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非定常方形波 펄즈 加熱에 의한 세라믹 誘電體의 熱物性値 測定에 관한 硏究
차경옥 대한기계학회 1988 대한기계학회논문집 Vol.12 No.1
본 연구에서는 열물성치 측정시 여러가지 어려운 수고를 가급적 줄이고 측정시간도 짧도록 하기 위해서 방평파 펄즈상가열법을 채용하여 이론적 검토와 고온에 유한원형인 시료로 부터 복사열손실을 최소화할 수 있는 방법을 고려하였다. 물론 시료는 전지회로의 용량소자, 콘텐서(condenser) 또는 전기절연이 주용도이며 유전율이 서로 다른 5종류의 세라믹 유전체에 관해서도 상온으로부터 약 1300k 까지 열물성치를 계측하였다. 특히 세라믹 유도체에는 유전율 및 기공율에 의한 열물성치가 가 다르기 때문에 그들사이의 관계에 대해서도 검토하였다. In recent years, attention has been paid to the ceramic material next to metals and plastics due to its inherent characteristics, i.e., good hardness, resistance to heat and corrosion. Recently, various kinds of ceramic dielectrics have been developed for application in industry. It is of prime importance to know the thermophysical properties for wider use of these new materials. However, no extensive effort has been made for systematic measurement of the properties. In this paper, the dielectric constant of five different kinds of ceramic dielectrics ware measured. We call these samples as MgO.SiO$_{2}$, MgTiO$_{3}$, TiO$_{2}$, CaTiO$_{3}$, and BaTiO$_{3}$. Which are currently in commercial sue. The values of thermal dirrusivities, specific heats, and thermal conductivities of these ceramic dielectrics sere measured as a function of temperature ranging from room temperature to about 1300k.
非定常熱源인 펄즈狀加熱法에 의한 强誘電體 Ceramic의 熱物性 測定
車京玉 明知大學校 産業技術硏究所 1992 産業技術硏究所論文集 Vol.11 No.-
The square wave pulse heating method of measuring thermophysical properties has been developed. The cylindrical of a specimen in the ferroelectricity ceramincs are heated square wave for a few second by a film heater which is placed between the plates. The resulting temperature history of the opposite surface is attached to make it hove high thermal and conductivites, is measured by pressing seperated C-A thermocouple wires against the surface. From a compassion between the measured and theoretical temperature histories, the thermal diffusivity, the specific heat and t conductivity of the specimen can be deformined automatically in a few minuted by a computer. The values of thermophysical properties were measured as a function of temperature ranging from room temperature to 1000℃ Thus, the effects of dielectricity upon themophysical properties were analyzied in detail.
車京玉 명지대학교 1983 明大論文集 Vol.14 No.-
The analysis of unsteady state heat transfer in the straight fin of rectangular cross section has been made by making use of the theory of finite difference method and variational method. The heat transfer coefficient in the fin is given as a function of position(x), ie h=(r+1)(x/L)^r(h_a), which was suggested by L.S Han and S.G Lefkowitz. And the results are compared with the analytical solution which was obtained by assuming the heat transfer coefficient to be constant. These results show good agreement between the solution of finite difference method and analytical solution in all dimensionless time(e=αE/L^2)domain. But the solution of variational method has been found to have discrepancies with analytical solution in the some region of dimensionless time domain. When the dimensionless number N(=[√(h_a,P)/(kA)]·L) is 0.5 and 1.0, the larger the dimensionless time(e), the larger the effect of an exponential (r) to the temperature distribution. On the other hand, in the range of small N(N≤0.01), the effect of exponential (r) to the temperature distribution has been found to be negligible. The efficiency of the fin having large number of N(N≥0.5), ie heat conductivity (k) is small and length(L) is long, is decreased as the exponential (r) is increased. And the fin having small number of N, ie heat conductivity (k) is large an length(L) is short, shows that the efficiency of fin is almost constant regardless the value of exponential (r). Nomenclature A; area of cross-section of fin a; dimensionless semithickness of fin(=(b)/(l)) B; Biot number(=hl/k) b; semithickness of fin C; specific heat of fin E; time (sec) e; dimensionless time(=(αE)/(L^2)) h; convective heat transfer coefficient h_a; average heat transfer coefficient k; thermal conductivity of material of fin L; length of fin N=√[(h_a·p)/(kA)]·L P; perimeter of fin Q; heat transfer rate T; temperature of fin T_o; fin base temperatures T_∞; convection fluid temperature x; distance from base of fin X; dimensionless distance from base of fin(=(x)/(L)) α; thermal diffusivity(=k/ρ·c) θ; dimensionless temperature(=(T-T_∞)/(T_o-T_∞)) ρ; density of fin [ ] ; square matrix
방형파펄즈가열법에 의한 세라믹스의 열물성 측정에 관한 연구
차경옥,이경희,임굉,Cha, K.O.,Lee, K.H.,Yim, Going 한국결정성장학회 1999 韓國結晶成長學會誌 Vol.9 No.6
본 연구에서는 방형파 펄즈 가열법을 이용하여 세라믹 고유전체 열물성치의 측정에 활용하는 것에 대한 가능성을 검토하였다. 여기서 측정의 이론을 설정하고 측정의 자동화를 시도함으로써 매우 짧은 시간내 시료의 열확산계수, 비열 및 열전도율을 얻을 수 있었다. 또한 시료는 실온으로부터 약 1300 K 온도 범위까지 측정하였다. Thermophysical properties of the high-dielectric ceramics were measured by a single rectangular pulse heating method. The values of thermal diffusivities, specific heats, and thermal conductivities were measured as a function of temperature ranging from room temperature to 1300 K.
난류유동장에서 Shear - thinning 유체에 의한 마찰저항 감소에 관한 연구
차경옥,김재근,오율권 한국마린엔지니어링학회 1997 한국마린엔지니어링학회지 Vol.21 No.2
Drag reduction in polymer solutions is the phenomenon where by extremely dilute solutions of high molecular weight polymers exhibit frictional resistance to flow much lower than the pure solvent. This effect, largely unexplained as yet, has attracted the attention of polymer scientists and fluid flow specialists. Although applications are beginning to appear, the principle interest to data has been in attempting to relate the effect to the fluid mechanics of turbulent flow. Drag reduction in two phase flow can be applied to the transport of crude oil, phase change system such as chemical reactor, and pool and boiling flow. But the research on drag reduction in two phase flow is not intensively investigated. Therefore, experimental investigations have been carried out to analyze the drag reduction produced by polymer addition in the single phase and two phase flow system. The objectives of the proposed investigation are primarily in identifying and developing high performance polymer additives for fluid transportations with the benefits of turbulent drag. Also we want to is to evaluate the drag reduction in horizontal flow by measuring pressure drop and mean velocity. Experimental results show higher drag reduction using co - polymer(A611P) then using polyacrylamide (PAAM) and faster degradation using PAAM than using A611P under the same superficial velocity.