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渣漿泵蝸殼、導葉及吸入室轉能裝置
添加時間:2020.03.10

渣漿泵蝸殼、導葉及吸入室轉能裝置

蝸殼和導葉是离心泵的轉能裝置,它们的作用是把从叶轮出來的液體收集起來,使體流速降低把部分速度能頭轉變爲壓力能頭後再均勾地引下一級成經過擴出。

1. 蝸殼

蝸殼的形状通常是按照泵在设计流量下液体在叶轮中作稳定的相对运动,离开叶轮后不受外力作用,按其慣性作自由流動的軌迹而做成。當自葉輪流出的液體不受外力(摩擦力等)作用時,則液流對旋轉軸中心的動量矩保持不變.故有:
    根据流体连续性方程,蝸殼任意半径R處的忀^蚍炙CRr (不計阻塞系數影響):
    若蝸殼宽度不变,即bR爲定值时,则在定常流动时有:
                                CRuR=常數
    由此可见,液流在平行板式蝸殼内作自由流动时,其流动轨迹的份^蚪遣槐洌瑺懸惶醵允菪撸缤1-59所示。隨著半徑R的增加,對應的CRce.均減小,故液流速度CR及速度能头也将减小,而逐渐转换爲静压能。如果想使速度能充分转换爲压力能,液流必经流过較长的路程,径向尺寸必然过于庞大。因此,限制蝸殼螺旋线的包角不大于360。爲了减小径向尺寸,根据cRr與蝸殼轴面宽度成反比的关系,用不断擴大的擴张形轴面宽度,如图1-60所示。這樣,液流份^蚪a不再是常數,而是隨半徑R6R增大而减小。但蝸殼截面的擴张角0不應大于60°,以免因蝸殼通流面擴大太快使液流发生严重的边界层分离。蝸殼尺寸小後液体在螺旋线部分只有小部分动能转变爲静压能。爲此,在螺旋线末端加一擴压管,其张角爲8°~12°,长度爲擴压管进口截面直径的2.5~3.0倍。在擴压管内可使80%~85%的动能转变爲静压能。
    蝸殼的截面有圆形、矩形和倒梯形几种,其中,圓形截面用于高比轉速泵,倒梯形截面用于中比轉速泵,矩形截面用于低比轉速泵。
    蝸殼结构多用于单級离心泵和水平中开式多級泵中。

2. 導葉

導葉的作用與蝸殼相同,多用于分段式多級泵中,按其结构形式,可分爲径向式導葉和流

道式導葉。径向式導葉是由正向導葉、環形空間和反向導葉组成其结构如图1-61所示。 正向導葉内螺旋线AB部分是按照設計工況下液體的自由流動軌迹得出的,用于收集液體和保證液體在葉道中自由流動;而擴散段BC部分则用来把大部分动能转变爲静压能;環形空間CD则用于改变液流份^颉7聪驅~DE的作用是消除旋轉速度,並把液體在無預選條件下引下一級葉輪進口。 導葉的叶片数與叶轮叶片数不应相等,一般爲4~7片。
    流道式導葉如图1-62所示,其结构與径向式導葉基本相同,所不同的是径向式導葉从正向導葉出来的液体在環形空間内混合在一起,之后进入反向導葉。 而流道式導葉的正向導葉和反向導葉是铸在一起的 ,中間形成單獨的小流道,各流道的液體不能混合,不易形成死角和突然擴散,速度变化比較均匀,水力性能較好,但結構複雜,制造工藝性差。
    與蝸殼相比,導葉具有外形尺寸較小通用性大和制造方便等特点.因爲它可以用数量不同、尺寸相同的導葉组成叶轮尺寸相同的分段式多級泵。但是采用蝸殼作爲轉能裝置的中开

,具有安裝檢修方便和的高效率區寬的優點而導葉作爲轉能裝置的分段式多級泵,安装、检修不方便高效率区較窄。因爲在偏離設計工況時,液流對每個葉片都會産生沖擊損失而在蝸殼中只有个隔舌,所以導葉式泵的H-Qn-Q性能曲線均比蝸亮泵要陡,平均效率也較低。
3.吸入室
    室位于葉輪前,其作用是將液體以最小的損失均勻地引葉輪。吸室有錐形管吸室螺旋形吸室和圓形吸入室三種形式。
    (1)锥形管吸入室用于小型单級单吸悬臂式离心泵中,其結構簡單、 制造方便,如圖1- 63(a)所示。在葉輪入口前使液流造成集流和加速度, 流速均匀,损失較小。
    (2)螺旋形吸入室如圖1- 63(b)所示,流动情况較好,速度比較均匀,但液流進入葉輪前有預旋,在一定程度上會降低揚程 ,對低比轉速泵,这种影响不明显。目前,我国悬臂式离心油泵和中开式多級蝸殼泵都采用这种吸入室。
    (3)圓形吸入室如圖1- 63(o)所示,結構簡單,軸向尺寸短,但液流進入叶轮前有撞击和旋涡损失,液流也不太均匀,常用于多級分段式离心泵中。

Energy transfer device for volute, guide vane and suction chamber of slurry pump

The volute and guide vane are the energy conversion devices of centrifugal pumps. Their functions are to collect the liquid thrown out from the impeller, reduce the liquid flow rate, change part of the speed energy head into the pressure energy head, and then all lead into the next stage to discharge through the diffusion tube.

