• 설비공학논문집
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• 제2권1호
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• pp.37-48
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• 1990

The drag and heat transfer reduction phenomena and degradation effects of drag reducing polymer solutions which are known as the viscoelastic fluids are investigated experimentally for the turbulent circular tube flows. Two stainless steel tubes are used for the experimental flow loops. Aqueous solutions of Polyacrylamide Separan AP-273 with concentrations from 300 to 1000 wppm are used as working fluids. Flow loops are set up to measure the friction factors and heat transfer coefficients of test tubes in the once-through system and the recirculating flow system. Test tubes are heated by power supply directly to apply constant heat flux boundary conditions on the wall. Capillary tube viscometer and falling ball viscometer are used to measure the viscous characteristics of fluids and the characteristic relaxation time of a fluid is determined by the Powell-Eyring model. The order of magnidude of the thermal entrance length of a drag reducing polymer solution is close to the order of magnitude of the laminar entrance length of Newtonian fluids. Dimensionless heat transfer coefficients of the viscoelastic non-Newtonian fluids may be represented as a function of flow behavior index n and newly defined viscoelastic Graetz number. As degradation continues viscosity and the characteristic relaxation time of the testing fluids decrease and heat transfer coefficients increase. The characteristic relaxation time is used to define the Weissenberg number and variations of friction factors and heat transfer coefficients due to degradation are presented in terms of the Weissenberg number.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.75-79
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• 2008

In this study, the numerical process for analyzing the automotive louver fin heat exchanger was developed with a 3D microscopic and semi-microscopic analysis. In the microscopic analysis, the simulation with the detailed meshes was performed for obtaining the characteristics of the heat exchanger. From this simulation, the numerical correlations of the heat transfer and flow friction were obtained. In the semi-microscopic analysis, the Semi-microscopic Heat Exchanger (SHE) method, which is characterized by a conjugate heat transfer and porous media analysis was used with the numerical correlation from the microscopic analysis. This analysis predicted the flow and heat transfer characteristics of the louver fin heat exchanger in the wind tunnel and vehicle. In the design of the louver fin heat exchanger, this numerical process can predict the performance and characteristic of the louver fin heat exchanger.

• Nuclear Engineering and Technology
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• 제41권7호
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• pp.929-944
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• 2009

The present study is concerned with the extension of the Effective Convectivity Model (ECM) to the phase-change problem to simulate the dynamics of the melt pool formation in a Light Water Reactor (LWR) lower plenum during hypothetical severe accident progression. The ECM uses heat transfer characteristic velocities to describe turbulent natural convection of a melt pool. The simple approach of the ECM method allows implementing different models of the characteristic velocity in a mushy zone for non-eutectic mixtures. The Phase-change ECM (PECM) was examined using three models of the characteristic velocities in a mushy zone and its performance was compared. The PECM was validated using a dual-tier approach, namely validations against existing experimental data (the SIMECO experiment) and validations against results obtained from Computational Fluid Dynamics (CFD) simulations. The results predicted by the PECM implementing the linear dependency of mushy-zone characteristic velocity on fluid fraction are well agreed with the experimental correlation and CFD simulation results. The PECM was applied to simulation of melt pool formation heat transfer in a Pressurized Water Reactor (PWR) and Boiling Water Reactor (BWR) lower plenum. The study suggests that the PECM is an adequate and effective tool to compute the dynamics of core melt pool formation.

• 한국의류학회지
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• 제18권2호
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• pp.244-251
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• 1994

The purpose of this study was to analyze conductive convective and radiative heat transfer characteristic of the nonwovens were studied by measuring thermal conductance at atmospheric and low air pressure. The results obtained were as follows . 1) As thickness of air layer Increased, overall heat transfer was decreased by reducing conductive and radiative heat trasfer. 2) The conductive and convective heat trasfer by air were in the range of 79~8971 of overall heat transfer. 3) As thickness of nonwoven increased for a given solidity, overall heat trasfer was decresed by increasing total thickness of air layer and by reducing conductive and radiative heat transfer. 4) For a given weight, increasing thickness is more effective than increasing solidity.

