DESIGN AND EXPERIMENTAL STUDY OF THE INFLUENCE OF THE DIFFERENCES OF PITCHES AND SHAFT SLOPES TO MECHANICS PERFORMANCE OF 2-BLADES SCREW TURBINE MODEL IN LOW HEAD FLOW
1. Dr. Ir. Bambang Yulistianto
2. Ir. Suryo Darmo, M.T.
CHAPTER I: INTRODUCTION
CHAPTER II: LITERATURE REVIEW
CHAPTER III: RESEARCH METHODOLOGY
CHAPTER IV: RESULT AND DISCUSSION
CHAPTER V: CONCLUSION, SUGGEST AND REFERENCE
Indeed, Indonesia is a rich country of potential renewable energies such as mini / micro hydro, biomass energy, solar energy, wind energy, geothermal energy, ocean energy, and nuclear energy. Especially for micro hydro, the development usually exploit the potential of water flow that have certain head and the specific discharge is converted into electrical energy through a turbine and generator. In reality, in Indonesia, the average of water resource potential has a large discharge and low head. Thus, the development of a low head turbine (low head) or the head is very low (ultra low head) is very suitable to be developed in Indonesia.
Then from the above problems, the researcher was interested to develop the type of turbine that can operate optimally at low head but high discharge. In this study, the researcher developed the research on turbine screw. This turbine operates with low rotation speed and is still relatively new to be developed in Indonesia, ye this turbine has several advantages among other types of low head turbines. The screw turbine do not require special control system, the equipment and generator units are standard, easy in construction, easy installation and maintenance, environmentally friendly and fish-friendly, high efficiency turbine at low head and high discharge operation.
The performance of a screw turbine is affected by parameters related to the design of turbine screw itself. One important parameter in the design of screw turbine is pitch or period of a blade (blade). Another aspect of the design consideration is mounting the screw turbine shaft or slope. Based on the description above, the researcher interested in developing research on screw turbine which aims determine the effect of differences in pitch and slope distance on the performance of the mechanical axis of the turbine blade and screw 2 as a reference in the development of turbine propulsion screw as the first (prime mover) in generating small-scale (micro hydro).
Archimedes screw is a type of screw that has been known since ancient times and has been used as pumps for irrigation in the park in Babylon. Along with the energy crisis that occurred in the world and the limited potential of water energy source that requires high head, then started in the year 2007, an engineer suggested the idea to invert the rotating screw pumps and then let the water pump is mounted below a generator then the electricity will be generated along the generator is not exposed to water or wet. So in principle the screw turbine is a reversal of the screw pump function itself (Adly and Irfan, 2010).
Rorres (1998) stated that the geometry of an Archimedes screw (Archimedean screw) is determined by some external parameter, that is the outer radius of the screw, total screw length, and slope. Other parameters that affect the internal parameters such as the inner radius, the number of blades, and blade pitch. External parameters are usually determined by the placement of Archimedes screw locations and how much water to be removed. While the internal parameters are freely determined to optimize the performance or the performance of the screw.
According to the FAO Corporate Document Repository, the Archimedean screw pump is a pump oldest ever existed since people pay attention to fluid removal. However, this type of pump is still widely used because of several advantages. These pumps can work at its optimum at the installation angle of 30 ° to 40 °.
According to the Ritz-Atro Pumpwerksbau Gmb (2009), the working principle of the Archimedean screw turbine is a reversal of the pump hydrodynamic Archimedean where these turbines harness water flow energy into mechanical energy. Power output range is the range of 1-250 kW, flow rates ranged from 100-5000 l / s, and the slope ranges from 22 ° – 36 °.
3.1. Flowchart of Research
3.2. Research tools
The main equipment used in this study are:
1. Screw turbine model to be tested
2. Tachometer to measure the rotation speed of the turbine
3. Measuring capacity of 60 liter bucket and a stopwatch to measure the discharge.
4. Arc to measure the slope of the turbine shaft.
5. Steel ruler to measure the water level.
6. Balance spring and a digital balance to measure the load in the measurement of braking torque.
7. Tools box containing wrenches, pliers and a screwdriver as an aid in assembling a model turbine replacement screw pitch variation.
3.3. Research Variables
This research is experimental and existing variables are divided into:
a. Independent variables (independent variables), is a variable that is not dependent or affected by other variables. The independent variable in this study is the pitch (Λ) and the slope of the turbine shaft (θ).
b. Dependent variable (dependent variable), is a variable that is dependent or influenced by other variables. Dependent variable in this study is the turbine rotational speed (n), torque (T), the theoretical power turbine (Pf), the power turbine (PT), and turbine efficiency (η).
3.4. Place and Time of Research
The research was conducted at the Hydraulics Laboratory of the University of Gadjah Mada Civil D3. The research was conducted from June 2011 to August 2011.
RESULT AND DISCUSSION
4.1. No Load Testing
No-load test aims to see the effect of variations in pitch and slope of the three models of the turbine shaft to the screw rotation speed of the turbine when the turbine has not been loaded. Variations of the slope of turbine shaft are 25º, 30º, 35º, 40º and 45º. Flow rate used is a constant that is 0.00728 m3 / s. The relationship between the tilt axis and the rotation speed of the turbine without a load can be seen in Figure 4.1.
Changes in turbine rotation speed was caused by the influence of power flows which strike the blade. On the variation of the slope of 25 º to 35 º, the flow pattern remains stable and does not occur when mashing the circle stepping blade screw so that the force Fa efficient work flow to produce a tangential force and spin turbines. However, the variation of tilt axis 40 º and 45 º, seen a change in the form of streams where water flow tends to jump from the end of the flume and no longer just mashing the circle first screw blade. The flow of water tends to pound the middle of the rotor or shaft in (In) before mashing the circle of the first screw turbine blade. Style Fa reduced water flow on the blade caused the decrease in tangential force, so that the turbine rotation speed is also reduced.
