雙螺桿泵的選型技巧
性能參數(shù)的選擇：
Performance parameters of choice:
1.流量Q：
1. Flow rate Q:
作為容積式泵，影響雙螺桿泵流量的因素主要有轉(zhuǎn)速n，壓力p，以及介質(zhì)的粘度v。
As a positive displacement pump, the factors that affect the twin-screw pump flow main speed n, the pressure p, as well as the medium viscosity v.
1.1 轉(zhuǎn)速 n 的影響：
1.1 Speed n impact:
螺桿泵在工作時，兩螺桿及襯套之間形成密封腔，螺桿每轉(zhuǎn)動一周便由進口向出口移出一個密封腔，即一個密封腔的體積的液體被排出去。理想狀態(tài)下，泵內(nèi)部無泄漏，那么泵的流量與轉(zhuǎn)速成正比。即：
Screw pump at work, the two form a seal between the screw and the bushing cavity, screw each week, turning it from import to export out of a sealed chamber, namely, the volume of a sealed chamber to the liquid being discharged. Ideally, the internal pump leak, then the pump is proportional to the flow and speed. Namely:
Qth=n*q
Qth = n * q
n----轉(zhuǎn)速；
n ---- rotational speed;
q----理論排量，即泵每轉(zhuǎn)一周所排出的液體體積；
q ---- theory of displacement, that is, transfer pumps for each week of the emission of liquid volume;
Qth----理論排量。
Qth ---- theory of displacement.
1.2 壓力△P的影響：
1.2 Pressure △ P impact:
泵實際工作過程中，其內(nèi)部存在泄漏，也稱滑移量。由于泵的密封腔有一定的間隙，且密封腔前、后存在壓差△P，因此，有一部分液體回流，即存在泄漏，泄漏量用△Q表示，則
Pump actual work process, their internal leakage there is, also known as slippage. As the pump seal chamber has a certain gap, and the sealed chamber before and after the existence of differential pressure △ P, therefore, some of the liquid return, that is, there is leakage, leakage with △ Q, said the
Q=Qth-△Q
Q = Qth-△ Q
顯而易見，隨著密封腔前、后壓差△P升高，泄漏量△Q逐漸增大。對于不同型線和結(jié)構(gòu)，影響大小也各不相同。
Obviously, with the sealed chamber before and after the pressure difference △ P rise, leakage △ Q is gradually increasing. For the different types of lines and structures, affecting the size of different.
1.3 粘度v的影響：
1.3 Viscosity v of the impact:
試想：將清水和粘稠的漿糊以相同的體積從漏斗式的容器中泄漏出去。顯然水比漿糊要泄漏得快。
Consider: The water and viscous paste in the same volume of container from the funnel-type leak. Obviously the water to leak faster than the paste.
同理，對于雙螺桿泵，粘度大的流體比粘度小的液體的泄漏要小，泄漏量與介質(zhì)粘度有一定的比例關(guān)系。
Similarly, for the twin-screw pump, the fluid viscosity smaller than the viscosity of the liquid leakage is smaller, leakage volume and viscosity of a certain percentage of media relations.
綜上所述，要綜合地考慮以上各種因素，通過一系列的計算才能精確地知道泵的實際流量是否符合工況要求。
To sum up, we should consider these factors in an integrated manner, through a series of calculations in order to accurately know the actual flow of the pump meets required conditions.
2.壓力△P：
2. Pressure △ P:
與離心泵不同，雙螺桿泵的工作壓力△P由出口負載決定，即出口阻力來決定。出口阻力與泵的出口處的壓力是匹配的，出口阻力越大，工作壓力也越大。若想知道壓力，則需要用流體力學的知識對出口阻力精確的計算。
With the centrifugal pump is different twin-screw pump working pressure △ P export-load decision that the export of resistance to decide. Export resistance and the pump outlet pressure is matched, export the resistance the greater the greater the work pressure. If you want to know the pressure, you need to export the knowledge of fluid mechanics resistance calculations.
3.軸功率N：
3. Shaft power N:
泵的軸功率分為兩部分，即：
The pump shaft power is divided into two parts, namely:
Nth----液壓功率，即壓力液體的能量；
Nth ---- hydraulic power, that is, the pressure energy of the liquid;
Nr----摩擦功率。
Nr ---- friction power.
對于確定的壓力和流量，其液壓功率是一定的，因此影響軸功率的因素為摩擦率Nr。
For determining the pressure and flow, the hydraulic power is certain, therefore shaft power of the factors affecting the friction rate of Nr.
摩擦功率是由于運動部件的摩擦而消耗的那部分功率。這些摩擦功率顯然是隨著工作壓差的增加而增加的，并且介質(zhì)粘度的增加也會引起液體摩擦功率的增加。
Friction power is due to friction of moving parts of that part of the power consumed. The friction power is clearly increased as the work pressure increased, and the media can also cause an increase in viscosity of the liquid friction power increases.
由此，泵的軸功率除了液壓功率外，其中摩擦功率隨介質(zhì)粘度及工作壓力而增加，因此在選擇配套電機時，介質(zhì)的粘度也是一個非常重要的參考數(shù)據(jù)。尤其在輸送高粘度介質(zhì)時，需要作比較精確的計算。
As a result, the pump shaft power In addition to hydraulic power, the friction power as a medium in which the viscosity and pressure increase, and therefore choose matching motor, the medium viscosity is also a very important reference. Particularly in the transport of high viscosity medium, you need to make more precise calculations.
