• Applied Chemistry for Engineering
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• v.25 no.4
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• pp.401-408
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• 2014

In membrane bio-reactor (MBR), the aeration control is one of the important independent variables to decrease fouling and to save energy with shear stress change on the membrane surface. The paper was carried out for numerical simulation of 3-dimensional fluid flow phenomena of the cylindrical bioreactor with submerged flat membranes equipped in the center and supplied the air from the bottom by using the COMSOL program. The viscosity and temperature of solution were assumed to be constant, and the specific air demand based on permeate volume ($SAD_p$) defined as scouring air per permeate rates was used as a variable. The calculated CFD velocities were compared with those of the velocity meter measurement and video image analysis, respectively. The results were good agreement each other within 11% error. For fluid flow in the reactor the liquid velocity increased rapidly between the air diffuser and membrane module, but the velocity decreased during flowing of the membrane module. Also, the velocity increased as it was near from the reactor wall to the central axis. The calculated shear stress on the membrane surface showed the highest value at the center part of the module bottom side and increased as aeration rate increased. Especially, the wall shear stress increased dramatically as the aeration rate increased from 0.15 to 0.25 L/min.

• The Korean Journal of Food And Nutrition
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• v.26 no.4
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• pp.731-736
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• 2013

To improve their shelf-life, domestic peaches were treated with hot air($46^{\circ}C$) for 0~9 hour, and the spoilage rate, changes of physico-chemical and sensory properties were investigated. The control showed spoilage at day 4, and then 50% of control showed spoilage on day 6. However, 12.5% of samples treated with hot air($46^{\circ}C$) for 6 hr showed spoilage on day 4. After 6 days, the spoilage rates of peaches treated with hot air treated for 3~9 hr were 16.7, 25.0, and 25.0%, respectively. Weight change of control was higher than that of hot air-treated samples for 6 days storage. There were no differences in pH of samples among the treatments, but pH increased with storage time. Hardness of hot air-treated samples was higher than that of control in the initial stage of storage. And then hardness of control sample was decreased faster than that of the hot air-treated samples for 6 days of storage. No significant changes in lightness and redness of the samples were observed after hot air treatment. Changes in yellowness of control occurred faster than that of hot air-treated samples during storage. The sensory parameters including taste, flavor, color, texture and overall acceptance at initial period were not different among treatments. The scores for taste, flavor, texture and overall acceptance of control decreased faster than those of hot airtreated samples during storage.

• The Korean Journal of Air & Space Law and Policy
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• v.30 no.1
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• pp.65-94
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• 2015

Since American Airlines launched AAdvantage which was the first Frequent Flyer Program in 1981, many people has accumulated mileage credits, and now, frequent flyer program(FFP) is the universal marketing tool to the airlines. These days, airlines establish a strategic alliance with domestic and foreign companies of various fields ; other airlines, travel agencies, car hire firms, hotels, department stores, even credit card companies. However, more people want to use their mileage credits, more airlines reject to approve that or change frequent flyer program against their customers. Last year, Northwest, Inc. v. Ginsberg, the United State Supreme Court made a decision that the preemption provision of Airlines Deregulation Act(ADA) preempts state laws related to rates, routes and services for air carriers including implied covenant of good faith and fare dealing. Thus, the claim of Ginsberg was canceled, it means that Northwest Inc. could terminated one-sidedly his membership in the frequent flyer program. In the contrast, Korea does not have the statute like ADA. If customers file a claim on FFP like Ginsberg, the courts of Korea judge whether the clauses of standard form contract are unfair or not. Therefore, in this article, Ginsberg would be checked on legal issues and be compared briefly with the courts' ruling in Korea.

• Journal of the Korean GEO-environmental Society
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• v.14 no.8
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• pp.11-21
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• 2013

In-situ test to find the change of $Fe^{2+}$ and $Mn^{2+}$ concentrations and ion contents in groundwater was conducted during two pumping tests at the riverbank filtration site, where is the riverine area of the Nakdong River in Changnyeong-Gun. Groundwater was sampled at one pumping well and 10 monitoring wells during a 5 steps drawdown pumping test with the rates from $500m^3/day$ to $900m^3/day$ and a constant pumping test with $800m^3/day$. The change in ion concentration of groundwater was more remarkable during a step drawdown pumping test than a constant pumping test. Especially, the decrease in $Fe^{2+}$ and $Mn^{2+}$ concentrations was distinct in a step drawdown pumping test and it happens predominantly along the direction that the radius of pumping influence was small due to a good aquifer connectivity to a pumping position. The precipitation and the oxidation of iron and manganese were caused by an air inflow and a disturbance in groundwater flow due to an abrupt change in pumping rate. The pumping rate and spatial distribution of an aquifer around a pumping well need to be considered as an important factor for the development of in-situ iron and manganese treatment technology.

• Journal of Energy Engineering
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• v.20 no.1
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• pp.44-53
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• 2011

The laminar natural convection of air in 2-D rectangular enclosure in which two opposing isothermal walls were kept at different temperatures is investigated numerically for Rayleigh number up to $10^6$. Computations were performed for the width-to-height ratios of 1, 2, and 4, and for the inclination angle range of $0^{\circ}{\leq}{\theta}{\leq}90^{\circ}$. For each aspect ratio, the influence of the inclination angle on the flow patterns and heat transfer rates were examined for $10^3{\leq}Ra{\leq}10^6$. It is found that the growth of secondary flow in the corners led to the decrease in overall heat transfer for small aspect ratio case, and the transition from a three-cell structure to a unicell flow pattern in large aspect ratio led to a step-like change in heat transfer. A new correlation of mean Nusselt number is presented for the vertical case of ${\theta}=90^{\circ}$.

