• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.10
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• pp.1346-1354
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• 2001

The heat transfer characteristics off swirling air jet impinging on a heated flat plate have been investigated experimentally. The main object is to enhance the heat transfer rate by increasing turbulence intensity of impinging jet with a specially designed swirl generator. The mean velocity and turbulent intensity profiles of swirling jet were measured using a hot-wire anemomety. The temperature distribution on the heated flat surface was measured with thermocouples. As a result the swirl effect on the local heat transfer rate on the impinging plate is confined mainly in the small nozzle-to-plate spacings such as L/D<3 at the stagnation region. For small nozzle-to-plate spacings, the local heat transfer in the stagnation region is enhanced from the increased turbulence intensity due to swirl motion, compared with the conventional axisymmetric impinging jet without swirl. For example, the local Nusselt number of swirling jet with swirl number Sw=0.75 and Sw=1 is about 9.7-76% higher than that of conventional impinging jet at the radial location of R/D=0.5. With the increase of the nozzle-to-plate distance, the stagnation heat transfer rate is decreased due to the diminishing axial momentum of the swirling jet. However, the swirling impinging jet for all nozzle-to-plate spacings tested in this study does not enhance the average heat transfer rate.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.7
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• pp.504-512
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• 2008

The characteristics of nonpremixed oxy-fuel flame in a multi-jet burner were experimentally and numerically investigated. The overall flow rate of fuel and oxygen was fixed, and the oxygen feeding ratio (OFR) was varied by 0.25, 0.5, and 0.75. The results of numerical simulation were compared with the measured results which are temperature profile and direct flame observation. The probability density function (PDF) model was applied accounting to the description between turbulence and chemistry, and standard ${\kappa}-{\varepsilon}$ model was used for turbulent flow field. Equilibrium assumption is very reasonable due to fast chemistry of the oxy-fuel combustion. Thus, the equilibrium calculation based on Gibbs free energy minimization was guaranteed to generate the solution of the oxy-fuel combustion. The result was obtained by numerical simulation. The predicted radial temperature profiles were in good agreement with the measured results. The flame length was shorten and was intensified with the decrease of OFR because the mixture of fuel and oxidizer are fast mixed and burnt. The maximum temperature became lower as the OFR increased, as a consequence of large flame surface area.

• Transactions of the Korean hydrogen and new energy society
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• v.30 no.6
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• pp.585-592
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• 2019

In this study, a flashing boiling phenomenon of pressurized water jet was numerically studied and validated against an experimental data in the literatures. The volume of fluid (VOF) technique was used to consider two-phase behavior of water, while the homogeneous relaxation model (HRM) model was used to provide the velocity of phase change. During the flashing boiling through a nozzle, a mach disk was observed near nozzle exit because of pressure drop resulting from two-phase under-expansion. The flashing jet structure, local distributions of temperature/vapor volume fraction/velocity, and position of the mach disk were examined as nozzle inlet temperature changed.

• Geomechanics and Engineering
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• v.32 no.3
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• pp.293-305
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• 2023

To ensure the safety of underground infrastructures, ground can sometimes be first treated by cement slurry and then stabilized using artificial ground freezing (AGF) technique before excavation. The hydration heat produced by cement slurry increases the soil temperature before freezing and results in an extension of the active freezing time (AFT), especially when the Metro Jet System (MJS) treatment is adopted due to a high cement-soil ratio. In this paper, by taking advantage of an on-going project, a case study was performed to evaluate the influence of MJS and AGF on the ground temperature variation through on-site measurement and numerical simulation. Both on-site measurement and simulation results reveal that MJS resulted in a significant increase in the soil temperature after treatment. The ground temperature gradually decreases and then stabilized after completion of MJS. The initiation of AGF resulted in a quick decrease in ground temperature. The ground temperature then slowly decreased and stabilized at later freezing. A slight difference in ground temperature exists between the on-site measurements and simulation results due to limitations of numerical simulation. For the AGF system, numerical simulation is still strongly recommended because it is proven to be cost-effective for predicting the ground temperature variation with reasonable accuracy.

• Transactions of the Korean hydrogen and new energy society
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• v.16 no.1
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• pp.1-8
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• 2005

Transition of momentum-controlling hydrogen jet to buoyant jet is experimentally investigated in order to develop a prediction model for the moving trajectory of hydrogen leaked from hydrogen devices. In the experiments, room-temperature helium, that has a similar density to the hydrogen leaked from high pressure tank, is horizontally injected through a 4mm tube and its moving trajectory is visualized by the shadowgraph method. The moving trajectories are found to be parabolic, thereby exhibiting increasing influence of the buoyancy. In analyzing the experimental results, the vertical movement is assumed to be controlled by the buoyancy while the horizontal movement is controlled by the air entrainment caused by the initial momentum. The resealing based on this assumption yields a single curve fitting to the all experimental results.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.7 s.250
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• pp.656-662
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• 2006

