• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.9
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• pp.1209-1218
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• 2001

The present paper proposes a new correlation for the flow boiling heat transfer coefficients in the low flow rate condition (Re(sub)LF$\leq$200) within horizontal rectangular channels with small gaps (heights). The gap between the upper and the lower plates of each channel ranges from 0.4 to 2mm while the channel width being fixed to 20mm. Refrigerant 113 was used as the test fluid. The mass flux ranges from 50 to 200kg/㎡s and the channel walls were uniformly heated with the heat flux range of 3-15kW/㎡. The quality range covers from 0.19 to 0.76 and the flow pattern is considered to be annular. The measured heat transfer coefficients increase with the mass flux and the local quality; however the effect of the heat flux appears to be minor. At the low mass flux condition, which is more likely with the smaller gap size, the heat transfer is primarily controlled by the liquid film thickness. The proposed F factor for the heat transfer coefficient in the range of Re(sub)LF$\leq$200 well represents the experimental data within the deviation of $\pm$20%. The Kandlikars flow boiling correlation covers the higher flow-rate range(Re(sub)LF>200) within the deviation of $\pm$20%.

• Journal of the Korean Society for Nondestructive Testing
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• v.24 no.6
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• pp.566-572
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• 2004

It is necessary to measure the direct current with a non-contact methodology for the liquid or gas phase, as welt as the conducting metals. This paper described a theoretical consideration and experimental verification for a non-contact quantitative direct current measurement system using the Faraday effect and magnetic flux leakage. The leakage of magnetic flux occurs around a gap when a ferromagnetic core including the discontinuous gap is magnetized. Two large anisotropic domains in a magneto-optical film are occurred by the vertical component of leaked magnetic flux and the domain walls are paralleled to the center of the gap. Here, the symmetrical arrangement of domains are deflected when a vertical magnetic field is applied to the magneto-optical film. The domain wall of the magneto-optical film are relocated when a measuring current passes through the ferromagnetic core. Therefore, a direct current passing through the core can be determined quantitatively by the measurement of moving distance of the domain wall.

• Structural Engineering and Mechanics
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• v.75 no.5
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• pp.571-583
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• 2020

Permeation grouting is of great significance for consolidating geo-materials without disturbing the original geo-structure. To dip into the filtration-induced pressure increment that dominates the grout penetration in permeation grouting, nonlinear filtration coefficients embedded in a convection-filtration model were proposed, in which the volume of cement particles in grout and the deposited particles of skeleton were considered. An experiment was designed to determine the filtration coefficients and verify the model. The filtration coefficients deduced from experimental data were used in simulation, and the modelling results matched well with the experimental ones. The pressure drop revealed in experiments and captured in modelling demonstrated that the surge of inflow pressure lagged behind the stoppage of flow channels. In addition, both the consideration of the particles loss in liquid grout and the number of filtrated particles on pore walls presented an ideal trend in filtration rate, in which the filtration rate first rose rapidly and then reached to a steady plateau. Finally, this observed pressure drop was extended to the grouting design which alters the water to cement (W/C) ratio so as to alleviate the filtration effect. This study offers a novel insight into the filtration behaviour and has a practical meaning to extend penetration distance.

• Korean Journal of Materials Research
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• v.25 no.11
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• pp.602-606
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• 2015

Porous W with spherical and directionally aligned pores was fabricated by the combination of sacrificial fugitives and a freeze-drying process. Camphene slurries with powder mixtures of $WO_3$ and spherical PMMA of 20 vol% were frozen at $-25^{\circ}C$ and dried for the sublimation of the camphene. The green bodies were heat-treated at $400^{\circ}C$ for 2 h to decompose the PMMA; then, sintering was carried out at $1200^{\circ}C$ in a hydrogen atmosphere for 2 h. TGA and XRD analysis showed that the PMMA decomposed at about $400^{\circ}C$, and $WO_3$ was reduced to metallic W at $800^{\circ}C$ without any reaction phases. The sintered bodies with $WO_3$-PMMA contents of 15 and 20 vol% showed large pores with aligned direction and small pores in the internal walls of the large pores. The pore formation was discussed in terms of the solidication behavior of liquid camphene with solid particles. Spherical pores, formed by decomposition of PMMA, were observed in the sintered specimens. Also, microstructural observation revealed that struts between the small pores consisted of very fine particles with size of about 300 nm.

