• 동력기계공학회지
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• 제5권3호
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• pp.31-37
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• 2001

A study to obtain the enhancement of turbulence at low Reynolds number is carried out by adding ultrasonic force into the jet flow field of a coaxial circular pipe which can afford the sufficient data of flow characteristics with the shear flow and turbulence flow in spite of its simple shape. A coaxial circular flow field is made vertically in a large and transparent acryl tank. The time mean velocity vector, distribution, kinetic energy and turbulence intensity formed in the complex flow field of turbulence enhancement are investigated, observed and discussed at Reynolds number of 2,000, 3,000 and 5,000 by using PIV measurement, in results, the validity of ultrasonic to obtain the enhancement of turbulence is certified.

• Journal of Advanced Marine Engineering and Technology
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• 제29권1호
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• pp.25-33
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• 2005

When a circular tube with uniform heat generation within the wall was placed in a cross flow, heat flows by conduction in the circumferential direction due to the asymmetric nature of the fluid flow around the perimeter of the circular tube The circumferential heat flow affects the wall temperature distribution to such an extent that. in some cases, significantly different results may be obtained for geometrically similar surfaces. In the present investigation, the effect of circumferential wall heat conduction is investigated for forced convection around circular tube in cross flow of air and water Two-dimensional temperature distribution $T_w(r,{\theta})$ is calculated through the numerical analysis. The difference between one-dimensional and two-dimensional solutions is demonstrated on the graph of local heat transfer coefficients. It is observed that the effect of working fluid is very remarkable.

• 설비공학논문집
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• 제16권6호
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• pp.546-555
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• 2004

With circular tube heated directly or indirectly placed in a cross flow, heat flows circumferentially by conduction due to the asymmetric nature of the fluid flow around the perimeter of the circular tube. The circumferential heat flow affects the wall temperature distribution to such an extent that in some cases. The effects of circumferential wall heat conduction on local convective heat transfer is investigated. The wall heat conduction parameter which can be deduced from the governing energy equation should be used to express the effect of circumferential heat conduction. Two-dimensional temperature distribution is presented through the numerical analysis. The comparison of one-dimensional and two-dimensional solutions is demonstrated on graph of local Nusselt numbers.

• 대한기계학회논문집B
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• 제28권8호
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• pp.989-995
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• 2004

This paper presents a semi-empirical model to predict the frost growth formed on the cold cylinder surface. The model is composed of the correlations for frost properties including the various frosting parameters and local heat transfer coefficient. The effects of varying the correlations for local heat transfer coefficient on the frost growth are examined to establish the model. The numerical results are compared with experimental data obtained by the previous researchers. The results agree well with the experimental data within a maximum error of $13\%$. As the results, the frost thickness decreases with changing angular position from front stagnation to separation point. Also, the effects of air velocity on the frost growth are negligible, as compared to the other frosting parameters.

• 대한기계학회논문집
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• 제5권2호
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• pp.131-138
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• 1981

The effect of axial stress on the plastic deformation of rigid-perfectly plastic cylindrical tube under the impulsive band pressure is investigated. It is assumed that the tube is constructed with the material of Tresca's yield criterion. A closed from sloution is obtained for a rectangular pulse shape of uniform band pressure by using the circumscribed yield surface. The analysis shows that the effect ot exial stress is negligible when the dimensionless axial stress(n$\sub$x/= N$\sub$x/.delta.$\sub$y/H) is less than 0.2 or the dimensionless whdth of band pressure(.xi.=C/.root.RH) is greater than 2, but the effect of axial stress is of considerable importance when the axial stress is greater than 0.3 and the width of band pressure is less than 1.

• 대한기계학회논문집
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• 제6권2호
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• pp.147-159
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• 1982

내부에 정방형, 외부에 원형인 두 정온동심수평관으로 이루어진 폐쇄공간에서 열부력으로 야기된 대류열전달 현상을 연구하였다. 주어진 비정규적 형상에서의 층류 정상 Boussinesq 유동을 해 석하기 위하여, 지구중력방향에 대하여 가능한 두 개의 대칭형 위치에 관하여, Galerkin 유한요 소법을 사용하였다. 이론의 결과를 확증하기 위하여 실험적으로도 온도측정과 유선의 가시화를 수행하였다. 정방형내관의 직각인 선단은 국소 및 총체열전달에 있어서 소극적인 역할을 하지만, 이들로 인한 경계층 유동의 박리는 발생하지 아니함을 보였다. 이 내관의 상부 수평면상에서는 유동속도와 온도구배가 낮기는 하나 확연한 대칭형의 열상승류(Plume)가 가능하였다. 내관의 벽면들이 지구중력방향에 관하여 .+-.45.deg.의 각을 이룰 경우 과류의 중심부가, Rayleigh수가 6.5*$10^{4}$보다 작을 때는 4개, 이보다 클때는 2개가 폐쇄공간 안에서 발생하였다.

• 한국자동차공학회논문집
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• 제11권6호
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• pp.44-50
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• 2003

Cooled EGR is an effective method for the reduction of NOx from a diesel engine and an EGR Cooler is the key component of the system. High efficiency, low pressure loss and compactness are required for the EGR Cooler. To meet these requirements, new geometric tube must be developed. In this paper, a full size EGR cooler test bench has been developed to validate the CFD flow and heat transfer models. Fluid temperature and pressure drop measurements are provided. fillet temperature is $200^{\circ}C$ and $300^{\circ}C$, and flow rates vary from 0.008 kg/sec to 0.019 kg/sec. The gas flow and heat transfer in a single tube cooler have been studied using computational fluid dynamics(CFD). Analysis has been carried out in a single tube with a plain tube and six spirally enhanced tubes of varying pitch to depth ratio(p/e).

• 대한기계학회논문집
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• 제17권8호
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• pp.2079-2087
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• 1993

The effects of subcooling and natural convection are studied numerically on the melting process of an initially subcooled phase-change medium filled inside a horizontal circular cylinder. It is postulated that melting continues with the tube wall kept at a constant temperature and with the unmelted solid core fixed. Primary emphasis is placed on the evolution of interface morphology, the local/overall heat transfer rate at the tube wall and at the interface, and the structure of natural convection. The numerical results are mainly presented in terms of the Rayleigh and subcooling numbers. As the degree of subcooling intensifies, the melting rate and the movement of the interface are impeded but the interfaces are of similar shape with the passage of time. The heat transfer characteristics are found to be mostly governed by the formation pattern of natural convection in the liquid phase. Good agreement with available experimental data is found.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2002년도 춘계학술대회 논문집
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• pp.220-224
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• 2002

In this paper, flow in the wake region of a butterfly valve is studied numerically and experimentally. The disk angle of the valve is fixed as $30^{\circ}$ and the free stream velocity as 0.13m/s in the experiment. Numerical analysis is performed in similitude of the experiment. The standard LES model is used to represent the turbulence effect in the commercial code Fluent 5.5. It is shown that the numerical result is similar to the experimental result for the wake flow of a butterfly-type valve.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2012년도 제45회 KOSCO SYMPOSIUM 초록집
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• pp.115-118
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• 2012

The configurations of the heat exchanger of the boiler can be determined from the trade-off between the heat transfer area which is related to the capital cost and the pressure drop which is related to operating cost. In this study, 3.5 ton/hr small size marine boiler having concentric annuli tubes is the design boiler. To determine the optimizing point, according to diameter, number, length of tube, heat transfer, pressure drop, operating cost and capital cost have been calculated. Also, when the fin tube is replaced by the bare tube design parameters changed have been calculated.