• Journal of Korean Tunnelling and Underground Space Association
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• v.22 no.1
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• pp.121-133
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• 2020

Globally, the frequency and intensity of abnormal climate events are increasing. Since this can directly damage lives and property, it is important to establish and implement an appropriate maintenance strategy in response to abnormal weather. Facilities built in cold regions where cold wave or heavy snow occurs frequently can be more damaged by freeze-thaw than facilities located in other regions. However, there are no clear criteria for quantitatively identifying the damage of freeze-thaw and how to cope with it. Therefore, based on the results of indoor freezing tests, the freezing conditions considering regional climate characteristics were selected as one day at -14℃, two days at -7℃ or three days at -5℃. As a result, it was confirmed that they were in the freeze-thaw environment in order of Daegwallyeing (8.3 times), Cheorwon (5.3 times) and Taebeak (4.9 times) in Gangwon region. Through this study, the evaluation criteria of freeze-thaw of road tunnels were newly proposed. The freeze-thaw evaluation criteria of the road tunnel presented in this study can be used for the quantitative evaluation and maintenance strategy of tunnels in cold regions.

• Journal of Acupuncture Research
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• v.21 no.1
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• pp.119-135
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• 2004

Objective: The purpose of this study is to investigate the mechanism and effect of moxibustion with salt objectively, to be used as the quantitative data through the measurement of temperature, and to grasp the thermodynamic characteristics of moxibustion with salt. Methods: We have selected of the moxibustion with salt of indirect moxibustion. We make a comparative study of the thermodynamic characteristics of moxibustion with salt as a kind of the 4 salt. We examined combustion times, temperatures, temperature gradients in each period during a combustion of moxa. Results: 1. We make out that it is not significantly change the time of thermal conduction of moxibustion with salt as a kind of 4 salt. 2. The heating period of Refined Salt was long and that of Sun-dried Salt was a short time respectively. The heating period of maximum tamperature is high Sun-dried Salt, Mechanical Salt and Refined Salt orderly. Maximun heating speed in the heating period was $0.151{\sim}0.184^{\circ}C/sec$ and at the same tendency of the maximum temperature in the heating period. 3. The retaining period was shorter than the heating period respectively, that is 15~24% of the combustion time of in the heating period. We make out that it is not significantly different the time of the retaining period as a kind of 4 salt. The mean temperature of retaining period was $43.2{\sim}48.1^{\circ}C$, that was extraordinarily high temperature. 4. We make out that it is not significantly different the time of the cooling period as a kind of 4 salt. The cooling period was measured 223~233sec. Beacuse the same density and size of moxa combustion was made an experiment. 5. The effective combustion time of Refined Salt is longer(259sec) than that of Sun-dried Salt(173sec). It is significantly different the time of the combustion time as a kind of 4 salt. 6. It is significantly different the Sample deviation of the combustion time as a kind of 4 salt because of the water content of the 4 salt individually. Conclusions: As the base on this study, we obtained the conclusion as the follows. The salt of moxibustion with salt was fitted for Sun-dried Salt due to making to Mechanical Salt recently. The Refined Salt is composition rate to another and small size comparatively. So It was fitted for the salt of moxibustion with salt. It is necessary to study continuously about the more suitable moxibustion with salt and quantitative analysis about the moxibustion with salt.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.2
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• pp.127-134
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• 2020

High supersonic aircraft are exposed to high temperature environments by aerodynamic heating during supersonic flight. Thermal protection system structures such as double-panel structures are used on the skin of the fuselage and wings to prevent the transfer of high heat into the interior of an aircraft. The thin-walled double-panel skin can be exposed to acoustic loads by supersonic aircraft's high power engine noise and jet flow noise, which can cause sonic fatigue damage. Therefore, it is necessary to examine the behavior of supersonic aircraft skin structure under thermal-acoustic load and to predict fatigue life. In this paper, we designed and fabricated thermal-acoustic test equipment to simulate thermal-acoustic load. Thermal-acoustic testing of the titanium specimen under thermal-acoustic load was performed. The analytical model was verified by comparing the thermal-acoustic test results with the finite element analysis results.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.9
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• pp.895-900
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• 2012

