• Journal of the Korea Computer Graphics Society
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• v.29 no.3
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• pp.93-103
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• 2023

The problem of reconstructing three-dimensional models of people and objects from color and depth images captured by low-cost RGB-D cameras has long been an active research area in computer graphics. Color and depth images captured by low-cost RGB-D cameras are represented as point clouds in three-dimensional space, which correspond to discrete values in a continuous three-dimensional space and require additional surface reconstruction compared to rendering using polygonal models. In this paper, we propose an effective ray-tracing based technique for visualizing point clouds rather than polygonal models. In particular, our method shows the possibility of an effective rendering method even in mobile environment which has limited performance due to processor heat and lack of battery.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.5
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• pp.327-333
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• 2011

In the present work, a new freeze protection method has been proposed for a natural circulation system of solar water heater. Though electrothermal wire is popularly used for the purpose, there are freezing troubles by wire cut-off and shortage of excessive electric power consumption. In the experimental device, hot water in storage tank was used to heat the outlet pipe from the tank if the pipe surface temperature falls lower than a set point. The cold water pipe to the storage tank was installed to directly contact the hot water pipe surface temperature rose by transferred heat.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.6
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• pp.859-867
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• 2002

Radiative transfer in energy systems such as furnaces, combustors, boilers and high temperature machineries is a significant mode of heat transfer. Although there are many solution schemes suggested for analysis of radiative transfer in multi-dimensional systems, the applicabilities and accuracies of these schemes have not fully tested for nongray gases. Especially reference data for enclosures of non-orthogonal shapes are not yet enough. In this paper we present some precise radiative transfer solutions for a black walled 3-dimensional cylindrical system filled with nongray gases. The SNB(statistical narrow band) model and the ray-tracing method with the T$_{N}$ quadrature set are used for finding nongray solutions. Although the solution method used in this study is not suitable for engineering purposes, the resulting solutions are proved to be quite accurate and can be regarded as the exact solutions and the results presented in this paper can be used in developing various solution schemes fur radiative transfer by real gas mixtures.s.

• Fire Science and Engineering
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• v.28 no.1
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• pp.52-57
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• 2014

In this paper, the unsteady incompressible Navier-Stokes equations coupled with energy equation were solved to find out the optimal location of electrical heat trace for anti-freeze of water inside the pipe for fire protection. Since the conduction equation of pipe was coupled with the natural convection of water, the analysis of conjugate heat transfer was conducted. A commercial code (ANSYS-FLUENT) based on SIMPLE-type algorithm was used for investigating the unsteady flows and temperature distributions in water region. From the numerical experiments, the isotherms and the vector fields in water region were obtained. Furthermore, it was found that the lowest part of the pipe cross-section was an optimal position of electrical heat trace assuming the constant thermal expansion coefficient of water since the minimum temperature of the water with the position is higher than those with the other positions.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.25 no.5
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• pp.289-296
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• 2013

A near infrared (NIR) heating system has advantages over the conventional convection-based systems, in terms of heating uniformity and energy efficiency. When it is over-heated during its operation, the radiation lamp gets blackened, and the life of the radiation module becomes severely limited. The heat transfer system in the module is based on a high operating-temperature, and the radiation makes it difficult to analyze in detail the reliability issue, with an experimental approach alone. We developed a numerical heat-transfer model of the NIR heating system. We applied a ray-tracing method on the radiative heat transport, and a finite volume method on the conductive and convective systems, respectively. The cooling performance of the system is presented, based on the energy and flow distributions in the module. The factors that directly affect the module life are analyzed, such as the surface temperatures of the lamp glass and the reflector, and design improvements are discussed.

