• Nuclear Engineering and Technology
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• v.28 no.4
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• pp.405-414
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• 1996

In this paper, the unsteady 2-dimensional turbulent flow model for thermal stratification in a pressurizer surge line of PWR plant is proposed to numerically investigate the heat transfer and flow characteristics. The turbulence model is adapted to the low Reynolds number K-$\varepsilon$ model (Davidson model). The dimensionless governing equations are solved by using the SIMPLE (Semi-Implicit Method for Pressure Linked Equations) algorithm. The results are compared with simulated experimental results of TEMR Test. The time-dependent temperature profiles in the fluid and pipe nil are shown with the thermal stratification occurring in the horizontal section of the pipe. The corresponding thermal stresses are also presented. The numerical result for thermal stratification by the outsurge during heatup operation of PWR shows that the maximum dimensionless temperature difference is about 0.83 between hot and cold sections of pipe well and the maximum thermal stress is calculated about 322MPa at the dimensionless time 28.5 under given conditions.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.119-122
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• 2009

The purpose of this study is to design of film-cooling ring for the small thrust rocket engine using green propellants(Hydrogen peroxide and kerosene). Cold flow test was carried out to measure the mass flow rate and atomizing characteristic. Required mass flow rate was obtained from thermal analysis of the engine, and measured flow rate 42.25g/s was in the range of permissible coolant flow rate. With the same mass flow rate, cooling ring with more hole and high velocity shows better spray pattern. The result of thermal analysis, cooling ring has enough cooling performance.

• Fire Science and Engineering
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• v.34 no.3
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• pp.28-34
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• 2020

In this study, an ISO 5660-1 cone calorimeter experiment was conducted to examine the effects of changes in flow and thermal thickness around solid combustibles on heat release rate characteristics. Polymethyl methacrylate (PMMA) is a solid combustible material that does not generate char during the combustion reaction. Hence, it was selected for the experiment, and the thermal penetration depth was calculated to distinguish the thermal thickness of PMMA. Furthermore, the thermal decomposition characteristics were analyzed by measuring the heat release rate measured during the combustion of PMMA. This was performed after generating the forced flow around the combustibles by setting the duct flow of the cone calorimeter to 12, 24, and 40 L/s. The results confirmed that the thermal release rate of the thermally thin combustible material was not significantly affected by the change in the surrounding flow. Hence, the thermally thick combustible material was significantly affected by the change in the flow rate.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2009.10a
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• pp.591-592
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• 2009

• Journal of Korean Society on Water Environment
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• v.33 no.4
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• pp.449-459
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• 2017

In Geum River of Korea, three multi-purpose weirs were built at the downstream of Daecheong Reservoir during the Four Major River Restoration Project (FMRRP). The weirs have altered the hydraulic characteristics of the river, and consequently transformed the large areas of flowing ecosystem to deep and wide stagnant environment. In every summer, a thermal stratification occurred near the Baekje Weir having mean depth of 4.0 m, and the surface algal blooms dominated by buoyant cyanobacteria have been frequently formed after the FMRRP. The objective of this study was to investigate the relationship between flow velocity and thermal stability of the waterbody using a three-dimensional (3D) hydrodynamic model (EFDC+) after calibration against the thermistor chain data obtained in 2014. A new Sigma-Zed vertical grid system of EFDC+ that minimize the pressure gradient errors was used to better simulate the thermodynamics of the waterbody. The model reasonably simulated the vertical profiles of the observed water temperatures. The vertical mean flow velocity and the Richardson Number (Ri) that represents the stability of waterbody were estimated for various management water levels and flow rates scenarios. The results indicated that the thermal stability of the waterbody is mostly high ($Ri{\gg}0.25$) enough to establish stratification, and largely depend on the flow velocity. The critical flow velocity that can avoid a persistent thermal stratification was found to be approximately 0.1 m/s.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.1
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• pp.95-104
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• 2003

