• Transactions of the Korean Society of Pressure Vessels and Piping
• /
• v.7 no.3
• /
• pp.48-53
• /
• 2011

A PHE (Process Heat Exchanger) is a key component required to transfer heat energy of $950^{\circ}C$ generated in a VHTR (Very High Temperature Reactor) to the chemical reaction that yields a large quantity of hydrogen. A small-scale PHE prototype made of Hastelloy-X is being tested in a small-scale gas loop at Korea Atomic Energy Research Institute. In this study, as a part of the evaluation on the high-temperature structural integrity of the small-scale PHE prototype, we carried out macroscopic high-temperature structural analysis of the small-scale PHE prototype under the gas loop test conditions considering the pipeline stiffness.

• Journal of the Korean Society of Mechanical Technology
• /
• v.20 no.6
• /
• pp.763-769
• /
• 2018

In this research, in order to improve the heat retention of greenhouse, comparative analysis of the heat flux of the marketed multi-later insulating curtain was carried out. Experiments is conducted by fabricating a test apparatus for investigating the heat flux characteristics. The multi-later insulating curtain used for the experiment was compared using the P, N, S, U and T company, which are commercially available, and the heat flux due to temperature difference between the experimental apparatus and the outside was compared and analyzed. When the internal temperature of the experimental result is the maximum temperature $60^{\circ}C$, the heat flux of multi-later insulating curtain is T Co.($73.1W/m^2$) > S Co.($119.5W/m^2$) > U Co.($155W/m^2$) > N Co.($163.1W/m^2$) > P Co.($177.7W/m^2$). The heat flux means the quantity of heat passing through the unit time per unit area, and the higher the numerical value, the higher the quantity of heat passing through the multi-layer insulating curtain. This can be determined that high heat fluxes produce low heat resistance. Further, it has been found that the weight of the insulating curtain is largely unrelated to the heat insulating property, and the heat insulating curtain having a thickness containing a high internal air layer is excellent in the heat insulating property. In the future when manufacturing a heat insulating curtain, It is judged that it is desirable to manufacture a combination of heat insulating materials that contain a high internal air layer content and that can maintain the air layer even for long-term use while minimizing the volume.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2000.10b
• /
• pp.1163-1168
• /
• 2000

The method for preventing thermal cracks is necessary in mass concrete structures. So various experiments were carried out for the controls of thermal cracks and we substituted fly ash for a quarter of cement quantity in order to decrease hydration heat. The maximum block size is determined by numerical analysis as well. Hydration heat and thermal stress were measured through various gauges and analysis considering the steps of concrete placement were carried out. It was found from this study that the appropriate block size was able to be determined properly by numerical analysis.

• Journal of the Korean Society for Precision Engineering
• /
• v.24 no.9
• /
• pp.44-51
• /
• 2007

There are many methods to assemble various parts of a product, and one of them is the bolting system widely used in a industrial field due to the merits; easiness to obtain strong tightening force, simplicity of assemble or disassemble in order to repair, substitution or cleaning, and so on. But this bolting system needs attachments not to let a bolt loose and they are an important factor to cost a great deal. In this study, some equations are suggested and FE analyses are carried out to verify the cause of the bolt looseness occurring in the tightening process. And because the number of bolts in the bolting system has been decided by empirical know-how of designers in the field, safety rate in the plate type heat exchanger is often too high. Therefore the equations to decrease in quantity are suggested in consideration of the relationship between a critical shearing force acting on the screw and a normal force acting on the cooling plate by the working fluid.

• Design & Manufacturing
• /
• v.13 no.3
• /
• pp.41-47
• /
• 2019

In conventional machining, the use of cutting fluid is essential to reduce cutting heat and to improve machining quality. However, to increase the performance of cutting fluids, various chemical components have been added. However, these chemical components during machining have a negative impact on the health of workers and cutting environment. In current machining, environment-friendly machining is conducted using MQL (minimum quantity lubrication) or cryogenic air spraying to minimize the harmful effects. In this study, the injection nozzle that can combined injecting minimum quantity lubrication(MQL) and cryogenic gas was designed and the shape optimization was performed by using computational fluid dynamics(CFD) and design of experiment(DOE). Performance verification was performed for the designed nozzle. The diameter of the sprayed fluid at a distance of 30 mm from the nozzle was analyzed to be 21 mm. It was also analyzed to lower the aerosol temperature to about 260~270K.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.24 no.12
• /
• pp.875-880
• /
• 2012

The field of the large volume heat exchanger for wasted heat recovery ventilation system is being expanded enormously seeing as the fact that the quantity of reducing energies are huge due to the large volume heat exchanger for wasted heat recovery system at large buildings and factories, which consume large amount of energies while it has been arising huge amount of losses in Korea because of the lack of technology. To develop large volume waste heat recovery heat exchanger, rotor type heat exchanger was simulated for the surface corrugation. Based on the simulation results produced $30,000m^3/h$ grade waste heat recovery, heat exchanger was performed for the actual experiment. In addition, performance tests exceed the capacity of a large waste heat recovery heat exchanger performance test methods proposed.

