Development of efficiency curves of Pump as Turbine (PaT) and their cost-benefit comparison to Conventional Turbines
1 Introduction (Pumps and Turbines)
1.1 Pump Performance Curves
All types of pumps have performance curves that describe the flow rate produced at total head. The pump specifications relating head and flow rate correlate to those found on its characteristic curve.
Figure 1.0. Simplified pump Performance curve
Pump best efficiency Point (BEP) is the optimum where pump manufacturers designate performance.
1.2 Fundamental Parameters of the pump
Pump efficiency, this defines percentage of the energy supplied to the pump that is converted into useful work. It is the ratio between water horsepower and brake horsepower. (Pout/Pin
Pressure; this is a measure of resistance in the operating system. The pressure (F/unit area) rating of the pump defines how much resistance can handle or overcome. Pressure therefore is used to measure pump performance
Pump Head; this is the height above the suction inlet that a pump can lift a fluid against the gravity. Centrifugal pumps use head instead of pressure to describe the energy or the pressure of the pump. Head is expressed as the column of height (m) of water.
Pump Power; this is the net head normally called output power (Pout).it is the horsepower ratings which describe the useful work the pump will do to the fluid.
1.3 Pumps and their types
Pump can be defined as mechanical devices which are used for transferring fluid of any kind to someplace. The mechanism of the pump is that because of the flow and the pressure of the liquid which can be at the same altitude, higher or lower altitude by converting the mechanical energy, which can be generated by the flow of the fluid, or the pressure into different kind of hydraulic energy. Pumps are of various kinds and also have different uses structures and sizes (En.wikipedia.org, 2018).
The pump thus acts as a device which increases the existing fluid pressure, transfer of fluid to a higher altitude area or creating a hydraulic force. Once the liquid exits the pump, the fluid energy stile exists. Similarly, energy changes can be made in the pump by simply altering the fluid pressure inside the pump. In layman’s term, one of the most important application of a pump is to transport the fluid to a higher displacement or location by converting the fluid pressure or simply, by creating a hydraulic force.
Three major types of pumps are discussed below, each having its own application and its advantages/disadvantages.
1: Centrifugal pumps
2: Return and return pumps
3: Gear pumps
1: Centrifugal pumps
Centrifugal pumps are the most commonly used pumps for the fluid. This type of pump receives its propulsion through an electromotor and can be transmitted at a continuous rate from the fluid. There is an axis called shaft through which the propulsion force is transmitted from the engine to the pump by a device known as a coupling, which is a mechanical device. The power is transferred from the shaft of the electric motor to the shaft of the pump. These kind of pumps are cone shaped attached with a casing. Each shaft has either one or more mounted wheels over the axel or the shaft. Each wheel is fitted with a number of blades, where the energy transfer work takes place. A mechanical device called flood is used to avoid any leakage and so that the fluid does not leave the chassis of the shaft . After installation and upgradation it must be ensured that the air or gas is completely discharged in the pump, which is one of the most important specification to be known about these centrifugal pumps. These pumps come in different sizes and are made for different uses.
2: Return and return pumps
These types of pumps transfer energy to fluid periodically. The propulsion which is used in these types of pumps are provided by the electric motors. The mechanism of these types of pumps works in a way that the camshaft rotational motion is converted into the movement of the piston in the cylinder. Once this is done, it gives way to the formartion of suction which in turn is responsible for drowning of the fluid through the inlet valve inside the cylinder. The piston can also be moved to the front of the inlet valve. In this case, the liquid will come out of the outlet valve to the outside.
One of the aspect of the mechanism of the return pumps is that both the inlet and the outlet valves are constructed unilaterally. They are done so to prevent the fluid which, if introduced in the cylinder at a low pressure. These pumps can be polarized pumps, diaphragm pump etc. It is converted into a diaphragm pump if the plan run moves the diaphragm of the pump. When it comes to the piston pumps, they are usually low capacity, however the outlet pressure of the fluid can be increased by a large extent if intended to. These kind of pumps are only used when the fluid is to be displaced from a low pressure to high pressure. The flow of fluid in these pumps is uneven. One most important thing about these pumps is that these pumps should be lit when the pump valve is closed.
