Minimum Number of Experimental Data for the Thermal Characterization of a Hot Water Storage Tank

[EN] This paper demonstrates that it is possible to characterize the water temperature profile and its temporal trend in a hot water storage tank during the thermal charge process, using a minimum number of thermocouples (TC), with minor differences compared to experimental data. Four experimental tests (two types of inlet and two water flow rates) were conducted in a 950 L capacity tank. For each experimental test (with 12 TC), four models were developed using a decreasing number of TC (7, 4, 3 and 2, respectively). The results of the estimation of water temperature obtained with each of the four models were compared with those of a fifth model performed with 12 TC. All models were tested for constant inlet temperature. Very acceptable results were achieved (RMSE between 0.2065 degrees C and 0.8706 degrees C in models with 3 TC). The models were also useful to estimate the water temperature profile and the evolution of thermocline thickness even with only 3 TC (RMSE between 0.00247 degrees C and 0.00292 degrees C). A comparison with a CFD model was carried out to complete the study with very small differences between both approaches when applied to the estimation of the instantaneous temperature profile. The proposed methodology has proven to be very effective in estimating several of the temperature-based indices commonly employed to evaluate thermal stratification in water storage tanks, with only two or three experimental temperature data measurements. It can also be used as a complementary tool to other techniques such as the validation of numerical simulations or in cases where only a few experimental temperature values are available.This research was supported by the Plan Nacional de I+D+i del Ministerio de Ciencia e Innovacion (ENE2009-13376).Gasque Albalate, M.; Ibáñez, F.; González Altozano, P. (2021). Minimum Number of Experimental Data for the Thermal Characterization of a Hot Water Storage Tank. Energies. 14(16):1-16. https://doi.org/10.3390/en14164741S116141

Modelo numérico de cavitación para geometrías sencillas utilizando FLUENT V6.1

[EN] Cavitation is a phenomenon that can be present in several agro-forestry applications such as irrigation pressure-reducing valves, sprinkler orifices or even in the flow through xylem vessels inside plants. In the present research, numerical predictions of cavitation in a series of orifices, nozzles and venturis were compared to experimental measurements to show the possibilities and performances of the new cavitation model in the commercial Computational Fluid Dynamics (CFD) code FLUENT V6.1. A flashing study is also presented for the nozzle case. Model predictions for the orifice cases accurately capture cavitation inception and its influence on the orifice discharge coefficient. However, when an unsteady flow is modeled, the cavitation phenomenon is not simulated properly and leads to a steady situation. In general, the new cavitation model in FLUENT V6.1 provides very reliable simulation for easy geometries when steady flow is assumed.[ES] Los procesos de cavitación tienen relevancia en diferentes aspectos del área agroforestal, como en válvulas reductoras de presión para riego, chorros en aspersores e incluso en el flujo de savia en el xilema de las plantas. En este trabajo se ha validado el nuevo modelo de cavitación incluido en el programa comercial de mecánica de fluidos computacional FLUENT V6.1 en varios orificios, estrechamientos y venturis, comparando los resultados experimentales con los obtenidos por el modelo. También se presenta un estudio del fenómeno «flashing» producido en el estrechamiento. Las predicciones del modelo en el caso de los orificios muestran una buena estimación del momento de inicio de la cavitación así como de su desarrollo, estimado con el coeficiente de descarga del orificio. Sin embargo, cuando se trata de modelar el flujo en estado no estacionario, el proceso de cavitación no es simulado correctamente conduciendo a una situación estacionaria. De todo ello podemos concluir que el nuevo modelo de cavitación simula adecuadamente la cavitación en el flujo a través de geometrías sencillas, como los orificios y estrechamientos, en estado estacionario.Palau-Salvador, G.; González Altozano, P.; Arviza Valverde, J. (2007). Numerical modeling of cavitating flows for simple geometries using FLUENT V6.1. Spanish Journal of Agricultural Research. 5(4):460-469. https://doi.org/10.5424/sjar/2007054-2694604695

New Approaches for Teaching Irrigation Scheduling. Improving Understanding through Modeling Applications

