• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.4
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• pp.94-105
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• 2021

A graphical user interface (GUI) program for steam tracing system selection was developed by using a theoretical model. We derived the model on the basis of the one-dimensional heat transfer theory of conduction and convection through a composite wall. Computational fluid dynamics (CFD) and experiments were performed for validation at steam temperatures of 120.4[℃] and 158.9[℃]. The temperature of a pipe's outer surface obtained through CFD matched well with that predicted by the proposed model for both conditions. By contrast, the experiment results showed a small error at 120.4[℃] and a large error at 158.9[℃] because of the melting of the heat transfer compound and water phase transition. Thus, the steam temperature range of the proposed model is below 120.4[℃].

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.8
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• pp.945-956
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• 1999

This work reports a set of approximate analytical solutions describing the initial transient process of close-contact melting between a rectangular parallelepiped solid and a flat plate on which either constant temperature or constant heat flux is imposed. Not only relative motion of the solid block tangential to the heating plate, but also the density difference between the solid and liquid phase is incorporated in the model. The thin film approximation reduces the force balance between the solid weight and liquid pressure, and the energy balance at the melting front into a simultaneous ordinary differential equation system. The normalized model equations admit compactly expressed analytical solutions which include the already approved two-dimensional solutions as a subset. In particular, the normalized liquid film thickness is independent of all pertinent parameters, thereby facilitating to define the transition period of close-contact melting. A unique behavior of the solid descending velocity due to the density difference is also resolved by the present solution. A new geometric function which alone represents the three-dimensional effect is introduced, and its properties are clarified. One of the representative results is that heat transfer is at least enhanced at the expense of the increase in friction as the cross-sectional shape deviates from the square under the same contact area.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.9
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• pp.2353-2364
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• 1995

The ignition phenomena of a solid fuel plate of polymethyl-methacrylate(PMMA), which is vertically positioned and exposed to a thermal radiation source, is numerically studied here. A two-dimensional transient model includes such various aspects as thermal decomposition of PMMA, gas phase radiation absorption, gas phase chemical reaction and air entrainment by natural convection. Whereas the previous studies considers the problem approximately in a one-dimensional form by neglecting the natural convection, the present model takes account of the two-dimensional effect of radiation and air entrainment. The inert heating of the solid fuel is also taken into consideration. Radiative heat transfer is incorporated by th Discrete Ordinates Method(DOM) with the absorption coefficient evaluated using gas species concentration. The thermal history of the solid fuel plate shows a good agreement compared with experimental results. Despite of induced natural convective flow that induces heat loss from the fuel surface, the locally absorbed radiant energy, which is converted to the internal energy, is found to play an important role in the onset of gas phase ignition. The ignition is considered to occur when the rate of variation of gas phase reaction rate reaches its maximum value. Once the ignition takes place, the flame propagates downward.

• 한국연소학회:학술대회논문집
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• 2006.04a
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• pp.49-54
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• 2006

The present study conducted a numerical modeling on the diesel SCR (selective catalytic reduction) system using ammonia as a reductant over vanadium-based catalysts $(V_2O_5-WO_3/TiO_2)$. Transient modeling for ammonia adsorption/desorption on the catalyst surface was firstly carried out, and then the SCR reaction was modeled considering for it. In the current catalytic reaction model, we extended the pure chemical kinetic model based on laboratory-scale powdered-phase catalyst experiments to the chemico-physical one applicable to realistic commercial SCR reactors. To simulate multi-dimensional heat and mass transfer phenomena, the SCR reactor was modeled in two dimensional, axisymmetric domain using porous medium approach. Also, since diesel engines operate in transient mode, the present study employed an unsteady model. In addition, throughout simulations using the developed code, effects of space velocity on the DeNOx performance were investigated.

• Journal of Power System Engineering
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• v.9 no.2
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• pp.73-80
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• 2005

Both theoretical and experimental investigations were conducted to analyze defrosting behavior of a window heater operating in the low outdoor temperature($-20^{\circ}C$). To achieve this purpose, first a warm-chamber experiment($23^{\circ}C$) was performed to measure inner and outer surface temperature of the rear window(heated by the electric heater supplying 195 W) as functions of both time and position. Secondly, a cold chamber experiment was made to continuously record defrosting process of the frosted window. From the comparisons of the two experimental results, it was found that there was a similarity between the spatial distributions of both temperature and remaining frost. Thus, the temperature data from the warm-chamber experiments can be utilized to predict an expected zone covered with remaining frosts, and this approach can also be adopted in the inspection process in order to economically guarantee optimized performance of the window heater. Finally, an analytical model based on one-dimensional, steady-state heat transfer theories was proposed and successfully predicted the outer surface temperature of the rear window surrounded by cold air($-20^{\circ}C$) for the given operating conditions(heater power, inside and outside heat transfer coefficients, and surrounding air temperature, etc.).

