FRI-9.2-1-THPE-02
SPECIFICS IN THE OPERATION OF CENTRIFUGAL PUMPS WHEN TRIMMING THEIR IMPELLERS
Abstract
This paper presents results obtained by studying some operating parameters, such as: power, coefficient of efficiency (effectiveness) and specific speed of rotation (ns) of centrifugal pumps when trimming their impellers. The materials (catalog data) provided by some manufacturers of centrifugal pumps, such as GRUNDFOS, KSB and VIPOM, are studied. It was found that the power index (exponent of power) varies within very wide limits and does not meet the recommendations provided in the well-known literature sources. The lowest coefficient value is obtained for KSB pumps and it mainly varies between 2 and 3, with small exceptions - sometimes values achived are above 3. For pump produced by GRUNDFOS, the exponent varies in values between 3 and 4. In case of pumps that are manufactured by VIPOM, this index (exponent) varies in a much wider range - from 2 to 4, as values above 4 are also being considered.
In studyiung the coefficient of efficiency exponent (index), when trimming a pump impeller, a variation in the range from 0 to 0.8 is obtained, however for the main number of pumps this variation is in the range from 0.2 to 0.5. For some rates of trimming, this exponent takes negative values.
When trimming a pump impeller, the specific speed of rotation (ns) increases. The average increase in ns is in the range of 20...50%. This leads to variation in the structure of the flow and makes it very difficult to predict the performance of pumps when trimming their impellers.
In studyiung the coefficient of efficiency exponent (index), when trimming a pump impeller, a variation in the range from 0 to 0.8 is obtained, however for the main number of pumps this variation is in the range from 0.2 to 0.5. For some rates of trimming, this exponent takes negative values.
When trimming a pump impeller, the specific speed of rotation (ns) increases. The average increase in ns is in the range of 20...50%. This leads to variation in the structure of the flow and makes it very difficult to predict the performance of pumps when trimming their impellers.
Keywords
centrifugal pump, impeller trimming, power, coefficient of efficiency, specific speed of rotation, trimming indexes (power exponents)
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