• Journal of the Korean Society for Heat Treatment
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• v.36 no.5
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• pp.277-284
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• 2023

Hardness and damping characteristics of fine discontinuous precipitates (DPs) microstructure generated by low temperature long term isothermal aging were investigated in comparison with those of T6 heat-treated microstructure composed of DPs and continuous precipitates (CPs) in Mg-9%Al alloy. In this study, T6 and fine DPs microstructures were obtained by isothermal aging at 453 K for 24 h and at 413 K for 336 h, respectively, after solution treatment at 693 K for 24 h. The DPs microstructure exhibited higher hardness than the T6 microstructure, which is related to the lower (α + β) interlamellar spacing of the DPs. The DPs microstructure possessed better damping capacity than the T6 microstructure in the strain-amplitude independent region, whereas in the strain-amplitude dependent region, the reverse behavior was observed. The damping tendencies depending on strain-amplitude were discussed based on the microstructural features of the T6 and DPs microstructures.

• Applied Chemistry for Engineering
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• v.23 no.5
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• pp.456-461
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• 2012

To verify the utilization of biomass as energy, the combustion characteristic has been studied by an experimental combustion furnace under an isothermal and non-isothermal combustion. The wood pellet, rice straw and rice husk were used as biomass samples in this work. The characteristics of emission gases, dusts and residues from biomass combustion have been analyzed and compared with those of reuse derived fuel (RDF). From isothermal combustion experiments, it was found that the incomplete combustion of rice straw was greater that that of rice husk, wood pellet and RDF. This is due to the fact that the combustion reaction rate of the rice straw was faster than that of other samples, and the oxygen concentration in rice straw combustion was rapidly decreasing. It was also found that $NO_{X}$ concentration of emission gas from wood pellet combustion was the lowest. From non-isothermal combustion experiments, it was found that all samples were burned before $900^{\circ}C$. Also, the temperature range of $NO_{X}$ emission was similar to that of CO emission, on the other hand, $SO_{2}$ was emitted at a higher temperature than that of CO emission.

• Journal of Adhesion and Interface
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• v.14 no.1
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• pp.21-27
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• 2013

Cellulose-based rayon fibers or fabrics can be thermally decomposed very fast within a narrow temperature window during stabilization process. Therefore the stabilization stage is critically important for producing rayon-based carbon fibers. Consequently, in the present study the effects of isothermal stabilization and ultrasonic cleaning on the weight loss, chemical composition, microstructure, and fabric texture of cellulose-based rayon fabrics were explored. The temperature of the isothermal stabilization process performed in the range of $200{\sim}240^{\circ}C$ influenced the processing time, carbon and oxygen contents, cellulose structural change, and fabric texture. The ultrasonic cleaning, which was conducted prior to the stabilization process, played a role in shortening the stabilization time, increasing the carbon contents, decreasing the oxygen contents, and changing the XRD pattern. Also, it was considered that the ultrasonic cleaning contributed to retarding the weight loss, to reducing the thermal shrinkage, and further to reducing the fast physical change of rayon fabrics.

• Korean Journal of Materials Research
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• v.18 no.1
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• pp.38-44
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• 2008

The micro-structural changes, strength characteristics, and micro-fractural behaviors at the joint interface between a Sn-4.0wt%Ag-0.5wt%Cu solder ball and UBM treated by isothermal aging are reported. From the reflow process for the joint interface, a small amount of intermetallic compound was formed. With an increase in the isothermal aging time, the type and amount of the intermetallic compound changed. The interface without an isothermal treatment showed a ductile fracture. However, with an increase in the aging time, a brittle fracture occurred on the interface due mainly to the increase in the size of the intermetallic compounds and voids. As a result, a drastic degradation in the shear strength was observed. From a microshear test by a scanning electron microscope, the generation of micro-cracks was initiated from the voids at the joint interface. They propagated along the same interface, resulting in coalescence with neighboring cracks into larger cracks. With an increase in the aging time, the generation of the micro-structural cracks was enhanced and the degree of propagation also accelerated.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.2
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• pp.224-234
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• 1997

