• Journal of Mechanical Science and Technology
• /
• v.17 no.12
• /
• pp.2042-2052
• /
• 2003

An experimental study was performed to investigate heat transfer characteristics of turbulent swirling flow in an axisymmetric annuli. The static pressure, the local flow temperature, and the wall temperature with decaying swirl were measured by using tangential inlet conditions and the friction factor and the local Nusselt number were calculated for Re=30000∼70000. The local Nusselt number was compared with that obtained from the Dittus-Boelter equation with swirl and without swirl. The results showed that the swirl enhances the heat transfer at the inlet and the outlet of the test tube.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.20 no.4
• /
• pp.1491-1500
• /
• 1996

Unstable performance deterioration was found on the performance curve of a small propeller fan with a back plate. To investigate this phenomenon and the effects of the back-plate on the performance of the fan, performance tests and flow measurement using 3-hole pitot tube were carried out. Measurements showed that when the flow rate is small, the radial flow dominates, and when the flow rate is large, the axial flow dominates. Performance characteristic of the propeller fan changes from radial to axial type as the flow rate increases. Unstable performance changes are the result of type change of the flow through the fan.

• 유체기계공업학회:학술대회논문집
• /
• 2004.12a
• /
• pp.160-165
• /
• 2004

MPA (Multi-Point Averaging) flow element is a new type of differential pressure (DP) flow-sensing device that was developed by Seojin Instech to improve the operating characteristics of the conventional Averaging Pilot Tube (APT) flow elements. Operating characteristics of a flowmeter in general can be defined in terms of measurement accuracy and range. Improvement of accuracy and expanding the range of flow measurement were the two main objectives of the development. To achieve these dual objectives several upstream and downstream pressure-sensing holes were placed in MPA flow element. During the course of the development it was found that certain arrangements of the pressure-sensing holes improved measurement accuracy but did not expand operating flow range of Averaging Pilot Tubes. Development tests were performed with water between Reynolds number of 50,000 and 1,000,000 in the four-inch test line at the Alden Research Laboratory, U.S.A. Purpose of this paper is to present the relationship between the various locations of the pressure-sensing holes and the performance characteristics of MPA flow element. Furthermore, the operating characteristics of the best performing MPA are compared with those of typical orifice and APT.

• Journal of the Society of Naval Architects of Korea
• /
• v.51 no.4
• /
• pp.311-320
• /
• 2014

Test uncertainty of a towed underwater Stereoscopic Particle Image Velocimetry (SPIV) system was assessed in a towing tank. To estimate the systematic error and random error of mean velocity and turbulence properties measurement, velocity field of uniform flow was measured. Total uncertainty of the axial component of mean velocity was 1.45% of the uniform flow speed and total uncertainty of turbulence properties was 3.03%. Besides, variation of particle displacement was applied to identify the change of error distribution. In results for variation of particle displacement, the error rapidly increases with particle movement under one pixel. In addition, a nominal wake of a model ship was measured and compared with existing experimental data by five-hole Pitot tubes, Pitot-static tube, and hot wire anemometer. For mean velocity, small local vortex was identified with high spatial resolution of SPIV, but has serious disagreement in local maxima of turbulence properties due to limited sampling rate.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.24 no.9
• /
• pp.1139-1147
• /
• 2000

This paper describes that the size of inactive zone can be directly applied to design multiblade fan/scroll system. From the experimental studies using a five hole pitot tube and smoke test, it is found that the size of inactive zone has linear relations with the mean velocity of impeller inlet and cut-off angle gives a great influences to the fan efficiency. For the practical design, a function related with geometric parameters(i.e. inner radius, cord length, cut-off clearance and cut-off angle) of fan/scroll system is suggested. By using these formulas, the size and distribution of inactive zone can be predicted without the measurements through the full domain, it can be possible to use them to know the efficiency improvement for new model designed.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.7 no.2
• /
• pp.217-224
• /
• 1995

The effects of duct inlet conditions on fan characteristics and upper wind velocity fields were investigated for two kinds of impellers. As the duct inlet condition, the relative positions between duct inlet and fan impeller and the size of baffle plate mounted on a duct inlet were selected. The 3-dimensional velocity components in flow fields were measured by a 5-holes pitot tube. From the results of measurements, it was found that the size of baffle plate scarecely effect on upper wind flow fields and characteristics of fan. It was also confirmed that the upper wind velocity distributions can be estimated by the potential flow field with large baffle plate at duct inlet.

