• Journal of Microbiology and Biotechnology
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• v.21 no.2
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• pp.115-123
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• 2011

To investigate the effects of pipe materials on biofilm accumulation and water quality, an annular reactor with the sample coupons of four pipe materials (steel, copper, stainless steel, and polyvinyl chloride) was operated under hydraulic conditions similar to a real plumbing system for 15 months. The bacterial concentrations were substantially increased in the steel and copper reactors with progression of corrosion, whereas those in stainless steel (STS) and polyvinyl chloride (PVC) reactors were affected mainly by water temperature. The heterotrophic plate count (HPC) of biofilms was about 100 times higher on steel pipe than other pipes throughout the experiment, with the STS pipe showing the lowest bacterial number at the end of the operation. Analysis of the 16S rDNA sequences of 176 cultivated isolates revealed that 66.5% was Proteobacteria and the others included unclassified bacteria, Actinobacteria, and Bacilli. Regardless of the pipe materials, Sphingomonas was the predominant species in all biofilms. PCR-DGGE analysis showed that steel pipe exhibited the highest bacterial diversity among the metallic pipes, and the DGGE profile of biofilm on PVC showed three additional bands not detected from the profiles of the metallic materials. Environmental scanning electron microscopy showed that corrosion level and biofilm accumulation were the least in the STS coupon. These results suggest that the STS pipe is the best material for plumbing systems in terms of the microbiological aspects of water quality.

• Journal of the Korean Magnetics Society
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• v.12 no.2
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• pp.73-79
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• 2002

Compared with Newtonial fluids, magnetic fluids have effects on magnetic force. In this study, the purpose is to research the heat transfer characteristic of magnetic fluids which have metalic and fluid characteristics as the external pipe is being cooled and internal pipe is heated. This study found the experimental results from the study of the variety of natural convection for magnetic fluids and the characteristics of the heat transfer by using numerical analysis according to the strength and direction of the magnetic fields from being imposed from the outside. Natural convection of magnetic fluids was controlled by the impressed magnetic fields, and the result of mean nusselt number was calculated. If the impressed magnetic field is in the direction of gravity or the strength of impressed magnetic field is more than -14 mT in the opposite direction, the heat transfer is more than that without the impressed magnetic field. If the strength of impressed magnetic field is less than -14 mT in the opposite direction, it is smaller than that without the impressed magnetic field. Especially, when the strength of the magnetic field is -14 mT, the heat transfer was at the minimum.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.9
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• pp.1217-1228
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• 1998

In order to elucidate the operational characteristics of rotating heat pipes, the internal flow patterns and heat transfer performance are investigated. Flow patterns and its transition are studied with various rotational speeds by visualizing flows established inside a rotating tube. To verify those results of analysis, 2 heat pipes of the same geometries but fill charge rates of 7, 30% were manufactured and submitted to operating tests. Comparison of experimental results on heat transfer rate show a fairly good agreement with the analytical results. The analysis reveals that the optimum charge ratio is ranged in 4~7% depending on the quantity of thermal loads. but the heat pipe with 7% of fill charge ratio reached dry-out limitation at heat flux of $q^{{\prime}{\prime}}=6.2kW/m^2$ lower than that of analytic results. Transition of flow regime was well related to the correlation by Semena & Khmelev on transient centrifugal Froude Number Frc. But hysteresis phenomenon was observed in transition of flow regime, when the rotational speed was stepwisely changed in the way to undergo 1 cycle.

• Journal of the Korean Society of Visualization
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• v.4 no.2
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• pp.76-80
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• 2006

The data for friction factor of the pipe correlated by Reynolds number and relative roughness have been reported well as a Moody chart. However, the results for corrugated shapes have been not investigated sufficiently. In this research, therefore, the pressure drop and friction factor are obtained. Flexible metal tubes with corrugations for the measurement are made of stainless steel plates. The kinds of tubes for the measurement are 5 annular types and helical types. The pressure drop & the velocity of the flow are obtained by micromanometer & digital pressure sensor, supplying dry air at several steps. Then the pressure drop is calculated for each tube, using the obtained data. The result shows that the pressure drop is strongly influenced by the viscous dissipation of kinetic energy due to the circulation of flows, rather than a viscous friction loss. The pressure drop increased consistently as the Reynolds number increases.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.1
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• pp.1-9
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• 1999

For roughened annular pipes with diameter ratios of 0.26, 0.39, and 0.56 and with Reynolds numbers ranging 13,000 to 67,000, friction factor, autocorrelation coefficients, power spectral density functions, and integral length scales for each flow condition using X-type hot wire anemometry system are experimentally investigated. Distributions of these quantities show that the times which the streamwise autocorrelation coefficients become zero first increase with decreasing the radius ratios of concentric annuli and Reynolds numbers, however the power spectra density functions increase with increasing the radius ratios and Reynolds number.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.22 no.1
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• pp.227-237
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• 1998

