Fictitious Centrifugal Force
Centrifugal force1 is often confused with centripetal force2. Centrifugal force is most commonly introduced as an outward force apparent in a rotating frame of reference3. It is apparent (fictitious) in the sense that it is not part of an interaction but is a result of rotation - with no reaction-force counterpart4. This type of force is associated with describing motion in a non-inertial reference frame5, and referred to as a fictitious or inertial force (a description that must be understood as a technical usage of these words that means only that the force is not present in a stationary or inertial frame).
There are three contexts in which the concept of fictitious centrifugal force arises when describing motion using classical mechanics:
In the first context, the motion is described relative to a rotating reference frame about a fixed axis at the origin of the coordinate system. For observations made in the rotating frame, all objects appear to be under the influence of a radially outward force that is proportional to the distance from the axis of rotation and to the square of the rate of rotation (angular velocity) of the frame.
The second context is similar, and describes the motion using an accelerated local reference frame attached to a moving body, for example, the frame of passengers in a car as it rounds a corner. In this case, rotation is again involved, this time about the center of curvature of the path of the moving body. In both these contexts, the centrifugal force is zero when the rate of rotation of the reference frame is zero, independent of the motions of objects in the frame.
The third context arises in Langrangian mechanics6, and refers to a subset7of generalized forces that often are not equivalent to the vector forces of Newtonian mechanics.
1. centrifugal force – центробежная сила
2. centripetal force – центростремительная сила
3. frame of reference – система отсчёта, система координат
4. counterpart – контршаблон, дубликат, копия
5. non-inertial reference frame – неинерциальная система координат
6. Langrangian mechanics –механика Лагранжа
7. subset – подмножество
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Centrifugal Compressors
Centrifugal compressors1, sometimes termed radial compressors, are a sub-class of dynamic axisymmetric work-absorbing turbomachinery2.
The idealized compressive dynamic turbo-machine achieves a pressure rise by adding kinetic energy/velocity to a continuous flow of fluid through the rotor or impeller. This kinetic energy is then converted to an increase in potential energy/static pressure by slowing the flow through a diffuser3.
Theory of operation
Imagine a simple case where flow passes through a straight pipe to enter centrifugal compressor. The simple flow is straight, uniform and has no vorticity4. As illustrated below α1=0 deg. As the flow continues to pass into and through the centrifugal impeller5, the impeller forces the flow to spin faster and faster. According to a form of Euler's fluid dynamics6equation, known as "pump and turbine equation," the energy input to the fluid is proportional to the flow's local spinning velocity7 multiplied by the local impeller tangential velocity8.
In many cases the flow leaving centrifugal impeller is near the speed of sound (340 metres/second). The flow then typically flows through a stationary compressor causing it to decelerate9. As described in Bernoulli's principle10, this reduction in velocity causes the pressure to rise leading to a compressed fluid.
1. сentrifugal compressors –центробежные компрессоры
2. turbomachinery –турбины
3. diffuser –диффузор; распылитель
4. vorticity –завихренность; турбулентность
5. impeller -импеллер, лопастное колесо, крыльчатка
6. fluid dynamics –гидродинамика
7. spinning velocity –скорость вращения
8. tangential velocity –касательная скорость
9. decelerate –уменьшать скорость, ход, число оборотов; замедлять, тормозить
10. Bernoulli's principle –закон Бернулли
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Common Types of Pneumatic Valves1
Pneumatic valves1 are one of an array2 of components responsible for controlling the pressure, rate, and amount of air as it moves through a pneumatic system. Pneumatic systems, which depend on the force of compressed air to transmit power, can be found in countless industrial applications, from pneumatic pressure power tools3 to diesel engines. Based on other components within a given application and the type of pneumatic system used, one of several types of pneumatic valves may be found at the heart of the device. Functional directional control valves4, those that control the direction of air flow or inhibit5 flow all together, are a large class of pneumatic valves that houses multiple variants.