Modeling and experimental research on adjustable ejector in fuel cell gas circulation system

Abstract

Fuel cells can be made to operate under a variety of conditions by implementing adjustable ejectors in their anode gas circulation systems. Based on a quasi-two-dimensional model and considering factors such as friction and variable area effects, a theoretical model of ejectors with needles was established to predict their primary and secondary flow rates. Theoretical calculations were used to analyze the variations in internal parameters and flow losses along the ejector, explain the reasons and laws behind the effect of needle position on ejector performance, and explore the control mechanism of different needle shapes on ejector flow rates. Finally, flow control experiments were conducted on three types of adjustable needle shapes–oblique straight, quadratic, and parabolic–to validate the precision of the adjustable ejector theoretical model and the controls of different shapes on the ejector flow rates. The research indicates that the relative errors of the quasi-two-dimensional model in predicting primary and secondary flow rates are within ± 5 % and + 20 % to −5%, respectively. Both the primary and secondary flow rates were impacted by the needle position variation, though the impact on the secondary flow was weaker. The parabolic shape was optimal for the linear control of primary flow rates, followed by the oblique straight shape. The quadratic shape was the weakest, although the quadratic-shaped needle had a wider range of flow rate control. Modeling and experimental research on the adjustable ejector contributes to understanding the influence of the needle on the ejector performance under different working conditions, broadening the application range of the ejector, and providing a basis for flow control in the fuel cell system.