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Background: Transumbilical laparoscopic appendectomy (TULA) may be a feasible alternative to conventional laparoscopic appendectomy. However, a transumbilical incision may increase incisional surgical site infections (SSIs) compared to conventional laparoscopic appendectomy. This study aimed to investigate the relationship between the morphology of the umbilicus and the incidence of SSIs in patients who underwent TULA. Patients and Methods: This retrospective study analysed the medical records of consecutive patients who underwent surgery for acute appendicitis at our institution from June 2016 to October 2020. The patients were assigned to the SSI group (those with an SSI) or the non-SSI group. The morphology of the umbilicus was calculated by measuring its width and depth on preoperative computed tomography images and was compared between the SSI and non-SSI groups. Results: The SSI group included 23 patients, while the non-SSI group included 252 patients. The width of the umbilicus was significantly shorter in the SSI group than in the non-SSI group (29 ± 10 mm vs. 34 ± 9 mm, P = 0.027). The umbilicus was slightly deeper in the SSI group than in the non-SSI group; however, the difference was not significant (16 mm vs. 15 mm, P = 0.384). Conclusions: This was the first study investigating the correlation between the morphology of the umbilicus and SSI development in TULA. SSIs tended to occur more commonly in a narrow and deep umbilicus. An extension of the umbilical incision may help prevent SSI in patients with this umbilical morphology.

Background and objectives: Single-port laparoscopic appendectomy (SLA) in most previous studies has used intracorporeal excision of the appendix and needed a longer operative time than multi-port laparoscopic appendectomy (MLA), although SLA does have the potential benefit of an almost invisible scar within the umbilicus. Some studies have reported that extracorporeal transumbilical single-incision laparoscopic-assisted appendectomy (TULAA) in children took a considerably reduced operative time compared to MLA. We adopted TULAA in adults, adding routine dissection of the peritoneal attachment of the appendix. The aim was to compare the operative outcomes between TULAA and MLA. Materials and Methods: Between March 2013 and January 2016, 770 patients with acute uncomplicated and complicated appendicitis from 15 to 75 years of age were enrolled retrospectively. The operation was performed as early (EA) and interval appendectomy (IA). Results: Operative time was shorter in the TULAA group than in the MLA group, except for IA. No open conversion occurred in the TULAA group, except one case of ileocecal resection for IA. No intra-abdominal fluid collection was found in the TULAA group. Extended resection (especially partial cecectomy) was performed less frequently in the TULAA group than in the MLA group for IA. Mean postoperative hospital stay was shorter in the TULAA group for uncomplicated appendicitis. When the data of the EA group and the IA group were compared, operative time was significantly shorter in the IA group for both MLA and TULAA. The open conversion rate and the complication rate tended to be lower in the IA group. Confined to IA, the TULAA group tended to have shorter mean initial, postoperative, and total hospital stays. Conclusions: TULAA can be a useful surgical alternative to MLA in adults and young adolescents, because it lacks open conversion and provides both a shorter operative time and a shorter postoperative hospital stay. TULAA is feasible for IA in that it showed a lower rate of extended resection and complications.

Breast surgery is a common procedure performed in women. Many women who undergo breast surgery suffer from ill-defined pain syndromes. A nerve block is used in the treatment of the acute and chronic pain, but the effectiveness of the treatment has been limited because of its short duration. Recently, the advent of pulsed radiofrequency lesioning (PRF) has proved a successful treatment for chronic refractory pain involving the peripheral nerves. We experienced a case of a 52-year-old female patient complaining of chronic breast neuropathic pain after breast reduction, which was relieved after PRF lesioning of the 4th thoracic spinal nerve and its root.

