• Title/Summary/Keyword: convection tube

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An Experimental Study on Hydration Heat Control in The Mass Concrete Using Oscillating Capillary Tube Heat Pipe (진동세관형 히트파이프(OCHP)를 이용한 매스콘크리트의 수화열 제어에 관한 실험적 연구)

  • Beak, Dong-Il;Kim, Myung-Sik;Lee, Moon-Sik;Kim, Kang-Min;Yum, Chi-Sun
    • Proceedings of the Korea Concrete Institute Conference
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    • 2006.05b
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    • pp.409-412
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    • 2006
  • In process of reinforced concrete(RC) box structure, the heat of hydration may cause serious thermal cracking problems. In order to eliminate hydration heat of mass concrete, this paper reports results of hydration heat control in mass concrete using the OCHP(Oscillating Capillary tube Heat Pipe). Recently OCHP is drawn special attention from these points of low cost as well as short construction schedule for the manufacturing of heat exchanger, flexibility, simplification and high performance. There were three RC box molds$(1.2{\times}1.2{\times}1.2m)$ which shows a difference as compared with each other. One was not equipped with OCHP. While others were equipped with OCHP and these were cooled with air natural convection and spraying water respectively. The OCHP was composed of copper pipe with 12 turns(O.D : 4mm, I.D : 2.8mm). The working fluid was R-22 and its charging ratio was 30(Vol. %). In order to analyze the distribution of temperature and index figure of thermal crack in sequential placement of mass concrete, we used HYCON of computer program. As a result of the experiment, the peak temperature decreased about $15.6\sim23.4^{\circ}C$ than the general specimen and the probability of thermal crack generated in mass concrete decreased up to 0%.

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A Study on Field Applications of Hydration Heat Control in the Mass Concrete Using Oscillating Capillary Tube Heat Pipe (OCHP를 이용한 매스콘크리트 수화열 제어의 현장적용에 관한 연구)

  • Yum, Chi-Sun;Bae, Won-Mahn;Kim, Myung-Sik;Beak, Dong-Il;Kim, Kang-Min
    • Proceedings of the Korea Concrete Institute Conference
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    • 2006.05b
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    • pp.413-416
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    • 2006
  • In process of the mass concrete structure, the heat of hydration may cause serious thermal cracking. In order to eliminate hydration heat of mass concrete, this paper reports results of hydration heat control of mass concrete using the Oscillating Capillary tube Heat Pipe(OCHP). There were the several RC box molds which shows a difference as compared with each other. One was not equipped with OCHP. The others were equipped with OCHP. All of them were cooled with natural air convection. The OCHP was composed of copper pipe with 11 turns(outer diameter : 4mm, inner diameter : 2.8mm) and heat type was non-looped type. The working fluid was R-22 and its charging ratio was 40% by volume. The core of the concrete temperature was approximately $55^{\circ}C$ in the winter without OCHP. But the concrete temperature with OCHP was reduced its difference in temperature with the outdoor temperature to $12^{\circ}C$. Finally we saw the index figure of the thermal crack of the structures were varied from 0.75 to 1.47.

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Heat transfer characteristics of R - 407C condensing inside smooth horizontal tubes (냉매 R-407c의 수평평골 응축관내 열전달특성에 관한 연구)

  • 오후규;문정욱;노건상
    • Journal of Advanced Marine Engineering and Technology
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    • v.21 no.2
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    • pp.144-156
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    • 1997
  • Experimental results for forced convection heat transfer of pure refrigerant and nonrefrigerant mixtures during condensing inside horizontal smooth tubes, double pipe heat exchanger of 7.5 mm ID and 4 000 mm long inside tube, are presented. Pure refrigerant R - 22 and R - 407 c, the mixture of R - 32 + R - 125 + R - 134a (23/25/52, wt %) are used as the test fluids. The ranges of parameters are $114.3{\sim}267.1 kg/(m^2 {\cdot} s)$ of mass velocity, <0$\sim$1.0 of quality. The vapor pressure, vapor temperature and tube wall temperature were measured. Using these data, the local and average heat transfer coefficients for the condensation are obtained. At the same given experimental conditions, the condensation heat transfer coefficients for NARMs R - 407c were lower than those for the pure refrigerant of R - 22. Local heat transfer characteristics for R - 407c were different from pure refrigerant R - 22. The condensaheat transfer coefficients for R - 407c and R - 22 increased with mass velocity. Based on the data a prediction method was presented for the calculation of dimensionless average heat transfer coefficient.

