• The Journal of the Korea Contents Association
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• v.12 no.7
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• pp.445-452
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• 2012

This study is used to analyze the distribution of resistance factors and the relationships of flow resistance with the field measurements which consist of the total 2,604 rivers for 1,865 bed material in natural channels and 739 vegetation in vegetated channels. Resistance factor relationships and distribution range of Manning roughness coefficients and Darcy-Weisbach friction coefficients by the regression analysis are derived from the power law form as a function of flow discharge and friction slope with bed materials and vegetations in natural and vegetated rivers, respectively.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.4
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• pp.229-238
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• 2017

This study started to deduce a permeability relationship that can consider the geometric features of various porous media under different flow regimes. With reference to the previous works of Kozeny and Carman, the conventional Darcy-Weisbach relation (Darcy's friction flow equation) was reviewed and expanded for porous flow analysis. Based on the capillary model, this relation was transformed to the friction equivalent permeability (FEP) definition. The validity of the FEP definition was confirmed by means of comparison with the Kozeny-Carman equation. Hereby, it was shown that the FEP definition is the generalized form of the Kozeny-Carman equation, which is confined to laminar flow through a circular capillary. In conclusion, the FEP definition as a new permeability estimation method was successfully developed by expanding the Darcy-Weisbach relation for porous flow analyses.

• The Journal of the Korea Contents Association
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• v.16 no.4
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• pp.614-623
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• 2016

Grid(pipe network) design is an important element of Smart Water Grid, which essential to estimate hydraulic parameters such as the pressure, friction factor, friction velocity, head loss and energy slope. Especially, friction velocity in a grid is an important factor in conjunction with energy gradient, friction coefficient, pressure and head loss. However, accurate estimation friction head loss, friction velocity and friction factor are very difficult. The empirical friction factor is still estimated by using theory and equation which were developed one hundred years ago. Therefore, in this paper, new equation from maximum velocity and friction velocity is developed by using integration relationship between Darcy-Weisbach's friction head loss equation and Schlichting equation and regression analysis. To prove the developed equation, smooth pipe data areis used. Proposed equation shows high accuracy compared to observed data. Study results are expected to be used in stability improvements and design in a grid.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.3
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• pp.254-260
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• 2002

There have been many studies for the flow through internally finned tube, since the heat exchangers with fin device derive much attention in heat transfer enhance cent. In this study, analysis of laminar flow through the circular tube with longitudinal fins are investigated. The height and the number of fins are arbitrary. The flow field is assumed to be laminar and conformal mapping is used to obtain analytic solution. From the analytic solution, equi-velocity lines are shown, and the flow rate through the finned tube is calculated for various fin heights and numbers of fins. Darcy friction factor for this finned tube and shear stress distributions on the wall and fin are also considered.

• International Journal of Air-Conditioning and Refrigeration
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• v.15 no.1
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• pp.17-24
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• 2007

An experimental investigation was carried out for 4 different types of the aluminum foam heat sinks which were inserted into the annulus. The purpose of this study is to examine the feasibility of a heat sink with high performance forced convective water cooling in the annulus. The local wall temperature distribution, inlet and outlet pressures and temperatures, and heat transfer coefficients were measured for heat flux of 13.6, 18.9, 25.1, 31.4 $kW/m^2$ and Reynolds number ranged from 120 to 9,000. Experimental results show that the departure from the Darcy's law is evident from the pressure loss and the friction factor is much higher while the significant enhancement in Nusselt number is obtained, and average Nusselt number of aluminum foam with high pore density is much higher than that of aluminum foam with low pore density. Correlations for the friction factor is proposed and used for design of thermal applications.

• Journal of Energy Engineering
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• v.15 no.1 s.45
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• pp.60-66
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• 2006

An experimental investigation on the flow and convective heat transfer characteristics has been carried out far aluminum foam heat sink inserted into the annulus to examine the feasibility as a heat sink. Two aluminum foams or different permeability were selected to provide the friction factor and heat transfer correlations as function of Darcy, Reynolds and Prandtl number. Experimental results show that the friction factor is higher than clear annulus without aluminum foam, while $6\sim10$ times augmentation in Nusselt number is obtained. This technique can be used for the compactness of the heat exchanger.

