• 한국정밀공학회지
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• 제15권4호
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• pp.76-82
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• 1998

Sealing an oil-air mixture plays important roles to have an enhanced lubrication for high speed spindle. Current work is emphasized on the investigation of the air jet effect on the protective collar type labyrinth seal. To improve the sealing capability of conventional labyrinth seal, air jet is injected against through the leakage flow. It has a combined geometry of a protective collar type and an air jet type. In this study, both of a numerical analysis by CFD(Computational Fluid Dynamics) and experimental measurements are carried out to verify sealing improvement. Both of the turbulence and the compressible flow model are introduced in CFD analysis. The sealing effect of the leakage clearance and the air jet magnitude are studied for various parameter in the experiment. The results of pressure drop in the experiment match reasonably to those of the simulation by introducing a flow coefficient. Effects of sealing improvement are explained as decreasing of effective leakage clearance by air jetting. Thus, sealing effect is improved by amount of air jetting even though clearance becomes larger.

• Nuclear Engineering and Technology
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• 제52권7호
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• pp.1417-1428
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• 2020

The design of a nuclear reactor core requires basic thermal-hydraulic information concerning the heat transfer regime at which onset of nucleate boiling (ONB) will occur, the pressure drop and flow rate through the reactor core, the temperature and power distributions in the reactor core, the departure from nucleate boiling (DNB), the condition for onset of flow instability (OFI), in addition to, the critical velocity beyond which the fuel elements will collapse. These values depend on coolant velocity, fuel element geometry, inlet temperature, flow direction and water column above the top of the reactor core. Enough safety margins to ONB, DNB and OFI must-emphasized. A heat transfer package is used for calculating convection heat transfer coefficient in single phase turbulent, transition and laminar regimes. The main objective of this paper is to study the possibility of power upgrading of WWR-S research reactor from 2 to 10 MW_th. This study presents a one-dimensional mathematical model (axial direction) for steady-state thermal-hydraulic design and analysis of the upgraded WWR-S reactor in which two types of plate fuel elements are employed. FOR-CONV computer program is developed for the needs of the power upgrading of WWR-S reactor up to 10 MW_th.

• 대한기계학회논문집B
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• 제26권5호
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• pp.658-665
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• 2002

This paper presents a new winding method in electronic descaling (ED) technology. Conventional ED technology Produces an oscillating electric field via Faraday's law to provide the necessary molecular agitation to dissolve mineral ions. However, the proposed method produces an additional agitation force for mineral ions, called Lorentz's force. Experiments were performed using various Renolds numbers. A series of tests was conducted to measure the pressure drop across the test section and the overall heat transfer coefficient as a function of time. In order to accelerate the rate of fouling, artificial hard water, 1000ppm CaCO$_3$, was used throughout the tests. The results show that the new winding method accelerates the collision of the mineral ions, thereby improving the system efficiency. The present study can develope more effective fouling-removing equipment with change of estabishment method of coil.

• Journal of Advanced Marine Engineering and Technology
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• 제30권2호
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• pp.275-283
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• 2006

Experiment and three dimensional numerical investigations of incompressible turbulent flow through square channels with one- and two-sided ribbed walls are performed to determine pressure drop and heat transfer. The CFX(version 5.7) software package is used for the computation. The ribbed walls have a $45^{\circ}$ inclined square rib. Uniform heat flux is maintained on whole inner heat transfer channel area. The numerical results coincide with experimental data that obtained for $7,600{\le}Re{\le}24.900$, the pitch-to-rib height ratio (p/e) of 8.0. and the rib height-to-channel hydraulic diameter ratio ($e/D_h$) of 0.0667. The results show that values of local heat transfer coefficient and friction factor in the channel with two-sided ribbed wall are higher than those in the channel with one-sided ribbed walls.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1997년도 춘계학술대회 논문집
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• pp.625-629
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• 1997

Sealing an oil-air mixture plays important roles to have an enhanced lubrication for high speed spindele. Current work was emphased on the investigation of air jet effect on the protective collar type labyrinth seal. To improve the sealing capability of conventional labyrinth seal,ari jet was injected against through the leakage flow. It has a combined geometry of a protective collar type and an air jet type. In this study, both of a numerical analysis by CFD (Computational Fluid Dynamics) and experimental measureements are carried out of verify sealing improvement. But of the turbulence and the compressible flow model were introduced in CFD analysis. The sealing effect of the leakage clearance and the air jet magnitude were studied for variousparameter in the experiment. The results of pressure drop in the experiment match reasonably to those of the simulation by introducing a flow coefficient. Effects of sealing improvement are explained as decreasing of effective leckage clearance by air jetting. Thus, sealing effect is improved by amount of air jetting even though clearance become larger.

