• Title/Summary/Keyword: heat transfer method

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Development of a Simultaneous CAE System for the Application to Large Steel Castings (대형주강품에 대한 CAE 시스템 개발 연구)

  • Lee, Young-Chul;Lee, Doo-Ho;Kim, Jong-Ki;So, Chan-Young;Choi, Jeong-Kil;Hong, Chun-Pyo
    • Journal of Korea Foundry Society
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    • v.17 no.5
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    • pp.465-471
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    • 1997
  • An integrated computer program consisting of a pre-processor, main solver, and post-processor was developed for the design of large steel castings. The pre-processor, based on the AutoCAD, enables the user to produce approval drawings, casting design drawings and mesh diagrams in sequence using a personal computer. In the main solver, two numerical models were employed; one models the fluid flow during mold filling, and the other models the heat transfer and solidification. The post-processor can be used to present simulation results such as flow pattern, mold filling sequences, solidification times, temperature gradients and location of shrinkage defects by color graphics. In order to validate the applicability of the present integrated program, a series of experiments on simple-shaped steel castings were carried out. After the validation of the present model, it was applied to the casting design of the large steel anchor of an SC42 alloy. Various solidification parameters such as a temperature distribution and a solidification time in the casting and the mold were compared with those obtained experimentally. Simulated results predicting shrinkage defects were in good agreement with those obtained experimentally. It was found that the present method can be successfully applied to the quantitative casting design for complex-shaped large steel castings.

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Overall Heat Transfer Coefficient Measurement of Covering Materials with Thermal Screens for Greenhouse using the Hot Box Method (핫박스를 이용한 온실 피복재 및 보온재의 조합에 따른 관류열전달계수 측정)

  • Diop, Souleymane;Lee, Jong-Won;Na, Wook-Ho;Lee, Hyun-Woo
    • Journal of The Korean Society of Agricultural Engineers
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    • v.54 no.5
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    • pp.1-7
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    • 2012
  • 본 연구의 목적은 국내에서 상용되고 있는 온실 피복재 및 보온재의 조합에 따른 관류열전달계수를 핫박스를 이용하여 평가하는 것이다. 온실용 일중 및 이중 피복재와 이중 보온재의 조합에 대하여 야간천공복사 차단여부에 따른 관류열전달계수를 핫박스를 이용하여 실외에서 측정하였다. 처리조건은 일중피복, 이중피복, 이중피복과 이중 마트보온재 및 이중피복과 이중 다겹보온재의 조합조건과 천공복사 유무에 따른 조건이며 총 8가지이다. 제작된 핫박스는 상시 변화하는 외부의 기상조건하에서도 내부온도를 설정된 온도로 일정하게 잘 유지할 수 있었다. 온실 피복재 및 보온재의 관류열전달계수를 측정하는 실내용 측정장치는 반드시 야간천공복사를 모의할 수 있는 측정장치가 되어야 할 것이다. 야간복사를 차단함으로서 온실의 열 손실을 줄여 보온효과를 얻을 수 있을 것으로 분석되었다. 모든 피복방식에 대해 야간복사 차단장치 유무에 관계없이 높은 풍속에서의 관류열전달계수가 낮은 풍속에서보다 더 큰 것으로 나타났다. 본 연구에서 사용된 측정기법을 사용하면 국내에서 생산되는 피복재 및 보온재의 관류열전달 특성을 정량적으로 비교할 수 있을 것으로 기대된다.

A Study on the Characteristics of Time Dependent Temperature Change in a Automobile Washer Heater (자동차 워셔액 가열시스템의 온도 변화 특성에 관한 연구)

  • Ha, Ji-Soo;Lee, Seong-Bong;Lee, Dong-Kwon
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.14 no.3
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    • pp.1040-1044
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    • 2013
  • The present paper has been accomplished to elucidate the characteristics of temperature change in a car washer heater system for removal of frost formed at the surface of a car. The previous studies had used a simplified mathematical modeling to analyse the temperature change characteristics for a car washer heater system. In the present study, an unsteady computational fluid flow and heat transfer analysis for a washer heater system has been done by using computational fluid dynamic analysis method. From the present CFD analysis, the time dependent temperature change in a car washer heater system has been analysed and derived the heating time and ejection temperature of the washer liquid to establish the optimal design basis for a washer heater system.

