• Title/Summary/Keyword: High Cooling Characteristics

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Study on three-dimensional numerical simulation of shell and tube heat exchanger of the surface ship under marine conditions

  • Yi Liao;Qi Cai;Shaopeng He;Mingjun Wang;Hongguang Xiao;Zili Gong;Cong Wang;Zhen Jia;Tangtao Feng;Suizheng Qiu
    • Nuclear Engineering and Technology
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    • v.55 no.4
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    • pp.1233-1243
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    • 2023
  • Shell-and-tube heat exchanger (STHX) is widely used by virtue of its simple structure and high reliability, especially in a space-constrained surface ship. For the STHX of the surface ship, roll, pitch and other motion of the ship will affect the heat transfer performance, resistance characteristics and structural strength of the heat exchanger. Therefore, it is urgent to carry out numerical simulation research on three-dimensional thermal hydraulic characteristics of surface ship STHX under the marine conditions. In this paper, the numerical simulation of marine shell and tube heat exchanger of surface ship was carried out using the porous media model. Firstly, the mathematical physical model and numerical method are validated based on the experimental data of a marine engine cooling water shell and tube heat exchanger. The simulation results are in good agreement with the experimental results. The prediction errors of pressure drop and heat transfer are less than 10% and 1% respectively. The effect of marine conditions on the heat transfer characteristics of the heat exchanger is investigated by introducing the additional force model of marine condition to evaluate the effect of different motion parameters on the heat transfer performance of the heat exchanger. This study could provide a reference for the optimization of marine heat exchanger design.

Solidification Characteristics of Squeeze Cast Al Alloy Composites (Squeeze Cast한 Al기지 금속복합재료의 응고거동)

  • Kim, Dae-Up;Kim, Jin;Park, Ik-Min
    • Journal of Korea Foundry Society
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    • v.11 no.3
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    • pp.208-216
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    • 1991
  • The solidification behavior of the squeeze cast composites of aluminum alloys reinforced with boron fiber($100{\mu}m$) and silicon carbide fibers($140{\mu}m$ and $15{\mu}m$) were investigated. Al-4.5wt%Cu and Al-l0wt%Mg were chosen for the matrix phase of the composites. In the squeeze cast specimen with high thermal difference between fiber and melt, the average secondary dendrite arm spacing(DAS) in reinforced alloy is smaller than that in unreinforced alloy. It was also observed that primary ${\alpha}$ and non-equilibrium eutectic, which seems to be penetrated and solidified at the final stage of the solidification of the matrix, are irregularly distributed around fibers. It is considered that cold fibers serve as heterogeneous nucleation site. While in the remelted and resolidified specimen without temperature difference, the DAS was not changed with reinforcement and microstructure reveals non-equilibrium eutectic with relatively uniform thickness around fibers. It might be evident the nucleation starts at interfiber region. Microsegregation decreases with the decrease in cooling rate and with reinforcement in the as-squeeze cast specimen. Al-10wt% Mg alloy shows less microsegregation than Al-4.5wt%Cu alloy.

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Characteristic Analysis of the Cooling System Using Ice Slurry Type Heat Storage System (아이스슬러리형 빙축열 시스템을 이용한 냉각 시스템의 성능에 관한 실험적 연구)

  • Lee, Dong-Won;Kim, Jeong-Bae
    • Journal of Energy Engineering
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    • v.20 no.1
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    • pp.30-35
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    • 2011
  • To clarify the hydraulic and thermal characteristics of ice slurry which made from 6.5% ethylene glycol-water solution flow in the double tube and plate type heat exchanger, experimental studies were performed. The mass flux and ice fraction of ice slurry were varied from 800 to 3500 kg/$m^2s$(or 7 to 17 kg/min) and from 0 to 25%, respectively. Through the experiment, it was found that the measured pressure drop and heat transfer rate increase with the mass flux and ice fraction; however the effect of ice fraction appears not to be significant at high mass flux region. At the region of low mass flux, a sharp increase in the pressure drop and heat transfer rate were observed depends on mass flux.

