• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.24 no.5
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• pp.401-408
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• 2012

Volumetric mass transfer coefficient was measured with carbon dioxide and deionized water for the gas-liquid cocurrent slug flow in 2, 5 and 8 mm tubes. Measurement was repeated with and without a vertical section in an experimental setup and entrance effect was found greater for smaller tubes. Volumetric mass transfer coefficient in the vertical section was found generally a strong function of gas- and liquid-phase superficial velocities. 5 mm- and 8 mm-tube data are highly consistent each other but not with 2 mm tube.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.48 no.2
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• pp.113-118
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• 1999

In this, sensitivity based approach to estimate BITC(bilateral interchange transfer capacity) considering the real power flow control function of FACTS devices is presented. The real power flow setting of the FACTS devices is adjusted so that it transfers the power flow from the first violation point of transmission capacity to other transmission lines in the power system, thus allowing more power to be transferred from the specified generator bus to the specified load bus. The transfer between the two bus locations is increased from this new operating condition until a violation of transmission capacity limits occurs or until the setting of the FACTS devices can no longer be adjusted. The proposed algorithm is illustrated using examples of small and real life power system.

• Proceedings of the KIEE Conference
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• 1998.07c
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• pp.880-883
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• 1998

In this paper, sensitivity based approach to estimate BITC(bilateral interchange transfer capacity) considering the real power flow control function of FACTS device is presented. The real power flow setting of the FACTS device is adjusted so that it transfer the power flow from the first violation point of transmission capacity to other transmission lines in the power system, thus allowing more power to be transferred from the specified generator bus to the specified load bus. The transfer between the two bus locations is increased from this new operating condition until a violation of transmission capacity limits occurs or until the setting of the FACTS device can no longer be adjusted. The proposed algorithm is illustrated using examples of small and real life power system.

• Analytical Science and Technology
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• v.19 no.4
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• pp.323-332
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• 2006

This paper discusses several low-temperature heat-tranfer fluids, including water-based inorganic salt, organic salt, alcohol/glycol mixtures, silicones, and halogenated hydrocarbons in order to choose the best heat-transfer fluid for the newly designed direct contact refrigeration system. So, it contains a survey on commercial products such as propylene glycol and potassium formate as newly used in super market and food processing refrigeration. The stability of commercial fluids at the working temperature of $-20^{\circ}C$ was monitored as a function of time up to two months. And organic and inorganic compositions of candidate fluids were obtained by analytical instruments such as ES, XRF, AAS, ICP-AES, GC, and GC-MS. Analysis results indicate that commercial propylene glycol is very efficient and safe heat transfer fluids for the direct cooling system with liquid phase.

• Journal of the Korean Physical Society
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• v.73 no.9
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• pp.1295-1302
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• 2018

In the present investigation, we have studied the magnetohydrodynamic (MHD) heat transfer of peristaltic flow in a tube. The analysis is made without imposing any assumption to obtain the streamline and isothermal line directly. Galerkin's finite element method has been used on the governing Navier-Stoke's equation in the form of ${\psi}-{\omega}$. The graphs of the computed longitudinal velocity, temperature and pressure are plotted against different value of the emerging parameter by using the stream function and vorticity. The results are valid beyond the long wavelength and the low Reynolds number limits. We conclude that higher values of the parameters are not independent of the time mean flow rate.

• Journal of the Society of Naval Architects of Korea
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• v.43 no.3 s.147
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• pp.285-293
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• 2006

Three-dimensional and time-dependent solution for the fluid flow and heat transfer past a circular cylinder with fins is obtained using accurate and efficient spectral methods. A Fourier expansion with a corresponding uniform grid is used along the circumferential direction. A spectral multi-domain method with a corresponding Chebyshev collocation is used along r-z plane to handle fins attached to the surface of a circular cylinder. At the Reynolds number of 300 based on a cylinder diameter, results with fins are compared with those without fins in order to see the effects of the presence of fins on three-dimensional and unsteady fluid flow and heat transfer past a bluff body. The detail structures of fluid flow and temperature field are obtained as a function of time to investigate how the presence of fins changes heat transfer mechanism related to the vortical structure in the wake region.

