• Transactions of the Korean Society of Automotive Engineers
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• v.9 no.4
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• pp.10-17
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• 2001

The performance of a radiator is generally determined using a wind tunnel, in which the air velocity is uniform. However, when it is installed in a car, the distribution of the air velocity becomes nonuniform due to front-end openings, cross members, and horns etc., resulting in lower performance. In this study, several underhood flow simulations have been first performed to get flow rates and velocity distributions over the radiator. Secondly heat release rates are calculated by both a performance curve and a radiator model. Finally, using an engine cooling system simulator, radiator-top-tank temperature is predicted and the variations of heat release rate and radiator-top-tank temperature with nonuniformity of air velocity distributions are analyzed. The results show that the current engine cooling model successfully accounts for the nonuniformity effects that should be considered for higher accuracy in predicting engine cooling performance.

• International Journal of Air-Conditioning and Refrigeration
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• v.11 no.1
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• pp.17-23
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• 2003

A design procedure for cooling towers was set up using the Merkel theory In the past, the design data could be different depending on the characteristic curve that the engineer adopted. Therefore, consistent and reasonable criteria are required, which are based on the exact information of the cooling tower performance. In this study, analysis program for both the design and off-design for a counterflow-type cooling tower was developed and verified by comparing with experimental data. The off-design performance with various operating conditions was analyzed, as well.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.1
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• pp.55.2-56
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• 2021

The progenitor of Type Ia supernovae (SNe Ia) is mainly believed to be a close binary system of acarbon-oxygen white dwarf (CO WD) and non-degenerate companion (single degenerate) or another WD (double degenerate). However, it is unclear which system is more prevalent. Here, we present a high cadence optical/Near-IR light curve of normal but slightly faint type Ia SN 2019ein from IMSNG project. We fit the early light curve (t <+8.3 days from the first detection) with various models to find the shock-heated cooling emission from SN ejecta-companion interaction. No significant shock-heated cooling emission is found, from which we constrain the progenitor star size as the following. The upper limit (R_upper,*) of the companion size in R-band is ~0.2R_⊙ when forcing the first light time (t_fl) to have one value and ~0.9R_⊙ when using the mean value of tfl from the fitting in each band. Assuming the source of the I-band curve is almost powered from the radioactive decay, we obtained R_upper,*~1.2R_⊙. The early B-V color curve is in agreement with the model color curve of the 2M_⊙ main sequence companion. These results allow us to at least rule out large stars like red giants as a companion star of the binary progenitor system of this supernova. B-R and V-R color do not show any significant signs of a red bump, which shows a thin helium shell (MHe<0.1M_⊙) for the sub-Mch WD (double detonation model). In addition, we estimated the distance to NGC 5353 as 37.098±0.028Mpc.

• Journal of Powder Materials
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• v.3 no.1
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• pp.25-32
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• 1996

Flying and solidification behaviors of the particles manufactured by centrifugal atomization were investigated. Both models were solved by the explicit FDM. Flying calculation supported the experimental results that the finer particles flied shorter than coarser particles and that particles flied shorter for lower rotation velocity than for higher velocity. Cooling curve and dendrite arm spacing were predicted by use of heat transfer analysis.

• Journal of the Korean Society for Heat Treatment
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• v.5 no.3
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• pp.171-178
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• 1992

The effect of nozzle characterristics on the mist-cooling heat transfer was investigated under the various flow conditions. Two different types of twin fluid nozzle were used, one is a $90^{\circ}$ angle tip nozzle with needle and the other is a $90^{\circ}$ angle tip non-needle nozzle. The cooling rate from the heated surface was measured and obtained the boiling curve as a function of surface temperature. An immersion sampling was employed for the measurement of droplet size of the spray. As a result of this experiment, the liquid sheet type nozzle shows better atomization when the mass ratio Mr>2.0, and collects more liquid droplets on the heated surface that results in better cooling effect. It was found that the maximum heat flux and heat transfer coefficient increased with increase in the volumetric flow rate, whereas the maximum heat flux decreased with increase in spray distance. The cooling effect depends upon the amount of collected droplet and droplet size, but it strongly depends upon the amount of collected droplet.