Growth of GaAs Crystal by an Improved VGF Apparatus

  • Chul-Won Han;Kwang-Bo Shim;Young-Ju Park;Seung-Chul Park;Suk-Ki Min
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.1 no.1
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    • pp.17-25
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    • 1991
  • The construction details of VGF apparatus with a DM(direct monitoring) furnace for the growth of low defect crystal and characteristics of GaAs crystal grown by this apparatus are described. The average dislocation densities and EL2 concentration of as-grown undoped GaAs along the different solidified fractions exhibit $4{\times}10^{2}-7{\times}10^{3}cm^{-2}$ and $6{\times}10^{14}-4{\times}10^{15}cm^{-3}$, which are less than those observed for liquid encapsulated Czochralski(LEC) or high-pressure vertical gradient freeze(VGF) crystals. These remarkable reduction of the dislocation densities and EL2 concentrations were explained by the lower temperature gradient ($dT/dx-10^{\circ}/cm$) and slower rates of post - growth cooling ($20^{\circ}C/hr:1240-1000^{\circ}C,\;30^{\circ}C/hr:1000-700^{\circ}C$). Also, The Hall mobilities, carrier concentrations show uniform distribution throughtout 80% of the ingot length.

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Effect of Si on Mechanical Properties and Microstructure in 0.27% C-1.5% Mn-1.0% Cr Steel (0.27% C-1.5% Mn-1.0% Cr 강의 미세조직과 기계적성질에 미치는 Si의 영향)

  • Jeong, Woo Chang
    • Journal of the Korean Society for Heat Treatment
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    • v.30 no.3
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    • pp.117-126
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    • 2017
  • The variation in microstructure and mechanical properties during heat treatment was examined in a series of 0.27% C-1.5% Mn-1.0% Cr steels with silicon contents in the range of 0 to 1.0 wt%. It was found that addition of 0.5%~1.0% silicon increased both tensile strength and impact toughness through solid solution strengthening and microstructural refinement. 0.27% C-1.0% Si-1.5% Mn-1.0% Cr steel showed tensile strength of 1,700 MPa in the as-quenched condition and the steel revealed a full martensitic structure even after air cooling from $900^{\circ}C$ to room temperature, showing air hardening characteristics. Tempering at $150^{\circ}C$ which corresponds to the typical paint-baking temperature after painting of body in white, slightly decreased the tensile strength and increased elongation, but substantially increased the impact toughness compared to the as-quenched steel.

A Comparative Analysis of the Energy Load due to Window Area Ratio of Domestic Public Buildings

  • An, Kwang-Ho;Hyun, Eun-Mi;Kim, Yong-Sik
    • KIEAE Journal
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    • v.15 no.1
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    • pp.21-27
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    • 2015
  • In the case of public buildings, fast communication and transparency in the administration and the public, as well as ensuring visibility and lighting performance using a glass curtain wall is symbolically expressed through the transparent glass skin. This study is a simulation in order to derive the basic data for the establishment of the improvement of the heating and cooling load analysis according to the window area ratio changes with respect to the high effectiveness of the government's large public building energy consumption analysis and green building certification system of guidelines was analyzed by a change in the energy load. Glass curtain wall is light and visibility, the symbolic meaning of communication, etc., but is widely used in a variety of characteristics, in terms of energy consumption being disadvantaged sheath plan should have been. Design, including the Atrium, is much less energy than energy consumption by the window area ratio. Thus, while compliance with design guide lines, the atrium and I like the burden of a large space ratio and energy load consists of only glass suggest that require more research on that given in the guidelines.

Economic Evaluation of HTS Transformer by Predicting Market Penetration Price (초전도변압기 시장진입가격 예측을 통한 경제성 분석)