• Journal of the Korean Society of Safety
• /
• v.19 no.1
• /
• pp.60-65
• /
• 2004

The PVC insulated flexible cords are used mainly as power supply cords of electric appliance. This electric wire is a stranded wire consisted of dozens of strands. In case stranded wires are disconnected by mechanical stress, it weakens electrically. Finally, the over current flows through stranded wires, and electrical fire occurs. In this study, we analyzed the melting properties of strands by over current, such as melting process, melting current and melting time. And we analyzed that quantity of heat for melting, a cross sectional structure, and surface structure by optical microscope and SEM. As analysis results, melting time decreased as melting current increased. And quantity of heat for melting was low, too. From the cross sectional structure of melted wire, when a melting current low and melting time long, it was found that the dendrite structure grew. However, the dendrite structure is hard to grow because growing time is not enough when a melting current high and melting time short.

• Transactions of the Korean hydrogen and new energy society
• /
• v.30 no.6
• /
• pp.621-628
• /
• 2019

The use of the ammonia-water zeotropic mixture as a working fluid in the power generating system has been considered as a proven technology for efficient recovery of low-grade heat sources. This paper presents a thermodynamic performance analysis for ammonia-water evaporator using low-grade heat source, based on the exergy and entransy which has been recently introduced as a physical quantity to describe the heat transfer ability of an object. In the analysis, effects of the ammonia mass fraction and source temperature of the binary mixture are investigated on the system performance such as heat transfer, effectiveness, exergy destruction, entransy dissipation, and entransy dissipation based thermal resistance. The results show that the ammonia mass concentration and the source temperature have significant effects on the thermodynamic system performance of the ammonia-water evaporator.

• Journal of Korean Elementary Science Education
• /
• v.22 no.1
• /
• pp.15-28
• /
• 2003

The purpose of this study was to explore the relationships between the concept of heat and that of temperature for elementary students. Eight multiple choice type questions with explanation of reasons for selection were developed based on previous researches and the analysis of science curriculum for elementary students. The students of 9, 10, 11 years(n=292) were selected from two elementary schools in Taegu City. The responses of students' multiple choice and their explanations were analysed in each items χ² test used for the relationships between types of heat and temperature conceptions Half of elementary student could discriminate the two terms of heat and temperature, majority of them thought that heat is likely to be hot and temperature is the quantity of heat, which is not based on scientific conception. Elementary students thinkings about heat could be classified with material type of heat and molecular kinematics type. Material type of heat were more popular than with molecular kinematics type, although the latter is increased. Majority of students answered correctly in qualitative questions of mixing of hot and cold water, but about only one third of them answers in quantitative questions. Subtraction of cold temperature from hot temperature was the most popular explanation, even though one-quarter of students summed up the two temperature in quantitative situation of mixing hot and cold waters. Those who thought heat as the molecular kinetic responded more correctly in most difficult questions than those who as the material. Therefore, we concluded that the types of heat conceptions affected the concept formation of temperature.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.18 no.4
• /
• pp.320-327
• /
• 2006

Numerical analysis and experimental study are performed to investigate the effect of heat load and operating temperature on the thermal performance of several variable conductance heat pipe (VCHP) with screen meshed wick. The heat pipe is designed in 200 screen meshes, 500 mm length and 12.7 mm outer diameter tube of copper, water (4.8 g) is used as working fluid and nitrogen as non-condensible gas (NCG). Heat pipe used in this study has evaporator, condenser and adiabatic section, respectively. Analysis values and experimental data of wall temperature distribution along axial length are presented for heat transport capacity, condenser cooling water temperature change, degrees of an inclination angle and operating temperature. These analysis and experiment give the follow findings: For the same charging mass of working fluid, the operating temperature of heat pipe becomes to be high with the increasing of charging mass of NCG. When the heat flux at the evaporator section increases, the vapor pressure in the pipe rises and consequently compresses the NCG to the condenser end part and increases the active length of the condenser. From previous process, it is found out we can control the operating temperature effectively and also the analysis and experimental results are relatively coincided well.