Papers by Stephen Asomani
Performance analysis of geometrically optimized PaT at turbine mode: A perspective of entropy production evaluation
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, Aug 8, 2022
In the field of hydroelectric power, Pump as Turbine (PaT) is an important tool to achieve recycl... more In the field of hydroelectric power, Pump as Turbine (PaT) is an important tool to achieve recycling the redundant kinetic energy in small stream/rivers. However, due to the contradiction between the reverse fluid flow working at turbine mode and the designed flow passage of pump geometry, the internal hydraulic loss in PaT is excessive. As a result, it renders the PaT performance extremely low affecting its wide applications with the demand of high efficiency operation. Therefore, this paper aims to optimize the geometric parameters of the impeller in PaT turbine mode under three different typical flow conditions (i.e. rated, best efficiency, and overload working conditions). After the geometric optimization, the internal energy losses among the flow passages are analyzed by using the entropy production method. The results show that the impeller passage exhibits obviously higher entropy loss in comparison to the volute and the outlet pipe. Inside the impeller, the blade leading and trailing edges on both suction and pressure sides are the locations where the majority of the impeller energy losses occur, and the high entropy area is concentrated at the impeller inlet area. Moreover, The energy loss gradually decreases from blade leading edge (BLE) to blade trailing edge (BTE), and the entropy production decreases from the blade pressure side (PS) to the blade suction side (SS) due to the large mixing flow loss from PS to SS. It is concluded that the entropy production analysis is effective in explaining the PaT power losses caused by the geometric mismatch of different components including inlet, impeller, and outlet, providing the reference value for the geometric optimization of other turbine machinery.
Current Science, 2020
With the rise in fuel prices as well as energy cost, hydroelectric power is the best alternative ... more With the rise in fuel prices as well as energy cost, hydroelectric power is the best alternative for energy generation in rural industries and villages. Small hydropower (SHP) is the largest and oldest source of renewable energy which converts the energy of flowing water into electricity. Small hydroelectric power is entering this field for improving and saving energy in several developing countries through the use of pump in reverse mode as hydraulic turbine; pump as turbine (PAT). It is one of the best alternatives that could meet energy needs by providing electricity in villages and rural settlements as Southern Africa is endowed with a huge untapped SHP energy potentials. In this study, the importance of PAT energy generation for sustainable power, based on its capacity to provide electricity to the rural communities along with contributing to the national grid towards alleviating serious shortage of electricity within Southern African continent, has been discussed. This paper discusses the potentials and the need for SHP development sites in Southern Africa.
Energies, 2020
Pump-as-turbine (PAT) technology permits two operating states—as a pump or turbine, depending on ... more Pump-as-turbine (PAT) technology permits two operating states—as a pump or turbine, depending on the demand. Nevertheless, designing the geometrical components to suit these operating states has been an unending design issue, because of the multi-conditions for the PAT technology that must be attained to enhance the hydraulic performance. Also, PAT has been known to have a narrow operating range and operates poorly at off-design conditions, due to the lack of flow control device and poor geometrical designs. Therefore, for the PAT to have a wider operating range and operate effectively at off-design conditions, the geometric parameters need to be optimized. Since it is practically impossible to optimize more than one objective function at the same time, a suitable surrogate model is needed to mimic the objective functions for it to be solvable. In this study, the Latin hypercube sampling method was used to obtain the objective function values, the Adaptive Neuro-Fuzzy Inference Syst...
Advances in Mechanical Engineering, 2020
A pump-as-turbine is a hydraulic machine that can operate as a pump and turbine at the same time.... more A pump-as-turbine is a hydraulic machine that can operate as a pump and turbine at the same time. Pump-as-turbine happens to be the most appropriate method for meeting the world’s energy demands, particularly in rural and isolated areas of a country. Furthermore, the operating cost of microhydropower systems is lower compared to conventional hydrodynamic turbines, but it requires high initial investment. Pump-as-turbine has been applied in many engineering fields such as irrigation, sewage, reverse osmosis, water distribution systems, farms, small pump storage power house, and pressure dropping valves. However, pump-as-turbine operates inefficiently at part-load due to lack of flow control device. In addition, the pump generates high flow instabilities in pump-as-turbine mode due to the shift of the best efficiency point toward higher head and discharge. This study extensively discusses the flow mechanism, modifications, and flow instabilities in the pump-as-turbine mode operation. ...
Experimental and numerical investigations on pressure pulsation in a pump mode operation of a pump as turbine
Energy Science & Engineering, 2019
Hydropower has been the leading renewable source and cheapest ways to generate electrical energy ... more Hydropower has been the leading renewable source and cheapest ways to generate electrical energy in the world. In recent years, there has been a major upsurge in the hydropower development because of the use of pump as turbine (PAT). However, the operational reliability of a PAT is greatly affected by the unsteady flow fields; therefore, it is important to examine the unsteady flow behavior which can be used as a reference to reduce the noise, vibration, and cavitation performance for centrifugal pumps working as turbines. Thus, the objective of this study was to evaluate the unsteady flow fields by analyzing the distribution of the pressure pulsations using both numerical and experimental measurements in a PAT operating in pump mode. Firstly, the three‐dimensional (3D) unsteady flow equations were solved using SST k‐ω turbulence model during the numerical calculations. Secondly, the numerical results of the hydraulic pump performance were validated by the experimental measurements ...
