The blockage rate for three kinds of nets commonly used in agricultural facilities was assessed by using the image acquisition and its relevant processing. By using both empirical relations presented by Idel’chik and Richards and Robinson, and the blockage rate obtained from the image processing, the pressure drop through the nets was predicted and also compared with wind tunnel experiment results. The results of the study showed that the blockage rate of the net was discriminated according to such factors as the magnitude of nets, the existence of inside threads, the thickness and number of threads. In addition, the blockage rate for the incident angle of 0° when the wind blew at the front had the range of 0.22－0.29 (0.22－0.32 when considering whole incident angles from 0° to 45° by 15°). For the nets with the blockage rate of about 30% or below, the prediction by the empirical relations of by Idel’chik and Richards and Robinson showed a little higher pressure drop overall than that of the wind tunnel test, but the use of the empirical relations and the blockage rate could be thought of as providing effectively meaningful guidelines for the safe design of agricultural facilities including nets because the wind tunnel test has been tedious and expensive. Further research and potential application on the prediction technique of the pressure drop, regarding both a subtle deformation by the wind and manufacturing methods with regard to the level of knots and the existence of inside threads, needs to be done for the nets with higher blockage rate.

In order to analyze the pressure drop of the fluid passing through the hydraulic coupler, a flow model using the Computational Fluid Dynamics (CFD) analysis technique was developed and the fluid flow rate and pressure distribution inside the coupler were analyzed. The analysis model was corrected by comparing the pressure drop measurement using a 6.35mm hydraulic coupler with the ISO reference value and the simulation prediction value. Using the calibrated model, the flow rate and pressure drop of 13 types of hydraulic couplers distributed on the market were analyzed, and their performance was determined by comparing them with ISO reference values. In the case of type A coupler, the pressure drop was generally higher than the ISO reference value, and in the case of type B coupler, the pressure drop was similar to or lower than the ISO reference value. It was confirmed that the complex flow analysis inside the hydraulic coupler could be easily performed through computational fluid dynamics (CFD) modeling, and based on this, problems could be identified and performance could be improved performance.

Heat transfer and pressure drop of horizontal heat exchangers with different configurations and installations numerically characterized. Three different heat exchangers were used and shaped as linear, wavy, and horizontal slinky, respectively. Installation depth was set from 0.5m to 3.0m and pipe spacing was ranged from 0.3m to 2.1m. The results showed that heat transfer rate and pressure drop were increased with the increase in the installation depth and the pipe spacing. The horizontal slinky heat exchanger carried more heat compared to others due to the greater effective heat transfer surface area per installation area. In terms of a ratio of heat transfer rate to pressure drop indicating the system efficiency, the linear heat exchanger performed better than others. On the other hand, the horizontal slinky heat exchanger was the most effective with respect to a ratio of heat transfer rate to installation cost.

At a two phase flow, according to gas and liquid phase flow rates, various flow regimes are developed such as bubbly, slug/plug, churn, annular, droplet flow and so on. At a two phase flow in small scaled channels, among various flow regimes, the intermittent flows such as bubbly, slug/plug flow are developed in the broad regions of two phase flow pattern map. In particular, the flow regimes are influenced by surface wettability. In a case of slug flow in hydrophobic small scaled channels, gas and liquid phases are perfectively separated by interfaces and contact line. The pressure drop of the two-phase flow is largely generated at moving contact line. Therefore, to well design two-phase flow system with small scales, it is important to estimate the pressure drop at moving contact line. In this study, on the basis of previous research, the pressure drop at moving contact line is experimentally measured for a various fluids (0-40% water-ethanol mixtures). And, the previous correlation to estimate pressure drop at moving contact line is verified by experimental data. In an addition, we discuss interfacial broken phenomena of slug flow in a minichannel. (D=1.555mm).

In this study, the air-side cooling capacity and pressure drop of an evaporator for a refrigerator unit were experimentally investigated. Using the calorimeter, the performance of the evaporator was verified by changing the fin shape, fin pitch, tube row and air flow rate. The experimental apparatus consisted of the calorimeter which functioned as a constant temperature and humidity chamber and the refrigeration cycle. In order to select the heat exchanger suitable for the evaporator, both air-side cooling capacity and pressure drop should be considered at the same time. From the evaporator performance test by pin type, wavy pin was selected. The optimal performance of the evaporator was observed at the fin pitch of 5 mm, the tube row of 6 row, and the air flow rate of 40㎥/min.

