• Journal of Korean Society of Water and Wastewater
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• v.37 no.4
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• pp.203-214
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• 2023

In this study, the physical properties and fracture characteristics according to the tensile load are evaluated on the materials of the polymeric filler and carbon fiber-based composite sleeve technique. The polymeric filler and the composite sleeve technique are applied to areas where the pipe body thickness is reduced due to corrosion in large-diameter water pipes. First, the tensile strength of the polymeric filler was 161.48~240.43 kg_f/cm², and the tensile strength of the polyurea polymeric filler was relatively higher than that of the epoxy. However, the tensile strength of the polymeric filler is relatively very low compared to ductile cast iron pipes(4,300 kg_f/cm²<) or steel pipes(4,100 kg_f/cm²). Second, the tensile strength of glass fiber, which is mainly used in composite sleeves, is 3,887.0 kg_f/cm², and that of carbon fiber is up to 5,922.5 kg_f/cm². The tensile strengths of glass and carbon fiber are higher than ductile cast iron pipe or steel pipe. Third, when reinforcing the hemispherical simulated corrosion shape of the ductile cast iron pipe and the steel pipe with a polymeric filler, there was an effect of increasing the ultimate tensile load by 1.04 to 1.06 times, but the ultimate load was 37.7 to 53.7% compared to the ductile cast iron or steel specimen without corrosion damage. It was found that the effect on the reinforcement of the corrosion damaged part was insignificant. Fourth, the composite sleeve using carbon fiber showed an ultimate load of 1.10(0.61T, 1,821.0 kg_f) and 1.02(0.60T, 2,290.7 kg_f) times higher than the ductile cast iron pipe(1,657.83 kg_f) and steel pipe(2,236.8 kg_f), respectively. When using a composite sleeve such as fiber, the corrosion damage part of large-diameter water pipes can be reinforced with same level as the original pipe, and the supply stability can be secured through accident prevention.

• Computers and Concrete
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• v.19 no.6
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• pp.745-753
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• 2017

Dynamic analysis of a concrete pipes armed with Silica ($SiO_2$) nanoparticles subjected to earthquake load is presented. The structure is modeled with first order shear deformation theory (FSDT) of cylindrical shells. Mori-Tanaka approach is applied for obtaining the equivalent material properties of the structure considering agglomeration effects. Based on energy method and Hamilton's principle, the motion equations are derived. Utilizing the harmonic differential quadrature method (HDQM) and Newmark method, the dynamic displacement of the structure is calculated for the Kobe earthquake. The effects of different parameters such as geometrical parameters of pipe, boundary conditions, $SiO_2$ volume percent and agglomeration are shown on the dynamic response of the structure. The results indicate that reinforcing the concrete pipes by $SiO_2$ nanoparticles leads to a reduction in the displacement of the structure during an earthquake.

• Computers and Concrete
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• v.21 no.1
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• pp.31-37
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• 2018

This paper deals with the stability analysis of concrete pipes mixed with nanoparticles conveying fluid. Instead of cement, the $Fe_2O_3$ nanoparticles are used in construction of the concrete pipe. The Navier-Stokes equations are used for obtaining the radial force of the fluid. Mori-Tanaka model is used for calculating the effective material properties of the concrete $pipe-Fe_2O_3$ nanoparticles considering the agglomeration of the nanoparticles. The first order shear deformation theory (FSDT) is used for mathematical modeling of the structure. The motion equations are derived based on energy method and Hamilton's principal. An exact solution is used for stability analysis of the structure. The effects of fluid, volume percent and agglomeration of $Fe_2O_3$ nanoparticles, magnetic field and geometrical parameters of pipe are shown on the stability behaviour of system. Results show that considering the agglomeration of $Fe_2O_3$ nanoparticles, the critical fluid velocity of the concrete pipe is decreased.