[EN] This paper presents a teaching methodology for introducing specific modeling tools and their methods in the contents of the subject Irrigation Engineering, corresponding to the degree of Agricultural Engineering in Spanish universities. Modeling tools can be powerful educational resources allowing for a better understanding of the physical problems addressed in different subjects of scientific-technological careers. In particular, a Gene Expression Programming based approach is applied for estimating stem water potential, a key variable in irrigation scheduling, and, consequently, a crucial issue for Agricultural Engineers. This activity is scheduled in three practical sessions for the mentioned subject. Students learn a crucial topic in irrigation engineering and the fundamentals of a very robust modeling tool. The application of this methodology for solving a specific problem contributes to improving the understanding of the theoretical topic scheduled in the subject program. At the same time, students learn a new way of facing specific problems that might be encountered in their professional practice.Martí Pérez, PC.; Shiri, J.; Gasque Albalate, M.; González Altozano, P. (2017). New Approaches for Teaching Irrigation Scheduling. Improving Understanding through Modeling Applications. International Journal of Information and Education Technology. 7(2):95-99. doi:10.18178/ijiet.2017.7.2.848S95997

Comparative evaluation of two photovoltaic multi-pump parallel system configurations for optimal distribution of the generated power

[EN] The suitability of a strategy for distributing the power generated by a photovoltaic pumping system equipped with two equal pumps working in parallel is proven. This strategy aims to improve energy management and consists of feeding a single pump with all the power generated until it exceeds a threshold value from which the power distribution must be at 50% between the two pumps. This pumping method was compared with the operation mode usually applied in parallel PV pumping facilities (50% of the power always assigned to each pump). A system equipped with two 0.75 kW pumps was employed. The assessment of the facility's performance under the two alternative working conditions and several pumping heads was conducted using simulation techniques. Both the pumped annual volume and the annual efficiency of the motor-pump group increased when the strategy was applied compared to operation with power distribution at 50%. This increase was greater the higher the head (6.21% at H = 18 m vs. 57.60% at H = 48 m for pumped annual volume and 6.42% at H = 18 m vs. 57.51% at H = 48 m for annual efficiency). The halving of the irradiance threshold and the improved efficiency (36.4% vs. 34.8%) may explain this increase.Gasque Albalate, M.; González Altozano, P.; Gutiérrez-Colomer, RP.; García-Marí, E. (2021). Comparative evaluation of two photovoltaic multi-pump parallel system configurations for optimal distribution of the generated power. Sustainable Energy Technologies and Assessments. 48:1-11. https://doi.org/10.1016/j.seta.2021.1016341114

Simple inlet devices and their influence on thermal stratification in a hot water storage tank

[EN] Thermal energy storage is a technology used mostly in buildings and industries in order to preserve thermal energy so that the stored energy can be used at a later time. Thermal stratification during the charge process in a cylindrical water tank was investigated using tools of Computational Fluid Dynamics (CFD). Simulations were validated by means of experimental measurements of time-dependent temperature profiles. The results showed that the model was able to adequately capture the experimental temperature evolution in the tank for all the validation cases. Once validated the model, simple modifications of the usual inlet devices and inflow rate by CFD techniques were accomplished with the intention of improving the tank performance. It was found that the modifications of the simulated inlet devices affected the stratification level. This could lead to improve designs and optimize system efficiency. The analyses confirmed numerically the results obtained experimentally, and it was evidenced that a sintered bronze conical diffuser can improve stratification compared to a conventional bronze elbow inlet. Therefore, CFD techniques proved to be quite a valuable complement of experimental studies. The use of low inflow, smooth out inlet velocity and operate inflow upwards near the top of the tank enhanced stratification. (C) 2017 Published by Elsevier B.V.This research was supported by the Plan Nacional de I+D+i del Ministerio de Ciencia e Innovacion (ENE2009-13376). The authors would like to thank L.H. Sanchis for his valuable and constructive suggestions during the planning and development of this research.Moncho Esteve, IJ.; Gasque Albalate, M.; González Altozano, P.; Palau-Salvador, G. (2017). Simple inlet devices and their influence on thermal stratification in a hot water storage tank. Energy and Buildings. 150:625-638. https://doi.org/10.1016/j.enbuild.2017.06.012S62563815

