Yong Woo Rho

Mass transport phenomena in proton exchange membrane fuel cells using O[sub 2]/He, O[sub 2]/Ar, and O[sub 2]/N[sub 2] mixtures; 1: Experimental analysis

The theoretical analysis of mass-transport phenomena at the cathode in proton exchange membrane fuel cells is a consequence of the experimental analysis, reported in Part I of this paper. A one-dimensional model for the substrate-gas diffusion and active layers was assumed to elucidate the contributions to mass-transport overpotentials. The results of the theoretical analysis show that, first, the higher slope of the pseudo-linear region of the potential (E) vs. current density (i) plot with air or the gas mixtures (O 2 /He, O 2 /Ar, O 2 /N 2 ), rather than with O 2 , as the cathodic reactant, is predominantly due to mass-transport limitations in the active layer, and, second, the departure from linearity of the E vs. i plot is due to mass transport in the substrate-diffusion layer

Modeling and Simulation for PIG Flow Control in Natural Gas Pipeline

This paper deals with dynamic analysis of Pipeline Inspection Gauge (PIG) flow control in natural gas pipelines. The dynamic behaviour of PIG depends on the pressure differential generated by injected gas flow behind the tail of the PIG and expelled gas flow in front of its nose. To analyze dynamic behaviour characteristics (e.g. gas flow, the PIG position and velocity) mathematical models are derived. Two types of nonlinear hyperbolic partial differential equations are developed for unsteady flow analysis of the PIG driving and expelled gas. Also, a non-homogeneous differential equation for dynamic analysis of the PIG is given. The nonlinear equations are solved by method of characteristics (MOC) with a regular rectangular grid under appropriate initial and boundary conditions. Runge-Kutta method is used for solving the steady flow equations to get the initial flow values and for solving the dynamic equation of the PIG. The upstream and downstream regions are divided into a number of elements of equal length. The sampling time and distance are chosen under Courant-Friedrich-Lewy (CFL) restriction. Simulation is performed with a pipeline segment in the Korea gas corporation (KOGAS) low pressure system, Ueijungboo-Sangye line. The simulation results show that the derived mathematical models and the proposed computational scheme are effective for estimating the position and velocity of the PIG with a given operational condition of pipeline.

Speed control of PIG using bypass flow in natural gas pipeline

This paper introduces a simple nonlinear control method for pipeline inspection gauge (PIG) flow in a natural gas pipeline. The PIG is controlled using the amount of bypass flow across its body. The dynamic behavior of the PIG depends on the different pressure across its body and the bypass flow through it. The system dynamics includes: dynamics of driving gas flow behind the PIG, dynamics of expelled gas in front of the PIG, dynamics of bypass flow and dynamics of the PIG. The method of characteristics (MOC) and Runge-Kutta method are used to solve the dynamics of flow. To control the PIG velocity, a simple nonlinear controller is proposed based on the back-stepping method. The closed loop system is stable in the sense of Lyapunov stability. To derive such a controller, three system parameters should be measured: the PIG position, its velocity and the velocity of bypass flow across the PIG body. To show the effectiveness of the proposed controller, the simulation has been done with three cases: the PIG starts to move at its launcher, the PIG arrives at its receiver and the PIG restarts after stopping in the pipeline. The simulation results show that the proposed controller can be used for controlling the PIG velocity with good performance when it runs in the natural gas pipeline.

Dynamic modeling and its analysis for PIG flow through curved section in natural gas pipeline

Dynamic modeling and its analysis for the PIG (pipeline inspection gauge) flow through a 90/spl deg/ curved pipe with compressible and unsteady flow are studied. The PIG dynamics model is derived by using a Lagrange equation under the assumption that it passes through 3 different sections in the curved pipeline such that it moves into, inside and out of the curved section. The downstream and up stream flow dynamics including the curved sections are solved using the method of characteristic. The effectiveness of the derived mathematical models is estimated by simulation results for a low pressure natural gas pipeline including downward and upward curved sections. The simulation results show that the proposed model and solution can be used for estimating the PIG dynamics when we pig the pipeline including curved sections.

Verification of the Theoretical Model for Analyzing Dynamic Behavior of the PIG from Actual Pigging

This paper deals with verification of the theoretical model for dynamic behavior of Pipeline Inspection Gauge (PIG) traveling through high pressure natural gas pipeline. The dynamic behavior of the PIG depends on the differential pressure across its body. This differential pressure is generated by injected gas flow behind the tail of the PIG and expelled gas flow in front of its nose. To analyze the dynamic behavior characteristics such as gas flow in pipeline, and the PIG position and velocity, not only the mathematical models are derived, but also the theoretical models must be certified by actual pigging experiment. But there is not any found results of research on the experimental certification for dynamic behavior of the PIG. The reason is why the fabrication of the PIG as well as, a field application are very difficult. In this research, the effectiveness of the introduced solution using the method of characteristics (MOC) was certified through field application. In-line inspection tool, 30” geometry PIG, was fabricated and actual pigging was carried out at the pipeline segment in Korea Gas Corporation (KOGAS) high pressure system, Incheon LT(LNG Terminal) -Namdong GS(Governor Station) line. Pigging is fulfilled successfully. Comparison of simulation results with experimental results show that the derived mathematical models and the proposed computational schemes are effective for predicting the position and velocity of the PIG with a given operational conditions of pipeline.

