet of the economizer passage was taken into account. The part-load efficiency was measured while changing the opening ratio for the first and second variable inlet guide vanes. The predicted part-load efficiency corresponded to the one that was measured. The predicted flow pattern indicated that higher efficiency could be obtained by adjusting the opening ratio for the first and second variable inlet guide vanes to suppress excessive prewhirl from the first impeller and stall from the second impeller.

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