• Solar Energy
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• v.15 no.3
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• pp.15-27
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• 1995

This study presents experimental and numerical results of the temperature characteristics, the heat transfer phenomema, and the heat storage quantity during the heat storage process with sodium phyrophosphate decahydrate($Na_4P_2O_7{\cdot}10H_2O$)-Phase Change Material(PCM) in a latent heat storage tank(cubic type). It was proved that heat transfer by conduction was dominant because PCM($Na_4P_2O_7{\cdot}10H_2O$) during heating processes was gel phase, not liquid phase The gap ratio(rate of air content) of PCM became smaller, the thermal capacity of PCM became larger, therefore the temperature distribution of PCM slowly increased than that of large gap ratio. There was maximum 15% difference between measured temperatures and calculated temperatures.

• Fire Science and Engineering
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• v.23 no.5
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• pp.143-152
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• 2009

The numerical analyses for each single simplified shaft with three type openings were carried out by using computational fluid dynamics model for the calculation of the pressure difference and the location of the neutral plane and the visualization of stack effect. As the height of shaft heighten, the pressure difference of stack effect is much deviated against the theoretical value. For the Type A models shorter than 30 m height of shaft and the Type B models longer than 30m, the simulation results for the location of the neutral plane are well agreed to the theoretical values with 5% less deviations just after the beginning of simulation (t = 10s). For the Type B models longer than 30m with multiple openings, therefore, it is possible to calculate the location of the neutral plane by using a CFD model. The phenomenon of the air flow of stack effect can be easily understood with the visualization of stack effect.

• Fire Science and Engineering
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• v.21 no.4
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• pp.38-43
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• 2007

The aim of this paper is to investigate the change of pressure differential and smoke propagation characteristics in the elevator lobby with the resident's evacuation scenarios using fire modelling technique. The results showed absolute pressures in the fire room and elevator lobby can significantly increase to cause fire door to the stairway unclosed once it is open. This is due to constant pressure differentials, the increasing reference pressure of fire lobby and pressure leak from elevator lobby to fire lobby. Smoke exhaust mechanism was needed to prevent the continuous pressure rise in the living room. Over 200 Pa was expected upon closing the door during pressurization, which provide difficulties in opening the door for next refugee. Opening both fire door and entrance door may induce smoke flow from fire room to elevator lobby and stairway.

• The KSFM Journal of Fluid Machinery
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• v.15 no.5
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• pp.60-66
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• 2012

One of commonly physical phenomena encountered in pump sump systems in which its significant influence to the hydraulic performance of pump system plays an important role in the field of fluid engineering, is the appearance of free surface and submerged vortices. In this paper, a study of the vortices behavior and their formative mechanism of asymmetry is considered in this paper by using numerical approach. The Reynolds-Averaged Navier-Stokes (RANS) equations and k-omega Shear Stress Transport turbulence model used to describe the properties of turbulent flows, in company with VOF multiphase model, are implemented by Fluent code with multi-block structured grid system. In the numerical simulation, the calculated elevation of air-water interface and vortex core contours are used to classify visually surface vortices as well as submerged vortices. It is shown that the free surface vortex is identified by the concavity of liquid region from the free surface and swirling flow at that own plane. To investigate the distinctive behavior of these vortices corresponding to each given flow rate at the same water level, some numerical testing of them are considered here in such a manner that the flow pattern of surface vortex are obtained similarly to the obtained results from experiment. Furthermore, the influence due to the change of grid refinement and the variation of depth of the concavity are also considered in this paper. From that, these influential factors will be implemented to design a good pump sump with higher performance in the future.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.1
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• pp.266-274
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• 1996

An experimental work was conducted to investigate the characteristics of the onset of flooding in vertical annuli with a direct injection mode using air and water. The onset of flooding was determined by means of pressure drop measurement while the air velocity was increased gradually under fixed liquid flow rates. Data of the onset of flooding were collected for various combinations of the tube size and the nozzle number. A theoretical analysis of the onset of flooding was also performed based on an envelope theory. The result shows that the onset of flooding in small-scale annuli can be predicted relatively well by the theory. A modified Wallis parameter was used to investigate the scaling effect of flooding phenomena in the annuli, indicating a relatively reasonable result. The number of nozzle has no effect on the flooding velocity when liquid was injected through 2, 3, 4 and 6 nozzles but the initiation of flooding was significantly expedited when 12 nozzles were employed for liquid injection.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.4
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• pp.449-455
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• 2015