Modeling and Simulation for PIG with Bypass Flow Control in Natural Gas Pipeline

This paper introduces modeling and simulation results for pipeline inspection gauge (PIG) with bypass flow control in natural gas pipeline. The dynamic behaviour of the PIG depends on the different pressure across its body and the bypass flow through it. The system dynamics includes: dynamics of driving gas flow behind the PIG, dynamics of expelled gas in front of the PIG, dynamics of bypass flow, and dynamics of the PIG. The bypass flow across the PIG is treated as incompressible flow with the assumption of its Mach number smaller than 0.45. The governing nonlinear hyperbolic partial differential equations for unsteady gas flows are solved by method of characteristics (MOC) with the regular rectangular grid under appropriate initial and boundary conditions. The Runge-Kuta method is used for solving the steady flow equations to get initial flow values and the dynamic equation of the PIG. The sampling time and distance are chosen under Courant-Friedrich-Lewy (CFL) restriction. The simulation is performed with a pipeline segment in the Korea Gas Corporation (KOGAS) low pressure system, Ueijungboo-Sangye line. Simulation results show us that the derived mathematical model and the proposed computational scheme are effective for estimating the position and velocity of the PIG with bypass flow under given operational conditions of pipeline.

Design and implementation of 30„ geometry PIG

This paper introduces the developed geometry PIG (Pipeline Inspection Gauge), one of several ILI (In-Line Inspection) tools, which provide a full picture of the pipeline from only single pass, and has compact size of the electronic device with not only low power consumption but also rapid response of sensors such as calipers, IMU and odometer. This tool is equipped with the several sensor systems. Caliper sensors measure the pipeline internal diameter, ovality and dent size and shape with high accuracy. The IMU (Inertial Measurement Unit) measures the precise trajectory of the PIG during its traverse of the pipeline. The IMU also provide three-dimensional coordination in space from measurement of inertial acceleration and angular rate. Three odometers mounted on the PIG body provide the distance moved along the line and instantaneous velocity during the PIG run. The datum measured by the sensor systems are stored in on-board solid state memory and magnetic tape devices. There is an electromagnetic transmitter at the back end of the tool, the transmitter enables the inspection operators to keep tracking the tool while it travels through the pipeline. An experiment was fulfilled in pull-rig facility and was adopted from Incheon LT (LNG Terminal) to Namdong GS (Governor Station) line, 13 km length.

Development of the Caliper System for a Geometry PIG Based on Magnetic Field Analysis

This paper introduces the development of the caliper system for a geometry PIG (Pipeline Inspection Gauge). The objective of the caliper system is to detect and measure dents, wrinkles, and ovalities affect the pipe structural integrity. The developed caliper system consists of a finger arm, an anisotropic permanent magnet, a back yoke, pins, pinholes and a linear hall effect sensor. The angle displacement of the finger arm is measured by the change of the magnetic field in sensing module. Therefore the sensitivity of the caliper system mainly depends on the magnitude of the magnetic field inside the sensing module. In this research, the ring shaped anisotropic permanent magnet and linear hall effect sensors were used to produce and measure the magnetic field. The structure of the permanent magnet, the back yoke and pinhole positions were optimized that the magnitude of the magnetic field range between a high of 0.1020 Tesla and a low of zero by using three dimensional nonlinear finite element methods. A simulator was fabricated to prove the effectiveness of the developed caliper system and the computational scheme using the finite element method. The experimental results show that the developed caliper system is quite efficient for the geometry PIG with good performance.

Defect estimation of a crack in underground pipelines by CMFL type NDT system

A defect which is axially oriented with small size is hard to detect in conventional system. CMFL (Circumferential Magnetic Flux Leakage) type PIG (Pipelines Inspection Gauge) in the NDT (Nondestructive Testing), is operated to detect this defect called axially oriented cracks in the pipe. It is necessary to decompose the size and shapes of cracks for the maintenance of underground pipelines. This article is focused on the decomposing method of the size and shape of the axially oriented cracks by using inspection signal data for defect.

A study on the measurement of axial cracks in the Magnetic Flux Leakage NDT system

Among the nondestructive testing methods, the MFL(Magnetic Flux Leakage) PIG(Pipelines Inspection Gauge) is especially suitable for testing pipelines because the pipeline has high magnetic permeability. MFL PIG showed high performance in detecting the metal loss and corrosions. However, MFL PIG is difficult to detect the crack which occurred by exterior-interior pressure difference in pipelines and the shape of crack is very long and narrow. Therefore, the new PIG is needed to be researched and developed for detecting the cracks. The CMFL(Circumferential MFL) PIG performs magnetic fields circumferentially and can maximize the magnetic flux leakage at the cracks. In this paper, CMFL PIG is designed and the distribution of the magnetic field is analyzed by using finite element method. Also, by simulating and measuring the magnetic leakage field, it is possible to detect of axial cracks in the pipeline.