Applied Mechanics and Materials Vols. 284-287

Abstract: This work obtained an analytical solution for a steady cylindrical MHD Couette flow in a porous medium between two perfectly conducting rotating cylinders under the influence of a non-uniform radial magnetic field. Since part of the analytical solution is expressed in terms of the integral of the Modified Bessel function of the first and second kinds of variable order, numerical integration was performed. Current results indicate that the flow may become more uniform when the strength of the external magnetic field is increased. The magnetic fluid tends to slow down if the permeability of the porous medium decreases. If the porous annulus is thick, the momentum of the flow is more difficult to propagate from the outer cylinder into the inner part of the annulus. If both the inner and outer cylinders rotate, the shear effect the inner cylinder imposes is only relatively influential in the region close to it. A decrease in Da no less than 10-2 may increase the amount of magnetic field induced. The transfer of momentum across the annular space is easier in a thin porous annulus than a thick one and hence induces a stronger magnetic field. If the inner cylinder rotates in the direction opposite of the outer one, the magnetic field in the clockwise direction will be induced in some region.

Abstract: As a branch of the Hydraulic Hybrid Vehicle (HHV) technology, Series Hydraulic Hybrid Vehicle (SHHV) has been an important research object of institutions and automotive manufacturers all over the world. With the flexibility of engine management and regenerative braking characteristics SHHV is expected to be a short-term solution to develop a higher efficiency, cleaner, and safer transportation. In this work, the function and parameter determination of key components for SHHV are discussed. Based on the analytical analysis, the suitable set of component parameters is selected. The model of SHHV is implemented via Simulink/MATLAB mostly based on SimScape toolbox. The proposed model can be used as a development tool to quickly simulate the real hybrid system when it allows applying different parameter sets and in various conditions. The performance of the system is evaluated through some specific cases and the capability of braking energy recovery of the system is also investigated. Simulation results indicate that for a 2.5 ton truck case, more than 86% of braking energy can be captured and more than 72% of that energy can be returned to the kinetic energy of vehicle motion.

Abstract: Abstract. The fuzzy dominant directed graph (fuzzy DDG) method is proposed in this paper to solve the multi-objective optimal mechanical turbine power of river current (RC) power generation system. Recently, there is great potential for the RC power generation system in renewable energy. The experimental Taguchi method is used to find the optimal solution for the power generation system. The optimization problem for the AC generator in RC power generation system is studied. The optimal output power with respect to three selected control factors is studied. By using Taguchi method, five cases are discussed. The testing case is the optimal output power problem. It is convinced that this method is applicable and easy to find the optimal solution quickly.

Abstract: This study used metal porous medium heat sink to replace traditional cooling fins to form a high performance LED cooling system. The metal foamed material has high permeability and cooling area as large as several times of that of traditional fins. With a proper configuration design, it can improve the heat transfer capability of natural convection effectively. This study experimentally investigated the natural convection heat transfer characteristics of the annular metal foamed material, and determined the optimal configuration. The experimental results showed that 1) the heat transfer coefficient (h) increased with ΔT; 2) the (h) decreased as PPI (pores per inch) increased when the thickness (t) of the annular metal foams equaled 5 mm, but the (h) increased as PPI increased when t=11 and 14.5 mm; 3) the (h) increased and then decreased as (t) increased, and there was better heat transfer effect when t=11 mm as shown in the experimental data.

Abstract: The present numerical study is conducted in three dimensional to investigate the crossflow of an external round jet and a horizontal stream of microchannel flow. The results of heat transfer performance for the cases with and without transverse jet are compared. The patterns of different crossflow jet were analyzed to understand the flow and heat transfer characteristics. The effect of jet nozzle position on the heat transfer is investigated. Generally, the heat transfer performance increases with the jet Reynolds number. However, some cases of weak jet are found to cause lower heat transfer rate relative to the case without external jet. When vertical weak jet encounter strong horizontal flow, the horizontal flow is dominant that the jet cannot reach the microchannel bottom wall but imposes resistance to the horizontal flow. The investigation on the jet nozzle location shows that the jet nozzle location closer to the channel inlet gives better heat transfer performance.

