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A leak-detection method has been developed by measuring the pressure variation between the inner and outer heattransfer tubes of a double-wall tube steam generator. An experiment was carried out to measure the leak rate in the gap between two surfaces pressed with a hydraulic press in order to simulate the phenomena, and a correlation was determined for the leak rate in a micro gap. However, in the correlation, the gap width and friction coefficient were coupled with the surface roughness, which affects the two parameters. The two parameters were separated using a surface-contact model to develop a correlation for the friction coefficient. The correlation was compared with the existing correlations used for crack analysis. Although the applied ranges of Reynolds numbers were different, the developed correlation for Reynolds numbers of 0.1.0.35 showed similar tendencies to existing correlations used for higher Reynolds numbers.

A steam generator poses many difficulties during the development of a sodium-cooled fast reactor because of the sodium-water-reaction problems. Until now, several types of steam generators have been developed, but the specifications of these generators differed in each country. Moreover, even if a country had developed a steam generator, it was not used in the subsequent reactor because the current techniques were not stabilized to select the proper steam generator. As a common development, the Benson steam cycle with few welding locations and high economical efficiency may be adopted. Moreover, the design is dwelled on the convenience of inspection, detection, control, and maintenance for the wear caused by sodiumwater reactions. The specifications of the designed steam generators were reviewed and the current technical problems for steam generators were analyzed. Concepts were proposed to overcome the current technical problems for steam generators.

The possibility of a sodium-water reaction occurring in a conventional single-wall-tube steam generator in an SFR is a major problem. To improve the reliability of a steam generator, a double-wall-tube steam generator that can reduce the possibility of the occurrence of a sodium-water reaction is being developed. Current developments are focusing on improving the heat-transfer capability of a double-wall tube; further, the development of a leak-detection method to detect the occurrence of a sodium-water reaction during the reactor operation is also underway. In this study, new concepts, which will solve the above-mentioned problems, have been developed. Accordingly, a double-wall tube has been designed, fabricated, and mechanically tested for the purpose.

In order to investigate the characteristics of an electromagnetic flowmeter in a liquid metal two-phase flow, AC electromagnetic flowmeters were designed and manufactured. Two-phase flow experiments, encompassing bubbly to slug flow regimes, were realized with a water-air mixture and a liquid sodium-nitrogen mixture, respectively. The relation ∆UTP=∆USP/(1−α), between the flow induced electromotive force (e.m.f.) of a single-phase flow and that of a two-phase flow, was verified by the measured e.m.f.s and the void fraction α for a bubbly flow regime. Whereas there is no difference in the shape of the flow induced e.m.f. between single-phase and bubbly flow, the signal amplitude of the bubbly flow is greater than that of the single-phase flow under the same water or liquid sodium flow rate, since the real liquid velocity is higher than that of the single-phase flow. In the case of a slug flow, the phase and the amplitude of the flowmeter output changed drastically when a slug bubble passed through the flowmeter. Therefore, the electromagnetic flowmeter shows good potential as a useful device for identifying the flow regimes. The void fraction in a bubbly flow can be measured using two electromagnetic flowmeters.

Based on the previous study for the water-air mixture, the characteristics of AC electromagnetic flowmeter were investigated in the liquid metal two-phase flow. Two-phase flow experiments, encompassing bubbly to slug flow regimes, were conducted with the liquid sodium–nitrogen mixture. The simple relation Δ U TP =Δ U SP (1− α ) , relating flowmeter signal between single-phase flow and two-phase flow, was verified with measurements of the potential differences and the void fraction α for a bubbly flow regime in water-air loop. Whereas there was no difference in the shape of the raw signal between single-phase flow and bubbly flow, the signal amplitude of bubbly flow was greater than that of single-phase flow under the same liquid flow (sodium or water) rates, since the passage area of the liquid flow was reduced. In the case of slug flow, the phase and the amplitude of the flowmeter output showed a change in the flow characteristics around each slug bubble and the position of a slug bubble itself. Therefore, the electromagnetic flowmeter shows a good potential as a useful device for identifying the flow regimes. The void fraction can be simply measured with two electromagnetic flowmeters for a low-void fraction flow such as bubbly flow. Thus, the flowmeters can be used to measure the void fraction for a liquid sodium.

