反击系数在低比转速叶轮几何参数优化中的应用

Application of reaction factor in optimizing geometries of low specific speed impellers

低比转速叶轮为产生较高的给定扬程,叶轮直径都相对较大。叶轮圆盘摩擦损失大约正比于叶轮直径的5次方,圆盘摩擦损失成为低比转速泵内损失的主要形式,也是这类泵效率甚低的基本原因。为改善这类泵的效率指标,曾提出了一以降低叶轮直径和圆盘摩擦损失为主要目标的优化模型。针对对这一数学模型的质疑,从叶轮的反击系数这一概念入手,论证了不可能通过叶轮几何尺寸优化同时把叶轮圆盘摩擦损失和叶轮出口冲击损失降低到最小值,由于在低比转速泵中前者占优势,因而降低这类泵的圆盘摩擦损失是提高这类泵效率的主要途径,从而在理论上论证了所讨论优化模型的正确性。

Impeller outlet diameters are relative large in low specifie speed impellers due to the required high heads to be generated.As disc frictional losses of impellers are proportional to the fifth power of impeller diameter, disc frictional losses is mainly responsible for the low efficiency of this kind of pump.In order to improve pump efficiency, authors established a math model aiming at reducing impeller diameter and disc friction of low specific speed impellers.This paper based on the concept of reaction factor, proved that it is impossible to minimize the disc friction losses and shock losses at impeller exit.As the former is dominant, minimizing the frictional losses is the main approach to raise the overall efficiency of low specific speed impellers and justify the correctness and reasonableness of the math model set up previously.