• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2003.04a
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• pp.494-499
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• 2003

This paper concerns the static, dynamic and thermal characteristics analysis of a high-speed spindle system for horizontal machining centers with 45mm x50,000rpm. The spindle system is designed based on the angular contact ceramic ball bearings, built-in motor, oil-air lubrication method and oil jacket cooling method. The structural and thermal analysis models of spindle system are constructed by the finite element method. The static and dynamic characteristics are estimated based on the static deformation, modal parameter, mode shape and frequency response function, and the thermal characteristics are estimated based on the temperature rise, temperature distribution and thermal deformation. The analysis results illustrate that the designed spindle system has excellent structural and thermal stabilities

• Korean Journal of Bronchoesophagology
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• v.14 no.1
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• pp.5-7
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• 2008

Subcutaneous cervicofacial, mediastinal emphysemas are complications associated with head and neck surgery, trauma, infectious processes, tooth extraction. Drill cooling stream and dental syringe air ject are the sources of high pressure air that may enter exposed soft tissue. Since the introduction of the high-speed air turbine drill in the 1960s, The incidence of iatrogenic subcutaneous emphysema has increased. Most cases begin to resolve after 2 to 3 days and residual swelling is usually minimal at the end of 7 to 10 days. Surgical approach is not advised because it is likely to be ineffective. The differential diagnosis of neck swelling after dental procedure includes hematoma, cellulitis, angioedema, allergic reaction, subcutaneous emphysema. We report a rare case of patient with subcutaneous cervicofacial emphysema and mediastinal emphysema secondary to third molar extraction.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.13 no.1
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• pp.17-25
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• 1977

For four calender years (1971-1974), daily observations of weather conditions (air temperature, humidity, wind speed, wind direction, cloud amount, fog, precipitation etc.) at six stations in the north western Pacific Ocean are used to calculate mean monthly values and to check extra-conditions. At Petropavlosk and Miko'skoe, where indicate the characteristics of modified continental climate, the temperature and humidity are high in summer, and Iow in winter. At A Dak and She Mya, where indicate the characteristics of warm current type maritime climate, humidity is high in all season and annual range of air temperature is nearly negligible. At Simusir and Vasi!' eva, where indicate the characteristics of cold current type maritime climate, humidity is high in all season and annual range of air temperature is $15^{\circ}C.$ As dry cooling power is relatively high in winter, working condition on deck is bad. Most of fogs are advection fog in the area of cold current type climate in summer.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.424-426
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• 2008

A parametric study was carried out to find the fuel lubrication performance of high speed small rolling element bearings. Both MIL-PRF-7808 turbine oil and JP-8 aircraft fuel were used as the lubricant to compare the operational characteristics. 17 mm inner diameter deep groove ball bearing and 20 mm cylindrical roller bearing were used. A high speed bearing test rig was developed and the testing was done with varying applied load, cooling air temperature, lubricant flow rate, and speed. Fuel caused more cage wear than oil for ball bearing with increasing axial load and rotational speed. The bearing temperature using fuel was lower than that using oil, and this seems to be the result of the high cooling capacity of fuel. According to various tests, the fuel lubrication is applicable for the lubrication on the main shaft bearings of expendable small gas turbines.

• Transactions of the Korean Society of Automotive Engineers
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• v.19 no.6
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• pp.119-125
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• 2011

The analysis of performance characteristics in a refrigerator truck using R404A and R744 was carried out by using theoretical method, and each performance was compared with a variation of operating conditions. The components and cycle simulation model were developed by using EES program. To investigate the performance characteristics with operating conditions, the performance of both systems was simulated according to indoor temperature, outdoor temperature, outdoor air velocity and compressor speed. As a result, the R744 system had a better COP than R404A system for given operating condition. The cooling capacity was not increased over the outdoor air velocity of 3 m/s. Besides, the performance of R404A system was more sensitive to operating conditions compared to that of R744 system.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.19 no.5
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• pp.418-425
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• 2007

The power consumption and heat generation in a chip increase as the components are miniaturized and the computing speed becomes faster. Therefore, suitable heat dissipation has become one of the primary limiting factors to ensure the guaranteed performance and reliable operation of the electronic devices. A pin-fin array which may be considered as a porous medium could be used as an alterative cooling system of the electronic equipment. The aim of the present study is to investigate the forced-convective heat transfer characteristics of pin-fin heat exchangers. Convective heat transfer through the pin~fin array is analyzed experimentally based on porous medium approach. The influence of the structure of the pin-fin array including the pin-fin spacing, the pin diameter and plate length on heat transfer characteristic is investigated and compared with the Previous analytical results and existing correlation equations. Nowadays, electronic and mechanical devices become smaller and smaller. In this sense, the main purpose of this study is to decide the optimum pin-fin arrangement to get similar heat transfer performance when the length of the existing cooling system is reduced as a half.