At no-load test, although the difference in rotational speed is generated between each screw turbine model is not so great, yet in general 2Ro pitch screw turbine model produces a higher rotational speed than the turbine model screw pitch 1.6 Ro and 1.2 Ro. The highest rotation speed generated by each turbine model on the slope of the screw shaft 35 º, in which the screw pitch 2Ro turbine model produces 255 rpm, the turbine model screw pitch 1.6 Ro produces 254 rpm, and the screw pitch turbine model produces 252 rpm 1.2 Ro.
4.2. Comparison of Mechanics Performance Between the Screw Turbine Testing Result to the Theoretical Result
Torque generated by each turbine model in this study can screw is determined theoretically. The parameters that must be known to find the theoretical torque generated by a screw turbine is a tangential force Ft generated by a circular screw, the torque radius r, and the total loop threaded nb.
Calculation to find the tangential force produced by a screw turbine can be determined theoretically by using the approach screw-threaded calculation in power (power screw). The forces acting on a circular blade screw axial force due to fluid flow of water Fa shown in Figure 4.2.
Figure 4.2 shows the fluid flow rate of water with some mashing the circle turbine blade axially threaded axial force Fa and generate a direction parallel to the axis of the shaft. The existence of axial force Fa elicit a reaction from the turbine in the form of tangential force Ft which direction perpendicular to the axis of the shaft. Meanwhile, the friction force F resulting from contact between the fluid and the blade screw water will reduce water Fluid force Fa. Price of the friction force F is the multiplication of the coefficient of friction that occurs with the normal force (F = μ. Rn).
a. Comparison between torque test result and theoretical torque
Graph comparison between the torque and torque test results are theoretically the variation of the slope of the shaft can be seen in Figure 4.3 – 4.5.
Figure 4.3 – 4.5 shows the comparison of theoretical torque to torque the test results of each turbine model pitch screw. Data theoretical torque of each screw pitch is determined by using the equations of power screw (power screw), while the data turbine test results obtained using direct measurement using the method of braking (pronny brake). In the graph theoretical seen each torque screw pitch tends to rise in every corner of the shaft increases, while the torsion test results showed a downward trend at every increase of shaft angle.
The difference in value between the theoretical torque with a torque test results are caused by differences in the way of data retrieval. Theoretical torque data of each pitch is determined by using the approach formulas or equations screw power, where the torque (torque) turbine model is generated by multiplication screw turbine tangential force Ft with radius r. Tangential style turbine fluid flow generated by the force Fa which are axially pound each circle screw blade on a turbine screw. Increased fluid flow force Fa at each variation increases shaft angle causes an increase in tangential force and torque turbine theoretically.
So the data is theoretically torque, the force of fluid flow which strike every screw circle is uniform. However, laboratory tests showed different flow patterns so that the fluid flow velocity which strike every circle of the screw is not uniform. This is what causes the tangential force and torque testing is lower than the theoretical torque. Other Possible causes of torque testing is lower than the theoretical torque is a measurement of the difference in weight is less accurate in the laboratory.
b. Comparison between power test result and theoretical power
Graph comparison between the test results and the theoretical power at shaft slope variations can be seen in Figure 4.6 – 4.8.
In the graph (Figure 4.6 – 4.8) above shows the theoretical power turbines tend to be larger than the power turbine test results. The highest power of the test results of each pitch threaded shaft is generated on the slope of 35 °, while the highest theoretical power produced at 40 ° tilt axis. Pitch turbine 2Ro gives better power than the turbine pitch 1.6 Ro and 1.2 Ro, where the supreme power is 18.51 W. pitch 2Ro The difference between the theoretical values with the results of this test due to differences in the value of torque on each screw pitch. The test results also indicate a general conformity with the approach to the theory of Archimedean screw pump in which the tilt angle of the screw pump installation optimal in the range 30° – 40°.
c. Comparison between efficiency test result and theoretical efficiency
Graph comparison between the efficiency of the test results and the theoretical efficiency of the variation of tilt axis can be seen in Figure 4.9 – 4.11.
The highest efficiency of the test results generated on the tilt axis 25°, while the highest theoretical efficiency is generated on the axis tilt of 40°. Pitch turbine 2Ro provide better efficiency than turbine pitch 1.6 Ro and 1.2 Ro, where the highest efficiency is 72.82% generated by pitch of 2Ro.
CONCLUSION, SUGGESTION, AND REFERENCES
- The result test of 2-blades screw turbine model worked well in laboratory using a constant flow rate of 0.00728 m3/s and the variations of the axis tilt angle of 25º, 30º, 35º, 40º, and 45º.
- At no-load test result, screw turbine model pitch of 2Ro produced higher rotation speed than 1.6 Ro and 1.2 Ro, that was 255 rpm at slope of 35º.
- Al load test result, each screw turbines produces the highest power at shaft slope of 35º, while the highest efficiency was generated at shaft slope of 25º.
- At the shaft slope of 25º, screw pitch of 2Ro produced power 15.89 W and efficiency 73.08% (the highest), while at the shaft slope of 35º, screw pitch of 2Ro produced power 18.51 W (the highest) and efficiency of 66.16%.
It is needed further research and development regarding Development and the need for further research regarding the design of turbine blades such as adding of external fin on the edge of the screw, the influence of variations in inner diameter to the outer diameter, and the use of materials in the manufacture of other types of screw turbine and its application in the field.
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