This paper aims to examine the effect of nanodroplets on pool-type absorption heat transfer enhancement and to find the relationship between the dispersion stability and the absorption performance. The concentrations of oil and surfactant are considered as the key parameters. $C_{12}E_4$ and Tween20 are used as the surfactants and N-decane oil is added to the $NH_3/H_2O$ solution to make the binary nanoemulsion fluids. Binary nanoemulsion fluids are dispersed by the ultrasonic vibrator and the stirrer under specific conditions. The dispersion stability of binary nanoemulsion fluids for each oil concentrations is evaluated from the droplet size and Tyndall effect analysis. The absorption performance of binary nanoemulsion fluids is compared with the result of dispersion stability. In addition, it is found that the binary nanoemulsion fluid is a strong candidate as a new working fluid for absorption applications.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.2
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• pp.161-168
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• 2011

The heating, ventilating, air conditioning (HVAC) system is a very important part of an automotive vehicle: it controls the microclimate inside the passenger's compartment and removes the frost or mist that is produced in cold/rainy weather. In this study, the numerical analysis of the defrost duct in an HVAC system and the de-icing pattern is carried out using commercial CFX-code. The mass flow distribution and flow structure at the outlet of the defrost duct satisfied the duct design specification. For analyzing the de-icing pattern, additional grid generation of solid domain of ice and glass is pre-defined for conductive heat transfer. The flow structure near the windshield, streakline, and temperature fields clearly indicate that the de-icing capacity of the given defrost duct configuration is excellent and that it can be operated in a stable manner. In this paper, the unsteady changes in temperature, water volume fraction, and static enthalpy at four monitoring points are discussed.

• Applied Chemistry for Engineering
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• v.29 no.5
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• pp.510-518
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• 2018

Recently, lots of interests have been concentrated on the scrubber system that abates waste gases produced from semiconductor manufacturing processes. An effective design of the thermal decomposition reactor inside a scrubber system is significantly important since it is directly related to the removal performance of pollutants and overall stabilities. In the present study, a computational fluid dynamics (CFD) analysis was conducted to figure out the thermal and flow characteristics inside the reactor of wet scrubber. In order to verify the numerical method, the temperature at several monitoring points was compared to that of experimental results. Average error rates of 1.27~2.27% between both the results were achieved, and numerical results of the temperature distribution were in good agreement with the experimental data. By using the validated numerical method, the effect of the reactor geometry on the heat transfer rate was also taken into consideration. From the result, it was observed that the flow and temperature uniformity were significantly improved. Overall, our current study could provide useful information to identify the fluid behavior and thermal performance for various scrubber systems.

• Journal of the Korean Society of Food Science and Nutrition
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• v.14 no.4
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• pp.359-364
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• 1985

Being used the three kinds of aqueous solution of tobacco extracts as a new experimental material, experiment and theoretical analysis are performed. Measurements are made with a apparatus designed and constructed by the author.The average diameter of the ice crystals is 0.04-0.1cm between 0.2 and $0.6^{\circ}C$ of the subcooling temperature of the solution. The growth rate of ice crystals in direction of axies A, $V_a$ is in proportion to the subcooling temperature, viz; $v_a=0.058{\Delta}t_b,\;where\;{\Delta}t_b<0.1^{\circ}C$ The growth rate of ice crystal have to be considered not only the mass diffusion and the heat transfer of rate controlling but also the process in ice crystallization. The growth rate of ice crystal is found to be independent on the concentration of the solution and a diameter of ice crystal.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.9
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• pp.69-76
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• 2018