Owing to the trend of an increase in capacity and high-efficiency requirement, the life and reliability of power transformer depend significantly on the amount of heat generation per unit volume and the degradation of insulation oil. These problems can be solved by enhancing the cooling performance of the radiator. The purpose of this study was to find a suitable position of fans for a better cooling effect given by the forced-convection of air in an ONAF (Oil Natural Air Forced) type transformer. In the simulation, commercial software was used for flow analysis, and the cooling passage of the oil was simplified to shorten the time taken for computation. With the diameter of the fan fixed at a constant value, the analysis was performed only by changing the position of the fans. As a result, a vertical position change of the fans does not affect the cooling performance significantly. However, the temperature drop given by the fans positioned on the front region of the transformer is larger than that on the rear region.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.3
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• pp.291-299
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• 2010

Aspect-ratio-based numerical analysis is carried out to investigate the air-side convective heat transfer characteristics in compact heat exchangers with circular tubes and flat tubes-plate fins. The RNG $k-{\varepsilon}$ model is adopted for turbulence analysis. The numerical analysis is carried out for aspect ratios ranging from 3.06 to 5.44 and for Reynolds numbers ranging from 1,000 to 10,000. The calculated results indicate a correlation between the friction factor and Colburn j factor in the compact heat exchanger system for the range of aspect ratios under consideration. The results obtained for circular tubes and flat tubes-plate fins in this study can be utilized to realize the optimal design of an air conditioning system.

• Solar Energy
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• v.15 no.1
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• pp.85-94
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• 1995

This research has been proceeded over the potential core region(H/B=2) of two-dimensional impinging air jet sytem, in which square rods(width of 6 mm) has been set up in front of heating surface in order to increase heat transfer. The objective of this research was to investigate the characteristics of heat transfer and air flow, in eases of the clearance from rods to heating surface(C=1, 2, 4, 6 mm) and the pitch between each rods(P=30, 40, 50 mm) changed. And this research compared the above with the experimentation without rods. As result, heat transfer performance was best under the condition of C=1mm, in case clearance changed, and there was no serious difference in the effect of heat transfer augmentation in the case of pitch of rods changed.

• Journal of Radiation Protection and Research
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• v.29 no.3
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• pp.173-177
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• 2004

The Chinese cabbage, being one of the principal foodstuffs in Asian countries, is tested for iodine exposure. As a radioactive source, iodine-125 of which the radiological half life is 60 days was used to measure the concentration change. Experiments were carried out four times with different times of exposure. The iodine source was prepared by the chemical reaction of NaI in order to avoid producing relatively large iodine which might be generated In the case of crystal evaporation. The deposition velocity was obtained from the integrated air concentration and surface concentration of the Chinese cabbage. The environmental half life was also calculated.

• Journal of the Korean Society of Propulsion Engineers
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• v.5 no.1
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• pp.18-25
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• 2001

The results of systematic numerical experiments of secondary gas injection thrust vector control are presented. The effects of secondary injection system such as injection location and nozzle divergent cone angle onto the overall performance parameters such as thrust ratio, specific impulse ratio and axial thrust augmentation, are investigated. Complex nozzle exhaust flows induced by the secondary jet penetration is numerically analyzed by solving unsteady three-dimensional Reynolds-averaged Navier-Stokes equations with Baldwin-Lomax turbulence model for closure. Numerical simulations compared with the experiments of secondary air injection into the rocket nozzle of $9.6^{\cire}$ divergent half angle showed good agreement. The results obtained in terms of overall performance parameters showed that locating the secondary injection orifice further downstream of primary nozzle ensures the prevention of occurrence of reflected shock wave, therefore is suitable for efficient and stable thrust vectoring over a wide range of use.