3: Gear pumps or pump pumps
There are two types of Gear Pumps which are respectively circular or rotary pumps. They are made up of two separate parts which are the fixed wall parts and the other is the rotating part. The rotating part includes a rotary shaft along with a gear. The mechanism of the pump is such that the traps, which are small fluids inside the gear of the pumps turns the gears which in turn drives ten fluid in the pump outlet. The main uses of these kinds of pumps are to let the low volume and medium pressure fluids. These pumps are circular or rotary pumps. They are made of two different parts, one fixed wall part and the other rotating which includes a rotary shaft with a gear. However they are designed such that the distance between the two is very low. One cautionery thing which is to be remembered for these pumps is that when the valve of the pump is closed, these pumps should never be switched on since without the safety valve on the discharging path, the disks of the pump breaks.
1.2. Turbines and their types
Turbine:
A turbine is a rotary device that uses fluid flow to convert kinetic energy into some useful work. The energy is extracted with the help of the fluid flow. A turbine has a moving part, a rotor assembly which is a shaft or drum with blades attached. The mechanism is the simple concept of the interchanging of the kinetic energy to work done, which happens with the help of the fluids which act on the blades of the turbine thereby moving them which in turn helps the rotors of the turbine to move becaue of the rotational force. Turbines work in two ways – an impulse and a reaction.
Impulse turbines:
In these kind of turbines, fast moving fluid is imparted on the blades of the turbine through a narrow nozzle to make the turbine spin around. The shape of the blade of turbines can be described as being bucket shaped which helps cathcing the fluid thereby directing it to an angle. This way is the most efficient way to transfer the energy from the fluid to that of the turbine. Since the nozzle from which the fluid is imparted is narrow, this helps in imparting a greater speed to the fluid to hit the turbine, thereby imparting the energy for the rotor to run.
Types:
1: Water wheel
2: Pelton wheel
3: Turqo turbine’
4: Cross flow turbine
5: Joval turbine
6: Reverse overshot water wheel
7: Screw turbine
8: Barkh turbine
Reaction turbine:
In the case of Reaction Turbine, unlike the impulse turbine, the fast moving as well as a larger volume of fluid sits on the blades of the turbine covering a much larger surface area , thus not affecting the direction of the fluid flow like in the impulse turbine, simply spins the turbine.
However, in this case, it is imperative that the water is in contact of the blades for as much time as possible which will in turn help impart as much energy as possible to the blades of the turbine. This will help the blades move with the flow of the fluid, i.e. they will be moving more smoothly than in the case of impulse turbines.
Some common types of reaction turbines are as follows:
1: VHL turbine
2: Francis turbine
3: Kaplan turbine
4: Tyson turbine
5: Gorloy helical turbine
1.3 Efficiency Curves
1.3.1 Efficiency curves for pumps
The figure of the curve shown below depicts the efficiency of the pump. This eficiency is measured in percentage(%). There are various factors on which the efficiency of the pump depends. The pump size as well as the quality of the construction are major factors on which the efficiency of the pump depends. The smaller the size of the pump, the greater the efficiency. The (ηmax), which is also known as the best point is a measure of when the pump is working at its maximum efficiency.
As understood by (En.wikipedia.org, 2018), the BEP, also known as the Best Efficiency Point depicts the operating region or the point in the pump performace curve. The point where the pump is operating at its maximum efficiency or optimum most efficiency for a particular diameter of the opening is known as the Best Efficiency Point, as the name states. Other common terms other than the Best Efficiency Point are terms like the Shut Off (SO) or Run Out Point (RO). However, when the pump is operated at a value eother greater or lesser than what is depicted by the Best Efficiency Point, it is said that the operating pump are away from the Best Efficiency Point. This can be altered by saying that the pump is operating to the right of the Best Efficiency Point if the flow is greater than the Best Efficiency Point and vice versa when the flow is lesser than thay certified by the Best Efficiency Point.
Talking of ideal conditions, the pumps usually operate within the purview of either 10% lesser or greater than the BEP, if at all. Otherwise usually the BEP is the ideal point at which speed the fluid flows since there are negative implications if the flow of the fluid strays too far away from the Best Efficiency Point for a period of time.
