• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.386-390
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• 2016

Water aeration is an effective water treatment process, which involves the injection of air or air-water mixture into water treatment reservoir commonly through pipes. The main purpose of water aeration is to maintain healthy levels of dissolved oxygen (DO), which is the most important water quality factor. The pipes' operating conditions are important for controlling the efficiency and effectiveness of aeration process. Many studies have been conducted on two-phase flows in pipes, however, there are a few studies to deal with small s ale in millimeter. The main objective of this study is to perform 2-dimensional two-phase simulations inside various straight pipes using the computational fluid dynamic (CFD) OpenFOAM (Open source Field Operation And Manipulation) tools to examine the influence of flow patterns on bubble size, which is closely related to DO concentration in a water body. The both flow regimes, laminar and turbulence, have been considered in this study. For turbulence, Reynolds-averaged Navier-Stokes (RANS) has been applied. The coalescence and breakage of bubbles caused by random collisions and turbulent eddies, respectively, are considered in this research. Sauter mean bubble diameter and water velocity are compared against experimental data. The simulation results are in good agreement with the experimental measurements.

• Journal of Bio-Environment Control
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• v.28 no.3
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• pp.204-211
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• 2019

The purpose of this study is to provide basic data for setting environmental design standards for domestic greenhouses. We conducted experiments on thermal environment measurement at two commercial greenhouses where hot water heating system is adopted. We analyzed heat transfer characteristics of hot water heating pipes and heat emission per unit length of heating pipes was presented. The average air temperature in two greenhouses was controlled to $16.3^{\circ}C$ and $14.6^{\circ}C$ during the experiment, respectively. The average water temperature in heating pipes was $52.3^{\circ}C$ and $45.0^{\circ}C$, respectively. Experimental results showed that natural convection heat transfer coefficient of heating pipe surface was in the range of $5.71{\sim}7.49W/m^2^{\circ}C$. When the flow rate in heating pipe was 0.5m/s or more, temperature difference between hot water and pipe surface was not large. Based on this, overall heat transfer coefficient of heating pipe was derived as form of laminar natural convection heat transfer coefficient in the horizontal cylinder. By modifying the equation of overall heat transfer coefficient, a formula for calculating the heat emission per unit length of hot water heating pipe was developed, which uses pipe size and temperature difference between hot water and indoor air as input variables. The results of this study were compared with domestic and foreign data, and it was found to be closest to JGHA data. The data of NAAS, BALLS and ASHRAE were judged to be too large. Therefore, in order to set up environmental design standards for domestic greenhouses, it is necessary to fully examine those data through further experiments.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.17 no.1
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• pp.29-34
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• 1981

More recently, unsteady flow in small-diameter pipes plays a major role in liquid propellantrocket systems, hydraulic and pneumatic control system, and elsewhere. And it has shown that line dynamics can have a marked effect on the hydraulic system characteristics. In this paper, transfer function of hydraulic lines with an accumulator and an outlet orifice is' developed and compared with experimental data from frequency response tests at various airvolume(V.) and the location of accumulator(ld1t), so that their performance may be correctly and easily predicted and the design of the systems incorporating them improved. The obtained results are as follows: 1. The dynamic response of hydraulic lines may be analyzed more accurately by use of the viscous term(22) in unsteady laminar flow. 2. There was good agreement between the theoretical and experimental results of this investigation, and hydraulic systems with liines included an accumulator can be analyzed more accurately by use of the pressure transfer function given by eq. (16). 3. For the mitigation of surge in hydraulic lines, it is more effective that the location ofaccumulator is close to the pipe outlet side. 4. According to the gas volume of accumulator is increased(the sealing pressure is close tomean line pressure), the damping effect of pressure wave is improved.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.6
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• pp.1959-1970
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• 1996

Effects of oscillatory flow upon heat transfer characteristics have been studied experimentally for oscillating flow in a circular tube. The experimental apparatus was designed to simulate the heat exchangers of the Stirling or Vuilleumier cycle machines and the test section consists of heater and cooler. Measurements were presented of heat flux, axial wall temperature distribution, and radial temperature profile of the working fluid for several cases of oscillation frequency and swept distance ratio. The influences of two main parameters, frequency and tidal displacement of the oscillation were investigated. Then the heat transfer coefficient at the heater is obtained. The carried by the authors with a assumption of oscillatory laminar slug flow.

• Journal of the Korean Society of Combustion
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• v.6 no.2
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• pp.65-70
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• 2001

To investigate statistics of flamelet in a turbulent premixed flame and to obtain components of their burning velocities in a vertical plane above a pipe-flow burner, the local motion of flamelets with respect to gas are measured by specially arranged diagnostics, composed of an electrostatic probe with four identical sensors and a two-color four-beam LDV system. With this technique, the three-dimensional local flame-front-velocity vector is measured by the electrostatic probe for the first time, and simultaneously the axial and radial components of the local gas-velocity vector in a vertical plane above the vertically oriented burner are measured by the LDV system. Two components of burning velocities of planar flamelets can be obtained from these results and are found to be distributed over different directions and to range in magnitude from nearly zero to a few times the planar, unstrained adiabatic laminar burning velocity measured in the unburnt gas. It may be concluded from these results that turbulence exerts measurable influences on flamelets and causes at least some of them to exhibit increased burning velocity.

