Efficiency improvement of an axial flow propeller pump for dewatering in kole lands of Kerala, India Ayisha, M. 1, Jayan, P.R. 2, Nithin, J.G. 3 and Saranya, R.N 4 1 Department of Farm Power Machinery and Energy, KCAET, Kerala agricultural University, Tavanur-679573, Kerala, India ABSTRACT The axial flow propeller pump installed at the farmer s fields of Kadumpattupadam kole padavu, in Thrissur kole lands of Kerala were studied in detail and its performance in terms of discharge and efficiency were analysed at varying input conditions. The experiment was conducted by regulating the inflow of water by using a wooden sluice valve installed at the centre of temporarily constructed earthen bund at the inlet side of the impeller. A rectangular weir was installed at the canal about 1.5m from the discharge end of the delivery pipe for measuring the discharge of the pump. The input energy was recorded using the energy meter fitted in the electrical panel. Study was also carried out to find out the optimum discharge and efficiency due to different sizes of impellers and by incorporating diffuser assembly just above the impeller in the suction side of the pump. Accordingly the most suitable impeller-diffuser combination was also selected based on the optimized efficiency and discharge rate of the pump. It was found out that pump with an impeller having vane thickness 6.35mm, outer diameter 435mm, impeller angle 25 0 and impeller height 125mm and with discharge of 571.81 lps was found to be more efficient. Keywords: Dewatering pump, Kole lands, Petti and Para, Axial flow propeller pump I. Introduction The Kole wetlands cover an area of about 13,632 hectares spread over Thrissur and Malappuram districts of the state. The area extents from Chalakudy river in south to Bharathapuzha river in the north and to some parts of Ponnani taluk. These Kole wetlands act as natural drainage system through a network of canals and ponds in Thrissur district, which connects different parts of Kole wetlands to river and Arabian sea. It is fertile with alluvium soil. Agriculture is the major occupation of the people of Kole wet land and ninety percent of people are practicing mostly paddy cultivation. The major problem faced by the farmers in these areas is inadequate drainage facility. Rice production in the coastal regions of Kerala is mainly influenced by improper water management practices. The important water management practice in these regions is the system of draining water from the segmented rice fields during the cropping season. In Kerala, low land paddy cultivation is generally practiced in Kuttanad, Kole, Pokkali and Kaipad lands which lye below mean sea level (MSL). Introduction of the locally made propeller pump, known as Petti and Para, had revolutionized the drainage pumping of the region in the early twentieth century. It is a traditional dewatering pumping system, which is driven by a heavy electric motor of 25 to 100 horse power and discharges water at 200-250 litres per second, against low heads [1]. It requires high installation cost and power consumption but its efficiency was significantly low. @IJAPSA-2016, All rights Reserved Page 1
As an alternative to these indigenous pumps, axial flow propeller pump are becoming popular in these fields. They are used as low head and high discharge dewatering pumps. Impeller is the major part of the pump for lifting water. Bibliography [2] conducted experiments on an axial flow pump and found out that, at a speed of 2500 rpm at a total head of 160.55 cm, the maximum efficiency was 18.05 percent and a discharge of 24.88 lps. The corresponding input power was only 2.95 hp. In this study, different sizes of impellers and diffuser assemblies were fabricated and tested to find the most suitable combination of impeller diffuser assembly for improving discharge and efficiency of axial flow propeller pump under varying input energy and head conditions. The three sets of impeller- diffuser assemblies were separately fabricated by attaching with the pump and tested at Kadumpattupadam kole padav in Thrissur Kole lands of Kerala. In order to test the pump, specially made wooden sluice valve was fixed at the inlet side of the pump and a rectangular weir was installed at the discharge side of the pump in a canal. II. Materials and Methods The vertical axial flow propeller pump