• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.2
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• pp.185-192
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• 1999

Effective thermal conductivities and pressure-drop-related properties of aluminum foam metals have been measured. The effects of porosity and cell size in the aluminum foam metal are investigated in detail. The porosity of the foam metal, considered in the present study, varies from 0.89 to 0.96 and the cell size from 0.65㎜ to 2.5㎜. The effective thermal conductivity is evaluated by comparing the temperature gradient of the foam metal with that of the thermal conductivity-known material. The pressure drop in the foam metal is measured by a highly precise electric manometer while air is flowing through the aluminum foam metal in the channel. The results obtained indicate that the effective thermal conductivities are found to be increased with a decrease in the porosity while the effective thermal conductivities ire little affected by the cell size at a fixed porosity. However, the pressure drop is strongly affected by the cell size as well as the porosity. It is seen that the pressure drop is increased as the cell size becomes smaller, as expected. The minimum pressure drop is obtained in the porosity 0.94 at a fixed cell size. A new correlation of the pressure drop is proposed based on the permeability and Ergun's coefficient for the aluminum foam metal.

• Nuclear Engineering and Technology
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• v.48 no.2
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• pp.376-385
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• 2016

A hexagonally arrayed 37-pin wire-wrapped rod bundle has been chosen to provide the experimental data of the pressure loss and flow rate in subchannels for validating subchannel analysis codes for the sodium-cooled fast reactor core thermal/hydraulic design. The iso-kinetic sampling method has been adopted to measure the flow rate at subchannels, and newly designed sampling probes which preserve the flow area of subchannels have been devised. Experimental tests have been performed at 20-115% of the nominal flow rate and $60^{\circ}C$ (equivalent to Re ~ 37,100) at the inlet of the test rig. The pressure loss data in three measured subchannels were almost identical regardless of the subchannel locations. The flow rate at each type of subchannel was identified and the flow split factors were evaluated from the measured data. The predicted correlations and the computational fluid dynamics results agreed reasonably with the experimental data.

• The Transactions of the Korean Institute of Power Electronics
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• v.26 no.5
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• pp.357-363
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• 2021

Eco-friendly hybrid railroad propulsion system with fuel-cell and battery was suggested to reduce carbon dioxide gas and replace retired diesel railroads. Lithium-ion battery with high energy/power density and long lifetime is selected as the energy source at the battery side due to its excellent performance. However, the performance of lithium-ion batteries was affected by temperature, current rate, and operating condition. Temperature is known to be the most influential factor in changing battery parameters. In addition, appropriate thermal management is required to ensure the safe and effective operation of lithium-ion battery. Electro-thermal coupled model with varying parameter depends on temperature, and state-of-charge (SOC) is suggested to estimate battery temperature. The electric-thermal coupled model contains diffusion current using parameter identification by adaptive control algorithm when considering thermal diffusion effect. An experiment under forced convection was conducted using cylindrical cell and 18 parallel-connected battery module to demonstrate the method.

• Korean Journal of Materials Research
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• v.31 no.11
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• pp.642-648
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• 2021

The precipitation effect of Al-6%Si-0.4%Mg-0.9%Cu-(Ti) alloy (in wt.%) after various heat treatments was studied using a laser flash device (LFA) and differential scanning calorimetry (DSC). Solid solution treatment was performed at 535 ℃ for 6 h, followed by water cooling, and samples were artificially aged in air at 180 ℃ and 220 ℃ for 5 h. The titanium-free alloy Al-6%Si-0.4%Mg-0.9%Cu showed higher thermal diffusivity than did the Al-6%Si-0.4%Mg-0.9%Cu-0.2%Ti alloy over the entire temperature range. In the temperature ranges below 200 ℃ and above 300 ℃, the value of thermal diffusivity decreased with increasing temperature. As the sample temperature increased between 200 ℃ and 400 ℃, phase precipitation occurred. From the results of DSC analysis, the temperature dependence of the change in thermal diffusivity in the temperature range between 200 ℃ and 400 ℃ was strongly influenced by the precipitation of θ'-Al₂Cu, β'-Mg₂Si, and Si phases. The most important factor in the temperature dependence of thermal diffusivity was Si precipitation.

• Nuclear Engineering and Technology
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• v.54 no.10
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• pp.3928-3942
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• 2022

Thermal striping is a complex thermal-hydraulic phenomenon caused by fluid temperature fluctuations that can also cause high-cycle thermal fatigue to the structural wall of sodium-cooled fast reactors (SFRs). Numerical simulations using large-eddy simulation (LES) were performed to predict and evaluate the characteristics of the temperature fluctuations related to thermal striping in the upper internal structure (UIS) of the prototype generation-IV sodium-cooled fast reactor (PGSFR). Specific monitoring points were established for the fluid region near the control rod driving mechanism (CRDM) guide tubes, CRDM guide tube walls, and UIS support plates, and the normalized mean and fluctuating temperatures were investigated at these points. It was found that the location of the maximum amplitude of the temperature fluctuations in the UIS was the lowest end of the inner wall of the CRDM guide tube, and the maximum value of the normalized fluctuating temperatures was 17.2%. The frequency of the maximum temperature fluctuation on the CRDM guide tube walls, which is an important factor in thermal striping, was also analyzed using the fast Fourier transform analysis. These results can be used for the structural integrity evaluation of the UIS in SFR.

