• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.3
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• pp.235-243
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• 2000

A theoretical model for laminar filmwise condensation along an isothermal vertical wall at constant pressure has been formulated on the basis of conservation laws and other fundamental physical principles. The model was applied to the prediction of the influences of variable thermophysical properties of liquid and vapor layers in the filmwise condensation of superheated vapor of Rl2, R134a, R142b and R152a. The dimensionless velocity component method was employed in the transformation of the governing equations and their boundary conditions, and the polynomial method was used for treating variable thermophysical properties of liquid and vapor. Physical quantities, such as the dimensionless thickness of the liquid layer, local heat transfer rate and mean heat transfer coefficient, were investigated for different values of the superheated temperature of the stagnant vapor far from the wall. It was found that the value of mean heat transfer coefficient of R134a was higher than other refrigerants for the change of the superheated temperature.

• Computers and Concrete
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• v.30 no.1
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• pp.1-8
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• 2022

The basic purpose of the current study is to compute the numerical analysis of heat source/sink for Darcy-Forchheimer three dimensional nanofluid flow with gyrotactic microorganism by rotatable disk via porous media under the slip conditions. Due to nanoparticles, random and thermophoretic motion phenomenon occurs. The governing mathematical model is handled numerically by shooting method. Additionally, the characteristics of velocities, mass, heat, motile microorganisms and associated parameters are thoroughly analyzed via plots and tables. Different physical parameters like Forchheimer number, slip parameters like velocity, porosity parameter, Prandtl number, Brownian number, thermophoresis parameter, heat sink/source parameter, bioconvected Rayleigh number, buoyancy parameteron dimensionless velocities, temperature. Approximate values of Sherwood microorganism are analyzed.

• Steel and Composite Structures
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• v.43 no.2
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• pp.221-228
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• 2022

Two-dimensional stagnation point slip flow of a Casson fluid impinging normally on a flat linearly shrinking surface is considered. The modeled PDEs are changed into nonlinear ODEs through appropriate nonlinear transformations.The flow is assumed to be steady and incompressible, with external magnetic field acting on it. Similarity transformation is utilized to investigate the behavior of many parameters for heat and velocity distributions using truncation approach.The influence of buoyancy parameter, slip parameter, shrinking parameter, Casson fluid parameter on the heat profile. The effect of the magnetic parameter on the streamwise velocity profile is also investigated.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.16 no.5
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• pp.504-515
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• 1987

This study conducts an analysis for the heat diffusion of an annular fin considering con-vection phenomena at the fin edge as well as along the fin perimeter. When the temperature of the fin base is given with an increasing exponential function, the exact series solutions of tem-perature distribution are obtained by laplace transformation in terms of dimensionless para-meters. From these solutions heat flux and fin efficiency can be obtained. These exact solu-tions converge rapidly for large values of dimensionless time, but slowly for small ones. To avoid this convergence difficulty, approximate solutions of the temperature distribution and heat flux for small values of dimensionless time are also presented. Substituting the variations of dimensionless parameters into the these exact solutions, the characteristics of these response are investigated.

• Korean Journal of Microbiology
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• v.30 no.3
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• pp.218-224
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• 1992

Recombinant plasmid shuttle vectors were constructed for genetic studies on the oxidation of carbon monoxide by carboxydobacteria. Two vectors. pYK322 (7.2 kb, Ap'. Tc') and pYK 324 (7.2 kb, Ap', Tc'), were constructed using pBR322 and pYK100. a small plasmid in Pseudomonas carbo,xydovorans. Four plasmids. pYK2IO (5.2 kb. Cm'), pYK220 (5.2 kb, Cmr), pYK230 (5.2 kb, Cm'), and pYK232 (5.2 kb. Cm'), were constructed using pACYC184 and pYK100. Transformation of several carboxydobacteria with pYK322 and pYK220 was round to be efficient when the cells were transformed by the methoti of Bagdasarian and Timmis (Curr. Top. Microbiol. Immunol. 96:47-67. 1982) with several modifications; cells growing on 0.2% succinate were harvested at the mid-exponential phase. 10 mM RbCl in transformation solution was substituted with 100 mM KCI. cclls in transformation solution were incubated for 12 h at 4'C before addition of DNA and heat shock was carried out for 3 min at 45$^{\circ}$C. Plasmid vectors used for transformation, however. were not detected from antibiotics-resistant transformants, suggesting that the vectors may be integrated into the chromosomal DNA.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.3
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• pp.497-504
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• 2002

The purpose of this study is to analyze thermal cycles and to investigate microstructures of heat affected zones for a low alloy carbon steel pipe under a multipass weld. The commercial finite element code SYSWELD is used to compute thermal cycles during multipass weld. The numerical results such as thermal cycles and size of heat affected zone are compared with those of the experiment and the two results show a good agreement. In addition, the microstructure and hardness are investigated from the weldment in detail. The weakest location is founded at intercritical region near the base metal.

