Analysis of the performance of a passive hybrid powerplant to power a lightweight unmanned aerial vehicle for a high altitude mission

The objective of this research is to analyze the performance of a passive hybrid powerplant control system to be implemented in a lightweight unmanned aerial vehicle capable to ascend up to the high troposphere (10, 000 m). The powerplant is based on a high-temperature PEM fuel cell connected in parallel to a set of lithium-polymer batteries and regulated by two power diodes. Test performed in steady state demonstrates that the use of the hybrid system increases the efficiency of the stack by more than 7% because the voltage at the main DC bus is limited by the batteries. The robustness of the passive control system is proved in a long-term test in which random perturbations of ±15% are applied to the average power that would be demanded during the ascent flight. The hybridization of the stack with the batteries eliminates sudden peaks in the current generated by the stack, which are responsible for prompt degradation phenomena that drastically reduce its useful lifetime. The study demonstrates that with the passive hybrid powerplant it is possible to reach the target height with the gas storage system considered in the application, contrary to what happens with the simple power plant

Selector de aerosol para la caracterización de atomizadores de orificios múltiples

Referencia OEPM: P200402228 .-- Fecha de solicitud: 17/09/2004.-- Titulares: Universidad de Matanzas, Consejo Superior de Investigaciones Científicas (CSIC).Dispositivo selector de un aerosol, especialmente diseñado para la caracterización de atomizadores con múltiples orificios de salida. Consta de un cuerpo cilíndrico mecanizado con aperturas en ambas caras, con un asentamiento interior para seleccionar el orificio de descarga que se pretende caracterizar. La forma en que están concebidos el diseño y construcción de la pieza permite adaptarlo a cualquier ángulo de salida y diámetro del orificio de descarga. Este dispositivo posibilita la realización de medidas de tamaños de gotas, ángulo del aerosol y caudal de líquido de cada uno de los orificios individuales en los atomizadores sin afectar el funcionamiento nominal del mismo. Con su uso se podrá mejorar el diseño de las boquillas que manejan grandes flujos de combustibles como las que se emplean para la atomización de petróleos pesados en centrales eléctricas, en los hornos de carbón, en la pulverización depinturas, etc.Peer reviewe

Optimal design and operational tests of a high-temperature PEM fuel cell for a combined heat and power unit

Development of new materials for polymer electrolyte membranes has allowed increasing the operational temperature of PEM fuel cell stacks above 120 °C. The present paper summarizes the main results obtained in a research devoted to the design, fabrication and operational tests performed on a high-temperature PEMFC prototype. A 5-cell stack has been assembled with commercial Celtec P-1000 high-temperature MEAs from BASF Fuel Cells, but the rest of elements and processes have been developed at LIFTEC research facilities. The stack includes different novelties, such as the way in which reactant gases are supplied to the flowfield, the design of the flowfield geometry for both anode and cathode plates, the concept of block that eases the assembling and maintenance processes, and the heating strategy for a very fast start-up. The different procedures comprising the assembly, closing and conditioning stages are also widely described and discussed. Results obtained in the preliminary operational tests performed are very promising, and it is expected that the 30-cells HT-PEMFC stack will deliver an electric power 2.3 times larger than the one initially predicted.Peer Reviewe

Influence of liquid properties on ultrasonic atomization

[EN] Ultrasonic atomization is very convenient because it can generate droplets with diameters of a few microns and with very narrow size distribution. Besides, opposite to twin fluid nozzles, in ultrasonic atomization, droplet generation and transport are decoupled processes. Droplets are ejected from the liquid surface with very low velocities, so driving them is relatively simple. Although this atomization method is now common in some specific applications, for example in household humidifiers, there are still some details about the physics of this process that are not completely understood. Up to date, most of the published results have been limited to experiments with water. However, it has been demonstrated that atomization rates quickly decrease as liquid viscosity increases. This work analyzes the characteristics of ultrasonic atomization of some alternative fluids to determine if there is any influence of other physical properties such as surface tension or vapor pressure. Experiments are performed using a commercial piezoceramic disk with a resonance frequency of 1.65 MHz. The disk is excited with a sinusoidal signal with voltage amplitudes that go up to 60 V. Sprays are visually characterized analyzing instantaneous images and high speed video sequences. Besides atomization rates are calculated by measuring the weight loss in a fixed time.This work has been partially funded by the Secretariat of State for Research of the Spanish Ministry of Economy and Competitiveness under project DPI2013-45814-P. Support of the RegionaLozano, A.; García, JA.; Alconchel, J.; Barreras, F.; Calvo, E.; Santolaya, JL. (2017). Influence of liquid properties on ultrasonic atomization. En Ilass Europe. 28th european conference on Liquid Atomization and Spray Systems. Editorial Universitat Politècnica de València. 35-42. https://doi.org/10.4995/ILASS2017.2017.4588OCS354

Placa de pila de combustible con varias áreas de reacción química

16 páginas, 9 figuras.-- Titulares: Consejo Superior de Investigaciones Científicas (CSIC) y Lincheta Mesa, Eduardo.-- Solicitud de patente con nº: P201031093.La placa de pila de combustible, que se utiliza generalmente para distribuir de forma homogénea los fluidos reactantes sobre las áreas de reacción química correspondientes a las capas catalíticas (electrodos), presenta, en al menos una de las dos caras, dos o más áreas de reacción química una geometría de flujo determinada, de manera que se optimiza la producción de corriente por celda utilizando ensamblajes de membrana y electrodo del mismo tamaño, reduciendo el espacio necesario, el peso final y los costes totales de la pila hasta en un 25%, en general.Peer reviewe