• Journal of Advanced Marine Engineering and Technology
• /
• v.20 no.1
• /
• pp.1-12
• /
• 1996

The fully developed tubulent momentum and heat transfer induced by the square- ribbed roughness elements on both the inner and outer wall surfaces in the concentric annuli are studied analytically based on a modified turbulence model. Heat transfer coefficients for two conditions, i.e, a) inner wall heated as constant heat flux and outer wall insulated b) inner wall insulated and outer wall heated as constant heat flux, are investigated. The analytical results of the fluid flow are verified by experiment. The experiment is done with a pitot tube and a X-type hot wire anemometer to measure the time mean velocity profiles, zero shear stress positions, maximum velocity profiles and friction factors, and etc. The resulting momentum and heat transfer are discussed in terms of various parameters, such as the radius ratio, the relative roughness, the roughness density, Nusselt number and Prandtl number.

• Journal of the KSME
• /
• v.23 no.5
• /
• pp.344-348
• /
• 1983

유속의 최초 측정방법은 Torricelli (1608-1647)가 Bernoulli 방정식을 오리피스에 적용하여 유속 계산식 v =k.root.2gh를 유도하였고, 그 이후 역시 Bernoulli 방정식을 이용하여 Henri Pitot (1695-1771)는 정체점에 대한 이론을 고려하여 정체압을 측정하는 방법으로 가는관을 이용하여 Seine 강의 유속을 측정하는데 성공하므로서 이론적인 유속계산식 v =k.root.2gh는 가장 원시적인 피토우관(Pito-tube) 이나 오리피스에 의한 유속계산식이지만, 현재에 아무리 전기적인 정밀측정 방법과 레이저에 의한 측정방법이 개발되어도 결국 피토우관에 의한 측정값이나 압력측정치와의 교정(Calibration)이 선행되지 않으면 안되기 때문에, 피토우관에 의한 측정방법은 가장 원시적 이면서 가장 정확한 측정방법의 하나이다. 다만 피토우관에 의한 측정은 속도장내의 평균속도를 측정하게 되고 난류성분의 해석이 불가능하며, 그 측정이 일차원 유동에 국한된다는 것이 단점 으로 되어 있다. 이러한 점들을 보완할 수 있는 측정장치 들이 많이 개발되고 있으나 본 해설 에서는 공기유동의 경우 우리가 가장 많이 사용하고 있는 열선풍속계에 대하여 그 용법을 논하기 로 한다.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.4 no.5
• /
• pp.26-36
• /
• 1996

The fully developed turbulent momentum and heat transfer induced by the square-ribbed roughness elements on both the inner and outer wall surfaces in concentric annuli are studied analytically based on a modified turbulence model. The analytical results of the fuid flow are verified by experiment. The experiment is done with a pitot tube and a X-type hot wire anemometer to measure the time mean velocity profiles, zero shear stress positions, maximum velocity positions and friction factors, and etc. shown in Fig.1. The resulting momentum and heat transfer are discussed in terms of various parameters, such as the radius ratio, the relative roughness, the roughness density, Reynolds number, Nusselt bumber and Prand시 number. The study demonstrates that certain artificial roughness elements may be used to enhance heat transfer rates with advantage from the overall efficiency point of view by investigating turbulent flows and heat transfer in Fig.1.

• Journal of Mechanical Science and Technology
• /
• v.18 no.11
• /
• pp.2032-2041
• /
• 2004

Results from an experimental study of flow distribution in a close-coupled catalytic converter(CCC) are presented. The experiments were carried out with a flow measurement system specially designed for this study under steady and transient flow conditions. A pitot tube was a tool for measuring flow distribution at the exit of the first monolith. The flow distribution of the CCC was also measured by LDV system and flow visualization. Results from numerical analysis are also presented. Experimental results showed that the flow uniformity index decreases as flow Reynolds number increases. In steady flow conditions, the flow through each exhaust pipe made some flow concentrations on a specific region of the CCC inlet. The transient test results showed that the flow through each exhaust pipe in the engine firing order, interacted with each other to ensure that the flow distribution was uniform. The results of numerical analysis were qualitatively accepted with experimental results. They supported and helped explain the flow in the entry region of CCC.