본 연구에서는 지름이 일정한 하나의 직선 관형 막을 가정하여 그 단위구간의 투과속도에 대한 물질수지를 세웠으며 이것을 기초로 하여 파이프의 정상상태 식과 함께 비선형 연립 2차 미분방정식을 이루었다. 이러한 관형 막의 압력손실을 표현한 연립방정식은 비선형이므로 Gauss-Seidel method와 같은 반복법에 의해서 해결될 수 있다. 이러한 수치해를 나타내기 위해 모사 알고리즘을 제시하였다. 또한 투과수는 운전 조건의 변화에 따라 변하므로 각 조건에서의 연립 방정식의 해를 수치적으로 적분하여 해결하였다. 모사의 결과를 검증, 해석하기 위해서 실제 중공사막과 유사한 관형 막을 사용하여 실험을 진행하였다. 본 연구에서는 중공사막을 유체가 흐를 때 발생하는 압력손실, 유량, 그리고 투과수의 관계를 분석적 방법을 이용해 제시하였고 이러한 이론적 기초를 바탕으로 실제 기공을 가진 막에 적용하여 그 정확성을 실험을 통하여 비교하였다.

500μm의 수력직경을 가진 마이크로 채널에서 유동 비등 시 물에 대한 마찰 압력 강하를 측정하기 위한 실험적 연구를 수행하였다. 실험은 열 유속 100-400kW/m2, 증기건도 0-0.2 그리고 질량 유속 200-600kg/m2s의 범위에서 이루어졌다. 유동 비등 시 마찰 압력 강하는 두 가지 모델을 사용하여 예측된다. 즉, 두 상의 속도가 동일하다고 가정한 균질 모델과 두 상 사이에 서로 다른 속도를 가지는 분리류 모델로 분류된다. 실험결과 이상 마찰 승수는 질량 유속이 증가함에 따라 감소한다는 것을 알 수 있었다. 측정된 압력 강하 데이터는 매크로 스케일과 미니/마이크로 스케일에서 제안된 기존의 여러 상관식들과 비교하였다. 균질 모델은 본 연구에서 고려한 실험 조건에서 29.4 %의 평균 오차내에서 마찰 압력 강하를 예측하였다.

本論文, 旨在要通過考察兩漢時期黃老學代表著作『淮南子』, 探討宇宙生成論的基本含義。宇宙生成論就探討如下幾個問題: 宇宙萬物之根源, 其根源如何發展到具體萬物, 天下萬物之最終根源是如何規定『淮南子』繼承了先秦時期老莊哲學思想、氣論和陰陽五行思想及兩漢時期所發展的自然科學之成果, 而使之適應於自己宇宙論體系之需要。.今爲止, 大多學者從以下方面起規定『淮南子』的宇宙生成論: 有些學者把『淮南子』規定爲‘雜家’而其理論體系最終落到於自相矛盾; .一些學者都從‘道’‘氣’.念的含義和兩者之間的關系問題出發, 建立起了其宇宙生成論的理解方式。從道氣兩個.念之間的關系問題上, 就發生了‘氣一元論’和‘以道爲主的自然觀’而再分爲‘道.氣’或‘道生氣’的觀點。那., 如何解釋『淮南子』所論的宇宙生成論才接近於其.正的含義? 筆者認爲,『淮南子』基本上堅持了宇宙萬物始於整體(‘一氣’)的立場。『淮南子』就把這種整體稱爲‘太昭=虛.=一’, 而從這個狀態起發生了‘陰陽二氣’的分化而最終形成了天地萬物。但在這個過程上, 我們必須解釋宇宙生成的動力是什., 因而『淮南子』提到了 ‘道始于虛.’、‘道始於一’的觀點。.是說, 道沒有直接參與於萬物生成過程, 而道就是所引起各個生成過程的基本動力, 所以『淮南子』把‘道’理解爲宇宙萬物的最終本原。如此, ..淮南子..就把‘道’和 ‘氣’綜合起來, 最終建立了‘以道爲本’的氣化宇宙論。對於向後中國哲學思想裏所發展的宇宙論體系, 『淮南子』的宇宙生成論.生了重大的影響。

본 연구는 산업용 열교환기 및 상용 파이프의 최적 설계를 위하여 열교환기 내의 사각형 단면 파이프의 shear-thickening 비뉴톤 유체의 압력강하 및 대류 열전달률을 수치해석적으로 수행하였다. shear-thickening 유체의 구성 방정식은 기존의 비뉴톤 유체 멱법칙을 보완한 확장 멱법칙 모델을 채택하였다. 파이프 내의 압력강하를 의미하는 마찰계수와 확장 레이놀즈 수의 곱은 기존 연구의 비교자료와 비교할 때 뉴톤 유체 영역과 멱법칙 영역에서 각각 0.018% 및 0.06% 내에서 일치함을 보였고, 대류 열전달률을 의미하는 뉴셀트 수는 문헌치와 비교할 때 뉴톤 유체 영역과 멱법칙 영역에서 각각 0.025% 및 0.14% 내에서 일치함을 보였다. 비뉴톤 확장 멱법칙 유체 모델의 형태를 띠는 shear-thickening 유체를 열교환기 또는 상용파이프 내의 사각형 단면 파이프 내에서 사용하면 유동지수(n)에 따라서 뉴톤 유체보다 최대 160%의 압력강하를 증가시켰고 최대 14%의 대류 열전달 감소를 발생시킬 수 있었다.

