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流體動力學
一、流速
1. 流速
流體質點在單位時間內流過的位移，稱為流速v
v=△s/△t
式中 v----流體的流速， m/s;
△s---流體質點的位移， m;
△t----流體質點位移 △s所經(jīng)過的時間，s。
2.平均流速
在某一斷面上，流速的平均值稱平均流速vcp，工程計算上常用的是平均流速。對于流體的流速、流量和過流斷面面積的關系，用以下公式表示。
對于質量流量q，可用下式表示:
q=ρFvcp
Vcp=q/pf
式中 q----質量流量，kg/s;
p----流體的密度，kg/m3 ;
F----過流斷面面積，m2 ;
Vcp-平均流速，m/s。
對于重量流量G,可用下式表示:
vcp=G/yF
式中G---重量流量， N/s或kgf/s;
y---流體的重度，N/m2 或kgf/m3。
當液體流動時，溫度和壓力不變的情況下，其密度p和重度y是不變的，所以可以用體積流量來表示:
Vcp=Q/F
式中Q----體積流量，m3/s
二、流體連續(xù)性方程
由圖1-3所示，在管道中，流體由1-1斷面流入，2-2斷面流出。 根據(jù)質 量守恒定
理，同一時間內流入的質量應該等于流出的質量。
式(1-12) 就是可壓縮流體的連續(xù)性方程。
如果流體的密度ρ為常數(shù)時，即不可壓縮流體，ρ1=P2
式(1-13)為不可壓縮流體的連續(xù)性方程。
三、流體能量守恒定理-柏努利方程
如圖1-4所示，假設一股液流，從管道的1-1斷面流入，經(jīng)過2-2斷面流出。若以0-0為基準線，則在1-1斷面處:位置高度為Z1，平均流速為v1，壓強為P1; 2-2斷面處:位置高度為Z2，平均流速為2，壓強為P2， 并且假設為理想流體，流體流動過程中沒有摩擦力的作用，并為恒定流動，根據(jù)能量守恒的原理，就有下式
這就是理想流體的柏努利方程，其幾何意義是單位重量的液體在流動中，其位置水頭Z,壓強水頭。及速度水頭”。三者之和為-常數(shù)。 并且三者在流動過程中是可以互相轉換的。
但實際流體是有黏性的，液體在流動過程中流體之間有內摩擦阻力，流體與固體壁面之間也有摩擦力，這種摩擦力將會引起水頭阻力損失，設為h_。則式(1-14)可寫成:
這就是實際流體的柏努利方程。渣漿泵
fluid dynamics
I. velocity
1. velocity
The displacement of fluid particles in unit time is called velocity v
V= Delta s/ delta T
Where V is the velocity of fluid, M / S;
△ s --- displacement of fluid particle, m;
△ T ---- the time for the displacement of fluid particle △ s, S.
2. Average velocity
In a certain section, the average velocity is called the average velocity VCP, which is commonly used in engineering calculation. For the relationship between flow velocity, flow rate and cross-section area of flow, the following formula is used.
For mass flow Q, it can be expressed as follows:
Q= P Fvcp
Vcp=q/pf
Where Q - mass flow, kg / S;
P - density of fluid, kg / m3;
F - cross section area of overcurrent, m2;
VCP mean velocity, M / s.
For weight flow g, it can be expressed as follows:
Vcp=G/yF
Where g --- weight flow, N / s or kgf / S;
Y is the gravity of the fluid, N / m2 or kgf / m3.
When the liquid flows, and the temperature and pressure are constant, its density p and density y are constant, so it can be expressed by volume flow:
Vcp=Q/F
Where Q ---- volume flow, m3 / S
Fluid continuity equation
As shown in Figure 1-3, in the pipeline, the fluid flows in from section 1-1 and out from section 2-2 Keep constant according to quality
In the same time, the quality of inflow should be equal to that of outflow.
Equation (1-12) is the continuity equation of compressible fluid.
If the density ρ of the fluid is constant, i.e. incompressible fluid, ρ 1 = P2
Equation (1-13) is the continuity equation of incompressible fluid.
3. Conservation of fluid energy Bernoulli equation
As shown in Figure 1-4, suppose a stream of liquid flows in from section 1-1 of the pipeline and flows out through section 2-2. If 0-0 is taken as the reference line, at section 1-1: the position height is Z1, the average flow rate is V1, and the pressure is P1; at section 2-2: the position height is Z2, the average flow rate is 2, and the pressure is P2, and it is assumed that it is an ideal fluid, there is no friction in the process of fluid flow, and it is a constant flow. According to the principle of energy conservation, it has the following formula
This is Bernoulli's equation of ideal fluid. Its geometric meaning is the position head Z and pressure head of unit weight liquid in flow. And velocity head ". The sum of the three is - constant And the three can transform each other in the flow process.
But the actual fluid is viscous. In the process of fluid flow, there is internal friction between the fluid and the solid wall. This friction will cause the loss of head resistance, which is set as H UU. Formula (1-14) can be written as follows:
This is Bernoulli's equation for real fluids. Slurry pump
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