1.3.2 Efficiency curves for turbines
As explained by (Thapar, 2018) ,the efficiency curve for turbine is somewhat explained by the figure below. The performace characterictic and the efficiency of the tiurbine are important aspects while the feasibility study of a project is being done. While the study is being done, it is also important that the model tests are done which will thereby ensure that the parameters which are guaranteed are met by the actual proto type of the turbine. For this reason, the efficiency and the output is also required for the head range of the turbine. This way a difference is made based on the different efficiencies of the turbine constructed by different bidders for the tender. Field tests are also performed for the measuring of the output of the turbine as well as the efficiency. These are tested at different valvle openings to find out the actual efficiency and the output parameters, the output of which, if not found according to the proto type values, penalties are specified for the same.
A can be seen from the figure below different turbines efficiencies are measured along its relative discharge in the graph below.
While pelton, Kaplan and francis have relatively low discharge with higher efficiency, propeller and crossflow shows a different result.
2. Problem statement (pump as turbine)
2.1 Problems with conventional turbines
Some of the main problems with conventional turbines are as follows:
● Need of high pressure hydraulic inlet to start up the turbine.
● Low pressure outlet of hydraulic because of the high pressure height and the constant hydraulic power.
3. literature review
3.1 Pressure Reduction Valves (PRV)
These valves are often used in order to control the pressure regime in the system as well as to face the topographical discontinuities during the pipeline path, to avoid high pressure in the network that can cause ruptures and water leakages. This is done because the water distribution systems are not as efficient as PRV’s for the water leakages as well as the energy consumption. Pressure Reduction Valves dissipates the hydraulic energy mechanically and thereby are used to control the pressure in the systems as well. The turbines used to reduce pressure is a good alternative since it is sustainable and also produces energy both in stable as well as unstable conditions.
3.2 Problems with Pumps
Some of the main problems with pumps as turbines includes:
• Pumps has no installed hydraulic control devices like in the conventional turbines. Efficient operations of pumps as turbine requires constancy of both flow and load conditions due to lack of hydraulic control devices.
3.3. Starting and Stopping pumps- Control Valve
The speed of the pump as turbine varies with load put onto the shaft. When directly driving mechanical equipment, the load on the turbine and consequently its speed varies with the operating conditions of coupled machines which might be critical for operating condition of that machine. Because of this reason, Control valve is necessary in most hydropower plants. The Control Valve is used to regulate the flow through the pump and the power output. This valve Help pump operator to monitor and maintain constant PAT speed by matching its power flow and the demand of power machines.
3.4. Efficiency of Pumps as Turbine (PaT)
(Pumps & Systems, 2018) states how in most of the applications high efficiency pumps should be selected because they can drastically reduce electric power costs. This becomes hard sometimes because of many units which are involved. Figure 1 explains how if 10 bags of energy enter while 7 bags are leaving then the efficiency is 70%. Similarly if 10 enter and 9 leave, the fficiency is 90% and finally if 9 enter and 7 leave then the efficiency will be 78%. Now the total efficiency of the pump can be calculated by multiplying 90% by 78%. Highly efficient pumps drastically reduce electric power costs.
Efficiency of a motor and pump when operating together is the product of their individual efficiencies and the product reduces the total efficiency value to well below the average.
Figure 1
This efficiency is also known as the wire to water efficiency, which is imperative in calculating the power cost for pumping a certain amount of water. The unit of cost per thousand galleons is calculated using the below Equation (Equatin 1)
Cost/1,000 gallons = (0.189 x Cost/kWh x Head) / (Pump eff x Motor eff x 60) Equation 1
Equation 1
Similarly, Figure 2 and 3 depict the power cost per thousand galleons for the two pumps. The BEP for both pumps is 1000 galleons per minute at a height of 127 feet. The power cost is 10 cents per kilowatt hour.
Figure 2. The power cost per thousand gallons pumped for a pump with a BEP efficiency of 85 percent driven by a motor with an efficiency of 93 percent
Figure 3. The power cost per thousand gallons pumped for a pump with a BEP efficiency of 73 percent driven by a motor with an efficiency of 93 percent
Similarly, figure 3 depicts the BEP of 73% which is driven by a motor of efficiency of 93%. The wire to water efficiency is hence calculated out to be 68%.
What are the cost effective and the benefits when we used the pump as turbine? And how can we use it as turbine.
(Thoma & Kettridge, 1931) During their research on characteristics of pumps, they found that pumps could operate more effectively in the turbine mode. Pump as a turbine (PaT) become an important research topic for many manufacturers as pumps were more prone to abnormal operating conditions.