Newly introduced vehicles come with various added functions, each time utilizing data from different sensors. One prominent related function is autonomous driving, which is performed in cooperation with multiple sensors. These sensors mainly include image sensors, depth sensors, and infrared detection technology for nighttime use, and they mostly generate data based on image processing methods. In this paper, we propose a model that utilizes a parallel transformer design to gradually reduce the size of input data in a manner similar to a stairway, allowing for the effective use of such data and efficient learning. In contrast to the conventional DETR, this model demonstrates its capability to be trained effectively with smaller datasets and achieves rapid convergence. When it comes to classification, it notably diminishes computational demands, scaling down by approximately 6.75 times in comparison to ViT-Base, all the while maintaining an accuracy margin of within ±3%. Additionally, even in cases where sensor positions may exhibit slight misalignment due to variations in data input for object detection, it manages to yield consistent results, unfazed by the differences in the field of view taken into consideration. The proposed model is named Stairwave and is characterized by a parallel structure that retains a staircase-like form.

Micromixers are important components of lab-on-a-chip systems, and also have many biological and chemical applications [...]

In this study, a numerical investigation based on the CFD method is carried out to study the unsteady laminar flow of Newtonian fluid with a high viscosity in a three-dimensional simulation of a twisted double planetary mixer, which is composed of two agitating rods inside a moving tank. The considered stirring protocol is a “Continuous sine squared motion” by using the dynamic mesh model and user-defined functions (UDFs)to define the velocity profiles. The chaotic advection is obtained in our active mixers by the temporal modulation of rotational velocities of the moving walls in order to enhance the mixing of the fluid for a low Reynolds number and a high Peclet number. For this goal, we applied the Poincaré section and Lyapunov exponent as reliable mathematic tools for checking mixing quality by tracking a number of massless particles inside the fluid domain. Additionally, we investigated the development of fluid kinematics proprieties, such as vorticity, helicity, strain rate and elongation rate, at various time periods in order to view the impact of temporal modulation on the flow properties. The results of the mentioned simulation showed that it is possible to obtain a chaotic advection after a relatively short time, which can deeply enhance mixing fluid efficiency.

Three-dimensional numerical investigations of a novel passive micromixer were carried out to analyze the hydrodynamic and thermal behaviors of Nano-Non-Newtonian fluids. Mass and heat transfer characteristics of two heated fluids have been investigated to understand the quantitative and qualitative fluid faction distributions with temperature homogenization. The effect of fluid behavior and different Al2O3 nanoparticles concentrations on the pressure drop and thermal mixing performances were studied for different Reynolds number (from 0.1 to 25). The performance improvement simulation was conducted in intervals of various Nanoparticles concentrations (φ = 0 to 5%) with Power-law index (n) using CFD. The proposed micromixer displayed a mixing energy cost of 50–60 comparable to that achieved for a recent micromixer (2021y) in terms of fluid homogenization. The analysis exhibited that for high nanofluid concentrations, having a strong chaotic flow enhances significantly the hydrodynamic and thermal performances for all Reynolds numbers. The visualization of vortex core region of mass fraction and path lines presents that the proposed design exhibits a rapid thermal mixing rate that tends to 0.99%, and a mass fraction mixing rate of more than 0.93% with very low pressure losses, thus the proposed micromixer can be utilized to enhance homogenization in different Nano-Non-Newtonian mechanism with minimum energy.

In this work, a design optimization study was conducted to improve the performance of a membraneless microfluidic fuel cell with a double-bridge cross-section of the flow channel. Governing equations including Navier–Stokes, mass-transport, and Butler–Volmer equations were solved numerically to analyze the electrochemical phenomena and evaluate the performance of the fuel cells. Optimization was performed to maximize the peak power density using a genetic algorithm combined with a surrogate model constructed by radial basis neural network. Two sub-channel widths of the flow channel were selected as design variables for the optimization. As a result, a large increase in the inner channel width and a small decrease in the outer channel width effectively increased the peak power density of the MMFC. The optimal design increased the peak power density by 57.6% compared to the reference design.

