Development of Synthetic Jet Air Blower for Air-breathing PEM Fuel Cell
This paper presents a synthetic jet air blower actuated by PZT for air blowing for air-breathing micro PEM fuel cell. The several factors to affect the performance of air-breathing PEM fuel cell such as air flow rate, opening ratio and cathode open type in the cathode side were studied. Especially, an air flow rate is critical condition to improve its performance. In this paper, we developed a synthetic jet air blower to supply a high stoichiometric air flow. The synthetic jet mechanism is a zero mass flux device that converts electrical energy into the momentum. The synthetic jet actuation is usually generated by a traditional PZT actuator, which consists of a small cylindrical cavity, in/outlet channel and PZT diaphragms. The flow rate of the fabricated synthetic jet air blower was 400cc/min at 550Hz and its power consumption was very low under 0.3W. The proposed air-breathing PEM fuel cell which installed synthetic jet air blower was higher performance and stability during continuous operation than the air-breathing fuel cell without auxiliary device to supply the air. The results showed that the maximum power density was 188mW/cm at 400mA/cm. This maximum power density and durability were improved more than 40% and 20%, respectively. Keywords— Air-breathing PEM fuel cell, Synthetic jet air blower, Opening ratio, Power consumption.
An adjustable synthetic jet by a novel PZT-driven actuator with a slide block
Synthetic jets have been identified and utilized widely in flow control applications. The synthetic jets are usually created by a traditional PZT-driven actuator, which consists of a small cylindrical cavity that has an emitting orifice and a PZT-diaphragm or two PZTdiaphragms. A novel synthetic jet actuator is composed of two emitting slots, two sealed cavity bounded on one end by a single PZT diaphragm, and a slide block. The flow fields of the novel synthetic jet actuator in the quiescent air and the cross-flow conditions were simulated. The results show the slide block of the novel synthetic jet actuator has an important regulating function and a unique adjustable synthetic jet can be generated with slight modifications of the slide block. The adjustable synthetic jet may potentially replace the traditional synthetic jets in various applications, and also extend the applications of the synthetic jet to more flow control systems that can't be implemented by the traditional synthetic jets.
Numerical analysis of surface crack propagation in flexible pavements using XFEM and cohesive zone model
Surface initiated (top-down) cracking in the longitudinal direction of pavements has become a predominant mode of failure in thick asphalt pavements. Most previous researchers studied crack propagation using the traditional Linear Elastic Fracture Mechanics (LEFM) method by calculating the stress intensity factor around the crack tip. In this paper, Extended Finite Element Method (XFEM) was used to study the key factors causing surface initiated crack propagation under surface tension and/or shear. A two-dimensional (2-D) finite element (FE) model for a two-lane flexible pavement was built to predict pavement responses and crack propagation potential under various scenarios. It was found that surface tension is the major driving force for crack propagation when the crack is at some distance away from tire loading. The results show that the distance from the location of crack to tire loading, the depth and direction of the crack, and the modulus ratio between the hot-mix asphalt (HMA) layer and the base layer have significant influences on crack propagation under surface tension. On the other hand, this study shows that shear stress can induce surface initiated crack propagation near the loading area as the shear resistance of material becomes low at the high temperature.