• Journal of Hydrogen and New Energy
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• v.28 no.4
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• pp.426-432
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• 2017

Hydrothermal carbonization (HTC) is an effective and environment friendly technique; it possesses extensive potential towards producing high-energy density solid fuels. it is a carbonization method of thermochemical process at a relatively low temperature ($180-250^{\circ}C$). It is reacted by water containing raw material. However, the production and quality of solid fuels from HTC depends upon several parameters; temperature, residence time, and pressure. This study investigates the influence of operating parameters on solid fuel production during HTC. Especially, when food waste was reacted for 2 hours, 4 hours, and 8 hours at $200^{\circ}C$ and 2.0-2.5 MPa, Data including heating value, proximate analysis and water content was consequently collected and analyzed. It was found that reaction temperature, residence time are the primary factors that influence the HTC process.

• Journal of computational fluids engineering
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• v.7 no.3
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• pp.17-26
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• 2002

Computational fluid dynamic(CFD) analysis has been frequently applied to the waste incinerators to understand the flow performance for various design and operating parameters. Since the computational modeling inevitably requires many simplifications and complicated sub-models, validity of the results should be carefully evaluated. In this study, major computational modeling and procedure of usual simulation methods for the grate-type waste incinerators were assessed. Usual simulation method does not explicitly incorporate the waste combustion, simply by assuming the combustion gas properties from the waste bed which is treated as an inlet plane. However, effect of this arbitrary assumption on the overall flow pattern is not significant, since the flow pattern is dominated by strong pattern of jet flows of the secondary air. Thus, this method is valid in understanding the effect of flow-related parameters. In analyzing the results, deriving conclusive information directly from temperature and chemical species concentration should be avoided, since the model prediction for the gaseous reaction and the radiation reveals significant discrepancies against the actual phenomena. Use of quantitative measures such as residence time is very efficient in evaluating the flow performance.

• Journal of the Korean Society of Combustion
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• v.4 no.1
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• pp.1-15
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• 1999

In order to analyze the sensitivity on the pulverized coal flames of the several variables, a numerical study was conducted at the gasification process. Eulerian approach is used for the gas phase, whereas lagrangian approach is used for the solid phase. Turbulence is modeled using the standard $k-{\varepsilon}$ model. The turbulent combustion incorporates eddy dissipation model. The radiation was solved using a Monte-Carlo method. One-step two-reaction model was employed for the devolatilization of Kideco coal. In pulverized flame of long liftoff height, the initial turbulent intensity seriously affects the position of flame front. The radiation heat transfer and wall heat loss ratio distort the temperature distributions along the reactor wall, but do not influence the reactor performance such as coal conversion, residence time and flame front position. The primary/secondary momentum ratio affects the position of flame front, but the coal burnout is only slightly influenced. The momentum ratio is a variable only associated with the flame stabilization such as flame front position. The addition of steam in the reactor has a detrimental effect on all the aspects, particularly reactor temperature and coal burnout.

• Journal of computational fluids engineering
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• v.10 no.1
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• pp.56-62
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• 2005

Large eddy simulation of vortexing flow of molten steel in the continuous casting mold with and without DC magnetic field was conducted. The influence of the position of magnetic field to the residence time and depth of the vortex was analyzed. The mechanism of the influence of magnetic field to the vortexing flow was found. The computational results show that the vortexing flow is the result of shearing of the two un-symmetric surface flows from the mold narrow faces when they meet adjacent to the SEN; the un-symmetric flow for turbulent vortex is caused by turbulent energy of the fluid and that for biased vortex is caused by biased flow and the turbulent energy of fluid; with the moving of the magnetic field from the centerline of the outlet of the SEN to the free surface, the surface velocity is decreased gradually and the depth of the turbulent vortex and the biased vortex is decreased, the residence time is increased with the magnetic field moves from DL=120mm to DL=60mm and then decreased; the turbulent vortex and the biased vortex can be eliminated when the magnetic field is located at the free surface.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.32 no.2
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• pp.26-34
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• 2000

Understanding the nip geometry and heat transfer phenomena of soft nip calenders, which has been used in the production of newsprint and coated papers for many years, is very important since improper setting of soft nip calendering conditions causes deterioration of paper quality and productivity. In this study theoretical analysis on nip pressure and heat transfer phenomena in the nip of soft nip calenders has been made. The variables examined were calendering pressure, surface temperature of the heating roll, nip residence time and ingoing sheet moisture, By measuring nip widths and maximum nip pressure with Prescale film at a normal temperature, accurate line load has been obtained. With this line load, nip pressures at different temperature and nip widths were calculated. Results showed that as temperature increased, nip widths increased and nip pressures decreased. Equations derived for the heat conduction phenomena in soft nip calender nip were derived based on the semi-infinite plate and finite difference method and were used for the analysis of heat transfer within the nip. Temperature profiles in z-direction of paper within the nip were obtained. Finite difference method allowed more accurate analysis of the heat transfer in the calender nip. In this study newsprint and coated paper were considered as a single plate and two-layer plate consisted of sheet and coating layers, respectively. Heat trans-fer to paper increased as heated roll surface temperature and nip residence time were increased.

