• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.4
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• pp.377-385
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• 2013

To identify the effects of an outflow area on pool boiling heat transfer in a vertical annulus, three different flow restrictors were studied experimentally. For the test, a heated tube of smooth stainless steel and water at atmospheric pressure were used. Both annuli with open and closed bottoms were considered. To validate the effects of the outflow area on the heat transfer, the results of the annulus with the restrictor were compared with the data for the plain annulus without the restrictor. The reduction of the outflow area ultimately results in a decrease in the heat transfer. As the outflow area is very small, a slight increase in heat transfer is also observed. The major cause of this tendency is explained as the difference in the intensity of liquid agitation cause by the movement of coalesced bubbles. It is identified that the convective flow, pulsating flow, and evaporative mechanism are considered as the important mechanisms.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2003.11a
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• pp.90-95
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• 2003

Chemical management of annulus gas system is carried out for the purpose of ensuring the safety and reliability of the system via securing the integrity of the system, detecting the D$_2$O in-leakage of coolant and/or moderator, and reducing the radiation dose. Since the quality of CO_2$ gas, which is used as a filling gas for annulus gas system at CANDU plants, has a propound effect on the integrity of the system material and the radiation dose, CO_2$ gas of high quality is needed. If the quality of CO_2$ gas does not meet the specification, it may give rise to undesirable effect not only on the annulus gas system, but also on the environment due to the production of radioactive nuclei. Therefore, it is very important to check the impurities of CO_2$ gas. Based on this background, the inventories of C-14 and Ar-41 in CO_2$ gas that is supplied as annulus gas were estimated using the data on concentrations of the impurities of $CO_2$ such as C, N_2$ and Ar. The results of this study is expect to give useful information on optimization of CO_2$ impurities maintenance and management of gaseous radioactive wastes produced at CANDU plants.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.1 no.4
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• pp.305-312
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• 1989

Laminal natural convection heat transfer in the annulus between isothermal horizontal non-circular cylinders is studied by solving the Navier-Stokes and energy equation using an elliptic numerical procedure. Results are obtained to determine the effects of the diameter ratio($D_o/D_i$) and Rayleigh number on heat transfer. The diameter ratio is varied from 1.5 to 13.0 at Pr=0.7, H/L=1.5 and $10^3{\leqslant}Ra_L{\leqslant}4{\times}10^4$. It is found that the diameter ratio causes a more significant on the local heat transfer coefficient of lower semi-circular cylinder and plate than upper semi-circular cylinder. The mean Nusselt number increases as the diameter ratio and Rayleigh number increase, and is higher than that of the circular annulus with a same wetted perimeter.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.4
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• pp.423-430
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• 1998

Single phase heat transfer coefficients were measured for turbulent water flow in a micro-fin tube by using Wilson plot technique. An experiment for counterflow heat exchange between the micro-fin tube and its outer annulus passage was performed. The annulus side heat transfer resistance was varied and the overall heat transfer coefficients were measured. The single-phase heat transfer coefficients in a micro-fin tube were obtained by Wilson plot technique. Nusselt numbers based on the real heat transfer area and the nominal area were about 35% and 50% larger than those for smooth tube respectively Also, single-phase heat transfer correlations based on real heat transfer area and nominal area have been proposed for a micro-fin tube.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.4
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• pp.467-474
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• 2004

A large-eddy simulation is performed for turbulent flow in a concentric annulus with the inner wall rotation at Re$\sub$Dh/=8900 for three rotation rates N=0.2145, 0.429 and 0.858. Main emphasis is placed on the inner wall rotation effect on near-wall turbulent structures. Near-wall turbulent structures close to the inner wall are scrutinized by computing the lower-order statistics. The anisotropy invariant map for the Reynolds stress tensor and the invariant function are illustrated to reveal the altered anisotropy in turbulent structure. Probability density functions of the splat/anti-splat process are explored to develop a sufficiently complete picture of the contributions of the flow events to turbulent production. The present numerical results show that the altered turbulent structures may be attributed to the centrifugal instability, which leads to the augmentation of sweep and ejection events.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.2
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• pp.654-660
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• 1991

Natural convection heat transfer in a horizontal annulus from an inner tube with two vertical fins has been studied for the effects of dimensionless fin length and Rayleigh number. The maximum local Nusselt number of inner tube was obtained at .theta. = 145.deg. and that of outer cylinder at .theta. = 0.deg. for the case of $l_{F}$=0.3 Local Nusselt number distributions for the lower fins show higher values than that of the upper fins. The mean Nusselt number of inner tube was increased with the values of dimensionless fin length. The mean Nusselt number can be represented in an exponential function of Grashof number at various fin lengths. As compared with experimental and numerical results, isotherms and local Nusselt number show good agreement.t.

• Journal of KSNVE
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• v.10 no.3
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• pp.536-550
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• 2000

Inversitgated in this study are the modal characteristics of the eccentric cylindrical shells with fluid-filled annulus. Theoretical method is developed to find the natural frequencies of the shell using the finite Fourier expansion and their results are compared with those of finite element method to verify the validation of the method developed. The effect of eccentricity on the modal characteristics of the shells is investigated using a finite element modeling.

• Journal of Chest Surgery
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• v.12 no.1
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• pp.56-60
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• 1979

Replacement of the aortic valve in a normal or large aortic root can be accomplished with ease and safety in most instances. The presence of a narrowed aortic annulus remains a problem in that the replaced smaller prosthetic valve has a significant resting pressure gradient across the orifice. This narrowing causes not only technical difficulties, but also increased mortality and post-op. complication. Therefore this problem deserves special attention. This report presents our experience with a case of a small aortic root caused by rheumatic heart disease [AI and MS]. This is the method of enlargement of the aortic annulus with a woven Dacron patch and replacement of a larger prosthetic aortic valve combined with mitral valve replacement.

• Journal of Chest Surgery
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• v.21 no.6
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• pp.984-989
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• 1988

2-D echocardiographic examination of the aortic root diameter was known to be useful in the selection of the size of the prosthetic valve. Valve-patient mismatch was occasionally a serious problem after valve replacement, especially in aortic valve disease. Preoperative knowledge of the patient`s valve annulus size is therefore of great importance in the surgical management of these patients. So the relationship between preoperative 2-D echocardiographic diameter of the annulus size and replaced prosthetic valve were evaluated. 13 patients were analyzed in this study. 2-D echocardiographic measurements of aortic annulus diameter, as determined from the parasternal long axis view and apical four chamber view, demonstrated a high correlation with actual prosthetic valve size implanted at surgery[r=0.86, p< 0.001, SEE=1.08].

• Journal of Chest Surgery
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• v.20 no.1
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• pp.60-64
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• 1987

We compared between prosthetic aortic valve size and aortic annulus size in supravalvular aortic cineangiogram in 30` RAO view postoperatively. Retrospectively, supraaortic cineangiogram of 27 patients among the patients underwent aortic valve replacement only or double valve replacement from April, 1986 to January, 1987 was examined and measured the aortic annulus size. In comparing the two values, the cases within 1mm is 22, and the cases within 2mm is 25, correlation coefficient yield r = 0.92. In two cases, the difference between two values is within 3mm We concluded that to prevent the complication from mismatching the prosthetic aortic valve size to patient`s annulus size [e.g. left ventricular failure, hemolysis, limited exercise tolerance], prediction of the prosthetic valve size preoperatively by use of cineangiogram is useful.