水在水泵流道中流动.doc

水在水泵流道中流动，速度在每个位置上是不一样的，导致其压力也不一样，当压力小于气体溢出压力时，就会发生气蚀和汽蚀。由于这个过程发生得时间非常短暂，所以就会发出噪声，同时由于汽和气得联合作用，既有物理反复敲击，又有化学腐蚀，于是就产生了破坏。水泵汽蚀主要是由于安装高度不当造成的。对于淹没式（自灌式）水泵一般不会发生汽蚀现象。对于非淹没式（非自灌式），安装高度是指从吸水池水位至水泵泵轴的高度，用Hss表示，应满足下式：? ? ? ? Hss≤[Hs]-(出水管流速的平方-吸水管流速的平方)/2g-△Z? ? 式中，[Hs]是水泵标准状态下的允许吸上真空高度，如果当地不是标准状态，尚需进行修正，可查《给水排水设计手册（第三册）》；g-重力加速度；△Z-水泵吸口与出口的高差。? ? ? ? 如果水泵安装高度超出了上述关系，吸水管中压强将低于水的汽化压力，除原先溶解于水中的气体会逸出外，部分水也会汽化，大量的气泡随水流进入水泵，到达叶轮背面后转变为高压，气泡遂在瞬间溃灭，频率之大以万甚至百万计，叶轮受到频率如此之高的敲击，外在表现为噪声，内在则伴随电化学腐蚀，叶轮会很快锈蚀或疲劳。此之谓汽蚀。? ? ? ? 当吸水管安装不当时，也容易发生气阻或气塞。比如吸水口与吸水管的连接采用了同心异径管（应该用偏心异径管），再比如吸水管上有向上突起，在负压作用下，原先溶解于水中的气体会逸出，堵塞在突起处，形成气阻。水泵也会出现噪声且输水能力大大下降。 A centrifugal pump is a rotodynamic pump that uses a rotating impeller to increase the pressure of a fluid. Centrifugal pumps are commonly used to move liquids through a piping system. The fluid enters the pump impeller along or near to the rotating axis and is accelerated by the impeller, flowing radially outward into a diffuser or volute chamber, from where it exits into the downstream piping system。 + E+ `6 Y% Z1 m* p0 V% |) @A centrifugal pump works on the principle of conversion of the kinetic energy of a flowing fluid (velocity pressure) into static pressure. This action is described by Bernoullis principle. The rotation of the pump impeller accelerates the fluid as it passes from the impeller eye (centre) and outward through the impeller vanes to the periphery. As the fluid exits the impeller, a proportion of the fluid momentum is then converted to (static) pressure. Typically the volute shape of the pump casing, or the diffuser vanes assist in the energy conversion. The energy conversion results in an increased pressure on the downstream side of the pump, causing flow.5 M6 t7 J! Z( m g u3 L Cavitation is a general term used to describe the behavior of voids or bubbles in a liquid. Cavitation is usually divided into two classes of behavior: inertial (or transient) cavitation and non-inertial cavitation. Inertial cavitation is the process wh