• 설비공학논문집
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• 제2권2호
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• pp.127-136
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• 1990

Air-solid bed has been known to be an effective heat transfer augmentation device which could be applied to heat exchangers. In this study, pressure drop and heat transfer characteristics of vertical annular fluidized bed heat exchanger with air flowing through were studied experimentally. The experiments was conducted to calculate overall heat transfer coefficient on fluidized bed heat exchangers immersed single vertical tube and investigate minimum fluidized velocity in fluidized bed of alumina beads and steel balls. The influence of flow direction, particle diameter, the heights of static bed and air mass fluidizing velocity has been examined. The experimental results showed the optimum operating condition and effective static bed height for fluidized bed heat exchangers. For the same power loss, comparisions of heat transfer effect between the fluidized bed heat exchanger and the single phase forced convetion heat exchanger indicate that both miniaturization of heat exchanger and heat transfer augmentation at low flow velocity are possible by application of the air-solid to heat exchangers.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.893-898
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• 2009

The quantity of discharged oil from a compressor is one of the most important issues for proper operation of refrigeration system. If the oil is increased in the system not only pressure drop is increased in other components, such as evaporator and gas cooler but also heat transfer coefficient in the heat exchangers is decreased. In addition, the lack of oil in the compressor may cause a critical of the system failure. In this study, one stage single rotary compressor is used for measuring oil circulation ratio(OCR). Carbon dioxide and PAG oil are used as refrigerant and lubricant. Using a U-tube densimeter, mixture density is measured. Characteristics of oil circulation ratio have been investigated for $CO_2$ rotary compressor in the range of operation frequency 45 Hz to 63 Hz and the suction temperature range of $0^{\circ}C$ to $15^{\circ}C$. The results obtained indicate that the oil circulation ratio is increased as the suction temperature or compressor operating frequency is increased.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2000년도 KIASC Conference 2000 / 2000년도 학술대회 논문집
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• pp.43-47
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• 2000

Two modes of shock waves, a compression shock wave and a thermal shock wave, propagating in He II have been investigated. The shock waves are at a time generated by the impingement of a gasdynamic shock wave onto a He II free surface in the newly developed superfluid shock tube facility. Superconductive temperature sensors, piezo-type pressure transducers and visualization photograph were used for the measurement of them and the phenomena induced by them were investigated in detail. It is found that the compression by a compression shock wave in He II causes temperature drop because He II has negative thermal expansion coefficient. the thermal shock wave is found to be of a single triangular waveform with a limited shock strength. The waveform is similar to that generated by stepwise strong heating from an electrical heater for relatively long heating time. In the experiments at the temperatures near the lambda temperature, no thermal shock wave is sometimes detected in shock compressed He II. It can be understood that shock compression makes He Ii convert to He I in which no thermal shock wave is excited.

• 대한기계학회논문집B
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• 제26권7호
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• pp.919-926
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• 2002

Down scaled combustor undergoes increased heat loss that results in incomplete combustion or quenching of the flame as a consequence. Therefore, effect of enhanced heat loss should be understood to design a MEMS scale combustion devices. Existing combustion models are inadequate for micro combustors because they were developed for analysis of regular scale combustor where heat loss can be ignored during the flame propagation. In this research a combustion model is proposed in order to estimate the heat loss and predict quenching limit of flame in a down scaled combustor. Heat loss in the burned region is expressed in a convective form as a product of wall surface area, heat transfer coefficient and temperature difference. Comparison to the measurements showed satisfactory agreement of the pressure and temperature drop. Quenching is accounted for by introducing a correlation of quenching parameter and heat loss. The present model predicted burnt fraction of gases with reasonable accuracy and proved to be applicable in thermal design of a micro combustor.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 하계학술발표대회 논문집
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• pp.754-757
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• 2008

To maintain the indoor air quality, many ventilation systems and technologies have been developed in the highly insulated and air tight buildings. In this study, a porous construction material, which is applicable to passive ventilation system, is developed and measured the performances of the permeability and the resistance of water vapor, and the dust collection efficiency. The average coefficient of water vapor permeability shows $3.6\;g/m^2{\cdot}h{\cdot}mmHg$, which is slightly higher than Hanji ($2.4{\sim}3.2\;g/m^2{\cdot}h{\cdot}mmHg$) and the average water vapor resistance factor shows $0.303\;g/m^2{\cdot}h{\cdot}mmHg/g$, which is slightly smaller than Hanji($0.309{\sim}0.315\;g/m^2{\cdot}h{\cdot}mmHg/g$). The pressure drop of the porous construction material is smaller than the HEPA filter and the minimum dust collection efficiency shows 82.8% in the range of $2{\sim}9\;cm/s$.