• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.21 no.10
• /
• pp.1303-1313
• /
• 1997

A micro-macroscopic analysis on the conduction-controlled directional casting of Al-Cu alloys is performed, in which emphases are placed on the microstructural features. In order to facilitate the solution procedure, an iterative micro-macroscopic coupling algorithm is developed. The predicted results show that the effect of finite back diffusion on the transient solidification process in comparison with the lever rule depends essentially on the initial concentration of an alloy. In the final casting, the eutectic fraction is distributed in an increasing-decreasing-increasing pattern, each mode of which is named the chill, interior and end zones. This nonuniformity per se suffices to justify the necessity of this work because it originates from the combined effects of finite back diffusion and cooling path-dependent nature of the eutectic formation. As the cooling rate is enhanced, not only the influence depths of boundaries narrow, but also the eutectic fractions in the chill and interior zones increase. In addition, it is revealed for the first time that the micro segregation band is formed in response to a sudden change in cooling rate during the directional casting. An increasing change creates an overshooting band in the eutectic fraction distribution, and vice versa.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2011.04a
• /
• pp.457-462
• /
• 2011

This paper presents a numerical investigation of deflagration to detonation transition (DDT) induced by shock wave and flame interaction in ethylene-air mixtures. Also shows the change of DDT triggering time by wall cooling effect. A model is consisted of the compressible reactive Navier-Stokes equations. And the effect of viscosity, thermal conduction, molecular diffusion, chemical reaction and wall effect are included. Using this model, the generation of hot spot by repeated shock and flame interaction, occurrence of detonation, and wall cooling effect of detonation confining boundaries are studied.

• Nuclear Engineering and Technology
• /
• v.56 no.3
• /
• pp.793-802
• /
• 2024

In the framework of the European project SAMOSAFER, this numerical study focuses on some thermal aspects of the Emergency Draining Tank (EDT) located underneath the core of a Molten Salt Reactor. In case of an emergency, this tank passively receives the liquid fuel salt and is designed to ensure a subcritical state. An important requirement is that the fuel does not overheat to maintain the EDT Hastelloy container integrity. The present EDT is based upon a group of hexagonal cooling assemblies arranged in a hexagonal grid and cooled down thanks to conduction through the inert salt layer up to an air flow in charge of removing the heat. This numerical thermal study relies on a conjugated heat transfer analysis coupling a Finite Element solid thermal code (SYRTHES) and two instances of a Finite Volume CFD codes (Code_Saturne). Calculations on an initial design suggest that a simple center airpipe flow is likely to not sufficiently cool the device. Alternative solutions have been evaluated. Introduction of fins to enhance the heat transfer do not bring a noticeable improvement regarding maximum temperature reached. However, a solution in which the central pipe air flow is replaced by several cooling channels located closer to the fuel is investigated and suggests a better cooling.

• The Journal of Korean Academy of Orthopedic Manual Physical Therapy
• /
• v.12 no.1
• /
• pp.37-43
• /
• 2006

