• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.5
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• pp.329-337
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• 2016

As a turbulence-enhancing device, a mixing vane, which is installed at a spacer grid of the fuel assembly, plays an important role in improving convective heat transfer by generating either swirl flow in the subchannels or cross flow between the fuel rod gaps. Therefore, both the geometric configuration and the arrangement pattern of a mixing vane are important factors in determining the performance of a mixing vane. In this study, in order to examine the flow-distribution features inside a $5{\times}5$ fuel assembly with split-type mixing vanes, which was used in the benchmark calculation of the OECD/NEA, we conduct simulations using the commercial computational fluid dynamics software, ANSYS CFX R.14. We compare the predicted results with measured data obtained from the MATiS-H (Measurement and Analysis of Turbulent Mixing in Subchannels-Horizontal) test facility. In addition, we discuss the effect of the split-type mixing vanes on the flow pattern inside the fuel assembly.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.2
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• pp.129-138
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• 2010

Technical ceramics, due to their unique physical properties, are excellent candidate materials for engineering applications involving extreme thermal and chemical environments. When ceramics are rapidly cooled, they receive thermal shock. The thermal shock parameter is defined as the critical temperature difference. The critical temperature difference for ceramic parts is influenced by its size, the convective heat transfer coefficient, etc. The thermal shock for a component is analyzed by using the transient thermal stress. If the transient thermal stress exceeds the modulus of rupture (MOR), cracking by thermal shock is initiated. The critical temperature difference for water is less than the critical temperature difference for air. The three-way catalyst substrate used in this study has an adequate performance against thermal shock because its radial and axial temperature differences existed below the critical temperature differences.

• Journal of Energy Engineering
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• v.7 no.1
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• pp.113-121
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• 1998

In natural convection flows, the fluid velocities are highly dependent on the thermal field and property variations can have a strong effect on both the flow and thermal fields. To examine the effect of property variations, at first, numerical analyses covering wide range of the Prandtl number under the same Rayleigh numbers have been carried out. Next, we have modeled the viscosity and thermal conductivity as parabolic functions of temperature and a comprehensive set of numerical solutions have been obtained to understand the effect. The Prandtl number dependence of Nusselt number is fairly strong even though the effect is still weak compared to the Rayleigh number dependence. When thermophysical properties are dependent on temperature, the flow field showed a fairly weak variation except near boundaries, whereas the temperature field is strongly affected, especially by the temperature dependent thermal conductivity.

• Nuclear Engineering and Technology
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• v.23 no.2
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• pp.183-199
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• 1991

Transient response of temperature distributions in a Pressurized Water Reactor (PWR) pressurizer vessel wall for the Inadvertent Auxiliary Spray transient has been analyzed with conservatism accounted for the resulting thermal stresses in the regions of the vessel wall which are wetted by the spray water droplets. In order to determine the forced convective heat transfer coefficient at the inner boundary surface of vessel wall where the droplets impinge on and flow down, the transient temperatures of spray droplets when they reach the inner surface of the vessel wall after travelling from the spray nozzle through the pressurizer interior space occupied with the saturated steam-noncondensable hydrogen gas mixture have been predicted. The transient temperature distributions in the vessel wall have been obtained by using the finite element method, and the typical results have been provided. It has been shown that the results of thermal analysis are consistent with representation of the input transient and have plausible physical meaning.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.33 no.6
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• pp.375-382
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• 2020

Owing to the rapid development of infrared guided weapon systems, the threat to aircraft survivability is constantly increasing, and research on infrared stealth technologies are being conducted to ensure aircraft survival. In this study, we analyze the minimum infrared signature of an aircraft according to its flight altitude by considering the characteristics of infrared guided missiles, which detect the contrast signature between the aircraft and background. We conducted computational fluid dynamics simulations for the convective coefficient, and heat transfer simulations were performed considering convection, conduction, and radiation for flight conditions. Thus, we obtained the surface temperature distribution of the aircraft and analyzed the aircraft infrared signature based on the flow characteristics around it. Furthermore, the optimum emissivity for the minimum infrared signature was derived, and the effect of the infrared signature was analyzed when this optimum emissivity was applied to the fuselage surface for each flight condition.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.10
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• pp.1161-1170
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• 2011

This paper presents a solution to the inverse problem for the service boundary conditions of thermal-flow and structure analysis in a catalyst substrate. The exhaust-gas purification efficiency of a catalyst substrate is influenced by the shape parameter, catalyst ingredients and so on and is estimated by the thermal flow uniformity. The formulations of the inverse problem of obtaining the thermal-flow parameters (inlet temperature, velocity, heat of reaction, convective heat-transfer coefficient) and the direct problem of estimating from a given outlet temperature distribution are described. An experiment was designed and the response-surface optimization technique was used to solve the proposed inverse problem. The temperature distribution of the catalyst substrate was obtained by thermal-flow analysis for the predicted thermal-flow parameters. The thermal stress and durability assessments for the catalyst substrate were performed on the basis of this temperature distribution. The efficiency and accuracy of the inverse approach have been demonstrated through the achievement of good agreement between the thermal-flow response surface model and the results of experimental vehicle tests.

