泵chanpter8-1

Pump Flash
Developed head
At pump itself, the liquid enters the suction connection at station a and leaves the discharge connection at station b .
A Bernoulli equation can be written between station a and b
Pipe and tubing
Fluids are usually transported in pipe or tubing.
There is no clear-cut distinction between the terms pipe and tubing.
Generally speaking, pipe is heavy-walled and relatively large in diameter and comes in moderate lengtht
The power delivered to the fluid is calculated from the mass flow rate and the head developed by pump.
It is denoted by Ne (or Pe) and defined by
Tubing is thin-walled and often comes in coils several hundred meter long.
For large pipe , more than 12 in . in diameter , the nominal diameters are the actual outside diameters;
The energy may be used to increase the velocity, the pressure, or the elevation of the fluid.
Two major classes of fluid-moving machinery: (1) those applying direct pressure to the fluid, include positive-displacement devices.
• 2 mechanical seals • Shown in fig.8.2 in your textbook
• Valves
• 1 gate and globe valves. • 2 check valves • Joints and fittings
Fluid-moving machinery
The power cost for turbulent flow varies with the -4.8 power of the pipe diameter. Equations have been presented giving the optimum pipe diameter as a function of flow rate and fluid density.
2 2 pb ub pa ua W gZb gZa 2 2
(8-1)
The equation(8-1) can be divided by g, gives
2 2 pb ub p a ua H g Z b 2 g g Z a 2 g
N e mW
(8-5)
If the power is calculated from the equation (8-1a) , then
N e mgH
(8-5a)
The power supplied to the pump drive from an external source is denoted by NB
(8-1a)
The quantity H is called developed (total) head, in which each term has the dimension of length. Often the head developed by a pump is expressed in meters of fluid.
since the only friction is that occurring in the pump itself and is accounted for by mechanical efficiency η, hf=0. Then equation(4-33) can be written
Fluids are moved through pipe, equipment, or the ambient atmosphere by pump, fans, blowers, and compressors.
Such devices increase the mechanical energy of the fluid.
Chapter8
Transportation and metering of fluids
The engineer is concerned with practical problems in transporting fluids from one place to another and in measuring their rates of flow.
The pump is installed in a pipeline to provide the energy needed to draw liquid from a reservoir and discharge a constant volumetric flow rate at the exit of the pipeline, Zb m above the level of the liquid.
pumps
In pumps, the density of the fluid is both constant and large. Pressure differences are usually considerable. A typical pump application is shown in Figure . Refer to Fig.
(2) those using torque to generate rotation. Pump is a device for moving a liquid; a fan , a blower, or a compressor adds energy to a gas. Centrifugal devices generate high rotational velocities, then convert the resulting kinetic energy of the liquid to pressure energy.
The first part of the chapter deals with the transportation of fluids, both liquids and gases.
The second part of the chapter discusses methods of measuring.
For turbulent flow of liquids in steel pipes larger than 25mm in diameter, optimum velocity is
uopt
12m
0.1
【8-1】

0.36
m=mass flow rate, lb/s ρ=fluid density, lb/ft3
If the suction pressure is actually less than the vapor pressure, cavitation will occur in the suction line, and no liquid can be drawn into the pump.
Selection of pipe sizes
The pipe size selected for a particular installation depends mainly on the cost of the pipe and fittings and the cost of energy needed for pumping the fluid. The cost of the pipe and the annual capital charges increase with about the 1.5 power of the pipe diameter.
Positive-displacement units apply pressure directly to the liquid by a reciprocating piston, or by rotating members which form chambers alternately filled by and emptied of the liquid. Refer to Fig.
For water and similar fluid uopt is 0.9 to 1.8m/s
For air or steam at low to moderate pressures uopt is 6 to 124m/s
When flow is by gravity from overhead tanks or when a viscous liquid is pumped, low velocities are favored, in the range of 0.06 to 0.24m/s