• Journal of the Korean Society of Combustion
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• v.7 no.2
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• pp.62-68
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• 2002

To investigate statistics of flamelet in a turbulent premixed flame and to obtain components of their burning velocities in a vertical plane above a pipe-flow burner, the local motion of flamelets with respect to gas are measured by specially arranged diagnostics, composed of an electrostatic probe with four identical sensors and a two-color four-beam LDV system. With this technique, the three-dimensional local flame- front-velocity vector is measured by the electrostatic probe for the first time, and simultaneously the axial and radial components of the local gas-velocity vector in a vertical plane above the vertically oriented burner are measured by the LDV system. Two components of burning velocities of planar flamelets can be obtained from these results and are found to be distributed over different directions and to range in magnitude from nearly zero to a few times the planar, un strained adiabatic laminar burning velocity measured in the unburnt gas. It may be concluded from these results that turbulence exerts measurable influences on flamelets and causes at least some of them to exhibit increased burning velocity.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.12
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• pp.1093-1099
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• 2010

For Very High Temperature Reactors (VHTR), the designs of the Intermediate Heat Transport Loop (IHTL) and the Intermediate Heat Exchanger (IHX) are particularly difficult because of the high-temperature operation (up to $950^{\circ}C$). In this study, Flinak molten salt, a eutectic mixture of LiF, NaF, and KF (46.5:11.5:42.0 mole %) is considered as the heat transporting fluid in the IHTL. To evaluate the flow and heat transfer performance of the Flinak molten salt in small channels with hydraulic diameters in the millimeter range, a double-pipe heat exchanger was constructed using small-diameter tubes for the heat exchange between the Flinak and the gas flow. The experimental data showed that, for laminar Flinak flow, the measured friction factors were close to the 64/Re curve and the Nusselt numbers were generally between 3.66 and 4.36.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.3
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• pp.14-21
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• 2017

The extreme floods recently are have been attributed global warming, The development of a canal tunnel to prevent floods by making a bypass or undercurrent to flood discharge in a major flooding area is required because urban flooding in heavy rainfall occurs frequently, increasing the impermeability according to lack of capacity in sewage to urbanization by the existing urban basin. In this study, a numerical simulation was performed to support design standards for a multi-purpose waterway tunnel combined road tunnel of canal tunnel. The numerical simulation showed that the size of the friction loss occurring in the tunnel section of the same channel occurred more than the theoretically calculated frictional loss derived from the numerical simulations. This is probably due to the additional frictional loss caused by the change in the flow structure due to the geometry of the pipe when the shape of the channel is non-circular. The increase in friction loss was more pronounced in the laminar flow than in the turbulent flow. Depending on the shape of the conduit, the friction loss should be adjusted for accurate flow calculations. This result can provide the basin information about the design of flood by a pass conduit.

• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.1
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• pp.145-152
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• 2021

The purpose of this study was to determine the optimal distances between pipes to minimize the pressure loss and turbulent intensity. This was accomplished by investigating the distances between sleeve-jointed pipes and the flow changes in pipes based on variations in the Reynolds (Re) number when installing adjusting pieces for the pipes. When the thickness tp of the sleeve-jointed piping was fixed at 5 mm and the pipe lengths Lp were 10, 50, 100, and 200 mm, the correlations with the velocity of the sleeve-jointed part, pressure distribution, length of the reattachment point in the recirculation area, and Re number were analyzed. The flow characteristic of the sleeve-jointed part from a laminar to a turbulent flow region was determined by setting the Re range to 200 ≤ Re ≤ 5,000. This was done by utilizing Ansys Fluent 18.1, which is a commercial program. The enlargement and contraction ratios of the sleeve-jointed part were 1.2 and 0.83, respectively, and the turbulent intensity of the sleeve downstream edge and pressure change both increased as the Re number increased while Lp remained constant. The fact that the flow on the sleeve wall surface was disturbed by tp resulted in losses in velocity energy. Therefore, the edge of the sleeve-jointed part was also effected. When Lp was 10 mm or less, the turbulent intensity of the edge part did not change significantly as the Re number increased. The reattachment point in the recirculation area did not appear at Lp of 10 mm or less and was not affected by the vortex. In the case of 3,000 ≤ Re, the reattachment length of the wall surface of the sleeve-jointed part was nearly constant as Lp increased.

• Advances in aircraft and spacecraft science
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• v.5 no.3
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• pp.363-383
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• 2018

One-dimensional (1D) models of incompressible flows, can be of interest for many applications in which fast resolution times are demanded, such as fluid-structure interaction of flows in compliant pipes and hemodynamics. This work proposes a higher-order 1D theory for the flow-field analysis of incompressible, laminar, and viscous fluids in rigid pipes. This methodology is developed in the domain of the Carrera Unified Formulation (CUF), which was first employed in structural mechanics. In the framework of 1D modelling, CUF allows to express the primary variables (i.e., velocity and pressure fields in the case of incompressible flows) as arbitrary expansions of the generalized unknowns, which are functions of the 1D computational domain coordinate. As a consequence, the governing equations can be expressed in terms of fundamental nuclei, which are invariant of the theory approximation order. Several numerical examples are considered for validating this novel methodology, including simple Poiseuille flows in circular pipes and more complex velocity/pressure profiles of Stokes fluids into non-conventional computational domains. The attention is mainly focused on the use of hierarchical McLaurin polynomials as well as piece-wise nonlocal Lagrange expansions of the generalized unknowns across the pipe section. The preliminary results show the great advantages in terms of computational costs of the proposed method. Furthermore, they provide enough confidence for future extensions to more complex fluid-dynamics problems and fluid-structure interaction analysis.