• Transactions of the KSME C: Technology and Education
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• v.2 no.2
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• pp.105-111
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• 2014

Generally the lower part of the Earth's atmosphere, which is 20km above the ground, is called "air." The composition of this area is almost consistent consisting of nitrogen, oxygen, and other gases. Air density refers to the mass per unit volume of earth atmosphere. Though air is made of the mixed gases in a constant composition, the water vapor is one of the very changeable components. The density of moist air is lower than the dry one at the same temperature and pressure. As the density varies according to the pressure and temperature, this paper attempts to explore the main factors in the air quantity calculation by examining first the density calculation process according to the air property, and second the relation between the actual and standard air flow.

• The KSFM Journal of Fluid Machinery
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• v.12 no.5
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• pp.19-24
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• 2009

This paper is performed to find out the stability of water-hammer in pipe line and pump station that is happened when additional water needs demanded. At first, the water supply construction project is planned to supply $6,000\;m^3/day$ through 17.9 km pipe line. But additional demand ($1,200\;m^3/day$) happened from Cheong-ra water reservoir. In this situation, air-chamber($4\;m^3$) and vacuum breaker valve(${\varphi}100\;mm$) are needed to prevent water-hammer. When the additional water is supplied, the existing facilities (air-chamber, vacuum breaker valve) are sufficient to alleviate shock not changing capacity alteration, judging from the airspace change and rise. Therefore, there is no problem for water-hammer by installing air-chamber($4\;m^3$) and vacuum breaker valve(${\varphi}100\;mm$) at the top of Yeo-ju hill.

• Journal of the Korean Chemical Society
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• v.51 no.6
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• pp.577-584
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• 2007

The purpose of this study is to suggest how to use the phase diagram for water to explain the evaporation and sublimation in the atmospheric condition. In principle, the phase diagram for water represents a one component system so it cannot be applied to the water contact with the air. When the liquid or solid phase of water exists in the air, always water vapor also exists in the air. In this case, we cannot present this state as a single point on the phase diagram because the pressure of the liquid or solid is different from that of the vapor in the air. However, since the saturation vapor pressure of liquid or solid is altered by negligible amount due to the presence of air, the evaporation and sublimation in the atmospheric condition can be explained using the vapor pressure line and sublimation line on the phase diagram.

• Journal of Energy Engineering
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• v.16 no.4
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• pp.187-193
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• 2007

Water hammer following the tripping of pumps can lead to overpressures and negative pressures. Reduction in overpressure and negative pressure may be necessary to avoid failure, to improve the efficiency of operation and to avoid fatigue of system components. The field tests on the water hammer have been conducted on the pump rising pipeline system with an air chamber. The hydraulic transient is modeled using the method of characteristics. Minimizing the least squares problem representing the difference between the measured and predicted transient response in the system performs the calibration of the simulation program. Among the input variables used in the water hammer analysis, the effects of the polytropic exponent, the discharge coefficient and the wave speed on the result of the numerical analysis were examined. The computer program developed in this study will be useful in designing the optimum parameters of an air chamber for the real pump pipeline system. The correct selection of air chamber size and the effects of related parameters to minimize water hammer have been investigated by both field measurements and numerical modeling.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.660-663
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• 2004

This paper investigate the qualities variety of concrete using recycling water under various kinds and contents of saccaric based stabilizing agent(SSA). Fluidity had little changes with the kinds and contents of SSA. Air contents of concrete with recycled water only shows the tendency. With an increase in SSA contents, air content recovered. For bleeding properties, bleeding shows to be decreased with an increase in SSA contents. The use of recycled water accelerated the setting time. However, with an increase in SSA, setting time showed the similar level of plain concrete. SSA (Btype) had better performance in enhancing compressive strength owing to loss of air content. Although the use of recycled water increased the drying shrinkage compared with that of plain concrete, it tended to decrease with an increase in SSA.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.30 no.1
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• pp.25-32
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• 1994

An underwater speaker was made of a moving coil driver unite of usual speaker, acryl-boards, polyester resin, rubber and castor oil and it's frequency characteristics was measured in range of 250~600Hz in air water tank and sea. The results of measurements are follows: 1. Transmitting and receiving frequency of measurement frequency were similar in air, water tank and sea. 2. The input and output wave forms of a manufactured speaker which is not water-proof in air were similar to each other in 300~450Hz, but other frequencies showed distorted wave forms. 3. The input and output wave forms of an underwater speaker in water thank and sea were similar to each other in 250~600Hz. But output wave forms showed combination waves with very low frequency. 4. Transmitting and receiving frequency wave forms and resisting pressure of an underwater speaker at 80m in the depth of water were in good condition. Therefore it can be possible to use it as an underwater speaker.

