• Journal of computational fluids engineering
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• v.15 no.1
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• pp.46-55
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• 2010

In this study, the heat transfer and fluid flow characteristics of a condenser for a refrigerator are analyzed with the numerical method. The main objective of the study is to obtain basic data in order to develop a new type of condenser focused on an influence of thermal resistance of air side and thermal contact resistance on the heat transfer performance. The CFD technique was used for whole study, and experiments were performed in order to verify the reliability of the numerical analysis and predict the thermal contact resistance. In this study, a heat exchanger sample was made of a part of condenser to make the experimental and numerical analysis simple and efficient. Water was used for the inner working fluid of the heat exchanger, and an experimental apparatus was composed concisely. A heat exchanger sample of tube type was used to verify the reliability of numerical analysis, and a heat exchanger of fin and tube type was used to predict the ratio of thermal contact resistance to the overall thermal resistance.

• Journal of Korean Society for Atmospheric Environment
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• v.31 no.4
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• pp.385-395
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• 2015

This study evaluated indoor environmental characteristics in an office room equipped both with ventilation window system and central cooling system. Fresh air is supplied only by the central cooling system whereas indoor air is discharged outside through both ceiling diffuser and a ventilation window system. Numerical study is conducted by changing the volumetric flow rates of exhaust ports of each system. For estimating the performance of this coupled system, $CO_2$ concentration and Predicted Mean Vote (PMV) were calculated using Computational Fluid Dynamics (CFD) simulation. The more the ceiling diffuser exhausts indoor air, the more the $CO_2$ concentration decreases. However, when the ventilation window system exhausts more indoor air, thermal comfort level gets improved in the office room with cooling system. Therefore, when the ventilation window system is operated, the coupled operation with central cooling system should be considered for enhancing indoor air quality and thermal comfort, together.

• Journal of Mechanical Science and Technology
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• v.15 no.2
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• pp.268-276
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• 2001

In order to improve the efficiency of a direct contact heat exchanger for a solar thermal energy system, the working fluid should be dispersed into small and uniform droplets, and stay within a heat exchanger for a long time. Therefore, installation of meshes in a direct contact heat exchanger is suggested in the present study, and the performance of the direct contact heat exchanger with several layers of meshes is experimentally investigated. Diethyl phthalate is used as the working fluid, and the performance of the heat exchanger is tested for several different operating conditions and compared to that of the heat exchanger without meshes. The results of this investigation show that meshes make droplets uniform and small when the flow rate is low. The relationship between the Peclet number and the Nusselt number becomes linear if it is steady. And, the Nusselt number for the direct contact heat exchanger with meshes becomes greater than that without meshes as the Peclet number increases.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.3
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• pp.95-103
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• 2010

Roll to Roll (R2R) is one of the most promising production technologies in the printed electronics such as OLEDs, e-paper, backplanes, RFID because this technology can save production cost and increase production speed. Printed electronics includes various processes such as printing, drying, winding, unwinding, and so on. In printed electronics R2R system, air-flotation oven is employed for drying process. Therefore, it is essential to introduce efficient and fast drying process when printing is finished. This paper considers the analysis of drying process in R2R that involves hot air flow. Air-flotation oven consists of non-contact supports and drying of coated web materials such as plastic films and paper. In this paper, experimental results and numerical analysis of pressure-pad air bar are investigated. The aerodynamic characteristics of pressure-pad air bar are numerically calculated using computational fluid dynamics (CFD) approach. Then the measured values of the aerodynamic forces for air bars are compared with those of CFD analysis.

• Journal of the Korea Institute of Military Science and Technology
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• v.20 no.3
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• pp.405-412
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• 2017

In the present study, two phase flows around a projectile vertically launched from an underwater platform have been numerically investigated by using a three dimensional multi-phase RANS flow solver based on pseudo-compressibility and a homogeneous mixture model on unstructured meshes. The relative motion between the platform and projectile was described by six degrees of freedom(6DOF) equations of motion with Euler angles and a chimera technique. The propulsive power of the projectile was modeled as the fluid force acting on the lower surface of the body by the compressed air emitted from the platform. Qualitative analysis was conducted for the time history of vapor volume fraction distributions. Uncorking pressure around the projectile and platform was analyzed to predict impact force acting on the surfaces. The results of 6DOF analysis presented similar tendency with the surficial pressure distributions.

