• Journal of Sensor Science and Technology
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• v.32 no.1
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• pp.39-43
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• 2023

Microscale thermophysical property measurements of liquids have been developed considering the increasing interest in the thermal management of cooling systems and energy storage/transportation systems. To accurately predict the heat transfer performance, information on the thermal conductivity, heat capacity, and density is required. However, a simultaneous analysis of the thermophysical properties of small-volume liquids has rarely been considered. Recently, we proposed a new methodology to simultaneously analyze the aforementioned three intrinsic properties using heater-integrated fluidic resonators (HFRs) in an atmospheric pressure environment comprising a microchannel, resistive heater/thermometer, and mechanical resonator. Typically, the thermal conductivity and volumetric heat capacity are measured based on a temperature response resulting from heating using a resistive thermometer, and the specific heat capacity can be obtained from the volumetric heat capacity by using a resonance densitometer. In this study, we analyze methods to improve the thermophysical property measurement performance using HFRs, focusing on the effect of the ambience around the sensor. The analytical method is validated using a numerical analysis, whose results agree well with preliminary experimental results. In a vacuum environment, the thermal conductivity measurement performance is enhanced, except for the thermal conductivity range of most gases, and the sensitivity of the specific heat capacity measurement is enhanced owing to an increase in the time constant.

• Journal of Mechanical Science and Technology
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• v.18 no.12
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• pp.2204-2208
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• 2004

Ti-8Ta-3Nb has been developed as a new biomaterial. The experimental specimens are as-cast and forged Ti-8Ta-3Nb alloys. Treatment in a solution, ranging from 760 to 960$^{\circ}C$ has carried out. The microstructural research has carried out after the solution treatment and the hardness was measured. The specific heat and the length variations of Ti-8Ta-3Nb were also measured. The optimum temperature for the solution heat treatment of Ti-8Ta-3Nb was found to be 880$^{\circ}C$. This was based on the mechanical properties and the volume fraction of ${\alpha}$ phase and their phases shown from the results of the solution heat treatment. From the results, the ${\beta}$ transition temperature of Ti-8Ta-3Nb was found to be between 860$^{\circ}C$ and 880$^{\circ}C$.

• Journal of the Korean Society for Heat Treatment
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• v.25 no.5
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• pp.233-238
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• 2012

The effect of subzero treatment on the mechanical properties of cold rolled high manganese austenitic stainless steel was investagated. ${\alpha}$'-martensite was formed by cold rolling, and it was formed with surface relief and specific direction or crossing each other. The volume fraction of martensite increased by subzero treatment, and it was increased with longer time of subzero treatment and higher temperature of subzero treatment. The hardness and strength increased by subzero treatment, while the elongation decreased. With the increase of volume fraction of martensite, the hardness and strength was increased steeply with proportional relationship, elongation was decreased slowly. The results show that the hardness and strength was strongly controlled by the volume fraction of martensite, and the elongation was affected by transformation behavior of deformation induced martensite in the initial stage of deformation.

• Journal of Welding and Joining
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• v.17 no.6
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• pp.84-89
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• 1999

Most of ferrous b.c.c weld materials may experience martensitic transformation during rapid cooling after welding. It is well known that volume expansion due to the phase transformation could influence on the relaxation of welding residual stress. To apply this effect practically, it is a prerequisite to establish a numerical model which is able to estimate the effect of phase transformation on residual stress relaxation quantitatively. For this purpose, the analysis is carried out in two regions. i.e., heating and cooling, because the variation of material properties following a phase transformation in cooling is different in comparison with the case in heating, even at the same temperature. The variation of material properties following phase transformation is considered by the adjustment of specific heat and thermal expansion coefficient, and the distribution of residual stress in analysis is compared with that of experiment by previous study. consequently, in this study, simplified numerical procedures considering phase transformation, which based on a commercial finite element package was established through comparing with the experimental data of residual stress distribution by other researcher. To consider the phase transformation effect on residual stress relaxation, the transition of mechanical and thermal property such as thermal expansion coefficient and specific heat capacity was found by try and error method in this analysis.