PURPOSE: Previous studies have documented the lack of ultrasound's non-thermal effects on nerve conduction using frequencies of 1 MHz and 870 kHz. The purpose of this study was to determine the biophysical effects of continuous ultrasound on median local forearm temperature and motor nerve conduction velocities using frequencies of 3.0 MHz. SUBJECTS: Twelve healthy subjects (6 males, 6 females, age $22.30{\pm}2.41$ yrs, weight $61.33{\pm}10.16$ kg, height $167.58{\pm}8.04$ cm) without a history of neurological or musculoskeletal injury to their dominant arm volunteered for this study. METHODS AND MATERIALS: Each subject received a total of five treatments, one each at .0, 0.5, 1.0, 1.5, 2.0 W/$cm^2$ of 3 MHz continuous ultrasound on the anterior surface of the middle area of dominant forearm for 10 minutes. Dependent measures for forearm local temperature and median motor nerve conduction velocity (MNCV) were taken pretreatment and immediately post-treatment. One-way ANOVA were used for each dependent measure. RESULTS: The posttreatment forearm local temperature were differed significantly (p<0.001) between intensities of ultrasound. The posttreatment forearm local temperature of the ultrasound treated with 1.0 w/$cm^2$, 1.5 w/$cm^2$ and 2.0 w/$cm^2$ were significantly higher than 0.5 w/$cm^2$ and 0.0 w/$cm^2$ of ultrasound (p<0.05). The posttreatment median MNCV were differed significantly from the respective pretreatment velocities (p<0.001). The MNCV of the ultrasound treated with 0.0 w/$cm^2$ and 0.5 w/$cm^2$ were significantly (p<0.05) slower than that observed pretreatment, while the three ultrasound intensities produced significantly increased posttreatment MNCV: 1.0 w/$cm^2$ and 1.5 w/$cm^2$ and 2.0 W/$cm^2$. The posttreatment MNCV at 2.0 w/$cm^2$ and 1.5 w/$cm^2$ was significantly faster than that at 0 w/$cm^2$, 0.5 w/$cm^2$ and 1.0 w/$cm^2$ (p<0.05), the MNCV at 1.0 w/$cm^2$ was significantly faster than that associated with 0 w/$cm^2$ and 0.5 w/$cm^2$ of ultrasound (p<0.05). CONCLUSIONS: The decreased median motor forearm local temperature and MNCV of the ultrasound treated with 0.0 w/$cm^2$ and 0.5 w/$cm^2$ were attributed to the cooling effect by ultrasound transmission gel. Local forearm temperature and nerve conduction velocity were directly related to the intensity of ultrasound. Alterations in MNCV from ultrasound on healthy nerves appeared to be related to temperature changes induced by thermal effects of ultrasound.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.20 no.11
• /
• pp.3655-3665
• /
• 1996

An analytical solution is presented for the conduction-dominated solidification of a binary mixture in a semi-infinite medium. The present approach differs from that of other solution by these four characteristics. (1) Solid fraction is determined from the phase diagram, (2) thermophysical properties in mushy zone are weighted according to the local solid fraction, (3) non-equilibrium solidification can be simulated and (4) the cooling condition of under-eutectic temperature can be simulated. Up to now, almost all analyses are based on the assumption of constant properties in mushy zone and solid fraction linearly with temperature or length. The validation for these assumptions, however, shows that serious error is found except some special cases. The influence of microscopic model on the macroscopic temperature profile is very small and can be ignored. But the solid fraction and average solid concentration which directly influence the quality of materials are drastically changed by the microscopic models. An approximate solution using the method of weighted residuals is also introduced and shows good agreement with the analytical solution. All calculations are performed for NH$_{4}$Cl-H$_{2}$O and Al-Cu system.

• Progress in Superconductivity and Cryogenics
• /
• v.4 no.2
• /
• pp.73-77
• /
• 2002

In order to derive the detailed design of Thermal Shield Cryopanel. which plays a role to make the Tokamak Nuclear Fusion Equipment work at both static and efficient conditions the commercially available software package FLUENT Version 5.3, was utilized. This study investigated the effects of thermal sources and distributions on the temperatures of Lid. Body. Base. and EH-Port Cryopanel by the numerical technique whose grid generations cover the solid and 9as region of the panel. The physical model of the Thermal Shield Cryopanel is that the 10mm diameter of the pipe with 1mm thickness is soldered on the Stainless steel Panel with 4mm thickness. The heat fluxes to the panel are assumed to be by thermal radiation in the vacuum space and by conduction through the supporters. The inlet conditions of Helium gas are 20 atmospheric Pressures and 60K temperature. The panel shapes with cooling Pipes and the operational conditions to keep appropriate temperature distribution of Thermal Shield Cryopanel Have been found and suggested.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.9 no.4
• /
• pp.552-560
• /
• 1997

