• Journal of Electrochemical Science and Technology
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• v.15 no.1
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• pp.132-151
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• 2024

Proton exchange membrane fuel cell (PEMFC) has received extensive attention as it is the most common hydrogen energy utilization device. This research not only investigated the effect of obstacle number and shape on PEMFC performance, but also studied the effect of the blockage degree in the channel of PEMFC on its performance. It was found that compared with traditional scheme, longitudinally distributed obstacles scheme can significantly promote reactants transfer to catalyst layer, and the blockage degree in the channel effect PEMFC performance most. The scheme with 10 rectangular obstacles in single channel and 60% channel blockage had the best output performance and the most uniform distribution of reactants and products. Obstacle height distribution can significantly affect PEMFC performance, the blockage degree in the whole basin was large, particularly as the channel was blocked to higher degree in region 2 and region 3, higher net power density and better mass transfer effect can be obtained. Among them, the fuel cell with the blockage degree of 40%, 60% and 60% in region 1, region 2 and region 3 have the best PEMFC output performance and mass transfer, the net power density was 29.8% higher than that of traditional scheme.

• Journal of the Korean Society of Safety
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• v.23 no.2
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• pp.81-86
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• 2008

Experimental studies have been performed to examine the influences of wall obstructions in a rectangular confinement. Three wall obstacles with blockage ratios ranging from 10 to 30% were used. Temporally resolved flame front images were recorded by a high-speed video camera to investigate the interaction between a propagating flame and the obstacle. The local flame displacement speed and its probability density functions(PDFs) were obtained for the wall obstructions. During the interaction with the sharp-edges of the wall obstacles, the local propagation speed increased. The increase of local speed became larger as the obstruction ratio increased. However, the averaged flame displacement speeds with different blockage ratios were not significantly different within the chamber as shown in the paper of Park et al. The flame front interaction investigated in this work was less dependent of the obstacle obstructions compared to that published in the literature for large L/D.

• Wind and Structures
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• v.12 no.4
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• pp.299-312
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• 2009

It has long been studied about the flow around bluff bodies, but the effect of aspect ratio on the sharp-edged bodies in thick turbulent boundary layers is still argued. The author investigates the flow characteristics around a series of rectangular bodies ($40^d{\times}80^w{\times}80^h$, $80^d{\times}80^w{\times}80^h$ and $160^d{\times}80^w{\times}80^h$ in mm) placed in a deep turbulent boundary layer. The study is aiming to identify the extant Reynolds number independence of the rectangular bodies and furthermore understand the surface pressure distribution around the bodies such as the suction pressure in the leading edge, when the shape of bodies is changed, responsible for producing extreme suction pressures around the bluff bodies. The experiments are carried out at three different Reynolds numbers, based on the velocity U at the body height h, of 24,000, 46,000 and 67,000, and large enough that the mean boundary layer flow is effectively Reynolds number independent. The experiment includes wind tunnel work with the velocity and surface pressure measurements. The results show that the generation of the deep turbulent boundary layer in the wind tunnel and the surface pressure around the bodies were all independent of Reynolds number and the longitudinal length, but highly dependent of the transverse width.

• Journal of the Korean Society of Safety
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• v.27 no.6
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• pp.70-77
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• 2012

Experimental investigations were performed to examine the characteristics of propagating flame fronts around multiple bars within a rectangular chamber. The explosion chamber is 400 mm in height, $700{\times}700mm^2$ in cross-section and has a large top-venting area, $A_v$, of $700{\times}210mm^2$. This results in a value of 0.44 for $A_v/V^{2/3}$ and a L/D value of 0.57. The multiple obstacles of length 700 mm with a blockage ratio of 30 % were placed within the chamber. Temporally resolved flame front images were recorded by a high speed video camera to investigate the interaction between the propagating flame and the obstacles. Results showed that the flame propagation speeds before the flame impinges onto the obstacle almost equal to the laminar burning velocity. As the propagating flame impinged on the obstacle, the central region of flame began to become concave, this resulted in the flame deceleration in the region. As the flame interacted with the modified flow filed generated behind the central obstacle, the probability density functions(PDFs) of the local flame displacement speed were extensively distributed toward higher speeds.