• Nuclear Engineering and Technology
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• v.56 no.1
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• pp.265-274
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• 2024

The current research focuses on the development of a numerical approach to forecast strongly subcooled flow boiling of FC-72 as the refrigerant in various vertical minichannel shapes for high-heat-flux cooling applications. The simulations are carried out using the Volume of Fluid method with the Lee phase change model, which revealed some inherent flaws in multiphase flows that are primarily due to an insufficient interpretation of shearlift force on bubbles and conjugate heat transfer against the walls. A user-defined function (UDF) is used to provide specific information about this noticeable effect. The influence of shape and the inlet mass fluxes on the flow patterns, heat transfer, and pressure drop characteristics are discussed. The computational results are validated with experimental measurements, where excellent agreements are found that prove the efficiency of the present numerical model. The findings demonstrate that the heat transfer coefficient decreases as the mass flux increases and that the constriction design improves the thermal performance by 24.68% and 10.45% compared to the straight and expansion shapes, respectively. The periodic constriction sections ensure good mixing between the core and near-wall layers. In addition, a slight pressure drop penalty versus the thermal transfer benefits for the two configurations proposed is reported.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.6
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• pp.587-595
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• 2005

The heat and flow characteristics in a parallel-flow heat exchanger were examined numerically to obtain its optimal design variables. A desirability function approach was introduced to optimize its performance with respect to the design parameters over the design domain. By varying the importance of heat transfer and pressure drop which are out put variables, the optimal values of the design parameters are examined. As a result, the us-age of the desirability function is very effective for the optimization of the design variables in a heat exchanger since the changes of optimal values are physically appropriate by varying the importance of each output variable.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.2
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• pp.229-239
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• 1998

The present paper examines the thermal and flow characteristics of a parallel flow heat exchanger and investigates the effects of the parameters on thermal performance by defining the flow nonuniformity. Thermal performance of a parallel flow heat exchanger is maximized by the optimization using Newton's searching method. The flow nonuniformity is chosen as an object function. The parameters such as the locations of separator, inlet, and outlet are expected to have a large influence on thermal performance of a parallel flow heat exchanger. The effect of these parameters are quantified by flow nonuniformity. The results show that the optimal locations of inlet and outlet are 19.73 mm and 10.9 mm, respectively. It is also shown that the heat transfer increases by 7.6% and the pressure drop decreases by 4.7%, compared to the reference model.

• Journal of computational fluids engineering
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• v.21 no.4
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• pp.1-10
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• 2016

The analysis of characteristics of turbulent flow and thermal boundary layer for natural convection caused by fire along vertical wall is performed. The 4m-high vertical copper plate is heated and kept at a uniform surface temperature of $60^{\circ}C$ and the surrounding fluid (air) is kept at $16.5^{\circ}C$. The flow and temperature is solved by large eddy simulation(LES) of FDS code(Ver.6), in which the viscous-sublayer flow is calculated by Werner-Wengle wall function. The whole analyzed domain is assumed as turbulent region to apply wall function even through the laminar flow is transient to the turbulent flow between $10^9$<$Gr_z$<$10^{10}$ in experiments. The various grids from $7{\times}7{\times}128$ to $18{\times}18{\times}128$ are applied to investigate the sensitivity of wall function to $x^+$ value in LES simulation. The mean velocity and temperature profiles in the turbulent boundary layer are compared with experimental data by Tsuji & Nagano and the results from other LES simulation in which the viscous-sublayer flow is directly solved with many grids. The relationship between heat transfer rate($Nu_z$) and $Gr_zPr$ is investigated and calculated heat transfer rates are compared with theoretical equation and experimental data.