An experimental study has been carried out to measure the pressure drop in a 271-pin fuel assembly of a liquid metal reactor. The rod pitch to rod diameter ratio~ P/D! of the fuel assembly is 1.2 and the wire lead length to rod diameter ratio~H/D! is 24.84. Measurements are made for five different sections in a fuel assembly; inlet orifice, fuel assembly inlet, wire-wrapped fuel assembly, fuel assembly outlet and fuel assembly upper region. A series of water experiments have been conducted changing flow rate and water temperature. It is shown that the pressure drops in the inlet orifice and in the wire-wrapped fuel assembly are much larger than those in other regions. The measured pressure drop data in a wire-wrapped fuel assembly region is compared with the existing four correlations. It is shown that the correlation proposed by Cheng and Todreas fits best with the present experimental data among the four correlations considered@DOI: 10.1115/1.1565076# The liquid metal reactor core consists of several fuel assemblies contained in a hexagonal shaped duct. There is no flow exchange between ducts. In order to efficiently extract the heat generated in a fuel assembly, it is important to distribute the flow rate among the fuel assemblies and to maintain the temperature distribution properly. The distribution of coolant flow rate in each fuel assembly is determined by the heat generation in each fuel assembly after the required whole coolant flow rate is determined to meet the reactor power. The reactor core is divided into a certain number of groups that have the same coolant flow rate, and then the temperature distribution of the fuel assembly is calculated and the coolant flow rate in each group is adjusted to have the same degree of peak temperature in the fuel rod. Then, the orifice in the bottom region of the fuel assembly is designed following the pressure drop of the fuel assembly. Thus, the information of pressure drop in a fuel assembly is very important in the thermal hydraulic design of the reactor core. The individual fuel assembly consists of inlet orifice, fuel assembly inlet, wire-wrapped fuel assembly, fuel assembly outlet and fuel assembly upper region. The primary objective of the present study is to measure the pressure drops in these regions for the design of Korea Advanced Liquid Metal Reactor ~KALIMER!. A series of experiments are conducted to measure the pressure drops in these regions. The relative magnitude of pressure drops in these regions is investigated from the measured data. As will be shown later, the pressure drops in the inlet orifice and in the wire-wrapped fuel assembly is much larger than the pressure drops in other regions. The design of the inlet orifice for KALIMER is not determined yet and the inlet orifice used in the present measurement is only a tentative design. Thus, the primary emphasis of the present study is placed on the analysis of pressure drop in the wire-wrapped fuel assembly. In order to maintain a proper spacing between fuel pins and promote the coolant mixing, several types of spacers are proposed. Among the various spacers the helical-type wire-spacers are widely used in the liquid metal reactor ~LMR! and are adopted in the design of KALIMER. However, the existence of spacers between fuel pins causes the increase of hydraulic resistance

We consider a one-dimensional mixed convection of liquid metal with forced circulation and unequal heating. The steady solution of the corresponding heat equation with proper boundary conditions is obtained analytically. The solution shows formation of a local circulation loop by unequal heating and deformation of the circulation loop by the forced circulation. It is also found that the heat transfer characteristics are almost independent of the unequal heating condition, although the deformation occurs more easily for a more symmetric case.

The main objective of the present study is to perform an experimental evaluation of five existing correlations for the subchannel pressure drop analysis of a wire-wrapped fuel assembly. For this purpose, a series of water experiments have been performed using a helical wire-wrapped 19-pin fuel assembly for various test parameters. For different test sections with different pitch to rod diameter ratios (P/D) and wire lead length to rod diameter ratios (H/D) have been fabricated. A series of pressure drop measurements were made to obtain friction factors for these four test sections. The new data along with existing data are used to evaluate existing correlations. Both the original and the simplified Cheng and Todreas correlations give the best agreement with experimental data for all flow regions.