(Agarwal, 2012) The main advantages includes availability of a wide range of heads and flows, availability in large number and standards sizes, low cost, easy availability of spare parts such as seals, bearings and easy installation. According to Williams, the greatest advantage of using pumps as a turbine for medium head sites is the practical advantage and cost advantage over other types of turbines.
(Garay, 1990) Primary advantage of using PAT instead of hydro-turbine is the potential cost savings. Due to large standard pumps produced, a standardized pump converted to a turbine can be significantly be less expensive than specifically designed hydraulic turbine. Other benefits include the simplified control due to absence of blade pitch change, simplified installation, ready adaptation to chemical or hot process fluids, and reduced delivery time.
(Chapallaz, Eichenberger, & Fischer, 1992) When operating a pump as a turbine, the flow pattern through the machine is similar to the conditions in a turbine. Thus the advantageous features of a turbine also occur for the pumps as turbines. The application range of these pumps can be widened by using multistage impeller pumps in single unit. Each pump picks up the flow from previous one and boost up the pressure thus making it possible to lift the water to higher elevations.
Figure 2.1 Different pumps suitable as turbines
Figure 2.3. The comparison of flow conditions in a pump impeller and turbine runner
The application range of these pumps can be widened by using multistage impeller pumps in a single unit. Each pump picks up the flow from the previous one and boost up the pressure thus making it possible to lift the water to higher elevations.
What is the different cost for install and after install between the pump and turbine? Means what is the required for design, install and take care. And what are the risks for both?
( Hydraulic Institute, 2001)This the general cost of the equipment to purchase (initial cost), installation energy cost, maintenance and repair environmental cost and decommissioning costs. Both machines, turbine and centrifugal pumps carry almost all this cost at their life cycles. The general study leads to general study of machine life cycle costs, Life cycle Costs (LCC)
Initial investment costs.
The organization or the individual first decides the design layout of the system before proceeding to designing stage. The designer, normally manager or engineer has variety of choices which may be made during first stage of design in consideration to initial investment costs. For example, the issue of quality of equipment considering the wear and tear rates, repairs and other control packages.
The investment cost usually includes the following analysis costs;
• Engineering, normally drawing and designing issues.
• Spare parts (Bolts and Nuts)
• Inspection and Testing
• Training (operator and safety)
Installation and start-up costs
Start-up costs includes payment of supplier (acquisition) and user personnel. This costs includes but not limited to;
• Technical skills of supervision personnel responsible for system operation
• Tools and Equipment needed to complete the installation
• Work rules governing the installation of the machine
System launching needs close attention to the equipment manual instruction for start-up and operations.
Operational Costs
Normally manpower costs (Labour) to the operation of the pumping system. Example of some duties on operating the system maybe observation, operational reliability, and monitoring of system if operating in accepted performance procedures. This is the risk stage of system functioning as it can help alert the owner of potential losses of the system.
Maintenance and Repair costs.
This is the continuous or routine maintenance cost of materials and services from the experts.
Other costs incudes; Downtime and loss of production costs, Environmental cost which includes disposal of parts and contaminations, and disposal costs.
System design
The required design bring into considerations the interaction of the pump and the rest of the system and the performance operations calculations. The piping system of the pump is calculated in order to determine the performance of the pump. Both acquisition and operational cost are put into consideration to make up total costs of installation during the system life cycle. The piping system costs mainly depend directly on its piping diameter and other components.
The piping diameter is selected based on the following factors;
• The economy of pumps and system installation
• Flow Velocity required for the application
• Minimum required internal diameter
Some cost increases with the increasing pipeline size and some decrease. Due to this, an optimum pipe size is found based on the minimizing costs over the life of the system
The Figure 1.0. Courtesy of Hydraulic Institute, Europump, and the US Department of Energy’s Office of Industrial Technologies (OIT).
The best efficiency point is the intersection between the pump and system curves
A pump user must carefully consider the duration of operation at the individual duty point to properly select the number of pumps in installation and to select output control.
Why the pump is cheaper and more available in the stores?