  • 김종율;이승렬;윤재영
    • The Transactions of the Korean Institute of Electrical Engineers A
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    • v.53 no.9
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    • pp.507-512
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    • 2004
  • HTS (High Temperature Superconducting) Transformer has the several useful characteristics in the viewpoints of technical and economical. Especially, an HTS transformer replaces the copper wire coils in a conventional transformer with lower loss HTS wire. In addition, inexpensive, environmentally benign liquid nitrogen replaces the conventional oil as the electrical insulation (dielectric) and provides the necessary cooling for the HTS transformer Therefore, the Life-cycle cost of an HTS transformer is much more attractive than conventional because it is more energy efficient, lighter in weight, smaller in size, and environmentally compliant. HTS transformer can be the best way to replace with conventional transformer in the future. In these days, companies world-wide have conducted researches on HTS transformer. A development project for a 154kV HTS transformer is proceeding at a research center and university in Korea. In this paper, we investigate the expected price of HTS transformer to have a merit in viewpoint of economic aspect. First, life-cycle cost of conventional transformer is calculated and based on this, the expected price of HTS transformer is evaluated. which HTS transformer is competitive against conventional transformer.

Study on the Feasibility of Applying Forecasted Weather Data for Operations of a Thermal Storage System (축열운전을 위한 기상예보치의 이용가능성에 대한 검토)

  • Jung Jae-Hoon;Shin Young-Gy;Park Byung-Yoon
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.18 no.1
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    • pp.87-94
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    • 2006
  • In this paper, we investigated a feasibility of applying highest and lowest temperatures of the next day forecasted from a meteorological observatory to operation of an air-conditioning system with thermal storage. First we investigated specific characteristics of the time series of forecasted temperatures and errors in Osaka from 1994 to 1996. Since the forecast error is not always small, it might be difficult to use the forecasted data without correction for the sizing and the control of the thermal storage system. On the other hand, the autocorrelation functions of the forecast errors decrease relatively slowly during high summer season when cooling thermal storage is required. Since the values of the autocorrelation function; for one day are larger than 0.4, not small, the forecast errors can be predicted by proper statistical analysis. Thus, the forecasted values of the highest temperatures for the next day were improved by using the stochastic time series models.

Detailed Measurement of Heat/Mass Transfer in a Rotating Equilateral Triangular Channel with Smooth Walls (회전하는 매끈한 정삼각 유로 내 열/물질전달 분포 측정)

  • Kim, Kyung-Min;Lee, Dong-Hyun;Cho, Hyung-Hee
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.31 no.7 s.262
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    • pp.628-634
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    • 2007
  • The present study investigated the heat/mass transfer characteristics in an equilateral triangular channel simulating the leading edge cooling passage in gas turbine blade. Using naphthalene sublimation method and pressure measurement experiments, local mass (heat) transfer and pressure coefficients were obtained. The experiments were conducted with three rotating numbers between 0.0 and 0.1; two channel orientations of $0^{\circ}$ (model A) and $30^{\circ}$ (model B); the fixed Reynolds number of 10,000. The results showed that the channel rotation caused the heat transfer discrepancy between suction and pressure sides. Due to the secondary flow induced by Coriolis force, the high heat transfer appeared on the pressure side. When the channel orientation was $30^{\circ}$ (model B), the secondary flow caused the more uniform heat transfer distribution among leading edge and inner wall on pressure side than that of the model A.

Characteristics of Scroll-type Stirling Engine for Solar Power (태양열 발전용 스크롤 방식 스털링 엔진의 특성)

  • Kim, Young-Min;Shin, Dong-Kil;Kim, Woo-Young;Kim, Hyun-Jin;Lee, Sang-Tae
    • 한국신재생에너지학회:학술대회논문집
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    • 2008.05a
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    • pp.169-173
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    • 2008
  • Stirling engine is a promising heat engine with a high efficiency, muti-fuel capability, low emission, quiet operation, very low maintenance and long life. As one of the promising applications, solar power system based on the Stirling dish, providing net solar-to-electric conversion efficiencies reaching 30%, can operate as stand-alone units in remote locations or can be linked together in groups to provide utility-scale power. This paper introduced a new Scroll-type Stirling engine, being developed for solar power, superior to conventional Stirling engines. The Scroll-type Stirling engine is characterized as traits of continuous and wholly separated compression and expansion; one-way flow system; direct cooling and heating the fluid in the working spaces through the extensive inner surfaces of scroll wraps. All theses traits contribute to achieving thermodynamic cycle closer to the ideal Stirling cycle (exactly speaking, Ericsson cycle).

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