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安徽快3开奖结果 News
渣浆泵摩擦阻力损失
添加时间:2020.01.27

渣浆泵摩擦阻力损失

摩擦阻力损失(简称摩阻损失)指液体流经吸室、叶轮流道蜗壳和扩压管(或导叶)时的沿程摩擦阻力损失以及液流因转弯、突然收缩或扩大等所产生的局部阻力损失。
    由流体力学可知,当黏性流体沿固体壁面流动时,流体流场可分为两个区域,紧靠壁面很薄的一层称为边界层,在边界层中必须考虑流体的黏性力,边界层中的流动可看成黏性流体的有旋流动。边界层虽然很薄,但沿其厚度方向流体速度急剧变化,它严重地影响着流体流动过程的能量损失及流体与壁面间的热交换等物理现象。实验证明,流体的摩阻损失集中在边界层中,边界层以外的中心部分,黏性力很小,可以看作是理想流体的无旋流动。
摩阻损失ht通常用达西公式计算,:

式中λ----沿程阻力系数, Re、流道表面相对粗糙度有关。

由于泵内液体流速大,进阻力平方区以后,可认为λ常数.因此把全部摩阻损失看成与速度平方,即与流量的平方成正比表示为

式中C----与流道表面粗糙度及过流面积有关的系数。

将式(1-35)用曲线表示,如图 1-29曲线6所示,是一 条过坐标原点的二次抛物线。

2)冲击损失

当液流进液道(或导叶流道),液流相对运动方向角β1与叶片进口角β1A不一致,以及体离开叶轮进入转能装置的液流角a2与转能装置中叶片角ax致而产生冲击所引起的能量损失,称为冲击损失。
    众所周知,离心泵是在一 定流量下设计的。叶轮叶片进口角β1A是按设计工况计算的,所以泵在设计流量Qd下工作时液体进入叶轮叶片的液流角β1与叶片β1A相符,在片进口速度三角形中,β1=β1A,则液流能平稳地进叶轮流道,不产生冲击。

当泵的工作流量Q≠Qd时,例如Q<Qd; 进口液流角β1;<β1A,因而液流便冲向叶片的工作面上,在非工作面上产生旋锅,造大的能量损失。这种损失就是冲击损失。冲击损失的大小与叶片角β1A和液流角β1间的差值β有关。β称为冲角,其定义为 β=β1A-β1。Q<Qdβ>0;Q>Qd时,β<0,如图1-28所示。
冲击损失大小可通过下面公式计算:
                                 hsh=C2(Q-Qd)2
式中hsh----叶轮叶片进口和压液室中液流冲击所造成的水力损失
     C2-----阻力系数.与过流面积有关。渣浆泵厂家
    将式(1- 36)用曲线表示,如图1- 29曲线7所示。在设计流量时没有冲击损失,与设计工况点偏离越多,即工作流量小于或大于设计流量越多,冲击损失越大。
    由以上分析可知,叶轮给予液体的能量,其中有一部分用于克服从泵口到排出口间过流部件的摩阻损失和冲击损失,使得泵的实际扬程H低于有限叶片理论扬程Ht,:
                         H=Ht-hr-hsh

Friction loss of slurry pump

Friction loss (referred to as friction loss) refers to the friction loss along the way when the liquid flows through the suction chamber, impeller passage, volute and diffuser (or guide vane), as well as the local resistance loss caused by turning, sudden contraction or expansion of the liquid flow。

According to the hydrodynamics, when the viscous fluid flows along the solid wall, the fluid flow field can be divided into two areas. The thin layer close to the wall is called the boundary layer. The viscous force of the fluid must be considered in the boundary layer, and the flow in the boundary layer can be regarded as the swirling flow of the viscous fluid. Although the boundary layer is very thin, the fluid velocity changes sharply along its thickness direction, which seriously affects the physical phenomena such as the energy loss in the process of fluid flow and the heat exchange between the fluid and the wall. The experimental results show that the friction loss of the fluid is concentrated in the boundary layer, and the central part outside the boundary layer has a small viscous force, which can be regarded as the irrotational flow of the ideal fluid.

The friction loss HT is usually calculated by Darcy formula, namely:

Where λ - resistance coefficient along the path, which is related to re and relative roughness of the channel surface.

Since the flow rate of liquid in the pump is large, λ can be considered as a constant after entering the square area of resistance. Therefore, the total friction loss is regarded as being proportional to the square of speed, that is, to the square of flow, which is expressed as:

Where C - coefficient related to surface roughness and flow area of flow passage.

安徽快3开奖结果Equation (1-35) is represented by a curve, as shown in Figure 1-29 curve 6, which is a quadratic parabola passing through the coordinate origin。

2) Impact loss

When the liquid flow enters the liquid channel (or guide vane channel), the energy loss caused by the impact is called impact loss because the relative direction angle β 1 of the liquid flow is not consistent with the inlet angle β 1a of the blade, and the liquid flow angle A2 of the liquid leaving the impeller and entering the energy conversion device is not consistent with the blade angle ax of the energy conversion device.

As we all know, centrifugal pump is designed at a certain flow rate. The impeller blade inlet angle β 1a is calculated according to the design working condition, so when the pump works at the design flow QD, the liquid flow angle β 1 entering the impeller blade is consistent with the blade angle β 1a. In the blade inlet speed triangle, β 1 = β 1a, the liquid flow can enter the impeller channel smoothly without impact.

When the working flow of the pump Q ≠ QD, for example, Q < QD; the inlet liquid flow angle β 1; < β 1a, so the liquid flow will rush to the working surface of the blade, which will produce a rotary pot on the non working surface, resulting in great energy loss。 This kind of loss is impact loss。 The impact loss is related to the difference △ β between blade angle β 1a and liquid flow angle β 1。 △ β is called angle of impact, which is defined as △ β = β 1A - β 1。 When Q < QD, △ β > 0; when Q > QD, △ β < 0, as shown in Figure 1-28。

The impact loss can be calculated by the following formula:

hsh=C2(Q-Qd)2

安徽快3开奖结果In the formula, HSH is the hydraulic loss caused by the impact of liquid flow at the inlet of impeller blade and in the pressure chamber;

C2 is the resistance coefficient, which is related to the flow area。 Slurry pump manufacturer

Equation (1-36) is represented by curve, as shown in Figure 1-29, curve 7. There is no impact loss in the design flow, and the more deviation from the design operating point, that is, the more the working flow is less than or greater than the design flow, the greater the impact loss.

It can be seen from the above analysis that part of the energy given by the impeller to the liquid is used to overcome the friction loss and impact loss of the flow passage components from the pump inlet to the discharge port, so that the actual lift h of the pump is lower than the theoretical lift ht of the finite blade, that is:

H=Ht-hr-hsh





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