Experiment on performance Characteristics of centrifugal pump
Presented by: Ram Krishna Singh Roll No: 065-MSREE-509
Objective Analyzing performance characteristics of centrifugal pump(s) with respect to head developed, discharge and Power Outcome, when operating •single • arranged in series and •Arranged in parallel Drawing Conclusion from the Experiment
Pump Pump is defined as a device that adds energy to the working fluid itself so that Mechanical Energy is converted into useful Fluid Energy. Objectives of the pump •Transfer of liquid from one place to another place (e.g. water from an underground aquifer into a water storage tank) •Circulate liquid around a system (e.g. cooling water or lubricants through machines and equipment)
Centrifugal pump Centrifugal Pump is a special kind of rotodynamic pump in which the fluid approaches the impeller axially, turns at the machine’s inlet so that flow out through the impeller is in the plane of impeller’s rotation.
How it works The impeller spins & throws water out. Like swinging a bucket of water above your head and staying dry or Throwing clay on a potter's wheel and wearing it. Low pressure is formed in the inlet. The lower the pressure, the higher the pump can "suck." Atmospheric pressure pushes more water in. It is this simple - this is the major part of pump theory ! PUMPS DON'T SUCK
Pumping System Characteristics • Head
destination
• Resistance of the system
Static head
• Two types: static and friction
• Static head
source
• Difference in height between source and destination of the pumped liquid • Independent of flow Static head
• Friction head • Loss needed to overcome that is caused by resistance to flow in pipe and fittings • Depends on size, pipes, pipe fittings, flow rate, nature of liquid • Proportional to square of flow rate • Closed loop system only has friction head (no static head)
Flow Friction head
Flow
Pumping System Characteristics Pump performance curve
Head
• Relationship between head and flow • Flow increase • System resistance increases • Head increases
Flow
• Flow decreases to zero
• Zero flow rate: risk of pump burnout •The head and flow rate determine the performance of a pump, which is graphically shown in the Figure as the performance curve or pump characteristic curve. •The figure shows a typical curve of a centrifugal pump where the head gradually decreases with increasing flow. •As the resistance of a system increases, the head will also increase. This in turn causes the flow rate to decrease and will eventually reach zero. A zero flow rate is only acceptable for a short period without causing to the pump to burn out.
Pumping System Characteristics In most cases: Total head = Static head + friction head System curve
Friction head
System head
System curve
System head
Friction head
Static head
Static head
Flow
Flow
In most cases the total head of a system is a combination of static head and friction head as shown in the figures Left figure is system with a high static head (i.e. the destination reservoir is much higher than the source) Right figure is system with a low static head (i.e. the destination reservoir is not much higher than the source)
Pump head - discharge curve When a pump is filled with the fluid to be operated at normal speed with discharge closed, the head developed Head is called shutoff head. Ideally, this would appear to be a case of a force vortex create with pressure head difference between eye and impeller periphery is (u22 –u12)/2g.
Flow
•The figure shows that the pump efficiency increases with the increase in discharge flow, until it reaches optimum value and starts to decrease. When pumps operate beyond this optimum condition, problems such as cavitation and hammering starts to occur.
Pump characteristics Usually manufacturers produces characteristics curves for the pump with different impeller diameter and operating speed. •Discharge is directly proportional to the speed •Head is proportional to square of speed •Power input is proportional to the cube of the speed Where, Q= discharge liter/sec H = head in meter Pi = power input
Pump characteristics If the pump operates at constant speed but at different diameter, the effect of discharge, head and power input becomes
Where D= diameter of impeller in meter
Characteristics of pump A pump is characterized by Head and Flow Rate developed for given Power supply and the given RMP of Impeller. Power developed to fluid
Po = Power developed to the fluid
EFFICIENCY OF PUMP
Pw = Power developed to the fluid / Electrical Power consumed
PUMPS IN SERIES
When pumps are arranged in series, the flow rate is constant but the head capacities of each pump adds to give total head.
PUMPS IN PARALLEL When pumps are arranged in parallel, the head is constant but the flow rate of each pump adds to give total flow rate.
Procedures Single pump was operated with control rate of flow taken for 0, 10, 15, 30, 30 liters per minute, observed in V notch.
Exact flow rate was measured with the help of pipe measurement and the stop watch. Observations for pressures at suction and delivery sides were done.
Corresponding electrical power drawn was observed. The process was repeated for the pumps in series as well as in parallel.
