• Proceedings of the KWS Conference
• /
• 2003.11a
• /
• pp.36-38
• /
• 2003

In order to understand the basic knowledge on the model of heat source in hybrid welding, authors have conducted finite element analysis to calculate heat distribution using three heat source models of non-split type and split type(Volume, Volume-Volume, Volume-Surface). From the research result, we can confirm that Volume-Volume heat source of split type is suitable for the analysis of heat distribution.

• Proceedings of the KWS Conference
• /
• 2000.10a
• /
• pp.201-203
• /
• 2000

In this study, effect of welding parameters on the defect density in the weldments produced by high frequency electric resistance welding process. The defect density measured by X-ray radiography showed a W-type curve as a function of heat input rate. The mechanisms of the such behavior were discussed based on the chemical compositions of the oxides formed at the weldments.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2003.10a
• /
• pp.117-121
• /
• 2003

In order to investigate the performance characters of the ramjet propulsion, at the first step, in this paper Ideal Brayton cycle is adopted. In the Ideal Ramjet cycle some of the Parameters are independent of the heat input, for example thermal efficiency but in the Ideal Brayton cycle, Mach number and the entry temperature of the combustion chamber are important variables with the heat input.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2012.05a
• /
• pp.369-370
• /
• 2012

• 한국연소학회:학술대회논문집
• /
• 2006.10a
• /
• pp.187-195
• /
• 2006

In this work, we introduce a newly constructed arc-jet device of 150 kW input power. The design of this device is a Huels type with a narrow downstream electrode. General features of this device are first described. From the measured values of electrical power input, heat discharged into cooling water, gas flow rate, and settling chamber pressure, average enthalpy was determined using the heat balance and sonic throat methods. Using the settling chamber pressure and average enthalpy values, the flow properties in the nozzle and the heat transfer rate to the stagnation point of a blunt body are calculated accounting for thermochemical nonequilibrium. The envelope of enthalpy, pressure, degree of dissociation, and heat transfer rate are presented. Stagnation temperature is predicted to be between 4630 to 6050 $^{\circ}K$, and the stagnation point heat transfer rate is predicted to be between 175 and 318 W/$cm^{2}$ for a blunt body of 3 mm nose radius. Degree of dissociation in the stagnation region of the blunt body exceeds 30%.

• Journal of Welding and Joining
• /
• v.5 no.1
• /
• pp.23-33
• /
• 1987

Plasma arc cutting is a fusion cutting process in which a gas constricted arc is employed to produce high temperature, high velocity jet at the workpiece. Even though the plasma arc cutting has been wid¬ely used in the industry, very little work has been done on the analysis of the process. In this paper, the kerf width was numerically analyzed by soving the temperature distribution in base metal under consideration of the latent heat effect. In modelling the heat flow problem, the heat intensity of the plasma arc was assumed to have a Gaussion distribution in the transverse direction and expone¬ntially decreasing in the thickness direction. The thermal efficiency and the heat input ratio of the top surface were experimentally deterimned for various thickness and cutting conditions, and used in numerical calculation of the kerf width. The experimental results were in eonsiderabely good agreement with the theoretically predicted kerf width.

• Journal of Mechanical Science and Technology
• /
• v.16 no.9
• /
• pp.1054-1064
• /
• 2002

Numerical prediction of welding-induced residual stresses using the finite element method has been a common practice in the development or refinement of welded product designs. Various researchers have studied several thermal models associated with the welding process. Among these thermal models, ramp heat input and double-ellipsoid moving source have been investigated. These heat-source models predict the temperature fields and history with or without accuracy. However, these models can predict the thermal characteristics of the welding process that influence the formation of the inherent plastic strains, which ultimately determines the final state of residual stresses in the weldment. The magnitude and distribution of residual stresses are compared. Although the two models predict similar magnitude of the longitudinal stress, the double-ellipsoid moving source model predicts wider tensile stress zones than the other one. And, both the ramp heating and moving source models predict the stress results in reasonable agreement with the experimental data.

• Proceedings of the KWS Conference
• /
• 2010.05a
• /
• pp.59-59
• /
• 2010

Friction stir welding has become a viable and important manufacturing alternative or fabrication component, especially in aerospace and automobile applications involving aluminium alloys. In recent years, there is an increasing interest for FSW of dissimilar metals and alloys, particularly systems which are difficult to weld by conventional, thermal (or fusion) welding. In this study we tried to analyse the complex heat distribution occurring in TIG assisted FSW of dissimilar butt joint (STS304 and Al6061). For this, an analytical model for heat generation by FSW based on contact conditions has been developed. The heat input was calculated considering the coefficient of friction and slip factor between each work piece material with the tool material. The thermal model is used to generate the temperature characteristics curve, which successfully predicts the maximum welding temperature in each alloys. The analysis was carried out using the in-house solver.

• Transactions of the Korean hydrogen and new energy society
• /
• v.27 no.1
• /
• pp.42-48
• /
• 2016

This study presents an experiment investigation on natural convection heat transfer of air-cooling Proton exchange membrane fuel cells (PEMFCs) in a enclosure system for unmanned aerial vehicles (UAVs). Considered are replacing fuel cell stack with Aluminum block for heat generating inside a enclosure chamber. The volume ratio of fuel cell stack and chamber for simulation to the actual size of aerial vehicle is 1 to 15. The parameters considered for experimental study are the environmental temperature range from $25^{\circ}C$ to $-60^{\circ}C$ and the block heat input of 10 W, 20 W and 30 W. Effect of the thermal conductivity of the block and power level on heat transfer in the chamber are investigated. Experimental results illustrate the temperature rise at various locations inside the chamber as dependent upon heat input of fuel cell stack and environmental temperature. From the results, dimensionless correlation in natural convection was proposed with Nusselt number and Rayleigh number for designing air-cooling PEMFC powered high altitude long endurance (HALE) UAV.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2005.10a
• /
• pp.224-230
• /
• 2005

In order to realize a three-dimensional shape on CAD, the machining process has been widely used because it offers practical advantages such as precision and versatility. However, the traditional machining process needs a large amount of time in cutting a product and the remained material causes trouble such as inconvenience due to cleaning process. This paper introduces a new rapid manufacturing process called Rapid Heat Ablation process (RHA) using the rotary hot tool to overcome limitations of traditional machining process. The rotary hot tool to satisfy requirements of RHA process is designed and produced. In order to examine relationships between kerfwidth and process parameters such as heat input, speed of tool and speed of revolution, experiments were carried out. In addition, relationship between the kerfwidth and the effective heat input was obtained. Based on the experimental results, double-curved shape was ablated to show the validity of proposed process. In the procedure, the rough cut and fine cut were performed according to the conditions of process parameters without tool change process. The practicality and effectiveness of the proposed process have been verified through ablation of three-dimensional shape.