• Nuclear Engineering and Technology
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• v.45 no.5
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• pp.613-624
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• 2013

Multi-dimensional two-phase phenomena occur in many industrial applications, particularly in a nuclear reactor during steady operation or a transient period. Appropriate modeling of complicated behavior induced by a multi-dimensional flow is important for the reactor safety analysis results. SPACE, a safety analysis code for thermal hydraulic systems which is currently being developed, was designed to have the capacity of multi-dimensional two-phase thermo-dynamic phenomena induced in the various phases of a nuclear system. To validate the performance of SPACE, a two-dimensional two-phase flow test was performed with slab geometry of the test section having a scale of $1.43m{\times}1.43m{\times}0.11m$. The test section has three inlet and three outlet nozzles on the bottom and top gap walls, respectively, and two outlet nozzles installed directly on the surface of the slab. Various kinds of two-dimensional air/water flows were simulated by selecting combinations of the inlet and outlet nozzles. In this study, two-dimensional two-phase void fraction profiles were quantified by measuring the local gap impedance at 225 points. The flow conditions cover various flow regimes by controlling the flow rate at the inlet boundary. For each selected inlet and outlet nozzle combination, the water flow rate ranged from 2 to 20 kg/s, and the air flow rate ranged from 2.0 to 20 g/s, which corresponds to 0.4 to 4 m/s and 0.2 to 2.3 m/s of the superficial liquid and gas velocities based on the inlet port area, respectively.

• The Plant Pathology Journal
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• v.32 no.5
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• pp.396-406
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• 2016

Continuous supplementation of mineral nutrients and salicylic acid (SA) as foliar application could improve efficacy in controlling basal stem rot (BSR) disease in oil palm seedling. It is revealed from the results that the highest disease severity index (58.3%) was recorded in T8 treatments at 9 months after inoculation. The best disease control was achieved by T7 treatments (calcium/copper/SA [Ca/Cu/SA]) (5.0%) followed by T1 (5.5%), T5 (5.8%), T3 (8.3%), T6 (8.3%), T4 (13.3%), and T2 (15.8%) treatments. Continuous supplementation of Ca/Cu/SA was found to be the most effective in controlling the disease and the high performance liquid chromatography results showed the detection of ergosterol at very low concentration in the treated samples. Moreover, the transmission electron microscopy analysis results clearly indicated that T7 treatment was also enhancing lignification, which was responsible for the thickness of the secondary cell walls and middle lamella compared to untreated samples. It was therefore, concluded that continuous supplementation of minerals nutrients and SA could effectively suppress disease severity by reducing ergosterol activity and also improve the process of lignification in the treated plants. Furthermore, this treatment also managed to delay the onset of BSR symptoms and promote the growth of the seedlings and eventually suppress the BSR disease.

• Journal of Radiation Protection and Research
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• v.46 no.1
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• pp.24-31
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• 2021

Decommissioning efforts are underway at the reactor where the accident occurred, namely the damaged Tokyo Electric Power Company (TEPCO) Fukushima Daiichi Nuclear Power Plant (FDNPP). However, a large amount of groundwater flowing into the site has become contaminated with radioactive substances and is stored in tanks on site, which has hampered the decommissioning work. Although the inflow of groundwater has been greatly reduced through measures such as the construction of frost walls, approximately 170 ㎥ of water treated by the Advanced Liquid Processing System (ALPS) is being stored in tanks, each day. The tanks used to store this treated water are expected to become full by around the summer of 2022. It is not easy to get people to understand the efforts of all concerned parties, and providing clear information to these concerned parties is also a challenge. Questions have also been raised regarding whether other alternatives have been fully explored in the ALPS subcommittee. Some people have commented that the answers to the questions raised regarding the biological effects of tritium transmutation are inadequate. Some suspect that the answers are too detailed and incomprehensible, and that the respondents may be manipulating the public with some malicious intent. In any case, each possible plan presents both advantages and disadvantages, depending on the people who are involved. That makes it an ethical and vexing issue that can sway decisions, as perspectives change. While the environmental release plan is scientifically safe, it may represent a painful alternative. On the other hand, a more careful and imaginative approach to the idea of continued storage in tanks or other forms of storage may reveal some troublesome hidden disadvantages. Under these circumstances, experts must be prepared to answer people's questions in a comprehensive and robust manner.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.1
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• pp.31-48
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• 2019