The present work performed a comprehensive investigation to find the effects of a dual-bleeding port recirculation channel on the aerodynamic performance of a single-stage transonic axial compressor, NASA Stage 37, and optimized the channel’s configuration to enhance the operating stability of the compressor. The compressor’s performance was examined using three parameters: The stall margin, adiabatic efficiency, and pressure ratio. Steady-state three-dimensional Reynolds-averaged Navier–Stokes analyses were performed to find the flow field and aerodynamic performance. The results showed that the addition of a bleeding channel increased the recirculation channel’s stabilizing effect compared to the single-bleeding channel. Three design variables were selected for optimization through a parametric study, which was carried out to examine the influences of six geometric parameters on the channel’s effectiveness. Surrogate-based design optimization was performed using the particle swarm optimization algorithm coupled with a surrogate model based on the radial basis neural network. The optimal design was found to increase the stall margin by 51.36% compared to the case without the recirculation channel with only 0.55% and 0.28% reductions in the peak adiabatic efficiency and maximum pressure ratio, respectively.

In this work, a numerical investigation was analyzed to exhibit the mixing behaviors of non-Newtonian shear-thinning fluids in Kenics micromixers. The numerical analysis was performed using the computational fluid dynamic (CFD) tool to solve 3D Navier-Stokes equations with the species transport equations. The efficiency of mixing is estimated by the calculation of the mixing index for different cases of Reynolds number. The geometry of micro Kenics collected with a series of six helical elements twisted 180° and arranged alternately to achieve the higher level of chaotic mixing, inside a pipe with a Y-inlet. Under a wide range of Reynolds numbers between 0.1 to 500 and the carboxymethyl cellulose (CMC) solutions with power-law indices among 1 to 0.49, the micro-Kenics proves high mixing Performances at low and high Reynolds number. Moreover the pressure losses of the shear-thinning fluids for different Reynolds numbers was validated and represented.

A double-bridge shape is proposed as a novel flow channel cross-sectional shape of a membraneless microfluidic fuel cell, and its electrochemical performance was analyzed with a numerical model. A membraneless microfluidic fuel cell (MMFC) is a micro/nano-scale fuel cell with better economic and commercial viability with the elimination of the polymer electrolyte membrane. The numerical model involves the Navier–Stokes, Butler–Volmer, and mass transport equations. The results from the numerical model were validated with the experimental results for a single-bridge channel. The proposed MMFC with double-bridge flow channel shape performed better in comparison to the single-bridge channel shape. A parametric study for the double-bridge channel was performed using three sub-channel widths with the fixed total channel width and the bridge height. The performance of the MMFC varied most significantly with the variation in the width of the inner channel among the sub-channel widths, and the power density increased with this channel width because of the reduced width of the mixing layer in the inner channel. The bridge height significantly affected the performance, and at a bridge height at 90% of the channel height, a higher peak power density of 171%was achieved compared to the reference channel.

A fluidic oscillator with a bent outlet nozzle was investigated to find the effects of the bending angle on the characteristics of the oscillator with and without external flow. Unsteady aerodynamic analyses were performed on the internal flow of the oscillator with two feedback channels and the interaction between oscillator jets and external flow on a NACA0015 airfoil. The analyses were performed using three-dimensional unsteady Reynolds-averaged Navier-Stokes equations with a shear stress transport turbulence model. The bending angle was tested in a range of 0–40°. The results suggest that the jet frequency increases with the bending angle for high mass flow rates, but at a bending angle of 40°, the oscillation of the jet disappears. The pressure drop through the oscillator increases with the bending angle for positive bending angles. The external flow generally suppresses the jet oscillation, and the effect of external flow on the frequency increases as the bending angle increases. The effect of external flow on the peak velocity ratio at the exit is dominant in the cases where the jet oscillation disappears.

