Tetsuhiko Maeda

Operational strategies of networked fuel cells in residential homes

Residential fuel cells (FCs) have been recently launched in the commercial markets in Japan. The introduction of FCs in residential homes has become a realistic option. We previously proposed energy networks that enabled the interconnection of homes via electricity, heat, and hydrogen networks in order to allow consumers to interchange energy. Further, we have developed a PC-based simulator and an experimental system to evaluate the proposed energy networks. In this paper, analyses on the strategies of the electricity dispatch of FCs and their load sharing in the interconnected homes equipped with the energy networks were performed. The analyses were conducted with the experimental system, PC-based simulator, and a newly constructed mathematical model that optimizes the operation of the FCs with the minimization of both annual energy cost and CO2 emission. The basic characteristics of FC stacks were obtained by experimentations, and these were stored in the PC-based simulator. Four different operational strategies were carried out for four FC stacks, and these strategies were compared. It was concluded from the results that the operational strategies, which have different advantages with regard to efficiency in electricity generation and heat recovery, should be applied depending on the seasonal demand variations

Gas Purge for Switching from Electrolysis to Fuel Cell Operation in Polymer Electrolyte Unitized Reversible Fuel Cells

Unitized reversible fuel cells (URFCs) combine the functionality of a fuel cell (FC) and of an electrolyzer (Ely) in a single device. In polymer electrolyte URFCs, gas purging is crucial in switching from the Ely to the FC operation. A gas purge model was developed here to clarify the relationship between the purge time and the gas flow rate. The model considers evaporation and diffusion of liquid water in the gas diffusion layer and membrane. To validate our model, we compared model predictions of high frequency resistance vs purge time with experimental results for two URFCs of different sizes at different purge flow rates. The simulated curves agree well with the experimental curves.

Effect of PTFE contents in the Gas Diffusion Layers of Polymer Electrolyte-based Unitized Reversible Fuel Cells

AbstractPolymer electrolyte-based unitized reversible fuel cells (URFCs) combine the functionality of a fuel cell and an electrolyzer in a single device. In this study, the influence of hydrophobic agent in the gas diffusion layer (GDL) of URFC was investigated. The titanium (Ti)-felt GDL which treated with different percent of PTFE emulsion was intensively tested with various humidification temperature conditions in the single cell of URFC. I-V performance curves and divided three overpotentials were compared and analyzed in the fuel cell mode. The electrolyzer performances were also evaluated with the I-V curves. Experimental results showed that the GDLs with high PTFE contents have better performance in the dry conditions. On the other hand, the increased PTFE contents accelerate flooding problem in the wet condition and it is related with rising concentration overpotential. The electrolyzer performances are almost same with different PTFE contents of GDL.

The Development of the Totalized Hydrogen Energy Utilization System for Commercial Buildings

We have proposed the Totalized Hydrogen Energy Utilization System(THEUS) for applying to commercial buildings. THEUS consists of fuel cells, water electrolyzers, metal hydride tanks and their auxiliaries. We evaluated the energy saving of the basic THEUS in view of an actual operation using thermal demand data of actual buildings. The THEUS have ability for achieving energy saving, in comparison with an ice storage system for cooling demand. We have developed the hydrogen storage system using metal hydride and unitized reversible cell (URC) combine the functionality of a fuel cell and an electrolyzer in a single device, these are important components of THEUS. The metal hydride tank designed and manufactured to evaluate that we assumed actual operation in the experiments. We developed the numerical simulation code, and simulation results are in good agreement with experimental data. The simulation about two tanks system was done by using this code. The heat utilization can be improved greatly. To achieve URC commercial use, improvement of durability was examined. It confirmed that our URC had durability for several thousand hours.

Feedback Control of Flow Separation on NACA0024 Airfoil under Periodic Wall Oscillation by Means of DBD Plasma Actuator and FBG Sensor

Feedback control of periodic flow separation on a NACA0024 airfoil has been investigated by using dielectric barrier discharge (DBD) plasma actuators and fiber Bragg grating (FBG) sensors under oscillation of the test section wall. A tangential jet is generated from sheet-type DBD plasma actuators placed at the leading edge of the airfoil. An FBG flow sensor is mounted at the root of a cantilever beam, which detects the vibrations of the cantilever tip by wake flow around the trailing edge. Flow separation can be detected by the standard deviation of Bragg wavelength (B’). A demonstration of flow separation control was conducted successfully under periodic flow separation by a feedback algorithm using a threshold level of B’ = 0.006 at Re = 5.3×10 4 and showed that the flow separation can be mitigated by more than 20%. In addition, string-type DBD plasma actuators were developed to apply DBD plasma actuators on metallic and three dimensional surfaces and their induced flow properties were investigated by PIV.