• Journal of computational fluids engineering
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• v.18 no.4
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• pp.25-34
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• 2013

A numerical study of a laminar natural convection of the CuO-water nanofluid in a square cavity using the Buongiorno's nonhomogeneous model is presented. All the governing equations including the volume fraction equation are discretized on a cell-centered, non-uniform grid employing the finite-volume method with a primitive variable formulation. Calculations are performed over a range of Rayleigh numbers and volume fractions of the nanopartile. From the computed results, it is shown that both the homogeneous and nonhomogeneous models predict the deterioration of the natural convection heat transfer well with an increase of the volume fraction of nanoparticle at the same Rayleigh number, which was observed in the previous experimental studies. It is also shown that the differences in the computed results of the average Nusselt number at the wall between the homogeneous and nonhomogeneous models are very small, and this indicates that the slip mechanism of the Brown diffusion and thermophoresis effects are negligible in the laminar natural convection of the nanofluid. The degradation of the heat transfer with an increase of the volume fraction of the nanoparticle in the natural convection of nanofluid is due to the increase of the viscosity and the decrease of the thermal expansion coefficient and the specific heat. It is clarified in the present study that the previous controversies between the numerical and experimental studies are owing to the different definitions of the Nusselt number.

• Journal of the Korean Mathematical Society
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• v.45 no.3
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• pp.645-681
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• 2008

The Navier-Stokes system for heat-conducting incompressible fluids is studied in a domain ${\Omega}{\subset}R^3$. The viscosity, heat conduction coefficients and specific heat at constant volume are allowed to depend smoothly on density and temperature. We prove local existence of the unique strong solution, provided the initial data satisfy a natural compatibility condition. For the strong regularity, we do not assume the positivity of initial density; it may vanish in an open subset (vacuum) of ${\Omega}$ or decay at infinity when ${\Omega}$ is unbounded.

• Food Science and Biotechnology
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• v.15 no.6
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• pp.860-865
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• 2006

The quality parameters of sponge cake supplemented with soy protein concentrate (SPC) were evaluated. The addition of SPC to wheat flour increased the protein content and alkaline water retention value, but decreased the sedimentation value. Protein content had a positive correlation with the alkaline water retention value, and a negative correlation with the sedintentation value. The higher the concentration of SPC, the higher the RVA pasting temperature and the lower the viscosity. Increasing the level of SPC in flour led to a decrease in mixogram peak time, whereas peak height, width at peak, and width at 8 min progressively increased. As the amount of SPC increased in the formulation, the pH and specific gravity of cake batter increased, whereas the volume and specific volume of sponge cake decreased. The total isoflavones content in SPC increased after heat treatment. The hardness, gumminess, and chewiness increased progressively in accordance with increasing level of SPC.

• Journal of Korea Foundry Society
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• v.15 no.2
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• pp.184-193
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• 1995

Effects of process parameters during thixocasting, such as solid volume fraction, mold temperature and extrusion ratio, on the mold filling behaviour and fluidity of Mg alloy(AZ91D) have been investigated. The semi-solid ingot held for 60 minutes at the semi-solid temperature range did not contain the equilibrium volume fraction of solid as expected from the phase diagram. Therefore, in order to obtain the desired solid fractions, and to suppress the exaggerated grain growth during heating, it was required to heat the ingot rapidly up to the temperature $10^{\circ}C$ higher than the semi-solid temperature suggested from the phase diagram for a specific volume fraction of solid. The experimental results show that mold filling behaviour and fluidity can be improved with the use of the higher mold temperature and the lower volume fraction of solid, but remain nearly unaffected by the change of extrusion ratio.

• Journal of Energy Engineering
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• v.14 no.2 s.42
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• pp.117-122
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• 2005

This study is performed to investigate the cooling characteristics of TMA $25\;wt\%$ clathrate compound with an additive; the phase change temperature, the degree of supercooling, specific heat and the rate of volume change. The used additive is ethanol and the heat source temperature is $-7^{\circ}C$. Experimental results are as follows: 1) The phase change temperature is increased by $0.32\~0.96^{\circ}C$ during the cooling process of TMA $25\;wt\%$ clathrate compound with ethanol. 2) The degree of supercooling is repressed by $0.9^{\circ}C$ in case of TMA $25\;wt\%$ clathrate compound with $0.5\;wt\%$ ethanol. 3) The specific heat is increased by $0.19\;kJ/kg^{\circ}C$ in case of TMA $25\;wt\%$ clathrate compound with $0.l\;wt\%$ ethanol. 4) The rate of volume change is decreased by $1.15\~l.5\%$ in case of TMA $25\;wt\%$ clathrate compound with ethanol.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.12 no.2
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• pp.17-28
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• 2004

In unmanned aerial vehicle (UAV), the high temperature results from friction with the air, combustion of fuel and combustion gas of a nozzle etc. It causes serious problems in the UAV structure. The characteristic analysis of heat resistant metal and ceramic materials and creep analysis for the functionally graded material (FGM) is presented in this paper. FGM is composed of two constituent materials that are mixed up according to the specific volume fraction distribution in order to withstand high heat condition. In addition, the creep behavior of FGM applied in duct structure of an engine is analyzed.