Membraneless microfluidic fuel cells (MMFCs) are being studied extensively as an alternative to batteries and conventional membrane fuel cells because of their simple functioning and lower manufacturing cost. MMFCs use the laminar flow of reactant species (fuel and oxidant) to eliminate the electrolyte membrane, which has conventionally been used to isolate anodic and cathodic half-cell reactions. This review article summarizes the MMFCs with six major categories of flow configurations that have been reported from 2002 to 2020. The discussion highlights the critical factors that affect and limit the performance of MMFCs. Since MMFCs are diffusion-limited, most of this review focuses on how different flow configurations act to reduce or modify diffusive mixing and depletion zones to enhance the power density output. Research opportunities are also pointed out, and the challenges in MMFCs are suggested to improve cell performance and make them practical in the near future.

During the last couple of decades, there have been rapid developments in analysis, design, and fabrication of micromixers [...]

A casing treatment using inclined oblique slots (INOS) is proposed to improve the stability of the single-stage transonic axial compressor, NASA Stage 37, during operation. The slots are installed on the casing of the rotor blades. The aerodynamic performance was estimated using three-dimensional steady Reynolds-Averaged Navier-Stokes analysis. The results showed that the slots effectively increased the stall margin of the compressor with slight reductions in the pressure ratio and adiabatic efficiency. Three geometric parameters were tested in a parametric study. A single-objective optimization to maximize the stall margin was carried out using a Genetic Algorithm coupled with a surrogate model created by a radial basis neural network. The optimized design increased the stall margin by 37.1% compared to that of the smooth casing with little impacts on the efficiency and pressure ratio.

In this work, a comparative investigation of chaotic flow behavior inside multi-layer crossing channels was numerically carried out to select suitable micromixers. New micromixers were proposed and compared with an efficient passive mixer called a Two-Layer Crossing Channel Micromixer (TLCCM), which was investigated recently. The computational evaluation was a concern to the mixing enhancement and kinematic measurements, such as vorticity, deformation, stretching, and folding rates for various low Reynolds number regimes. The 3D continuity, momentum, and species transport equations were solved by a Fluent ANSYS CFD code. For various cases of fluid regimes (0.1 to 25 values of Reynolds number), the new configuration displayed a mixing enhancement of 40%–60% relative to that obtained in the older TLCCM in terms of kinematic measurement, which was studied recently. The results revealed that all proposed micromixers have a strong secondary flow, which significantly enhances the fluid kinematic performances at low Reynolds numbers. The visualization of mass fraction and path-lines presents that the TLCCM configuration is inefficient at low Reynolds numbers, while the new designs exhibit rapid mixing with lower pressure losses. Thus, it can be used to enhance the homogenization in several microfluidic systems.

Optimum configuration of a micromixer with two-layer crossing microstructure was performed using mixing analysis, surrogate modeling, along with an optimization algorithm. Mixing performance was used to determine the optimum designs at Reynolds number 40. A surrogate modeling method based on a radial basis neural network (RBNN) was used to approximate the value of the objective function. The optimization study was carried out with three design variables; viz., the ratio of the main channel thickness to the pitch length (H/PI), the ratio of the thickness of the diagonal channel to the pitch length (W/PI), and the ratio of the depth of the channel to the pitch length (d/PI). Through a primary parametric study, the design space was constrained. The design points surrounded by the design constraints were chosen using a well-known technique called Latin hypercube sampling (LHS). The optimal design confirmed a 32.0% enhancement of the mixing index as compared to the reference design.

Submersible pumps are now in high demand due to the sporadic occurrence of recent torrential rains. The current study was carried out to investigate the hydraulic characteristics of a submersible axial-flow pump with a swept impeller and to optimize the impeller and diffuser shapes of the pump to enhance the hydraulic performance. Three-dimensional Reynolds-averaged Navier–Stokes equations were solved with the shear stress transport turbulence model. The governing equations were discretized using the finite volume method, and unstructured tetrahedral and hexahedral meshes were used in the grid system. The optimal grid system was selected through a grid dependency test. A performance test for the submersible axial-flow pump was carried out experimentally, and the results of the numerical analysis were validated against the experimental results. The hydraulic efficiency and the total head were used as objective functions. For the first optimization, a multi-objective optimization was carried out to simultaneously improve the objective functions through a hybrid multi-objective evolutionary algorithm coupled with a response surface approximation by varying the swept angle and pitch angle of the blades of the rotating impeller. The second multi-objective optimization was performed using two design variables, i.e., the inlet angle and the length of the diffuser vanes, to simultaneously increase the objective functions. Clustered optimum designs in the Pareto optimal solutions yielded significant increases in the objective function values as compared with the reference design.