is having its axis in vertical direction through which water enters and ejects parallel to the axis of rotation. The pump consists of an electric motor, thrust bearing, main shaft, stuffing box, elbow, delivery pipe, bell mouth and impeller. The rotation of the impeller is caused by the prime mover in on position. The pressure head is developed by the propelling or lifting action of the impellers as it rotates.the water enters to the impeller through screen provided beneath the bell mouth which removes the impurities and other debris from entry to suction side of the impeller. The bell mouth is a bell (curvilinear) shaped column assembly which allows water to enter smoothly in to the impeller. The impeller operates at the bottom of the delivery pipe. The impeller has 3-6 blades depending on the designed speed and is keyed at right angles at the bottom of the main shaft. A cone shaped cover is fitted over the locking nut to eliminate eddies and to prevent the entry of sand and grit into the lower pump bearings. A propeller pump develops pressure head by propelling action of the impeller blades in water. The blades propel water by the reaction to lift forces produced by its rotation. The parts of the propeller pump along with impeller and diffuser are shown in figure 1. Figure 1. Vertical axial flow propeller pump @IJAPSA-2016, All rights Reserved Page 2
Impeller is the major part of the pump for lifting water. It is a rotor used to increase the pressure and flow of water. The velocity achieved by the impeller from the motor transfers it into pressure energy during the upward movement of water. Three types of impellers were designed with 4 numbers of vanes. The outer diameter of 435mm and vane thickness of 6.35mm were selected based on the proper fitting and minimum clearance between the impeller and inner diameter of suction pipe. The different vane angles selected were 30 and 25 degree and height of impellers as 135,115 and 125mm respectively for the impellers A, B and C. The front view and top view of the three impellers with height and diameter are given in figure 2. Figure 2. Details of the three impellers A diffuser with 6 numbers of vanes with an outer diameter of 440 mm was selected, so as to increase the efficiency of the pump. A diffuser, specially made was attached just above the impeller at the suction side of the pump for the complete conversion of kinetic energy into pressure energy. The front view, side view, top view and isometric view of the impeller is shown in figure 3. 2.1. Testing Figure 3. Details of the diffuser (in centimeters) The flow of water at the inlet side of the pump was controlled by a wooden sluice consists of three wooden planks. The discharge was measured using a rectangular weir and the energy input was recorded using the energy meter fitted in the electrical control panel of the pump. The water level above @IJAPSA-2016, All rights Reserved Page 3
the weir (H) was measured using a tape. The suction and delivery heads were noted by using tape. The efficiency of the pump depends on its discharge rate against the operating head and the input electrical power. The performance curves of the pump were drawn as head and efficiency on ordinate and discharge on abscissa. The discharge rate was calculated by using the formula, Q= 0.0184LH 3/2 m 3 s -1 (1) Q= Discharge,m 3 s -1 H= Head on the weir, m L= Length of weir, m The power consumption was calculated using the equation, P= 3 VI cos ø (2) P= Input power, kw V= Voltage, volt I=Current, ampere,ὴ= 100 (3) III. Results and Discussions By studying in detail about various axial flow and mixed flow pumps of different manufacturers, it was decided to select highly efficient pumps having a discharge 1500 m 3 /hr and an operating head of 4.00 m for dewatering operations [3]. Bibliography [4] developed a small and compact pump designed specifically for low lift applications. It is easily installable, portable and can be fabricated from locally available materials. A 15.00 cm diameter pump powered by a 7 hp engine has an output of about 40.00 lps for a lift of 1.50 m. This capacity is 2-3 times higher than that of either a centrifugal pump. In an experiment, two types of propeller pumps inclined propeller pump and vertical pump were fabricated. The inclined pump was able to lift water at the rate of 44.00 to 35.00 lps against a