An Experimental Study on Thermal Damage and Spalling of Concrete Lining in Tunnel Fire (터널화재시 콘크리트 라이닝의 폭렬 및 화재손상에 관한 실험적 연구)

  • Kim, Heung-Youl;Kim, Hyung-Jun;Cho, Kyung-Suk;Lee, Jae-Sung;Kwan, Ki-Hyuk
    • Fire Science and Engineering
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    • v.23 no.3
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    • pp.110-120
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    • 2009
  • In tunnel, though the frequency of fire occurrence is relatively lower than other structures, the characteristics of sealed space tends to cause the temperature to rapidly rise to more than $1000^{\circ}C$ within 5minutes after fire, which might eventually lead to a large fire that usually results in a loss of lives and the damage to the properties, not to mention a huge cost necessary for repair and maintenance after fire. We have developed various conditions of the heating furnace and the method to install a thermo couple within the furnace based on EFNARC and KS F 2257-1. Referring to tunnel fire scenarios, it clarified the heat transfer characteristics of concrete PC panel lining depending on fire intensity (ISO, $1^{\circ}C$/SEC, MHC, RWS), and to identify the range of thermal damage, the evaluation was carried out using ITA standard. As a result, 30mm under ISO fire condition, 20mm under $1^{\circ}C$/SEC, 100mm under MHC and 50mm under RWS were measured. And when it comes to spalling, 30mm was measured under RWS and MHC.

An Experimental Study on Pressure Loss in Straight Cooling Channels (직선형 냉각채널에서의 압력손실에 대한 실험적 연구)

  • Yoon, Wonjae;Ahn, Kyubok;Kim, Hongjip
    • Journal of the Korean Society of Propulsion Engineers
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    • v.20 no.4
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    • pp.94-103
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    • 2016
  • A regeneratively-cooled channel in a liquid rocket engine is used to effectively cool a combustion chamber inner wall from hot combustion gas, and the heat transfer/pressure loss characteristics should be predicted in advance to design cooling channels. In the present research, five cooling channels with different geometric dimensions were designed and the channels were respectively manufactured using cutter and endmill. By changing coolant velocity and downstream pressure, the effects of manufacturing method, channel shape, and flow condition on pressure losses were experimentally investigated and the results were compared with the analytical results. At same channel shape and flow condition, the pressure loss in the channel machined by the cutter was lower than that by the endmill. It was also found that the pressure loss ratio between the experimental result and the analytical data changed with the channel shape and flow condition.

Improvement of the flow characteristics for a $90^{\circ}$ turning duct by the nonaxisymmetric endwall and endwall boundary layer fence ($90^{\circ}$ 곡관에서의 비축대칭 끝벽과 끝벽 경계층 판을 이용한 유동특성 향상)

  • Cho, Jong-Jae;Kim, Sang-Jo;Seo, Jong-Chul;Kim, Kui-Soon;Jeong, Eun-Hwan
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2011.04a
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    • pp.406-413
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    • 2011
  • This paper presents the shape optimization of a nonaxisymmetric endwall and endwall boundary layer fence which improve the aerothermal environment of a gas turbine passage. The endwall and fence methods were used simultaneously. The turbine passage was simulated by a $90^{\circ}$ turning duct ($Re_D$=360,000). The main purpose of the present investigation was to focus on finding a nonaxisymmetric endwall and boundary layer fence with minimum total pressure loss in the passage and heat transfer coefficient on the endwall of the duct. An approximate optimization method was used for the investigation to secure the computational efficiency. Results indicated that a significant improvement in aerothermal environment can be achieved through the application of a nonaxisymmetric endwall and boundary layer fence.

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Comprehensive Consideration on the Discharge of Gases from Pressurized Vessels through Pressure Relief Devices (압력용기로부터 압력방출장치를 통한 가스 방출에 관한 포괄적 고찰)

  • Chung, Chang-Bock
    • Journal of the Korean Society of Safety
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    • v.35 no.6
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    • pp.32-45
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    • 2020
  • The problem of determining the discharge rates of gases from pressurized vessels through pressure relief devices was dealt with comprehensively. First, starting from basic fluid flow equations, detailed modeling procedures were presented for isentropic nozzle flows and frictional flows in a pipe, respectively. Meanwhile, physical explanations were given to choking phenomena in terms of the acoustic velocity, elucidating the widespread use of Mach numbers in gas flow models. Frictional flows in a pipe were classified into adiabatic, isothermal, and general flows according to the heat transfer situation around the pipe, but the adiabatic flow model was recommended suitable for gas discharge through pressure relief devices. Next, for the isentropic nozzle flow followed by adiabatic frictional flow in the pipe, two equations were established for two unknowns that consist of the Mach numbers at the inlet and outlet of the pipe, respectively. The relationship among the ratio of downstream reservoir pressure to upstream pressure, mass flux, and total frictional loss coefficient was shown in various forms of MATLAB 2-D plot, 3-D surface plot and contour plot. Then, the profiles of gas properties and velocity in the pipe section were traced. A method to quantify the relationship among the pressure head, velocity head, and total friction loss was presented, and was used in inferring that the rapid increase in gas velocity in the region approaching the choked flow at the pipe outlet is attributed to the conversion of internal energy to kinetic energy. Finally, the Levenspiel chart reproduced in this work was compared with the Lapple chart used in API 521 Standatd.

