Energy Losses Assessment of Smallholder Farmers’ Surface Water Irrigation Pumps in South and Southeast Asia Using Entropy Generation Principle

One of the most serious problems among smallholder farmers in South and Southeast Asia associated with the use of a surface water irrigation pump is low engine performance. The main cause of this low performance is the decrease in the flow field energy conversion mechanism caused by irreversible processes. The energy conversion theory suggests that pump efficiency is maximum when the loss is minimum. Whatever the origin of the losses, the deterioration in engine performance is due to a deterioration in the reversibility of the pump system. In this study, the pump is classified as the propeller impeller (PI), the improved axial or typical impeller (TI), and the conical hollow-shaped impeller (CI). Entropy production is applied to the pump on design improvement and loss sources location and mechanisms. The entropy production consists of viscous dissipation and turbulent dissipation. In this study, the pump design improvement of various designs based on entropy production has been studied in detail to predict energy loss in areas such as the inlet section, impeller, or discharge pipe. With the entropy generation, the optimum efficiency of different pump designs CI, PI, and TI were determined. The results showed that in all designs, more than 63% of the total entropy generation came from turbulent distribution. The flow in the pumps was analyzed in detail in comparison with entropy generation. It was found that the entropy generation rate increased in the secondary flow direction and was consistent with free-stream velocity. The PI design at the inlet pipe should be modified for reducing flow separation and entropy generation. All design impellers showed high energy losses, especially near the hub and tip along the leading edge and trailing edge. Therefore, it is possible to determine which features of the flow and entropy generation are relevant to the pump improvement

Calculation of three-dimensional boundary layers on turbomachinery blades

The aerodynamic behaviour of turbomachinery is dominated by viscous effects. In the design of a component for the machine, inviscid methods are normally employed. However, it is useful to cover the viscosity in the calculation to achieve a better understanding of the fluid behaviour. This feature can be analysed by using Navier-Stokes calculations or simpler and more approximate techniques such as boundary-layer calculation. In recent years there have been a considerable number of Navier-Stokes solvers as well as boundary-layer solvers. However, Navier-Stokes methods require a large amount of computer storage and CPU time, which limits the number of grid points that can be used inside the boundary-layer. Hence, boundary-layer techniques become very attractive. The purpose of this study is to develop a boundary-layer calculation that is efficient, accurate and simple to implement, and can be applied to flow over complex geometry such as turbomachinery blades. To account for the surface curvature and rotation, the three-dimensional unsteady boundary layer equations are expressed in generalised curvilinear co-ordinate system on the body surface with respect to a rotating frame of reference. The equations are solved numerically by using Finite Difference Approximation without employing the similarity transformation. The steady state solutions are obtained by integrating the equations in time. Two methods, an interactive scheme and FLARE approximation scheme, are described for calculating separated flow. The concept of the interactive approach is general but its application, in this study, is limited to two-dimensional flow. The viscous losses, expressed in term of entropy generation, is also calculated from the computed flowfield. Computational results on a wide variety of flow situations and configurations are validated and show good agreement with analytical results and experimental measurements. Results reveal, in general, that the method holds a practical advantage, in both speed and accuracy of computation, for solving the boundary-layer problems to which it is best suited

Damping of power system oscillations by using HVDC-based multi-modal POD controller

© 2018 IEEE. Due to the increasing replacement of conventional generators with renewable energy sources (RESs), the number of power system stabilizers (PSSs) installed in power systems may decrease in the future, resulting in a reduced capability to control power oscillations. This paper presents a multi-modal power oscillation damping (POD) controller that can improve the damping of multiple low-frequency oscillations. The controller is designed and installed in a proposed future High Voltage Direct Current (HVDC) transmission system modelled in a reduced order dynamic equivalent model of Great Britain (GB) system. The design process has been analyzed concerning variable time delays associated with communication systems used with wide-area measurements. MATLAB and DIgSILENT are used in the design and simulation of the controller. The multi-modal controller is shown to provide a significant improvement in damping of multiple modes of oscillations

Damping of power system oscillations by using HVDC-based multi-modal POD controller

© 2018 IEEE. Due to the increasing replacement of conventional generators with renewable energy sources (RESs), the number of power system stabilizers (PSSs) installed in power systems may decrease in the future, resulting in a reduced capability to control power oscillations. This paper presents a multi-modal power oscillation damping (POD) controller that can improve the damping of multiple low-frequency oscillations. The controller is designed and installed in a proposed future High Voltage Direct Current (HVDC) transmission system modelled in a reduced order dynamic equivalent model of Great Britain (GB) system. The design process has been analyzed concerning variable time delays associated with communication systems used with wide-area measurements. MATLAB and DIgSILENT are used in the design and simulation of the controller. The multi-modal controller is shown to provide a significant improvement in damping of multiple modes of oscillations