Chongho Youn

Development of a Nozzle-Flapper-Type Servo Valve Using a Slit Structure

Pneumatic servo valves play a significant role in power transmission and system control using a pressurized gas. When pressurized air passes through servo valves, noise and pressure fluctuations are often experienced at the downstream side, and such fluctuations limit the value efficiency. In this paper, a novel four-port nozzle-flapper-type servo valve using a slit structure instead of an orifice plate is proposed. The slit structure maintains a laminar flow condition, and this provides an opportunity for the minimization of the noise and pressure fluctuations. The slit structure is fabricated using etching technology. The flow characteristics of the slit are investigated theoretically and experimentally in order to evaluate the design specifications and characteristics of the valve. The experimental results indicated that the noise level decreased by approximately 15 dB and could reduce the pressure fluctuation by 75%, compared with the previous valve. It is felt that the valve is more effective than many current valves.

Concentration measurement systems with stable solutions for binary gas mixtures using two flowmeters

The previously proposed gas concentration measurement system (Yamazaki et al 2007 Meas. Sci. Technol. 18 2762–8) shows a considerable error for some combinations of gases. The error increases when the system of equations determining mole fractions becomes a mathematically ill-conditioned system. Because the parameters of the equations reflect the material properties of the gases, the current paper considers flowmeters whose flow rate indication does not involve any gas property. This paper firstly illustrates the ill condition for the combination of venturi meter and laminar flowmeters. The paper then discusses the simultaneous measurement of flow rate and mole fractions by flowmeter combinations: an ultrasonic flowmeter and a venturi meter, an ultrasonic flowmeter and a laminar flowmeter. Experiments are conducted for a mixture of argon and air. When a venturi meter and a laminar flowmeter are used, the equations to evaluate the gas mixture ratio become an ill-conditioned system, and hence the evaluated mixture ratio shows a considerable error. On the other hand, the combination of an ultrasonic flowmeter and a laminar flowmeter detects the gas mixture ratio with proper accuracy.

Visualization of behaviors of a propagating flame quenching for hydrogen---air gas mixture

In this research, a flame arrester consisting of a slit structure was experimentally investigated. Experimental data show adequate maximum experimental safe gap (MESG) value for the flame arrester. The flow rate characteristics of the flame arrester were measured and compared with theoretical results. It was made clear that the flow impedance of convergent flow is 20% less than that of divergent flow. The experimental data and theoretical data show good agreement. The performance test by an EN12874 as ‘in-line stable detonation’ flame arrester was examined for a hydrogen–air gas mixture. The experimental data show that the gap was 0.2 times the MESG value in bi-directions for the flame arrester. The quenching and extinguishing processes were visualized by high-speed cameras.Graphical Abstract

Flow Characteristics of Pressure Reducing Valve with Radial Slit Structure for Low Noise

Pressure reducing valves are widely used to maintain the pressure of gas reservoirs to specific values. In a normal valve, supply pressure is decompressed with an orifice structure. When compressed air passes through the orifice structure, considerable noise occurs at the downstream side. In this paper, we have developed a radial slit structure that can reduce pressure without noise. The noise is reduced by changing the orifice structure into the radial slit structure. The radial slit structure valve reduces pressure without noise by suppressing the generation of turbulence and shock wave at the downstream. The analysis of the flow in radial slit structure was achieved by CFD2000 software. The flow rate and pressure distribution were simulated and compared with the experimental result. To confirm the generation of shock wave, the flow of orifice and radial slit structure at the downstream was visualized by Schlieren photography method. A shock wave was generated in the orifice structure, but no shock wave was generated in the radial slit structure. Noise reduction efficiency was investigated by the experiment. The experiment apparatus was set up to JIS standards. The experimental results indicated that the noise level decreased by approximately 40 dB in the slit structure. It is confirmed that the radial slit structure has effectiveness for low noise in the pressure reducing flow. And, it is expected that it can be applied to various kinds of industrial fields.

Pressure Change in Tee Branch Pipe in Oscillatory Flow

The purpose of this paper is to contribute to the understanding of unsteady flow of branch pipes in pneumatic systems. Branch pipes are used in pneumatic pipe systems in various industrial fields. To predict the unsteady pressure changes in the pneumatic piping systems, it is necessary that the dynamic characteristics of branch pipes are at hand, in addition to the dynamic characteristic of single pipe. However, while so many studies are accumulated for a single pipe dynamics, few studies have reported the pressure changes in branch pipes due to oscillatory flow. This paper reports an experimental study on the dynamic characteristics of the pressure change in a pneumatic branch pipe under given oscillatory flow. The paper also proposes a simulation method to predict the pressure changes in a pneumatic branch pipe under oscillatory flow. The validity of simulation is verified for oscillatory flows up to 5 Hz, comparing with the experimental results.

