• Journal of the Korean Society of Safety
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• v.22 no.4
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• pp.7-12
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• 2007

In order to evaluate the integrity of Zr-2.5Nb pressure tubes, probabilistic fracture mechanics(PFM) approach was employed. Failure assessment diagram(FAD), plastic collapses, and critical crack lengths(CCL) were used for evaluating the failure probability as failure criteria. The Kr-FAD as failure assessment diagram was used because fracture of pressure tubes occurred in brittle manner due to hydrogen embrittlement of material by deuterium fluence. The probabilistic integrity evaluation observed AECL procedures and used fracture toughness parameters of EPRI and recently announced theory. In conclusion, the probabilistic approach using the Kr-FAD made it possible to determine major failure criterion in the pressure tube integrity evaluation.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.7
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• pp.602-611
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• 2001

Experiments on the condensation heat transfer characteristics inside a smooth and a microfin tube with R410A/R22 are performed in this study. The test tubes 7/9.52 mm in outside diameters and 3m in length are used. Varying the mass flux of the refrigerant and the condensation temperatures, the average heat transfer coefficients and pressure drop are investigated. Most flows in this study are in the annular and/or wavy flow regime. It is shown that the heat transfer is enhanced and the pressure drops are larger in the microfin tube than the smooth tube. From the heat transfer enhancement coefficients and the pressure drops, it is found that the high heat transfer enhancement factors are obtained in the range of small mass flux while the penalty factors are almost equal. Experiments results show that average heat transfer coefficients of R410A is larger than that of R22 and pressure drop of R410A is less than R22.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.8
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• pp.612-620
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• 2008

New alternative refrigerants have been developed due to the ozone layer depletion and global warming. For this reason, carbon dioxide is believed to be a promising refrigerant for use in air conditioners and heat pumps. Evaporative heat transfer characteristics and pressure drop of $CO_2$ with outer diameter of 5 mm in inclined ($45^{\circ}$) smooth and micro-fin tubes have been investigated by the experiments with respect to several test conditions such as mass fluxes, heat fluxes, evaporation temperatures in this study. The inclined ($45^{\circ}$) smooth and micro-fin tubes with length of 1.44 m were installed to measure the evaporative heat transfer coefficients of $CO_2$ and heat was supplied to the refrigerant by direct heating method where the test tube was uniformly heated by electricity. The tests were conducted at mass fluxes from 212 to $656\;kg/m^2s$, heat fluxes from 15 to $60\;kW/m^2$ and evaporation temperatures from -10 to $20^{\circ}C$. The heat transfer coefficients of $CO_2$ are slightly increased with increasing mass flux, and the heat transfer characteristics in the inclined ($45^{\circ}$) tubes are enhanced about $5{\sim}10%$ compared with those in horizontal or vertical tubes.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.19 no.1
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• pp.27-35
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• 2023

Pressure tubes are the main components of PHWR core and serve as the pressure boundary of the primary heat transport system. However, because pressure tubes have changed their geometrical dimensions under the severe operating conditions of high temperature, high pressure and neutron irradiation according to the increase of operation time, all dimensional changes should be predicted to ensure that dimensions remain within the allowable design ranges during the operation. Among the deformations, the diameter expansion due to creep leads to the increase of bypass flow which may not contribute to the fuel cooling, the decrease of critical channel power and finally the deration of the power to maintain the operational safety margin. This study is focused on the modeling of the expansion of the pressure tube diameter based on the operating conditions and measured diameter data. The pressure tube diameter expansion was modeled using the neutron flux and temperature distributions of each fuel channel and each fuel bundle as well as the measured diameter data. Although the basic concept of the current modeling approach is simple, the diameter prediction results using the developed methodology showed very good agreement with the real data, compared to the existing methodology.

