This paper outlines the technical approach adopted to meet the specifications laid down for the '2001 Future Energy Challenge (FEC)' organized by the Department of Energy and IEEE in August 2001. Abstract -In this paper, the development of a low cost fuel cell inverter system is detailed. The approach consists of a three-terminal push-pull DC-DC converter to boost the fuel cell voltage (48V) to f2OOVDC. A four switch (IGBT) inverter is employed to produce 120V/240V, 60Hz AC outputs. High performance, easy manufacturability, lower component count., safety and cost are addressed. Protection and diagnostic features form an important part of the design. Another highlight of the proposed design is the control strategy, which allows the inverter to adapt to the requirements of the load as well as the power source (fuel cell). A unique aspect of the design is the use of the TMS320LF2407 DSP to control the inverter. Two sets of lead-acid batteries are provided on the high voltage DC bus to supply sudden load demands. Efficient and smooth control of the power drawn from the fuel cell and the high voltage battery is achieved by controlling the front end DC-DC converter in current mode. The paper details extensive experimental results of the proposed design on DOE National Energy Technology Laboratory (NETL) Fuel Cell.
Insects breathe using an extensive network of flexible air-filled tubes. In some species, the rapid collapse and reinflation of these tubes is used to drive convective airflow, a system that may have bio-inspired engineering applications. The mechanical behavior of these tracheal tubes is critical to understanding how they function in this deformation process. Here, we performed quasi-static tensile tests on ring sections of the main thoracic tracheal trunks from the American cockroach (Periplaneta americana) to determine the tracheal mechanical properties in the radial direction. The experimental findings indicate that the stress-strain relationships of these tracheal tubes exhibit some nonlinearities. The elastic modulus of the linear region of the stress-strain curves tubes was found to be 1660 ± 512 MPa. The ultimate tensile strength, ultimate strain and toughness were found to be 23.7 ± 7.33 MPa, 2.0 ± 0.7% and 0.207 ± 0.153 MJ m −3 , respectively. This study is the first experimental quantification of insect tracheal tissue, and represents a necessary step toward understanding the mechanical role of tracheal tubes in insect respiration.
The tracheal tubes of insects are complex and heterogeneous composites with a microstructural organization that affects their function as pumps, valves, or static conduits within the respiratory system. In this study, we examined the microstructure of the primary thoracic tracheae of the American cockroach (Periplaneta americana) using a combination of scanning electron microscopy and light microscopy. The organization of the taenidia, which represents the primary source of structural reinforcement of the tracheae, was analyzed. We found that the taenidia were more disorganized in the regions of highest curvature of the tracheal tube. We also used a simple finite element model to explore the effect of cross-sectional shape and distribution of taenidia on the collapsibility of the tracheae. The eccentricity of the tracheal cross-section had a stronger effect on the collapse properties than did the distribution of taenidia. The combination of the macro-scale geometry, meso-scale heterogeneity, and microscale organization likely enables rhythmic tracheal compression during respiration, ultimately driving oxygen-rich air to cells and tissues throughout the insect body. The material design principles of these natural composites could potentially aid in the development of new bio-inspired microfluidic systems based on the differential collapse of tracheae-like networks.
The insect cuticle serves the protective role of skin and the supportive role of the skeleton while being lightweight and flexible to facilitate flight. The smart design of the cuticle confers camouflage, thermo-regulation, communication, self-cleaning, and anti-wetting properties to insects. The mechanical behavior of the internal cuticle of the insect in tracheae remains largely unexplored due to their small size. In order to characterize the material properties of insect tracheae and understand their role during insect respiration, we conducted tensile tests on ring sections of tracheal tubes of American cockroaches (Periplaneta americana). A total of 33 ring specimens collected from 14 tracheae from the upper thorax of the insects were successfully tested. The ultimate tensile strength (22.6 ± 13.3 MPa), ultimate strain (1.57 ± 0.68%), elastic modulus (1740 ± 840 MPa), and toughness (0.175 ± 0.156 MJ m −3 ) were measured. We examined the high variance in mechanical properties statistically and demonstrated that ring sections excised from the same trachea exhibit comparable mechanical properties. Our results will form the basis for future studies aimed at determining the structure-function relationship of insect tracheal tubes, ultimately inspiring the design of multi-functional materials and structures.
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