The continuous transport of a liquid requires a pump, and the continuous transport of a gas or vapor requires a fan, blower, or compressor. All of these devices are described by the general term fluid movers. Specialized fluid movers are required for the transport of liquid-and-gas mixtures and of slurries and suspensions of solids in liquid or gas. The vast majority are mechanically driven. A few—eductors and ejectors—use another fluid as the motive source. In all cases the fundamental action of the device is to generate a localized increase of pressure, which then allows the fluid to overcome adverse differences and gradients of pressure that oppose its movement from source to destination.
Pasifik Blower
There are two general types of fluid movers, the dynamic and the positive displacement. The former imparts momentum to the fluid through principles of fluid dynamics, and the scale and direction of the momentum is usually different from that of the impelling element. The latter simply displaces the fluid, giving the fluid the velocity and direction of the impelling element.
Another major distinction is between the type of fluid being transported, i.e., liquid or gas. Liquids are somewhat simpler, but they require considerations of viscosity and of any tendency to vaporize under conditions of pressure at the inlet of the pump. Gases are subject to compression and to attendant changes in volume and temperature. The present account is organized into two broad sections—on liquid transport and on gas transport—and within each section it describes the technology of both the dynamic and the positive-displacement devices. In the case of gas compression, where pressure, volume, and temperature are all in flux, an outline of the relevant thermodynamics is provided.
Many ingenious devices for pumping liquids have been used over the ages. As stated, current pumps fall into one of two general types: the dynamic and the positive displacement.
Dynamic pumps are subject to inner losses of pressure because of, for instance, fluid acceleration and frictional forces. Achievable pressure rise across the pump decreases as liquid rate increases. There is generally a combination at which efficiency (to be defined) is greatest and close to which it is desired to operate
The capacity of a positive-displacement pump is largely independent of pressure rise across the pump, being subject only to backflowthrough clearances. An exception is that some types of screw pump allow backflow through the screw channels, which causes their capacity to depend significantly on the pressure rise.
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