A study on leak detection of a household gas supply system using pressure decay method

This paper reports a study on leak detection of a household gas supply system using pressure decay method. The leak is detected by monitoring the pressure decay of a pipe. Since pressure is influenced by temperature, a temperature change will influence the accuracy of leak detection using pressure decay method. This research focuses on the study of the effect of temperature change to the pressure responses of pipe. Experiments were done by recording the pressure responses of pipe and room/environment temperature at several points in various room temperatures, various leak rates and at 2 kPa of supply pressure. The pipe length and diameter were varied. The system was mathematically modeled. Its pressure and temperature responses were simulated. The simulations were done under three different conditions: a) Pressure responses of pipe subjected to pipe temperature change during charging, b) Pressure responses of pipe subjected to room temperature change and c) Pressure responses of pipe subjected to temperature fraction of gas within the pipe. The simulation results were compared with the experimental results and show that room temperature change has the highest effect on the pressure response of pipe.

Stabilization of pilot valve system using linear flow resistance

In a pilot valve system, the pressure in the control chamber of the main valve is straightforwardly affected by pressure oscillation in the downstream pipeline or the pilot tube. To solve this problem, an orifice is generally installed in the pilot tube to restrain the oscillation. However, the orifice is a nonlinear flow resistance; the amplitude of the oscillation alters the gain curve of the control pressure response. In this study, a linear flow resistance such as a porous material is employed to stabilize the pilot valve system. A test pilot valve was manufactured, and a pilot valve system was developed in the laboratory of the authors of this article. A mathematical model of the pilot valve system using linear and nonlinear flow resistances was simulated in MATLAB. The linearity of the P–Q characteristics of the linear flow resistance was confirmed, and a series of frequency response experiments were performed to examine the dynamic characteristics of the pilot valve system with various flow resistances. The experimental results were in accord with the simulation results. This implied that when porous materials were used in the pilot valve system, the gain of the pressure response did not vary regardless of the varying pressure vibration amplitude. Therefore, porous materials are suitable to be used in the pilot valve system instead of an orifice to enhance its stability.

Simulation of cooling system using internal air flow with bending flow passages

Cooling after the implementation of a high-density integrated circuit manufacturing process using internal air flow within the object to be cooled is often performed in the industry. In this study, the cooling performance is predicted using a numerical simulation model and examined by the experiment when the flow rate is within 30 L/min (ANR). Three types of flow passage shapes are made with the plate size of 13.4 mm × 13.1 mm and cooling performances are compared with each other. As a result, it was confirmed that the cooling time reduced when the number of turns in the flow passage was increased and the cooling efficiency reduced when the number of turns in the flow passage was increased. It is considered that the cooling system using a flow passage with four turns is the optimal system for practical use.

A Simulation Study of Radial Slits Pressure Regulator for Hydrogen Gas

Noise generation during decompressing hydrogen in fuel cell vehicles is an issue requiring technological solution. This paper studies noise reducing effect and the flow characteristic of radial slits installed in a pressure reducing valve. Simulation is carried out to estimate the pressure–flow characteristic of the radial slit as a noise reducing mean. The simulation indicates a decrease of Reynolds number in the downstream-side of the radial slits structure, which causes noise reduction. Moreover, we proposed installing radial slits to the downstream of a conventional valve. Noise reduction by this new design was verified with a series of experiments. As a result, the valve with radial slits has a noise reduction effect of about 12.1 dB (A) compared with the conventional valve.

Temperature measurement control problem of vibrational viscometers considering heat generation and heat transfer effect of oscillators

In viscosity measurement, temperature control is very important. In this research, temperature distribution effect of vibrational viscometers was analyzed. Vibrational viscometer was designated amongst other viscometer types due to inexpensiveness, handiness and efficacious continuous viscosity measurement capability. The research was conducted in three parts. In the first part; heat generation problem of boundary layers of oscillators of vibrational viscometers was analyzed. Experiments prove that due to the friction between the oscillators and the fluids, heat is generated from the vibrational boundary layer of the oscillators. In the second part, unequal temperature distribution problem of vibrational viscometers was analyzed. When heater generates heat during continuous viscosity measurement, temperature disperses every part of a fluid and affects the viscosity of the fluid. Therefore, it may not be possible to acquire a homogenous viscosity value from a fluid since temperature distribution cannot be equal at every point of a standard fluid. Experimental outcomes and mathematical calculations have also strengthened this conclusion. In the last part of the research, in order to solve the unequal temperature distribution problem, it is proposed to utilize a magnetic stirrer which will mix up the fluid throughout the viscosity measurement and constitute homogenous temperature.