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An Experimental Study on Fluid Flow and Heat Transfer Around Four Circular Cylinders of In-line (직렬 4원주 주위의 유체유동 및 열전달에 관한 실험적 연구)

  • Choe, Soon-Youl;Kim, Min-Soo
    • Journal of Advanced Marine Engineering and Technology
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    • v.32 no.5
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    • pp.691-697
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    • 2008
  • Heat exchangers are commonly used in practice in a wide range of application, from heat and air-conditioning system in a household, to chemical processing and power production in large plant. An Experimental study was conducted to investigated the fluid flow and heat transfer around four circular cylinders of in-line in a cross flow of air. The local and average heat transfer characteristics for tube banks are investigated in the present study. Heat transfer in a heat exchanger usually involves convection in each fluid and conduction through the wall separating the two fluid. The in-line pitch ratio was in the range $1.5{\leq}L/d{\leq}4.0$, where L is the center distance and d the cylinder diameter, and in the Reynolds number $8,000{\leq}Re{\leq}50,000$. The local and mean Nusselt numbers were estimated. Subsequently, the heat transfer characteristics of four circular cylinders are found to exhibit a strong dependency upon the separation point of their upstream cylinders.

The Elasto-Plastic Stress Analysis of Tube Expansion for Marine TEMA(Tubular Exchanger Manufactures Associations) Heat Exchangers (선박용 TEMA 열교환기의 전열관 확관시 탄소성 응력 해석)

  • Kim, Ok-Sam;Park, Jong-Dai
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.17 no.2
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    • pp.173-178
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    • 2011
  • Marine TEMA heat exchanger is the equipment to transfer the heat energy through both fluids that are enclosed separately by applying conduction and convection phenomena for a large vessels, Especially for heat exchanger working under the high temperature and high pressure, the expansion ratio should be taken into account other than under the low temperature and low pressure. This study was tried to find out the ideal expansion ratio through analyzing the elasto-plastic stress behavior of deformation while tubes are expanded with the finite element methods.

The finite difference analysis on temperature distribution by coordinate transformation during melting process of phase-change Material (상변화 물질의 용융과정에 있어서 좌표변환을 이용한 온도분포의 해석적 연구)

  • Kim, J.K.;Yim, J.S.
    • Solar Energy
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    • v.5 no.2
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    • pp.77-83
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    • 1985
  • An analysis is performed to investigate the influence of the buoyancy force and the thickness variation of melting layer in the containment that is filled with phase-change Material surrounding a cylindrical heating tube during melting process. The phase-change material is assumed to be initially solid at its phase-change temperature and the remaining solid at any given time is still at the phase-change temperature and neglecting the effect of heat transfer occuring within the solid. At the start of melting process, the thickness of melting layer is assumed to be a stefan-problem and after the starting process, the change of temperature and velocity is calculated using a two dimensional finite difference method. The governing equations for velocity and temperature are solved by a finite difference method which used SIMPLE (Semi Implicit Method Pressure linked Equations) algorithm. Results are presented for a wide range of Granshof number and in accordance with the time increment and it is founded that two dimensional fluid flow occurred by natural convection decreases the velocity of melting process at the bottom of container. The larger the radius of heating tube, the higher heat transfer is occurred in the melting layer.

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Assessment of CUPID code used for condensation heat transfer analysis under steam-air mixture conditions

  • Ji-Hwan Hwang;Jungjin Bang;Dong-Wook Jerng
    • Nuclear Engineering and Technology
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    • v.55 no.4
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    • pp.1400-1409
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    • 2023
  • In this study, three condensation models of the CUPID code, i.e., the resolved boundary layer approach (RBLA), heat and mass transfer analogy (HMTA) model, and an empirical correlation, were tested and validated against the COPAIN and CAU tests. An improvement on HMTA model was also made to use well-known heat transfer correlations and to take geometrical effect into consideration. The RBLA was a best option for simulating the COPAIN test, having mean relative error (MRE) about 0.072, followed by the modified HMTA model (MRE about 0.18). On the other hand, benchmark against CAU test (under natural convection and occurred on a slender tube) indicated that the modified HMTA model had better accuracy (MRE about 0.149) than the RBLA (MRE about 0.314). The HMTA model with wall function and the empirical correlation underestimated significantly, having MRE about 0.787 and 0.55 respectively. When using the HMTA model, consideration of geometrical effect such as tube curvature was essential; ignoring such effect leads to significant underestimation. The HMTA and the empirical correlation required significantly less computational resources than the RBLA model. Considering that the HMTA model was reasonable accurate, it may be preferable for large-scale simulations of containment.