Analysis is performed to determine the optimal lengths or cross-sectional areas of refrigerator-cooled current leads that can be applied to the conduction-cooled superconducting systems. The binary current lead is composed of the series combination of a normal metal at the upper(warm) part and a high $T_c$ superconductor(HTS) at the lower(cold) part. The heat conduction toward the cold end of HTS part constitutes a major refrigeration load. In addition, the joint between the parts should be cooled by a refrigerator in order to reduce the load at the low end and maintain the HTS part in a superconducting state. The sum of the work inputs required for the two refrigeration loads needs to be minimized for an optimal operation. In this design, three simple models that depict the refrigeration performance as functions of cooling temperature are developed based on some of the existing refrigerators. By solving one-dimensional conduction equation that take into account the temperature-dependent properties of the materials, the refrigeration works are numerically calculated for various values of the joint temperature and the sizes of two parts. The results show that for given size of HTS, there exist the optimal values for the joint temperature and the size of the normal metal. It is also found that the refrigeration work decreases as the length of HTS increases and that the optimal size of normal metal is quite independent of the size of HTS. For a given length of HTS, there is an optimal cross-sectional area and it increases as the length increases. The dependence of the optimal sizes on the refrigerator models employed are presented for 1kA leads.

• Journal of Energy Engineering
• /
• v.20 no.3
• /
• pp.185-190
• /
• 2011

This paper describes design, fabrication, and evaluation of the conduction cooled high temperature superconducting (HTS) magnet for superconducting magnetic energy storage (SMES). The HTS magnet is composed of twenty-two of double pancake coils made of 4-ply conductors that stacked two Bi-2223 multi-filamentary tapes with the reinforced brass tape. Each double pancake coil consists of two solenoid coils with an inner diameter of 500 mm, an outer diameter of 691 mm, and a height of 10 mm. The aluminum plates of 3 mm thickness were arranged between double pancake coils for the cooling of the heat due to the power dissipation in the coil. The magnet was cooled down to 5.6 K with two stage Gifford McMahon (GM) cryocoolers. The maximum temperature at the HTS magnet in discharging mode rose as the charging current increased. 1 MJ of magnetic energy was successfully stored in the HTS magnet when the charging current reached 360A without quench. In this paper, thermal and electromagnetic behaviors on the conduction cooled HTS magnet for SMES are presented and these results will be utilized in the optimal design and the stability evaluation for conduction cooled HTS magnets.

• Solar Energy
• /
• v.11 no.2
• /
• pp.51-62
• /
• 1991

Heat transfer characteristics for heat retrieving processes in a paraffin-filled horizontal circular cylinder was studied. Theoretical and experimental analyses were carried out. In the theoretical analysis, solid and liquid phases were treated separately. Namely, convection for liquid and conduction for solid phase were investigated respectively. The retrieved heat was calculated from the experimentally determined solidified mass. Furthermore, the effects of initial temperature of the liquid and cooling temperature on the heat discharge rate were also studied. In the heat retrieving process, the governing factor for the solidifying rate is the cooling temperature, because most of the liquid sensible heat is rapidly discharged in the initial stage of solidification. Hence heat transfer mechanism during heat retrieving process can be safely considered as conduction. In the cut of frozen paraffin, there showed an empty space in the upper region. It is caused by the temperature drop in the liquid paraffin. While volume shrinkage caused by phase transition was indiscernible. Irrespective of cooling temperature and initial liquid temperature, solidified mass was well-correlated with the product of Fourier number and Stefan number in the solid phase.

• Proceedings of the KSME Conference
• /
• 2004.11a
• /
• pp.1152-1157
• /
• 2004

Temporal behavior of the laser induced incandescence (LII) signal is often used for soot particle sizing, which is possible because the cooling behavior of a laser heated particle is dependent on the particle size. In present study, LII signals of soot particles are modeled using two non-linear coupled differential equations deduced from the energy- and mass-balance of the process. The objective of this study is to see the effects of particle size, laser fluence on soot temperature characteristics and cooling behavior. Together with this, we focus on validating our simulation code by comparing with other previous results. Results of normalized LII signals obtained from various laser fluence conditions showed a good agreement with that of Dalzell and Sarofim's. It could be found that small particles cool faster at a constant laser fluence. And it also could be observed that vaporization is dominant process of heat loss during first 100ns after laser pulse, then heat conduction played most important role while thermal radiation had little influence all the time.