• 대한기계학회논문집B
• /
• 제32권12호
• /
• pp.970-976
• /
• 2008

Characteristics of methane turbulent non-premixed flame have been studied experimentally in coflow jets with initial temperature variation. The results showed that the premixed flame model and the large-scale mixing model for turbulent flame stabilization were effective for methane fuel considered initial temperature variation. Especially, the premixed flame model has been improved by considering nitrogen dilution for the liftoff height of turbulent lifted flame. In estimating blowout velocity and the liftoff height at blowout with the premixed flame model and the large-scale mixing model, the two turbulent models were excellently correlated by considering the effect of physical properties and buoyancy for the initial temperature variation.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 1999년도 춘계 학술대회논문집
• /
• pp.192-198
• /
• 1999

The present study proposes modified temperature-dependent non-Newtonian viscosity model and investigates flow characters and heat transfer enhancement of the viscoelastic non-Newtonian fluid in a 2:1 rectangular duct. The proposed modified temperature dependent viscosity model has non-zero value near the high temperature and high shear rate region while on the existing viscosity models have zero value. Two versions of thermal boundary conditions involving difference combination of heated walls and adiabatic walls are analyzed in this study. The combined effect of temperature dependent viscosity, buoyancy, and secondary flow caused by second normal stress difference are ail considered. The Reiner-Rivlin model is adopted as a viscoelastic fluid model to simulate the secondary flow caused by second normal stress difference. Calculated Nusselt numbers by the modified temperature-dependent viscosity model gives under prediction than the existing temperature-dependent viscosity model in the regions of thermally developed with same secondary normal stress difference coefficients with experimental results in the regions of thermally developed. The heat transfer enhancement of the viscoelastic fluid in a 2:1 rectangular duct is highly dependent on the secondary flow caused by the magnitude of second normal stress difference.

• 한국연소학회:학술대회논문집
• /
• 한국연소학회 2004년도 제28회 KOSCO SYMPOSIUM 논문집
• /
• pp.158-164
• /
• 2004

In the present work, the numerical model was refined to predict the thermal analysis of energy storage in a fixed beds during charging mode. The governing energy equations of both fluid and the solid particles along with their initial and boundary conditions are derived using a two-phase, one dimensional model. The refined model is carried out by taking into account change of (air density , air specific heat) with air temperature and also by taking into considerations heat losses from bed to surrounding. Finite difference method was used to obtain solution of two governing energy equations of both fluid and solid particles through a computer program especially constructed for this purpose. The temperature field for the air and the solid are obtained, also energy stored inside the bed is computed. A comparison between refined model and non refined model is done. Finally using refined model the effect of bed material (Glass, Fine clay ,and aluminum ), and air flow rate per unit area Ga (0.3, 0.4, and 0.5 kg/$m^2$-s) on energy storage characteristics was studied.

• Journal of applied mathematics & informatics
• /
• 제14권1_2호
• /
• pp.193-212
• /
• 2004

A new model of generalized thermoelasticity equations for isotropic media with temperature-dependent mechanical properties is established. The modulus of elasticity is taken as a linear function of reference temperature. The present model is described both generalizations, Lord Shulman (L-S) theory with one relaxation time and Green-Lindsay (G-L) with two relaxation times, as well as the coupled theory, instantaneously. The method of the matrix exponential, which constitutes the basis of the state space approach of modern control theory, applied to two-dimensional equations. Laplace and Fourier integral transforms are used. The resulting formulation is applied to a problem of a thick plate subject to heating on parts of the upper and lower surfaces of the plate that varies exponentially with time. Numerical results are given and illustrated graphically for the problem considered. A comparison was made with the results obtained in case of temperature-independent modulus of elasticity in each theory.

• 한국레이저가공학회지
• /
• 제11권4호
• /
• pp.13-20
• /
• 2008

The damage threshold measurement of gold films is carried out with ultrashort-pulse laser. An enhanced two temperature model is developed to encounter the limitation of linear modeling during ultrashort pulse laser ablation. In which the electron heat capacity is calculated using a quantum mechanical approach based on a Fermi-Dirac distribution, temperature-dependent electron thermal conductivity valid beyond the Fermi temperature is adopted, and reflectivity and absorption coefficient are estimated by applying a temperature-dependent electron relaxation time. The predicted damage threshold using the proposed enhanced modelclosely agreed with experimental results, demonstrating the importance of considering transient thermal and optical properties in the modeling of ultrashort pulse laser ablation.

