Speed matching for the second impeller with equal power of two impellers is proposed to improve the performances of counter-rotating fan under off-design conditions
where the speed of second impeller is adjusted until the power of second impeller gets equal to one of first impeller. The fan performances during constant speed operating and during the second impeller speed matching operating are presented and discussed by theoretical analysis
numerical simulation and experimental research. It is revealed that the pressure-rise and power of the second impeller are changed significantly with varying mass flow during constant speed operating
leading to overload of the second motor under low flow rates and rapidly lowering pressure-rise and efficiency of the second impeller under high flow rates. The speed matching of the second impeller operating improves power and efficiency characteristics of the second impeller. Thus
pressure-rise and power characteristics of the fan become flatter. The load of the second impeller under low flow rates is lowered
and the pressure-rise and efficiency of the second impeller under high flow rates are heightened. The efficient working range of the fan is widened from 33.18% to 37.88%
and the blocking condition margin is widened from 36.9% to 48.2%.
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references
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