Effects of long-term summer deficit irrigation on 'Navelina' citrus trees

[EN] The effects of long-term summer deficitirrigation (RDI) strategies on ‘Navelina’ orange trees (Citrus sinensis L. Osbeck) were assessed in a drip-irrigated commercial orchard located in Senyera (Valencia, Spain). Three irrigation treatments were applied during five consecutive years (2007–2011): a controltreatment, without restriction, and two RDI treatments, in which the water reduction was applied during the summer (initial fruit enlargement phase). During the firstthree seasons,the trees under the controltreatment received 110% of the theoretically required irrigation dose (ID), and the RDI treatments received 40% and 60% of the full ID during the deficit period. During the last two years of the study, the control treatment was irrigated at 100% of the ID and the amount of water applied in the RDI treatments was additionally decreased 20% from the reduced ID of the preceding years. The crop’s response to summer deficit irrigation was analysed in relation to tree water status, which was assessed by relying on midday stem water potential (st). The lowest st values were reached, as expected, at the end of the water deficit period and with the most stressed treatment. These minimum st values ranged between −1.6 MPa in 2008 and −2.5 MPa in 2010. In most occasions, the trees under RDI treatments showed a fast hydric recovery and had completely re-hydrated one week after restarting irrigation. Summer RDI treatments did not cause negative effects on either the amount or on the quality ofthe yield ifthe threshold value of st = −2.0 MPa was not surpassed. According to the results, it can be concluded that long-term RDI strategies may be applied successfully on Navelina orange trees during summer without negatively affecting the studied parameters while allowing water savings between 12% and 27%. © 2016 Elsevier B.V. All rights reserved. 1.This experiment was funded by the company Tecnicas Valencianas del Agua S.A. (TECVASA), with financial support from the Conselleria de Agricultura, Pesca y Alimentacion de la Generalitat Valenciana for this purpose (DOCV 5493, 19 April 2007, no. exp.: 2007TAHAVAL00018).Gasque, M.; Martí, P.; Granero, B.; González Altozano, P. (2016). Effects of long-term summer deficit irrigation on 'Navelina' citrus trees. Agricultural Water Management. 169:140-147. doi:10.1016/j.agwat.2016.02.028S14014716

Geometric overlapping coefcients for calculating the required emitters per plant in drip irrigation