( Teuteberg, 2010),in recent times, Pumps as turbines(PAT) system have become popular in arears where the availability of turbines is limited as PaT are typically easier to get and hold of. (Derakhshan & Nourbakhsh, 2008(b)) In its support said that pumps are relatively simple and easy to maintain. They also have competitive maximum efficiency when compared to conventional turbines. Teuteberg (2010) in its review of previous authors said that pumps have major benefits if produced in mass because it’s cost effective than turbines. (Motwani, Jain, & Patel, 2012)Keeping other factors constant of the pump, the other benefits includes ease of availability, low initial and maintenance costs and wide range of operations. PAT applications as per many researchers is recommended for power generation in rural, remote and hilly arears. ( Raman, Hussein, Palanisamy, & Foo , 2013)The running cost for centrifugal pumps are very low because most don’t have fuel for engine to run. Though initial cost of acquisition are high, especially turbines cost, reduction in cost is possible in micro hydro installation. The hydro pumps (micro) utilizes standard equipments which are available in the markets with capability of good performance and reliability. (Frosina, Buono , & Senatore, 2017), small and micro hydropower systems presents an attractive solution for generating electricity at low cost and with low environmental impact. PAT approach has promise in this application due to its low purchase and maintenance costs. Pumps are relatively simple machines, cheap as compared to hydraulic turbines and readily available in markets. It has been estimated that the capital payback period of PAT is in the range of 5-50kW is less than two years. According to the rule of supply and demand, pumps are widely produce by numerous manufacturers as compared to turbines inversely this will reduce purchase cost of the pumps.in addition to its availability, pumps are mechanically simple and require less maintenance. (Derakhshan, Nourbakhsh, & Mohammadi, 2009) Moreover, an integral PAT and electric motor can be purchased for use as a turbine and generator set; Pumps are available in a wide range of heads and flows and in large number of standard sizes. Pumps also have short delivery times, readily available spare parts and simple installation using pipes and fittings.
The efficiency in different pressure and different flow, what’s the benefit when the flow and pressure are decreases and what is the situation?
( Tan & Zhang, 2018) The pressure rise of a pump decreases with the increasing of flow rate, and the pump efficiency decreases with the increasing ratio of the gas/water volume to the whole volume. Experiment results shows that dominant frequencies of pressure fluctuation in the impeller and the diffuser are much more than rotational frequency. Various simulations of multiphase pumps were conducted using the computation fluid dynamics software (CFx 14.5). In the calculations, the liquid phase was considered as a continuous fluid and the gas phase was considered as a dispersed fluid and data recorded in the table below.
Table 1. Multiphase pump pressure rise pr and efficiency η versus mesh elements.
Item Mesh 1 Mesh 2 Mesh 3 Mesh 4 Mesh 5
inlet pipe 103,132 201,780 201,780 201,780 443,916
Impeller 367,074 819,324 1,629,417 2,324,412 2,784,096
diffuser 297,880 387,244 476,608 518,925 518,925
outlet pipe 107,996 201,608 201,608 449,036 907,236
total meshes 876,082 1,609,956 2,509,413 3,494,153 4,654,173
pr (kPa) 190.34 196.74 197.63 198.79 198.74
η (%) 62.27% 62.61% 62.70% 62.73% 62.76%
pr/pr1 1 1.0336 1.0383 1.0444 1.0441
η/η1 1 1.0055 1.0069 1.0074 1.0079
Figure 1. Illustrate required pressure for the flow rates in the system.
Pressure (total Head) is required to increase as flow rate increases because of frictional forces and other losses in the system. The operating point of the pump in the system (PAT) should be where the pump curves and the system curve intersect.
Figure 2; Illustrative curve showing the relationship between pressure and flow rate.
The figure shows that the flow rate is much of independent on the pressure (Pump Head) because it did not utilize well the fluid momentum.
The pressure output of the PAT should changed at the same rate the flow rate because for every existing load the output should match to avoid system failure.
4. Methodology
Define methodology for lab experiments
(Himanshu, Sanjay, Varun, & Anoop, 2011)An experimental investigation of pumps has been carried out to study its characteristic in pump and turbine mode operation. By using the experimental results of tested pump and pumps of some previous researchers, new correlations have been developed by using its best efficiency and specific speed in pump mode. A lot of new correlations have been developed using test results from this researchers on pumps. The derived values from the correlations have been developed using their best efficiency curves and the pump manufactured speed mode. The correlation values can be of good use in predicting pump working as a turbine because it shows the match with the experimental results. (Derakhshan & Nourbakhsh, 2008(b)), (Derakhshan & Nourbakhsh, 2008(a))derived the values through theoretical analysis of previous researchers and their experimental works to predict BEP and pumps as turbines.