• 한국태양에너지학회 논문집
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• 제35권2호
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• pp.53-62
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• 2015

Boiling heat transfer characteristic is very important in the various industries such as solar thermal system, power generation, heat exchangers, cooling of high-power electronics components and cooling of nuclear reactors. Therefore, in this study, boiling heat transfer characteristics such as critical heat flux (CHF) and heat transfer coefficient under the pool boiling state were tested using graphene nanofluids. Graphene used in this study, which have the same thermal conductivity but with different sizes. The experimental results showed that the highest the CHF and boiling heat transfer coefficient increase ratio for graphene nanofluids was at the 0.01 vol.%. At the present juncture, the CHF and boiling heat transfer coefficient increase ratio of the small-sized graphene nanofluids was higher than the large-sized graphene nanofluids.

• 태양에너지
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• 제6권2호
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• pp.76-85
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• 1986

The study on the characteristics of heat transfer by various working fluid and wick structure is an important subject in order to design low temperature heat pipe. The purpose of this research was to study the heat transfer characteristics of heat pipe according to various working fluid and wick thickness by ADI method and experimental results. As the results the heat transfer by various working fluid could improve by good heat conductivity of fluid and small ratio t/k. The working fluid could be selected in close vicinity to boiling temperature among fluid properties the value of ratio little influenced heat transfer of heat pipe. In case of distilled water, the response of the effect in heat recovery was more rapidly showed than response of other working fluid. The maximum heat flux increased in proportion to the characteristics of working fluid but the pore and wick permeability among wick characteristic was little effect in the wetting state.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2006년도 제27회 추계학술대회논문집
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• pp.34-40
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• 2006

연소기 노즐은 고온 고압의 연소가스를 화학에너지에서 운동에너지로 변환시켜 추력을 발생시킨다. 따라서 노즐 내부 벽면은 고온 고압의 연소가스에 노출되며, 특히 노즐 목에서는 최대 열하중을 받는 구간으로서 열구조적으로 안정성을 확보한 냉각 시스템 설계가 이루어져야 한다. 본 연소기 노즐은 수냉 방식으로서 열전달 효율을 높이기 위해 냉각 채널 구조로 되어 있다. 본 연구에서는 연소기 노즐을 위한 냉각 채널 구조의 기본 설계안에 대해 유동 해석을 수행하고 공급 압력 및 유량 변화에 따른 입/출구 사이의 압력 강하량을 예측하여 초기 형상안에 대한 압력 손실 및 설계 유량 공급을 위한 압력 조건에 대해서 평가하고자 하였다. 최종 선정안에 대해서는 내부 열전달 및 유동장 해석을 수행하여 흐름 및 열구조 안정성을 평가하였다.

• Journal of Mechanical Science and Technology
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• 제16권9호
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• pp.1175-1182
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• 2002

The commercial viability of heat exchanger is mainly dependent on its long-term fouling characteristic because the fouling increases the pressure loss and degrades the thermal performance of a heat exchanger. An experimental study was performed to investigate the characteristics of fluid flow and heat transfer in a fluidized bed heat exchanger with circulating various solid particles. The present work showed that the higher densities of particles had higher drag force coefficients, and the increases in heat transfer were in the order of sand, copper, steel, aluminum, and glass below Reynolds number of 5,000.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.304-310
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• 2000

The experimental study has been conducted on heat transfer characteristics of the plate heat exchangers(PHE) by several researchers. However most of all were focused on a gasket-type plate heat exchanger. Therefore further studies are need for a brazed-type. In the present study, a brazed type plate heat exchanger was tested at a chevron angle of $70^{\circ},\;55^{\circ}$ and $45^{\circ}$ with R-22 and R-410A. Condensation temperatures were $24.5^{\circ}C$, and mass flux was ranged from 35 to $60kg/m^2s$. The inlet and exit conditions are in a superheated vapor and subcooled liquid, respectively. The heat transfer coefficient increased with the chevron angle. The heat transfer coefficient of R-22 was lamer than that of R-410A for all chevron angles.

• 대한기계학회논문집
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• 제13권5호
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• pp.1032-1043
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• 1989

본 연구에서는 해석적으로 열적 입구 길이를 규명하는데 필요한 와류 열확산 계수를 실험 결과를 이용하여 결정하고, 시험관 입구의 형상 변화가 열전달 특성에 미치는 영향을 실험적으로 결정하며, 열적 입구 길이 영역에서 국소 열전달 계수를 표시할 수 있는 실험식을 제시하고, 유체의 전단율에 따른 점성 계수의 실험 결과와 점탄성 유체의 특성시간을 이용한 새로운 무차원 수인 Weissenberg수를 결정하여 퇴화 현상을 분석하고저 한다.