CHAPTER 6
VELOCIS SOLUTIONS @2018
6
𝑊
𝑎𝑐𝑡
=
𝑊
𝑟𝑒𝑣
𝐸
This equation can be expressed in working form as:
𝑊 =
𝑞(𝑃
2
− 𝑃
1
)
𝐸
Where:
𝐸 − thermodynamic efficiency
𝑞 − flow rate
𝑃
2
−discharge pressure
𝑃
1
− suction pressure
The maximum volume flow rate through a pump occurs when its net head is zero, this flow rate is
called the pump’s free delivery. The free delivery condition is achieved when there is no flow
restriction at the pump inlet or outlet—in other words when there is no load on the pump. At this
operating point, flow rate is large, but head is zero; the pump’s efficiency is zero because the pump
is doing no useful work. At the other extreme, the shutoff head is the net head that occurs when
the volume flow rate is zero and is achieved when the outlet port of the pump is blocked off. Under
these conditions head is large, flow rate is zero; the pump’s efficiency is again zero, because the
pump is doing no useful work. Between these two extremes, from shutoff to free delivery, the
pump’s net head may increase from its shutoff value somewhat as the flow rate increases, but H
must eventually decrease to zero as the volume flow rate increases to its free delivery value. The
pump’s efficiency reaches its maximum value somewhere between the shutoff condition and the
free delivery condition; this operating point of maximum efficiency is appropriately called the best
efficiency point (BEP).
Dostları ilə paylaş: |