Applied Mechanics and Materials Vols. 284-287

Abstract: A novel continuous-flow polymerase chain reaction (PCR) chip has been analyzed in our work. It operates by cycling a prepared sample within three temperature zones. Two temperature zones are controlled by two external PID controllers. And the other is controlled by the flow rate of the fluid inside a water channel under the glass chip. The commercial software is utilized to determine the chip materials that are responsible for creating the denaturation, annealing and extension temperature zones within the chip. Therefore we utilize this PCR chip to perform PCR experiment. And DNA templates provided with the yT&A® cloning vector are amplified successfully.

Abstract: Numerical predictions of characteristics of turbulent flows through a square duct (30 30 mm) with twisted tape inserts and with twisted tape inserts plus interrupted ribs are conducted to investigate regionally averaged heat transfer and friction factors by using CFX 11.0 commercial code. The validity of the numerical results is confirmed by measurement. Reynolds numbers are varied between 8,900 and 29,000. A rib height-to-channel hydraulic diameter (e/Dh) of 0.067 and a length-to hydraulic diameter (L/Dh) of 30 are considered. The square ribs are arranged to follow the trace of the twisted tape and along the flow direction defined as axial interrupted ribs. The twisted tape is 0.1 mm thick carbon steel sheet with diameter of 28mm, length of 900mm and 2.5 turns. Each wall of the square channel is composed of the isolated aluminum section. The present study demonstrates that the twisted tape with interrupted ribs provides a greater overall heat transfer performance over the twisted tape with no ribs in the square duct.

Abstract: In this paper, the use of the finite element method in conjunction with abductive network is presented to predict the maximum forging force and effective stress for strain-hardening material during near net-shape helical forging. The maximum forging load and effective stress are influenced by the material properties such as yielding stress, strength coefficient and strain hardening exponent. A finite element method is used to investigate the clamping-type forging of helical gear. In order to verify the prediction of FEM simulation for forging load, the experimental data are compared with the results of current simulation. A finite element analysis is also utilized to investigate the material properties on forging load and maximum effective stress. Additionally, the abductive network was applied to synthesize the data sets obtained from the numerical simulation. The prediction models are then established for the maximum forging load and maximum effective stress of near net-shape helical gear forging under a suitable range of material parameters.

Abstract: The present study investigates experimentally and numerically the single-phase flow of two-fluid mixtures (H₂SO4 and _NaHCO3 solutions) and of water in a Y-typed micromixer with uniform, converging, and diverging cross-sections. The mean hydraulic diameter of the three kinds of main channel is approximately 174 µm. The experimental data of pressure drop agree with the theoretical predictions and CFD simulation results within 10%. Furthermore, the pressure distribution prediction for converging and diverging microchannels is consistent with that from CFD results. The pressure falls rapidly in the diverging microchannel near the entrance and slowly near the outlet. Such the pressure distribution may enable the forward flow of a bubble in a diverging microchannel.

Abstract: A rule-based SCR control strategy is developed for a 5% biodiesel fueled heavy-diesel engine. The control objective is to reduce the tail-pipe NOx emission while minimizing the urea dosage in a reliable fashion. A total of 32 runs of experimental test in ESC and ETC driving modes are conducted to demonstrate the performance and reliability of the rule-based control strategy. Average NOx reduction rates of 78.5% and 60% are achieved for the ESC and ETC tests respectively. In the mean time, the average urea dosage is 160 gram for the ESC tests and 0.49 % of the fuel consumption for the ETC tests. Variation of less than 7.78% and 12.05% for the ESC and ETC tests respectively demonstrate the reliability of the rule-based control strategy.

Abstract: Log mean temperature difference (LMTD) method neglecting the influence of heat radiation is conventionally used to calculate the total heat transfer rate of heat exchangers. From recent investigation of a single-pipe heat exchanger in some practical situations, it is found that the total heat transfer rate error of single-pipe heat exchanger obtained by LMTD method is up to 40% in the situation of oxidized metal heat exchanger with higher surface emissivity located in ambient air with low heat convection coefficient. A log mean heat transfer rate (LMHTR) method considering heat radiation has been developed to calculate the total heat transfer rate of a single-pipe heat exchanger and more accurate results can be achieved. It is also found in the present investigation that LMTD method is also not suitable to apply to non-insulated double-pipe heat exchangers and a more accurate LMHTR method considering heat radiation is developed to obtain the more reasonable results.

Abstract: The weld bead temperature distribution and shape during pulsed Nd:YAG laser lap welding are studied. A volumetric heat source model is derived to include the surface flux and the keyhole heat transfer effects in the pulsed laser lap welding process. The proposed pulsed laser heat transfer mode is employed in a simulation with the commercial finite element software Marc. The numerically computed results of the weld pool dimensions are compared with the experimental results. The comparison shows a good agreement between the simulated and measurement results, indicating that the proposed model is feasible. The results reveal that the pulse duration and spot pitch have considerable influence on the temperature field distribution and the residual stress distribution.

Abstract: Optimization of a microchannel heat sink has been performed based on the analyses of fluid flow and heat transfer with phase change using three-dimensional Reynolds-averaged Navier-Stokes equations. The uniform heat flux condition is applied at the bottom of the heat sink. Three design variables, viz. ratio of microchannel width to height of the heat sink, ratio of fin height to heat sink height, and ratio of fin width to height of the heat sink are selected for the shape optimization. Latin hypercube sampling was used to determine the training points as a design of experiment, and the surrogate model is constructed using the objective function values at the training points. Sequential quadratic programming is used to search for the optimal point from the constructed surrogate model. The thermal resistance is set as the objective function. It was found that the thermal resistance increased with increasing ratios of the microchannel width-to-height of the heat sink and fin height to heat sink height, while the thermal resistance decreased with increasing ratio of the fin width-to-height of the heat sink. Through the optimization, the thermal resistance has been decreased by 37.3% compared to the reference geometry.

Abstract: This paper addresses the dynamic characteristics of SOFC with an emphasis on control strategy development for optimized temperature control during load change. A methodology on regulating fuel utilization (Uf) and air excess ratio (λ) is investigated to validate alleviation of temperature fluctuation. An integrated dynamic model of SOFC, composed of mass balance, temperature balance, and electrochemistry, collaborates with Model Predictive Controller (MPC) in MATLAB/Simulink to verify the dynamic characteristic during load change process in the paper. A variable λ strategy is proposed and compared with traditional fixed λ strategy. Simulation results show the variable λ strategy can reduce the temperature variation for a safe operation, in comparison with that by the fixed λ strategy.

Abstract: This paper applies the software of Computational Fluid Dynamics (CFD)-FLUENT to analyze the flow field in the engine compartment of a light aircraft. The simulation results of the prototype model indicates that the airflow rapidly flows to the back of the engine compartment along the inside cowling after entering the engine compartment, rather than to the engine cylinder which will result in a very high cylinder temperature. Hence, this paper designs the air inlet, air duct, guide vane, and air outlet to improve the airflow in the engine compartment according to the drawbacks of the prototype model. The results show that the air duct and the guide vane help lead the airflow to the cylinder, and the air outlet effectively reduces the pressure in the engine compartment so that the airflow accelerates through the engine compartment, which is considered a feasible and economic improvement method in terms of the production cost.