A study on the use of momentum interpolation method and higher-order bounded convection schemes for simulation of oscillatory natural convection of liquid metal in a square cavity is presented. The original Rhie and Chow scheme is modified for unsteady flows to obtain the converged solutions which are independent of the time step size. Two higher-order bounded convection schemes, SOUCUP and COPLA are evaluated, together with HYBRID and QUICK, to test their capability for predicting the oscillatory natural convection. The calculations are performed forG r=107, Pr=0.005 employing 42x42 and 82x82 nonuniform grids. The COPLA and QUICK schemes have shown the capability of predicting the oscillatory motion while the HYBRID and SOUCUP schemes have not.

SUMMARY In this paper, an efficient numerical method for unsteady free surface motions, with simple geometries, has been devised. Under the potential flow assumption, the governing equation of free surface flows becomes a Laplace equation, which is treated here by means of a series expansions of the velocity potential. The free surface is represented with a height function. The present method is applied to surface gravity waves to test the stability and accuracy of the method. To show the versatility of the method, a model for a dip formation is considered. © 1998 John Wiley & Sons, Ltd.

An experimental and theoretical study has been carried out to derive the wave height and transition criterion from wavy to slug flow in horizontal air-water countercurrent stratified flow conditions. A theoretical formula for the wave height in a stratified wavy flow regime has been developed using the concept of total energy balance over a wave crest to consider the shear stress acting on the interface of two fluids. From the limiting condition of the formula for the wave height, a criterion for transition from a stratified wavy flow to a slug flow has been derived. A series of experiments have also been conducted changing the non-dimensional water depth and the flow rates of air in a horizontal pipe and a duct. Comparisons between the measured data and the predictions of the present theory show that the agreement is within ±10%.

This article presents a detailed three-dimensional evaluation of a higher-order bounded convection scheme. A high-resolution and bounded discretization scheme named COPIA, which is composed of piecewise linear functions in the normalized variable diagram, is proposed. The scheme is applied to the three-dimensional test problems to assess its capabilities. The results of numerical experiments show that the tested bounded scheme resolves the boundedness problem white retaining the accuracy of a higher-order scheme.

A high resolution and bounded convection scheme is proposed for the simulation of steady incompressible flows with finite volume method. The scheme is formulated on a nonuniform, nonorthogonal grid so as to be applicable to the simulation of practical engineering problems. The relative performance of the scheme is evaluated through applications to the test problems. The results of numerical experiments show that the proposed scheme yields similiar solutions which are as good as those obtained with the QUICK scheme, but without exhibiting the physically unrealistic overshoots and undershoots.

This paper presents a comparison of recently developed four higher-order bounded convection schemes SOUCUP, HLPA, SMARTER and LPPA which employ different characteristics in a normalized variable diagram. All the schemes are formulated on a non-uniform, non-orthogonal grid and their relative performances are compared through applications to the several test problems. The results of numerical experiments show that all the tested bounded schemes resolve the boundedness problem retaining the accuracy of the higher-order scheme. The HLPA, SMARTER and LPPA schemes result in nearly the same solution behaviours and the SOUCUP scheme is shown to be relatively more diffusive than the other three bounded schemes.

This article presents a detailed comparison of two finite-volume calculation methods for incompressible flows in complex geometries, one with a staggered grid arrangement and the other with a nonstaggered grid arrangement. The relative performance of the two schemes is examined through applications to test problems. Several numerical experiments are performed, changing the numerical grids and the flow nonlinearity. The results of these numerical experiments show that the staggered grid-based method generally reaches the grid-independent solutions earlier. However, both schemes result in nearly the same converged solutions when the numerical grids are properly refined.

A comparative study of two finite-volume calculation methods for incompressible flows on nonorthogonal grids with different grid arrangements is presented. One of the methods is based on the conventional staggered grid arrangement, and the other method is based on the nonstaggered grid arrangement of Rhie and Chow. The existing schemes have been slightly modified to employ the same dependent variables in the momentum equations and the same pressure and velocity coupling technique, in order to compare effectively the relative performances of the two schemes. Both schemes are applied to test problems, and the computed results are compared with the analytic solution and the experimental data available in the literature.