The objective of this work is to investigate the turbulent reacting flow in a three dimensional combustor with emphasis on thermal NO emission through a numerical simulation. Flow field is analyzed using the SIMPLE method which is known as stable as well as accurate in the combustion modeling, and the finite volume method is adopted in solving the radiative transfer equation. In this work, the thermal characteristics and NO emission in a three dimensional combustor by changing parameters such as equivalence ratio and inlet swirl angle have investigated. As the equivalence ratio increases, which means that more fuel is supplied due to a larger inlet fuel velocity, the flame temperature increases and the location of maximum temperature and thermal NO has moved towards downstream. In the mean while, the existence of inlet swirl velocity makes the fuel and combustion air more completely mixed and burnt in short distance. Therefore, the locations of the maximum reaction rate, temperature and thermal NO were shifted to forward direction compared with the case of no swirl.

• 한국신재생에너지학회:학술대회논문집
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• 2008.05a
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• pp.182-185
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• 2008

The thermal performance of air receiver with a change of flow direction for dish solar collector. This system is installed and operated in Incheon, Korea. The thermal capacity of the system is about 5 kW thermal. The aperture diameter of the cylindrical-shape receiver which is made of stainless steel is 100 mm, and the height is 210 mm. Experiments are being carried out to investigate the thermal performance variation of the receivers with several design parameters such as the shape of the receiver, the flow directions and the flow rate of air. First, air flows into the upper part of the receiver, which is the opposite side of the aperture. After the air flows through the inside receiver, that goes out of the receiver through 3 exits which are located near the aperture. Second, air flows into the backside of the receiver, Which is the forward side of the aperture. After the air flows through the inside receiver, that goes out of the receiver through 1 exit. The results show that the system efficiency and receiver efficiency increase as the volume flow rate increases as expected.

• Journal of the Korean Society of Visualization
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• v.17 no.3
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• pp.52-58
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• 2019

Thermal performance and flow patterns inside the closed loop pulsating heat pipe (CLPHP) were experimentally investigated. For investigating the effect of working fluids, CLPHP was filled with various working fluids including methanol, acetone and ethanol. The thermal resistance was calculated by temperatures in evaporator and condenser and flow patterns were visualized by a digital camera. The thermal resistances for all fluids were decreased as the heat increases. Flow patterns change from static slug to elongated slug flows, bulk circulation and annular flows as the heat increases. Dry-out occurs after annular flows. For reasonable comparison of thermal performances, normalized CHF, Kutateladze number (K_u), was compared. Even though ethanol has smallest CHF, K_u of ethanol is similar with that of methanol. In addition, acetone has the highest K_u that means CLPHP with acetone provides the higher thermal performance compared with CLPHP with other fluids.

• Journal of the Korean Solar Energy Society
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• v.29 no.4
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• pp.22-27
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• 2009

This study focus on verification of the thermal efficiency of volumetric receiver with 5k Wth Dish-type solar thermal system. Spiral flow path shaped on receiver and working fluid(steam) flow along with this flow path. Porous material for radiation-thermal conversion used in former researches are substituted with the stainless steel wall installed along the spiral flow path. Numerical analysis for the flow path and temperature distributions are carried out. Numerical results are compared with experimental data. Using the numerical model, the heat transfer characteristics of spiral type receiver for dish-type solar thermal systems are known and the thermal performance of the receiver can be estimated.

• Journal of the Korean Solar Energy Society
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• v.31 no.5
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• pp.140-145
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• 2011

In this study, the performance and behavior of solar heating system according to the system control scheme, variable flow control (proportional control) and constant flow control (on-off control) was carried out by experiment. The on-off control is used generally for solar thermal system by now. But the proportional control is used for the solar district heating system which is supplied the higher temperature of water than that of desired. The proportional control logic that pump speed is varied in an attempt to maintain a specified outlet temperature of solar heating system was developed and tested for the use widely for the small and medium solar thermal system. The results are as following. First, the proportional controller which is made here could be adopted the characteristics for setting temperature control. Second, the proportional control is better than the on-off control in the side of the performance of thermal stratification in storage tank. Third, the operating energy(electricity consumption by pump) of solar thermal system can be saved more than 60% using the proportional control comparing to the on-off control.