1. volute

The shape of the volute is usually made according to the relative movement of the liquid in the impeller under the design flow of the pump. After leaving the impeller, it is not affected by the external force, and it is made according to its inertia as the path of free flow. When the liquid from the impeller is not affected by external forces (friction, etc.), the momentum moment of the liquid flow to the center of the rotating shaft remains unchanged

According to the fluid continuity equation, the radial velocity CRR at any radius r of volute (excluding the influence of blocking coefficient) is as follows:

If the width of the volute is constant, that is to say, when BR is a constant value, there are:

CRuR= constant

It can be seen that when the liquid flows freely in the parallel plate volute, the direction angle of its flow path is unchanged, which is a logarithmic helix, as shown in Figure 1-59. With the increase of radius r, the corresponding Cr and CE decrease, so the liquid velocity Cr and velocity head will also decrease, and gradually convert to static pressure energy. If we want to convert the velocity into the pressure energy, the liquid flow must go through a long distance, and the radial dimension must be too large. Therefore, the wrap angle of spiral is limited to no more than 360. In order to reduce the size of the minor diameter, according to the inverse ratio between the CRR and the width of the volute axial surface, the expanding axial surface width is used, as shown in Figure 1-60. In this way, the flow direction angle a is no longer constant, but decreases with the increase of radii R and 6R. However, the expansion angle 0 of the volute section should not be greater than 60 ° to avoid serious boundary layer separation due to the rapid expansion of the volute flow passage section. When the volute size is reduced, only a small part of the kinetic energy of the liquid in the helix changes into the static energy. For this reason, a diffuser is added at the end of the helix, its expansion angle is 8 ° ~ 12 °, and its length is 2.5 ~ 3.0 times of the diameter of the inlet section of the diffuser. 80% ~ 85% of kinetic energy can be converted into static energy in the diffuser.

The section of volute includes circle, rectangle and inverted trapezoid. Among them, circle section is used for high specific speed pump, inverted trapezoid section is used for medium specific speed pump and rectangle section is used for low specific speed pump.

Volute structure is mostly used in single-stage centrifugal pump and horizontal split multistage pump.

2. guide vane

The function of the guide vane is the same as that of the volute. It is mostly used in the segmented multistage pump. According to its structure, it can be divided into radial guide vane and flow

Channel guide vane. Radial guide vane is composed of forward guide vane, annular space and reverse guide vane. Its structure is shown in figure 1-61. Part ab of the helix in the forward guide vane is obtained according to the free flow path of the liquid under the design condition, which is used to collect the liquid and ensure the free flow of the liquid in the blade passage; part BC of the diffusion section is used to convert most of the kinetic energy into the static energy; and part CD of the annular space is used to change the direction of the liquid flow. The function of the reverse guide vane De is to eliminate the rotation speed and introduce the liquid into the inlet of the next stage impeller without preselection. The number of guide vane and impeller vane should not be equal, generally 4-7.

The runner guide vane is as shown in figure 1-62. Its structure is basically the same as the radial guide vane. The difference is that the liquid from the radial guide vane is mixed together in the annular space, and then enters the reverse guide vane. The forward guide vane and the reverse guide vane of the runner type guide vane are cast together, and a separate small runner is formed in the middle. The liquid in each runner cannot be mixed, and it is not easy to form dead angle and sudden diffusion. The speed change is relatively uniform, and the hydraulic performance is good, but the structure is complex, and the manufacturing process is poor.

Compared with the volute, the guide vane has the characteristics of small size, large universality and convenient manufacture, because it can be used to form a segmented multistage pump with the same impeller size with different number of guide vanes of the same size. But the spiral case is used as the middle opening of the energy conversion device

The multi-stage pump of type B has the advantages of convenient installation and maintenance as well as wide high efficiency area of the pump, while the segmented multi-stage pump of the guide vane as the energy conversion device is inconvenient for installation and maintenance, and the high efficiency area is narrow. Because of the impact loss of the liquid flow to each blade when it deviates from the design condition, and there is only one tongue in the volute, the H-Q and n-q performance curves of the guide vane pump are steeper than those of the bright volute pump, and the average efficiency is lower.

3. inhalation room

The suction chamber is located in front of the impeller, and its function is to introduce the liquid evenly into the impeller with the minimum loss. There are three types of suction chamber: spiral suction chamber and circular suction chamber.

(1) The conical tube suction chamber is used in a small single-stage single suction cantilever centrifugal pump, with simple structure and convenient manufacture, as shown in Fig. 1-63 (a). In front of the impeller inlet, the liquid flow causes the collection and acceleration, the flow velocity is uniform, and the loss is small.

(2) As shown in Fig. 1-63 (b), the spiral suction chamber has good flow condition and uniform speed, but there is pre rotation before the liquid flows into the impeller, which will reduce the head to a certain extent, and the effect on the low specific speed pump is not obvious. At present, cantilever centrifugal pump and split type multi-stage volute pump all use this kind of suction chamber.

(3) As shown in Fig. 1-63 (o), the circular suction chamber is simple in structure and short in axial dimension, but there is impact and vortex loss before the liquid flows into the impeller of slurry pump manufacturer, and the liquid flow is not uniform, so it is commonly used in multistage segmented centrifugal pump.





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