Effect of Water-Jumper Slope on Performance of Breastshot Wheel

Common problem in the operation of breastshot water wheel in Indonesia is discontinuity operation of the wheel due to very low stream velocity in the channel during dry season. In order to minimize the problem, it is important to study the method of maintaining the continuity operation of the wheel during dry season. Thus, the installation of water-jumper at upstream of the wheel is proposed in the present work. The laboratory models of the water channel and breastshot water wheel were fabricated. The water jumper is attached at the upstream whose slope angle can be adjusted. The present work investigates the effect of water-jumper slope on the performance of the breastshot wheel. The slope angles are set at 5°, 10°, 15°, 20°, 25°, 30°, 35°, and 40°and the upstream velocities are 1.1, 1.2, 1.3, 1.4, 1.5, and 1.6 m/s. The result reveals that the use of water-jumper can increase the gross head and hydraulic power of very low stream, and hence the torque and the output power of the breastshot wheel are enhanced. The highest efficiency is achieved at the slope angle of 10o for stream velocity of 1.3 m/s. The water-jumper gives significant effect at stream velocity lower than 1.3 m/s. The hydraulic power is influenced by both discharge and gross head where they increase at increasing slope angle of the water-jumper. However, higher momentum losses occurs at the wheel for stream velocity higher than 1.3 m/s, thus output power and efficiency of the breastshot decreases even though hydraulic power increases. The water-jumper can keep continuous operation of the breastshot wheel in the irrigation channel during dry season.


INTRODUCTION
In present, renewable energy generation becomes important due to environmental concern, increasing energy demand globally and fossil fuel limitation [1]. In order to be independent from fossil energy resources, various renewable energy sources have been considered worldwide, such as biomass, solar energy, hydro energy, etc. As each country evaluates its resources, many have recognized hydrokinetic energy as a significant contributor to its renewable energy portfolio [2], for example modelling of water scenarios in Southern Marocco for renewable energy development has been conducted by Ersoy et al. [3] Access to electricity is crucial to human development as electricity is essential for certain basic activities like lighting, refrigeration, running household appliances, and so on [4]. Many rural regions in poor and developing countries lack reliable access to national power grids, thus they utilize hydro energy for electrification. Decentralized micro hydro power plant has been developed in North Eastern Afghanistan [5]. Another work in boosting of hydro power by using underwater power generator based on gravity vortex siphon has been also reported [6]. Hydropower has come up as an attractive source of renewable energy for electricity generation. Hydropower has advantages of its ecofriendly pollution free nature and favorable future development [7] [8]. The hydropower can provide cheap, clean and reliable electricity [9]. However, hydropower plants are highly water intensive, because large volumes of water evaporate from the increased reservoir surface [10]. There is a significant but unused hydropower potential with head differences below 2.5 m in many countries. Standard turbine types are considered not economical in this situation, since large turbine diameters and extensive civil engineering works are required. In addition, ecological effects need to be considered [11]. The role of the hydropower plants is to capture the energy in flowing water and convert it into useful energy. Recent studies have shown that conventional technologies such as water wheels are suitable devices for very low-head sites [12].
Many irrigation channels have been used for pico-hydro and micro-hydro power plants in many countries, such as a 0.5 kW electric power generation in Padang Panjang-Indonesia [13], a 160 kW hydro power in Thailand [14], and a micro-hydro in Srilangka [15]. Typically, the capacity of a micro hydro power plant is less than 500 kW [16]. Due to simplicity and low cost installation, micro hydro power plants have attracted increasing attention for renewable energy conversion systems. Many micro hydro plants have been successfully developed and tested as reported by Kamran et al. [17], Jawahar and Michael [18], Nasir [19], and Pigaht and Van der Plas [20]. For an irrigation channel, a stream water wheel seems to be suitable for micro hydro power plant.
Stream water wheel can be divided into three categories: (a) undershot, (b) overshot, and (c) breastshot [21] as shown in schematic diagram in Figure 1. Experimental works on stream water wheel have been reported by many researchers. Quaranta and Ravelli [22] investigated output power and power losses estimation for an overshot water wheel. They [23] also evaluated breastshot water wheels performance using different inflow configurations. Meanwhile, Quaranta et al. [24] analyzed efficiency of traditional water wheel. Other works on the performance evaluation of breastshot water wheel have been experimentally conducted by Vidali et al. 2016 [25], and Muller and Kauppert [26]. Meanwhile, small hydro power plants intended for low head difference such as irrigation channel, have been also reported by Bakis et al. [27] and Senior [28]. Other researchers performed simulation work to investigate performance of breastshot waterwheel. Adanta et al., 2020 [29] simulated an effect of channel slope on performance of breastshot waterwheel and Budiarso et al. 2018 [30], simulated an effect of bucket shape and kinetic energy on breastshot waterwheel performance. The selection for a suitable type of stream water wheel can be conducted by using the diagram in   [29] The common problem in micro hydro power plant is discontinuity of operation due to very low stream velocity in the channel during dry season. In order to achieve a sustainability of operation during dry season, the use of the water-jumper at the upstream of the wheel can be tried. The blocking effect of the water-jumper may increases the depth of the water in the conveying channel during the dry season. Increasing the depth of the water leads to increase potential energy of the stream. However, the blocking of the flow may also affect the velocity of the water downstream. This may also affect the kinetics energy of the stream. The effect of water-jumper on depth and velocity results in availability of the flow gross head.
In the present work, the breastshot water wheel is designed and manufactured for a laboratory scale open channel. The aim of the present work is to investigate the effect of slope angle of water-jumper on the performance of the breastshot wheel. The experimental work is conducted at various upstream velocities. No similar work has been performed and reported by other researchers to date.