• 한국연소학회:학술대회논문집
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• 2004.06a
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• pp.149-157
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• 2004

In the present paper we studied experimentally fundamental optimization of oxygen enriched pyrolysis melting incinerator, Characteristics of this system was confirmed dealing with the gas flow and combustion properties for the inside secondary air injection. The experiment setup has a disposal rate of 30kg/hr which was measured by the inside temperature and gas. Along with above experiments, the three-dimensional computation was employed to analyse the combustion fluid dynamics and gas residence time. Equations for turbulence and heat - transmission as well as chemical reactions were solved by using common codes. The experimental combustion chamber was composed of staged combustion types structure for reducing NOx. Finally, it was verified that the control of the secondary air and air ratio of thermo stack were important. In the computational analysis, it showed reasonable agreement with the experimental results regarding the temperature and discharged gas concentration.

• Ocean and Polar Research
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• v.37 no.3
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• pp.179-188
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• 2015

This study was carried out to determine the optimal number of ARGO floats in the East Sea in order to maximize their applications. The dominant spatio-temporal scale, size of the domain, and the typical float lifetimes in the East Sea were taken into consideration. The mean spatial de-correlation scale of temperature on isobaric surfaces reaches about 60 km. The minimum necessary number of floats is about 82 on average in order to secure independent ARGO profiles with the de-correlation scale. Considering the float lifetimes, about 27 floats per year should be deployed to maintain the 82 ARGO float array every year. To obtain spatially uniform distribution of ARGO float data, mean residence time and dispersion rate (basin area/residence time) of ARGO floats were evaluated in each basin of the East Sea. A faster (slower) dispersion rate requires more (less) ARGO floats to maintain the spatially uniform number of floats. According to the analysis, it is likely that the optimal ratio of the number of floats for each basin is 1:2:4 corresponding to Ulleung Basin:Yamato Basin:Japan Basin. In order to maintain relatively uniform ARGO observing networks, it is necessary to establish a long-term plan for deployment strategy based on float pathways and the dispersion rate parameters estimated by using currently active ARGO float trajectory data as well as reanalysis data.

• Journal of ILASS-Korea
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• v.21 no.2
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• pp.78-87
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• 2016

This study experimentally investigated the effects of droplet temperature on the heat transfer characteristics during collision of a single droplet on a heated wall above the Leidenfrost temperature. Experiments were performed by varying temperature from 40 to $100^{\circ}C$ while the collision velocity and wall temperature were maintained constant at 0.7 m/s at $500^{\circ}C$, respectively. Evolution of temperature distribution at the droplet-wall interface as well as collision dynamics of the droplet were simultaneously recorded using synchronized high-speed video and infrared cameras. The local heat flux distribution at the collision surface was deduced using the measured temperature distribution data. Various physical parameters, including residence time, local heat flux distribution, heat transfer rate, heat transfer effectiveness and vapor film thickness, were measured from the visualization data. The results showed that increase in droplet temperature reduces the residence time and increases the vapor film thickness. This ultimately results in reduction in the total heat transfer by conduction through the vapor film during droplet-wall collision.

• Journal of Environmental Science International
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• v.23 no.6
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• pp.1151-1156
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• 2014

The photocatalytic decomposition characteristics of single n-pentane, n-pentane mixed with methyl ethyl ketone (MEK), and n-pentane mixed with ethyl acetate (EA) by cylindrical UV reactor installed with $TiO_2$-coated perforated plane were studied. The effects of the residence time, the inlet gas concentration, and the oxygen concentration were investigated. The removal efficiency of n-pentane was increased with increasing the residence time and the oxygen concentration, but decreased with increasing the inlet concentration of n-pentane. The photocatalytic decomposition rates of single n-pentane, n-pentane mixed with MEK, and n-pentane mixed with EA fitted well on Langmuir-Hinshelwood kinetics equation. The maximum elimination capacities of single n-pentane, n-pentane mixed with MEK, and n-pentane mixed with EA were obtained to be $465g/m^3{\cdot}day$, $217g/m^3{\cdot}day$, and $320g/m^3{\cdot}day$, respectively. The presence of coexisting MEK and EA vapor had a negative effect on the photocatalytic decomposition of n-pentane and the negative effect of MEK was higher than that of EA.

• International Journal of Control, Automation, and Systems
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• v.1 no.2
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• pp.210-214
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• 2003

This paper presents a residence time distribution (RTD) measurement method using a radioisotope tracer and the estimation method of RTD model parameters to analyze a submerged bio-reactor. The mathematical RTD models have been investigated to represent the flow behavior and the existence of stagnant regions in the reactor. Knowing the parameters of the RTD model is important for understanding the mixing characteristics of a reactor The radioisotope tracer experiment was carried out by injecting a radioisotope tracer as a pulse into the inlet of the reactor and recording the change of its concentration at the outlet of the reactor to obtain the experimental RTD response. The parameter estimation was performed by the Levenberg-Marquardt optimization algorithm. The proposed scheme allowed the parameter estimation of RTD model suggested by Adler-Hovorka with very low deviations. The estimation procedure is shown to lead to accurate estimation of the RTD parameters and to a good agreement between experimental and simulated response.