Influence of Different Gas Diffusion Layers on the Water Management of Polymer Electrolyte Unitized Reversible Fuel Cell

Unitized reversible fuel cells (URFC) combine the functionality of a fuel cell and electrolyzer in one unitized device. For a URFC with proton exchange membrane, the Ti-felt is applied to the GDL substrate at the oxygen electrode, and responsible for an optimum humidification state and liquid water distribution in the catalyst layer during both operations of a fuel cell and an electrolysis. The experimental result indicates that the loading PTFE on the Ti-felt substrate brings a negative effect on the mass transport of liquid and gas during the fuel cell operation and no effect on the electrolysis performance. The larger fiber diameter of Ti-felt brings better performance of the fuel cell, whereas the electrolysis performance is degraded.

Effect of the Metal Hydride Tank Structure on the Reaction Heat Recovery for the Totalized Hydrogen Energy Utilization System

A Totalized Hydrogen Energy Utilization System (THEUS) is proposed for load leveling and stabilizing the grid. The THEUS is a novel unitized regenerative fuel cell system that achieves high overall efficiency through optimized heat utilization. In this paper, a metal hydride tank (MHT) is chosen as hydrogen storage. In the MHT, the heating and cooling from adsorption/desorption processes is used to produced heated and chilled water for building ventilation systems. A new horizontal type MHT was developed to enhance the recovery rate of the reaction heat. This tank has a double coil heat exchanger and contained 50kg of AB5 metal hydride. The experimental results were compared with the results which were developed previously at AIST. The new tank results showed an improvement for the heat recovery rate which is the ratio of recovered energy to the entire reaction heat of the metal hydride. The reaction heat recovery was improved due to the decrease of the thermal capacity of the tank.

STUDY ON THERMAL DIFFUSION IN ARTIFICIAL AIR NEAR THE CRITICAL POINT

Air is absolutely essential for our everyday life and also very important in the field of industry. The major part of it is composed of nitrogen and oxygen. We investigated the Soret effect in artificial air, which was a nitrogen-oxygen binary mixture with the composition of 0.791 mole fraction of nitrogen and 0.209 mole fraction of oxygen near the critical point. In the case of the artificial air, the estimated critical temperature and the estimated critical pressure are 132.61 K and 3.8381 MPa, respectively. We carried out the experiments by using a single stage two-chamber cell. We made a temperature difference between the two chambers, which were separated by a porous diaphragm. After an experiment had run for sufficient time to reach steady state, the concentration of oxygen in each chamber was measured by using a gas chromatograph. From the experiments, we observed that the thermal diffusion factor showed a strong drop near the critical point. The thermal diffusion ratio indicated was negative and b...

A network of residential fuel cells and operational strategies: evaluation with a PC simulator and an experimental system

Introduction of fuel cells into residential homes would be a realistic option of near future in present state in Japan. Research and development on polymer electrolyte fuel cell (PEFC) for residential use is at the final stage toward commercial market launch. This paper presents the concept of the interconnection of residential homes with energy networks, and a PC simulator and an experimental system for evaluation of the advantages and disadvantages of the networks, and the result of simulation and experimentation with those evaluation tools. The homes can share their energy equipment virtually by the networks. It provides flexible and efficient operation of the equipment, and reduces partial load operation and start-stop operation which damage the efficiency or the life time of fuel processors. Some operational strategies of the fuel cells were proposed and evaluated with both simulation and experimentation. The evaluation result also revealed that fuel cell systems should be installed to not all homes but some homes within residential areas to realize efficient operation.

Studies on energy networks of electricity, heat and hydrogen for residential dwellings equipped fuel cells

Introduction of fuel cells into residential dwellings would be a realistic option of near future in present state in Japan. Research and development on polymer electrolyte fuel cell (PEFC) for residential use is at the final stage toward commercial market launch. This paper presents the concept of interconnection of residential dwellings with energy networks, and experimental systems and PC simulators for evaluation of the advantages and disadvantages of the networks. The dwellings can share their energy equipment virtually by the networks. It provides flexible and efficient operation of the equipment, and reduces partial load operation and start-stop operation which damage the efficiency or the life time of fuel processors. Authors construct experimental systems and PC simulators to evaluate the networks. The experimental systems consist of fuel cells, electronic load devices and instrument control systems. The data which is obtained by the experimentation is provided to the PC simulators. The simulators demonstrate the more complicated analyses beyond the experimental systems, as the simulators are easily expandable. Combining the experimental systems and the simulators would provide more valuable intelligence