• Transactions of the Korean hydrogen and new energy society
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• v.27 no.2
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• pp.155-162
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• 2016

A proton exchange membrane fuel cell (PEMFC) produces only water at cathode by an electrochemical reaction between hydrogen and oxygen. The generated water is transported across the membrane from the cathode to the anode. The transported water collected in water-trap and drained to the cathode within the humidifier outlet. If the condensate water is not being drained at the appropriate time, condensate water in the anode can cause the performance degradation or fuel efficiency degradation of fuel cell by the anode flooding or unnecessary hydrogen discharge. In this study, we proposed an optimization method of condensate water drain logic for the water drain performance and the water drain algorithm as considered the condensate water generating speed prep emergency case. In conclusion, we developed the water management strategy of fuel processing system (FPS) as securing fuel efficiency and operating stability.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2720-2724
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• 2007

Field measurements have revealed that the pressure drop over a borehole during drilling of a slim oil well or a well with a long reach can depend significantly on the rotation speed of the drill pipe. An accurate prediction of the annular frictional pressure drop is therefore important for conditions where the annular clearance is small. An experimental study was carried out to study solid-liquid two phase flow in a slim hole annulus. Annular velocities of carrier fluids varied from 0.2 m/s to 1.5 m/s. The carrier fluids which were utilized included tap water and CMC water solutions. Pressure drops and average flow rates were measured for the parameters such as inner-pipe rotary speed, carrier fluid velocity, hole inclination and particle injection rate. For both water and CMC solutions, the higher the concentration of the solid particles is, the larger the pressure gradients become.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.1974-1979
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• 2007

In this study, Ice slurry generator heat transfer characteristics are experimentally investigated for the ice slurry generating system with scraper which is pneumatically operated. The ice slurry generator has the same shape as the vertical double tube type heat exchanger. Refrigerant is flowing in the outside tube and ethylene glycol solution in the inside tube. Refrigerant and solution water are parallel flow type which entering bottom of generator and leaving top of generator. The experimentations are conducted under the various test conditions such as compressor speed and cooling water temperature. For the above experimental conditions, heat transfer characteristics of the ice slurry generating system are evaluated in terms of the overall heat transfer coefficient and the heat transfer rate. And the experimental results show that the heat transfer rate of the system is increased as the compressor speed increases and the cooling water temperature decreases.

• Proceedings of the Korean Environmental Health Society Conference
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• 2005.12a
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• pp.51-53
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• 2005

Disposal of waterwork sludge is important problem in WTP(water treatment plant). Purpose of this study is treated municipal waste water chemically using sludge that is produced in waterwork plant by link to reutilize waterwork sludge. Municipal waste water that use in an experiment used is produced at C university, and is SS 220 mg/L, BOD 145 mg/L, COD 160 mg/L, T-N 52 mg/L and T-P 2.6 mg/L. Used Alum, polymer coagulant and coagulant aid (diatomite, powered activated carbon) as CaO, coagulant as alkaline aid by chemical treatment medicine. In case of does slow speed agitation and stations after pours waterwork sludge in sewage and alkaline aid and coagulant at rapidly mixing the colloidal creation speed is fast and fine colloids concentration was high but settling time is shortened a little and removal rate of pollutant improved by $60{\sim}99%$.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.1
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• pp.38-47
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• 2017

This paper presents experimental data on water droplet breakup in high-speed air flows. Exact-time-dependent evolution of wave and droplet interaction as well as breakup processes were optically visualized using a shadowgraph technique. Droplet experiments were conducted in a shock tube. Five flow conditions were used with an incident shock wave Mach number from 1.40 to 2.19 with Weber number based on the droplet initial diameter from 2300 to 38000, respectively. This corresponds to post-shock flow speeds varying from subsonic to supersonic. The considered droplet diameters were 2.0 mm to 3.6 mm. Some interesting wave patterns in the near wake were found. The present data shows that with an increase in the Weber number the droplet acceleration coefficient decreases and the level of decrease was weaker for the case of higher Mach numbers. This state of affair is different to the existing data in literature. Possible reasons are discussed.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.607-616
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• 2006

More strict construction control of railway roadbeds is demanded in high speed railway system because of heavier repeated dynamic loading than conventional railways. The aim of this study is to propose a compaction control methodology of crushed-rock-soil-fills including as large particles as $200\sim300mm$ in diameter, which are easily encountered in high speed railway roadbed. Field tensity evaluation and in turn compaction control of such crushed-rock-soil-fills are almost impossible by conventional methods such as in-situ density measurements or plate loading tests. The proposed method consists of shear wave measurements of compaction specimens in laboratory and in-situ measurements of fills. In other words, compaction control can be carried out by comparing laboratory and field shear wave velocities using as a compaction control parameter. The proposed method was implemented at a soil site in the beginning and will be expanded to crushed-rock-soil-fills in future. One interesting result is that similar relationship of shear wave velocity and water content was obtained as that of density and water content with the maximum value at the optimum moisture content.

