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

TURBOMACHINERYTurbomachines 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

CLASSIFICATION ACCORDING TO EXTENT OF FLUIDIn general, the two kinds of turbomachines encountered in practice are open and closed turbomachines. Open machines such as propellers, windmills, and unshrouded fans act on an infinite extent of fluid, whereas, closed machines operate on a finite quantity of fluid as it passes through a housing or casing.

CLASSIFICATION ACCORDING TO TYPE OF FLOWTurbomachines are also categorized according to the type of flow. When the flow is parallel to the axis of rotation, they are called axial flow machines, and when flow is perpendicular to the axis of rotation, they are referred to as radial (or centrifugal) flow machines. There is also a third category, called mixed flow machines, where both radial and axial flow velocity components are present.

CLASSIFICATION ACCORDING TO ENERGYTurbomachines may be further classified into two additional categories: those that absorb energy to increase the fluid pressure, i.e. pumps, fans, and compressors, and those that produce energy such as turbines by expanding flow to lower pressures. Of particular interest are applications which contain pumps, fans, compressors and turbines. These components are essential in almost all mechanical equipment systems, such as power and refrigeration cycles.

CENTRIFUGAL PUMPSCentrifugal pumps are used to transport fluids by the conversion of rotational kinetic energy to the hydrodynamic energy of the fluid flow. The rotational energy typically comes from an engine or electric motor.

Centrifugal pumps are a sub-class of dynamic axisymmetric work-absorbing turbomachinery.

Figure 1: CENTRIFUGAL PUMP

Characteristics of Centrifugal pumpsHead—Resistance to FlowIn 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.

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 HeadPressure 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.

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.

Positive displacement pumpsA 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 PUMPBased on the construction, Hydrostatic pumps are classified

1. Gear Pumps ( fixed displacement pumps)

(a) External gear pump

(b) Internal gear pump

a. Lobe pump

b. Gerotor pump

(c) Screw pump

2. Vane Pumps ( fixed or variable displacement pumps)

(a) Balanced Vane pump

(b) Unbalanced Vane pump

3. Piston Pumps ( fixed or variable displacement pumps)

(a) Axial piston pump b) Radial piston pump

Various positive displacement pumps

Rotary lobe pump Progressive cavity pump Rotary gear pump Piston pump Diaphragm pump Screw pump Gear pump Hydraulic pump Rotary vane pump Regenerative (peripheral) pump Peristaltic pump Rope pump Flexible impeller

characteristics of positive displacement pumps

MechanicsCaptures confined amounts of liquid and transfers it from the suction to the discharge port (flow is created and pressure results).

PerformanceFlow is constant with changing pressure.

ViscosityEfficiency increases with increasing viscosity.

EfficiencyEfficiency increases with increasing pressure.

Inlet ConditionsNegative pressure is created at the inlet port. A dry pump will prime on its own.