• Journal of Mechanical Science and Technology
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• v.14 no.10
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• pp.1159-1167
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• 2000

Particles in liquid-solid suspension flow might enhance or suppress the rate of heat transfer and turbulence depending on their size and concentration. The heat transfer characteristics of liquid-solid suspension in turbulent flow are not well understood due to the complexibility of interaction between solid particles and turbulence of the carrier fluid. In this study, the heat transfer coefficients of liquid-solid mixtures are investigated using a double pipe heat exchanger with suspension flows in the inner pipe. Experiments are carried out using spherical fly ash particles with mass median diameter ranging from 4 to $78{\mu}m$. The volume concentration of solids in the slurry ranged from 0 to 50% and Reynolds number ranged from 4,000 to 11,000. The heat transfer coefficient of liquid-solid suspension to water flow is found to increase with decreasing particle diameter. The heat transfer coefficient increases with particle volume concentration exhibiting the highest heat transfer enhancement at the 3% solid volume concentration and then gradually decreases. A correlation for heat transfer to liquid-solid flows in a horizontal pipe is presented.

• 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.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.9
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• pp.870-878
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• 2000

An experimental study and a modeling are peformed to investigate the pressure drop of combining junctions in two-phase flows. Experiments on tripod geometry used in a condenser or an evaporator, are conducted with inlet mass fluxes from 200 to$ 400 kg/m^2$s, and pipe diameters of 7 m and 9.52 m. The working fluid is R22. The result shows that the pressure drop increases as the quality does, but the effect of the increase of the pressure decreases when the diameter of a pipe increases. When the mass flux increases, the pressure drop linearly does. Furthermore, when the pipe diameter decreases, the pressure drop has a quadratic increase.

• Journal of the Korean Society of Visualization
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• v.10 no.3
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• pp.11-15
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• 2012

Inertial migration phenomena of phytoplankton in pipe flows were investigated using a digital holography technique. As the Reynolds number increases, the microorganisms suspended in a pipe flow are focused at a certain radial position which is called equilibrium position or pinch point. In this study, the effects of the size of microorganism and Reynolds number in the range of 1 < Re < 78 on the inertial migration were investigated and the results are compared with those for solid particles under similar experimental conditions. As a result, the equilibrium position for the elastic microorganisms is not so distinct, compared to the solid particles. This results from deformation of elastic body shape caused by shear-gradient of surrounding flow.

• Journal of ILASS-Korea
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• v.20 no.1
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• pp.1-6
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• 2015

Visualization of the mixing pattern in a non-element mixer was carried out using laser induced fluorescence(LIF) to evaluate characteristics of mixer consisting of the main flow pipe and branch flow pipes. The branch flows were injected periodically with the period $T_{in}$ normal to the main flow, and rhodamine B was mixed into the most upstream branch flow to visualize mixing pattern in the main flow pipe by LIF. The length of boundary line L of the LIF image was measured. In this study, a numerical analysis was performed to identify the mixing process of the non-element mixer, and the results were compared with experimental results. Each result was almost the same. When the number of branch flows is increased, the mixing pattern became complicated and was supposed to become chaotic. The length of boundary line L increased exponentially with an increase in the number of branch flows.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.04a
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• pp.297-302
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• 2000

Pipe cooling method is widely used for reduction of hydration heat and control of cracking in mass concrete structures. However, in order to effectively apply pipe cooling systems to concrete structure, the coefficient of flow convection relating the thermal transfer between inner stream of pipe and concrete must be estimated. In this study, a device measuring the coefficient of flow convection is developed. Since a variation of thermal distribution caused by pipe cooling has a direct effect in internal forced flows, the developed testing device is based on the internal forced flow concept. Influencing factors on the coefficient of flow convection are mainly flow velocity, pipe diameter and thickness, and pipe material. finally a prediction model of the coefficient of flow convection is proposed using experimental results from the developed device. According to the proposed prediction model, the coefficient of flow convection increases with increase in flow velocity and decreases with increase in pipe diameter and thickness. Also, the coefficient of flow convection is largely affected by the type of pipe materials.

