• Journal of Biosystems Engineering
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• 제12권2호
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• pp.38-43
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• 1987

An experimental study was conducted to develop a thin-layer rewetting equation of short grain rough rice of Akihikari variety. Four thin-layer rewetting equations were experimentally determined from $25^{\circ}C$ to $45^{\circ}C$ and 70%RH to 85%RH conditions. Diffusion, Henderson, Page, and Thompson equations widely used as thin-layer drying equations were selected. Experimental data were fitted to these equations using linear regression analysis except diffusion equation. The diffusivity in the diffusion equation was determined by optimization method. Four equations were highly significant. In order to compare the goodness of fit of each equation, the error mean square of each equawas calculated. The diffusion model was not a very good model because the error mean square was very large. The other three models showed the same level or error mean square and could predict satisfactorily the rewetting rate or short grain rough rice.

• 한국재료학회지
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• 제6권7호
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• pp.716-722
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• 1996

박막 형 가스 센서의 막 두께가 가스 감지 특성에 미치는 영향을 단순화된 모델로부터 수식으로 유도하여 해석하였고, 그것을 ${SnO}_{2}$와 CuO-${SnO}_{2}$ 박막의 ${H}_{2}S$ 감응 특성에 대한 실험 결과에 적용하였다. 유도된 수식으로부터 박막 가스 센서의 가스 감지 특성은 가스의 박막 안으로의 확산성에 크게 의존하며, 그 가스 확산성은 박막의 두께, 가스의 센서 재료의 반응성, 작동 온도 등에 의해서 결정됨을 알 수 있었다. 또한 이 수식은 CuO-${SnO}_{2}$ 박막의 ${H}_{2}S$ 감응 특성에 대한 실험 결과와 비교적 잘 일치하였고, CuO-${SnO}_{2}$ 박막과 ${SnO}_{2}$ 박막의 서로 판이한 ${H}_{2}S$ 감응 특성에 대한 설명에 적용되었다. 이로부터, 일반적인 산화물 반도체식 가스 센서의 가스 감지 특성이 가스 확산성에 의해서 어떻게 지배되는가를 구체적으로 제안하였다.

• Journal of Biosystems Engineering
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• 제23권1호
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• pp.21-30
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• 1998

A theoretical model was developed to evaluate the effects of soil and airflow characteristics on the soil-air heat exchanger performances. The model, which includes three-dimensional transient energy and mass equilibrium-equation, was solved by using a computer program that uses Finite Difference Methods and Gauss-Seidel iteration computation. Energy gains, heat exchange efficiencies, and outlet air temperature are presented including the effects of soil moisture content, soil conductivity, soil thermal diffusivity, and soil initial temperature. Also, data related to the effects of airflow rate and inlet air temperature on the thermal performance of the system are presented. The results indicated that energy gains depend on soil conductivity, soil thermal diffusivity, and soil initial temperature. Heat exchange efficiencies relied on air mass flow rate and soil moisture content.

• 태양에너지
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• 제17권3호
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• pp.13-21
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• 1997

장기 성층 온수 저장조 내의 중간 경계면에서 전달되는 열량을 예측하기 위하여 이론식을 유도 확립하고 이론적인 축열효율을 구하였다. 그리고 이론 축열효율값과 비교 고찰하기 위하여 여러 실험 조건을 통한 실제 축열효율을 구하였고, 저장조 내의 중간 경계면에서 일어나는 혼합정도를 효과적으로 해석하기 위하여 유효 열확산 계수를 정량화하였다. 중간 경계면에서 열전도에 의한 손실이 일회 충수 시간이 짧을수록 즉, Pe 수가 증가할 수록 많이 발생함을 알았다.

• Journal of the Korean Wood Science and Technology
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• 제37권2호
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• pp.141-147
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• 2009

The fluctuation of physical properties in wood or wood composites is an important subject when the materials in building and construction. Sorption and desorption occur in wood when exposed to the open air, and the temperature distribution in wood can fluctuate as a result of changes in environmental temperature, solar radiation, humidity, and wind velocity. In this study, the temperature difference and fluctuation caused by outdoor environment among different wood species were analyzed using a numerical method. The effect on the process of heat transfer in wood caused by environmental factors was investigated using 1-dimensional partial differential equation with real boundary and initial conditions. The experimental data have been used to check the accuracy of programming code. Through analysis, it was found out that density and moisture content have a negative effect on thermal diffusivity of wood.

• 대한화학회지
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• 제7권3호
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• pp.203-206
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• 1963

The eddy diffusion in the pulsed wetted wall column, where the spherical balls are consecutively arrayed along the axis of the column and turbulence is caused around the balls by pulsation, has been studied both theoretically and experimentally. A diffusion equation is solved for a longitudinal column where a concentration impulse is given at the top of the column, and the experimental results, which are the impulse response measurements at the half of the total height of the column, have shown a good agreement with the developed theory. A method of measuring the eddy diffusivity, which is based on the slope of concentration vs. time in the particular interval of concentration, is proposed and the measured diffusivity is used as a criterion of comparing the theory and the experiment. The eddy diffusion is remarkably increased as the amplitude and the frequency of the pulsation increase but the increasing rate is decreased as the pulsation increases.