EXPERIMENTAL WORK
The experimental work is started by setting up the experimental test rig and measurement devices, and then followed by data collection and analysis.

Description of Experiment
The experimental test rig was built and installed at laboratory of Institut Sains &Teknologi AKPRIND Indonesia. Figure 3(a) shows the experimental test rig which consists of (1) water pump (2) plenum chamber, (3) adapter, (4) jumping-water, (5) breastshot wheel, (6) conveying channel, (7) exit gate, (8) draught passage, and measurement devices (i.e. digital flow meter, disk brake, load cell, and tachometer) as shown in Figure 3 (b). The channel is made of Mild Steel plate which dimension of 10 m in length x 0.56 min width x 0.4 min depth. The jumping-water is attached at upstream of the wheel and its angle (α) can be adjusted. The breastshot wheel has a total diameter 0.8 m of and 16 galvanized blades. Each blade has width of 0.4 m and length of 0.5 m. The wheel is hand-made from MS plate. The velocity of the stream is measured using a digital flow meter. A tachometer is used to measure rotational speed of the wheel. A disk brake dynamometer is used to obtain torque of the wheel. The experiment was conducted at stream velocities of 1.1, 1.

Data Analysis
A schematic diagram of a breastshot wheel in the channel without water-jumper is shown in Figure 4. Water flows with velocity v1 and depth h1 at the upstream, and velocity v2 and depth h2 at the downstream. The diagram is used to govern head gross equation of the flow. Head gross is head available that will be converted to rotate the wheel, hence produce mechanical energy. Head gross of the flow is defined as the difference between energy head (pressure, kinetics, and potential) at the upstream and at the downstream as shown in Eq. 1. Since the pressure at the upstream and the downstream are same (p1 = p2) and the channel is horizontal (z1 = z1), Eq. (1) can be simplified as Eq. (2): where Hgr is the head gross (m), v the stream velocity (m/s), h the height of the stream (m),g the gravitational acceleration (9.81 m/s 2 ), and subscripts 1 and 2 respectively indicate the upstream and downstream of the wheel.
Based on hydraulic jump theory and the use of water-jumper with length of 0.4 m and slope angle of , the height of hydraulic jump at the upstream of the wheel becomes: By substituting Eq. (4) into Eq. (3), the head gross for channel with water-jumper is given by Eq. (5): Substituting Eq. (6) into Eq. (7) and replacing the width of the water-jumper (b) by 0.56 m, the volumetric flow rate becomes: Once the head gross and volumetric flow rate are known, input hydraulic power to the water wheel is then calculated by using Eq. (9), where is the density of water (1000 kg/m 3 ) The actual torque and output power generated by the wheel and efficiency of the wheel are obtained using Eq. (10) to Eq. (12), respectively.
where Ta is the torque (Nm), mb is the mass of the load cell (kg), l is the distance from axis of the wheel to the load cell (0.4 m), Pin is the output power of the wheel (W), and Na is the rotational speed of the wheel (rpm). .