• Journal of Environmental Science International
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• v.22 no.11
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• pp.1451-1456
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• 2013

This study was conducted to investigate the timely characteristics of phytoncide in forest trail of Ulsan Metropolitan. Air samples were collected from July to October 2011. The phytoncide were detected and quantified using a Gas Chromatograph Mass Spectrometer(GC/MSD). This study are summarized as follows ; The highest levels of phytoncide concentration of August is higher than other months in Munsu Mt. and Samho Mt.(town mountains). The higher phytoncide emission rates found in the morning and in the evening. The concentration of phytoncide was understanded to be greatly influenced by environment change of day time.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.11
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• pp.1434-1443
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• 1999

The turbulent fluctuations of temperature and two components of velocity have been measured with hot- and cold-wires in the Thermally Stratified Wind Tunnel(TSWT). Using the fin-tube heat exchanger type heaters and the neural network control algorithm, both stable ($dT/dz=109.4^{\circ}C$) and unstable ($dT/dz=-49.1^{\circ}C$) stratifications were realized. An ambient air jet was issued normally into the cross flow($U_{\infty}=1.0 m/s$) from a round nozzle(d = 6 mm) flushed at the bottom waII of the wind tunnel with the velocity ratio of $5.8(U_{jet}/U_{\infty})$. The characteristics of turbulent dispersion in the cross flow jet are found to change drastically depending on the thermal stratification. Especially, in the unstable condition, the vertical velocity fluctuation increases very rapidly at downstream of jet. The fluctuation velocity spectra and velocity-temperature cospectra along the jet centerline were obtained and compared. In the case of stable stratification, the heat flux cospectra changes Its sign from a certain point at the far field because of the restratification phenomenon. It is inferred that the main reason in the difference between the vertical heat fluxes is caused by the different length scales of the large eddy motions. The turbulent kinetic energy and scalar dissipation rates were estimated using partially non-isotropic and isotropic turbulent approximation. In the unstable case, the turbulent energy dissipation decreases more rapidly with the downstream distance than in the stable case.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.10
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• pp.639-647
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• 2017

This basic study is focused on the physically removal method of carbon dioxide from the decomposition of ammonium carbarmate to prevent the recombination of ammonium salts. A basic visual experimental set-up was designed and constructed to observe the recombination phenomena from the proper composition of ammonia gas, carbon dioxide gas, and compressed air dilution gas. To quantify the recombination phenomena, a simple device was designed to measure the weight change under severe cases for three different tube sizes. The temperature and pressure in the visual tube and the volumetric flow rates of the nitrogen dilution gas were studied and the conditions to avoid recombination were analyzed according to mean free path theory. Diffusivity values based on the Chapman-Enskog theory were calculated from the experimental data. These value may serve as an index for the prevention of recombination.

• Environmental Engineering Research
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• v.18 no.3
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• pp.169-176
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• 2013

The present study was designed to examine the concentrations, emission rates, and source characteristics of a variety of volatile organic compounds (VOCs) in 30 newly-constructed apartment buildings by measuring indoor and outdoor VOC concentrations over a 2-year period. For comparison, seven villa-type houses were also surveyed for indoor and outdoor VOC concentrations over a 3-month period. Indoor and outdoor air samples were collected on Tenax-TA adsorbent and analyzed using a gas chromatograph (GC)/mass spectrometer system or a GC/flame ionization detector system coupled to a thermal desorption system. The long-term change in indoor VOC concentrations depended on the type of VOCs. Generally, aromatic (except for naphthalene), aliphatic, and terpene compounds exhibited a gradual deceasing trend over the 2-year follow-up period. However, the indoor concentrations of the six halogenated VOCs did not significantly vary with time changes. Similar to these halogenated VOCs, the indoor naphthalene concentrations did not vary significantly with time changes over the 2-year period. Unlike the halogenated VOCs, the indoor naphthalene concentrations were much higher than the outdoor concentrations. The indoor concentrations of aliphatic and aromatic compounds were higher for the villa-type houses when compared to those of apartment buildings. In addition, four source groups (floor coverings and interior painting, household products, wood paneling and furniture, moth repellents) and three source groups (floor coverings and interior painting, household products, and moth repellents) were considered as potential VOC sources inside apartment buildings for the first- and second-year post-occupancy stages, respectively.

• Journal of the Korean Institute of Gas
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• v.23 no.6
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• pp.8-16
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• 2019

One of the methods for low-pollution combustion, flue gas recirculation(FGR) is effective to reduce nitrogen oxides and it was applied in CH₄/air premixed counterflow flames to identify the change of flame characteristics and NOx mechanisms. Considering that the mole fraction of the products varied depending on the strain rates, the major products: CO₂, H₂O, O₂ and N₂ were recirculated as a diluent to reflect the actual combustion system. With the application of the FGR technique, a turning point of maximum flame temperature under certain strain rate condition was found. Furthermore as the recirculation ratio increased, the tendency of NO was changed before and after the turning point and the analysis on thermal NO and Fenimore NO production was conducted.