Abstract: Baffles loaded by split-ring resonator (SRR) are proposed to reduce the mutual coupling for ±45° dual-polarized multiple-input–multiple-output (MIMO) antenna. Each baffle consists of two rectangular SRR printed on one side of a 1 mm FR4 substrate. The final decoupling structure contains four baffles forming a barrier wall that reduces the coupling over the 5G band of 3.4–3.8 GHz. Dual-polarized cross-dipole array with SRR loading baffles is simulated and measured to demonstrate their effectiveness in the coupling reduction. The results show that the mutual coupling can be effectively reduced below −25 dB over the entire bandwidth while maintaining a compact array.

Abstract: Microfluidics is recognized as a powerful tool to perform series of experiments with high efficiency and low reagent consumption. Micromixers are known to be a very important part of the integrated microfluidic systems. The present work investigates the mixing enhancement of microfluids using a micromixer through a passive method. New type of baffles based on topology optimization are presented to augment the advection part of the mixing. Numerical simulation is carried out using Comsol Multiphysics software. The results are verified using experimental findings collected from a manufactured sample of the designed micromixer. The demonstrated geometry causes the entire mixing to take place at a short time and the length of a microchannel. The mixing quality was declined by increasing Reynolds number from Re = 0.2–5. In addition, the mixing mechanism in this range is a pure diffusion. Consequently, an increase of the Reynolds number results in lower residence time and mixing index. By increasing the Reynolds number (exceeding Re = 5), the mixing index can be improved (reaching MI = 0.98 at Re = 100). The formation of vortexes behind the designed baffles (exceeding Re = 5) is the main proof for the enhanced mixing.

Abstract: In mountainous terrain, landslide debris is a common occurrence around the world that can potentially result in catastrophic consequences to downstream residents and facilities. Arrays of baffles are increasingly used as energy dissipaters for the protection from debris flow due to their low cost and environmental impact. However, the development of a numerical tool for the rational design of such structures is still a challenge. In this work, a material point method computational framework is presented, using two contact models to describe the landslide debris movement and interaction with structures, respectively. Flume model experiments are adopted as calibration and good agreements are exhibited in flow kinematics between computed results and physical model tests. Simulations on an idealized scenario of landslide debris flow show how the baffle geometry/arrangement has key effects on the debris movement and deposition. The impact force in soil-structure interaction has also been studied, showing the ability of this method on evaluation force characteristics acted on baffle structures.

Abstract: Concentrated Solar Power (CSP) technology captures solar radiation and converts it into heat for electricity production. It has received an increasing attention because integrated thermal energy storage (TES) systems can largely enhancing the reliability and the dispatchability. Over the last decade, low-cost single storage tank based on the thermocline technology becomes an alternative to commonly-used two-tank TES system. However, the improper inlet/outlet manifolds may cause the strong mixing of hot and cold fluids and disturb the temperature stratification, resulting in reduced thermal performances of the storage tank. This study aims at solving the flow maldistribution problem in the single-tank thermocline storage system by appropriately structuring the inlet/outlet manifolds. The technical solution is based on the insertion of optimized perforated baffles in the manifolds. 2D Computational fluid dynamics simulations were performed to calculate the transient flow and temperature profiles in the storage tank during the charging and discharging operations. The optimal size distribution of orifices on the upper baffle has been determined for homogenizing passage times of the thermal front, so as to enhance the temperature stratification. A novel intermediate evaluation indicator was introduced to characterize the real-time thermal behavior, which could reduce the computational cost of the optimization problem by a factor of 6 at least. Numerical results shown that the proposed optimization algorithm could significantly improve the thermal performances, indicated by the increased values of charging/discharging efficiency, the capacity ratio and the overall efficiency, ex., the fully charging efficiency be increased by 29% by comparing the unstructured manifold geometry and the one with optimized baffles. The parametric study on certain geometry and operating factors also demonstrated that the proposed method for flow distribution optimization was robust, effective and efficient.

Abstract: In the present study, the fluid flow and heat transfer of a Cu-water nanofluid in a L-shaped enclosure with a baffle is numerically simulated using the Lattice Boltzmann Method (LBM). The implementation of different baffle combinations with the L shape cavity is the novel contribution of this study. The effect of baffle configuration on natural convection in different parameter ranges of Rayleigh number ( 10 3 – 10 5 ) and nanoparticle volume fraction (0–0.05) is investigated. Various baffle configuration cases are examined based on baffle length (L) and position (S). The baffled L shape results are also compared to the results obtained from a L shape without a baffle that were also achieved in this study and are validated with excellent agreement with existing data. Different models are used for evaluating the dynamic viscosity and thermal conductivity, to compare the effects of nanofluid properties. The results show that at low Rayleigh numbers ( 10 3 – 10 4 ), the addition of baffle always enhances natural convection. In high Rayleigh numbers ( 10 5 ), only the longer baffle (L = 0.30 m) can improve natural convection regardless of its positioning. The longer baffle is always more effective with proper positioning (S = 0.4 m) and the case C baffle configuration (L = 0.30 m, S = 0.4 m) is the most effective in all conditions.

