• 설비공학논문집
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• 제10권4호
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• pp.389-397
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• 1998

A loop duct system is often found in a VAV-HVAC(variable air volume heating, ventilating and air conditioning) design. It is known that the simple T-method is not be applicable to the loop duct system and cannot be used to calculate the flow rate and the pressure drop at each duct section of the loop duct system. In this paper, the extended T-method has been developed and it is found to be applicable to the loop duct system to which the simple T-method cannot be applied. The validity of the extended T-method has been verified by using to solve for a simple, ideal loop duct system for which there exists analytical solution. In addition, the extended T-method is employed to compute the loop duct system of a real building with an area of 380$m^2$. The results show that the computed flow rate at the exit differs from the designed flow rate by a range of -13.6~43.5 %. Consequently, three design factors must be adjusted in order that the flow rate may be balanced. These include the duct sizes, in terms of their lengths and diameters, the sub-duct locations and the positioning of damper which is found upstream of the exit duct.

• 한국가시화정보학회지
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• 제8권2호
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• pp.23-30
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• 2010

Regarding the aircrafts with a rotor blade system, the miniaturization of them is limited due to the rotor blade length and the tail rotor system. To miniaturize an aircraft, an equipment is required that increases thrust and also shortens the length of the rotor blade. The present study will conduct the flow analysis for miniaturizing the aircraft by applying a duct to the coaxial rotor blade system without tail rotor. First, the verification on the calculated results was conducted through the computational flow analysis on the coaxial rotor blade system without a duct. Then, the flow analysis for the coaxial rotor blade systems was performed including Ka-60 duct, Single duct, Twin duct, and Double duct, respectively. From the numerical results, the thrust coefficient appeared higher with the duct than without a duct for the coaxial rotor blade system. Especially, in the case of Double duct, the thrust was improved due to the increase of incoming flow and the extension of the wake area. These results will be used as the basic concepts for miniaturizing the aircraft with the rotor blade system. The flow analysis on the coaxial rotor blade system including the fuselage remains as a future work.

• 한국자동차공학회논문집
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• 제16권4호
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• pp.88-96
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• 2008

Effects of the duct inlet guide vane on the flowrate distribution characteristics of the defroster nozzle exit in a defrost duct system were investigated experimentally to design the optimum heating, ventilation and air conditioning (HVAC) system applied in an automotive compartment. A 3-dimensional hot-wire anemometer system was used to measure the velocity field in the vicinity of the defroster nozzle jet flow and the velocity distributions near the windshield interior surface. At first, two cases of with- and without-duct inlet guide vanes were considered as the test condition, and then three cases of the duct inlet guide vane were tested to determine the optimum guide vane shape and their positions. The arrangement of the duct inlet guide vanes has an effect on the improved flowrate distribution at the defroster nozzle exit and near the windshield interior surface. However, the application of the lots of guide vane to control the flow direction leads to increase the flow resistance, resulting in the decreased flowrate issuing from the defroster nozzle. The shape of the duct inlet guide vane affects not only the flowrate distribution between the driver side and the assistant driver side but also the reduction of the flow resistance in the defrost duct system.

• 설비공학논문집
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• 제12권2호
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• pp.120-130
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• 2000

A flow uniformity in a duct cooler of duct system of FGD(Flue Gas Desulfurization) linking a reheater and a absorber has been investigated in the present study. For this purpose, the flow characteristics according to the geometry of a vertical and horizontal vane in a curved duct of the duct system has been examined with the aid of a numerical simulation. The results indicate that the vertical vane with a little deflection toward a recirculation region makes the flow distribution in the duct cooler more uniform than that without deflection, and horizontal vane does not effect the change of the flow distribution for an angle of inclination. The mean flow uniform factor shows its maximum for duct system without the vane(case NP) and its minimum for the vertical vane with a little deflection(case P-0.8-0) .

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2003년도 추계 학술대회논문집
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• pp.200-205
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• 2003

The Canard rotor/wing (CRW) aircraft concepts offer great potential for application by allowing the use of a common propulsion system for high-speed cruise and low-speed powered lift. Using the rotor for lift in both flight modes increases its utility. In the hovering mode, the exhausted gas from an gas turbine engine is accelerated through the duct system and it provides the tipjet power for rotor system enough to lift the aircraft. In the cruise mode, the rotor is fixed and the exhausted gas is extracted through the main nozzle, such that the aircraft is able to flight with high speed. The duct system was designed using 1-D fanno line flow theory and empirical data. However, the empirical data of the pressure loss coefficient for various bending and dividing ducts were not enough to design our duct system adaptively. Therefore, using 3-D CFD analysis we obtained the pressure loss coefficient for our duct models and chose the appropriate bending or diving duct type. In this paper, we used the CFD-ACE+ software package for the CFD analysis and the modeling of duct system. Through the 3-D CFD analysis, we investigated also the pressure loss and the velocity distributions of the designed whole duct system as well as the blade duct. Comparing the 3-D CFD result with 1-D analysis result, we lessened the uncertainty of the designed duct system and speculated the problem that was not concerned in design state.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 추계학술대회논문집
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• pp.875-879
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• 2006

