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[en] In this work, shape optimization of seven pin wire wrapped fuel assembly has been carried out in conjunction with RANS analysis in order to evaluate the performances of surrogate models. Previously, Ahmad and Kim performed the flow and heat transfer analysis based on the three-dimensional RANS analysis. But numerical optimization has not been applied to the design of wire-wrapped fuel assembly, yet. Surrogate models are being widely used in multidisciplinary optimization. Queipo et al. reviewed various surrogates based models used in aerospace applications. Goel et al. developed weighted average surrogate model based on response surface approximation (RSA), radial basis neural network (RBNN) and Krigging (KRG) models. In addition to the three basic models, RSA, RBNN and KRG, the multiple surrogate model, PBA also has been employed. Two geometric design variables and a multi-objective function with a weighting factor have been considered for this problem
[en] An optimization of rapid thermal processing (RTP) was conducted to obtain uniform temperature distribution on a wafer surface by using linear programming and radiative heat transfer modeling. The results show that two heating lamp zones are needed to maintain uniform wafer temperature and the optimal lamp positions are unique for a given geometry and not affected by wafer temperatures. The radii of heating lamps, which were obtained by optimization, are 45 mm and 108 mm. The emissivity and temperature of the chamber wall do not significantly affect the optimal condition. With obtained optimum geometry of the RTP chamber and lamp positions, the wafer surface temperatures were calculated. The uniformity allowance of the wafer surface is less than ±1 .deg. C when the mean temperature of the wafer surface is 1000 .deg. C
[en] An investigation is made of oscillatory phenomenon induced by an exothermic reaction. This oscillatory phenomenon occurs in a very thin mixing layer between two miscible and reacting fluids. A qualitative model based on the interaction among reaction, molecular momentum transfer, molecular heat transfer, molecular mass transfer and forced convective transfer was proposed by Kuroda and Ogawa [1994. Nonlinear waves in a shear flow with a diffusive exothermic reaction and its qualitative reasoning. Chem. Eng. Sci. 49(16), 2699-2708]. It is experimentally shown in the present study that the oscillatory patterns change in the flow direction. In the upstream area where oscillatory patterns are nearly straight stripes, effects of viscosity on those stripes are investigated. In the downstream area where stripes are wavy and disordered, fractal analysis is introduced to investigate the relationship between the transition of oscillatory flow patterns and process factors, i.e. the viscosity ratio, the entire viscosity, flow rate and the flow rate ratio. Fractal analysis is also applied to temperature oscillation, and it is confirmed that the characteristic patterns of oscillation become obscure as the entire viscosity increases. The entire viscosity is an important factor for controlling both oscillatory patterns of flow and temperature in this reactive flow system.
[en] In this study, we investigated the hydrodynamic and thermal performance of constructal architectures based on the mass flow rates for the given pressure drop and identify the required pumping power and thermal resistance. The five flow configurations described in this paper are the first, second constructs with optimized hydraulic diameters and nonoptimized hydraulic diameter, respectively, including the serpentine configuration. The results suggest that best fluid flow structure is the second constructal structure with optimized constructal configurations. We also found that the optimized structure of cooling plates could enhance heat transfer remarkably and decrease pumping power dramatically compared with the traditional channels.
[en] We measured and analyzed the quench development in coated conductor(CC) tapes. The CC was grown on hastelloy substrates and has an Ag protection layer. The tapes were subjected to simulated AC fault currents for quench development measurement. They were immersed in liquid nitrogen during the experiment. The quench resistance increased rapidly first, and the increase slowed down afterwards. It increased linearly with applied voltage at lower voltages, and depended less strongly on applied voltage at higher voltages. The resistance was compared with that of Au/YBCO films grown on sapphire substrates, and found to increase more monotonously than the latter. Data were analyzed quantitatively with the concept of heat transfer within the tape and the surrounding liquid nitrogen. A heat balance equation was derived and solved, taking into consideration temperature dependence of thermal parameters of the tapes. Solutions, together with values of thermal parameters taken from the literature, explained the data well. Cooling by liquid nitrogen affected the quench development considerably at lower applied voltages. Dependence on applied voltages could be also understood quantitatively.
[en] The question if and how streamers (i.e., radially elongated vortices) can lead to an enhancement of the electron heat transport in electron temperature gradient turbulence is addressed. To this aim, the electrons are treated as passive tracers, and their decorrelation mechanisms with respect to the advecting electrostatic potential are studied. A substantial transport enhancement is found in a wide region of parameter space.
[en] The main structure of heat and mass transfer equations in the reacting diffusion system with allowing for the heat and diffusion relaxation under conditions of space heterogeneity of reagents fluids in the apparatuses have been obtained. (author)
[en] This paper presents an optimal design of a micro evaporator which maximizes the heat transfer coefficient. Number of gaps, spanwise distance and streamwise distance are selected as the geometric design parameters. Mass flow rate of the refrigerant is selected as the non-geometric design parameter. Temperature at the surface of the heater is measured to valuate the heat transfer coefficient. Nine experiments are conducted using L9(34) orthogonal array. Maximum heat transfer coefficient is 640 W/m2K at the parameters of 2 gaps, 0.2 mm spanwise distance, 1.0 mm streamwise distance and 0.72 g/s mass flow rate. Among the 3 geometric parameters, the spanwise distance is the most sensitive parameter influencing the heat transfer coefficient. We conduct a second stage of experiment to increase the heat transfer coefficient by reselecting the mass flow rate. We concluded that 0.87 g/s is the optimized flow rate for an active micro cooler resulting in a heat transfer coefficient of 651 W/m2K
[en] Hot closed-forging process and the die used for forming an automotive flange were analyzed from the viewpoints of heat transfer, grain-flow lines, and stresses to obtain a forged product without defects such as surface cracks, laps, cold shots, and partial filling. The forging process including up-set, pre-forging, final forging and pressing forces was investigated using finite element analysis. The influence of the preform die and the ratio of the heights of the upper die to lower die on the forging process and die were investigated and a die shape (10 .deg. for the preform die, and 1.5:1 ratio for the final die) suitable to achieve successful forging was determined on the basis of a parametric study. All parametric design requirements such as strength, full filling, and a load limit of 13,000 KN were satisfied for this newly developed flange die. New dies and flanges were fabricated and investigated. Defects such as partial filling and surface cracks were not observed
[en] Here, the homotopy analysis method (HAM), which is a powerful and easy-to-use analytic tool for nonlinear problems and dose not need small parameters in the equations, is compared with the perturbation and numerical and homotopy perturbation method (HPM) in the heat transfer filed. The homotopy analysis method contains the auxiliary parameter h, which provides us with a simple way to adjust and control the convergence region of solution series