• Transactions of the Korean hydrogen and new energy society
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• v.8 no.1
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• pp.5-10
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• 1997

Because of environmental pollution and reserve limitations of fossil fuels, several alternative energies have been developing. One of them, the hydrogen is researched as a highly probable solution. In this study pure hydrogen gas and oxygen gas are burned in combustor to reduce the emission, and a gas turbine is used. Cooling water around the combustor recovers the cooling heat loss to useful work by being expanded from liquid to vapor, being injected into the combustor and making pressure rise with working fluid to get more turbine power. Because pure hydrogen and oxygen are used, there is no carbonic emission such as CO, $CO_2$, HC nor $NO_x$, and $SO_x$. The power is obtained by turbine system, which makes lower noise and vibration than any reciprocating engine. Running of a turbine is searched under various conditions of hydrogen flow rate and water injection rate. Maximum speed of the turbine is obtained when the combustion reaches steady state. It is enable to determine the optimum rate between hydrogen flow and water injection which makes turbine run maximum speed.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.1 s.244
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• pp.67-73
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• 2006

This investigation deals with the spin-up flows in a circular container of aspect ratio, 2.0. Shear front is generated in the transient spin-up process and propagating from the side wall to the central axis in a rotating container. Propagation of the shear front to the axis in a rotating container means the region acquires an angular momentum transfer from the solid walls. Propagating speed of the shear front depends on the apparent viscosity of polymer solution. Two kinds of polymer solutions are considered as a working fluid: one is CMC and the other is CTAB solution. CMC solution has larger apparent viscosity than that of water, and CTAB shows varying apparent viscosities depending on the applied shear rates. Transient and spatial variations of the apparent viscosities of the present polymer solutions (CTAB and CMC) cause different speeds of the propagating shear front. In practice, CMC solution that has larger values of apparent viscosity than that of water always shows rapid approach to the steady state in comparison of the behavior of the flows with water. However, for the CTAB solution, the speed of the propagating of the shear front changes with the local magnitude of its apparent viscosity. Consequently, the prediction of Wedemeyer's model quantitatively agrees with the present experimental results.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.631-636
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• 2000

The experimental study concerns the characteristics of a transitional flow in a concentric annulus with a diameter ration of 0.52, whose outer cylinder is stationary and inner one rotating. The pressure drops and skin-friction coefficients have been measured for the fully developed flow of water and that of glycerine-water solution (44%) at a inner cylinder rotational speed of $0{\sim}600$ rpm, respectively. The transitional flow have been examined by the measurement of pressure drops and the visualization of flow field, to reveal the relation of the Reynolds and Rossby numbers with the skin-friction coefficients and to understand the flow instability mechanism. The present results show that the skin-friction coefficients have the significant relation with the Rossby numbers, only for laminar regime. The occurrence of transition has been checked by the gradient changes of pressure drops and skin-friction coefficients with respect to the Reynolds numbers. The increasing rate of skin-friction coefficient due to the rotation is uniform for laminar flow regime, whereas it is suddenly reduced for transitional flow regime and, then, is gradually declined for turbulent flow regime. Consequently, the critical (axial-flow) Reynolds number decreases as the rotational speed increases. Thus, the rotation of inner cylinder promotes the early occurrence of transition due to the excitation of taylor vortices.

• Agricultural and Biosystems Engineering
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• v.6 no.2
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• pp.65-69
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• 2005

A windheat generation system with a Savonius windturbine was developed and the performance was evaluated through field tests. The system consisted of a heat generation drum, heat exchanger, water storage tank, and two circulation pumps. Frictional heat is created by rotation of a rotor inside the drum containing thermo oil, and was used to heat water. In order to estimate the capacity of this windheat generation system, weather data was collected for one year at the site near the windheat generation system. Wind Power from the savonius wind turbine mill was transmitted to the heat generation system with an one-to-three gear system. Starting force to rotate the savonius wind turbine and the whole system including the windheat generation system were 1.0 and 2.5 kg, respectively. Under the outdoor wind condition, maximum speed of the rotor in the drum was 75rpm at wind speed 6.5 m/sec, which was not fast enough to produce heat for greenhouse heating. Annual cumulative hours for wind speeds greater than 5 m/sec at height of 10, 20, 30 m were 190, 300 and 1020 hrs, respectively. A $5^{\circ}C$ increase in water temperature was achieved by the windheat generation system under the tested wind environment.