• Fire Science and Engineering
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• v.29 no.6
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• pp.33-39
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• 2015

In this paper, a numerical experiment was conducted to find out the optimal location of electrical heat trace for anti-freeze of water inside the CPVC pipe for fire protection. The unsteady incompressible Navier-Stokes equations coupled with energy equation were solved. Since the conduction equation of pipe was coupled with the natural convection of water, the analysis of conjugate heat transfer was conducted. A commercial code (ANSYS-FLUENT) based on SIMPLE-type algorithm was used for investigating the unsteady flows and temperature distributions in water region. From the present numerical experiment, it has been found that the vector field of water inside the PVC pipe is opposite to the case of steel because of the huge difference of material properties of the two pipes. Furthermore, it was found that the lowest part of the pipe was an optimal position for electrical heat trace since the minimum water temperature of the case was higher than those of the other cases.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.50 no.1
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• pp.67-74
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• 2014

Most of steam power plants in Korea are using the method of heating the feed water whenever the ambient temperature around the power plant area below $5^{\circ}C$ to prevent freezing water flowing in the pipe in winter time. But this kind of heat supplying system is not useful to save energy. If we take the method that the temperature of the each pipe is controled by direct measure of temperature by attaching sensor on the outside surface of the feed water tubes, then we can expect that a plenty of energy can be saved. In this study, the computer simulation is used to compare the energy consumption loads of both systems. Energy saving rate is calculated for the location of Incheon area in winter season. Four convection heat transfer coefficients for the ambient air and three initial flowing water temperature inside the tube were used. The result shows that the temperature control system using sensor represents more than 95% of energy saving rate in Incheon area. Even in the severe January weather condition, the energy saving rate is almost 75% in two days basis and even 83% in one day basis.

• Computers and Concrete
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• v.20 no.5
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• pp.529-537
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• 2017

Excessively elevated temperature can lead to cracks in prestressed concrete (PC) continuous bridge with box girder on the pier top at cement hydration age. This paper presents a case study for evaluating the behavior of PC box girder during the early hydration age using a two-stage computational model, in the form of computer program ANSYS, namely, 3-D temperature evaluation and determination of mechanical response in PC box girders. A numerical model considering time-dependent wind speed and ambient temperature in ANSYS for tracing the thermal and mechanical response of box girder is developed. The predicted results were compared to show good agreement with the measured data from the PC box girder of the Zhaoshi Bridge in China. Then, based on the validated numerical model three parameters were incorporated to analyze the evolution of the temperature and stress within box girder caused by cement hydration heat. The results of case study indicate that the wind speed can change the degradation history of temperature and stress and reduce peak value of them. The initial casting temperature of concrete is the most significant parameter which controls cracking of PC box girder on pier top at cement hydration age. Increasing the curing temperature is detrimental to prevent cracking.

• 한국태양에너지학회:학술대회논문집
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• 2009.11a
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• pp.259-264
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• 2009

Most of the fossil power plants firing lower grade coals are challenged with maintaining good combustion conditions while maximizing generation and minimizing emissions. In many cases significant derate, availability losses and increase in unburned carbon levels can be attributed to poor combustion conditions as a result of poorly controlled local fuel and air distribution within the boiler furnace. The poor combustion conditions are directly related to the gas flow deviation in upper furnace and convection tube-bank but a less reported issue related to in large-scale oppose wall fired boilers. In order to develop a on-line combustion monitoring system and suggest an alternative heat flux estimation method at tube bank, which is very useful information for boiler design tool and blower optimizing system, field test was conducted at operating power boiler. During the field test the exhaust gases' temperature and tube metal temperature were monitored by using a spatially distributed sensors grid which located in the boiler's high temperature vestibule region. At these locations. the flue gas flow is still significantly stratified, and air in-leakage is minimal which enables tracing of poor combustion zones to specific burners and over-fire air ports. Test results showed that the flue gas monitoring method is more proper than metal temperature distribution monitoring for real time combustion monitoring because tube metal temp. distribution monitoring method is related to so many variables such as flue gas, internal flow unbalance, spray etc., Heat flux estimation at the tube bank with flue gas temp. and metal temp. data can be alternative method when tube drilling type sensor can't able to use.

• 한국연소학회:학술대회논문집
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• 2012.11a
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• pp.101-103
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• 2012

Characteristic of aluminum ignition under high temperature and high pressure is studied using lasers. The laser ablation method is used to generate aluminum particles exposed to a high pressure by using a nanosecond pulsed laser where the range of ablation pressure varies between 0.35 and 2.2 GPa. A $CO_2$ laser is used to supply radiative heat to the aluminum target surface for providing high temperature ranging between 5000~9300 Kelvin. The ignition is confirmed using spectroscopy analysis of AlO vibronic band 484 nm wavelength. Also the radiative temperature is measured in various high pressure range for tracing the ignition temperature in high pressure conditions.