• 한국정밀공학회지
• /
• 제21권2호
• /
• pp.122-129
• /
• 2004

There is an increasing need for large flat panel display devices. PDP (Plasma Display Panel) is one of the most promising candidates for this need. Thermal shock failure of PDP glass during manufacturing process is a critical issue in PDP industry since it is closely related to the product yield and the production speed. In this study, thermal shock resistance of PDP glass is measured by water quenching test and an analysis scheme is described for estimating transient temperature and stress distributions during thermal shock. Based on the experimental data and the analysis results, a simple procedure for predicting the thermal shock failure of PDP glass is proposed. The fast cooling process for heated glass plates can accelerate the speed of PDP production, but often leads to thermal shock failure of the glass plates. Therefore, a design guideline for preventing the failure is presented from a viewpoint of high speed PDP manufacturing process. This design guideline can be used for PDP process design and thermal -shock failure prevention.

• The Journal of the Acoustical Society of Korea
• /
• 제15권4E호
• /
• pp.72-77
• /
• 1996

A relatively simple theoretical model for predicting the shock thickness is applied to the weak shock propagation through sea water, where the boric acid and the magnesium sulfate are the major relaxation processes. The relaxation effects increases the shock thickness by the factor of 103 compared with the thickness based on the classical absorption only. In seawater with the ambient pressure of 125 atm and 15℃ temperature, the effects of the boric acid are dominant when the peak pressure is less than 0.3 atm and 3 atm. For the shocks of peak pressure greater than 5 atm, the effects of the classical absorption theory is enough to describe the shock thickness. The effects of the ambient pressure and temperature on the shock thickness are also evaluated.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2003년도 제20회 춘계학술대회 논문집
• /
• pp.164-167
• /
• 2003

열충격은 재료가 갑작스런 온도나 압력변화 혹은 급냉 조건하에 있을때 발생하는 물리적 현상이다. 본 논문에서는 레이저 조사를 이용하여 열충격 강도와 열충격 파괴인성을 평가하였다. 시험편의 온도 분포는 타입 K와 C 열전대를 이용하여 측정하였다. 조사된 표면은 SEM을 이용하여 관찰하였다. 파괴에 필요한 임계 레이저 파워가 재료의 열충격 강도와 열충격 파괴인성을 결정짓는 주요한 요소라고 할 수 있다.

• 대한기계학회논문집B
• /
• 제32권11호
• /
• pp.832-840
• /
• 2008

Ablation occurs at irradiance beyond $10^9\;W/cm^2$ with nanosecond and short laser pulses focused onto any materials. Phenomenologically, the surface temperature is instantaneously heated past its vaporization temperature. Before the surface layer is able to vaporize, underlying material will reach its vaporization temperature. Temperature and pressure of the underlying material are raised beyond their critical values, causing the surface to explode. The pressure over the irradiated surface from the recoil of vaporized material can be as high as $10^5\;MPa$. The interaction of high power nanosecond laser with a thin metal in air has been investigated. The nanosecond pulse laser beam in atmosphere generates intensive explosions of the materials. The explosive ejection of materials make the surrounding gas compressed, which form a shock wave that travels at several thousand meters per second. To understand the laser ablation mechanism including the heating and ionization of the metal after lasing, the temporal evolution of shock waves is captured on an ICCD camera through laser flash shadowgraphy. The expansion of shock wave in atmosphere was found to agree with the Sedov's self-similar spherical blast wave solution.

• 천문학회보
• /
• 제44권2호
• /
• pp.55.2-55.2
• /
• 2019

The firehose instability is driven by a pressure anisotropy in a magnetized plasma when the temperature along the magnetic field is higher than the perpendicular temperature. Such condition occurs commonly in astrophysical and space environments, for instance, when there are beams aligned with the background magnetic field. Recently, it was argued that, in weak quasi-perpendicular shocks in the high-β intracluster medium (ICM), shock-reflected electrons propagating upstream cause the temperature anisotropy. This electron temperature anisotropy can trigger the electron firehose instability (EFI), which excites oblique waves in the shock foot. Scattering of electrons by these waves enables multiple cycles of shock drift acceleration (SDA) in the preshock region, leading to the electron injection to diffusive shock acceleration (DSA). In the study, the kinetic properties of the EFI are examined by the linear stability analysis based on the kinetic Vlasov-Maxwell theory and then further investigated by 2D Particle-in-Cell (PIC) simulations, especially focusing on those in high-β (β~100) plasmas. We then discuss the basic properties of the firehose instability, and the implication of our work on electron acceleration in ICM shock.