• Corrosion Science and Technology
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• v.19 no.2
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• pp.89-99
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• 2020

The inhibition of pitting corrosion failure of copper sprinkler tubes in wet sprinkler systems was studied. First, an apparatus and technology for removing air in the sprinkler tubes by vacuum pumping and then filling the tubes with water were developed. Using this apparatus and technology, three methods for inhibiting the pitting corrosion of the copper sprinkler tubes installed in several apartment complexes were tested. The first one was filling the sprinkler tubes with water bubbled by high-pressure nitrogen gas to reduce the dissolved oxygen concentration to lower than 2 ppm. In the second method, the dissolved oxygen concentration of water was further reduced to lower than 0.01 ppm by sodium sulfite. In the third method, the sprinkler tubes were filled with benzotriazole (BTAH) dissolved in water. The third method was the most effective, reducing the failure frequency of the sprinkler tubes due to pitting corrosion by more than 80%. X-ray photoelectron spectroscopy analyses confirmed that a Cu-BTA layer was well coated on the inside surface of the corrosion pit, protecting it from corrosion. A potentiodynamic polarization test showed that BTAH should be very effective in reducing the corrosion rate of copper in the acidic environment of the corrosion pit.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.04a
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• pp.603-608
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• 2014

Underwater acoustic materials are installed in order to reduce reflection, transmission and radiation of an underwater structure. The acoustic performance of the materials should be evaluated in accurately-controlled environment in terms of temperature and static pressure. In this paper, three pulse tubes, which is equipped with temperature and pressure controllers, are designed and developed to evaluate echo reduction and transmission loss for evaluating the performance below 10 kHz and 30kHz, respectively. The new procedures of the evaluation are suggested to improve the accuracy and the validation for the developed pulse tubes is carried out by comparing theoretical values to experimental ones.

• International Journal of Air-Conditioning and Refrigeration
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• v.7
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• pp.45-54
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• 1999

In this study, condensation heat transfer experiments were conducted in two small diameter (ø17.5, ø4.0) tubes. Comparison with the existing in-tube condensation heat transfer correlations indicated that these correlations over predict the present data. For example, Akers correlation over predicted the data up to 104 %. The condensation heat transfer coefficient of the ø4.0 I.D. tube was smaller than that of the ø7.5 I.D tube; at the mass velocity of 300 kg/$m^2$s, the difference was 12 %. The pressure drop data of the small diameter tubes were highly (two to six times) over predicted by the Lockhart-Martinelli correlation. Sub-cooled forced convection heat transfer test confirmed that Gnielinski's single phase heat transfer correlation predicted the data reasonably well.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2000.10a
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• pp.74-77
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• 2000

Porthole die extrusion has a great advantage in the forming of hollow section tubes difficult to produce by conventional extrusion with a mandrel on the stem. Because of the complicated structure of die assembly, extrusion process as a forming of hollow section tubes has been investigated experimentally Therefore, analytic approaches that are useful in profitable die design and in the improvement of productivity are inevitably demanded Welding strength is affected by many parameters, which are such as extrusion ratio, extrusion speed, die shape, porthole number, bearing length, billet temperature and mandrel shape. In this paper, the parameters, which are such as billet temperature, bearing length and tube thickness, are examined. The welding pressures are examined through 3D simulation of non steady state and compared with experimental results.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.378-379
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• 2008

Recently, composite hollow bushings have been increasingly employed mainly from the various characteristics. Composite bushings are superior to porcelain bushings in several respects, including lighter weight, better anti-pollution and anti-explosion properties, and easer manufacturing. Filament wound GRP tubes which have various winding angle were manufactured by using a filament winding machine. This paper will show some design issues and winding condition for composite bushing. And, results show that the winding condition of composite GRP tubes can be used to improved their bending strength and pressure, For bending and pressure tested, tubes with the hybrid winding pattern show higher strength than those of unit winding pattern. Also, the influence of absorption was evaluated through such as measurement of the dye penetration test and water diffusion test, also aspects of surface state using scanning electron microscopy.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.6 no.3
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• pp.193-205
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• 1994

A simulation program of the plate finned-tubes condenser widely used in the air conditioning system was developed. The program took into account the variations of the flow properties and fluid friction factor of refrigerant, and the heat transfer coefficients of refrigerant and air sides. The program was applied to a copper tube condenser which has outside diameter of 10.05mm, inside diameter of 9.35mm, length of 5.20m and three rows arraied staggered. Simulation results were such that refrigerant was super-heated state from the entrance to the 0.14m point, two-phase flow from the 0.14m point to the 4.10m point, sub-cooled state from the 4.10m point to the outlet. The degree of sub-cooled was $6.1^{\circ}C$. The variations of refrigerant quality, temperature, pressure, velocity, specific enthalpy, specific volume and air temperature, tube temperature were showed.