CHAPTER 6
VELOCIS SOLUTIONS @2018
16
may be noisy and unstable, which indicates that the fan may be oversized (larger than necessary).
For these reasons, it is usually best to run a propeller fan at, or slightly above, its maximum
efficiency point.
Figure 7.13: Performance curves of an axial pump
POSİTİVE DİSPLACEMENT PUMP
People have designed numerous positive-displacement pumps throughout the centuries. In each
design, fluid is sucked into an expanding volume and then pushed along as that volume contracts,
but the mechanism that causes this change in volume differs greatly among the various designs.
Some designs are very simple, like the flexible-tube peristaltic pump that compresses a tube by
small wheels, pushing the fluid along. (This mechanism is somewhat similar to peristalsis in your
esophagus or intestines, where muscles rather than wheels compress the tube.) Others are more
complex, using rotating cams with synchronized lobes, interlocking gears, or screws. Positive-
displacement pumps are ideal for high-pressure applications like pumping viscous liquids or thick
slurries, and for applications where precise amounts of liquid are to be dispensed or metered, as
in medical applications.
Dostları ilə paylaş: | 