• Journal of Korean Society of Water and Wastewater
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• v.27 no.3
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• pp.351-361
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• 2013

In this study the Principal Component Analysis (PCA) was applied to flow data in a water distribution pipe system to analyze the relevance between the flow observation dates, which have the outliers of observed night flows, and the maintenance records. The data was obtained from four small size water distribution blocks to which 13 maintenance records such as pipe leak and water meter leak belong. The flow data during four months were used for the analysis. The analysis was carried out to identify an appropriate analysis period for a PCA model for a water distribution block. To facilitate the analyses a computational algorithm was developed. MATLAB was utilized to realize the algorithm as a computer program. As a result, an appropriate PCA period for each of the case study small size water distribution blocks was identified.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.8 no.3
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• pp.330-337
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• 1996

The effects of pump and temperature on drag reducing characteristics were investigated with a polymer(PAAM : Polyacrylamide) and three kinds of surfactants(CTAC, STAC, Habon-G) in fully developed turbulent pipe flows with various experimental parameters such as additive concentration(30~500ppm), pipe diameter(4.65mm, 10.85mm), Reynolds number($4{\times}10^4{\sim}10^5$) and working fluid temperature($20{\sim}80^{\circ}C$). The pump effect on PAAM was severe such that the drag reduction rates obtained with pump were decreased upto 30% as compared with those obtained with compressed air in 4.65mm test section. The temperature effect on PAAM was noticeably considerable, that is, the higher temperaute, the less drag reduction rate. On the other hand, no significant pump effect on the surfactants was observed. The drag reducing effectiveness of CTAC was totally lost in the temperature ragne of 60 to $80^{\circ}C$, whereas STAC and Habon-G kept their distinct drag reducing capability at a temperature of $80^{\circ}C$. This study clearly elucidated that for DHC application of drag reducing additives, the pump and temperature effects as well as additive concentration and pipe diameter should be carefully taken into consideration.

• Journal of Advanced Marine Engineering and Technology
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• v.24 no.3
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• pp.79-87
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• 2000

This paper describes experimental investigations of helium-air exchange flow through openings with vertical partitions. Such exchange flows may occur following rupture accident of stand pipe in high temperature gas cooled reactor. Exchange flow rates are investigated experimentally by using partitioned opening and opening with extended partition to assess fluids interference of the exchange flow at the stand pipe rupture accident. A tests vessel with the two types of opening on top of test cylinder is used in the experiments. An estimation method of mass increment is developed and applied to measure the exchange flow rate. A technique of flow visualization by Mach-Zehnder interferometer is provided to recognize the exchange flows. Amplitude and progress of interference fringes of the flows are observed and used as a support in comparison with the exchange flow rates. Flow passages of upward flow of the helium and downward flow of the air for both two types of the opening are separated by inserted partition within the opening, but in the case of partitioned opening, unseparated flow is formed at the opening entrance and the two flows interface. The exchange flow rate for the partitioned opening is not greater than that of the opening with extended partition because of the fluids interference at the entrance of opening. Finally, the fluids interference at the opening entrance is found to be one of important factors on the helium-air exchange flow rate.

• Journal of the Korean Society of Propulsion Engineers
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• v.9 no.1
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• pp.53-60
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• 2005

The use of pipe-bends brings about non-uniform flows at the exit of them due to the velocity difference between inner and outer flows inside the bend. These phenomena may cause turbopump of satellite launch vehicle to run off-design and reduce its efficiency, and also introduce unstable influx of propellants to engine manifold after passing through a turbopump. In order to improve the uniformity of flow at the bend exit, certain turning vanes are set up in the bend pipe normally. Correspondingly the design is an $90^{\circ}\;and\;45^{\circ}$ bend pipes that incorporate with the maximum three turning vanes. All designs were analyzed with numerical analysis by solving the Navier-Stokes equations in three dimensions in case of each respective fuel and oxidizer. Evaluations of the vaned pipe bends designs were accomplished by the velocity magnitude distributions and the predicted pressure drops. We could find that the more vaned bend pipe and larger angle pipe under consideration effectively, the more uniform velocity magnitude of the bend and pressure losses.