• Journal of Environmental Science International
• /
• v.21 no.6
• /
• pp.713-724
• /
• 2012

Emission rates of biogenic hydrocarbon emitted from broad-leaved trees grown at Jeju Island were estimated using a dynamic enclosure method. Leaf temperature, PAR and relative humidity were monitored during the sampling time. The emission rates of isoprene and monoterpene were measured for five plants(Carpinus laxiflora, Quercus serrata, Styrax japonicus, Quercus acutissima, Quercus crispula) during the sampling period at the Halla mountain sites. Among five tree species, the highest isoprene emission rate of 10.60 ${\mu}g\;gdw^{-1}hr^{-1}$ was observed for Quercus serrata. The seasonal emission rates were the highest during summer and the emission of isoprene was highly affected by light and temperature variations. The highest emission rate of isoprene was occurred between 13:00 and 14:00, but isoprene was not emitted in nighttime because of the absence of light.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.32 no.2
• /
• pp.135-142
• /
• 2008

Experimental studies on the aerodynamic coupling effect on natural frequencies, critical speed and flutter instability of rotating disks are investigated in this paper. The theoretical analysis uses a fluid-structure model where the aerodynamic effects are represented in terms of elastic, lift and damping and stiffness components. The experiments performed using a vacuum chamber and ASMO/DVD disks rotating in vacuum, open and enclosure in several gaps with stationary wall give three main results. One is that the aerodynamic effect by the surrounding air reduces the natural frequencies and critical speeds of the vibration modes. The second is that natural frequency of disks rotating in open air is larger than that in enclosure. Finally, it is shown that the disk vibration is reduced as the gap between the disk and the rigid wall decreases.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2003.05a
• /
• pp.998-1003
• /
• 2003

The aerodynamically excited vibration and natural frequency of rotating CD and DVD disks are analytically and experimentally studied in this paper The theoretical analysis uses a fluid-structure model where the aerodynamic effects are represented in terms of elastic, lift and damping components. The explicit expression on natural frequency of the air coupled disk is obtained as functions of the three aerodynamic coefficients. The experiments performed using a vacuum chamber and CD/DVD disks rotating in vacuum, open air and enclosure give three main results. One is that the aerodynamic effect by the surrounding air reduces the natural frequencies and critical speeds of the vibration modes. The second is that natural frequency of disks rotating in open air is larger than that in enclosure. Finally, it is shown that the disk vibration is reduced as the gap between the disk and the rigid wall decreases.

• Journal of Environmental Science International
• /
• v.32 no.2
• /
• pp.131-137
• /
• 2023

Filter and microbalance sensitivity in measuring fine particulate matter mass is greatly influenced by particulate properties and environmental factors. Temperature and humidity control inside a measuring chamber with a microbalance, and neutralization of static charges on filters are essential for consistent filter weighing. Commercial weighing chambers are expensive with a unit price of tens of millions won. This study developed an inexpensive weighing chamber for weighing fine particulate matter and evaluatedits weighing performance. A microbalance with 1 ㎍ precision was used to measure the weight of a filter. The microbalance was set in a transparent acrylic enclosure (100 × 60 × 65 cm³) equipped with temperature and humidity control equipments. Weighing performance of the chamber was examined using Teflon filters with or without different particulate sample types. Temperature and humidity were maintained at approximately 23.2±1.2 ℃ and 36.2±1.8℃ for 8 days, respectively.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.24 no.8
• /
• pp.791-797
• /
• 2013

This paper proposes a new way to verify the performance of an absorber lined shielded enclosure(ALSE) in accordance with CISPR25, EMC standards dedicated to testing automotive components. CISPR16 requires the use of NSA and VSWR methods to test the performance of a chamber. As for CISPR25, however, there hasn't been standardized ways to verify the performance of ALSE. This paper purports to present an improved method for the verification based on a long-wire antenna method under discussion at CISPR25 JFT. Existing discussions on a long-wire antenna method proposes that an antenna should reach 500 millimeters in length, while this paper adopts the antenna length of 1,700 millimeters. This paper also assesses the effects of matching conditions and studies problems related to methods which have been already proposed and key parameters in order to improve verification methods.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.22 no.5
• /
• pp.429-436
• /
• 2012

In concert halls and auditoriums, acoustic reflector and stage enclosure is one of the main factors on the room and stage acoustic characteristics. As a stage enclosure and acoustic reflector honey comb based light-weight reflector is widely used, because it is easy to install. However, there was not enough research on the surface density effect on room and stage acoustics. In this study, sound absorption coefficient tests on three kinds of wooden acoustic reflectors with different surface density were conducted. Surface density of acoustic reflector was changed from 11 kg/$m^2$ to 41 kg/$m^2$. For the low frequency excitation, sub-woofer was used with omnidirectional loud-speaker simultaneously. From the experiments, it was found that sound absorption coefficient below 250 Hz band was decrease by the increment of surface density. In order to check the influence of the surface density on room and stage acoustic parameters, room acoustic simulation was conducted with sound absorption coefficients, which were tested in reverberation chamber. By the increment of surface density of acoustic reflector, RT(reverberation time) and EDT(early decay time) were increased. Also, ST(stage support) was improved in low frequency bands.