• Journal of computational fluids engineering
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• v.6 no.2
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• pp.22-31
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• 2001

The two-dimensional unsteady incompressible viscous flow behind rectangular bluff bodies between two parallel plates was analyzed numerically. The steady state flow and the vortex flow behind rectangular bluff bodies in the channel were investigated for two regimes i.e., the laminar(Re = 100, 300, 500) and the turbulent flows(Re = 10⁴∼10/sup 6/). The vortex shedding was generated by a physical disturbance(6%) numerically imposed at the rear of the bluff bodies for a short time. It was observed that the perturbed flow became periodic after a transient period. And in the case of unsteady inflow, the sinusoidal pulsatile flow was applied as the inlet condition in the turbulent flow of Reynolds number of 1.0×10/sup 5/. FLUENT code was employed to solve the problems. The power-law scheme was used to get stable linearized equations and the PISO algorithm was applied to finding the solution of them.

• Journal of the Korean Institute of Telematics and Electronics
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• v.26 no.6
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• pp.1-6
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• 1989

Narrowband bandpass weveguide filters using inductive post obstacles in rectangular waveguide are designed and constructed to have an equal-ripple bandwidth of 50MHz (0.56% fractional band-width) at a center frequency of 9GHz. Both the triple-post and the single-post configurations are realized and compared. The measured center frequency, bandwidth, and attenuation characteristics for both filters show good agreement with the theoretical calculations. When the two filters are compared, the insertion loss characteristic of the triple-post filter is better than that of the single-post filter by 0.8dB at the passband.

• The KSFM Journal of Fluid Machinery
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• v.17 no.6
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• pp.69-73
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• 2014

To predict flow fields and chemical agent dispersion in urban area, wind tunnel experiments was performed. The agent was adopted MS (methyl salicylate) because the real chemical agent is unsafe. The exact concentration of methyl salicylate was generated by the commercial gas generator (STI-2500) and three different obstacle shapes were applied (i.e., rectangular, cylinder and pyramid). The concentration was measured with the qualified ion mobility sensor and gas chromatography. The data necessary for virtual test method of the real chemical agent were obtained.

• 제어로봇시스템학회:학술대회논문집
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• 1989.10a
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• pp.166-171
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• 1989

In the view of the fact that mobile robot in nuclear facilities should be able to turn in narrow space, go over obstacles, and climb stairs for the inspection and maintenance, a robot, named as KAEROT, is developed. It adopts 2DWIS (2-Driving Wheels, 1-Steering) and has three planetary wheels that are composed of two star-like arms and three small wheels. The experiments were carried out in two locomotion methods; (1) by controlling the rear wheel speed as a function of steering angle, and (2) by using inclination and stair-detection sensor to control the position of planetary and small wheel. The developed robot moved on the floor with stability. Results from the experiment on the rectangular obstacle as well as the computer simulation showed a feasibility on the stairs.

• Journal of the Korean Society of Safety
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• v.26 no.2
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• pp.32-35
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• 2011

Experimental studies were carried out in an explosion chamber to investigate the influences of multiple cylinder obstacles on local flame propagation. The chamber dimension is 235 mm in height with a $1,000{\times}950\;mm^2$ rectangular cross section and a large vent area of $1,000{\times}320\;mm^2$. Multiple cylinder bars with obstruction ratio of 30% were used. In order to examine the interaction between the propagating flames and the obstacles, temporally resolved flame front images were recorded by a high speed video camera. The propagation behaviour of local flame fronts around the left obstacle was analyzed in terms of two different methods such as the incremental burnt area divided by the flame front length and the average of the local propagation velocity determined at each point along the flame front. It was found that two methods give good consistency.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.23 no.3
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• pp.248-257
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• 2011

In the present study, we proposed a new numerical wave tank model to analyze the vertical tension-leg circular floating bodies, using a 2-D Navier-Stokes solver. An IBM(Immersed Boundary Method) capable of handling interactions between waves and moving structures with complex geometry on a standard regular Cartesian grid system is coupled to the VOF(Volume of Fluid) method for tracking the free surface. Present numerical results for the motions of the floating body were compared with existing experimental data as well as numerical results based on FAVOR(Fractional Area Volume Obstacle Representation) algorithm. For detailed examinations of the present model, the additional hydraulic experiments for floating motions and free surface transformations were conducted. Further, the versatility of the proposed numerical model was verified via the numerical and physical experiments for the general rectangular floating bodies. Numerical results were compared with experiments and good agreement was archived.