Noise reduction has become a major issue of the duct air-conditioners. This paper describes the reduction of noise and vibration of rotational slim duct system. The design of slim duct system is the most important point of noise reduction in terms of the motor of 2f line noise, resonance noise between forced frequency and natural frequency of Sirocco fan, unbalance noise of motor axis and the noise induced refrigerant. The noise of duct system is mainly measured from diffuser and bottom of duct. The optimal design was implemented after measuring the effect of noise and vibration in each part which is composed of duct system. In this paper, experimental results show that the main elements in air-conditioner duct design. These elements are anti-vibration rubber of motor, axis length of motor, rubber coupler, materials of sirocco fan and control method of motor which are the most vital factors in reducing noise.

• 생물환경조절학회지
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• 제13권3호
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• pp.162-166
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• 2004

동절기 시설내 온도분포를 균일하게 하기 위하여 온풍난방기용 이중덕트를 개발하고자 본 연구를 수행한 결과 관행 온풍덕트의 각 지점간 토출구 송풍온도 차이가 13 ～ $14^{\circ}C$인데 비하여 개선형 덕트인 이중덕트의 토출구 송풍온도 차이가 3 ～ $4^{\circ}C$로 나타나 각 지점간의 온도 불균형이 크게 개선되었으며 이중덕트의 각지점간의 생육정도도 관행덕트에 비해 크게 향상 된 것으로 나타났다. 수량에 있어서도 관행덕트를 사용한 재배시설에서 10a당 3,924kg에 비하여 이중덕트를 사용한 재배가 4,616kg으로 약 17%가 증수되었다. 그리고 반촉성 재배기간 동안 난방에 소요된 연료소모량은 관행덕트가 3,724ι/10a인데 비하여 이중덕트가 3,233ι 13%의 연료절감효과가 있다.

• 한국유체기계학회 논문집
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• 제16권1호
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• pp.40-46
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• 2013

Recently, the duct system with a cross flow fan was used to improve the ventilation in various industrial fields. For the efficient ventilation, it is necessary to design the duct system based on the flow characteristics around the cross flow fan. In the present study, the flow characteristics around a cross flow fan in the ventilation duct were predicted by using the moving mesh and sliding interface techniques for the rotation of blades. To design the duct system with the high performance of ventilation, the CFD simulations were repeated with the revised duct model based on the DOE. With the numerical results of flow rate through the ventilation duct with various geometric parameters, the optimized geometry of ventilation duct to maximize the flow rate was obtained by using the Kriging approximation method. From the performance curves of cross flow fan in the original and optimized models of ventilation duct, it was observed that the flow rate through the optimized model is about 16 percent larger than that through the original model.

• Nuclear Engineering and Technology
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• 제33권3호
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• pp.298-306
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• 2001

As fuel burnup proceeds, thermal gradients, differential swelling, and inter-assembly loading may induce assembly duct bowing. Since duct bowing affects the reactivity, such as long or short term power-reactivity-decrement variations, handling problem, caused by top end deflection of the bowed assembly duct, and the integrity of the assembly duct itself. Assembly duct bowing were first observed at EBR-ll in 1965, and then several designs of assembly ducts and core restraint system were used to accommodate this problem. In this study, NUBOW-2D KMOD was used to analyze the bowing behavior of the assembly duct under the KALIMER(Korea Advanced Liquid MEtal Reactor) core restraint system conditions. The mechanical behavior of assembly ducts related to several design parameters are evaluated. ACLP(Above Core Load Pad) positions, the gap distance between the ducts, and the gap distance between the duct and restraint ring were selected as the sensitivity parameter for the evaluation of duct deflection.

• KIEAE Journal
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• 제9권4호
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• pp.17-22
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• 2009

It is common to design the duct branches where to supply the required air flow for individual room in residential apartment house. However it is difficult to adjust the air volume adequately in small air duct branches in residential ventilation system. The purpose of this study is to figure out the performance of Multidrop chamber coupling system for the residential ventilation system. The experiments were designed to simulate apartment of $84m^2$ and established multidrop chamber duct and general duct on the ceiling of the apartment. Distribution performance of air supply rate were evaluated in this experiments. As a result, distribution performance of air supply rate in the general duct is different from designed air supply rate by about 35% ~ 50% and about 10% in the multidrop chamber system. In additional the sound insulation performance of the multidrop chamber system decreased about 20% compared with general duct system. Therefore, the multidrop chamber system is considered to satisfy proper air supply rate of each room and to improve the sound insulation performance in apartment Houses.