• Journal of Powder Materials
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• v.13 no.5 s.58
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• pp.360-365
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• 2006

The phase stability of tetragonal phase in Y-TZP was investigated in terms of the distribution of grain sizes and heat-treating atmosphere. Y-TZP with various grain sizes were prepared using duration time at $1600^{\circ}C$ as experimental parameter. Accumulated grain size distributions were built from the SEM micrographs and the amount of tetragonal phase were measured using XRD. Both results were compared to determine the critical grain size before and after heat-treatment in vacuum. The critical grain size drastically decreased compared with the small increase of average grain size due to the autocatalytic effect which critically affects the tetragonal to monoclinic phase transformation. After heat-treatment in reductive atmosphere critical grain size relatively increased due to the stabilization of tetragonal phase. The formation of oxygen vacancies during heat-treatment was ascribed to the increase of stability.

• Korea-Australia Rheology Journal
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• v.17 no.2
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• pp.47-62
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• 2005

The present study deals with a mathematical model describing the dynamic response of heat and mass transfer in blood flow through bifurcated arteries under stenotic condition. The geometry of the bifurcated arterial segment possessing constrictions in both the parent and the daughter arterial lumen frequently appearing in the diseased arteries causing malfunction of the cardiovascular system, is formulated mathematically with the introduction of the suitable curvatures at the lateral junction and the flow divider. The blood flowing through the artery is treated to be Newtonian. The nonlinear unsteady flow phenomena is governed by the Navier-Stokes equations while those of heat and mass transfer are controlled by the heat conduction and the convection-diffusion equations respectively. All these equations together with the appropriate boundary conditions describing the present biomechanical problem following the radial coordinate transformation are solved numerically by adopting finite difference technique. The respective profiles of the flow field, the temperature and the concentration and their distributions as well are obtained. The influences of the stenosis, the arterial wall motion and the unsteady behaviour of the system in terms of the heat and mass transfer on the blood stream in the entire arterial segment are high­lighted through several plots presented at the end of the paper in order to illustrate the applicability of the present model under study.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.30 no.10 s.253
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• pp.1284-1292
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• 2006

Heat treatment is a controlled heating and cooling process to improve the physical and/or mechanical properties of metal products without changing their shapes. Today finite element method is widely used to simulate lots of manufacturing processes including heat treatment and surface hardening processes, which aims to reduce the number of time- and cost-consuming experimental tryouts. In this study we tried, using this method, to simulate the full carburizing process that consists of carburizing, diffusing and quenching, and to predict the distribution of carbon contents, phase fraction and hardness, thermal deformation and other mechanical characteristics as the results. In the finite element analysis deformation, heat transfer, phase transformation and diffusion effects are taken into consideration. The carburizing process of a lock gear, a part of the car seat recliner, that is manufactured by the fine blanking process is adopted as the analysis model. The numerical results are discussed and partly compared with experimental data. And a combination of process parameters that is expected to give the highest surface hardness is proposed on the basis of this discussion.

• Journal of Powder Materials
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• v.12 no.1
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• pp.36-42
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• 2005

Four different mechanical alloying(MA) processes were employed to fabricate very fine intermetallic compound $Al_3Zr$ particles dispersed Al composite materials(MMC) with Al-4at.%Zr composition. Phase transformations including phase stability during MA and heat treatment processes were investigated. Part of Zr atoms were dissolved into Al matrix and part of them reacted with hydrogen produced by decomposition of PCA(methanol) to form hydride $ZrH_2$ during first MA process. These $ZrH_2$ hydrides disappeared when alloy powders were heat treated at $500^{\circC}$. Stable $Al_3Zr$ dispersoids with $DO_23$ structure were formed by heat treating the mechanically alloyed powders at $400^{\circC}$. On the other hand, metastable $Al_3Zr$dispersoids with $L1_2$ structure were formed during first MA of powers with Al-25at.%Zr composition. These metastable $Al_3Zr$ dispersoids transformed to stable $Al_3Zr$ with $DO_23$ structure when heat treated above $450^{\circC}$.