Ammonia can be stored as a liquid under relatively easy conditions (Ambient temperature by applying 10 bar or Ambient pressure with the temperature of 239 K). At the same time, liquid ammonia has a high hydrogen storage density and is, therefore, a particularly promising carrier for hydrogen storage. At the same time, the current large-scale industrial synthesis of ammonia has long been mature, and in the future, it will be possible to achieve a zero-emission ammonia regeneration cycle system by replacing existing energy sources with renewable ones. Ammonia does not contain carbon, and its use in fuel cells can avoid NOx production during energy release. high temperature solid oxide fuel cells can be directly fueled by ammonia and obtain good output characteristics, but the challenges inherent in high temperature solid oxide fuel cells greatly limit the implementation of this option. Whereas PEMFC has gained initial commercial use, however, for PEMFC, ammonia is a toxic gas, so the general practice is to convert ammonia to pure hydrogen. Ammonia to hydrogen requires decomposition under high temperature and purification, which increases the complexity of the fuel system. In contrast, PEMFC that can use ammonia decomposition gas directly can simplify the fuel system, and this option has already obtained preliminary experimental validation studies. The energy efficiency of the system obtained from the preliminary validation experiments is only 34–36%, which is much lower than expected. Therefore, this paper establishes a simulation model of PEMFC directly using ammonia decomposition gas as fuel to study the maximum efficiency of the system and the effect of the change of system parameters on the efficiency, and the results show that the system efficiency can reach up to 45% under the condition of considering certain heat loss. Increasing the ammonia decomposition reaction temperature decreases the system efficiency, but the effect is small, and the system efficiency can reach 44% even at a temperature of 850°C. The results of the study can provide a reference for a more scientific and quantitative assessment of the potential value of direct ammonia decomposition gas-fueled PEMFC.
The configuration of a new swirlmeter is designed. The hollow cylindric fluid axial-symmetrically in cylindric pipe is analyzed, and then the algebra expression of meter coefficient is deduced. An impeller of swirl generator attaching to a specimen of swirlmeter is designed according to the deducing process. Simulations and experiments test the method of measuring flowrate by measuring the rotation frequency of ball is feasible. Comparing the results of simulations and experiments with that of algebra expression derived from deducing in theory the maximal error is 7.8%. At last, the reasons resulting in the errors are discussed which the next researches will continue to minus the errors. The conclusion will be applied in designing the impeller of swirl generator and measuring the flow by the new swirlmeter.
Compared with hydrogen, ammonia has the advantages of high gravimetric hydrogen densities (17.8 wt.%), ease of storage and transportation as a chemical hydrogen storage medium, while its application in small-scale on-site hydrogen production scenarios is limited by the need for complex separation equipment during high purity hydrogen production. Therefore, the study of PEMFC, which can directly utilize ammonia decomposition gas, can greatly expand the application of fuel cells. In this paper, the output characteristics, fuel efficiency and the variation trend of hydrogen concentration and local current density in the anode channel of fuel cell with the output voltage of PEMFC fueled by ammonia decomposition gas were studied by experiment and simulation. The results indicate that the maximum output power of the hybrid fuel decreases by 9.6% compared with that of the pure hydrogen fuel at the same inlet hydrogen equivalent. When the molar concentration of hydrogen in the anode channel is less than 0.12, the output characteristics of PEMFC will be seriously affected. Employing ammonia decomposition gas as fuel, the efficiency corresponding to the maximum output power of PEMFC is approximately 47%, which is 10% lower than the maximum efficiency of pure hydrogen.
Performances of vanes with various numbers and front oriented-body with different shapes such as half sphere, half ellipsoid and cone are simulated by RNG κ-ε model and standard wall functions method in order to optimize the parameters of the front oriented-body attached on the new bidirectional flowmeter. The performances of weakening-vortex and the pressure losses attaching to various models are analyzed and compared with each other. The results show that the structure with cone guide-head and 6 vanes can obtain the minimum range of flow pulsation, the least pressure loss and the least reverse flow. The simulation methods and results will be used for reference to analyze the similar annular flow and design the steady device.
In this paper, the optimal experimental conditions for the ammonia thermal cracking reaction with Ni-TiO2-Al2O3 complex as the catalyst were obtained through experimental studies, and the designed ammonia to hydrogen reaction generator was modeled and the parameters of the ammonia thermal cracking reaction were simulated and analyzed by COMSOL Multiphysics software based on the experimental data. The results show that the reaction is basically completed at the inlet flow rate of 1.5 L/min, the reactor temperature range of 500 °C-750 °C, and the molar fraction of remaining ammonia at the outlet is about 1 wt%, which indicates the feasibility of the model and verifies the accuracy of the experiment in reverse.
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