• Journal of Microbiology and Biotechnology
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• v.25 no.4
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• pp.423-430
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• 2015

Aerobic CH₄ oxidation is an important CH₄ sink in landfills. To investigate the distribution and community diversity of methanotrophs and link with soil characteristics and operational parameters (e.g., concentrations of O₂, CH₄), cover soil samples were collected at different locations and depths from the Mengzi semi-aerobic landfill (SAL) in Yunnan Province of southern China. Specific PCR followed by denaturing gradient gel electrophoresis and realtime PCR were used to examine methanotrophs in the landfill cover soils. The results showed that different locations did harbor distinct methanotroph communities. Methanotrophs were more abundant in areas near the venting pipes because of the higher O₂ concentrations. The depth of 20-25 cm, where the ratio of the CH₄ to O₂ was within the range from 1.3 to 8.6, was more conducive to the growth of CH₄-oxidizing bacteria. Type II methanotrophs dominated in all samples compared with Type I methanotrophs, as evidenced by the high ratio of Type II to Type I methanotrophic copy numbers (from 1.76 to 11.60). The total copy numbers of methanotrophs detected were similar to other ecosystems, although the CH₄ concentration was much higher in SAL cover soil. Methylobacter and Methylocystis were the most abundant Type I and Type II methanotrophs genera, respectively, in the Mengzi SAL. The results suggested that SALs could provide a special environment with both high concentrations of CH₄ and O₂ for methanotrophs, especially around the vertical venting pipes.

• Fire Science and Engineering
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• v.32 no.4
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• pp.17-24
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• 2018

This paper presents a numerical analysis of flow inside a water nozzle for fire fighting and observes the effect of the variation in primary components on internal flow. In order to observe the performance of water nozzles, they have been systematically designed and modelled, applying boundary conditions obtained from field experiments (inlet pressure at pump : 4 bar, and pressure outlet : atmospheric pressure). In addition, the governing equations were calculated to obtain velocity, pressure inside the nozzle. Two main parameters (the presence and length of sub-pipes) were considered with the aim to observe the detail internal flow characteristics. It is found that the base model is not significant on flow characteristics, but a negative effect (i. e. the reverse flow) at the entrance region of sub-pipe. On the other hand, the reverse flow was vanished when making the length of sub-pipe double.

• Nuclear Engineering and Technology
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• v.52 no.6
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• pp.1164-1171
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• 2020

T-junction structures play an important role in nuclear power plant systems. Research on liquid entrainment is mostly based on small-scale branch pipes (d/D ≤ 0.2) and attention paid to large-scale branch pipes (0.33 < d/D < 1) is insufficient. Accordingly, this study implements a series of experiments on the liquid entrainment of T-junction with different angles (32.2°,47.9°,62.3°,90°) through a large-scale branch (d/D = 0.675). The onset liquid entrainment is related to the gas phase Froude number Fr_g, the dimensionless gas chamber height h_b/d and the branch pipe angle 𝜃. As Fr_g increases, h_b/d also rises. With a constant h_b/d, the onset liquid entrainment changes from droplets entrainment by the gas phase to that by the rising liquid film. The steady-state liquid entrainment is related to w_3g, h/d and 𝜃. With constant w_3g and h/d, the branch quality grows as the branch angle increases. With a certain h/d, the branch quality increases, as the w_3g number increases.

• Computers and Concrete
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• v.21 no.4
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• pp.431-440
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• 2018

Fluid velocity analysis on the instability of pipes reinforced by silica nanoparticles ($SiO_2$) is presented in this paper. Mori-Tanaka model is used for obtaining the effective materials properties of the nanocomposite structure considering agglomeration effects. The well known Navier-Stokes equation is used for obtaining the applied force of fluid to pipe. Based on the Reddy higher-order shear deformation theory, the motion equations are derived based on energy method and Hamilton's principal. The frequency and critical fluid velocity of structure are calculated using differential quadrature method (DQM) so that the effects of different parameters such as volume fractions of SiO2 nanoparticles, SiO2 nanoparticles agglomeration, boundary conditions and geometrical parameters of pipes are considered on the nonlinear vibration and instability of the pipe. Results indicate that increasing the volume fractions of SiO2 nanoparticles, the frequency and critical fluid velocity of the structure are increased. Furthermore, considering SiO2 nanoparticles agglomeration, decreases the frequency and critical fluid velocity of the pipe.