• Fisheries and Aquatic Sciences
• /
• 제4권3호
• /
• pp.112-119
• /
• 2001

Aim of this research is to investigate the effect of temperature shocks on the physiological responses of cultured olive flounder (Paralichthys olivaceus) and black rockfish (Sebastes schlegeli). Olive flounder and black rockfish were suffered with high and low temperature shocks for 4 and 8h, respectively, in laboratory conditions and then the changes in glucose, lactate, total protein, uric acid, and triglycerides-glycerol in blood plasma were analyzed. We observed that lactate and uric acid increased for up to 4h and then decreased for up to 8h by the high and low temperature shocks, and total protein decreased for up to 4h and then recovered for up to 8h by the high temperature shock in both fishes. Glucose by the high and low temperature shocks and triglycerides-glycerol by the low temperature shock increased for up to 4h, and then decreased in olive flounder, but increased for up to 8h in black rockfish. From the result, we speculated that the two fishes have an interspecific variation in the regulatory systems of glucose and triglycerides-glycero1. Glucose would play important role as an energy source during the temperature shocks and for an intermediate substance for low temperature tolerance, and glycerol of triglycerides-glycerol would play an important role for low temperature tolerance. In olive flounder, the turnover of chemical change by temperature shock took more than 4h, all chemicals returned almost to the initial level for up to 8h, but fish death followed only in 8h with the high temperature shocked group within two days. Therefore, we suggested that fish would be damaged severely by the longer time exposure of high temperature and mortality would occur after a certain time later than the shocked time as a post-effect.

• International Journal of Aeronautical and Space Sciences
• /
• 제10권1호
• /
• pp.1-14
• /
• 2009

When the stagnation temperature increases, the specific heat does not remain constant and start to vary with this temperature. The gas is perfect, it's state equation remains always valid, except, it was called by gas calorically imperfect or gas at high temperatures. The purpose of this work is to develop a mathematical model for a normal shock wave normal at high temperature when the stagnation temperature is taken into account, less than the dissociation of the molecules as a generalisation model of perfect for constant heat specific. A study on the error given by the perfect gas model compared to our model is presented in order to find a limit of application of the perfect gas model. The application is for air.

• 한국초전도저온공학회:학술대회논문집
• /
• 한국초전도저온공학회 2002년도 학술대회 논문집
• /
• pp.202-204
• /
• 2002

The supurfluid shock tube facility has been developed as a versatile tool for experimental research of low-temperature thermo-fluid dynamic phenomena The shock tube is designed to operate with the He II filled test section which is immersed in superfluid helium. The thermo-dynamic phenomena occurred in this facility are measured using pressure transducers, superconductive temperature sensor and visualization method. In this paper, the design and performance of the superfluid shock tube facility and the superconductive temperature sensor is presented.

• The Korean Journal of Ceramics
• /
• 제3권3호
• /
• pp.195-198
• /
• 1997

Post-firing process of electronic ceramic, such as electroding and encapsultion with resin, often causes damage by thermal shock. The thermal shock behavior of $BaTiO_3$ ceramics was investigated by the down-quench test, where the relative strength retained is determined after the sample is quenched from an elevated temperature into a fixed temperature bath. The critical temperature drop, $\DeltaTc$, was evaluated for three kinds of sintered $BaTiO_3$ ceramics, which were formed by extrustioin, uniaxial pressing using granules, and uniaxial pressing using powders. A drastic loss in strength caused by microcracking was observed for the specimens quenched with $\DeltaT\geq150^{\circ}C$. This concentp can be adopted as a method of the quality control by monitoring the sudden drop of the strength of capacitor products after each exposure to heat.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2011년도 제37회 추계학술대회논문집
• /
• pp.178-181
• /
• 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.