• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.178-181
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• 2011

Recently, micro shock tube is being extensively used in various fields of engineering applications. The flow characteristics occurring in the micro shock tube may be significantly different from that of conventional macro shock tube due to very low Reynolds number and Knudsen number effects which are, in general, manifested in such flows of rarefied gas, solid-gas two-phase, etc. In these situations, Navier-Stokes equations cannot properly predict the micro shock tube flow. In the present study, a two-dimensional CFD method has been applied to simulate the micro shock tube, with slip velocity and temperature jump boundary conditions. The effects of wall thermal conditions on the unsteady flow in the micro shock tube were also investigated. The unsteady behaviors of shock wave and contact discontinuity were, in detail, analyzed. The results obtained show much more attenuation of shock wave, compared with macro-shock tubes.

• International Journal of Air-Conditioning and Refrigeration
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• v.12 no.4
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• pp.192-197
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• 2004

A capillary tube, which is a common expansion device in small sized refrig-eration and air-conditioning systems, should be redesigned properly to establish an optimum operation cycle of a refrigerating system with alternative refrigerants. Based on experimental data for R-22, R-290, and R-407C, an empirical correlation is developed to predict mass flow rate through capillary tubes. Dimensionless parameters are derived from the Buckingham Pi theorem, considering the effects of operating conditions and capillary tube geometry on mass flow rate. Approximately $97\%$ of the present data are correlated within a relative deviation of $\pm\;10\%.$ The present correlation also predicts the data obtained from open literature within $\pm\;15\%.$ In addition, rating charts of refrigerant flow rate for R-12, R-22, R-134a, R-152a, R-407C, R-410A, R-290, and R-600a are developed.

• KIEE International Transactions on Electrophysics and Applications
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• v.2C no.5
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• pp.262-267
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• 2002

In this paper, we first studied the factors affecting the motor current (MC) signal, which was strongly affected by the systematic hardware noises depending on polishing such as pad conditioning and arm oscillation of platen and recipe, head motor. Next, we studied the end point detection (EPD) for the chemical mechanical polishing (CMP) process of shallow trench isolation (STI) with reverse moat structure. The MC signal showed a high amplitude peak in the fore part caused by the reverse meal. pattern. We also found that the EP could not be detected properly and reproducibly due to the pad conditioning effect, especially when conventional low selectivity slurry was used. Even when there was no pad conditioning effect, the EPD method could not be applied, since the measured end points were always the same due to the characteristics of the reverse moat structure with an open nitride layer.

• Journal of Mechanical Science and Technology
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• v.15 no.12
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• pp.1609-1615
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• 2001

This paper presents the characteristics of a general structured observer and presents an estimation algorithm for a system with external disturbances which are added to the input of the system. By using a disturbance model, the general structured observer can estimate the states of the system is spite of disturbances, where the system is affected from external disturbances. Also, the general structured observer can include the function of a PI observer or high gain observer by properly adjusting the observer's gain matrices. The existence condition for the observer is derived, which can be checked by the system's observability condition and the pole-zero cancellation of the system's polynomial matrix. Through a numerical example, it is verified that the proposed observer is effective estimating the system and the input disturbance.

• Journal of Mechanical Science and Technology
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• v.18 no.5
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• pp.838-846
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• 2004

Minimum ignition energies of hydrogen/air and methane/air mixtures have been investigated numerically by solving unsteady one-dimensional conservation equations with detailed chemical kinetic mechanisms. Initial kernel size needed for numerical calculation is a sensitive function of initial pressure of a mixture and should be estimated properly to obtain quantitative agreement with experimental results. A simple macroscopic model to determine minimum ignition energy has been proposed, where the initial kernel size is correlated with the quenching distance of a mixture and evaluated from the quenching distance determined from experiment. The simulation predicts minimum ignition energies of two sample mixtures successfully which are in a good agreement with the experimental data for the ranges of pressure and equivalence ratio.

• International Journal of Fluid Machinery and Systems
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• v.2 no.4
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• pp.449-455
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• 2009

A reversible axial flow fan called jet fan has been widely used for longitudinal ventilation in road tunnels to secure a safe and comfortable environment cost-effectively. As shifting the flow direction is usually made by only switching the rotational direction of an electric motor due to heavy duty, rotor blades having identical aerodynamic performance for bidirectional flow should be necessary. However, such aerodynamically desirable blades haven't been developed sufficiently, since most of the related studies have been done from the viewpoint of unidirectional flow. In the present paper, we demonstrate a method to profile the blade section suitable for bidirectional flow, which is validated by studying the aerodynamic performances of rotor blades of a two-stage jet fan experimentally and numerically.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2000.10a
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• pp.230-235
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• 2000

In this paper, a surface generation model is presented to simulate surface roughness profile in turning operation. The simulation model takes into account the effect of tool geometry, process parameters, rotational errors of spindle, and the relative vibration between the cutting tool and workpiece. The surface roughness profiles are simulated based on the surface-shaping system. The model has been verified by comparing the experimental values with the simulation values. It is shown that the surface simulation model can properly predict the surface roughness profile.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.15 no.2
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• pp.9-18
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• 2019

The objective of this study is to investigate the feasibility of simulating the mechanical properties of irradiatied austenitic stainless steels by cold-working. In this study, the tensile properties, cyclic hardening behaviors and fracture toughness of cold-worked TP316L stainless steel were compared with those of austenitic stainless steels irradiated by neutrons. It showed that cold-working can properly simulate the increase in strength and the decrease in ductility and fracture resistance of austenitic stainless steels by neutron irradiation, even though it could not perfectly simulate the microstructures of irradiated austenitic stainless steels. Also, cold-working can appropriately simulate the hardening behaviors of neutron irradiated austenitic stainless steels under monotonic and cyclic loading conditions.

• Journal of Sensor Science and Technology
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• v.13 no.3
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• pp.244-251
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• 2004

In general, the braking system of high speed train has an important role for the safety of the train. To stop safely the train at its pre-decided position, it is necessary to combine properly the various brakes. Korean high speed train (HSR 350x) has adopted a combined electric and mechanic (friction) braking system. Electric brakes are consist of rheostatic brake, regenerative brake and eddy current brake and mechanical brakes are composed of disc brake, wheel disc brake and tread brake. In this paper, the measuring method that can take a measurement of the braking forces for disc brake and wheel disc brake has been suggested and we have verified that this method is valid through on-line test of HSR 350x.

• Journal of the Korean institute of surface engineering
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• v.36 no.5
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• pp.398-405
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• 2003

The stainless steel wire requires good corrosion resistance and mechanical properties, such as drawing ability, combined with a high resistance to corrosion. For increasing drawing ability of stainless steel, Ni coating methods have been used in this study. However, there is no information on the electrochemical corrosion behavior of drawed wires after Ni coating. To investigate corrosion resistance and mechanical property of drawed wire, the characteristics of Ni coated wires have been determined by tensile strength tester, hardness tester, field emission scanning microscope, energy dispersive x-ray analysis and potentiodynamic method in 0.1 M HCl. The drawed stainless steel wires showed the strain-induced martensitic structure, whereas non-drawed stainless steel wire showed annealing twin in the matrix of austenitic structure. The hardness and tensile strength of drawed stainless steel wire were higer than that of non-drawed stainless steel wire. Electrochemical measurements showed that, in the case of drawed stainless steel o ire after Ni coating, the corrosion resistance and pitting potential increased compared with non-coated and drawed stainless steel wire due to decrease in the surface roughness.