The heat transfer and pressure drop characteristics of $CO_2$ during supercritical region in a horizontal tube (초임계 영역에서 수평관내 $CO_2$ 열전달과 압력강하)

  • 이동건;오후규;김영률;손창효
    • Journal of Advanced Marine Engineering and Technology
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    • v.28 no.3
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    • pp.500-508
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    • 2004
  • The heat transfer coefficients during gas cooling process of carbon dioxide in a horizontal tube were investigated. The experiments are conducted without oil in the refrigerant loop. The main components of the refrigerant loop are a receiver, a variable-speed pump, a mass flow meter, a pre-heater, and a gas cooler(test section). The water loop consists of a variable-speed pump, an isothermal tank, and a flow meter. The gas cooler is a counterflow heat exchanger by cooled water flowing in the annulus. The $CO_2$ flows in the horizontal stainless steel tube. which is 9.53mm in O.D. and 7.75mm in I.D. The gas cooler is 6 [m] in length. which is divided into 12 subsections, respectively. The experimental conditions considered in the study are following range of variables : refrigerant temperature is between 20 and $100^{\circ}C$. mass fluxes ranged from 200 to 400kg/($m^2$.s), average pressure varied from 7.5 to 10.0MPa. The main results were summarized as follows : The friction factors of $CO_2$ in the gas cooler show a relatively good agreement with those predicted by Blasius' correlation. The local heat transfer coefficient in the gas cooler has compared with most of correlations, which are the famous ones for forced convection heat transfer of turbulent flow. The results show that the local heat transfer coefficient of gas cooler agrees well with the correlation by Bringer-Smith except that at the region near pseudo critical temperature. while that at the near pseudo critical temperature is higher than the correlation.

Investigation of Characteristics of Passive Heat Removal System Based on the Assembled Heat Transfer Tube

  • Wu, Xiangcheng;Yan, Changqi;Meng, Zhaoming;Chen, Kailun;Song, Shaochuang;Yang, Zonghao;Yu, Jie
    • Nuclear Engineering and Technology
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    • v.48 no.6
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    • pp.1321-1329
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    • 2016
  • To get an insight into the operating characteristics of the passive residual heat removal system of molten salt reactors, a two-phase natural circulation test facility was constructed. The system consists of a boiling loop absorbing the heat from the drain tank, a condensing loop consuming the heat, and a steam drum. A steady-state experiment was carried out, in which the thimble temperature ranged from $450^{\circ}C$ to $700^{\circ}C$ and the system pressure was controlled at levels below 150 kPa. When reaching a steady state, the system was operated under saturated conditions. Some important parameters, including heat power, system resistance, and water level in the steam drum and water tank were investigated. The experimental results showed that the natural circulation system is feasible in removing the decay heat, even though some fluctuations may occur in the operation. The uneven temperature distribution in the water tank may be inevitable because convection occurs on the outside of the condensing tube besides boiling with decreasing the decay power. The instabilities in the natural circulation loop are sensitive to heat flux and system resistance rather than the water level in the steam drum and water tank. RELAP5 code shows reasonable results compared with experimental data.

Numerical Study of Forced Convection Nanofluid in a U-Bend Tube (U-밴드 관 내부 나노유체의 강제대류에 관한 수치적 연구)

  • Jo, Sung-Won;Choi, Hoon-Ki;Park, Yong-Gap
    • Journal of Convergence for Information Technology
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    • v.12 no.3
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    • pp.141-150
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    • 2022
  • Fluid flow and thermal characteristics of laminar nanofluid(water/Al2O3) flow in a circular U-bend tube have been studied numerically. In this study, the effect of Reynolds number and the solid volume fraction and the impact of the U-bend on the flow field, the heat transfer and pressure drop was investigated. Comparisons with previously published experimental works on horizontal curved tubes show good agreements between the results. Heat transfer coefficient increases by increasing the solid volume fraction of nanoparticles as well as Reynolds number. Also, the presence of the secondary flow in the curve plays a key role in increasing the average heat transfer coefficient. However, the pressure drop curve increases significantly in the tubes with the increase in nanoparticles volume fraction.