為了使混凝土能夠符合施工現場要求，混凝土在運輸過程中必須保持一定的流塑性，以便可以澆注成任意的形狀已達到施工要求?；炷潦且环N由多種材料組成的流體，因此其具有一般流體的特性。流體主要有以下特征：

In order to make the concrete meet the requirements of the construction site, the concrete must maintain a certain flow plasticity during transportation, so that it can be poured into any shape to meet the construction requirements. Concrete is a fluid composed of many materials, so it has the characteristics of general fluid. Fluid mainly has the following characteristics:

①在靜止狀態下流體僅僅能夠承受法向應力，即靜壓強；而在運動狀態下流體可以同時具有法向應力和切向應力的作用；

① In the static state, the fluid can only bear the normal stress, that is, the static pressure; In the moving state, the fluid can have the effect of normal stress and tangential stress at the same time;

②流體的形狀不固定，在剪切力的作用下可以發生形狀的變化，當外力消失時只能夠停止變形，而不能恢復流體原有的形狀；③使流體產生變形所需的剪切力非常小，所以流體很容易根據容器的空間來改變自身的形狀。

② The shape of the fluid is not fixed, and it can change under the action of shear force. When the external force disappears, the deformation can only be stopped, but the original shape of the fluid cannot be restored; ③ The shear force required to deform the fluid is very small, so the fluid can easily change its shape according to the space of the container.

正是由于流體具有以上特點，所以在流體靜止時不能承受切向應力，在運動時，則會對相鄰兩層流體間的相對運動有抵抗性，這種抵抗分子間相對運動的力被稱為流體間的粘性力。這種抵抗兩層流體間相對滑動的速度的性質，稱為粘性。

It is precisely because the fluid has the above characteristics that it cannot bear the tangential stress when the fluid is stationary, and it will resist the relative motion between adjacent two layers of fluid when it is moving. This force against the relative motion between molecules is called the viscous force between fluids. This property of resisting the relative sliding velocity between two layers of fluid is called viscosity.

粘性的大小取決于流體的種類，不同的流體，其粘性是不同的，而且經過實驗表明，流體間的這種粘性力的大小與流體自身具有的粘性和流體分子之間的相對速度成正比，當流體的粘性較?。ㄈ缈諝夂退恼承远己苄。r，流體之間相對運動速度不大時，流體分子間的粘性力相比于其他外力可忽略。

The size of viscosity depends on the type of fluid. Different fluids have different viscosities, and experiments show that the size of this viscous force between fluids is directly proportional to the viscosity of the fluid itself and the relative velocity between fluid molecules. When the viscosity of the fluid is small (such as the viscosity of air and water is small), and the relative velocity between fluids is small, the viscous force between fluid molecules can be ignored compared with other external forces.

流體是分層流動的，層與層之間因速度不等而會產生相對運動，速度快的流層帶動速度慢的流層，反之，速度慢的流層會阻止速度快的流層。帶動力與阻力是一對大小相等、方向相反的作用力，這就是流層之間的內摩擦力（或黏性摩擦力）。流體的黏性是阻止發生剪切變形的一種特性，而內摩擦力則是黏性的動力表現。

The fluid flows in layers, and the relative motion between layers will occur due to different speeds. The fast flow layer will drive the slow flow layer, on the contrary, the slow flow layer will prevent the fast flow layer. The driving force and resistance are a pair of equal and opposite forces, which is the internal friction (or viscous friction) between the flow layers. The viscosity of fluid is a characteristic of preventing shear deformation, and the internal friction is the dynamic performance of viscosity.

混凝土攪拌機的攪拌筒旋轉與之相似，攪拌筒內的混凝土拌合料在攪拌筒旋轉帶動下，圓周外層部分拌合料被螺旋葉片推動沿筒壁上升，到達某處后由于重力和攪拌離心力的共同作用，從高點斜拋下來與其他混凝土混合；半徑r內的混凝土拌合料在螺旋葉片的帶動下做圓周運動，外層流體流速快，越靠近軸線處流速越小。

The rotation of the mixing drum of the concrete mixer is similar. Driven by the rotation of the mixing drum, the concrete mixture in the mixing drum is driven by the spiral blade to rise along the drum wall. After reaching a certain place, due to the combined action of gravity and mixing centrifugal force, it is thrown down obliquely from the high point to mix with other concrete; The concrete mixture within radius r moves in a circular motion driven by the helical blades. The outer fluid flow rate is fast, and the closer it is to the axis, the smaller the flow rate.

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