total head ranging from 1.20 to 2.90 m and correspondingly the efficiency varied from 50.00 percent to 80.00 percent at 2600 rpm. When operated at 3000 rpm it delivered water at the rate of 56.30 to 43 lps. For heads of 1.67 to 3.68 m and the efficiency varied from 65.00 percent to 31.00 percent. The pumping tests on vertical propeller pumps showed that at 2800 rpm, the discharge varied from 32.00 to 19.00 lps at static heads ranging from 84.00 cm to 250.00 cm. The efficiency of the pump was found to vary from 65.00 percent to 31.00 percent [5]. Installation of vertical axial flow propeller pump with different impellers was carried out at the testing field during the year 2013-14. The discharge and efficiency calculated at varying head and input voltage for the three impellers are given in figure 4. The pump with three different impellers was tested at six different heights and the performance curve of the pump was plotted with discharge in the abscissa and head and efficiency in the ordinate. At the lowest head of 0.57m, impeller A of height 135mm and outer diameter of 108.5mm had a discharge of 521 lps and an efficiency of 11.30 %. Efficiency was then increased from 22% at 1.32 m height and 31.07% at 2.51m height. It then showed a greater efficiency of 32% at 3.13m with a discharge of 380 lps. While impeller B of height 115mm and an outer diameter of 108.5mm had a discharge of 478.43 lps @IJAPSA-2016, All rights Reserved Page 4
and an efficiency of 21.02% at 0.57m height. It was then noted as 42.06, 35.48, 39.78 and 39.90 percentages at 1.32m, 1.58m, 2.13m and 2.51 m height respectively. The highest efficiency was reported as 41.18% at a height of 3.13m with a discharge of 555.40 lps. And impeller C with diffuser showed relatively higher range of efficiency. At 0.57m, discharge was 448.72 lps and the efficiency was noticed to be 18%. It then showed a discharge of 450.96 lps and an efficiency of 40.09% at 1.32, height. Efficiency then increased from 43.6% to 52.43% at 1.58m and 2.13m height respectively. A greater efficiency of 53.55% was shown at a height of 2.5m with a discharge of 560.82 lps and the maximum output was obtained at a height of 3.13m with a discharge of 571.81 lps and an efficiency of 56.69 %. Head and efficiency (%) 60 50 40 30 20 10 0.... Efficiency of impeller A -- --Efficiency of impeller B..- - Efficiency of impeller C Impeller A Impeller B h Impeller C 571.81 560.82 540.33 493.64 450.96 448.72 555.40 530.21 490.99 488.82 480.93 478.43 380.99 470.80 528.44 528.68 530.20 521.31 Discharge (lps) Figure 4. Performance curve of the pump with three impellers IV. Conclusions The axial flow propeller pump installed at Kadumpattupadam kole padavu, Thrissur Kole lands of Kerala were studied in detail. Its discharge and efficiency were increased due to calibration of the obtained impeller-diffuser assembly at the suction side. The experiment was conducted by regulating the inflow of water at the inlet side of the impeller. A rectangular weir was installed at the canal at the discharge end of the delivery pipe for measuring the discharge of the pump. The input energy was calculated using the energy meter fitted in the electrical panel. Study was also carried out to find the improvement in efficiency and discharge due to changing impellers and diffuser assemblies. The impeller with diffuser was selected based on the higher efficiency recorded as 56.69% obtained at varying head and voltage conditions. Bibliography [1] Abraham, J. 1988. Evaluation of the characteristics of Petti and Para (Axial flow pump). MSc.Thesis, Kerala Agricultural University,Thrissur, Kerala, 67pp. [2] Rani, R.(1998). Performance and evaluation of high discharge low head pump. MSc. (Agrl. Engg.)Thesis no. 84. Kelappaji College of Agricultural Engineering and Technology, Kerala Agricultural University, Tavanur, Kerala,72pp. [3] Anoop, V. V. (2010). Status of dewatering in kole lands of Kerala. B.Tech(AG) Thesis, Kelappaji College of Agricultural Engineering and Technology, Kerala Agricultural University, Tavanur, Kerala 48p. [4] IRRI [International Rice Research Institute].1979.Annual Report 1978-1979.axial flow pump. International Rice Research Institute, Philippines,97p. [5] Kausal, N. and Thaneja, N. 1986. Design and fabrication of propeller pump. Icrier. 35(4): 371-374. @IJAPSA-2016, All rights Reserved Page 5