• Journal of the Korean Solar Energy Society
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• v.31 no.3
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• pp.73-79
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• 2011

ORC(organic Rankine cycle) has potential of reducing consumption of fossil fuels and has many favorable characteristics to exploit low-temperature heat sources. This work analyzes performance of ORC with superheating using low-temperature energy sources in the form of sensible energy. Maximum mass flow rate of a working fluid relative to that of a source fluid is considerd to extract maximum power from the sources. Working fluids of R134a, $iC_4H_{10}$ and $C_6C_6$, and source temperatures of $120^{\circ}C$, $200^{\circ}C$ and $300^{\circ}C$ are considered in this work. Results show that for a fixed source temperature thermal efficiency increases with evaporating temperaure, however net work per unit mass of source fluid has a maximum with respect to the evaporating temperature in the range of low source temperature. Results also show that the maximum power extraction is possible with R134a for the source temperature of $120^{\circ}C$, with $iC_4H_{10}$ for $200^{\circ}C$, and with $C_6C_6$ for $300^{\circ}C$.

• Journal of Wetlands Research
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• v.19 no.4
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• pp.451-458
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• 2017

In this study, the removal efficiency of the wetland in terms of particulate matter and dead water zone through the application of baffles in the sedimentation were simulated with the use of Computational Fluid Dynamics (CFD) to determine the design of a cost-effective constructed wetland. As a result, it was analyzed that the application of the baffle in the sedimentation tank affect the flow and sedimentation rate. Fine particles such as $2{\mu}m$ and $5{\mu}m$ showed high sedimentation rate when the baffles are installed horizontally. large particles such as $10{\mu}m$ and $20{\mu}m$ showed also high deposition rate when the baffles are installed vertically. In addition, the vertical baffles is considered to be more efficient than other baffle types in terms of maintenance since the particulate matter are concentrated in narrow areas. Therefore, it is considered that the selection of the most applicable type of baffle depends on the design purpose of the wetland to be constructed.

• Journal of the Korean Solar Energy Society
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• v.22 no.1
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• pp.23-30
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• 2002

This study concerns the performance of the heat transfer of the thermosyphon having 80 internal fins in which boiling and condensation occur. Water has been used as the working fluid. The Liquid filling as the ratio of working fluid volume to total volume of thermosyphon have been used as the experimental parameters. The heat flux and heat transfer coefficient at the condenser are estimated from the experimental results. The experimental results have been assessed and compared with existing theories. As a result of the experimental investigation we can state that the maximum heat flow rate in the thermosyphon prove to depend upon the liquid fill quantity. The relatively high rates of heat transfer have been achived operating in the thermosyphon with axial internal fins. Also, the thermosyphon with internal micro fins can be used to achieve some inexpensive and compact heat exchangers in low temperature. In addition, it is to obtain the overall heat transfer coefficients and the characteristics as a operating temperature for the practical applications.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.16 no.1
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• pp.95-104
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• 2003

This paper deals with the analytic and FEM analyses of sloshing frequency response of incompressible, invicid and irrotational flow in two dimensional rectangular tank. We use Laplace equation based on potential theory as governing equation. For small amplitude sloshing motion, the linearized free surface condition was applied and the analytic solution as obtained by the separation of variables. To simulate the effect of the energy dissipation due to viscous damping, artificial viscous coefficient is introduced and the divergence of response at resonance frequencies may be avoided by this coefficient. This problem was solved by FEM using 9-node elements in order to predict the maximum amplitude of sloshing response. Numerical results of free surface height, fluid pressure and fluid force show good agreement with those by analytic solution. After verifying the test FEM program, we analyze the frequency response characteristics of sloshing to the fluid height.

• Journal of Biosystems Engineering
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• v.43 no.1
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• pp.21-29
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• 2018

Purpose: The objective of this study is to evaluate the performance of the conical solar concentrator (CSC) system, whose design is focused on increasing its collecting efficiency by determining the optimal conical angle through a theoretical study. Methods: The design and thermal performance analysis of a solar concentrator system based on a $45^{\circ}$ conical concentrator were conducted utilizing different mass flow rates. For an accurate comparison of these flow rates, three equivalent systems were tested under the same operating conditions, such as the incident direct solar radiation, and ambient and inlet temperatures. In order to minimize heat loss, the optimal double tube absorber length was selected by considering the law of reflection. A series of experiments utilizing water as operating fluid and two-axis solar tracking systems were performed under a clear or cloudless sky. Results: The analysis results of the CSC system according to varying mass flow rates showed that the collecting efficiency tended to increase as the flow rate increased. However, the collecting efficiency decreased as the flow rate increased beyond the optimal value. In order to optimize the collecting efficiency, the conical angle, which is a design factor of CSC, was selected to be $45^{\circ}$ because its use theoretically yielded a low heat loss. The collecting efficiency was observed to be lowest at 0.03 kg/s and highest at 0.06 kg/s. All efficiencies were reduced over time because of variations in ambient and inlet temperatures throughout the day. The maximum efficiency calculated at an optimum flow rate of 0.06 kg/s was 85%, which is higher than those of the other flow rates. Conclusions: It was reasonable to set the conical angle and mass flow rate to achieve the maximum CSC system efficiency in this study at $45^{\circ}$ and 0.06 kg/s, respectively.