본 연구에서는, 혈관 내 폐 보조장치를 설계할 때 혈액의 압력손실에 대한 영향을 받지 않는 최적의 설계조건을 찾기 위하여 압력손실을 예측할 수 있는 관계식을 유도하고자 하였다. 정맥 내경의 직경을 3 cm로 고정하고 삽입되는 중공사 개수의 변화에 따른 압력손실을 측정하였으며 실험에 의하여 얻어진 압력손실과 장치의 전면면적과의 상관관계를 curve fitting을 통하여 유도하였고, 유도되어진 관계식을 이용하여 정맥 내에 삽입되는 중공사 개수의 변화에 따른 압력손실을 예측하였다. 그리고 실험을 통하여 예측되어진 값과 비교 검토하여 유사성을 찾고자 하였다. 실험결과 장치에서 액체 유속의 변화에 따라 압력손실은 2차 함수 형태로 변화됨을 알 수 있었다. 또한 장치의 전면면적이 감소하면 압력손실은 증가하였고 충진율이 증가하면 압력손실도 증가함을 알 수 있었다. 장치 내에서의 압력손실에 대한 관계식을 장치의 전면면적과 충진율의 함수로 유도할 수 있었으며, 관계식에 의하여 압력손실을 예측할 수 있었다. 또한, 실험에 의한 압력손실과 비교하였을 때 유사한 경향성을 보여 줌으로써 압력손실 예측의 신뢰성을 얻을 수 있었다.

Heat transfer performance improvement by fin and groovs is studied for condensation of R-11 on integral-fin tubes. Eight tubes with trapczodially shaped integral-fins having fin density from 748 to 1654fpm(fin per meter) and 10, 30 grooves are tested. A plain tube having the same diameter as the finned tubes is also used for comparison. R-11 condensates at saturation state of 32 ℃ on the outside tube surface coded by inside water flow. All of test data are taken at steady state. The heat transfer loop is used for testing singe long tubes and cooling is pumped from a storage tank through filters and folwmeters to the horizontal test section where it is heated by steam condensing on the outside of the tubes. The pressure drop across the test section is measured by menas pressure gauge and manometer. The results obtained in this study is as follows : 1. Based on inside diameter and nominal inside area, overall heat transfer coefficients of finned tube are enhanced up to 1.6 ~ 3.7 times that of a plain tube at a constant Reynolds number. 2. Friction factors are up to 1.6 ~ 2.1 times those of plain tubes. 3. The constant pumping power ratio for the low integral-fin tubes increase directly with the effective area to the nominal area ratio, and with the effective area diameter ratio. 4. A tube having a fin density of 1299fpm and 30 grooves has the best heat transfer performance.

Polyester, polyacrylics, nylon과 cotton을 이용해 이들의 막지지천으로의 사용가능성을 조사하였다. 압축률, membrane embossing, 유량과 물리적·화학적 특성 등을 고려한 결과 50 번수의 polyester가 막지지천으로 적당함을 알았다. 이 polyester를 막지지천으로 사용해 압력 강하, 조업압력, 점도 등이 막지지천을 통한 유체 흐름에 미치는 영향을 조사하였는데, 이 막지지천을 통한 유체 흐름은 Darcy's law를 만족시켰다.

With continuous industrial development, the types, and amount of particulate matter (PM) have been increasing. Since 2018, environmental standards regarding PM have become more stringent. Pulse air jet bag filters are suitable for PM under the 20㎛ and, can function regardless of size, concentration and type. Filtration velocity and shape are important factors in the operation and design of the pulse air jet bag filters however, few established studies support this theory. In this research, numerical simulations were conducted based on experimental values and, several methods were employed for minimizing the pressure drop. In the pilot system, as the inlet duct velocity was faster than 19 m/sec, flow was not distributed equally and, re-entrainment occurred due to the hopper directional vortex. The multi-inlet system decelerated the hopper directional vortex by 25 ~ 30% , thereby decreasing total pressure drop by 6.6 ~ 14.7%. The guide vane system blocked the hopper directional vortex, which resulted optimal vane angle of 53°. The total pressure of the guide vane system increased by 0.5 ~ 3% at 1.5 m/min conditions. However, the filtration pressure drop decreased by 4.8 ~ 12.3% in all conditions, thereby reducing the operating cost of filter bags.