• 한국전산구조공학회논문집
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• 제28권1호
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• pp.79-83
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• 2015

본 논문에서는 헤테로 애피택시(heteroepitaxy) 박막의 표면확산계수를 국부적으로 제어하여 표면에서 형성되는 나노구조물이 정렬되는 과정을 수치해석적으로 연구하였다. 격자 불일치 물질계(lattice-mismatched materials system)의 탄성변형에너지와 표면자유에너지, 그리고 습윤에너지를 고려하여 박막의 변형거동에 대한 지배방정식을 도출하였으며, 확산계수의 활성화 조건이 성장에 미치는 영향을 살펴보았다. 해석결과는 주기함수 형식으로 표면확산계수를 제어하면 표면구조물이 배열 형태로 정렬됨을 나타내며, 이는 노광 및 식각 과정을 거쳐야 하는 포토리소그래피(photolithography)로부터 탈피한 바텀업(bottom-up) 방식의 공정방법에 규칙성을 부여하여 차세대 나노기기의 개발에 일조할 것으로 기대된다.

• 한국식품과학회지
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• 제18권1호
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• pp.24-30
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• 1986

전분, 단백질 및 수분으로 주로 구성된 한국의 일반 식품과 유사한 모형식품을 이들 세가지 주성분을 조합하여 만들었으며, 이 모형식품의 열확산도를 측정하고 주성분과의 관계를 구명하였다. 모형식품의 열확산도는 수분함량에 비례하는 경향이었고, 동일 수분함량에서는 전분질식품이 단백질 식품보다 높은 값을 나타냈으며 성분간의 교호작용은 유의석이 인정되지 않았다. 측정치와 계산치간의 오차는 잔여율이 3.60%로서 부함도가 높았다. 모형식품에서 열확산도와 수분함량, 단백질 및 전분함량과의 관계식은 다음과 같다. 즉, ${\alpha}20^{\circ}C$ = 0.04911M+0.37355P+3.73072, ${\alpha}60^{\circ}C$ = 0.05353M-0.4766P+4.15136, 이식을 이용한 산술치와 측정치간의 상관계수는 $20^{\circ}C$에서 $0.9650^{**}$, $60^{\circ}C$에서 $0.9002^{**}$로 고도의 유의 상관관계를 나타내었다.

• Journal of Biosystems Engineering
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• 제41권4호
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• pp.342-356
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• 2016

Purpose: The drying of a thin layer of native cassava starch in a tray dryer was modeled to establish an equation for predicting the drying behavior under given conditions. Methods: Drying tests were performed using samples of native cassava starch over a temperature range of $40-60^{\circ}C$. We investigated the variation in the drying time, dynamic equilibrium moisture content, drying rate period, critical moisture content, and effective diffusivity of the starch with temperature. The starch diffusion coefficient and drying activation energy were determined. A modification of the model developed by Hii et al. was devised and tested alongside fourteen other models. Results: For starch with an initial moisture content of 82% (db), the drying time and dynamic equilibrium moisture content decreased as the temperature increased. The constant drying rate phase preceded the falling rate phase between $40-55^{\circ}C$. Drying at $60^{\circ}C$ occurred only in the falling rate phase. The critical moisture content was observed in the $40-55^{\circ}C$ range and increased with the temperature. The effective diffusivity of the starch increased as the drying temperature increased from 40 to $60^{\circ}C$. The modified Hii et al. model produced randomized residual plots, the highest $R^2$, and the lowest standard error of estimates. Conclusions: Drying time decreased linearly with an increase in the temperature, while the decrease in the moisture content was linear between $40-55^{\circ}C$. The constant drying rate phase occurred without any period of induction over a temperature range of $40-55^{\circ}C$ prior to the falling rate period, while drying at $60^{\circ}C$ took place only in the falling rate phase. The effective diffusivity had an Arrhenius relationship with the temperature. The modified Hii et al. model proved to be optimum for predicting the drying behavior of the starch in the tray dryer.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집D
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• pp.97-103
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• 2001

The effects of the electrohydrodynamic (EHD) flow and turbulent diffusion on the collection efficiency of a model ESP composed of the plates with a cavity were studied through numerical computation. The electric field and ion space charge density were calculated by the Poisson equation of the electrical potential and the current continuity equation. The EHD flow field was solved by the continuity and momentum equations of the gas phase including the electrical body force induced by the movement of ions under the electric field. The RNG $k-{\varepsilon}$ model was used to analyze the turbulent flow. The particle concentration distribution was calculated from the convective diffusion equation of the particle phase. As the ion space charge increased, the particulate collection efficiency increased because the electrical potential increased over the entire domain in the ESP. The collection efficiency decreased and then increased, i.e. had a minimum value, as the EHD circulating flow became stronger when the electrical migration velocity of the charged particle was low. However, the collection efficiency decreased with the stronger EHD flow when the electrical migration of the particle was higher relatively. The collection efficiency of the model ESP increased as the turbulent diffusivity of the particle increased when the electrical migration velocity of the particle was low. However, the collection efficiency decreased for increasing the turbulent diffusivity when the electrical migration of the particle was higher relatively.