Advanced Materials Research Vols. 455-456

Abstract: Two-dimensional numerical simulation of heat storage characteristics in a horizontal rectangular enclosure heated from below by natural convection has been investigated with the microencapsulated phase change material (PCM) slurry. Effects of PCM on heat storage and heat transfer are discussed, in which PCM slurry exhibits the pseudoplastic non-Newtonian fluid behavior and a peak value in the specific heat capacity with latent heat in phase temperature range. And their characteristics between the slurries with and without phase change of PCM are compared in the phase change temperature range. And vertical temperature distributions at the middle position are given. This paper shows streamlines and isotherms in the enclosure for phase change process.

Abstract: this paper studies the typical irreversible processes such as combustion and heat transfer with temperature difference based on the theory of thermodynamics, analyzes the influencing factors on exergy loss in irreversible processes, on the basis of this analysis, proposes the energy-saving optimization measures on design and operation management of the organic heat transfer material heater, and specially points out that in the design process, objective function can be constructed with the exergy loss as evaluation index to determine the outlet flue gas temperature of furnace and the flue gas temperature, and provides theoretical basis for the determination of design parameters.

Abstract: In order to obtain fire retardant mechanism of gas deflagration flame in narrow channel, a numerical simulation adopting PISO algorithm and self-adapted grids was presented based on the single-step irreversible chemical reaction and the combustion model of EBU-Arrhenius. The numerical dates are well compatible with experimental results and indicate that the initial flame velocity and gap of channel are directly responsible for the quenching distance. And the smaller the flame velocity or gap of channel, the shorter the quenching distance, which means simpler to quench gas deflagration flame.

Abstract: Numerical simulations of flows over two-dimensional vertical axis tidal turbines are carried out. Unsteady Reynolds averaged Navier-Stokes Equations are applied to model turbulent flows. Influence of the central shaft and number of blades on flow field and thus performances of turbines are investigated. Performances in terms of torque and power coefficients are obtained for different types of turbines. Results demonstrates that the central shaft has a negative influence on flow field and power coefficients. Solidity and tip speed ratio are two important factors to affect turbine’s performances. This paper provides useful information for future studies.

Abstract: Nuclear main pumps are one of the most important devices in nuclear plants. Hence hydraulic performances of the nuclear main pump are important. Compared with the traditional speed coefficient method, a revised speed coefficient method is employed to design a nuclear main pump, which is based on the extension chart of the traditional speed coefficient chart. Meanwhile numerical simulations are carried out to examine performances of the designed pump. Results show that performances of the designed pump meet specifications. Clearance leakage causes decrease in head and efficiency of the pump (about 4%). This work provides useful information for the study of nuclear main pumps.

Abstract: The blisk (bladed disk) is a new structural component of the modern aero-engine and plays an important role in improving its performance. Ti-6Al-4V alloy joints welded by electron beam have been widely used for compressor blisk in advanced aero engine. It is necessary to analyze microstructure and mechanical properties of Ti-6Al-4V welded structure by electron beam welding (EBW) for failure analysis and structure design of blisk. Microstructure of Ti-6Al-4V welded structure by EBW was investigated by microscopic observation and micro indentation testing. Experiment results show grain coarsening in fusion zone (FZ) and heat affected zone (HAZ) appears large gradient organization structure, which presents significant local heterogeneity. On the centerline perpendicular to the welding direction, Vickers microhardness was measured in increments of 1mm, 0.5mm, 0.25mm and 0.1mm. Due to the presence of martensite, microhardness of the fusion zone is about 20% higher than that of the base material. The size of joints in different regions was acquired, 2.5 to 3.0-mm-wide in FZ and about 0.7-mm-wide in HAZ respectively. Three different types of EBW samples were designed for tensile test, including welded structure, welded joint and base material. Three different stress-strain curves of specimens were acquired, including welded joint. The experiment data indicates that the tensile strength of welded joints is 8% more than that of the base metal.

Abstract: In this paper, the transient of the flow field of the nuclear main pump has been analyzed in the SBLOCA and the half mass flow rate time is obtained through the simulation. The results of the simulation show that, as nuclear main pump runs down, the mass flow rate and head of the pump drops as well. The blade surface pressure is not evenly distributed. The blade bears the force of the flow. So Pump unit should have sufficient moment of inertia, so that when the reactor in an emergency shuts down caused by the failure of power supply, nucleate burning down can be avoided by cooling the core. On the braking operation condition, the half mass flow rate time required should be guaranteed. Through simulation, we find when the half time is equal to 10s, the half mass flow rate time is about 4.6s Though it is a little shorter than 5s required, the AP1000 model selected basically meet the idle requirement.

Abstract: Based on the YD4A75-C3 electronically controlled common rail diesel engine, using CFD simulation software, the combustion and emission’s behavior in cylinder was simulated on the numbers, diameter and arrangement of nozzles. The research results showed: in the condition of the certain total nozzle flow area, the proper nozzle numbers could improve fuel’s atomization quality and increase the uniformity degree of gas mixture. The staggered arrangement of nozzles could reduce interference and overlap among the adjacent fuel sprays and increase the air utilization and the space distribution of fuel, finally, the degree of mixing was increased obviously.

Abstract: This paper presents the influence of the body-force in large centrifugal acceleration field on the shapes and extinction limits of the premixed flame of liquefied petroleum gas (LPG) and air. Experiments of combustion in various centrifugal acceleration fields were performed. The results indicate that the magnitude of the resultant body-force, composed mainly of centrifugal force and Coriolis force, is not the only cause of the extinction of flames, but the direction between the resultant body-force and jet direction of the premixed gases plays more important role. Coriolis force, which is always perpendicular to jet direction of the gases, results in the flame turning to sides of the nozzle, even extinction. The buoyancy effect is the mainly element to make the flame shape change: shorten, lengthen or deflect, and improve or weaken combustion. It is favorable for stability of the flame as the included angle of rotating tangent direction to gas flow jet direction is positive.

Abstract: This paper presents an analysis on the performance of vertical axis wind turbine of two types, namely straight-blade vertical axis wind turbine (SB-VAWT) and twisted-blade vertical axis wind turbine (TB-VAWT). An attempt of this simulation is to identify which type performs better in the same wind conditions and swept area. Three-dimensional computational fluid dynamics (CFD) was adopted in this analysis, after solid models of them were generated. Preliminary results of torque, power and aerodynamics in the fluid field were obtained for discussion. Finally, there provided some guidance for future wind tunnel tests.