Corrosion behavior of tantalum coatings on AISI 316L stainless steel substrate for bipolar plates of PEM fuel cells

Corrosion resistance of tantalum coatings 30 μm thick deposited by chemical vapor deposition on SS316L coupons has been evaluated by electrochemical impedance spectroscopy (EIS). To this end, anodic and cathodic operating conditions of proton exchange membrane fuel cells (PEMFC) have been simulated in a three-electrode heated corrosion cell. Interfacial contact resistance (ICR), contact angle and durability tests have been performed in long-term tests (> 100 h) polarizing the electrode to 1.193 V vs. Ag/AgCl. Results obtained by different experimental techniques show a dense coating structure with a high polarization resistance, mainly formed by surface crystals of α-Ta (bcc), Ta2O5 and carbon. An atomic ratio (in %) of oxide to metallic species (Taox/Tamet) of 4.8 was verified from XPS spectra, which is slightly increased to 6.23 after the anodizing treatment. The modified surface composition yielded a coating capacity higher than the amorphous oxide, favoring the in-plane electrical conduction. After the treatment, no noticeable changes were observed neither in surface morphology nor in contact angle (>90°). ICR values in the range of 22.3 − 32.6 mΩ cm2 were obtained for a clamping pressure of 140 N cm-2. No morphological changes or loss of coating adherence were observed during the long-term tests

Use of fuel cell stacks to achieve high altitudes in light unmanned aerial vehicles

A study is presented to determine if substituting an internal combustion engine (ICE) by an electric motor powered by a fuel cell stack can be a viable option to increase the service ceiling of an available light unmanned aerial vehicle (UAV), extending it to 10,000 m. As a first condition, the stack has to be capable of supplying the minimum power required for horizontal leveled flight at this altitude, which is a function of the UAV total mass. A second step examines if the UAV can transport the energy required to reach the desired service ceiling without exceeding the maximum mass that can be loaded, considering that both hydrogen and oxygen have to be carried on-board. A particularly light PEM fuel cell stack is proposed as a suitable power source. A realistic system is described to store the required amount of reactant gases maintaining the mass below the allowable limits. Results indicate that with its aerodynamic characteristics, the UAV should be capable of ascending up to 10,000 m with the described fuel cell and gas storage system. Some multivariable maps that include service ceiling, total payload and required power are provided to perform this type of analysis

Experimental determination of the heat transfer coefficient for the optimal design of the cooling system of a PEM fuel cell placed inside the fuselage of an UAV

The objective of this research is to calculate the heat transfer coefficients needed for the further design of the optimal cooling system of a high-temperature polymer electrolyte membrane fuel cell (HT-PEMFC) stack that will be incorporated to the powerplant of a light unmanned aerial vehicle (UAV) capable of reaching an altitude of 10,000 m. Experiments are performed in two rectangular tunnels, for three different form factors, in experimental conditions as close as possible to the actual ones in the HT-PEMFC stack. For the calculations, all the relevant thermal processes are considered (i.e., convection and radiation). Different parameters are measured, such as air mass flow rate, inlet and outlet air temperatures, and wall temperatures for bipolar plates and endplates. Different numerical models are fitted revealing the influence of the diverse relevant non-dimensional groups on the Nusselt number. Heat transfer coefficients calculated for the air cooling flow vary from 8 to 44 W m2 K1. Results obtained at sea level are extrapolated for a flight ceiling of 10 km. The flow section is optimized as a function of the power required to cool the stack down to the temperature recommended by the membrane-electrode assembly (MEA) manufacturer using a numerical code specifically developed for this purpose

Diseño e implementación de los sistemas electrónicos de control para refrigeración y humidificación por cortocircuitos en una pila PEM de cátodo abierto

El objetivo del trabajo es desarrollar 2 sistemas de control para pilas de combustible de tipo PEM de baja temperatura. El primero consiste en un sistema de suministro de aire y refrigeración mediante ventiladores axiales que proporcionará el caudal necesario para el funcionamiento óptimo de la pila, y mantendrá la temperatura de trabajo en el rango definido por los fabricantes de los sistemas membrana electrodos (MEAs). El segundo sistema consiste en un método de humidificación de las MEAs mediante cortocircuitos periódicos en los bornes de la pila para mejorar el rendimiento y evitar un sistema extra de humidificación de los gases reactantes.<br /

Evaluation of the corrosion resistance of Ni(P)Cr coatings for bipolar plates by electrochemical impedance spectroscopy

Trabajo presentado en el VII Symposium on Hydrogen, Fuel Cells and Advanced Batteries (HYCELTEC 2019), celebrado en Barcelona del 1 al 3 de julio de 2019.This research has been supported by the MEC, DPI2015-69286-C3-1-R (MINECO/FEDER, UE). Technical and human support of the Materials and Surfaces service provided by SGIker (UPV/EHU/ ERDF, EU) is also appreciated