Author: Jonathan Colton
Much of South Asia experiences a monomodal rainfall pattern with a distinct dry season following the annual monsoon. Enabling irrigation during the dry season has therefore been crucial in assuring improved productivity and double‐cropping. This is particularly the case in southern Bangladesh, where recent government initiatives have called for an expansion of surface water irrigation to reduce pressure on groundwater tables in intensively cultivated areas in the north of the country, where dry season boro rice is grown. This paper describes a method based on first principles of fluid mechanics to characterize the performance of surface water irrigation pumps used by small‐scale farmers in South Asia and Bangladesh. This method is unique, as it incorporates an optimized protocol suitable for resource‐limited conditions found in many developing countries and provides a comprehensive yet simple‐to‐use pump selection method for surface water irrigation pump customers. Using pump impellers as a case study, the method also characterizes the effect of pump geometric variations resulting from the variable production and assembly practices found in different manufacturing workshops. This method was validated with a case study in Bangladesh supported by both full‐scale field testing and numerical simulation results. © 2018 The Authors. Irrigation and Drainage published by John Wiley & Sons Ltd on behalf of International Commission for Irrigation and Drainage
Irrigation methods Pumps Axial Flow Pump Small Scale Farmers Manufacturing Analysis Computer Aided Engineering Full Scale Field Test PUMPS FARMERS MANUFACTURING SIMULATION MODELS IRRIGATION CIENCIAS AGROPECUARIAS Y BIOTECNOLOGÍA
New irrigation pumps and pumping practices need to be continually tested and evaluated to determine how changes in pump designs or management affect the ability of farmers to irrigate their crops in a cost effective and energy efficient manner. This document provides a standardized testing protocol that can be used to effectively and reliably assess pump performance by accurately measuring key variables such as water-discharge and fuel-consumption. This standardization of testing is intended to improve the quality of pump manufacture in South Asia by assuring reliable irrigation pump test results. We first present a general description and overview of a pump test bed and testing procedure, with more details on engineering specifics in subsequent sections. The document concludes with useful annexes to aid researchers in evaluating pumps. Pumps are characterized by pump curves, which are visual representations of the way that pumps perform under certain loads and rates of discharge. Total dynamic head (TDH), wich is the height of water pumping plus friction losses, can be plotted against discharge flow rate (0) to give a "TDH-Q" curve. Fuel use efficiency (EFF), measured as pump discharge divided by fuel consumption, can be plotted against discharge to give an "EFF-Q" curve. The best operating conditions (BOC) for the pump can be inferred from these curves, where the peak of the "EFF-Q" curve tells the operator at what head and flow rate that the pump is most fuel efficient. This is also known as the Best Operating Point, or BOP (Figure 1). To generate these curves, irrigation pumps should be tested and performance data recorded at various operating conditions, for example at different pumping heights, flow rates, and with observations of fuel consumption and shaft speed. However, this protocol does not detail longer duration stress tests, which should also be considered in separate testing programs. Surface water irrigation pump testing requires the proper facilities, including a source of water and a stable earthbank upon which the tests can be conducted. This testing procedure utilizes a flow meter (Woltman type) (Figure 2 and Figure 3) designed to be built into a 150 mm (6 inch) nominal diameter (DN) steel pipe system so that the pump's discharge can be merged directly with it. The Woltman flow meter has a mechanical counter that shows the water volume passing through the impeller embedded inside the body of the meter. This type of meter is rated to measure a certain range of flow rates depending on the diameter of the meter, as shown in Table 1. For instance, a 150 mm nominal diameter Woltman flow meter built by Bermad Irrigation (model WPH-150) has a nominal flow rate of 150 m3 V and a maximum flow rate of 300 m3h-1(Bermad Irrigation, 2013). If the meter operates at the maximum flow rate, then the meter will impart a pressure loss of 0.1 bar, which will cause the flow readings to be lower than when no meter is attached. If this causes problems, then a larger meter with a higher maximum flow rating should be used a 150 mm DN Woltman flow meter should meet the needs of most irrigation pumps intended for small-scale irrigation in South Asia. To use a flow meter for pump testing, the initial volume value (V1) can be subtracted from the final volume value (Vf) to calculate the flow rate. This is accomplished by dividing by a particular interval of time (At), further described in Section 4. A butterfly control valve is used to change the applied pressure drop simulating an increase (or decrease) in dynamic head (the height at which the water is lifted), which can be read by a pressure gauge (Po) ) (Figure 4). For the purposes of this document, only the Woltman flow meter protocol will be described, as it tends to be the easiest to implement to collect reliable data. It also allows reliable comparisons across pump types. Note that Woltman flow meters are readily available and can be purchased in machinery markets throughout South Asia for a cost of $200— $500 (depending on the diameter of the meter).