It was demonstrated earlier that for laminar, isothermal flow of the lubricant in long journal bearings, inertia has negligible effect on the load carrying capacity and influences only the stability characteristics of the bearing. The question in the present paper is: 'will these conclusions of the isothermal theory remain valid in the presence of significant dissipation, or will lubricant inertia and dissipation interact non-linearly to bring about qualitative changes in bearing performance\ulcorner' The results obtained here assert that the effect of lubricant inertia on load carrying capacity remains negligible, irrespective of the rate of dissipation. The stability of the bearing is, however, affected by lubricant inertia. These results, although obtained here for long bearings with Sommerfeld and Gumbel boundary conditions, are believed to be applicable to practical bearing operations and affirm that bearing load may be calculated from classical, i. e., non-inertial theory.

• Journal of the Korean institute of surface engineering
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• v.43 no.6
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• pp.309-314
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• 2010

The numerical study for the effect of various factors that affect the temperature distribution of the process glass installed above the large rectangular heater plate was carried out. For the calculation, heat flux, distance between heat source and process glass plate, effect of vacuum condition and convection in a chamber were considered as important factors. The results showed that the temperature gradient on the glass was increased at the natural convection because of the buoyancy force increases due to the heated air. Also, the more heat flux and distance between the heater plate and glass increases, the more increasing the temperature gradient was. In the case of isothermal heating wall, the temperature variation was smaller than the uniform heat flux condition.

• International Journal of Air-Conditioning and Refrigeration
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• v.7
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• pp.91-100
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• 1999

This paper investigates ventilation characteristics of an environmental chamber simulating an under-floor air conditioning system for isothermal and cooling supply air conditions. The tracer gas sulfur-hexafluoride (SF$F_6$) was injected into a supply duct using step-up and step-down methods. Local mean and room mean ages were calculated from the concentrations measured at internal points and at the exhaust duct. The air change efficiency of the chamber has been found to be greater in cooling conditions than in isothermal conditions. Also the room air change efficiency is not significantly affected but slightly improved by the presence of a supply diffuser.

• JSTS:Journal of Semiconductor Technology and Science
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• v.15 no.2
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• pp.243-248
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• 2015

We prepared semi-insulating CdTe for radiation detectors by isothermal annealing of single crystals grown by Bridgeman technique in a sealed quartz container filled with Sn vapor. The resistivity of CdTe:Sn samples thus obtained was of order of $10^{10}Ohm{\cdot}cm$ at room temperature with electrons lifetime of $2{\times}10^{-8}$ s, which is appropriate for the applications desired. Analysis of electric transport characteristics depending on temperature, sample thickness and voltage applied revealed the presence of traps with concentration of about $(4-5){\times}10^{12}cm^{-3}$ with the corresponding energy level at 0.8 - 0.9 eV counted from the bottom of conduction band. The conductivity was determined by electron injection from electrodes in space charge limited current mode.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.1
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• pp.161-169
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• 1989

A stability problem on wave instability of natural convection flow along isothermal vertical cylindrical surfaces has been formulated, accounting for the non-parallelism of the basic flow and thermal fields. Then the problem is solved numerically under the simplifying assumption of the parallelism of the basic flow quantities. It is shown that the flow corresponding to the same characteristic boundary layer thickness becomes more stable as the value of the curvature parameter increases. The stability characteristics for Pr=0.7 appear to be more sensitive to the curvature parameter than those for Pr=7.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1412-1417
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• 2004

Concentric annular heat pipes having the length of 200 mm and the outside diameter of 25.4 mm were manufactured and tested. The inside diameters of the heat pipes were 11.3 mm and 8.1 mm and the material of the container was copper. To compare with thermal performances between the concentric annular heat pipe and a copper block with same shape, start-up and isothermal performance were tested. In the result, the start-up of the concentric annular heat pipe was influenced by the start-up of their heat source. The concentric annular heat pipe reached at steady state faster then the same shape of copper block. The maximum wall temperature difference of the concentric annular heat pipe on whole surface was $4.6^{\circ}C$, and the case of the copper block was $16.5^{\circ}C$.