The effects of concave hemispherical surface with inclined angle on the local heat transfer from a turbulent round jet impinging were experimentally investigated using transient liquid crystal method. This method suddenly exposes a preheated wall to an impinging jet and then the video system records the response of liquid crystals for the measurement of the surface temperature. The Reynolds numbers were used 11000, 23000 and 50000, nozzle-to-surface distance ratio from 2 to 10 and the surface angles $\alpha=0^{\circ},\;15^{\circ},\;30^{\circ}\;and\;40^{\circ}$. Correlations of the stagnation point Nusselt number according to Reynolds number, jet-to-surface distance ratio and dimensionless surface angle are investigated. In the stagnation point, in term of $Re^n$, n ranges from 0.43 in case of $2{\leq}L/d\leq6$ to 0.45 in case of $6. The maximum Nusselt number occurs in the direction of upstream. The displacement of the maximum Nusselt number from the stagnation point increases with increasing surface angle or decreasing nozzle-to-surface distance. The maximum displacement is about 0.7 times of the jet nozzle diameter.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.4
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• pp.371-380
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• 2000

The turbulent heat transfer from a round oblique impinging jet on a concave surface were experimentally investigated. The transient measurement method using liquid crystal was used in this study. In this measurement, a preheated wall was suddenly exposed to an impinging jet while recording the response of liquid crystals to measure surface temperature. The Reynolds numbers were 11000, 23000 and 50000, nozzle-to-surface distance ratio was from 2 to 10 and the surface angles were a =$0^{\circ}\;15^{\circ},\;30^{\circ}and\;40^{\circ}$. Correlations of the stagnation point Nusselt numbers with Reynolds number, jet-to-surface distance ratio and dimensionless surface angle, which account for the surface inclined angle, are presented. The maximum Nusselt numbers, in this experiment, occurred in the direction of upstream. The displacement of the maximum Nusselt number from the stagnation point increases with increasing surface angle or decreasing nozzle-to-surface distance. In this experiment, the maximum displacement is about 0.7 times of the jet nozzle diameter when surface curvature, D/d is 10.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.2
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• pp.218-225
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• 1999

Flow visualization study has been conducted to simulate the turbulent dispersion behavior of a crossflow jet physically under the conditions of various thermal stratification in a wind tunnel. A smoke jet with the constant ratio of the jet to freestream velocity is injected normally to the cross flow of the thermally stratified wind tunnel(TSWT) for flow visualization. The typical natures of the smoke dispersion under different thermal stratifications such as neutral, weakly stable, strongly stable, weakly unstable, strongly unstable and inversion layer are successfully reproduced in the TSWT. The Instantaneous velocity and temperature fluctuations are measured by using a cold and hot-wire combination probe. The time averaged dispersion behaviors, the centerline trajectories, the spreading angles and the virtual origins of the cross jet are deduced from the edge detected images with respect to the stability parameter. All the general characteristics of the turbulent dispersion behavior reveal that the definitely different dispersion mechanisms are inherent in both stable and unstable conditions. It is conjectured that the turbulent statistics obtained in the various stability conditions quantitatively demonstrate the vertical scalar flux plays a key role in the turbulent dispersion behavior.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.06a
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• pp.195-199
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• 2005

As vehicles are recently becoming more important in our life, the study for engine capacity has been conducted for many years. Specially, the study on lubrication in the engine is needed to develop engine capacity. The role of lubrication is to reduce fraction, manage the temperature and protect from corrosion etc. At the view point of the engine, lubrication and cooling of the engine have an effect on the life and efficiency, so we have to study this problem. Ball check valve is located in the inlet of the Oil Jet. Ball check valve is used to control the flow rate of the engine oil, which cools and lubricates the engine. Flow rate at the oil jet is very important, so the study for this problem is needed to conduct researches. The point of this study is to compute the flow rate and the flow in oil jet. The results of this study is that the mass flow rate is satisfied with the research which is obtained at the experiment.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.3
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• pp.359-364
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• 2004

For the development of high efficiency and low emission combustion systems, high temperature air combustion technology has been tested by utilizing preheated air over 1100 K and exhaust gas recirculation. In this system, combustion air is diluted with large amount of recirculated exhaust gases, such that the oxygen concentration is relatively low in the reaction zone, leading to low flame temperature. Since, the temperature fluctuations and sound emissions from the flame are small and flame luminosity is low, the combustion mode is expected to be flameless or mild combustion. Experiment was performed to investigate the turbulent flame structure and NO$_x$ emission characteristics in the high temperature air combustion focused on coflowing jet diffusion flames which has a fundamental structure of many practical combustion systems. The effect of turbulence has also been evaluated by installing perforated plate in the oxidizer inlet nozzle. LPG was used as a fuel. Results showed that even though NO$_x$ emission is sensitive to the combustion air temperature, the present high temperature air combustion system produce low NO$_x$ emission because it is operated in low oxygen concentration condition by the high exhaust gas recirculation.