• 한국우주과학회:학술대회논문집(한국우주과학회보)
• /
• 한국우주과학회 2008년도 한국우주과학회보 제17권2호
• /
• pp.24.2-24.2
• /
• 2008

We have examined the relative contributions of representative space weather proxies (geomagnetic aa index) to global warming (Global temperature anomaly) and compared them with that of green house effect characterized CO2 content from 1868 to 2005. For this we used Hadcrut3 temperature anomaly (Ta) data, aa index taken at two anti-podal subauroral stations (Canberra Australia and hartland England), and the CO2 data come from historical ice core records. From the comparison between Ta and aa index, we found several interesting results: (1) the linear correlation coefficient between two parameters increases until 1990 and then decreases rapidly, and (2) the scattered plots between two parameters shows different patterns before and after 1990. A partial correlation of Ta and two quantities (aa, CO2) also shows that the geomagnetic effect (aa index) is dominant until about 1990 and the CO2 effect becomes much more important after then. These results imply that the green house effect become very important since at least 1990. For a further analysis, we simply assume that Ta (total) = Ta (aa) + Ta (CO2) and made a linear regression between Ta and aa index from 1868 to 1990. A linear model is then made from the linear regression between energy consumption (a proxy of CO2 effect) and Ta (total) - Ta (aa) since 1990. This linear model makes it possible to predict the temperature anomaly in 2030, about 1 degree higher than the present temperature, which is much larger than in the previous century.

• 한국추진공학회지
• /
• 제15권4호
• /
• pp.65-72
• /
• 2011

수직온도구배를 가진 유체 내의 기포유동을 수치해석적 방법으로 연구하였다. 본 연구의 목적은 Eulerian-Lagrangian 방정식모델을 적용하여 온도가 수직으로 층상화된 기-액 2상류(two phase flow)의 대류유동을 정확하게 해석할 수 있는 프로그램의 개발과 온도가 층상화된 유체의 기포에 의한 온도혼합과정의 가시화 그리고 유체역학적 특성을 이해하는 것이다. 또한, 기포반경, 보이드율, 그리고 유량이 기포에 의해 야기된 대류유동에 미치는 영향을 함께 검토하였다.

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 2004년도 ICCAS
• /
• pp.1201-1204
• /
• 2004

This paper suggests a DCS (Distributed Control System) model for steam temperature system of the thermal power plant. The model calculated within sectional range is linear. In order to calculate mathematical models, the system is partitioned into two or three sectors according to its thermal conditions, that is, saturated water/steam and superheating state. It is divided into three sections; water supply, steam generation and steam heating loop. The steam heating loop is called 'superheater' or steam temperature system. Water spray supply is the control input. A first order linear model is extracted. For linear approach, sectional linearization is achieved. Modeling methodology is a decomposition-synthetic technique. Superheater is composed of several tube-blocks. For this block, linear input-output model is to be calculated. Each tiny model has its transfer function. By expanding these block models to total system, synthetic DCS linear models are derived. Control instrument include/exclude models are also considered. The resultant models include thermal combustion conditions, and applicable to practical plant engineering field.

• International Journal of Air-Conditioning and Refrigeration
• /
• 제10권1호
• /
• pp.1-9
• /
• 2002

Effects of temperature coefficients fur dielectric constants on transient reflectances and thermal responses have been investigated for a metal(gold) thin-film during ultrashort pulse laser heating. Heating processes are simulated using the conventional conduction model(parabolic one-step, POS), the parabolic tow-step model(PTS), the hyperbolic two-step model(HTS). Results fro the HTS model are very similar to those from the PTS model, since the laser heating time in this study is considerably greater than the electron relaxation time. PTS and HTS models, however, result in completely different temperature profiles from those obtained by the POS model due to slow electron-lattice interactions compared to laser pulse duration. Transient reflectances are directly estimated from the linear relationship between electron temperature and complex dielectric constants, while conventional approaches assume that the change in reflectances is proportional to that in temperatuer. Reflectances at the front surface vary considerably for various dielectric constants, while those at the rear surface remain unchanged relatively.

• Earthquakes and Structures
• /
• 제8권6호
• /
• pp.1299-1323
• /
• 2015

A model for reflection and refraction of magneto-thermoelastic SV-waves at the interface of two transversely isotropic and homogeneous solid half spaces under initial stress by applying classical dynamical theory of thermoelasticity is purposed. The reflection and refraction coefficients of SV-waves are obtained with ideal boundary conditions for SV-wave incident on the solid-solid interface. The effects of magnetic field, temperature and initial stress on the amplitude ratios after numerical computations are shown graphically with MATLAB software for the particular model.