RESULTS AND DISCUSSION
An effect of slope angle on gross head, hydraulic power, torque, output power, and efficiency are analysed and discussed Figure 6 shows the effect of slope angle of water-jumper on head gross. Head gross increases significantly at jumper's slopes above 10º. It is due to the height of the hydraulic jump increases as the slope increases. With increasing the hydraulic jump, the potential head also increases and ultimately results in increasing in gross head. From the graph in Figure 6, it can be seen that the gross head increases with the increase in water velocity in the upstream for the same jumper angle. The higher the upstream velocity, the higher the gross head for a fixed slope angle. It is because the hydraulic jump is getting higher with increasing upstream velocity.

Effect of slope angle on hydraulic power
The effect of slope angle of water-jumper on hydraulic power of the wheel is shown in Figure 7. At the same upstream velocity, the hydraulic power increases from a slope angle of 15º. The hydraulic power steps up significantly at an angle of 10º -20º. The hydraulic power is influenced by both discharge and gross head, so the trend of the hydraulic power graph is similar to the trend of the gross head and that of the discharge where they increase at increasing slope angle of the water-jumper. Meanwhile, for the particular slope angle of the water-jumper, the hydraulic power enhances with an increasing upstream velocity. Effect of slope angle on torque Figure 8 presents an effect of slope angle of the water-jumper on torque. The graph shows that the torque increases with increasing slope angle. A larger slope angle results in a larger input power so more power is available that improves the torque. It can also be seen that the torque trend is similar to the hydraulic power trend in Figure 7.

Effect of slope angle on output power
Effect of slope angle on the actual power of the breastshot is shown in Figure 9. The actual power improves significantly at the slope angle of 10º-20º at all upstream velocities. The actual power tends to remain or even decreases when the slope angle is greater than 20º. The decrease in output power at a slope angle above 20º is the result of decreasing the rotational speed of the breastshot at that slope angle. Output power of the wheel is directly proportional to rotational speed of the wheel as can be revealed from Eq. (11). However, different trend of output power at slope angle higher than 30º is observed for stream velocity of 1.6 m/s. The output power decreases significantly from slope angle of 35º to 40º, even though the hydraulic power increases. This is due to more momentum losses occurs at slope angle of 35º to 40º for higher stream velocity, i.e. 1.6 m/s.

Effect of slope angle on efficiency
The effect of slope angle on efficiency is shown in Figure 10. The highest efficiency of the wheel for each upstream velocity is achieved when the slope angle of the water- jumper is 10º. At slope angle of 10º, maximum efficiency of 41.73% is obtained for upstream velocity of 1.3 m/s. The efficiency steps up for slope angle from 5º to 10º and reaching a maximum value at slope angle of 10º. The efficiency decreases at slope angle higher than10º. The slope angle of the water-jumper higher than 10º is ineffective to improve the breastshot performance. It can be stated that the slope angle of water jumper have to be set at 10º when the stream velocity varies from 1.1 m/s to 1.6 m/s Figure 10. An effect of slope angle of water-jumper on efficiency

CONCLUSION
The experimental work investigated the effect of slope angle of water-jumper on performance of breastshot water wheel at very low stream velocities. It can be concluded that the use of water-jumper able to increase gross head, hydraulic power, torque, and output power. However, the highest efficiency is achieved at slope angle of 10º when the stream velocity of 1.3 m/s. The water-jumper gives a significant effect on performance of the waterwheel, especially when stream velocity lower than 1.3 m/s. The hydraulic power is influenced by both discharge and gross head where they increase at increasing slope angle of the water-jumper. However, higher momentum losses occurs at the wheel for stream velocity higher than 1.3 m/s, thus output power and efficiency of the breastshot decreases even though hydraulic power increases. The use of water-jumper keeps continuous operation of the breastshot wheel in the irrigation channel during dry season. For effective used of the water-jumper, it is recommended the slope angle of the jumper have to be set at 10º