The artificial ground freezing (AGF) method is a groundwater cutoff and/or ground reinforcement method suitable for constructing underground structures in soft ground and urban areas. The AGF method conducts a freezing process by employing a refrigerant circulating through a set of embedded freezing pipes to form frozen walls serving as excavation supports and/or cutoff walls. However, thermal expansion of the pore water during freezing may cause excessive deformation of the ground. On the other hand, as the frozen soil is thawed after completion of the construction, mechanical characteristics of the thawed soil are changed due to the plastic deformation of the ground and the rearrangement of soil fabric. This paper performed a field experiment to evaluate the freezing rate of marine clay in the application of the AGF method. The field experiment was carried out by circulating liquid nitrogen, which is a cryogenic refrigerant, through one freezing pipe installed at a depth of 3.2 m in the ground. Also, a piezo-cone penetration test (CPTu) and a lateral load test (LLT) were performed on the marine clay before and after application of the AGF method to evaluate a change in strength and stiffness of it, which was induced by freezing-thawing. The experimental results indicate that about 11.9 tons of liquid nitrogen were consumed for 3.5 days to form a cylindrical frozen body with a volume of about $2.12m^3$. In addition, the strength and stiffness of the ground were reduced by 48.5% and 22.7%, respectively, after a freezing-thawing cycle.

• Restorative Dentistry and Endodontics
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• v.27 no.6
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• pp.577-586
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• 2002

The purpose of this in vitro study was to compare the effects of root canal cleanness following two Ni-Ti rotary instruments with different rake angle. Thirty-six sound, extracted human premolars with single root were randomly divided into three groups. The used rotary instruments were HEROShaper (Group 1, Micro-Mega, Besancon, France, n=12) and ProFile (Group 2, Maillefer, Ballaigues, Switzerland, n=12). Control group (n=12) was only extirpated with barbed broach (Mani, Matsutani Seisakusho Co., Japan) Group 1 & 2 teeth were prepared to a #40/.04 taper at the apex followed by 1 mm using crown-down technique. After canal preparation and frequent irrigation with 5.25% sodium hypochlorite, the roots split longitudinally into a bucco-lingual direction. Root halves were cross-sectioned in apical third portion again. All root specimens were processed for SEM investigation and photographed. Separate evaluations by one endodontist were undertaken for smear layer on prepared walls with a five score-index for each using reference photograph in root halves. The penetration depth of smear layer into dentinal tubules was also estimated in the other halves. Following results were obtained: 1. Smear layer was observed on all the prepared walls with two experimental groups except control group. 2. Smear layer characteristics in two experimental groups; 1) HEROShaper group showed snowy, dusty appearance and were shown open dentinal tubuli on the prepared walls of almost specimens, and the thickness of smear layer covering onto dentinal surfaces was within 1-2 ${\mu}m$ in a few specimens. 2) ProFile group showed shiny, burnished appearance and complete root canal wall covered by a homogenous smear layer with no open dentinal tubuli in all specimens. The penetration of smear layer into dentinal tubules was found in all specimens and the thickness was at 2-4 ${\mu}m$ in all specimens. These results demonstrated that a completely clean root canal could not be achieved regardless of positive or negative rake angle, which is in accordance with the majority of previous studies on root canal cleanliness In conclusion, through irrigation with antibacterial solutions or chelating agents is recommended to remove the smear layer on prepared canal wall in spite of Ni-Ti instrumentation.

• Journal of Korean Society of Forest Science
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• v.90 no.3
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• pp.277-294
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• 2001

This study is aimed to analyze and to evaluate the technology development for sanddune fixation and sandy land conservation in China, resulting from the project of "Studies on the desertification combating and sand industry development". There are various types of sanddunes, including shrub-bunch type, dendritic, honey combed lattice, crescentic, parabolic, pyramid, complex and irregular types, domed, and so on. The height distribution ratios of these sanddunes are 13% of less than 5m, 17% of 6~10m, 18% of 11~25m, 14% of 26~50m, 28% of 51~100m, 10% of more than 100m, and so on. In dry land of China, shifting direction of the sanddune is mainly varying with main direction of wind, but types of shifting sanddunes have many differences in accordance with region, topography, size and shape of sanddunes. The main sanddune fixation technologies could be divided into the bio-ecological measures, physical measures and chemical measures. The bio-ecological measures include such vegetation measures as shrub-grasses measures, sandbreaks between sand dunes, sand fixation shelterblets and establishment of farmland shelterbelts, etc. The physical measures include establishment of high-sanddune stabilization walls and low-sanddune stabilization walls, sanddune fixation levees and coverage method with sediment clay, etc. The chemical measures include fixation-materials spraying and synthetical liquid spraying methods, etc. Besides, irrigation and sand settlement measures, shifting sand trapping channel, ditchsand fixation measures, etc. have been effectively applied.