Numerical investigation on the heat transfer characteristics of a liquid-metal pool subjected to a partial solidification process

The main purpose of this paper is to investigate numerically the effects of solidification on the heat transfer characteristics of the liquid metal layer, for use in accident analyses. The situation is very similar to an overlying liquid melt pool that could be fooned in the reactor lower head during the late phase of a severe nuclear accident. Based on a computational model, MPCOOL, the numerical predictions were then assessed through a comparison with the experimental data that was obtained with various boundary temperature conditions and geometrical aspect ratios, especially for the Ra-Nu relationship. For the cases with solidification, the results of the comparison show that(a) the computational model does show a good agreement with heat transter rates inferred from the experimental data, with a few exceptions at the Ra numbers which suggest a turbulent transport; and also (b) the computational model underpredicts the heat transfer rates by about 6% than that inferred from the experimental data when it is integrally evaluated with the Ra-Nu correlation. The foregoing results are mainly due to the currently limited applicability of the computational model up to the laminar-to-turbulence transition flows and its application to the turbulence flows because it is always subjected to a model uncertainty between the laminar and turbulence. Next, an additional comparison for the cases with and without solidification was made to examine the effects of the solidification on the energy partition within the liquid metal layer and its effects on the directional heat transfer rates. The results of the comparison show that the computational model for the case without solidification predicts higher heat transfer rates by about 15% than when solidification is included, but there isn't any experimental data that directly supports this trend.     

Development and analysis of LOCA sequences for severe accident risk database

Although a Level 2 PSA has been performed for the Korean Standard Power Plants (KSNPs), and that it considered the necessary sequences for an assessment of the containment integrity and source term analysis. In terms of an accident management, however, more cases causing severe core damage need to be analyzed and arranged systematically for an easy access of the results. At present, KAERI is intensively calculating the severe accident sequences for various initiating events and generating a database for the accident progression including thermal hydraulic and source term behaviors. The developed database (DB) system includes a graphical display for a plant and equipment status, previous research results by a knowledge-based technique, and the expected plant behavior. The plant model used in this paper is oriented to the cases of LOCAs related to severe accident phenomena and thus can simulate the plant behaviors of a severe accident. Therefore, the developed system may play a central role as an information's source during the decision-making for a severe accident management, and be used as a training simulator for a severe accident management.     

Adhesion characteristics of the snail foot under various surface conditions

Recently, there have been many studies on the adhesion mechanisms of various mollusca such as snails, clams and octopi. Understanding their magnitude and working force is advantageous for application in specially designed robotic systems. The adhesion mechanism in these animals is effectively generated by a complex biological system that is able to operate under various surface conditions. In this work, fundamental research was conducted to understand the adhesion mechanism of living snails. Pull-off and lateral forces were measured while the snail was adhered to various surfaces in order to investigate the effects of surface conditions such as surface energy, surface roughness and surface type on the adhesion or suction of the snail. In order to understand the relationship between suction and adhesion of the snail, pull-off and suction forces were simultaneously measured using a custom-built apparatus. The average adhesion and suction force was estimated to be 0.2 kgf and 0.44 kgf, respectively. It was found that the snail effectively used both capillary adhesion and suction mechanisms to attach to and move on the surface.     

Experimental investigation on two-phase flow boiling heat transfer of five refrigerants in horizontal small tubes of 0.5, 1.5 and 3.0 mm inner diameters

An experimental investigation on two-phase flow boiling heat transfer with refrigerants of R-22, R-134a, R-410A, C₃H₈ and CO₂ in horizontal circular small tubes is presented. The experimental data were obtained over a heat flux range of 5–40 kW m^?2, mass flux range of 50–600 kg m^?2 s^?1, saturation temperature range of 0–15 °C, and quality up to 1.0. The test section was made of stainless steel tubes with inner diameters of 0.5, 1.5 and 3.0 mm, and lengths of 330, 1000, 1500, 2000 and 3000 mm. The experimental data were mapped on Wang et al. (1997) [5] and Wojtan et al. (2005) [6] flow pattern maps. The effects of mass flux, heat flux, saturation temperature and inner tube diameter on the heat transfer coefficient are reported. The experimental heat transfer coefficients were compared with some existing correlations. A new boiling heat transfer coefficient correlation that is based on a superposition model for refrigerants in small tubes is presented with 15.28% mean deviation and ?0.48% average deviation.     