• Journal of the Korean Society for Heat Treatment
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• v.4 no.3
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• pp.39-46
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• 1991

The effects of austenitizing temperatures and times and cooling rate on the characteristics of continuous air cooling have been investigated for 0.3%C-Mn steels microalloyed with vanadium. Transformation start temperatures have been found to be measured from temperature-time curve directly obtained with continuous air cooling and to decrease with increasing austenitizing temperature, cooling rate and Mn contents. The coarsening behavior of austenite grain size has been measured to abnormally grow at $1050^{\circ}C$ and rapidly grow at $1200^{\circ}C$. It has been found that the volume fraction of pearlite was linealy proportional to the reciprocal square root of austenite grain size. The hardness has been measured to increase with increasing cooling rate up to $250^{\circ}C/min.$ and to remain relatively unchanged in the range of $250{\sim}400^{\circ}C/min.$ showing that hardness valves for steel with a higher Mn content increase more than those for steel with a lower Mn content. The impact property has been found to decrease with increasing of austenite grain size but does not linealy change with the reciprocal square root of austenite grain size.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.8
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• pp.562-570
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• 2011

In this research, an experimental study is performed to investigate the effects of system operating variables on the cooling and heating characteristics of heat pump system using geothermal heat source and carbon dioxide as a refrigerant. System variables analyzed include compressor frequency, electronic expansion valve opening, refrigerant charge, secondary fluid temperature and flow rate. Results show that optimum refrigerant charge and electronic expansion valve opening position exist at the maximum point of COP curve, and both cooling and heating capacity increase but COPs decrease with the increase of compressor frequency. The change of a secondary fluid temperature leads to variation of overheat area and enthalpy difference in the evaporator and gas cooler. which again results in considerable variations of cooling and heating capacity and COP. In the case of effects of secondary water fluid flow rate, both cooling capacity and COP increase with the increase of secondary flow in evaporator or gas cooler, whereas heating capacity and COP decrease with the increase of flow rate in gas cooler.

• International Journal of CAD/CAM
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• v.12 no.1
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• pp.9-19
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• 2012

Generation of optimum planar B-spline curve in terms of minimum deviation and required fairness to approximate a target shape defined by a strip-shaped unorganized 2D point cloud is studied. It is proposed to use the location of control points as variables within the geometric optimization framework of point distance minimization. An adaptive simulated annealing heuristic optimization algorithm is developed to iteratively update an initial approximate curve towards the target shape. The new implementation comprises an adaptive cooling procedure in which the temperature change is adaptively dependent on the objective function evolution. It is shown that the proposed method results in an improved convergence speed when compared to the standard simulated annealing method. A couple of examples are included to show the applicability of the proposed method in the surface model reconstruction directly from point cloud data.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.34 no.2
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• pp.41-47
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• 2024

In this study, the resistance characteristics of semi-insulating SiC single crystals grown using the PVT method were investigated, considering the purity level of SiC source powders used in PVT growth and the cooling procedure after crystal growth. Two β-SiC powders with different purities were employed, and the cooling rate after growth was adjusted to achieve various resistance values. 4-inch HPSI-SiC ingots were grown using the PVT method, utilizing SiC powders with low nitrogen concentration and relatively high nitrogen concentration. These ingots were then subjected to different cooling procedures to modify the cooling rate. Transmission/absorption spectra and crystal quality of the grown crystals were analyzed through UV/VIs/NIR spectroscopy and X-ray rocking curve analysis, respectively. Additionally, electrical properties were investigated through non-contact resistivity analysis to identify the dominant factors influencing resistivity properties.

• Advances in concrete construction
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• v.14 no.1
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• pp.57-70
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• 2022

The spiral case concrete (SCC) used in the underground powerhouse of large hydropower stations is complex, difficult to pour, and has high requirements for temperature control and crack prevention. In this study, based on the closed-loop control theory of "multi-source sensing, real analysis, and intelligent control", a new intelligent cooling control system (ICCS) suitable for the SCC is developed and is further applied to the Wudongde large-scale underground powerhouse. By employing the site monitoring data, numerical simulation, and field investigation, the temperature control quality of the SCC is evaluated. The results show that the target temperature control curve can be accurately tracked, and the temperature control indicators such as the maximum temperature can meet the design requirements by adopting the ICCS. Moreover, the numerical results and site investigation indicate that a safety factor of the spiral case structure was sure, and no cracking was found in the concrete blocks, by which the effectiveness of the system for improving the quality of temperature control of the SCC is verified. Finally, an intelligent cooling control procedure suitable for the SCC is proposed, which can provide a reference for improving the design and construction level for similar projects.