The improvement in energy saving aspects in water systems is currently a topic of major interest. The utilization of pumps working as turbines is a relevant strategy in water distribution networks consisting of pressurized pipes, using these machines to recover energy, generate green energy and reduce leakages in water systems. The need to develop energy studies, prior to the installation of these facilities, requires the use of simulation tools. These tools should be able to define the operation curves of the machine as a function of the flow rate. This research proposes a new strategy to develop a mathematics model for pumps working as turbines (PATs), considering the modified affinity laws. This proposed model, which can be input into hydraulic simulation tools (e.g., Epanet, WaterGems), allows estimation of the head, efficiency, and power curves of the PATs when operating at different rotational speeds. The research used 87 different curves for 15 different machines to develop the new model. This model improves the results of the previously published models, reducing the error in the estimation of the height, efficiency, and power values. The proposed model reduced the errors by between 30 and 50% compared to the rest of the models.
The present research depicts an analysis of the implementation of computational fluid dynamics (CFD) in the study of pumps such as turbines and PATs. To highlight the benefits of CFDs for PAT studies, results from both experimental tests have been compared to better understand the reproduction error phenomena. For this, data analysis used in successful models has been applied to determine variables and parameters, and to report a low relative error. The results show that most of the studies focused on fixed speed rotation with some cases of variable speed rotation. Furthermore, there is not enough information in the academic literature for PAT of axial and mixed flows with fixed and variable speed. Finally, turbulence models based on Reynolds average Navier–Stokes (RANS) have been used to simulate PATs with fixed speed rotation in most cases.
The selection of pumps as turbines (PATs) for their respective use in energy optimisation systems is a complicated task, because manufacturers do not provide the characteristic curves. For this reason, some research has been carried out to predict them with computational fluid dynamics (CFD) and mathematical models. The purpose of this study is to validate these two prediction methodologies of flow (Q) vs. head (H) curves through numerical modelling using the computational package OpenFOAM, together with a comparison with the experimental data obtained from a PAT for the case in which the nominal rotation speed of the machine varies. Depending on the configuration and working conditions of the PAT, the simulation performed with OpenFOAM was validated by calibrating it with the nominal curve of the pump and with another simulation performed with CFD workbench SOLIDWORKS FloEFD. Subsequently, the second methodology related to the analyses and mathematical models proposed to predict the Q vs. H curves were also validated with new models in OpenFOAM and the experimental data. The results show that these prediction methods are effective when a machine’s operating point is close to the BEP (best efficient point). The absolute error ranges obtained with these two prediction methodologies for rotation speeds of 880 rpm, 1020 rpm, 1200 rpm, and 1500 rpm are between 5 and 24%, 2 and 17%, 0 and 12%, and 1 and 24%, respectively.
Pumps as turbines (PATs) are the typical solution for electrification using micro hydropower plants (MHP) in the rural sector. Other engineering applications where lately the use of PATs have increased are irrigation, water supply, and energy recovery systems due to their availability, short delivery time, long service life, economic feasibility, construction, and maintenance advantages. However, selecting the suitable pump(s) is difficult because manufacturers only provide performance curves when operating in pump mode; therefore, there is no universal method to predict that issue. For this reason, theoretical, analytical, experimental, and numerical simulation research have been made to predict these curves and the PATs' performance. The present paper analyzes PATs with Computational Fluid Dynamics (CFD) based on advanced research. For this aim, information from a wide range of types of pumps with different rotation speeds was classified to examine case approaches, computational domains, mesh generation, boundary conditions, optimization of elements, and CFD package used to establish the effectiveness of this tool and to find characteristics which have not been enough investigated at present. Most studies used CFD simulations with ANSYS code and K- turbulence closure model, which presented adequate results. Finally, this paper shows that numerical simulations with CFD analysis were successfully carried out to determine pump performance and predict curves in direct and reverse mode, improving certain components and conducting more profound research on certain specific issues.
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