PERFORMANCE CHARACTERISTICS OF CENTRIFUGAL PUMPS Observation for single centrifugal pump
Results S.N
Volume Inlet flow rate (Q pressure liters/min) (bar)
Outlet Electric Head( Pump pressur power m) Hydraulic e(bar) input(wat power(W t) watt) h
1
0
0
0.6
90
6.11
0
2
8.05
0
0.5
110
5.09
8.313667
3
12.5
0
0.48
118
4.89
11.9805
4
21.42
0
0.38
142
3.87
12.642
5
28
0
0.3
155
3.05
15.94133
PERFORMANCE CHARACTERISTICS OF CENTRIFUGAL PUMPS Observation for centrifugal pumps in parallel
Results
S.N Volume flow Inlet Outlet power rate (Q pressure(bar) pressure(bar input(watt liters/min) ) )
Head
1
0
0
0.6
190
6.11
2
8.57
0
0.53
225
5.4
3
15.65
0
0.51
232
5.19
4
21.17
0
0.50
250
5.09
5
36
0
0.49
295
4.99
PERFORMANCE CHARACTERISTICS OF CENTRIFUGAL PUMPS Observation for centrifugal pumps in series
Results
S.N Volume flow Inlet Outlet power rate (Q pressure(bar) pressure(bar input(watt liters/min) ) )
Head
1
0
0
0.6
210
6.11
2
8.57
0
0.55
235
5.6
3
15
0
0.50
250
5.09
4
18
0
0.49
300
4.99
5
32.72
0
0.2
390
2.03
PERFORMANCE CHARACTERISTICS OF CENTRIFUGAL PUMPS Discharge Vs Head Analysis
Discharge Vs Head (ideal case)
Head, H
Discharge, Q
Discharge Vs Efficiency
Electric power input vs Flow rate
Hydraulic power vs Flow rate
Single vs Parallel operation Figure illustrates the characteristic of single vs. parallel operation. Two identical pumps operating in parallel are capable of producing twice the flow of a single pump at any given TDH.
However, the actual flow rate realized in the system is dictated by the intersection of the system curve with the pump curve. Unless the system curve is variable, the flow increase may not be that significant.
Single vs Parallel operation (contd…) For example, assume that there is a set of fixed spray nozzles, where the system resistance is purely frictional, and varies only as a result of flow change.
When a second pump is introduced, resistance in the system increases as the flow increases. The flow will increase only to where the system curve intersects the two-pump curve, as shown in figure.
The amount of flow increase is dictated not only by the system curve, but also by the steepness of the pump curves. Pumps with flat curves will have less TDH separation than pumps with steep curves and therefore will have less of a flow rate change.
Single vs Parallel operation (contd…) A fire pump installation would be an example of a system that has a variable system curve. Figure illustrates this.
Each time an additional fire nozzle is activated, the system resistance is decreased. This causes the system curve to move to a higher flow on the pump curve, increasing the kW load on the pump and decreasing the amount of TDH available.
Eventually, another fire pump may need to be activated to maintain the system pressure as more nozzles come on line.
Unstable Operation
The sketch shows a system curve crossing a pump curve twice. This is an example of unstable operation. Note that if the first pump is operating at point 'C' when the second pump is started, the second pump will operate at shut head, delivering no flow as it will never be able to open the non return valve (required to prevent one pump discharging through the other when only one pump is operating). If this was to occur, the pump could eventually explode! In some cases it may be possible to change the order of starting the pumps, and the curves can be drawn to check this operation, however if there is any indication of unstable operation or possibility of one pump being 'over powered' by another, contact us for assistance.
Analysis From the experiments, characteristics of pumps ran at different conditions are observed and drawn in graphs. These characteristics curves are essential in defining the properties of a pump, since only size and shape cannot be sufficient to select a pump for certain purpose. Standard test were done according to the procedures defined by the lab manual and characteristics curves are drawn.
Analysis • Initially, we study the variation of head available with change in flow rate. With pumps in parallel we can increase the flow almost twice for the same head delivered, while head delivered can be increased twice by arranging pumps in series. Hence, where a single pump is inappropriate for large flow rate or high head, pumps can be arranged in series and parallel or combination of both to suite our requirement. • we see that overall efficiency of the pumps against flow rate. It should be efficiency of pumps in combination is higher than a single pump. Even, efficiency of pumps in series is higher than that in parallel. More closely, we can also see that efficiency of pumps in series is better in lower flow rate ie at higher head delivered and pumps in parallel is better for higher flow rates and low
Analysis •
The hydraulic power produced by pumps against flow rate are drawn. In case of series connection the hydraulic power produced by a pump is higher than that of parallel connection at lower flow rates. At higher flow rates we can predict that curve of pumps in parallel will cross that of in series. • As the pumps are connected in series or parallel, the input power to the pumps increases than that of a single pump. • In case of field operation to select a particular type of pump or a particular combination of the pump, first of all the characteristics curves, provided by manufacturer, should be studied carefully and then only it should be use in field.
Conclusion • The main aim of the practical was to drawn up the characteristics curve. With the help of characteristics curve and the actual field conditions (ie. Head available, input power required, required flow rate). We should have to compromise in efficiency for the fulfillment of the actual field condition situations. So the characteristics curve helps to optimize the field conditions and to select a particular type of pump or a combination of pump for a particular site.