Preparation of CoFe2O4 Nanoparticle Decorated on Electrospun Carbon Nanofiber Composite Electrodes for Supercapacitors (코발트 페라이트 나노입자/탄소 나노섬유 복합전극 제조 및 슈퍼커패시터 특성평가)

  • Hwang, Hyewon;Yuk, Seoyeon;Jung, Minsik;Lee, Dongju
    • Journal of Powder Materials
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    • v.28 no.6
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    • pp.470-477
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    • 2021
  • Energy storage systems should address issues such as power fluctuations and rapid charge-discharge; to meet this requirement, CoFe2O4 (CFO) spinel nanoparticles with a suitable electrical conductivity and various redox states are synthesized and used as electrode materials for supercapacitors. In particular, CFO electrodes combined with carbon nanofibers (CNFs) can provide long-term cycling stability by fabricating binder-free three-dimensional electrodes. In this study, CFO-decorated CNFs are prepared by electrospinning and a low-cost hydrothermal method. The effects of heat treatment, such as the activation of CNFs (ACNFs) and calcination of CFO-decorated CNFs (C-CFO/ACNFs), are investigated. The C-CFO/ACNF electrode exhibits a high specific capacitance of 142.9 F/g at a scan rate of 5 mV/s and superior rate capability of 77.6% capacitance retention at a high scan rate of 500 mV/s. This electrode also achieves the lowest charge transfer resistance of 0.0063 Ω and excellent cycling stability (93.5% retention after 5,000 cycles) because of the improved ion conductivity by pathway formation and structural stability. The results of our work are expected to open a new route for manufacturing hybrid capacitor electrodes containing the C-CFO/ACNF electrode that can be easily prepared with a low-cost and simple process with enhanced electrochemical performance.

Technical Review on Liquid/Solid (Slush) Hydrogen Production Unit for Long-Term and Bulk storage (장주기/대용량 저장을 위한 액체/고체(Slush) 수소 생산 장치의 해외기술 동향분석)

  • LEE, CHANGHYEONG;RYU, JUYEOL;SOHN, GEUN;PARK, SUNGHO
    • Journal of Hydrogen and New Energy
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    • v.32 no.6
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    • pp.565-572
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    • 2021
  • Hydrogen is currently produced from natural gas reforming or industrial process of by-product over than 90%. Additionally, there are green hydrogens based on renewable energy generation, but the import of green hydrogen from other countries is being considered due to the output variability depending on the weather and climate. Due to low density of hydrogen, it is difficult to storage and import hydrogen of large capacity. For improving low density issue of hydrogen, the gaseous hydrogen is liquefied and stored in cryogenic tank. Density of hydrogen increase from 0.081 kg/m3 to 71 kg/m3 when gaseous hydrogen transfer to liquid hydrogen. Density of liquid hydrogen is higher about 800 times than gaseous. However, since density and boiling point of liquid hydrogen is too lower than liquefied natural gas approximately 1/6 and 90 K, to store liquid hydrogen for long-term is very difficult too. To overcome this weakness, this paper introduces storage method of hydrogen based on liquid/solid (slush) and facilities for producing slush hydrogen to improve low density issue of hydrogen. Slush hydrogen is higher density and heat capacity than liquid hydrogen, can be expected to improve these issues.

Approximate Optimization with Discrete Variables of Fire Resistance Design of A60 Class Bulkhead Penetration Piece Based on Multi-island Genetic Algorithm (다중 섬 유전자 알고리즘 기반 A60 급 격벽 관통 관의 방화설계에 대한 이산변수 근사최적화)

  • Park, Woo-Chang;Song, Chang Yong
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.20 no.6
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    • pp.33-43
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    • 2021
  • A60 class bulkhead penetration piece is a fire resistance system installed on a bulkhead compartment to protect lives and to prevent flame diffusion in a fire accident on a ship and offshore plant. This study focuses on the approximate optimization of the fire resistance design of the A60 class bulkhead penetration piece using a multi-island genetic algorithm. Transient heat transfer analysis was performed to evaluate the fire resistance design of the A60 class bulkhead penetration piece. For approximate optimization, the bulkhead penetration piece length, diameter, material type, and insulation density were considered discrete design variables; moreover, temperature, cost, and productivity were considered constraint functions. The approximate optimum design problem based on the meta-model was formulated by determining the discrete design variables by minimizing the weight of the A60 class bulkhead penetration piece subject to the constraint functions. The meta-models used for the approximate optimization were the Kriging model, response surface method, and radial basis function-based neural network. The results from the approximate optimization were compared to the actual results of the analysis to determine approximate accuracy. We conclude that the radial basis function-based neural network among the meta-models used in the approximate optimization generates the most accurate optimum design results for the fire resistance design of the A60 class bulkhead penetration piece.