(Chapallaz, Eichenberger, & Fischer, 1992)We assume that project implementation has been justified previously in a feasibility study, that is, hydropower is the most economical solution to supply the energy for agro-processing or electrification. In our case experiment, we are taking a pump and or conventional turbine. It is therefore acceptable to use an economic calculation which does not take into account indirect costs and benefits created outside the project itself such as socio-economic and environmental effects.
Equipment required?
( Ismail, Muzammil, Rahman, Ibrahim, & Misran, 2017) During their experiment, they designed and constructed hydraulic test rig and the turbine performance experiment procedures. The main equipments for the assembly of experiment was as following;
[1] Control Valves- This was to be a control mechanism within the rig test to regulate the flow and pressure generated at the pump outlet. The two control valve control the water flow rate by adjusting the portion from piping system to the water tank through the pump as turbine.
[2] Flowmeter (Digital Flowmeter), Propeller type flowmeter that had an NPT connector at both ends, this was to record flow rate of water in real-time. The flow range was 76.0 to 760 litres per minute. The maximum pressure rating was 225 psi at 23 degrees Celsius. The diameter of the flow rate was 50.0mm same as the PVC piping system.
[3] Feed Pump, This was a monoblack pump used to supply pressurised water for the PAT with power rating of 2.2 kW and 2900 rpm maximum speed. The pump used an induction generator with a single-phase power input. It was mounted on a large fixed frame bed and tightened by a bolt to bring stability reducing vibrations responsively. This pump will produce a maximum water pressure of 18 m at flow rate of 20.0 litre per second. The additional pressure at the pump inlet will be added to the total pressure generated at the pump outlet.
[4] Pump as Turbine (Centrifugal Pump), the pump manufactured locally by Euroflo in Malaysia, with low specific speed but with high pressure at a low flow rate. The specific features of the pump was; 214.0 mm impeller diameter, 50.0 mm flange diameter at an inlet and outlet of 65.0mm.Its power rating was 2.2 kW with rotational speed of 1450 rpm.
[5] Pressure Gauge, this was placed at pumps inlet and outlet so as to measure the pressure difference across the PAT system.
[6] Two Water Tanks, which was connected by PVC pipe at their side walls with control valve at the centre to adjust water flow between the tanks. Each water tank hold 90 litres of water kept at the defined height level which can generate sufficient pressure at the feed pump inlet.
[7] Torque Sensor
[8] Monitor
[9] PVC piping Networks (tees and Bends)
Table.1.0. Feed pump versus Centrifugal pump (PAT) specifications
parameters Feed Pump PAT
Max Flow rate, Q(l/S) 20.0 8.0
Max Pressure, H(m) 18.5 14.0
Suction Head (m) 7.0 4.0
Specific Speed 1453.0 1075.9
Figure 1. Diagram of the hydraulic text rig
Himanshu and colleagues gave 65.0% as their best efficient point (BEP) with the corresponding pressure of 14.0 m and water flow rate of 8.0 litres per second with their non-dimensional specific speeds (Ns) as shown in table 1 of the experiment.
Equipment assembly and procedures
( Ismail, Muzammil, Rahman, Ibrahim, & Misran, 2017)The equipments was assemble to form a simple system rig to suit the existing hydraulic lab facilities as shown in the figure 2.
Time plan of the project
Capstone Project Time plan
Week 1 Discussion about the project.
Week 2 Discussion about the project.
Week 3 Time planning and methodology and differences between pumps and turbine.
Week 4 Cost effective of pump and pump as turbine.
Week 5 Pump cheaper then turbine.
Week 6 Efficiency curves development (different pressure and different flows).
Week 7 Cost comparison between pump as turbine and conversion turbine.
Week 8 Cost benefits analysis.
Week 9 Order and purchase the pump.
Week 10 Installation and setting up the pump.
Week 11 Finish the report and final review.
Week 12 Work shop.