A wide range of existing passive micromixers are reviewed, and quantitative analyses of ten typical passive micromixers were performed to compare their mixing indices, pressure drops, and mixing costs under the same axial length and flow conditions across a wide Reynolds number range of 0.01–120. The tested micromixers were selected from five types of micromixer designs. The analyses of flow and mixing were performed using continuity, Navier-Stokes and convection-diffusion equations. The results of the comparative analysis were presented for three different Reynolds number ranges: low-Re (Re ≤ 1), intermediate-Re (1 < Re ≤ 40), and high-Re (Re > 40) ranges, where the mixing mechanisms are different. The results show a two-dimensional micromixer of Tesla structure is recommended in the intermediate- and high-Re ranges, while two three-dimensional micromixers with two layers are recommended in the low-Re range due to their excellent mixing performance.

Background: To date, most intradialytic hypotension (IDH) studies have proposed technologies to comprehensively predict the occurrence of IDH using the patient’s baseline information and ultrafiltration (UF) information, but it is difficult to apply the technologies while identifying the patient’s condition in real time. Methods: In this study, we propose an IDH indicator that uses heart rate (HR) change information to identify the patient’s condition in real time and visually shows whether IDH has occurred. The data used were collected from 40 dialysis patients in a clinical trial conducted in the Artificial Kidney Unit at Yeungnam University Medical Center, Korea, from 18 July to 29 November 2023. Results: The IDH indicator infers changes in the patient’s blood pressure during dialysis by analyzing the upper and lower maximum HRs based on the real-time average HR. Medical staff can respond to IDH in real time by looking at the IDH indicator, which visually expresses changes in the patient’s HR. In addition, we propose a multilayer perceptron structure that inputs upper and lower maximum HR information based on the average HR for the time interval accumulated in real time. In learning using 40 min of data up to 5 min before IDH occurred, models using two and five layers showed excellent performance, with accuracy of 88.6% and 85.2%, respectively. Conclusions: By combining IDH visual indicators and the multi-layer perceptron method, medical staff can effectively respond to IDH in real time.

This study numerically evaluates the performance of flow control using fluidic oscillators on the NACA 0015 airfoil with a flap at different flap angles and different pitch angles of the oscillators. An inline array of fluidic oscillators is located just in front of the flap. Aerodynamic analysis was carried out using three-dimensional unsteady Reynolds-averaged Navier-Stokes equations in a computational domain that consists of the external domain around the airfoil and the internal domains in three fluidic oscillators. Flap angles of 20°, 40°, and 60° were tested with a fixed angle of attack of 8°. For each flap angle, the effects of the pitch angle of the oscillators on the aerodynamic performance were evaluated in a range of 60° to the negative value of the corresponding flap angle. It was found in this work that the oscillator jets parallel to the flap showed the best performance, which was achieved by using negative pitch angles and also bending the outlets of the oscillators. The results indicate that the aerodynamic performance varies significantly with the flap and pitch angles.

In this study, a fluidic oscillator was optimized based on the three-dimensional unsteady Reynolds-averaged Navier-Stokes analysis to enhance peak jet velocity at the outlet and simultaneously reduce pressure drop. A multi-objective genetic algorithm performed the optimization with surrogate modeling. The ratios of the inlet nozzle width and the distance between the splitters to the throat width were chosen as the design variables. And, two objective functions related to peak jet velocity at the outlet and pressure drop through the fluidic oscillator were selected for the optimization. Ten design points were selected in the design space using a Latin hypercube sampling method; the objective functions were calculated by unsteady Reynolds-averaged Navier-Stokes analysis at these design points to construct surrogate models that were used to approximate the objective functions. Two different surrogate models, namely response surface approximation and Kriging models were tested. Pareto-optimal front representing a compromise between the two objective functions was obtained from the multi-objective optimization. The optimization results indicated that a jet velocity-oriented optimum design increased the peak jet velocity ratio at the outlet and the friction factor by 11.18% and 16.82%, respectively, when compared to those of a friction factor-oriented design.