• Journal of Electrical Engineering and Technology
• /
• v.5 no.4
• /
• pp.631-636
• /
• 2010

Gas-insulated transmission lines (GITL) are valued as technological solutions in hydro-power stations due to their enormous power handling capabilities. The performance of GITL is a function of the size of metallic particles inside the gas-insulated chamber. Electrostatic field (E-field) enhancement is a common phenomenon in gas-insulated lines due to these metallic particles. In this study, the E-field enhancement factor is calculated by considering metallic particles at various locations in the gas-insulated line/bus section, such as high-tension (HT) conductor, high-voltage shields, support insulator, and inner surface of grounded enclosure. For this purpose, a two-dimensional model based on finite element (FE) method is developed. The length of the metallic particle is in the range of 1 to 10 mm while the diameter is between 1 to 3 mm. E-field enhancement is also computed for various particle configurations of the gas-insulated system, with focus on dielectric coating made of epoxy on HT conductor and inner surface of grounded enclosure.

• Journal of Korean Society for Atmospheric Environment
• /
• v.16 no.5
• /
• pp.499-509
• /
• 2000

Next to carbon dioxide, methane is the second largest contributor to global warming among anthropogenic greenhouse gases. Methane is emitted into the atmosphere from both natural and anthropogenic sources. Natural sources include wetlands, termites, wildries, ocean and freshwater. Anthropogenic sources include landfill, natural gas and oil production, and agriculture. These manmade sources account for about 70% of total global methane emissions; and among these, landfill accounts for approximately 10% of total manmade emissions. Solid waste landfills produce methane as bacteria decompose organic wastes under anaerobic conditions. Methane accounts for approximately 45 to 50 percent of landfill gas, while carbon dioxide and small quantities of other gases comprise the remaining to 50 to 55 percent. Using the closed enclosure technique, surface emission fluxes of methane from the selected landfill sites were measured. These data were used to estimate national methane emission rate from domestic landfills. During the three different periods, flux experiments were conducted at the sites from June 30 through December 26, 1999. The chamber technique employed for these experiments was validated in situ. Samples were collected directly by on-site flux chamber and analyzed for the variation of methane concentration by gas chromatography equipped with FID. Surface emission rates of methane were found out to vary with space and time. Significant seasonal variation was observed during the experimental period. Methane emission rates were estimated to be 64.5$\pm$54.5mgCH$_4$/$m^2$/hr from Kimpo landifll site. 357.4$\pm$68.9mgCH$_4$/$m^2$/hr and 8.1$\pm$12.4mgCH$_4$/$m^2$/hr at KwanJu(managed and unmanaged), 472.7$\pm$1056mgCH$_4$/$m^2$/hr at JonJu, and 482.4$\pm$1140 mgCH$_4$/$m^2$/hr at KunSan. These measurement data were used for the extrapolation of national methane emission rate based on 1997 national solid waste data. The results were compared to those derived by theoretical first decay model suggested by IPCC guidelines.

• Journal of Korean Society of Forest Science
• /
• v.110 no.1
• /
• pp.13-21
• /
• 2021

In this research, monoterpene emissions were investigated from pine trees(Pinus densiflora) and in the forest air in Simwon village at the Jiri Mountain. Air samples from an enclosed chamber and pine forest air were collected using a Tenax TA Tube five times a day(at 09:00, 11:00, 13:00, 15:00, and 17:00) on 1 day per month from March to November 2014. Selected needles and branches from individual pine trees were enclosed for the measurement of their monoterpene emissions. The concentration and composition of emitted monoterpenes were analyzed in a time series. The major components of monoterpenes emitted from pine trees were α-pinene, β-myrcene, β-phellandrene, and β-pinene. Seasonal data showed that the concentration of monoterpenes emitted from pine trees began increasing in June and reached its peak in August, decreasing thereafter. In addition, seasonal emissions of monoterpenes were dependent on environmental factors such as temperature. The major species of monoterpenes in forest air were α-pinene, β-pinene, and camphene. The concentration of monoterpenes in forest air began rising from March to April and reached its peak in May; multiple peaks subsequently formed in July and November. Diurnal variation in monoterpenes decreased from 09:00-10:00, reaching a low and high at 13:00-14:00 and 17:00-18:00, respectively.

• 한국전산유체공학회:학술대회논문집
• /
• 2009.04a
• /
• pp.176-182
• /
• 2009

In the present study, a numerical simulation for the diffusion of hydrogen jet in a enclosure was performed to aid the leakage test of the hydrogen for the safety of the hydrogen vehicle. The temporal and spatial distributions of the hydrogen concentration in the test chamber are predicted from the present numerical analyses. Flammable region of 4-74% and explosive region of 18-59% hydrogen by volume was identified from the present results. Factors influencing the diffusion of the hydrogen jet were examined to evaluate the effectiveness of forced ventilation for relieving the accumulation of the leaked hydrogen gas in the chamber, which include location of open windows, size of leakage nozzle, and leakage rate among others. The distribution of the concentration of the leaked hydrogen for various cases can be used as a database in various applications for the hydrogen safety.