• Journal of Mechanical Science and Technology
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• 제20권2호
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• pp.242-250
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• 2006

Detailed structures of the counterflow flames formed for different inlet fluid temperatures and different amount of additives are studied numerically. The detailed chemical reactions are modeled by using the CHEMKIN-II code. The discrete ordinates method and the narrow band based WSGGM with a gray gas regrouping technique (WSGGM-RG) are applied for modeling the radiative transfer through non-homogeneous and non-isothermal combustion gas mixtures generated by the counterflow flames. The results compared with those obtained by using the SNB model show that the WSGGM-RG is very successful in modeling the counterflow flames with non-gray gas mixture. The numerical results also show that the addition of $CO_2\;or\;H_2O$ to the oxidant lowers the peak temperature and the NO concentration in flame. But preheat of fuel or oxidant raises the flame temperature and the NO production rates. $O_2$ enrichment also causes to raise the temperature distribution and the NO production in flame. And it is found that the $O_2$ enrichment and the fuel preheat were the major parameters in affecting the flame width.

• Journal of Welding and Joining
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• 제8권4호
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• pp.58-68
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• 1990

The formation of thermal stresses by plasma spraying is generally considered as adverse. Therefore, the knowledge of stress distribution in the deposited layer during and after plasma spraying will be of special interest. In this study finite difference heat transfer analysis and finite element stress analysis were carried out to predict the change of stress distribution in the plasma coated layer with the variations of preheat temperature, number of scan, particle size, and bond coat. The results of the numerical analysis were as follows: 1) Transient stresses developed in the coated layer were up to the level of yiedl strength at the temperature. 2) The tensile stresses were developed in the deposited layer and the surface of the substrate, but the compressive stresses were developed in the rest of the substrate. 3) Transient and residual stresses were significantly affected by the preheat temperature. 4) The variations of temperature of powder particle and number of torch scan changed tensile stress distribution, but made no difference on the magnitude of the stresses. 5) Bond coated layer reduced the stree level of deposited layer.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.79-84
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• 2004

This paper report our preliminary results of characterizing the jet structures of kerosene injection into quiescent atmosphere and a Mach 2.5 crossflow at various preheat temperature. A heating system has been designed and tested that can prepare heated kerosene of 0.8 kg up to 670 K at a pressure of 5.5 ㎫. Temperature measurement near the injector shows that the temperature of pressurized kerosene can be kept constant during the experimental duration. Comparison of kerosene jet structures in the preheat temperature range of 290-550 K demonstrates that with injection pressure of 4 ㎫ the jet plume turns into vapor phase completely at injection temperature of 550 K, while keeping the penetration depth essentially unchanged. The results suggest that the injection of vaporized fuel would improve the performance of a liquid hydrocarbon-fueled supersonic combustor because the evaporation process is now omitted.

• Journal of Welding and Joining
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• 제16권5호
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• pp.67-75
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• 1998

This study aimed at he experimental and finite element analytic investigation of the effect of preheating on he residual stress of weldment. In this study, an autogenous arc welding was used on type 304 stainless steel and MARC as F.E.M. common code was utilized in analysis The analyses include transient and moving heat source and thermal properties as function of temperature. During welding, the thermal cycles of four locations in the weldment were recorded to investigate of the behavior of thermal stress and residual stress. The experimental and analytic results had good coincidence and show that there are two factors influencing the formation of welding residual stress in preheat process. One is the elevation of welding equilibrium temperature and the other is the increase of amount of heat input. The former decrease welding residual stress and the latter increase welding residual stress. Therefore, the cumulative effects result in the welding residual stress not being improved significantly with preheating in 304 stainless steel.

• 대한기계학회논문집B
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• 제27권9호
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• pp.1201-1208
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• 2003

The thickness of flame and preheat zone from burning velocity which was computed by using Premix code of Chemkin program for methane-air mixture. Also the thickness was evaluated from temperature profile which is also obtained from Premix code for the equivalence ratio of 0.5 to 1.6. The computations were carried out for the laminar flame thickness and burning velocity under the unburned gas temperature 0.5bat-30bar and temperature of 300K-700K at ${\Phi}=l.0$. Comparison of the results showed no difference between these two methods. The flame thickness was decreased by increasing the pressure and temperature, but, the affect of pressure is more significant than the effect of temperature on the flame thickness. The thickness of preheat zone was about 66.5% of the flame thickness, and flame thickness and burning velocity were also predicted by using empirical equation.

• 한국에너지공학회:학술대회논문집
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• 한국에너지공학회 2000년도 춘계 학술발표회 논문집
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• pp.57-62
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• 2000

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 1995년도 특별강연 및 추계학술발표 개요집
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• pp.208-211
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• 1995

Five cast gamma titanium aluminides, Ti-45~48%Al-2%Nb-2%Cr (nominal composition in at. %), were laser welded and their weld cracking susceptibilities were evaluated. Laser power, traversing rate and preheat temperature were systematically varied to generate a series of welds exhibiting a wide range of cooling rate ($100^{\circ}C/s-10,000^{\circ}C/s$). As Al content increased and the weld cooling rate decreased, solidification cracking susceptibility increased while solid-state cracking susceptibility decreased. Through laser beam energy input control and preheat, it was determined possible to produce high quality laser welds.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2005년도 춘계학술발표대회 개요집
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• pp.180-181
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• 2005

• Computers and Concrete
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• 제13권3호
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• pp.325-342
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• 2014

The use of lightweight aggregate (LWA) instead of ordinary aggregate may make lightweight aggregate concrete, which possesses many advantages such as lightweight, lower thermal conductivity, and better fire and seismic resistance. Recently the developments of LWA have been focused on using industrial wastes as raw materials to reduce the use of limited natural resources. In view of this, the intent of this study was to apply Taguchi optimization technique in determining process condition for producing synthetic LWA by incorporating waste thin film transition liquid crystal displays (TFT-LCD) glass powder with reservoir sediments. In the study the waste TFT-LCD glass cullet was used as an additive. It was incorporated with reservoir sediments to produce LWA. Taguchi method with an orthogonal array L16(45) and five controllable 4-level factors (i.e., cullet content, preheat temperature, preheat time, sintering temperature, and sintering time) was adopted. Then, in order to optimize the selected parameters, the analysis of variance method was used to explore the effects of the experimental factors on the performances (particle density, water absorption, bloating ratio, and loss of ignition) of the produced LWA. The results showed that it is possible to produce high performance LWA by incorporating waste TFT-LCD glass cullet with reservoir sediments. Moreover, Taguchi method is a promising approach for optimizing process condition of synthetic LWA using recycled glass cullet and reservoir sediments and it significantly reduces the number of tests.

• 대한기계학회논문집A
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• 제25권3호
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• pp.381-389
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• 2001

The objective of this paper is to evaluate the fracture resistance characteristics of SA508 Cl.1a to SA508 Cl.3 welds manufactured for the reactor coolant loop piping system of nuclear power plants. The effect of the crack plane orientation to the welding process orientation and the preheat temperature on the fracture resistance characteristics were discussed. Results of the fracture resistance test showed that the effect of the crack plane orientation to the welding process orientation of the fracture toughness is significant, while that of preheat temperature on the fracture toughness is negligible. The micro Vickers hardness test, the metallographic observation and the fractography analysis were conducted to analyse the crack jump phenomenon on the L-R crack plane orientation in the multi-pass welding zone. As these results, it is shown that the crack jump phenomenon was produced because of the inhomogeneity between welding beads and the crack plane orientation must be considered for the safety of the welding zone in the piping system.