Abstract: An analysis for operating characteristics of journal bearing lubrication system is performed based on the numerical model. Dynamic bearing lubrication characteristics such as oil film pressure and thickness distribution can be analyzed through a numerical model with an integration of elastohydrodynamics and multi-flexible-body dynamics (MFBD). In particular, the oil film thickness variation by elastic deformation is considered in the elastohydrodynamic analysis by applying the bending stiffness effect of journal. And the oil film thickness variation by the bending stiffness effect is applied to the fluid governing equations to calculate the oil film pressure in the elastohydrodynamic lubrication region. A series of process proposed in this study is available for the analysis of realistic elastohydrodynamic lubrication phenomenon. Also, a numerical example for the journal bearing lubrication system is demonstrated and compared with the experimental results. The numerical results considering the bending stiffness effect show a good agreement with the experimental results.

Abstract: Performance of a CO boiler has a detrimental influence on the operation and production of related industries. In a previous study, we have presented a numerical study of the influence of refractory thickening on the heat transfer and fluid flow in a CO boiler. In this paper, the influence of refractory thickening on the reacting flow and DeNOx effect in a CO boiler is discussed. It is found that refractory thickening can reduce the temperature and the skin friction in the DeNOx section. Furthermore, NOx formation in the DeNOx section is also alleviated by refractory thickening.

Abstract: Planetary gear trains are commonly used in various transmissions due to the following reasons: compact size, light weight, and multi-degrees of freedom. For example, planetary gear trains can be designed for following functions: gear reducers for power machinery, internal gear hubs for bicycle, gear increasers for wind generator, gear reducers for robot. In general, the reduction of non-coupled planetary gear train is less than 10. The purpose of this paper is to introduce the planetary gear train with high reduction ratio. Coupled planetary gear train can be designed to has high reduction ratio. Hence, this paper focuses on innovative, kinematic, and engineering design of coupled planetary gear train with high reduction ratio. The coupled planetary gear train synthesized in this paper is a planetary gear train with simple planet gears. It can be used as the gear reducer for a robot. Refer to the train value equation, the reduction-ratio equation of coupled planetary gear train is derived for the design purpose. Then, the coupled planetary coupled gear train with simple planet gears is synthesized based on the above reduction-ratio equation. Finally, the corresponding engineering design drawing is accomplished.

Abstract: This paper presents a parametric study on aerodynamic performance of a transonic axial compressor combined with a casing groove and tip injection using three-dimensional Reynolds-average Navier-Stokes equations. The front and rear lengths and height of the groove are selected as the geometric parameters to investigate their effects on the stall margin and peak adiabatic efficiency. These parameters are changed with constant injection. The validation of the numerical results is performed in comparison with experimental data for the total pressure ratio and adiabatic efficiency. As the results of the parametric study, the maximum stall margin and peak adiabatic efficiency are obtained in the axial compressor having 70% groove height of the reference groove. The stall margin and peak adiabatic efficiency in other cases are also improved in comparison with the axial compressors with the smooth casing and reference groove. The results show that both the stall margin and the peak adiabatic efficiency are considerably improved by the application of the casing groove combined with tip injection in an axial compressor.

Abstract: Under the rapid enhancement of CPU performance, the thermal management on the CPU becomes a challenging task, especially for the industrial PC with a high system resistance. The traditional axial fan with heat sink assembly is not capable to solve this difficult thermal-dissipation problem. Thus, a combination of centrifugal fan and heat sink is utilized to solve this high system-resistance for a server. A centrifugal fan is utilized to offer extra static pressure for drawing the hot air inside this compact enclosure and discharging to the atmosphere. In this study, experimental measurement and numerical simulation are integrated to improve the aerodynamic performance of a blower (80x 80x15 mm3) by redesigning its housing and rotor. Also, fan performance and acoustic experiment are conducted in an AMCA 210-99 test chamber and a semi-anechoic chamber following CNS-8753 code for ensuring a reliable test platform. In conclusion, based on experimental and CFD outcomes, the maximum flow rate and the static pressure of the improved design alternative are successfully increased by 19.5% and 25.53%, respectively.