Study Of Model For Heat And Mass Transfer In Solid Oxide Fuel Cell

Fuel cell is a device that converts chemical energy into electricity directly from the reaction of fuel and oxidant. It can achieve higher electrical efficiency than that obtained from conventional heat engine and it is also an environmentally benign method of electric power production. Furthermore, solid oxide fell cell (SOFC) is operated at high temperature, so it has the advantage of high temperature waste heat recovery.Planar and tubular geometries are the two popular designs for SOFC. The technique of designing and manufacturing tubular type SOFC is relatively mature. Since the SOFC is operated at the temperatures as high as 1000℃, it is difficult to measure the distributions of current density, temperatures of solids and gases, and gas composition. Computational modeling can be used to investigate the characteristics for the SOFC at various operating conditions and it is an effective tool for optimization of SOFC and predicting their characteristics at the steady and transient operating states.In this paper, a model was developed to simulate the operation of a tubular SOFC. A flat-plane SOFC was manufactured and an experiment system was fabricated to measure its performance. Three SOFC power systems fed by methane respectively were examined. Full analysis of the energy and exergy at each node of the systems was conducted. The main work and result of this paper are given as follows:1. A model was developed to simulate the operation of a tubular SOFC at the steady and transient operation states. The model includes all the three polarizations: ohmic, activation and concentration polarization. The radiation between the cell tube and the air feed tube and heat transfer by convection and conduction are also included in this model.The effects on the average current density, the inlet flow rate and inlet temperature of the fuel and oxidant on the performance of the steady and transient operation are analyzed in detail. The ohmic polarization is the main cause of decreasing of the output power and increasing the thickness of electrolyte results in the decrease of output power of cell. The influence of the length of combustion zone on the steady and transient operation of tubular SOFC was calculated.2. A flat-plane SOFC of Ni-YSZ | YSZ | LSM was manufactured and an experiment system was fabricated to measure its performance. H2 was used as the fuel and O2 was used as the oxidant. The open-circuit voltage was measured at different temperatures ranged from 400 °C to 1000°C and at different flow rate of fuel gas. At the same time, the voltage-current characteristics and power-current characteristics of the SOFC with two thickness of solid electrolyte were evaluated.3. Three SOFC power systems fed by methane were examined with thermodynamic modeling of SOFC. In order to obtain high efficiency and optimize the total system, the exergy concept has been used to analyze these systems, and pinpoint the thermodynamic losses in each unit and to access the work potentials of the streams of matter. The results show that an internal-reforming hybrid SOFC-gas turbine system could achieve an electrical efficiency of more than 60% and a total efficiency of about 80%.