• Korean Journal of Food Science and Technology
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• v.41 no.4
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• pp.369-373
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• 2009

${\alpha}$-Waxy corn starch was used as a feed for twin-screw extrusion in order to enhance starch liquefaction with added thermostable ${\alpha}$-amylase (derived from Bacillus licheniformis). The residence time distribution and starch liquefaction were investigated. The starch liquefaction was analyzed in terms of reducing sugar contents, molecular size from gel permeation chromatography (GPC), and microstructure from scanning electron microscopy (SEM). The use of ${\alpha}$-starch contributed to the production of more reducing sugar than the use of raw starch use alone. From GPC, the effect of ${\alpha}$- starch on the molecular size reduction was shown to be small. From SEM, irregular and damaged surface were observed on the extrudate from ${\alpha}$-starch, as compared to those from raw starch. The spread of residence time distribution curves was greater with feed of ${\alpha}$-starch than raw starch, indicating that ${\alpha}$-starch was hard to flow forward during extrusion. This could be improved by increasing the feed moisture content and barrel temperature of extruder.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.1
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• pp.1-6
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• 2006

Using In-113m emitting gamma ray of 0.392MeV at radioisotope tracer the RTD (residence time distribution) of water in the flocculator of wastewater treatment facility was measured. The result was analyzed mathematically using K-RTD program constructed on the basis of CFSTR (constant flow stirred tank reactor) model. The mean residence time and the tank number are the main parameters which describe the flow behavior of the system. Those parameters were obtained in the fitting profess of the simulated curves to the experimental results. It was suggested to construct a modified numerical model to describe the bypass flow which was observed in the experiment.

• Journal of the Korean Ceramic Society
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• v.33 no.8
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• pp.935-941
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• 1996

Two-dimensional carbon/carbon preforms made of PAN-based carbon yarn and phenolic resin were densified with pyrolysis of propane by pulse chemical vapor infiltration where repeated the cycle of gas introduction residence and evacuation. Maximim density increment was 14% when infiltration temperature and time were 100$0^{\circ}C$ and 21.25 hrs respectively. The distribution of deposits of pyrocarbon by this process has been occurred uniformly in the bottom middle and top of carbon/carbon composite preform Pulse CVI with residence is most effective in increasing density and shortening infiltration time among isothermal CVI and pulse CVI with and without residence.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.1
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• pp.485-492
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• 2013

The effect on collection efficiency with 2-stage vortex finder diameter and back mixing of solid flow due to swirling intensity, turbulence eddies, wall bouncing using the residence time distribution of particle flow in a common and modified cyclone. Higher collection efficiencies of fly ash in a modified cyclone(S = 13, 15cm) are showed than common cyclone. Collection efficiency in modified cyclone was highest at 2-stage vortex finder diameter, S = 13 cm. Variances of residence time distribution and average residence times of glass bead were increased with a diameter(S) of 2-stage vortex finder due to swirling intensity and turbulence eddies. Back mixing of solid flow in a modified cyclone were increased with a gas inlet velocity and showed higher than a common cyclone.

• Journal of Ocean Engineering and Technology
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• v.23 no.2
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• pp.47-52
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• 2009

A Lagrangian particle tracking model coupled with the Princeton Ocean Model were used to estimate the average residence time of coastal water in Masan Bay, Korea. Our interest in quantifying the transport time scales in Masan Bay was stimulated by the search for a mechanistic understanding of this spatial variability, which is consistent with the concept of spatially variable transport time scales. Tidal simulation was calibrated through a comparison with the results of semi-diurnal current and water elevation measured at the tidal stations of Masan, Gadeokdo. In the model simulations, particles were released in eight cases, including slack before ebb, peak ebb, slack before flood, and peak flood, during both spring and neap tides. The averaged values obtained from the particle release simulations were used for the average residence times of the coastal water in Masan Bay. The average residence times for the southeastern parts of Somodo and the Samho River, Masan Bay were estimated to be about 20~50days and 70~80days, respectively. The spatial difference for the average residence time was controlled by the tidal currents and distance from the mouth of the bay. Our results might provide useful for understanding the transport and behavior of coastal water in a bay and might be used to estimate the dissimilative capacity for environmental assessment.

• Journal of the Korean Operations Research and Management Science Society
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• v.19 no.3
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• pp.235-241
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• 1994

We consider a B/G/1 queueing with vacations, where the server closes the gate when it begins a vacation. In this system, customers arrive according to a Bernoulli process. The service time and the vacation time follow discrete distributions. We obtain the distribution of the number of customers at a random point in time, and in turn, the distribution of the residence time (queueing time + service time) for a customer. It is observed that solutions for our discret time B/G/1 gated vacation model are analogous to those for the continuous time M/G/1 gated vacation model.