Estimation of temperature-induced reactor coolant system and steam generator tube creep rupture probability under high-pressure severe accident conditions

A severe accident has inherently significant uncertainties due to the complex phenomena and wide range of conditions. Because of its high temperature and pressure, performing experimental validation and practical application are extremely difficult. With these difficulties, there has been few experimental researches performed and there is no plant-specific experimental data. Instead, computer codes have been developed to simulate the accident and have been used conservative assumptions and margins. This study is an effort to reduce the uncertainty in the probabilistic safety assessment and produce a realistic and physical-based failure probability. The methodology was developed and applied to the OPR1000. The creep rupture failure probabilities of reactor coolant system (RCS) components were evaluated under a station blackout severe accident with all powers lost and no recovery of steam generator auxiliary feed-water. The MELCOR 1.8.6 code was used to obtain the plant-specific pressure and temperature history of each part of the RCS and the creep rupture failure times were calculated by the rate-dependent creep rupture model with the plant-specific data.     

Interim check and practical accuracy improvement for machine tools with sequential measurements using a double ball-bar on a virtual regular tetrahedron

This study proposes a method for a quick, simple interim check and practical accuracy improvement of machine tools using just a double ball-bar. The double ball-bar is used to measure sequentially the length of the six sides of a virtual regular tetrahedron within the workspace of the machine tool. Then, the scale and squareness errors of and between the three linear axes are calculated from the length results, and the measured lengths and the calculated errors can be used as criteria for the interim check. The calculated errors can also be compensated for to improve the accuracy of experimented machine tools practically. A sample machine tool was subjected to experimental interim checks applying the proposed method; it showed primarily large length deviations for the six sides due to geometric errors mainly. To improve the geometric accuracy practically, the calculated errors were compensated for and the measurements were repeated, showing significantly improved length deviations for the six sides. The main advantage of the proposed method is that it requires only a double ball-bar and sequential measurements; thus, it is a simple procedure with a measuring time of ～5 min for a virtual regular tetrahedron. Additionally, the size of the virtual regular tetrahedron can be readily modified by changing the nominal length of the double ball-bar, increasing measurement flexibility. Thus, the proposed method is suitable for quick, simple, cost-effective daily and periodic interim checks, with practical improvement of machine tool accuracy.     

Electrochemical performance of nano-Pt-supported carbon anode for lithium ion batteries

A nano-Pt-supported carbon anode was prepared by supporting Pt nanoparticles onto carbon powder. Ultrafine Pt nanoparticles could be well distributed on the surface of carbon particles. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), cyclic voltammetry (CV), FTIR, and impedance spectroscopy were used to study on the electrode structure and electrochemical performance. Nano-Pt-supported carbon anode enhanced the Li discharge reaction and suppressed the solvent decomposition reaction, which are favorable for lithium batteries.     

Effective product assignment based on association rule mining in retail

Much academic research has been conducted about the process of association rule mining. More effort is now required for practical application of association rules in various commercial fields. A potential application of association rule mining is the problem of product assignment in retail. The product assignment problem involves how to most effectively assign items to sites in retail stores to grow sales. Effective product assignment facilitates cross-selling and convenient shopping for customers to promote maximum sales for retailers. However, little practical research has been done to address the issue. The current study approaches the product assignment problem using association rule mining for retail environments. There are some barriers to overcome in applying association rule mining to the product assignment problem for retail. This study conducts some generalizing to overcome drawbacks caused by the short lifecycles of current products. As a measure of cross-selling, lift is used to compare the effectiveness of various assignments for products. The proposed algorithm consists of three processes, which include mining associations among items, nearest neighbor assignments, and updating assignments. The algorithm was tested on synthetic databases. The results show very effective product assignment in terms of the potential for cross-selling to drive maximum sales for retailers.     

Characteristic analysis and design of a B14 rotary ultrasonic motor for a robot arm taking the contact mechanism into consideration

The ultrasonic motor (USM) has many merits for use in a robot arm application. Therefore, the disk-type traveling wave B₁₄ rotary ultrasonic motor (RUSM) is proposed in this paper for that application. Up to the present time, the analysis and design of the USM have been almost always performed using rough analytic methods or using commercial analysis tools. As a result, it was impossible to achieve an exact analysis and design of the USM. In order to address this problem, this paper proposes the analysis and design methodology of the B₁₄ RUSM using a numerical method (3-D FEM) combined with an analytic method taking the contact mechanism into consideration in a linear operation. This methodology is applicable to many other kinds of USMs that use similar mechanisms. In addition, the mechanical system and the driving circuit of the B₁₄ RUSM are designed and prototyped. Finally, the proposed analysis and design methodology is validated by comparing its outcomes with the experimental data. Also, the appropriateness of the suggested RUSM for the application of a robot arm was verified