• Proceedings of the SAREK Conference
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• 2007.11a
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• pp.570-575
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• 2007

The thermal performance of the air receiver filled with porous material for 5kWt dish solar collector installed in Inha University, Korea, is experimentally investigated. The diameter of the parabolic dish is 3.2 m, and its focal length is 2 m. It consists of 10 small pieces of glasses which have their own curvatures, and the effective reflecting area is 5.9 m2. The reflectivity of the glass is 0.95, and the thermal capacity of the system is about 5 kW thermal. The aperture diameter of the cylindrical-shape receiver which is made of stainless steel is 100 mm, and the height is 210 mm. A quartz window is installed at the receiver aperture to minimize the convective heat loss and prevent air leakages. In order to increase the heat transfer area, porous material (nickel-alloy) is inserted into the receiver. Air flows into the upper part of the receiver, which is the opposite side of the aperture. After the air flows through the inside receiver, that goes out of the receiver through 3 exits which are located near the aperture. The volumetric flow rates of air are varied from 600 to 1200 L/min. The thermal efficiency of the receiver ranges from 82% - 92% depending upon the flow rate. The results show that the system efficiency and receiver efficiency increase as the volume flow rate increases as expected. These results from the experiment will be useful for the applications to air heating receivers and solar reactors.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.39 no.4
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• pp.309-316
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• 2015

Numerical analysis and experimental verification of a thermal liquid mass flow meter (LMFM) were performed. The configuration of the LMFM was the same as a gas mass flow meter (GMFM), but the opposite results in temperature difference between upstream and downstream thermistors occurred. In the case of the gas, the convection depending on the flow of thermal mass was small and comparable to the conduction through the sensor tube wall. The temperature difference was proportional to the mass flow rate due to their interaction. For the liquid flow, the convection overwhelmed the wall conduction because of the large flow of thermal mass caused by high density. The temperature difference in this case was inversely proportional to the mass flow rate. The tube diameter and heater wiring width are important design parameters, and the optimized sensor can be used to measure and control the infinitesimal liquid flow rate.

• Journal of Advanced Marine Engineering and Technology
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• v.41 no.3
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• pp.182-190
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• 2017

All liquids contain a small amount of gaseous components and the amount of gases dissolved in a liquid is in accordance with Henry's Law. In a multi-stage thermal-type seawater desalination plant, as the supplied seawater undergoes variations in temperature and pressure in each evaporator, the gases dissolved in the seawater are discharged from the liquid. The discharged gases are carbon dioxide, nitrogen, oxygen, and argon, and these emitted gases are non-condensable. From the viewpoint of convective heat transfer, the evaluation of non-condensable gas released during a vacuum evaporation process is a very important design factor because the non-condensable gases degrade the performance of the cooler. Furthermore, in a thermal-type seawater desalination plant, most evaporators operate under vacuum, which maintained through vacuum system such as a steam ejector or a vacuum pump. Therefore, for the proper design of a vacuum system, estimating the non-condensable gases released from seawater is highly crucial. In the study, non-condensable gases released in a thermal-type seawater desalination plant were calculated quantitatively. The calculation results showed that the NCG releasing rate decreased as the stage comes getting a downstream and it was proportional to the freshwater production rate.

• Solar Energy
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• v.14 no.2
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• pp.75-90
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• 1994

Thermal energy transport in a two-dimensional horizontal and vertical channel with an isothermal rectangular beam attached to one adiabatic wall is investigated from the numerical solution of Navier-Stokes and energy equations. The solutions have been obtained for dimensionless aspect equations. The solutions have been obtained for dimensionless aspect ratios of beam, H/B=$0.25{sim}4$, Reynolds numbers, Re=$50{\sim}500$ and Grashof numbers, Gr=$0{\sim}5{\times}10^4$. The mean Nusselt number, $\overline{Nu}$ for horizontal and vertical channels shows same value at Gr=0 and increases as Gr increases and decreases as H/B increases at Re=100. $\overline{Nu}$ of vertical channel shows higher in $0.25{\leq}H/B<1.1$ and lower in $1.1{\leq}H/B{\leq}4.0$ than that of horizontal channel at $Gr=10^4$, Re=100. $\overline{Nu}$ of vertical channel shows higher in $0.25{\leq}H/B<1.1$ and lower in $1.1{\leq}H/B=1.0$ than that of horizontal channel at Re=100, $0<Gr{\leq}5{\times}10^4$. A comparison between the experimental and numerical results shows good agreement.