• Journal of KSNVE
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• v.9 no.6
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• pp.1247-1258
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• 1999

This paper presents vibration control of a CD-ROM(compact disc-read only memory) drive feeding system consisting of a new type of CD-ROM mount using an electro-rheologocal(ER) fluid. Chemically treated starch particles and silicon oil are used for EF fluid, and its field-dependent yield stresses are experimentally distilled under both the shear and the flow modes. On the basis of the yield stress, an appropriate size of ER CD-ROM mount adapted to conventional feeding system is designed and manufactured. Vibration isolation performance of the proposed mount is evaluated in the frequency domain and compared with that of conventional rubber mount. The ER CD-ROM mount is then installed to the drive feeding system and the system equation of motion is derived. The skyhook controller is then incorporated with the fuzzy technique to improve the performance of ER CD-ROM mount. A set of fuzzy parameters and control rules are obtained from a relation between vertical displacement and pitching motion of the feedng system. Followingthe formulation of the fuzzy-skyhook controller, computer simulation is undertaken in order to evaluate vibration suppression of the CD-ROM drive feeding system subjected to various excitations.

• The KSFM Journal of Fluid Machinery
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• v.18 no.1
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• pp.20-28
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• 2015

The pump-turbine impeller is the key component of pumped storage power plant. Current design methods of pump-turbine impeller are private and protected from public viewing. Generally, the design proceeds in two steps: the initial hydraulic design and optimization design to achieve a balanced performance between pump mode and turbine mode. In this study, the 3D inverse design method is used for the initial hydraulic impeller design. However, due to the special demand of high performance in both pump and reverse mode, the design method is insufficient. This study is carried out by modifying the geometrical parameters of the blade which have great influence and need special consideration in obtaining the high performance on the both modes, such as blade shape type at low pressure side (inlet of pump mode, outlet of turbine mode) and the blade lean at blade high pressure side (outlet of pump mode, inlet of turbine mode). The influence of the geometrical parameters on the performance characteristic is evaluated by CFD analysis which presents the efficiency and internal flow results. After these investigations of the geometrical parameters, the criteria of designing pump-turbine impeller blade low and high sides shape is achieved.

• Journal of Society of Preventive Korean Medicine
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• v.27 no.3
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• pp.35-46
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• 2023

Objectives : Gumiganghwal-tang and its main components have been used for treatment of cough, headache, joint pain and fever. Using a respiratory inflammatory model, we intend to demonstrate the its anti-inflammatory effect and immune mechanism of Gumiganghwal-tang. Methods : We induced the respiratory inflammation mouse model by papain treatment. Female BALB/C mice (8 weeks old) were divided into three groups as follows: saline control group, papain treatment group (vehicle), papain and Gumiganghwal-tang (200 mg/kg) treatment group (n=4). To verify the anti-inflammatory effect of Gumiganghwal-tang extracts, we measured the infiltration of inflammatory cells in bronchoalveolar lavage fluid (BALF) and nasal lavage fluid (NALF). Additionally, the efficacy of Gumiganghwal-tang extracts on Th2 cell population and alveolar macrophage in lung were analyzed by using flow cytometry. Results : Gumiganghwal-tang extracts administration decreased inflammatory cell infiltration in BALF and NALF, especially of eosinophils. Furthermore, interleukin-5 level was reduced in lung by drug administration. Interestingly, Gumiganghwal-tang extracts treatment also decreased the Th2 cell (CD4⁺GATA3⁺) population and increased the alveolar macrophage (CD11b⁺CD11c⁺) population in lung. Conclusions : Our findings indicate that Gumiganghwal-tang extracts have anti-inflammatory effects by mediating Th2 cell and alveolar macrophage cell activation.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.19 no.2
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• pp.109-116
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• 2023

This study presents a CRUD modelling to simulate the thermal resistance behavior of CRUD, deposited on the surface of a cladding tube of a fuel assembly. When heat produced from fuels transfers to a coolant through a cladding tube, the CRUD acting as an additional thermal resistance is expressed as two layers, i.e., a solid oxide layer and an imaginary fluid layer, which are added to the experimental tube's heat structure of the MARS-KS input data. The validation calculation for the experiments performed in UNIST-DISNY facility showed that the center and surface temperatures of the cladding tube increased as the porosity and the steam amount inside pores of the CRUD got higher. In addition, the temperature gradient in the imaginary fluid layer was calculated to be larger than that in the solid oxide part, indicating that the steam amount inside the layer acted more largely as thermal resistance. It was also evaluated through sensitivity calculations that the cladding tube temperature was more sensitive to the CRUD porosity and the steam amount in pores than to the inlet flow rate of the coolant.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.12
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• pp.5661-5668
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• 2012

In the era of water scarcity, saving toilet water is one of the most effective ways to save water. In this study, two-phase flow for the development of highly-efficient toilet has been analysed with VOF(Volume Of Fluid) method. Since the whole model requires extensive computing time, part of the whole model has also been adopted to reduce the analysis time. Four different rim models were considered for flow distribution analysis and sizes of rim holes were found to become more important rather than locations or numbers of rim holes in achieving flow distribution effectively. In addition, velocity and pressure of two-phase flow due to siphon phenomenon have been studied through the analysis of whole model. Therefore, this study provides a variety of fundamental data for the development of highly-efficient toilet.