A three-dimensional finite-volume calculation procedure for incompressible flows in complex geometries is presented. The scheme is based on the modified Rhie and Chow momentum interpolation method [1], in which the original scheme has been modified to employ the curvilinear covariant velocity components as cell face velocities to provide always a simple and diagonal dominant pressure or pressure correction equation. The coupling between the continuity equation and the momentum equations is effected using the SIMPLE algorithm. The present scheme is applied to test problems, and the results are compared with available experimental data and other numerical results.

The momentum interpolation method developed by Rhie and Chow [1rsqb; is further refined and extended to employ the curvilinear covariant velocity components as cell face velocities. The related pressure-velocity coupling technique is described. The relative performances of the proposed scheme and of the scheme based on the contravariant cell face velocities are examined through applications to several test problems. The present scheme, based on the covariant cell face velocities, always provides simple and diagonal-dominant pressure and pressure-correction equations and shows good convergence and stability behavior even in a strongly nonorthogonal grid situation.

The effect of choice of cell face velocities on the solution behaviours in the three dimensional incompressible flow calculations on nonorthogonal grids are investigated in detail. The calculation schemes based on the curvilinear contravariant and covariant cell face velocities are developed and are applied to the test problems to assess their relative performances. It is observed that the accuracy of the converged solution is not affected by the different choice of cell face velocities. However, the scheme based on the covariant cell face velocities shows better convergence behaviours when the numerical grids are strongly nonorthogonal.

Improved analytical models have been proposed that can predict the lower and upper limits of the waterhammer region for given flow conditions by incorporation of recent advances made in the understanding of phenomena associated with the condensation-induced waterhammer into existing methods. Present models are applicable for steamwater counterflow in a long horizontal pipe geometry. Both lower and upper bounds of the waterhammer region are expressed in terms of the ‘critical inlet water flow rate’ as a function of axial position. Waterhammer region boundaries predicted by present and typical existing models are compared for particular flow conditions of the waterhammer event occurred at San Onofre Unit 1 to assess the applicability of the models examined. The result shows that present models for lower and upper bounds of the waterhammer region compare favorably with the best performing existing models.

An experimental study has been performed to investigate the frequency of a free surface fluctuation in a vessel with and without an internal structure. Water flows in from the bottom nozzle and flows out at the side wall nozzles. There are two dominant frequency regions which are generated by a standing wave and a jet. In the standing wave region, the frequency is well described by f(4πdV/g)1/2 = 1.07 in a circular vessel. The frequency generated by a jet can be described by a dimensionless period and Froude number according to its fluctuation stability. In the case of a vessel with an internal structure, it needs a geometry factor which is described by a vessel diameter to a hydraulic diameter ratio in a standing wave region.

An experimental study was performed to measure the fluctuation phenomena of a free surface in a vessel with or without an internal structure. A flow enters from the bottom and flows out of the side wall nozzles. Characteristics of the free surface fluctuation are investigated in terms of the geometry factors of the vessel and the flow rate. A modified Froude number is proposed to describe the amplitude of a free surface fluctuation. The fluctuation amplitude increases stably with an increase in the ratio of the vessel diameter to the water level in a vessel without an internal structure. When the ratio is greater than about 2, the fluctuation decreases suddenly with an increase in the ratio and it becomes unstable. The fluctuation amplitude is linearly proportional to the square of the Froude number. The amplitude of a free surface fluctuation increases with an increase in the height of an internal structure, but this increasing ratio is reduced when the height becomes higher. Two correlations were developed in terms of the Froude number and geometry factors to predict the amplitude of the free surface fluctuation in a vessel with or without an internal structure.

A computational study for the evaluation of the current turbulence models for the prediction of a thermal striping in a triple-jet is performed. The tested turbulence models are the two-layer model, the shear stress transport model and the elliptic relaxation model. These three turbulence models are applied to the prediction of the thermal striping in a triple-jet in which detailed experimental data are available. The performances of the tested turbulence models are evaluated through comparisons with the experimental data. The predicted mean and root-mean-square values of the temperature are compared with the experimental data, and the capability of predicting the oscillatory behavior of the ensemble-averaged temperature is investigated. From these works it is shown that only the elliptic relaxation model is capable of predicting the oscillatory behavior of the ensemble-averaged temperature. It is also shown that the elliptic relaxation model predicts best the time-averaged and root-mean-square of the temperature fluctuation. However, this model predicts a slower mixing at the far downstream of the jet.Copyright © 2005 by ASME