Abstract: Methanol as a hydrogen carrier can be reformed with steam over Cu/ZnO/Al2O3 catalysts. In this paper a comprehensive pseudo-homogenous model of a multi-tubular packed-bed reformer has been developed to investigate the impact of operating conditions and geometric parameters on its performance. A kinetic Langmuir-Hinshelwood model of the methanol steam reforming process was proposed. In addition to the kinetic model, the pressure drop and the mass and heat transfer phenomena along the reactor were taken into account. This model was verified by a dynamic model in the platform of ASPEN. The diffusion effect inside catalyst particles was also estimated and accounted for by the effectiveness factor. The simulation results showed axial temperature profiles in both tube and shell side with different operating conditions. Moreover, the lower flow rate of liquid fuel and higher inlet temperature of thermal air led to a lower concentration of residual methanol, but also a higher concentration of generated CO from the reformer exit. The choices of operating conditions were limited to ensure a tolerable concentration of methanol and CO in H2-rich gas for feeding into a high temperature polymer electrolyte membrane fuel cell (HT-PEMFC) stack. With fixed catalyst load, the increase of tube number and decrease of tube diameter improved the methanol conversion, but also increased the CO concentration in reformed gas. In addition, increasing the number of baffle plates in the shell side increased the methanol conversion and the CO concentration.

Abstract: In the present work, heat transfer and pressure drop characteristics in flow through a tube with inline and staggered baffles having angular cut at the edge are reported for various operating conditions. An experimental test rig is designed and developed to investigate heat transfer and pressure drop behavior for different conditions. Effects of different geometrical parameters, i.e., pitch ratios, baffle arrangement and cutting angle of baffles on heat transfer rate and pressure drop characteristics, have been investigated for turbulent flow regime. Reynolds number ranging from 10,000 to 52,000 has been considered in the present study. The maximum heat transfer rate has been observed for staggered arrangement with pitch ratio of 0.1 and cutting angle of 60°, while minimum heat transfer rate has been observed for inline arrangement with pitch ratio of 0.2 and cutting angle of 30°. Empirical correlations for Nusselt number and friction factor have been developed as a function of geometrical and flow parameters. The deviations between experimental and predicted values of Nusselt number and friction factor for staggered arrangements have been observed as ± 10%, ± 4%, respectively, whereas for inline arrangement the deviation has been observed as ± 12%, ± 5%, respectively. Results from empirical correlations are well agreed with the experimental data.

Abstract: Drainage channels with step-pool system are widely used to control debris flow. The blocking of debris flow often gives rise to local damage at the steps and baffles. Hence, the estimation of impact force of debris flow is crucial for designing step-pool channel. Existing empirical models for impact pressure prediction cannot consider the influence of baffle shape. In this work, a three-dimensional smoothed particle hydrodynamics (SPH) study on the impact behavior of debris flows in step-pool systems is presented, where debris material is modeled using the regularized Bingham model. The SPH method is first checked using the results from two laboratory tests. Then, it is used to investigate the influence of baffle shape and flow density. Numerical results show that the impact pressure at the first baffle highly depends on the baffle shape; however, the largest impact pressure usually occurs at subsequent baffles due to the violent impact induced by jet flows. The peak impact pressure at the first baffle initially grows with increasing flow density; however, it starts to drop as density is beyond a threshold. Based on the numerical results, an empirical relation considering the influence of baffle shape is proposed for better prediction of debris impact pressure.

Abstract: The performance of corrugated baffles inserted in a rectangular channel heat exchanger is investigated. The fluid flows and thermal distribution are determined via numerical simulations. The working fluid has a shear thinning behavior. The influence of the baffle design is explored, we interest to the “wavy” shape. The corrugation angle of baffle (α) is changed from 0° (i.e. a straight baffle) to 45°. Also, the height (h) of the corrugated baffle is changed and three cases are considered, namely: h/H = 0.4, 0.5 and 0.6, where “H” is the channel height. In comparison with the unbaffled channel, the overall performance factor has increased from 1.27 up to 1.53 when the corrugation angle is increased from 0° to 45°. Concerning the corrugation height, the predicted results allowed us to select the case h/H = 0.5 as the best configuration from the cases studied.