• Nuclear Engineering and Technology
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• v.52 no.7
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• pp.1417-1428
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• 2020

The design of a nuclear reactor core requires basic thermal-hydraulic information concerning the heat transfer regime at which onset of nucleate boiling (ONB) will occur, the pressure drop and flow rate through the reactor core, the temperature and power distributions in the reactor core, the departure from nucleate boiling (DNB), the condition for onset of flow instability (OFI), in addition to, the critical velocity beyond which the fuel elements will collapse. These values depend on coolant velocity, fuel element geometry, inlet temperature, flow direction and water column above the top of the reactor core. Enough safety margins to ONB, DNB and OFI must-emphasized. A heat transfer package is used for calculating convection heat transfer coefficient in single phase turbulent, transition and laminar regimes. The main objective of this paper is to study the possibility of power upgrading of WWR-S research reactor from 2 to 10 MW_th. This study presents a one-dimensional mathematical model (axial direction) for steady-state thermal-hydraulic design and analysis of the upgraded WWR-S reactor in which two types of plate fuel elements are employed. FOR-CONV computer program is developed for the needs of the power upgrading of WWR-S reactor up to 10 MW_th.

• 한국신재생에너지학회:학술대회논문집
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• 2006.06a
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• pp.567-570
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• 2006

A numerical study has been carried out for a solar water heater which consists of double skin solar vacuum tubes. Water is heated as it flows through the coaxial fluid conduit inserted in each tube. The space between the exterior of the fluid conduit and the glass tube is tilled with antifreeze solution. This is to facilitate heat transfer from the solar heated absorber surface to water and to prevent the functional problems due to freezing in frigid weather conditions. A one-dimensional steady state model is fully described which will be used to develop three-dimensional model using STAR-CD. These models could be used efficiently in designing double skin solar collector tubes with different geometrical parameters other than those considered in the present analysis. Results show a good agreement when compared with other experimental data demonstrating the reliability of the one-dimensional model employed.

• Journal of the Korean Institute of Gas
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• v.7 no.4 s.21
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• pp.44-52
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• 2003

In this work dynamic heat transfer in a CPFS (cable penetration fire stop) system built in the firewall of nuclear power plants is three-dimensionally investigated to develop a test-simulator that can be used to verify effectiveness of the sealant. Dynamic heat transfer in the fire stop system is formulated in a parabolic PDE (partial differential equation) subjected to a set of initial and boundary conditions. First, the PDE model is divided into two parts; one corresponding to heat transfer in the axial direction and the other corresponding to heat transfer on the vertical planes. The first PDE is converted to a series of ODEs (ordinary differential equations) at finite discrete axial points for applying the numerical method of SOR (successive over-relaxation) to the problem. The ODEs are solved by using an ODE solver In such manner, the axial heat flux can be calculated at least at the finite discrete points. After that, all the planes are separated into finite elements, where the time and spatial functions are assumed to be of orthogonal collocation state at each element. The initial condition of each finite element can be obtained from the above solution. The heat fluxes on the vertical planes are calculated by the Galerkin FEM (finite element method). The CPFS system was modeled, simulated, and analyzed here. The simulation results were illustrated in three-dimensional graphics. Through simulation, it was shown clearly that the temperature distribution was influenced very much by the number, position, and temperature of the cable stream, and that dynamic heat transfer through the cable stream was one of the most dominant factors, and that the feature of heat conduction could be understood as an unsteady-state process.

• Transactions of the Korean hydrogen and new energy society
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• v.33 no.6
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• pp.808-818
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• 2022

In this research paper, we investigated the cryogenic line chill down characteristics of liquefied natural gas (LNG). A numerical analysis model was established and verified so that it can calculate the precise cooling characteristics of cryogenic fluid for the stable and safe utilization especially such as LNG and liquid hydrogen. The numerical modeling was programmed by C++ as an one-dimensional homogeneous model. The thermohydraulic cooling process was simulated using mass, momentum, energy conservation equations and appropriate heat transfer correlations. In this process, the relevant heat transfer correlations for nuclear boiling, transition boiling, film boiling, and single-phase heat transfer that can predict the experimental results were implemented. To verify the numerical modeling, several cryogenic line chill down experiments using LNG were conducted at the Korea Institute of Machinery & Materials (KIMM) LNG and Cryogenic Technology Center.

• 한국연소학회:학술대회논문집
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• 2006.04a
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• pp.181-188
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• 2006

Operation parameters for large scale industrial facility such as iron making plant are carefully selected through elaborate tests and monitoring rather than through a mathematical modeling. One of the recent progresses for better energy utilization in iron ore sintering process is the distribution pattern of fuel inside a macro particle which is formed with fines of iron ore, coke and limestone. Results of model tests which have been used as a basis for the improved operation in the field are introduced and a theoretical modeling study is presented to supplement the experiment-based approach with fundamental arguments of physical modeling, which enables predictive computation beyond the limited region of tests and adjustment. A single fuel particle model along with one-dimensional bed combustion model of solid particles are utilized, and thermal processes of combustion and heat transfer are found to be dominant consideration in the discussions of productivity and energy utilization in the sintering process.