• The Journal of Engineering Research
• /
• v.1 no.1
• /
• pp.23-30
• /
• 1997

Energy transfer by free convection arises in many engineering applications, such as a hot steam radiator for heating a room, refrigeration coils, electric transformers, heating elements and electronic equipments. Generally unsteady natural convection flow in a horizontal channel with arbitrary wall temperatures and the mathematical and physical basis of convection transport has been considered in general. A physically meaningful exact solution of the problem has been obtained in a closed form by the application of the standard finite sine transform technique. Influences of the governing parameters, the Prandtl number and the Rayleigh number, to bring the flow and heat transfer to final steady states have been discussed separately. For constant values of the arbitray wall temperatures and of the function, determining the average axial velocity, the final steady state is approached in different times respectively for the cases when the Prandtl number Pr>1 and Pr<1. It is also seen that the function, representing the axial temperature gradient, is influenced by none of the governing parameters : but the steady state flow is influenced only by the Rayleigh number. There are, of course, many applications. Free convection strongly influences heat transfer from pipes and transmission lines, as well as from various electronic devices. It is also relevant to the environmental sciences, where it is responsible for oceanic and atmospheric motions, as well as related heat transfer processes.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.37 no.12
• /
• pp.1573-1579
• /
• 2013

To test the performance of nuclear fuels, coolant needs to be circulated through the test rig installed in the test loop. Because the pressure and temperature of the coolant is 15.5 MPa and $300^{\circ}C$ respectively, coolant sealing is one of the most important processes in fabricating a nuclear fuel test rig. In particular, 15 instrumentation cables installed in a test rig pass through the pressure boundary, and brazing is generally applied as a sealing method. In this study, an induction brazing system has been developed using a high frequency induction heater including a vacuum chamber. For application in the nuclear field, BNi2 should be used as a paste, and optimal process variables for Ni brazing have been found by several case studies. The performance and soundness of the brazed components has been verified by a tensile test, cross section test, and sealing performance test.

• Korean Journal of Food Science and Technology
• /
• v.18 no.3
• /
• pp.187-191
• /
• 1986

Vitamin retention in rice bran during the extrusion cooking adapted for the rice bran stabilization was studied. The rice bran of different moisture content (9.5% and 15.6%) were extruded with cooking extruder (screw dia: 100mm. strew rpm:900. L/D ratio: 10.0) under the given conditions of specific power consumption(42.1 67.9 W/Kg) and extrusion temperatures $(99-135^{\circ}C)$. The affected retention rates of thiamine, riboflavin and niacin in extruded rice bran were determined. The extruded rice bran with higher moisture level had a lower or similar vitamin retention rate at lower specific power consumption and extrusion temperatures, relatively. The vitamin retention in extruded rice brail with the same moisture level were gradually decreased by the increased specific politer consumption and extrusion temperatures. The vitamin retention of rice bran during the extrusion cooking for the rice bran stabilization were observed as 89.9-97.0% for thiamin, 83.4- 97.3% for riboflavin and 94.0 - 97.7% for niacin, respectively.

• Fire Science and Engineering
• /
• v.23 no.6
• /
• pp.126-134
• /
• 2009

In an attempt to control the spalling in high strength concrete, spalling reducer was mixed to identify the effect and thermal characteristics of concrete beam member at high temperature. The member was manufactured in such as way of adding 40~60MPa of high strength concrete into spalling reducer, and then fire resistance performance were monitored under the ISO standard fire load condition in accordance with KS F 2257. As a result of test, fore rate performance of 40MPa beam without spalling reducer was 180minutes, 50MPa was 174minutes and 60MPa was 152minutes, indicating that 50MPa and 60MPa beam appeared 6~28minutes short to become a 3-hour rate. However, 50 and 60MPa beam mixed with spalling reducer appeared to have satisfied the requirements for 180minutes. A spalling was occurred in surface of 50 and 60MPa beam mixed without spalling reducer, while no spalling or surface failure was occurred with 50 and 60MPa beam mixed with spalling reducer. Thus polypropylene fiber mixed with the concrete proved to be effective, but viewing that the surface of 60MPa was peeled off partially, the steel fiber mixed appeared not to be effective for the beam more than 60MPa.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.17 no.9
• /
• pp.206-211
• /
• 2016

Various applications require dry air at low temperature, such automation equipment, semiconductor manufacturing, chemical production lines, and coating processes for the shipbuilding industry. Four evaporators for low temperature (below $0^{\circ}C$) were installed for a dehumidification system. Moist air is cooled sequentially over three evaporators. The first evaporator has an evaporation temperature of $13^{\circ}C$, that of the second evaporator is $5^{\circ}C$, and that of the third evaporator is maintained at $-1.3^{\circ}C$. In the fourth evaporator implantation thereby the moisture contained in the moisture air. A pressure regulator (CPCE 12) is used at this point and is defrosted when the vapor pressure is below a set value. The non-implantation moisture of the air is a heating system that uses the waste heat of a condenser with high temperature. It develops the cooling type's dehumidifier, which is important equipment that prevents the destruction of protein and measures the temperature and humidity at each interval by changing the front air velocity from 1.0 m/s to 4.0 m/s. The cooling capacity was also calculated. The greatest cooling capacity was 1.77 kcal/h for a front air velocity of 2.0 m/s

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.25 no.4
• /
• pp.468-475
• /
• 2019

