1. COMSATS Institute of Information and Technology
Defence road, off Raiwind Road, Lahore
Department of Chemical Engineering
Title
“ASSIGNMENT NO 4”
TURBOMACHINERY,CENTIFUGAL PUMP,PD PUMP
Course code: CHE230
Course Instructor: Engr. HAMOOD UR REHMAN
Student Name: ZUHAIR-BIN-JAWAID
Registration No: DDP-SP14-BEC-094
2. TURBOMACHINERY
Turbomachines are machines that transfer energy between a rotor and a fluid, including both
turbines and compressors. While a turbine transfers energy from a fluid to a rotor, a compressor
transfers energy from a rotor to a fluid. The two types of machines are governed by the same
basic relationships including Newton's second Law of Motion and Euler's energy equation for
compressible fluids. Centrifugal pumps are also turbomachines that transfer energy from a rotor
to a fluid, usually a liquid, while turbines and compressors usually work with a gas.
CLASSIFICATION
CLASSIFICATIONACCORDING TOEXTENT OFFLUID
In general,the twokindsof turbomachinesencounteredinpractice are openandclosedturbomachines.
Openmachinessuchas propellers,windmills,andunshrouded fansacton an infiniteextentof fluid,
whereas,closedmachinesoperate onafinite quantityof fluidasitpassesthrougha housingorcasing.
CLASSIFICATIONACCORDING TOTYPE OFFLOW
Turbomachinesare alsocategorizedaccordingtothe type of flow.Whenthe flow isparallel tothe axis
of rotation,theyare calledaxial flowmachines,andwhenflow isperpendiculartothe axisof rotation,
theyare referredtoasradial (or centrifugal) flow machines.There isalsoathirdcategory,calledmixed
flowmachines,wherebothradial andaxial flow velocitycomponentsare present.
CLASSIFICATIONACCORDING TOENERGY
Turbomachinesmaybe furtherclassifiedintotwoadditional categories:those thatabsorbenergyto
increase the fluidpressure,i.e. pumps,fans,andcompressors,andthose thatproduce energysuchas
turbines byexpandingflowtolowerpressures.Of particularinterestare applicationswhichcontain
pumps,fans,compressorsandturbines.These componentsare essential inalmostall mechanical
equipmentsystems,suchaspowerand refrigerationcycles.
3. CENTRIFUGAL PUMPS
Centrifugal pumps are usedtotransportfluidsbythe conversionof rotational kineticenergytothe
hydrodynamicenergyof the fluidflow.The rotationalenergytypicallycomesfromanengine orelectric
motor.
Centrifugal pumps are asub-classof dynamicaxisymmetricwork-absorbingturbomachinery.
Figure 1: CENTRIFUGAL PUMP
Characteristics ofCentrifugal pumps
Head—Resistance to Flow
In Newtonian (true) fluids (non-viscous liquids, such as water or gasoline), the term head is the
measurement of the kinetic energy that a pump creates. Imagine a pipe shooting a jet of water
straight into the air. The height that the water reaches is the head. Head measures the height of a
liquid column, which the pump could create resulting from the kinetic energy the pump gives to
the liquid. The main reason for using head instead of pressure to measure a centrifugal pump’s
energy is that the pressure from a pump will change if the specific gravity (weight) of the liquid
changes, but the head will not change. End users can always describe a pump’s performance on
any Newtonian fluid, whether it is heavy (sulfuric acid) or light (gasoline), by using head. Head
is related to the velocity that the liquid gains when going through the pump.
4. Friction Head (hf)
Friction head is the head required to overcome the resistance to flow in the pipe and fittings. It
depends on the size, condition and type of pipe; the number and type of pipe fittings; flow rate;
and nature of the liquid.
Velocity Head (hv)
Velocity head is the energy of a liquid as a result of its motion at some velocity (V). It is the
equivalent head in feet through which the water would have to fall to acquire the same velocity
or, in other words, the head necessary to accelerate the water.
Pressure Head
Pressure head must be considered when a pumping system either begins from or empties into a
tank that is under some pressure other than atmospheric. The pressure in such a tank must first be
converted to feet of liquid. A vacuum in the suction tank or a positive pressure in the discharge
tank must be added to the system head, whereas a positive pressure in the suction tank or vacuum
in the discharge tank would be subtracted. The following is a formula for converting inches of
mercury vacuum into feet of liquid.
Pumps in series
Centrifugal pumps are connected in series if the discharge of one pump is connected to the
suction side of a second pump. Two similar pumps, in series, operate in the same manner as a
two-stage centrifugal pump.
Each of the pumps is putting energy into the pumping fluid, so the resultant head is the sum of
the individual heads.
Some things to consider when you connect pumps in series:
Both pumps must have the same width impeller or the difference in capacities (GPM or
Cubic meters/hour.) could cause a cavitation problem if the first pump cannot supply
enough liquid to the second pump.
Both pumps must run at the same speed (same reason).
Be sure the casing of the second pump is strong enough to resist the higher pressure.
Higher strength material, ribbing, or extra bolting may be required.
The stuffing box of the second pump will see the discharge pressure of the first pump.
You may need a high-pressure mechanical seal.
Be sure both pumps are filled with liquid during start-up and operation.
5. Start the second pump after the first pump is running.
Pumps in parallel
Pumps are operated in parallel when two or more pumps are connected to a common discharge
line, and share the same suction conditions.
Some things to consider when pumps are operated in parallel:
Both pumps must produce the same head this usually means they must be running at the
same speed, with the same diameter impeller.
API 610, states that when pumps are run in parallel, "the head shall rise at least 10% of
the head at rated capacity."(this is called a "stable curve because there is a continious rise
to shutoff.)
Two pumps in parallel will deliver less than twice the flow rate of a single pump in the
system because of the increased friction in the piping.
The shape of the system curve determines the actual increase in capacity. If there is
additional friction in the system from throttling (see dotted line in the following diagram),
two pumps in parallel may deliver only slightly more than a single pump operating by its
self.
If you run a single pump only, it will operate at a higher flow rate (A) than if it were
working in parallel with another pump (B) because it will be operating further out on the
curve requiring increased power. The rule is that if a pump is selected to run in parallel,
be sure it has a driver rated for single operation.
6. Positive displacement pumps
A positive displacement pump makes a fluid move by trapping a fixed amount and forcing
(displacing) that trapped volume into the discharge pipe.
Some positive displacement pumps use an expanding cavity on the suction side and a decreasing
cavity on the discharge side. Liquid flows into the pump as the cavity on the suction side
expands and the liquid flows out of the discharge as the cavity collapses. The volume is constant
through each cycle of operation.
CLASSIFICATION OF POSITIVE DISPLACEMENT PUMP
Basedon the construction,Hydrostaticpumpsare classified
1. Gear Pumps( fixeddisplacement pumps)
(a) External gearpump
(b) Internal gearpump
a. Lobe pump
b. Gerotorpump
(c) Screw pump
2. Vane Pumps( fixedorvariable displacementpumps)
(a) BalancedVane pump
(b) UnbalancedVane pump