In case the systems have radioactivity, toxic liquid or expensive fluid, and have to be performed repair work at one point of the system pipe, the formation of an internal ice plug by the removal of heat from the pipe is often consideredas a useful method. In this procedure, an annular jacket is placed around the pipe, and the jacket is then filled with liquid Nitrogen(-196.deg. C). Thermal analysis by the finite element method based on the laboratory experiments has been constructed. The result of the finite element analysis on the experimental model shows to be reasonable, and thus the finite element analysis for different pipe size, material and thickness has been performed to see if the ice plugging procedure in various applications can be safely performed without possibility of damage to the pipe. It has been confirmed that in carbon steel pipes the maximum stress is found around the boundary of the freezing jacket, and the stress increases as pipe thickness increases, but the maximum stress shows no consistency along the increment of the pipe diameter. The maximum stresses appear lower than yield stress in carbon steel. It has been also shown that in stainless steel pipes the maximum stresses are also found around the boundary of the freezing jacket, but almost the same value in spite of different pipe size an thickness, and the maximum stresses show slightly higher than the yield stress of the stainless steel.

• Industrial Engineering and Management Systems
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• v.15 no.4
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• pp.396-402
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• 2016

In this study, hydraulic analysis of water-supply networks in Marivan was performed by modeling. WATERGEMS was used for modeling and it was calibrated using existing rules and regulations. The purpose of this research is modeling urban water network and its analysis based on hydraulic criteria and meeting pressure conditions at the nodes and complying the economic speed. To achieve this goal, first the pipelines of city streets was designed in AutoCAD on a map of the city. It should be mentioned that it was tried to prevent from creating additional loops in the network and the optimal network was designed by a combination of annular and branch loops. In the next step, the pipes were called in WATERGEMS and then we continue the operation by the allocation of elevation digits to the pipes. Since the topography of this city is very specific and unique, the number of pressure zones was increased. Three zones created only covers about 20% of the population in the city. In this dissertation, the design was performed on the city's main zone with the largest density in the Figures 1,320-1,340. In the next step, the network triangulation was conducted. Finally, the Debiw as allocated based on the triangulation conducted and considering the density of the city for year of horizon. Ultimately, the network of Marivan was designed and calibrated according to hydraulic criteria and pressure zoning. The output of this model can be used in water-supply projects, improvement and reform of the existing net-work in the city, and various other studies. Numerous and various graphs obtained in different parts of a network modelled can be used in the analysis of critical situation, leakage.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.19 no.3
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• pp.14-22
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• 2023

Steel-pipe civil structures, including steel-pipe energy piles and cast-in-place piles (CIPs), utilize steel pipes as their primary reinforcements. These steel pipes facilitate the circulation of a working fluid through their annular crosssection, enabling heat exchange with the surrounding ground formation. In this study, the cooling performance of a ground source heat pump (GSHP) system that incorporated steel-pipe civil structures was investigated to assess their applicability. First of all, the thermal performance test was conducted with steel-pipe CIPs to evaluate the average heat exchange amount. Subsequently, a GSHP system was designed and implemented within an office container, considering the various types of steel-pipe civil structures. During the performance evaluation tests, parameters such as the coefficient of performance (COP) and entering water temperature (EWT) were closely monitored. The outcomes indicated an average COP of 3.74 for the GSHP system and the EWT remained relatively stable throughout the tests. Consequently, the GSPH system demonstrated its capability to consistently provide a sufficient heat source, even during periods of high cooling thermal demand, by utilzing the steel-pipe civil structures.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.4
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• pp.364-369
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• 2005

An experimental study was conducted on the thermal conductivity of various grouting materials for geothermal heat exchanger which is used as a heat sink or source in the heat pump system. The grouting of the vertical heat exchanger is important for environmental and heat transfer reasons and is generally accomplished by the placement of a low permeability material into the annular space between the borehole wall and the pipes suspended in the borehole. In this study, a lab scale test apparatus was made and measured the thermal conductivity of four grouting materials. As a result, the temperature rising tendency was similar among them, but the increasing rate was different. Thus the thermal conductivity showed a maximum difference of $27\%$ among grouting materials.

• Journal of Mechanical Science and Technology
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• v.17 no.10
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• pp.1507-1519
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• 2003

The two-phase flow patterns for both non-loop and loop type oscillating capillary tube heat pipes (OCHPs) were presented in this study. The detailed flow patterns were recorded by a high-speed digital camera for each experimental condition to understand exactly the operation mechanism of the OCHP. The design and operation conditions of the OCHP such as turn number, working fluid, and heat flux were varied. The experimental results showed that the representative flow pattern in the evaporating section of the OCHP was the oscillation of liquid slugs and vapor plugs based on the generation and growth of bubbles by nucleate boiling. As the oscillation of liquid slugs and vapor plugs was very speedy, the flow pattern changed from the capillary slug flow to a pseudo slug flow near the annular flow. The flow of short vapor-liquid slug-train units was the flow pattern in the adiabatic section. In the condensing section, it was the oscillation of liquid slugs and vapor plugs and the circulation of working fluid. The oscillation flow in the loop type OCHP was more active than that in the non-loop type OCHP due to the circulation of working fluid in the OCHP. When the turn number of the OCHP was increased, the oscillation and circulation of working fluid was more active as well as forming the oscillation wave of long liquid slugs and vapor plugs in the OCHP. The oscillation flow of R-142b as the working fluid was more active than that of ethanol and the high efficiency of the heat transfer performance of R -142b was achieved.