• Journal of Korea Water Resources Association
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• v.44 no.1
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• pp.9-22
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• 2011

A 1D numerical model for steady flow, based on the energy equation, was developed for natural rivers with emergent vegetations on floodplains and banks. The friction slope was determined by the friction law of Darcy-Weisbach. The composite friction factor of the each cross section was calculated by considering bottom roughness of the main channel and the floodplains, the flow resistance of vegetations, the apparent shear stress and the flow resistance caused by the momentum transfer between vegetated areas and non-vegetated areas. The interface friction factor caused by flow interaction was calculated by empirical formulas of Mertens and Nuding. In order to verify the accuracy of the suggested model, water surface elevations were calculated by using imaginary compound channels and the results of calculations were compared with that of the HEC-RAS. The sensitivity analysis was performed to confirm changed friction factors by vegetations density etc. The suggested model was applied to the reach of the Enz River in Germany, and estimated water surface elevations of the Enz River were compared with measured water surface elevations. This model could acceptably compute not only water surface elevations with low discharge but also that with high discharge. So, the suggested model in this study verified the applicability in natural rivers with emergent vegetations.

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.2
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• pp.244-251
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• 2009

Porous media have especially large surface area per volume, which contain complex fluid passage. If porous media can be applied to cool a CPU or an electronic device with large heat dissipation, it could result in heat transfer enhancement due to the enlargement of the heat transfer area and the flow disturbance. This study is aimed to identify the heat transfer and pressure drop characteristics of high-porosity metal foams in a horizontal channel. Experiment is performed with the various heat flux, velocity and pore density conditions. Permeabilities, which is deduced from Non-Darcy flow model, become lower with increasing pore density. Nusselt number also decreases with higher pore density. High pore density with same porosity case shows higher pressure loss due to the increase of surface area per unit volume. The fiction factor decreases rapidly with increase of Reynolds number in Darcy flow region. However, it converges to a constant value of the Ergun coefficient in Non-Darcy flow region.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.8 no.1
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• pp.88-98
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• 1996

The present study is concerned with the flow friction and heat transfer characteristics of the combination of various regenerator materials, using the different Darcy number and porosity, which is filled uniformly and partially in a tube under oscillating flow condition. The poros medium is adopted as Brinkmann-Forschheimer extended Darcy model. Numerical results are obtained or the flow and temperature fields and described the effect of the combination of various regenerator materials and Womersley number on the pressure drop, the heat transfer and the regenerator efficiency. The results obtained indicate that not only heat transfer between the tube wall and oscillating flow but also the pressure drop at both ends of the regenerator are increased, while the regenerator efficiency is decreased in the increase of womersley number. It is also found that the friction factor is increased as Reynolds number is increased. The comparison between the combination of the various regenerator materials and the homogeneous regenerator material shows that the regenerator efficiency can be enhanced with the proper combination of various regenerator materials even though the averaged porosity of the regenerator is same.

• Proceedings of the Korea Water Resources Association Conference
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• 2007.05a
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• pp.438-443
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• 2007

개수로 흐름에 대한 연구는 1700년대 중엽 Chezy에 의해 이론적인 기초를 다졌으며, 광범위하고 조직적인 관측연구는 Darcy(1803-1858)에 의해 약 150년 전에 폭 2m, 길이 600m에 이르는 수로에서 실험관측을 수행하고자 시도하였다. Darcy의 동료이자 후계자인 Bazin은 제한된 조건의 현장관측뿐 아니라 다양한 조건의 수로를 제작하여 실험관측을 수행하였으며 그의 실험자료는 Bazin 자신 뿐만 아니라 Manning이나 Ganguillet와 Kutter 등 여러 연구자들의 경험식 개발에도 이용되었다. Nikuradse(1933)의 균일조도 원형관수로 실험결과로부터 관로 흐름은 층류, 천이층류, 완난류, 천이난류, 전난류 등 다섯 종류의 흐름특성을 가지고 있음을 확인하였고 Bazin(1829-1917)과 varwick(1945)의 실험결과로부터 개수로 흐름에서도 관로 흐름과 마찬가지로 층류, 천이층류, 완난류, 천이난류, 전난류 등 다섯가지의 흐름특성이 존재함을 알 수 있다. 본 연구에서는 기존의 지수형 마찰계수 산정식에서 단순히 조고만의 함수였던 ${\alpha}$에 물의 기본적인 성질인 표면장력, 점성력, 밀도와 자연 하천의 경사, 수심, 수면, 폭, 조고의 영향을 고려한 수심에 관한 무차원수 $Y_h$, 수면 폭에 관한 무차원수 $Y_b$, 조고에 관한 무차원수 $Y_k$를 도입하였다. 따라서 개수로 흐름 해석에 있어서 기존의 마찰계수 산정치보다 여러 영향을 반영하여 정확한 값을 산정할 수 있을 것으로 판단된다.