• Structural Engineering and Mechanics
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• v.91 no.4
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• pp.383-391
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• 2024

Conical shell is a common engineering structure, which is widely used in machinery, civil and construction fields. Most of them are usually exposed to external environments, temperature is an important factor affecting its performance. If the external temperature is too high, the deformation of the conical shell will occur, leading to a decrease in stability. Therefore, studying the thermal-post buckling behavior of conical shells is of great significance. This article takes graphene platelets reinforced metal foams (GPLRMF) conical shells as the research object, and uses high-order shear deformation theory (HSDT) to study the thermal post-buckling behaviors. Based on general variational principle, the governing equation of a GPLRMF conical shell is deduced, and discretized and solved by Galerkin method to obtain the critical buckling temperature and thermal post-buckling response of conical shells under various influencing factors. Finally, the effects of cone angles, GPLs distribution types, GPLs mass fraction, porosity distribution types and porosity coefficient on the thermal post-buckling behaviors of conical shells are analyzed in detail. The results show that the cone angle has a significant impact on the nonlinear thermal stability of the conical shells.

• Tunnel and Underground Space
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• v.25 no.2
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• pp.155-167
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• 2015

The thermal-hydrological-mechanical (T-H-M) behavior of rock mass surrounding a high-temperature cavern thermal energy storage (CTES) operated for a period of 30 years has been investigated by TOUGH2-FLAC3D simulator. As a fundamental study for the development of prediction and control technologies for the environmental change and rock mass behavior associated with CTES, the key concerns were focused on the hydrological-thermal multiphase flow and the consequential mechanical behavior of the surrounding rock mass, where the insulator performance was not taken into account. In the present study, we considered a large-scale cylindrical cavern at shallow depth storing thermal energy of $350^{\circ}C$. The numerical results showed that the dominant heat transfer mechanism was the conduction in rock mass, and the mechanical behavior of rock mass was influenced by thermal factor (heat) more than hydrological factor (pressure). The effective stress redistribution, displacement and surface uplift caused by heating of rock and boiling of ground-water were discussed, and the potential of shear failure was quantitatively examined. Thermal expansion of rock mass led to the ground-surface uplift on the order of a few centimeters and the development of tensile stress above the storage cavern, increasing the potential of shear failure.

• Journal of the Korean Ceramic Society
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• v.39 no.9
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• pp.890-895
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• 2002

Effect of the sintering time on the microwave dielectric properties of the layered Functionally Graded Materials(FGMs) of the Mg0.93Ca0.07TiO3(MCT) with (Ca0.3Li0.14Sm0.42)TiO3(CLST) ceramics was investigated. The dielectric constant of layered FGMs specimens showed a nearly constant value and did not change significantly with sintering time. The quality factor, however, was affected by the relative density and thermal stress developed in each dielectric layer. With an increase of the relative density and the decrease of the induced thermal stresses, quality factor of the layered FGMs specimens increased and the quality factor was incluenced sensitively by the change of compressive stress developed in MCT layers which had a lower thermal expansion coefficient than that of CLST. For the layered FGMs specimen sintered at 1300$^{\circ}C$ for 9h, the compressive stress developed in MCT layer showed the maximum value, which, in turn, the quality factor of the specimen was the minimum value.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.7
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• pp.709-716
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• 2009

Thermal condition according to the operation attitude of a satellite in orbit would be essential to be known because the orbit attitude is a dominant factor to affect satellite thermal design. In this paper, the change in space thermal environment and the thermal effect in thermal design are studied for a low earth orbit satellite according to the yaw motion. The present satellite retains sun-pointing attitude during daylight due to the fixed type solar arrays. And it also moves along the orbit with constant yaw motion in a longitudinal axis so that a star tracker which is a star sensor for satellite's attitude control always looks into the deep space. This attitude is considered in its better visibility to the stars for a successful mission operation. Also, it is required to access the corresponding thermal effects due to the yaw motion. Therefore, we try to verify these by the thermal analysis for the satellite thermal model with the yaw motion.

• Design & Manufacturing
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• v.12 no.1
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• pp.41-46
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• 2018

This study proves the causes of cylinder and piston jam by scratches which is the fatal problem of hydraulic breaker through the thermal analysis and thermal-structural coupled field analysis. The trouble from the scratch is a complex problem which can be caused by manufacturing process (this is an internal factor) and the users mistake or contamination in the hydraulic circuit (these are an external factor). Hence, it's not easy to investigate the causes, also hard to prevent the recurrence. In this reason, hydraulic breaker manufacturers are trying to improve the manufacturing process such as machining, heat treatment, grinding, cleaning, also to prevent the contamination in hydraulic circuit and to remove the remains. It's being managed thoroughly by manufacturers. This study shows the effect of the temperature rise by the frictional heat generated when the piston hits the tool on the hydraulic oil while the hydraulic breaker is operating, also the temperature distribution when it starts to affect main components of hydraulic breaker. The stress and the amount of deformation also could be found through thermal-structural coupled field analysis. It proved that the stress and deformation are proportionally increased according to the temperature rise in hit area, and it affects the cylinder and the viscosity of hydraulic oil inside the cylinder when it heats up beyond the certain temperature.