• Proceedings of the SAREK Conference
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• 2005.11a
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• pp.353-358
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• 2005

The heat transfer and pressure drop of supercritical $CO_2$ cooled in a helically coiled tube was investigated experimentally. The experiments were conducted without oil in the refrigerant loop. The experimental apparatus of the refrigerant loop consist of receiver, a variable speed pump, a mass flowmeter, a pre-heater, a gas cooler(test section) and an isothermal tank. The test section is a helically coiled tube in tube counter flow heat exchanger with $CO_2$ flowed inside the inner tube and coolant( water) flowed along the outside annular passage, It was made of it copper tube with the inner diameter of 4.55[mm]. the outer diameter of 6.35 [mm] and length of 10000 [mm]. The refrigerant mass fluxes were $200^{\sim}600$ [kg/m2s] and the inlet pressure of gas cooler varied from 7.5 [MPa] to 10.0 [MPa]. The main results are summarized as follows : The heat transfer coefficient of supercritical $CO_2$ increases, as the cooling pressure of gas cooler decreases. And the heat transfer coefficient increases with the increase of the refrigerant mass flux. The pressure drop decreases in increase of the gas cooler pressure and increases with increase the refrigerant mass flux.

• Journal of the Korean Institute of Landscape Architecture
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• v.33 no.6 s.113
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• pp.98-108
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• 2006

The climate of urban area is an unstable type with considerable seasonal variation in precipitation wind speed, and temperature and it grows worse. Besides, ozone is a serious air pollutant in most of large cities. So worldwide, some of large cities are investing in forestry options to offset their climate problems, but lack of information has hindered comparisons of urban un cost effectiveness to other options. This research intends to study the economic benefits of tree shading of 19 parking lots in UCD campus. The economic benefits of tree shading are air conditioning savings, air quality, stormwater run-off, and other benefits. Especially, this study focuses how much the economic benefit of parking lot shading has been increased from 1995 to 2003 year by aerophoto. Some data on dimensions of parking lots and the number, size, tree species, and location of trees around each parking lot was inventoried. Two aerophotos(1995,2003) were used in order to analyze the increasement of tree canopy in 19 parking lots for 8 years. However, increasing coverage of trees and managing them for healthy growth would not be sufficient for avoiding adverse impacts by future climate change. Additional measures should be followed such as an increase of energy use efficiency and development of substitute energy. For example, coverage of trees help to save cooling energy by blocking solar radiation reaching parking cars and building structures through shading, and creating cool micro-climates through evapotranspiration. They also reduce heating demand by decreasing air infiltration and heat conduction out of the interior of buildings. Proper arrangement of vegetation over the parking lots can reduce cooling and heating costs. So proper planting design around hard space paving including species selection and location can significantly save cooling and heating energy. And a reduction in car and building's heating and cooling costs results in the reduction in energy demand which causes to emissions of air pollutants. Total increased tree canopy from 1995 to 2003 is $8,470.45m^2$ and the economic benefits is US$ 5,282.10. The economic benefit of one tree has been US$ 7.21 for 8 years. And an annually increased benefit is US$ 0.9 per a tree. If this kind of study is applied to studying the economic benefits of tree canopy in parking lots of Korea, it could result in guidelines of tree planting of parking lots. Because the trees selected for planting in parking lots were not suitable for an environment, the guidelines should contain a recommended list of trees. The guidelines should propose the shading percentage of parking lot when we plan a parking lot and contain the maintenance of trees in order to maximize the economic benefits of tree canopy.

• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.1225-1231
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• 2006

Recently, as the climate of temperature change has happened worldwide, To solve this problem, Kyoto protocol was taken to regulate global warming on Feb. 2005 and each country is making efforts to prevent global warming. In the automotive industry, R-134a refrigerant is widely used most these days because it has zero ODP(Ozone Depletion Potential). But R-134a GWP(Global Warming Potential) is so high. Therefore, replacement refrigerant desperately is needed as a alternative refrigerant. So, R-l52a is considered as one of the alternative refrigerants due to zero ODP and lower GWP against as required on Europe Committee. In this paper, performance of the air conditioning system between R-134a and R-152a is investigated experimentally. In the bench level, cooling capacity, condensing capacity, COP of automotive air conditioning system are ovaluated by means of air velocity entering the condenser and compressor revolution speed with optimized charge refrigerant quantity. Result of this study, R-152a refrigerant shows the possibility as alternative refrigerant of current R-134a in automotive air conditioning system.

• Journal of Korean Society for Atmospheric Environment
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• v.9 no.4
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• pp.303-309
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• 1993

An observational study of urban heat island was carried out using field data obatined during 6 days in May and August 1992 in Chunchon(population size 180.000). Air temperature was measured at 64 points along two sampling ruoutes by themisters attached to cars. Both routes cover urban and rural area and across the cneter of urban area. Continuous observation of air sonde was perfomed to clarify heights of nocturnal boundary layer(NBL) at the center of urban area. Surface meteorological observations were performed at both urban and rural sites. This study showed that heat island phenomena was obviously observed at the urbanized area during the night time with low wind speed. The average NBL heights exteded to about 10 meters, but varied with meteorological conditions. After sunset, the air temperature decreased with time at both sites and cooling rate at the urban site was greater than the rural site. The maximum heat island intensity was 7.5$^{\circ}$C at 21 LST, May 4. Usingthe two meteorological data sets obtained from urban and rural sites, the air pollutant concentration was calculated by Gaussian plume model which can obtain not only horizontal distribution of concentration but also vertical distribution. The result indicated that the concentration resulted from urban meteorological data set was lower than that from rural meteorological data set. It was also calculated that the air pollutant extended to higher level in urban meteorological data set than that in rural meteorological data set.