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 dynamics⁶ equation, 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

Text № 8 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.

Functional Directional Control Valve

Many functional directional pneumatic control valves are classified based on the number of entry and exit ports⁶ they possess, the number of flow paths they create, and the mechanism by which ports are opened and closed.

• Two-Way Directional Valve

A two-way directional valve passes air in two directions, through two ports which can be open or closed. If the valve ports are closed no air can flow through the valve. If the ports are open, air may move from the first port through the valve and through the second port or in the opposite direction.

• Three-Way Directional Valve

A three-way directional valve has three ports, each of which serves a different purpose. The first port is used to connect the valve to an actuator or another device. The second port is connected to an air flow. The third port is used as an exhaust exit.

1. pneumatic valve – пневмоклапан; пневмораспределитель

2. array – ряд; серия

3. pneumatic pressure power tool – пневмо-механический инструмент

4. directional control valve – направляющий гидро- или пневмораспределитель

5. inhibit – задерживать, сдерживать, препятствовать

6. entry and exit ports – входные и выходные отверстия

7. two-way directional valve – двухканальный направляющий клапан