• Textile Coloration and Finishing
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• v.34 no.1
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• pp.27-37
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• 2022

In this study, a study and interpretation of the spinning process in copolymerized aramid spinning was conducted. In order to proceed with the spinning process modeling and analysis, the spinning process was modeled through the physical property modeling of the spinning solution and the structural modeling of the spinneret, and structural stability and flow of the spinneret for this spinning were analyzed. After modeling the spinning solution and the spinneret in a virtual space, the pack pressure and flow rate when the spinning solution was discharged were simulated. Macroscopically, the structural stability of the spinneret was confirmed at the standard pack pressure (100 kg·f/cm²), and microscopically, the flow rate and pressure drop data of the spinning solution according to the L/D(Length (L)/Diameter (D)) value were analyzed. Based on the research and development of virtual engineering modeling and analysis, we present the possibility of changing the shape and mechanical properties of copolymer aramid fibers according to the spinning process.

• The korean journal of orthodontics
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• v.40 no.2
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• pp.66-76
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• 2010

Objective: Obstructive sleep apnea (OSA) is a common disorder which is characterized by a recurrence of entire or partial collapse of the pharyngeal airway during sleep. A given tidal volume must traverse the soft tissue tube structure of the upper airway, so the tendency for airway obstruction is influenced by the geometries of the duct and characteristics of the airflow in respect to fluid dynamics. Methods: Individualized 3D FEA models were reconstructed from pretreatment computerized tomogram images of three patients with obstructive sleep apnea. 3D computational fluid dynamics analysis was used to observe the effect of airway geometry on the flow velocity, negative pressure and pressure drop in the upper airway at an inspiration flow rate of 170, 200, and 230 ml/s per nostril. Results: In all 3 models, large airflow velocity and negative pressure were observed around the section of minimum area (SMA), the region which narrows around the velopharynx and oropharynx. The bigger the Out-A (outlet area)/ SMA-A (SMA area) ratio, the greater was the change in airflow velocity and negative pressure. Conclusions: Pressure drop meaning the difference between highest pressure at nostril and lowest pressure at SMA, is a good indicator for upper airway resistance which increased more as the airflow volume was increased.

• Journal of Korean Society of Environmental Engineers
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• v.31 no.11
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• pp.1033-1040
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• 2009

One thing to note in cyclone operation and design is to minimize the pressure drop with the enhancement of the efficiency of dust collection. This can be facilitated by the detailed resolution of complex fluid flow occurring inside a cyclone. To this end, the main objective of this study was to obtain the detailed fluid dynamics by the development of a reliable computation method and thereby to figure out the physics of dust collection mechanism for more extreme environment caused by high temperature and pressure condition. First of all, the computer program developed was evaluated against experimental result. That is, the numerical calculation predicts well the data of experimental pressure drop as a function of flow rate for the elevated pressure and temperature condition employed in this study. The increase of pressure and temperature generally affects significantly the collection efficiency of fine particle but the effect of pressure and temperature appears contrary each other. Therefore, the decrease of collection efficiency caused by the high operating temperature mainly due to the decrease of gaseous density can be remedied by increase of operating pressure. After the evaluation of the program, a series of parametric investigations are performed in terms of major cyclone design or operating parameters such as tangential velocity and vortex finder diameter for dusts of a certain range of particle diameters, etc. As expected, tangential velocity plays the most important effect on the collection efficiency. And the efficiency was not affected significantly by the change of the length of vortex finder but the diameter of vortex finder plays an important role for the enhancement of collection efficiency.

• The KSFM Journal of Fluid Machinery
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• v.11 no.6
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• pp.24-30
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• 2008

In order to enhance the heat/mass transfer, a turbulator has been installed at the exit of injection hole for the impingement/effusion cooling system. The local heat/mass transfer coefficients have been obtained by a naphthalene sublimation method. Experiments have been carried out at the fixed jet Reynolds number of 10,000. Two turbulators with different diameter have been used in the current study. The result presents that the turbulator leads to the increase in flow mixing and jet velocity, consequently enhancing the heat/mass transfer at a stagnation region. Further, the stagnation region is divided into four small areas with peak value. In the existence of initial crossflow, the stagnation regions move downstream and low heat/mass transfer regions are formed regardless of the installation of turbulator. However, the increased jet velocity by turbulator reduces the crossflow effect against the jet, resulting in decrease of low heat/mass transfer regions. Compared to the case without turbulator, the installation of turbulator yields $5{\sim}10%$ augmentation in averaged Sh value.

• Journal of Energy Engineering
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• v.21 no.4
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• pp.398-401
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• 2012

In this Study, efficiencies of the scroll expander under development for organic Rankine cycle using engine waste heat of vehicle have been analyzed and compared with the commercial scroll expander. While operating organic Rankine cycle for analysing expander efficiencies, power of expander, inlet temperature of expander, inlet pressure of expander and the flow rate of the working fluid(refrigerant R134a) have been measured. Overall efficiency of the expander has been shown the very low level compared with the overall efficiency of the commercial expander. Especially, because the low volumetric efficiency has much effect on overall efficiency, the working fluid leakage trouble of expander has to be solved surely for improvement of the expander overall efficiency.