Energies, 2019
Side channel pumps are important machines for handling toxic, explosive or other dangerous liquid... more Side channel pumps are important machines for handling toxic, explosive or other dangerous liquids in various engineering processes. However, the operational reliability of these pumps is directly affected by the intensity of the pressure and velocity fluctuations, thus the flow fluctuations existing within the pump cannot be neglected because of their direct influence on the noise, vibration and harshness performance. Therefore, describing precisely the zones of highly unsteady and turbulent flow fields is a key research topic. Moreover, the size of the wrapping angle strongly affects the levels of pressure and velocity fluctuations, thus numerical calculations of the pressure and velocity fluctuation intensities in side channel pump models with different wrapping angles were conducted in this work. The results indicated that the pressure fluctuation coefficient increased gradually from the inflow to the outflow. At the interrupter, the flow experienced the most irregular flow patt...
Materials Science for Energy Technologies, 2018
Numerical investigation of Transient vortices and turbulent flow behaviour in centrifugal pump op... more Numerical investigation of Transient vortices and turbulent flow behaviour in centrifugal pump operating in reverse mode as Turbine,
Energies, 2020
This paper presents a multi-objective optimization strategy for pump-as-turbines (PAT), which rel... more This paper presents a multi-objective optimization strategy for pump-as-turbines (PAT), which relies on one-dimensional theory and analysis of geometrical parameters. In this strategy, a theoretical model, which considers all possible losses incurred (mainly by the components of pipe inlet, impeller and volute), has been put forward for performance prediction of centrifugal pumps operating as turbines (PAT). With the established mathematical relationship between the efficiency of PAT (both at pump and turbine mode) and the impeller controlling variables, the geometric optimization of the PAT impeller is performed with constant rotational speed. Specifically, the optimization data consist of 50 sets of impellers generated from Latin Hypercube Sampling method with its corresponding efficiencies calculated. Subsequently, the pareto-based genetic algorithm (PBGA) was adopted to optimize the geometic parameters of the impellers through the theoretical model. To validate the theoretical o...
Energies, 2019
This paper seeks to predict the performance of the side channel pump by considering the influence... more This paper seeks to predict the performance of the side channel pump by considering the influences of different wrapping angles. Firstly, three pump cases 1, 2 and 3 are modeled with wrapping angles 15°, 30° and 45°, respectively. Secondly, different physical parameters comprising exchanged mass flow, pressure and velocity distributions are plotted at the best efficiency point (QBEP) to analyze the internal flow characteristics. Since the flow exchange times depend on the size of the wrapping angle, the size of the wrapping angle has significant effects on the pump head performance. Case 1 with the smallest wrapping angle recorded the largest head improvement at all operating conditions compared to case 2 and case 3. Case 1 at QBEP attained a head coefficient increase of about 9.8% and 38.6% compared to that of case 2 and case 3, respectively. However, the size of the wrapping angle had a slight effect on the pump efficiency; thus, case 1 still predicted a marginal increase in effic...
Mathematics
Rotor-stator interaction (RSI) in the centrifugal pump-as-turbine (PAT) is a significant source o... more Rotor-stator interaction (RSI) in the centrifugal pump-as-turbine (PAT) is a significant source of high amplitude of the pressure pulsation and the flow-induced vibration, which is detrimental to the stable operation of PAT. It is therefore imperative to analyze the rotor-stator interaction, which can subsequently be used as a guideline for reducing the output of PAT noise, vibration and cavitation. In addition, it is important for a PAT to have a wide operating range preferably at maximum efficiency. In order to broaden the operating range, this work proposes a multi-condition optimization scheme based on numerical simulations to improve the performance of a centrifugal PAT. In this paper, the optimization of PAT impeller design variables (b2, β1, β2 and z) was investigated to shed light upon its influence on the output efficiency and its internal flow characteristics. Thus, the aim of the study is to examine the unsteady pressure pulsation distributions within the PAT flow zones a...
Energies
Abstract: This paper seeks to predict the performance of the side channel pump by considering
the... more Abstract: This paper seeks to predict the performance of the side channel pump by considering
the influences of different wrapping angles. Firstly, three pump cases 1, 2 and 3 are modeled with
wrapping angles 15, 30 and 45, respectively. Secondly, different physical parameters comprising
exchanged mass flow, pressure and velocity distributions are plotted at the best efficiency point (QBEP)
to analyze the internal flow characteristics. Since the flow exchange times depend on the size of the
wrapping angle, the size of the wrapping angle has significant effects on the pump head performance.
Case 1 with the smallest wrapping angle recorded the largest head improvement at all operating
conditions compared to case 2 and case 3. Case 1 at QBEP attained a head coefficient increase of about
9.8% and 38.6% compared to that of case 2 and case 3, respectively. However, the size of the wrapping
angle had a slight effect on the pump efficiency; thus, case 1 still predicted a marginal increase in
efficiency compared to case 2 and case 3 at all operating conditions. Lastly, the numerical simulations
were validated with experimental data after manufacturing pump case 2.
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Papers by Stephen Asomani
the influences of different wrapping angles. Firstly, three pump cases 1, 2 and 3 are modeled with
wrapping angles 15, 30 and 45, respectively. Secondly, different physical parameters comprising
exchanged mass flow, pressure and velocity distributions are plotted at the best efficiency point (QBEP)
to analyze the internal flow characteristics. Since the flow exchange times depend on the size of the
wrapping angle, the size of the wrapping angle has significant effects on the pump head performance.
Case 1 with the smallest wrapping angle recorded the largest head improvement at all operating
conditions compared to case 2 and case 3. Case 1 at QBEP attained a head coefficient increase of about
9.8% and 38.6% compared to that of case 2 and case 3, respectively. However, the size of the wrapping
angle had a slight effect on the pump efficiency; thus, case 1 still predicted a marginal increase in
efficiency compared to case 2 and case 3 at all operating conditions. Lastly, the numerical simulations
were validated with experimental data after manufacturing pump case 2.