The present study analyzed the effect of film hole position of 45 degree ribbed cooling channel on film cooling performance of gas turbine blades. We also investigated the influence of the ribs under the fixed blowing ratio. Three-dimensional numerical model was constructed and extensive simulation was conducted using the commercial code (Fluent ver. 17.0) under steady-state condition. Base on the simulation results, We investigated the cooling effectiveness, flow velocity, streamline, and pressure coefficient. Moreover, We analyzed the effect of cooling hole position on ejection of the secondary flow caused by the rib structure. From the results, It was found that internal flow of the cooling channel forms a vortex pair in the counterclockwise from the top side, and clockwise from the bottom side. For the channels with ribs, the vortex flow generated by the ribs caused a higher pressure difference near the hole outlet, resulting in at least 12% higher cooling effectiveness than the channel without ribs. Additionally, when the hole is located on the left side of the ribbed channel (Rib-Left), it can be found that the secondary flow generated by the ribs hits against wall surface near the hole to form a flow in the direction of the hole inclination angle. Therefore, It is considered that the region where the cooling gas discharged to the blade surface stays in the main flow boundary layer is wider than the other cases. In this case, The largest pressure coefficient difference was observed near the outlet of the hole, and as a result, the discharge of the cooling gas was accelerated and the cooling efficiency was slightly increased.

• Tunnel and Underground Space
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• v.22 no.6
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• pp.429-437
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• 2012

This study predicted temperature in the disposal tunnels using computational fluid dynamics based on natural ventilation quantity that comes from high altitude and temperature differences that are the characteristics of high level waste repository. The result of the previous study that evaluated quantitatively natural ventilation quantity using a hydrostatic method and CFD shows that significant natural ventilation quantity is generated. From the result, this study performed the prediction of temperature in disposal tunnels by natural ventilation quantity by the caloric values of the wastes, at both deep geological repository and surface repository. The result of analysis shows that deep geological repository is effective for thermal control in the disposal tunnels due to heat transfer to rock and the generation of sufficient natural ventilation quantity, while surface repository was detrimental to thermal control, because surface repository was strongly affected by external temperature, and could not generate sufficient natural ventilation quantity. Moreover, this study found that in the case of deep geological repository with a depth of 200 m, the heatof about $10^{\circ}C$ was transferred to the depth of 500 m. Thus, it is considered that if the high level waste repository scheduled to be built in the country is designed placing an emphasis on thermal control, deep geological repository rather than surface repository is more appropriate.

• International Journal of Highway Engineering
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• v.15 no.2
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• pp.29-37
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• 2013

PURPOSES : This study aims to review the possibility of developing a road snow-melting system that can prevent slip accidents by maintaining a constant temperature of the winter roads and enhance performance of structures, including improvement of compressive strength by mixing carbon nanotube (hereafter referred to as CNT) with cement paste, the basic material. METHODS : To achieve the above purpose, an experiment was conducted by mixing power-type CNT and wrap-type CNT up to cement paste formulation by weight of 0.0wt%~4.1wt% in accordance with "KS L ISO 679(of cement strength test method)", and compressive strength was measured at 28 days of curing. In addition, the volume resistivity of the specimen was measured to test thermal and electrical characteristics, and the rate of temperature changes in specimen surface by power consumption was measured by passing electricity through the cross-sections of the specimen. Meanwhile, the criteria for checking the performance as a road snow-melting system was determined as volume resistivity of $100{\Omega}{\cdot}cm$ or less. RESULTS : A comparative analysis between specimen with 0wt% CNT content in plain status and specimen containing various types of CNTs was carried out. From its results, it was found that compressive strength increased approximately 19%, showing the highest rate when 0.2wt% of wrap-type CNT was contained, but volume resistivity of $100{\Omega}{\cdot}cm$ or less appeared only in specimens containing more than 0.2wt% CNT. In addition, it was observed that the surface temperature increased by $4.62^{\circ}C$ per minute on average in specimens containing 3.2wt% CNT. CONCLUSIONS : In this study, CNT was examined as an underlying material for a road snow-melting system, and the possibility of developing the road now-melting system was reviewed by conducting various experiments using CNT-Cement composites. From the experimental results, the specimens were found to have a superior performance when compared to the existing road snow-melting systems that place the heat transfer medium such as copper on the road. However, satisfactory strength performance were not obtained from the specimen containing CNT(2.0% or more) that functions as a heating element, which leads to the need for reviewing methods to increase the strength by using plasticizer or admixture.