[EN] The designer of irrigation systems must consider a complex combination of emitter type, emitter uniformity, hydraulics, topography, desired water distribution, crop salt tolerance, water requirements, water quality, fertilizer injection, soil salinity, cultural practices, and other site-specifc conditions. In contrast to the approaches applied for the hydraulic design of irrigation installations, there is not a clear, general and consolidated design criterion for calculating the number required emitters per plant. In most cases, given the wide spectrum of possible scenarios, only guideline recommendations can be found, and the fnal decision is often based on the subjective experience of the designer or grower. This paper aims at revising, clarifying and refning the existing published guidelines and methodologies for estimating the required emitters per plant in drip irrigation, focussing on the Montalvo approach. The agronomic design should satisfy, among others, two specifc conditions: (i) the emitters should wet at least a minimum threshold of the soil area (or volume) corresponding to the plant for ensuring a proper development of the roots; (ii) overlapping between emitter bulbs is required for merging wetted volumes and avoiding salt concentration near the root zone. Relying on this basis, a thorough theoretical geometric analysis of the overlapping between wet bulbs of contiguous emitters is carried out. As a result, Montalvo's overlapping coefcients are deduced here. This author assumes an identical net wetted area for all emitters in the laterals, but it can be stated that the overlapping areas between emitters difer in extreme emitters and interior emitters, as well as in confgurations with one lateral per plant row and two laterals per plant row. Therefore, this study proposes new formulations for the computation of the overlapping coefcient, which need to incorporate the number of emitters as an additional variable, as well as to distinguish between the presence of one or two laterals per plant row, and between grouped and non-grouped emitters. In one lateral per plant row, the original overlapping coefcient underestimates the net wetted area by one emitter and thus overestimates the theoretical number of required emitters. In the case of two laterals per plant row, the original overlapping coefcient overestimates the net wetted area in the interior emitters, and thus underestimates the theoretical number of required emitters per plant. The presented formulations are applied in diferent practical examples covering a wide range of scenarios. The results allow a general overview of the infuence of the soil type, the emitter fow rate, and the selected overlapping ratio in the number of required emitters per plant. The revision of guidelines and methods presented here, complemented with other experimental results and models of soil water dynamics under drip irrigation, might contribute to a better decision making of designers and feld engineers.Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature.Martí, P.; González Altozano, P.; Gasque Albalate, M.; Turegano Pastor, JV.; Royuela, A. (2023). Geometric overlapping coefcients for calculating the required emitters per plant in drip irrigation. Irrigation Science. 1-20. https://doi.org/10.1007/s00271-023-00898-z120Al-Ogaidi AAM, Wayayok A, Rowshon MK, Fikri Abdullah A (2016) Wetting patterns estimation under drip irrigation Systems using an enhanced empirical model. Agric Water Manag 176:203–213. https://doi.org/10.1016/j.agwat.2016.06.002ASAE EP 405.1 1988 (R2019) Design and installation of microirrigation systems. American Society of Agricultural Engineers. USAAtkinson D (1983) The growth, activity and distribution of the fruit tree root system. Plant Soil 71:23–35. https://doi.org/10.1007/BF02182638Ayars J E, Hutmacher RB, Schoneman RA, Vail SS, Patton SH, Felleke D (1985) Salt distribution under cotton trickle irrigated with saline water. In: Drip/Trickle Irrigation in Action. Proc. Third Drip/Trickle Irrigation Congress, Fresno, California. Nov. 18–21, 1985. ASAE. Vol 2:666–672Ayars JE, Bucks DA, Lamm FR, Nakayama FS (2007) Introduction. In: Lamm FR, Ayars JE, Nakayama FS (eds) Microirrigation for crop production. Design, operation, and management. Elsevier, Amsterdam, pp 1–26Bar-Yosef B, Sagiv B, Markovitch T (1989) Sweet corn response to surface and subsurface trickle phosphorus fertigation. Agron J 81:443–447Benami A, Ofen A (1983) Irrigation engineering. Irrigation Engineering Scientific Publication, Haifa, IsraelBielorai H (1985) Moisture, salinity, and root distribution in drip irrigated grapefruit. In: Drip/Trickle Irrigation in Action. Proc. Third Drip/Trickle Irrigation Congress, Fresno, California. Nov. 18–21, 1985. ASAE Vol 2:562–567Black JDF, West DW (1974) Water uptake by an apple tree with various proportions of the root system supplied with water. In: Proceedings of the 2nd International Drip Irrigation Congress. California, USA. pp 32–433Clark GA, Haman DZ, Prochaska JF, Yitayew M (2007) General system design principles. In: Lamm FR, Ayars JE, Nakayama FS (eds) Microirrigation for crop production. Design, operation, and management. Elsevier, Amsterdam, pp 161–220del Vigo Á, Zubelzu S, Juana L (2020) Numerical routine for soil dynamics from trickle irrigation. Appl Math Model 83:371–385. https://doi.org/10.1016/j.apm.2020.01.058del Vigo Á, Juana L, Rodriguez-Sinobas L (2022) Modelo numérico de simulación de flujo de agua en el suelo afectado por la absorción de la raíz. 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Optimization of an isolated photovoltaic water pumping system with technical-economic criteria in a water users association

[EN] With proper management, the modernization of irrigation systems makes it possible to improve the efficiency of application and use of water at the cost of an increase in pumping needs and, therefore, an increment of the energy consumed. The recent drastic price increase for energy put the viability of many farms at risk. In this context, using photovoltaic solar energy to power pumping stations has become an increasingly attractive alternative and a cheap and reliable option. The dimensioning of pumping systems powered by photovoltaic solar energy must be done considering the variability of solar radiation to take advantage of the available photovoltaic energy, especially during periods of less irradiation. By investigating a particular case, this paper studies the effect of increasing the number of pumps in parallel while maintaining the total power, as well as the relationship between the installed photovoltaic capacity and the power of the pumping system, to meet pumping requirements throughout the year. The pumped volume increased as the number of pumps installed in parallel increased for the same photovoltaic power generator. Although this increment has a limit, beyond which no greater significant rise in volume is achieved, installation costs increase. In addition, for the same pumping power installed, the required photovoltaic generator power decreases as the number of pumps in parallel increases. In the case studied, a 27% increase in the annual pumped volume was achieved by incrementing the number of pumps in parallel from one to five, thus leading to a 44.1% reduction in the size of the photovoltaic generator and a 13.3% reduction in the cost of installation compared with a system with only one pump. The procedure used to determine the most appropriate number of pumps to install in parallel when pumping water between two tanks, which minimizes the photovoltaic generator's size while guaranteeing pumping requirements, is easily generalizable for sizing isolated photovoltaic water pumping systems.Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. This study has received funding for the WATER¿ 4CAST project (PROMETEO/2021/074), funded by the Conselleria de Innovación, Universidades, Ciencia y Sociedad Digital of the Comu¿ nitat Valenciana.Carricondo-Antón, JM.; Jiménez Bello, MA.; Manzano Juarez, J.; Royuela, A.; González-Altozano, P. (2023). 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An artificial neural network approach to the estimation of stem water potential from frequency domain reflectometry soil moisture measurements and meteorological data

