Numerical Investigation of Two Double Swirl/Vortex Chamber Configurations for Turbine Blade Leading Edge Cooling

The objective of this work is to numerically assess the cooling performance of two double swirl/vortex chamber configurations (DSC and M-DVC). The predictive capability of five turbulence models is critically evaluated on fine and good-quality mesh for impinging and swirling flows. The averaged second norm  is employed to quantitatively measure the simulation error from each turbulence model compared to the experimental data. The RNG  turbulence model with enhanced wall treatment is found to be the most accurate and suitable for the simulation of impinging and swirling flows. Various key physical and dimensionless parameters, including thermal performance factor, turbulence kinetic energy and vorticity, are used to comparatively assess the cooling performance of DSC and M-DVC under the laboratory testing condition and the real operating condition at base load. The results reveal that DSC can enhance better heat transfer due to higher turbulence kinetic energy. Also, much more uniform Nusselt number distribution is obtained by DSC owing to more symmetric and uniformly distributed velocity and vorticity. With the real operating condition, DSC even performs much better than M-DVC

Mechanical Diaphragm Structure Design of a MEMS-Based Piezoresistive Pressure Sensor for Sensitivity and Linearity Enhancement

An improved design of the micro-electromechanical system (MEMS) piezoresistive pressure sensor with a combination of a petal edge, a beam, a peninsula, three cross beams and a center boss is proposed in this work for an operating range of low pressure in order to improve the sensor performance, i.e. the sensitivity and the linearity. The finite element method (FEM) is utilized to predict the stress and the deflection of the MEMS piezoresistive pressure sensor under the applied pressure of 1-5 kPa. The functional forms of the longitudinal stress, the transverse stress and the deflection are formulated by using the power law and then are used to optimize the geometry of the proposed design. The simulation results show that the proposed design is able to produce the high sensitivity up to 34 mV/kPa with the low nonlinearity of 0.11% full-scale span (FSS). The nonlinearity error is lowered by the proposed design of the peninsula, three cross beams and the center boss. The sensitivity is enhanced by increasing the petal edge width. The sensor performance of the proposed design is also compared to that of the previous design in the literature. The comparison reveals that the proposed design can perform better than the previous one

Activity for Diesel Particulate Matter Oxidation of Silver Supported on Al2O3, TiO2, ZnO, and CeO2: The Effect of Oxygen Concentration

Particulate matter (PM) is a problem for human health the major producer of PM are diesel engines. The diesel particulate filters (DPFs) are used for the limitation of the PM. The DPF operation consists of two sequential functions: PM filtering and regeneration. One of the main contributing factors affecting the regeneration of DPF is the oxygen concentration in the exhaust gas. This study investigates the impact of different oxygen concentrations (99.99%, 10%, and 5%) on (PM) oxidation when using silver catalysts supported on CeO2, ZnO, TiO2, and Al2O3. The synthesized catalysts were characterized using XRD, SEM, SEMEDX, and H2-TPR techniques, and the PM oxidation activity was evaluated using TGA. The results demonstrated that different oxygen concentrations had little effect on light VOCs oxidation compared to no catalyst or the same catalyst. However, heavy VOCs and soot combustion, which require a higher oxygen concentration, significantly reduce combustion performance when the oxygen concentration decreases

The Influence of Direct Non-Thermal Plasma Treatment on Soot Characteristics under Low Exhaust Gas Temperature

This study aimed to assess the effectiveness of nonthermal plasma (NTP) technology utilizing a dielectric barrier discharge (DBD) reactor, both with and without exhaust gas recirculation (EGR), in reducing soot particles and their impact on nitrogen oxides (NOx). The experiment involved maintaining a constant flue gas flow rate of 10 l/min, employing high voltage values of 0, 6, and 10 kV, fixed frequency of 500 Hz and setting the various IMEP of 5, 6, and 7 bar and the engine speed at 2,000 rpm. The findings demonstrated that NTP was successful in removing NOx by approximately 16.84% and 17.01%, achieving particle matter (PM) removal efficiencies of around 60.79% and 81.13%, and effectively reducing activation energy by approximately 18.34% and 31.5% (with and without EGR, respectively) at a high voltage of 10 kV. These results highlight the potential of NTP technology in mitigating emissions and reducing the environmental impact associated with diesel engines

CFD Investigation into Influences of a Transversely and Periodically Deforming Microchannel on Shear Stress Behavior in a Gut-on-a-chip Device

Organ-on-a-chip allows dynamic microenvironment of the actual organ to be simulated in vitro. In this study, the CFD simulation is used to investigate the behaviors of fluid flow and shear stress due to the effect of a transversely deforming membrane caused by the cyclic deformation of the microchannel sidewalls in a gut-on-a-chip device. The result reveals that the shear stress varies linearly along the length of the microchannel. The average shear stress per cycle is approximately three times greater than that of the stationary microchannel. The amplitude and frequency of the cyclic deformation also significantly affect the flow and shear stress behaviors. The highly dynamic shear stress in the gut-on-a-chip device could be one of the major factors that makes this kind of device more viable than the traditional static cell culture

Mixing-Performance Evaluation of a Multiple Dilution Microfluidic Chip for a Human Serum Dilution Process

This paper is aimed to propose a numerically designed multiple dilution microfluidic chip that can simultaneously deliver several serum dilutions in parallel. The passive mixing scheme is selected for dilution and achieved by the serpentine mixing channel in which Dean vortices are induced to increase the contact area and time for better diffusion. The mixing performance at the exit of this dilution chip is numerically evaluated using five commonly-used mixing indices with the goal that the homogeneity of the mixture over the exit cross-sectional area of the mixing channel must be greater than 93.319% to fulfill the six-sigma quality control