• 한국연소학회:학술대회논문집
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• 1999.10a
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• pp.139-148
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• 1999

In oder to analyze the effect of operating conditions on pulverized coal combustion, a numerical study is conducted at the pulverized coal combustor. Eulerian approach is used for the gas phase, whereas Lagrangian approach is used for the particle phase. Turbulence is modeled using standard ${\kappa}-{\varepsilon}$ model. The description of species transport and combustion chemistry is based on the mixture fraction/probability density function(PDF) approach. Radiation is modeled using P-l model. The turbulent dispersion of particles is modeled using discrete random walk model. Swirl number of secondary air affects the flame front, particle residence time and carbon conversion. Primary/Secondary air mass ratio also affects the flame front but little affects the carbon conversion and particle residence time. Air-fuel ratio only affects the flame front due to lack of oxygen. Radiation strongly affects the flame front and gas temperature distribution because pulverized coal flame of high temperature is considered.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 1993.04a
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• pp.49-56
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• 1993

We consider a B/G/1 queueing system with vacations, where the server closes the gate when it begins a vacation. In this system, customers arrive according to a Bernoulli process. The service time and the vacation time follow discrete distributions. We obtain the distribution of the number of customers at a random point in time, and in turn, the distribution of the residence time (queueing time + service time) for a customer. This system finds an application in the performance evaluation of the DQDB protocol which has been adopted as the standard protocol for IEEE 802.6 MAN.

• Journal of Environmental Science International
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• v.8 no.2
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• pp.171-176
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• 1999

To estimate the residence times of aerosols in air, the activities of $^{210}Pb$ and $^{210}Po$ in aerosols were measured at 4 sites in Pusan. All aerosol samples were collected by a high volume air sampler from January to October 1996. The activities $^{210}Pb$ and $^{210}Po$ in Pusan were varied from 11.77 to 67.57 dpm/1000$m^3$ and from 2.63 to 15.91 dpm/1000$m^3$, respectively. The mean activities were 34.62 dpm/1000$m^3$ for $^{210}Pb$ and 8.24 dpm/1000$m^3$ for $^{210}Po$. The highest values of the activities of $^{210}Pb$ and $^{210}Po$ were appeared at P3 site and the lowest values at P4 site. During the sampling period, the trends of the activities of $^{210}Po$ and $^{210}Pb$ were similar to total suspended particulate matter(TSP) concentrations. The mean residence times of atmospheric aerosols calculated from $^{210}Po$/$^{210}Pb$ activity ratio was about 60~80 days in Pusan. The longest residence time of atmospheric aerosols was in January because of the lack of rainout and washout, but the shortest residence time was in August, largely due to scavenging effect by frequent rains. The activities of $^{210}Po$ and $^{210}Pb$ in atmospheric aerosols were different in time and space, which seems that the distribution of $^{210}Po$ and $^{210}Pb$ activities and scavenging processes in air may be controlled by the local and meteorological conditions.

• The Korean Journal of Rheology
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• v.3 no.2
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• pp.135-147
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• 1991

압출공정 중에 화학반응이 수반되는 경우에 화확반응은 온도와 체류시간분포 (Residence Time Distribution (RTD))에 의해 결정되므로 압출기의 설계 및 공정조건의 확 립에 있어서 RTD를 정확히 측정하거나 예측하는 것은 매우 중요하다. RTD를 예측하기 위 해 제안된 종래의 방법은 압출기내에서의 유동을 2차원으로 단순화하여 RTD와 체류시간분 포함수 f(T)와 누적 체류시간 분포함수 F(T)를 해석적으로 구하였다. 그러나 이러한 종래의 RTD에 관한 해석방법은 실제압출기 내부에서 일어나는 3차원적 순환유동(Circulatory Flow)을 정확하게 고려하지 못하는 문제점을 갖고 있다. 본논문에서는 RTD를 정확하게 예 측하기 위하여 3차원 순환유동을 고려한 RTD를 구하는 방식을 제시하고 f(T)에 관한 새로 운 공식을 유도하였다. 새로운 방식을 적용하기 위해서 유사 3차원(Quasi-3-Dimensional) 유한요소 해석법을 이용하여 속도분포를 구한 후에 순환유동을 고려한 RTD 및 f(T), F(T) 를 계산하였다. 순환유동이 고려안된 종래의 방법에 따른 계산 결과와 비교한 결과로서 종 래의 방식은 순환유동이 고려안되었기 때문에 RTD를 과소평가하는 경향이 있음을 알수 있 었다.