Transactions of the Canadian Society for Mechanical Engineering
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Volume 37 (2013), Issue 1
Numerical investigation of the effect of inlet gases humidity on polymer exchange membrane fuel cell (PEMFC) performance
Nima Ahmadi1, Sajad Rezazadeh, Mirkazem Yekani, Alireza Fakouri, Iraj Mirzaee
A full three-dimensional, single phase model of a proton exchange membrane fuel cell (PEMFC) has been developed. A single set of conservation equations developed and numerically solved using a finite volume based computational fluid dynamics technique. In present investigation some parameters such as transport phenomena, fuel cell performance for conventional model (base case) and the effect of inlet gases humidity on cell performance were investigated in more details. The numerical results prove that the inlet gases humidity and membrane water management are most important parameters that affect cell performance and transport phenomena in fuel cell. Finally the numerical results are compared with experimental data, which represent good agreement.
The dynamic analyses and verifications of a hollowshaft with hot-fit component using 3d finite contact element
In general engineering practice, one key factor in designing a motor built-in high-speed spindle is to assemble the motor rotor and shaft by means of hot-fit to form a new rotor-shaft assembly. In this paper, the dynamic analysis of a hot-fit rotor in a rotor-shaft assembly by using 3D contact element is proposed. Contact pressure between the rotor and the shaft is firstly calculated through contact theory. The stress state is thus determined. The finite element modal analysis then follows with the stress state as a pre-stressed condition. The accuracy and the validity of the finite contact element results are verified by theoretical formulation, equivalent static analysis and experimental modal testing. The results presented herein indicate that it is accurate and effective in analyzing the dynamic behavior of the rotary shaft system with a hot-fit component by using contact element.
Improving the formability of stainless steel 321 through multistep deformation for hydroforming applications
Melissa Anderson, Javad Gholipour, Florent Bridier
Tube hydroforming (THF) is a well established process in the automotive industry and its application is being extended to the aerospace for manufacturing complex geometries. However, most of the alloys used in aerospace are high in strength and low in formability, which renders the application of THF more challenging. The objective of this paper is to present a method to increase the formability of an austenitic stainless steel. A multistep forming process was simulated through interrupted uniaxial tensile testing experiments to study the influence of the latter process on formability. The tensile test was divided into several deformation steps with a stress relief heat treatment after each forming step. The results indicated that the application of intermediate heat treatments considerably increased the formability of the stainless steel 321 alloy (SS321). Microstructure evolution as a function of deformation or heat treatment parameters was also investigated and revealed the formation of strain-induced martensite after the first deformation and heat treatment cycle without any deleterious effect on formability enhancement.
Use of spatiotemporal diagrams to characterize a silo discharging process
Blaise Nsom, Noureddine Latrache
To get a better knowledge of discharging flows of ensiled granular materials, a small scale silo was designed and built. It is equipped with a flat bottom and it has a rectangular cross section. Moreover, it is entirely transparent for image processing purpose. First of all, a physical and mechanical characterization of wood granules (inert materials) was performed using a shear box testing. Then, silo emptying flows were generated. Flow regimes and flow rate were determined using spatiotemporal diagrams extracted from images of the free surface of the ensiled material. The same method was then used to measure the flow rate of discharging flows of soya, colza and rye seeds which were characterized in a previous study. For each material studied, the flow rate measured with this non intrusive method was successfully compared with a direct method consisting in weighing a volume of grains discharged during a unit time and with Berveloo’s formula.
Design and modelling of fast switching efficient seat valves for digital displacement pumps
Daniel B. Roemer, Per Johansen, Henrik C. Pedersen, Torben O. Andersen
Digital Displacement Fluid Power Pumps/Motors are promising candidates for revolutionizing the efficiency of fluid power systems, which traditionally has suffered from poor efficiencies, especially at part load. The key to obtain efficient part load operation with digital displacement technology lies in the development of very fast switching seat valves with a corresponding low pressure loss. The present article is on design and modelling of such an efficient seat valve, which is a mechatronic approach where considerations of different technology fields must be taken into account. Models include valve orifice flow, valve movement and valve actuation. A design method for selecting the optimum valve diameter and stroke length for a given displacement volume is presented. Furthermore, a prototype valve is manufactured and experimental results show good correspondence with modelled results.
Free vibration and buckling of cantilever beams under linearly varying axial load carrying an eccentric end rigid body
Seyed Amir Mousavi Lajimi, Glenn R. Heppler
Natural frequencies of a clamped axially loaded beam carrying an eccentric end rigid body are computed. A linearly varying non-follower axial force representing the beam’s own weight is taken into consideration. An analytical form of the frequency equation of the structure is obtained and solved numerically. The parameters associated with the end rigid body, the mass, the rotary inertia and the eccentricity, are shown to considerably affect the natural frequencies of the structure. The modified orthogonality conditions of the system are presented. A closed-form of the frequency equation for a beam under constant axial load carrying an eccentric end rigid body is obtained and results are compared with the distributed load case. Based on the exact and approximate computations of the critical buckling load a recommendation is made on the method of including the effect of distributed load for practical purposes.
Numerical study of a hot-air-based aircraft wing anti-icing system using the box-behnken doe approach
Ridha Hannat, François Morency, Louis Decoster
This article proposes the use of the Box-Behnken design of experiment (DoE) methodology to study an aircraft anti-icing system. The anti-icing system consisted of a piccolo tube with round apertures for producing air jets inside a wing. Mass flow, jet to wall distance, and jet impact angle were varied, starting from an initial design, in order to maximize heat transfer effectiveness. A conjugate heat transfer procedure from commercial CFD software was used to solve for cold air external flow, compressible internal flow, and thermal conduction in the airfoil skin. The DoE methodology was validated using a single impinging jet. A quadratic model of the heat transfer effectiveness of the anti-icing system was then built using the methodology and the maximal value was sought.
Which will win in the gear pump technology
Hai-Lin Zhu, Jun Pan, Min Zou, Hong-Nen Wu, Xingpei Qin
There exist three major problems in current gear pumps. They are unbalanced radial force, big excessive flow pulsation and short working life. In order to solve the problems above, a new type of gear pump with flexible ring gear is introduced. Pumping action is achieved through meshing between a flexible ring gear and a rigid external gear. Thus radial pressure forces are hydraulically balanced and the volumetric displacement is doubled for the new pump.
Full journal title: Transactions of the Canadian Society for Mechanical Engineering
Abreviated journal title: Trans. Can. Soc. Mech. Eng.
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