• International Journal of Fluid Machinery and Systems
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• v.4 no.2
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• pp.255-261
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• 2011

Recently, as global-scale problems, such as global warming and energy depletion, have attracted attention, the importance of future environmental preservation has been emphasized worldwide, and various measures have been proposed and implemented. This study focuses on water hammer pumps that can effectively use the water hammer phenomenon and allow fluid transport without drive sources, such as electric motors. An understanding of operating conditions of water hammer pumps and an evaluation of their basic hydrodynamic characteristics are significant for determining whether they can be widely used as an energy-saving device in the future. However, conventional studies have not described the pump performance in terms of pump head and flow rate, common measures indicating the performance of pumps. As a first stage for the understanding of water hammer pump performance in comparison to the characteristics of typical turbo pumps, the previous study focused on understanding the basic hydrodynamic characteristics of water hammer pumps and experimentally examined how the hydrodynamic characteristics were affected by the inner diameters of the drive and lift pipes and the angle of the drive pipe. This paper suggests the effect of the air volume in the air chamber that affects the hydrodynamic characteristics and operating conditions of the water hammer pump.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.30 no.6
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• pp.242-252
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• 2018

It is well known that an Oscillating Water Column Wave Energy Converter (OWC-WEC) is one of the most efficient wave absorber equipment. This device transforms the vertical motion of water column in the air chamber into the air flow velocity and produces electricity from the driving force of turbine as represented by the Wells turbine. Therefore, in order to obtain high electric energy, it is necessary to amplify the water surface vibration by inducing resonance of the piston mode in the water surface fluctuation in the air chamber. In this study, a new type of OWC-WEC with a seawater channel is used, and the wave deformation by the structure, water surface fluctuation in the air chamber, air outflow velocity from the nozzle and seawater flow velocity in the seawater channel are evaluated by numerical analysis in detail. The numerical analysis model uses open CFD code OLAFLOW model based on multi-phase analysis technique of Navier-Stokes solver. To validate model, numerical results and existing experimental results are compared and discussed. It is revealed within the scope of this study that the air flow velocity at nozzle increases as the Ursell number becomes larger, and the air velocity that flows out from the inside of the air chamber is larger than the velocity of incoming air into the air chamber.

• Journal of Ocean Engineering and Technology
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• v.29 no.4
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• pp.317-321
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• 2015

Many kinds of generation systems have been developed to use ocean energy. Among these, with the use of an oscillating water column (OWC) for power generation is attracting attention. The OWC-type wave power generation system converts wave energy into electricity by operating a generator turbine with the oscillating water level in a column of water. There are two ways to convert wave power into electricity using an OWC. One uses a cross-flow turbine using the water level inside the OWC. The other method uses the flow of air in a Wells turbine, which depends on the water level. An experiment was carried out using a 2-D wave tank in order to minimize the number of empirical tests. The design factors were taken from Koo et al. (2012) and the experimental environment assumed by free surface motion. This paper deals with characteristics of two types of wave energy conversion systems combine with a breakwater. One model uses an air-driven Wells turbine and a cross-flow water turbine. The other type uses a cross-flow water turbine. Wave energy converters with OWCs have mostly been studied using air-driven Wells turbines. The efficiency of the cross-flow turbine was about 15% higher than that of the other model, and the water level of the OWC internal chamber for the cross-flow water turbine and air-driven Wells turbine was less than about 40% lower than the one using only the cross-flow water turbine.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.24 no.3
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• pp.189-202
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• 2012

An Oscillating Water Column (OWC) wave generation system uses the air flow induced by the vertical motion of water column in the air chamber as a driving force of turbine. It is well known that OWC is one of the most efficient devices to harness wave power. This study estimated the air flow velocity from the time variation of the water level fluctuation in the air chamber under regular wave conditions using 3-dimensional numerical irregular wave tank (3D-NIT) model that can simulate the 3-dimensional irregular wave field. The applicability of the 3D-NIT model was validated by comparing numerically predicted air flow velocities with hydraulic experimental results. In addition, the characteristics of air flow frequency spectrum variation due to the incident frequency spectrum change, and the variations of frequency spectrum and wave reflection due to the existence of converter inside the air chamber were discussed. It is found that the phase difference exists in between the air flow velocity and the water level fluctuation inside the air chamber, and the peak frequency of the spectrum in water level fluctuation is amplified by the resonance in the air chamber.