• Journal of Korean Society of Water and Wastewater
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• v.32 no.3
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• pp.261-268
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• 2018

Sludge transporting pipes in wastewater treatment plant are easy to be clogged with struvite when the digested sludge and dehydrated filtrate are transported through the pipes, which lowers the efficiency of sludge treatment system in a WWTP. pH is one of the most important factors in struvite formation, and carbon dioxide separated from biogas can be used to control pH and struvite formation. By controlling pH, the amount of dehydrating agent can be reduced by about 10%, which saves the budget for facility maintenance. As $CO_2$ is reused and dehydrating chemicals are saved, the approach can contribute to global warming gas reduction.

• Nuclear Engineering and Technology
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• v.55 no.5
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• pp.1604-1615
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• 2023

In an open-pool type research reactor with a downward forced flow in the core, pipes can be under sub-atmospheric pressure because of the large pressure drop at the reactor core in the atmospheric pool. Sub-atmospheric pressure can result in air inflow into the pipe from the pressure difference between the atmosphere and the inside of the pipe, which in a postulated pipe break scenario can lead to the breakdown of the cooling pump. In this study, a plant-scale experiment was conducted to study air inflow in large piping systems by considering the actual operational conditions of an advanced research reactor. The air inflow rate was measured, and the entrained air was visualized to investigate the behavior of air inflow and flow regime depending on the pipe break size. In addition, the developed drift-flux model for a large vertical pipe with a diameter of 600 mm was compared with other correlations. The flow regime transition in a large vertical pipe under downward flow was also studied using the newly developed drift-flux model. Consequently, the characteristics of two-phase flow in a large vertical pipe were found to differ from those in small vertical pipes where liquid recirculation was not dominant.

• Economic and Environmental Geology
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• v.55 no.4
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• pp.317-338
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• 2022

Physicochemical characteristics and evaluation were studied by subdividing the concretes, bricks and earth pipes on the site of the Japanese Ministry of General Affairs in Joseon Dynasty, known as modern architecture, into three periods. Concretes showed similar specific gravity and absorption ratio, and large amounts of aggregates, quartz, feldspar, calcite and portlandite were detected. Porosity of the 1907 bricks were higher than those of 1910 and 1950 bricks. All earthen pipe is similar, but the earlier one was found to be more dense. Bricks and earthen pipes are dark red to brown in color within many cracks and pores, but the matrix of the earthen pipe is relatively homogeneous. Quartz, feldspar and hematite are detected in bricks, and mullite is confirmed with quartz and feldspar in earthen pipes, so it is interpreted that the materials have a firing temperature about 1,000 to 1,100℃. Concretes showed similar CaO content, but brick and earthen pipe had low SiO₂ and high Al₂O₃ in the 1907 specimen. However, the materials have high genetic homogeneity based on similar geochemical behaviors. Ultrasonic velocity and rebound hardness of the concrete foundation differed due to the residual state, but indicated relatively weak physical properties. Converting the unconfined compressive strength, the 1st extended area had the highest mean values of 45.30 and 46.33 kgf/cm², and the 2nd extended area showed the lowest mean values (20.05 and 24.76 kgf/cm²). In particular, the low CaO content and absorption ratio, the higher ultrasonic velocity and rebound hardness. It seems that the concrete used in the constructions of the Japanese Ministry of General Affairs in Joseon Dynasty had similar mixing characteristics and relatively constant specifications for each year. It is interpreted that the bricks and earthen pipes were through a similar manufacturing process using almost the same raw materials.