Please login first

List of accepted submissions

Show results per page
Find papers
  • Open access
  • 51 Reads
Experimental Investigation on the Mechanical Endurance Limit of Nafion membrane used in Proton Exchange Membrane Fuel Cell
, ,
Nowadays, two pressing problems face the world: the energy crisis and environmental pollution. As a solution of high efficiency and clean energy, fuel cell technologies, especially proton exchange membrane fuel cell (PEMFC), have caught extensive attention. However, after decades of development, the word-wide commercialization of PEMFC has not started properly yet; due mainly to the barriers of high cost and durability. These days, the performances of PEMFCs are far from achieving the target from the Department of Energy (DOE). So, further understanding of the degradation mechanism is needed to overcome this obstacle. Due to the importance of proton exchange membrane in a PEMFC, the degradation of the membrane, such as hygrothermal aging effect on its properties, are particularly necessary. In this work, a thick membrane (Nafion N117) which is always used as an ionic polymer for the PEMFCs has been analyzed. Experimental investigation is performed for understanding the mechanical endurance of the bare membranes under different loading conditions. Tensile tests are conducted to compare the mechanical property evolution of two kinds of bare-membrane specimens including the dog-bone and the deeply double edge notched (DDEN) types. Both dog-bone and DDEN specimens were subjected to a series of degradation tests with different cycling times and wide humidity ranges. The tensile tests are repeated for both kinds of specimens to assess the strain-stress relations. Furthermore, the yielding stresses were obtained, as well as the work of fracture.
  • Open access
  • 46 Reads
Investigation of Various Levels of Cascade Multi-Level Inverter DVR for Improve Power Quality of Induction Motor Drive
This paper presents a direct torque control (DTC) of induction motor drive (IMD) using various levels of Cascade Multilevel DVR. The DTC is one of the most admirable strategies of flux ripples manage and torque of induction motor drives (IMD). The major problem of the DTC of IMD using conservative PI controller based SR is high torque, stator flux ripples and spee d of IMD is decreasing under transient and steady state operating conditions. This drawback was eliminated using In front of DTC IM drive connected Different levels of Cascade Multilevel DVR. The main objective of this paper is to present an approach capable of performing fast torque response and harmonics reduction in DTC drive. Because of that, a n efficient control strategy is applied, is needed to reduce the voltage fluctuations like sag and swell conditions and also to reduce current and voltage harmonics in the DTC drive system. In this paper, the work proposed is aimed at obtaining results exhibiting improved THD contents of various level cascade multilevel inverters at the ac mains and reduced the Torque ripples of the DTC IMD Drive.
  • Open access
  • 81 Reads
Why are some of the Sama Second Law Rules Routinely Violated in Practical Applications?
In 1989, Gaggioli, Sama and Qian published a series of 10 "second law guidelines" for design and process engineers, which were discussed for some time in thermodynamic conferences and papers under the name of "the Gaggioli-Sama rules", though some of them had been previously published by Sama between 1980 and 1983. These guidelines are in essence a list of "second law errors" to avoid in the design of energy conversion systems. The list was later rearranged several times, and its latest version, containing 21 rules, was published by Dominick Sama and Jan Szargut in 1995. Ever since, these guidelines came to be known as "the Sama-Szargut rules" The rules are sound, well-formulated, insightful, and reflect a thermodynamicist's idea that the "best design" is the one that minimizes the overall irreversibility in the process or plant under consideration. Characteristically, the idea of "optimality" is completely absent from all published formulations, the insistence being on the extensive inclusion of second law reasoning into design decisions. One would therefore expect that most, if not all, of the rules be routinely implemented in new designs and in retrofit projects. It turns out, that the contrary is rather true: even a superficial survey of some of the current most common energy conversion installations shows that most of the rules are actually disregarded in practice. This paper contends that the reason for this apparently irrational behavior is the neglection in the engineering design decision of the real cost of installation, operation and dismantling of a plant. It is argued that, if the production cost is assessed in terms of equivalent primary exergy and a proper exergy accounting for the externalities is introduced, the Sama-Szargut rules can be directly interpreted in this sense, and abidance by the rules results in the reduction of the resource cost for any given objective.