5. Results and discussions
( Ismail, Muzammil, Rahman, Ibrahim, & Misran, 2017)The sensor reading were recorded after the PAT was allowed to run nonstop for 15 minutes, all this was to allow the piping to be filled with water so as to provide steady readings. The reading results showed that the centrifugal pump was able to run in turbine mode without any mechanical failure though acceptable vibrations was observed. The rotational speed of the PAT system was maintain at a range of 800-1400 rpm by adjusting the break system. The experiment results, that is, flow rate, pressure and torque was measured and recorded. The mechanical and hydraulic power, and efficiency were determined basing on the observed parameters and mathematical expression of energy conversions as shown the tables below.
Table 2.0. Mean and standard deviation values for flow rate
Rotational speed, N (rev/min) Flow rate, Q (gal/s) Standard deviations, σ
1400 99.52 1.52
1300 119.81 1.60
1200 125372 1.48
1100 126.62 1.82
1000 128.40 1.39
900 131.50 1.22
800 133.40 1.80
Table 3. Mean and standard deviation values for pressure
Rotational speed, N (rev/min) Pressure, H (Psi) Standard deviation, σ
1400 17.00 0.21
1300 14.30 0.22
1200 14.11 0.19
1100 13.90 0.25
1000 12.90 0.31
900 12.30 0.19
800 12.09 0.24
Table 4. Mean and standard deviation values for torque
Rotational speed, N (rev/min) Torque. τ (Nm) Standard deviations, σ
1400 – –
1300 3.50 0.56
1200 3.70 0.63
1100 4.70 0.39
1000 4.80 0.55
900 5.10 0.66
800 6.40 0.77
Table 5. Experiment results
Rotational speed, N
(rev/min) Torque. τ (Nm) Mechanical
power, Pmechanical (watt) Flow rate, Q (l/s) Pressure, H (meters) Hydraulic
Power,
Phydraulic (watt) Efficiency, ɳ (%)
800 6.40 539.65 10.11 9.38 929.96 58.03
900 5.10 483.79 9.96 9.25 903.66 53.54
1000 4.80 505.92 9.73 9.03 861.56 58.72
1100 4.70 544.92 9.59 8.90 837.83 65.04
1200 3.70 467.98 9.30 8.84 806.41 58.03
1300 3.50 479.57 9.25 8.42 764.37 62.74
1400 0.00 0.00 7.54 7.00 517.58 0.00
From experiment, it was observed that the pressure and flow rate enters impeller steady decreasing between 800 to 1300 RPM. The steady decline of flow rate and pressure across the PAT is because at higher rotational speed faster flow of water. The torque as exerted by the impeller shows that higher torque was generated at lower speed.
From table 5, it was noted that the highest rotational speed was recorded at 1400RPM at free-running speed which was highest speed recorded by the torque sensor when no break force was applied at the shaft of the break system. The corresponding lowest rotational speed has been registered at 800RPM generating the highest torque at 6.40 Nm. The highest efficiency of the pump was at 65.0% at 8.0l/s and 14.0 m of pressure. The experimental work showed that the efficiency was higher in turbine mode than on pump mode. Overall performance take into account the component systems when considering efficiency in pump mode. Though this results are unique pump to the selected for analysis, the results should be applied to other pumps but with caution. The comparisons experiment should be made considering the same specific speed, but different sizes, shapes, and operation ratings.
(Chapallaz, Eichenberger, & Fischer, 1992) (Derakhshan & Nourbakhsh, 2008(a)), the cost/kW of the energy produced by small hydropower plants is usually higher than that of larger hydropower plants. They said that, the use of PAT in a wide range of small hydro sites has been gaining importance worldwide though the maximum results is yet to researched on.
6. Recommendation on performance improvement of PAT
For future research and experiments on PAT, many authors recommend that some system components be upgraded to allow higher flow rate and increase pressure which is transferred to the pump.
7. REFERENCES:
• En.wikipedia.org. (2018). Pump. [online] Available at: https://en.wikipedia.org/wiki/Pump [Accessed 5 Sep. 2018].
• En.wikipedia.org. (2018). Pump. [online] Available at: https://en.wikipedia.org/wiki/Pump [Accessed 5 Sep. 2018].
• Thapar, O. (2018). Modern Hydroelectric Engineering Practice. 1st ed. ahec.org, pp. 131-146.
• Pumps & Systems. (2018). The Cost of Pumping- Power Cost & Efficiency. [online] Available at: https://www.pumpsandsystems.com/cost-pumping-power-cost-efficiency[Accessed 5 Sep. 2018]
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