在計算功率后，選擇配套電機時應遵照樣本表格中所規(guī)定的有關(guān)規(guī)定。
In calculating the power, select the auxiliary motor should be in accordance with the form set forth in the sample of the relevant provisions
N(KW) N≤10 10＜N≤50 N＞50 N＞100
K 1.5 1.25 1.15 1.1
N (KW) N ≤ 10 10 <N≤50 N> 50 N> 100
K 1.5 1.25 1.15 1.1
Nm=N.K
Nm = N.K
Nm----電機功率 N----軸功率 K----功率儲備系數(shù)
Nm ---- Power N ---- shaft power coefficient K ---- Power Reserve
4.吸上性能的計算及選擇
4. Suction performance computing and select
泵工作分為以下幾個階段：
Pumps work is divided into the following phases:
4.1 吸入，此時液體連續(xù)不斷地沿吸入管道移動；
4.1 inhalation, this time along the suction pipe of liquid continuous movement;
4.2 旋轉(zhuǎn)的螺桿把能量傳給工作液體；
4.2 rotating screw to pass the energy working liquid;
4.3 壓出，此時液體帶有克服壓出管道系統(tǒng)所有阻力所必需的壓力從泵中排出。
4.3 Press out the liquid at this time to overcome the pressure out of pipeline systems with all the necessary resistance to the pressure from the pump discharge.
在以上三個階段中，為重要的階段是必須保證泵的吸上條件，泵才能正常工作，這是泵工作的重要條件，否則就會發(fā)生氣蝕，即引起振動，噪音等問題。
In the above three phases, the most important stage is the need to ensure that the conditions of the pump-priming the pump to work properly, this is an important condition for pump work, otherwise cavitation will occur, that is caused by vibration, noise and other issues.
5.汽蝕余量的計算：
5. NPSH calculation:
泵的汽蝕余量NPSHr與泵的轉(zhuǎn)速n，導程h以及泵所輸送介質(zhì)的粘度v等因素都有關(guān)系，對我廠引進的Bornemann雙螺桿泵用以下公式計算：
Pump NPSH NPSHr and pump speed n, lead h and the viscosity of the medium transport pumps and other factors, the relationship between v, to our factory introduced Bornemann twin-screw pump with the following formula:
NPSHr=(1.5+0.253VF 1.84345+0.0572VF 1.55)*v 0.4146
NPSHr = (1.5 +0.253 VF 1.84345 +0.0572 VF 1.55) * v 0.4146
VF----軸向流速，VF=n*h/60(m/s)；
n----轉(zhuǎn)速(r/min)；
h----導程(m)；
v----工作粘度(°E)。
VF ---- axial velocity, VF = n * h/60 (m / s);
n ---- Speed (r / min);
h ---- Lead (m);
v ---- Work viscosity (° E).
由此可見，泵的NPSHr是隨VF，v的增大而增大。因此在吸入條件不好的情況下，宜選擇小導程的雙螺桿泵。這在選型時是很重要的。
This shows that the pump is NPSHr with VF, v's increases. Therefore, in the case of inhalation are poor, should choose a small lead of the twin-screw pump. This is when the selection is very important.
5.1 裝置汽蝕余量NPSHa的計算，這里不再闡述。
5.1 Device NPSHa NPSH calculations, this is no longer described.
5.2 想要保持泵正常工作，即不發(fā)生汽蝕、振動等問題，必須保證以下條件：
5.2 want to maintain the pumps to work, that is, cavitation does not occur, vibration and so on, must ensure that the following conditions:
NPSHa＞NPSHr 這即是泵的吸入條件。
NPSHa> NPSHr This means that the pump suction conditions.
6.雙螺桿泵的轉(zhuǎn)速選擇：
NPSHa> NPSHr This means that the pump suction conditions.
選擇不同的轉(zhuǎn)速常牽涉以下問題：
Select a different speed often involves the following questions:
6.1 通過選擇合適的泵轉(zhuǎn)速，以達到適當?shù)男阅軈?shù)如流量等。
Select a different speed often involves the following questions:
6.2 隨著粘度的不同，泵的轉(zhuǎn)速亦應有所改變。
6.2 As the viscosity of the different pump speed should be changed.
對于Boremann雙螺桿泵，粘度的變化是決定轉(zhuǎn)速的主要條件，隨著粘度的增大，允許轉(zhuǎn)速也越低。
For Boremann twin-screw pump, the viscosity change is to determine the speed of the main conditions, with the viscosity increases, allowing the lower the speed.
轉(zhuǎn)速的選擇實質(zhì)也是吸上性能的問題，尤其是在高粘度的情況下，如果轉(zhuǎn)速選得過高，就會引起吸入不足，從而產(chǎn)生噪音和振動等問題。因此務(wù)必遵照有關(guān)原則選擇轉(zhuǎn)速。
Speed is also a choice of smoking on the performance of real problems, especially in high-viscosity case, if the speed of the election are too high, they cause less inhalation, resulting in noise and vibration issues. So be sure to comply with the principle of selection speed.
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