In this study, pressure drop was measured in the pulse jet bag filter without venturi on which 16 numbers of filter bags (Ø140 × 850 ℓ) are installed according to operation condition(filtration velocity, inlet dust concentration, pulse pressure, and pulse interval) using coke dust from steel mill. The obtained 180 pressure drop test data were used to predict pressure drop with multiple regression model so that pressure drop data can be used for effective operation condition and as basic data for economical design. The prediction results showed that when filtration velocity was increased by 1%, pressure drop was increased by 2.2% which indicated that filtration velocity among operation condition was attributed on the pressure drop the most. Pressure was dropped by 1.53% when pulse pressure was increased by 1% which also confirmed that pulse pressure was the major factor affecting on the pressure drop next to filtration velocity. Meanwhile, pressure drops were found increased by 0.3% and 0.37%, respectively when inlet dust concentration and pulse interval were increased by 1% implying that the effects of inlet dust concentration and pulse interval were less as compared with those changes of filtration velocity and pulse pressure. Therefore, the larger effect on the pressure drop the pulse jet bag filter was found in the order of filtration velocity(Vf), pulse pressure(Pp), inlet dust concentration(Ci), pulse interval(Pi). Also, the prediction result of filtration velocity, inlet dust concentration, pulse pressure, and pulse interval which showed the largest effect on the pressure drop indicated that stable operation can be executed with filtration velocity less than 1.5 m/min and inlet dust concentration less than 4 g/m3. However, it was regarded that pulse pressure and pulse interval need to be adjusted when inlet dust concentration is higher than 4 g/m3. When filtration velocity and pulse pressure were examined, operation was possible regardless of changes in pulse pressure if filtration velocity was at 1.5 m/min. If filtration velocity was increased to 2 m/min. operation would be possible only when pulse pressure was set at higher than 5.8 kgf/cm2. Also, the prediction result of pressure drop with filtration velocity and pulse interval showed that operation with pulse interval less than 50 sec. should be carried out under filtration velocity at 1.5 m/min. While, pulse interval should be set at lower than 11 sec. if filtration velocity was set at 2 m/min. Under the conditions of filtration velocity lower than 1 m/min and high pulse pressure higher than 7 kgf/cm2, though pressure drop would be less, in this case, economic feasibility would be low due to increased in installation and operation cost since scale of dust collection equipment becomes larger and life of filtration bag becomes shortened due to high pulse pressure.

본 논문에서는 초고압 특수 공간지를 활용한 다기능 포터블 카약을 제작하였다. 초고압 특수 공간지를 활용한 설계로 기존의 인플레터블 카약의 성능을 개선하여 하드쉘 카약의 성능에 근접하도록 제작하였다. 하드쉘 카약의 성능과 인플레터블 카약의 기능성 및 휴대성의 장점을 모두 가진 카약을 제작하였으며, 시제품 성능평가를 통해 기존 하드쉘 카약과의 성능을 비교하였다. 저항성능 검증결과는 목표속도 6knot에 대해 Hobie KONA kayak에 비해 Developed kayak이 12.33% 저항성능이 우수하였다. 경사시험결과는 동일배수량일 경우 Hobie KONA kayak 보다 Developed kayak의 무게중심이 선저를 기준으로 22.7% 낮게 분포하고 있으며, 이는 Hobie KONA kayak 보다 Developed kayak의 무게중심이 낮음으로 복원팔(GZ)에 대한 차이가 일정부분 감소된다. 선체 복원력에서는 Hobie KONA kayak이 약간 우수한 성능을 보여주었으나, 선회력과 저항계수면에서 Developed kayak이 더 우수한 결과를 보였다.

A pilot-scale pulse-jet bagfilter was designed, built and tested for the effects of four operating conditions (filtration velocity, inlet dust concentration, pulse pressure, and pulse interval time) on the total system pressure drop, using coke dust from a steel mill factory. Two models were used to predict the total pressure drop according to the operating conditions. These model parameters were estimated from the 180 experimental data points. The empirical model (EM) with filtration velocity, areal density, inlet dust concentration, pulse interval time and pulse pressure shows the best correlation coefficient (R=0.971) between experimental data and model predictions. The empirical model was used as it showed higher correlation coefficient (R=0.971) compared to that of the Multivariate linear regression(MLR) (R=0.961). The minimum pulse pressure predicted by empirical model (EM) was 5kg/㎠.