An end-line flame arrester allows free venting in combination with flame protection for vertical vent applications. End-line flame arresters are employed in various fields, especially in shipping. In flame arresters, springs are essential parts because the spring load and the spring's elasticity determine the hood opening moment. In addition, the spring has to work under a high-temperature condition because of the burning gas flame. Therefore, it is necessary to analyze the mechanical load and elasticity of the spring when the flame starts to appear. Based on simulations of the working process of a specific end-line flame arrester, a thermal and structural analysis of the spring is performed. A three-dimensional model of a burned spring is built using computational fluid dynamics (CFD) simulation. Results of the CFD analysis are input into a finite element method simulation to analyze the spring structure. The research team focused on three cases of spring loads: 43, 93, and 56 kg, correspondingly, at 150 mm of spring deflection. Consequently, the spring load was reduced by 10 kg after 5 min under a $1,000^{\circ}C$ heat condition. The simulation results can be used to predict and estimate the spring's load and elasticity at the burning time variation. Moreover, the obtained outcome can provide the industry with references to optimize the design of the spring as well as that of the flame arrester.

• Tunnel and Underground Space
• /
• v.30 no.6
• /
• pp.559-572
• /
• 2020

This paper performs laboratory experiments for borehole stability considering temperature and true triaxial stress condition, and observes a thermo-mechanical behavior of the rock under stress and temperature conditions of deep underground. China yellow sandstone and Hwangdeung granite specimens were used to perform a true triaxial compression test. Mechanical tests were carried out under nine confining pressure conditions, and thermo-mechanical tests using granite samples were carried out under six confining pressure conditions at 60-100℃. In the mechanical tests, maximum principal stress at borehole breakout was proportional to intermediate principal stress. In the thermo-mechanical tests, it was confirmed that thermal stress is added to the stress field of the borehole with the increase in temperature, resulting in additional breakout progress. To analyze the results of the laboratory experiment, Mogi-Coulomb failure criterion was used. The results of traditional triaxial compression test on cylindrical specimens and borehole breakout under true triaxial compressions matched well with Mogi-Coulomb failure criterion.

• Applied Chemistry for Engineering
• /
• v.22 no.3
• /
• pp.255-260
• /
• 2011

$NH_4{^+}-{\beta}^{{\prime}{\prime}}$-alumina which is expected to an inorganic solid electrolyte of high temperature polymer electrolyte membrane fuel cells (PEMFC) was prepared by ion-exchange reaction of $K^{+}-{\beta}^{{\prime}{\prime}}$-alumina pellet with $NH_4NO_3$ aqueous solution and molten $NH_4NO_3$ salts as an ion-exchange medium in the autoclave and the heating mentle reaction. In the autoclave reaction, the concentrations of $NH_4NO_3$ solution was chosen at 5 and 10 M. Each ion-exchange reaction was carried out at 130, 150, 170, and $200^{\circ}C$ for 2, 4, 6 and 8 h. In the heating mentle reaction, ion-exchange was performed at $200^{\circ}C$ for 2, 4, 6 and 8 h with molten $NH_4NO_3$ salts. In order to determine the effect of reaction times, each ion-exchange reaction was repeated 3 times. The phase stability and the ion-exchange rate of $NH_4{^+}-{\beta}^{{\prime}{\prime}}$-alumina were analyzed by XRD and ICP.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.32 no.3
• /
• pp.96-102
• /
• 2022

Hydroxyapatite (HAp) was synthesized from calcium hydroxide (Ca(OH)₂) reacting with phosphoric acid (H₃PO₄) in aqueous solution. HAp powders were synthesized from extremely high concentration of precursor solutions over 3 M of Ca(OH)₂ aqueous suspension using modified process parameters such as phosphoric acid (H₃PO₄) pouring rate, aging time and post ball milling process. Regardless of phosphoric acid pouring rate, the DCPD (dicalcium phosphate dihydrate) was formed at room temperature and when heated above 700℃, β-TCP (tricalcium phosphate) was synthesized and the amount reached its maximum at 900℃. When the synthesized powder was sintered at 1150℃, β-TCP, a high temperature impurity phase, remained. The single HAp phase without DCPD was obtained from post ball-milled precipitates followed by 3 day aging. For the ball-milled precipitates even without the aging process, the desired single HAp phase without β-TCP could be obtained by heat treatment above 500℃. The post ball milling process provided a convenient route for HAp synthesis.

• Journal of the Microelectronics and Packaging Society
• /
• v.29 no.2
• /
• pp.113-119
• /
• 2022

In order to improve the mechanical reliability of next-generation electronic devices including flexible, wearable devices, a high level of mechanical reliability is required at various flexible joints. Organic adhesive materials such as epoxy for bonding existing polymer substrates inevitably have an increase in the thickness of the joint and involve problems of thermodynamic damage due to repeated deformation and high temperature hardening. Therefore, it is required to develop a low-temperature bonding process to minimize the thickness of the joint and prevent thermal damage for flexible bonding. This study developed flexible laser transmission welding (f-LTW) that allows bonding of flexible substrates with flexibility, robustness, and low thermal damage. Carbon nanotube (CNT) is thin-film coated on a flexible substrate to reduce the thickness of the joint, and a local melt bonding process on the surface of a polymer substrate by heating a CNT dispersion beam laser has been developed. The laser process conditions were constructed to minimize the thermal damage of the substrate and the mechanism of forming a CNT junction with the polymer substrate. In addition, lap shear adhesion test, peel test, and repeated bending experiment were conducted to evaluate the strength and flexibility of the flexible bonding joint.