Stem water potential seems to be a sensitive measure of plant water status. Nonetheless, it is a labour-intensive measurement and is not suited for automatic irrigation scheduling or control. This study describes the application of artificial neural networks to estimate stem water potential from soil moisture at different depths and standard meteorological variables, considering a limited data set. The experiment was carried out with `Navelina¿ citrus trees grafted on `Cleopatra¿ mandarin. Principal components analysis and multiple linear regression were used preliminarily to assess the relationships among observations and to propose other models to allow a comparative analysis, respectively. Two principal components account for the systematic data variation. The optimum regression equation of stem water potential considered temperature, relative humidity, solar radiation and soil moisture at 50 cm as input variables, with a determination coefficient of 0.852. When compared with their corresponding regression models, ANNs presented considerably higher performance accuracy (with an optimum determination coefficient of 0.926) due to a higher input-output mapping ability.The authors are grateful to TECVASA, which obtained a subsidy from the Conselleria de Agricultura, Pesca y Alimentacion de la Generalitat Valenciana (DOCV 5493, 19 April 2007, no. exp.: 2007TAHAVAL00018), and to the Valencian Institute for Agricultural Research (IVIA) for providing the meteorological data for this study.Martí Pérez, PC.; Gasque Albalate, M.; González Altozano, P. (2013). An artificial neural network approach to the estimation of stem water potential from frequency domain reflectometry soil moisture measurements and meteorological data. Computers and Electronics in Agriculture. 91:75-86. doi:10.1016/j.compag.2012.12.001S75869

Energy Efficiency Optimization in Battery-Based Photovoltaic Pumping Schemes

[EN] This article deals with the analysis of energy efficiency optimization in battery-based photovoltaic pumping schemes. The study builds on previous findings derived from the comparison between a direct photovoltaic water pumping system (DPVWPS) and the equivalent system including a lithium-ion battery (LIB). The initial experimental results of the battery-based photovoltaic water pumping system (PVWPS+LIB) were obtained with the motor-pump group operating at its rated condition of 50 Hz. In the present work, an analysis of the efficiency and the performance ratio of the variable speed drive (VSD) and the motor-pump group, showed that both parameters improve when operating in the low frequency range of the VSD and far from the rated frequency where the flow rate is maximized. Several fitting models were performed with the data obtained with the monitoring system and it was concluded that an overall energy efficiency optimization can be achieved with a VSD frequency equal to 37 Hz. A comparison of the experimental results obtained with the VSD working in the direct mode and with the battery-based solution (setting different VSD frequencies - 50 Hz, 37 Hz, and a combination of the two frequencies designed as 37/50/37 Hz) was made to determine the efficiency and performance ratios in each case. The results presented in this study also establish criteria for improving efficiencies in the LIB charging and discharging processes.This work was supported in part by the Universitat Politecnica de Valencia (UPV) (Program ADSIDEO-Cooperation 2017 through the Project Characterization of Sustainable Systems for the Pumping of Water for Human Consumption in Developing Regions and/or Refugee Camps in Kenya Through the Implementation of Isolated Photovoltaic Systems With New Generation Lithium-Ion Batteries); and in part by the International Organization for Migration under a contract entitled `Design, Assembly, Testing and Documenting Parameters of Solar and Ion-Lithium Energy Storage Equipment for Powering of Water Pumps under Laboratory Conditions' with funding from the Bureau for Humanitarian Assistance-United States Agency for International Development (USAID).Gasque Albalate, M.; González Altozano, P.; Gimeno Sales, FJ.; Orts-Grau, S.; Balbastre Peralta, I.; Martíne-Navarro, G.; Segui-Chilet, S. (2022). Energy Efficiency Optimization in Battery-Based Photovoltaic Pumping Schemes. IEEE Access. 10:54064-54078. https://doi.org/10.1109/ACCESS.2022.317558654064540781