An experimental study has been carried out to measure the critical conditions for the inception of an air entrainment by breaking the surface wave at the free surface in the water test facility. The experimental parameters are the vessel diameter, the nozzle diameter, the mean water-level and the water flow rate. More than 400 experimental data which show whether the air is entrained or not at a given experimental condition are obtained, and an experimental correlation that describes the air entrainment condition is developed. The correlation is described by the ratio between the diameter and height of the vessel, the ratio between the diameter of the nozzle and the height of the vessel, the modified Froude number and a modified Weber number. In this experiment two cases of air entrainment are observed. One case is that the air entrainment occurred due to the destruction of the surface wave from the center, and the other case is due to the crash of the water wave to the vessel wall. Theses two cases occur irregularly and the entrained air bubble distributes uniformly in the water.Copyright © 2005 by ASME

Ultrafine NiO/8YSZ (8 mol% Yttria-Stabilized Zirconia) composite powders were prepared by using a glycine nitrate process (GNP) for anode material of solid oxide fuel cells. The specific surface areas of synthesized NiO/8YSZ composite powders were examined with controlling pH of a precursor solution and the content of glycine. The binding of glycine with metal ions occurring in the precursor solution was analyzed by using FTIR. The characteristics of synthesized composite powders were examined with X-ray diffractometer, a BET method with N/sub 2/ absorption, scanning and transmission electron microscopies. Ultrafine NiO/8YSZ composite powders of 15-18 m/sup 2//g were produced through the GNP when the content of glycine was controlled to 1 to 2 times of the stoichiometric ratio in the precursor solution. Strongly acid precursor solution increased the specific surface area of the synthesized composite powders. This is suggested to be caused by the increased binding of metal ions and glycine under strong acid solution of pH=0.5 that lets glycine of mainly the amine group of NH/sub 3//sup -/. After sintering and reducing treatment of NiO/8YSZ composite powders synthesized by GNP, the Ni/8YSZ pellet showed ideal microstructure: very fine Ni particles of 3-5 /spl mu/m were distributed uniformly and fine pores around Ni metal particles were formed, thus, leading to an increase of the triple phase boundary among gas, Ni and 8YSZ.

The present paper presents the experimental results for pressure drop in inclined tube bundles located in a rectangular duct. Measurements are made for pressure drop in triangular and rotated triangular tube arrays having P/d ratio of 1.6 and inclination angles of 30, 45, 60 and 90 degrees. The Reynolds number based on the free stream velocity and tube diameter ranges from 8×102 to 6.3×104 . The experimental results show that the magnitude of dimensionless pressure drop decreases significantly when the inclined angle is less than 45 degree. The measured data are compared with two existing correlations available in the literatures. The ESDU correlation agrees well with the present data for the triangular arrays. But some discrepancies are observed for the rotated triangular arrays when the inclined angles are 30 and 45 degrees. The Idel’chik correlation generally agrees well with the measured data for the rotated triangular arrays except for the inclined angle of 30 degree. The Idel’chik correlation needs modification for the triangular arrays. The modified Idel’chik correlation agrees well with the measured data within 10%. It is found that the present measured data can be applied to the evaluation and modification of previous correlations.Copyright © 2002 by ASME

An experimental study has been carried out to measure the pressure drop in a 271-pin fuel assembly of a liquid metal reactor. The rod pitch to rod diameter ratio (P/D) of the fuel assembly is 1.2 and the wire lead length to rod diameter ratio (H/D) is 24.84. Measurements are made for five different sections in a fuel assembly; inlet orifice, fuel assembly inlet, wire-wrapped fuel assembly, fuel assembly outlet and fuel assembly upper region. A series of water experiments have been conducted changing flow rate and water temperature. It is shown that the pressure drops in the inlet orifice and in the wire-wrapped fuel assembly are much larger than those in other regions. The measured pressure drop data in a wire-wrapped fuel assembly region is compared with the existing four correlations. It is shown that the correlation proposed by Cheng and Todreas fits the best with the present experimental data among the four correlations considered.Copyright © 2002 by ASME