Study on an ejector for anode gas recirculation in small-scale SOFC system

Experimental study and one-dimensional analysis were made to clarify fundamental characteristics of an ejector for anode gas recirculation in small-scale SOFC system. The experiments were carried out using an anode gas recirculation simulator where a part of temperature-controlled mixture of the driver gas and SOFC-simulating gas was suctioned by the feed of the driver gas at room temperature to the ejector and effect of temperature deference between the suctioned gas and the driver gas on the recirculation ratio was investigated. The experimental results showed that higher temperature of suction flow causes declination of the recirculation ratio. One-dimensional analysis predicts well the experimental results without temperature difference by the adoption of adequate values to the friction factor in mixing zone and to the diffuser efficiency in the pressure recovery zone. Furthermore, comparison of the experimental results at the elevated temperatures to the one-dimensional analysis considering temperature difference showed the importance of driver gas temperature at the ejector nozzle tip and the suction gas temperature at the mixing zone inlet on predicting the recirculation ratio, indicating that precise heat transfer experiments and analysis between the nozzle flow and the outer flow are needed to acquire more accurate prediction for these important temperatures.