To improve cooling effectiveness of film-cooling hole, bending of hole was investigated and optimized using surrogate modelling based on three-dimensional Reynolds-averaged Navier-Stokes analysis. The turbulence was modeled using a shear stress transport model. The spatially-averaged film-cooling effectiveness was employed as the objective function, and the injection angles of the lower and upper cylindrical parts and height of the bending point were selected as design variables for optimization. The Kriging model was used to approximate the objective function. 27 design points were selected by the Latin hypercube sampling, where objective function values were calculated to construct the surrogate models. The results at a blowing ratio of 0.5 showed that the optimum bended film-cooling hole improved the spatially-averaged film-cooling effectiveness by 39.9 % and 78.0 % compared to a reference bended hole and a cylindrical hole, respectively.

In this study, a numerical investigation on mixing and flow structure in a serpentine microchannel with non-aligned input channels was performed. The non-aligned input channels generate a vortical flow, which is formed by incoming fluid streams through tangentially aligned channels. Mixing index was evaluated to measure the degree of mixing in the micromixer. Analyses of mixing and flow field were investigated for a Reynolds number range starting from 0.1 to 120. The vortical structure of the flow was analyzed to find its effect on the mixing performance. Mixing of two working fluids in the micromixer was evaluated by using three-dimensional Navier–Stokes equations. In order to compare the mixing performance between the serpentine micromixers with and without non-aligned inputs, the geometric parameters, such as cross-section areas of the input channels and main channel, height of the channel, axial length of the channel, and number of pitches, were kept constant. Pressure drops were also calculated with fixed axial length in both cases.

A micromixer with unbalanced three-split rhombic sub-channels was proposed, and analyses of the mixing and flow characteristics of this micromixer were performed in this work. Three-dimensional Navier-Stokes equations in combination with an advection-diffusion model with two working fluids (water and ethanol) were solved for the analysis. The mixing index and pressure drop were evaluated and compared to those of a two-split micromixer for a range of Reynolds numbers from 0.1–120. The results indicate that the proposed three-split micromixer is efficient in mixing for a range of Reynolds numbers from 30–80. A parametric study was performed to determine the effects of the rhombic angle and sub-channel width ratio on mixing and pressure drop. Except at the lowest Reynolds number, a rhombic angle of 90° gave the best mixing performance. The three-split micromixer with minimum minor sub-channel widths provided the best mixing performance.

The three-dimensional geometry of a micromixer with an asymmetrical split-and-recombine mechanism was optimized to enhance the fluid-mixing capability at a Reynolds number of 20. Single and multi-objective optimizations were carried out by using particle swarm optimization and a genetic algorithm on a modeled surrogate surface. Surrogate modeling was performed using the computational results for the mixing. Mixing and flow analyses were carried out by solving the convection−diffusion equation in combination with the three-dimensional continuity and momentum equations. The optimization was carried out with two design variables related to dimensionless geometric parameters. The mixing effectiveness was chosen as the objective function for the single-objective optimization, and the pressure drop and mixing index at the outlet were chosen for the multi-objective optimization. The sampling points in the design space were determined using a design of experiment technique called Latin hypercube sampling. The surrogates for the objective functions were developed using a Kriging model. The single-objective optimization resulted in 58.9% enhancement of the mixing effectiveness compared to the reference design. The multi-objective optimization provided Pareto-optimal solutions that showed a maximum increase of 48.5% in the mixing index and a maximum decrease of 55.0% in the pressure drop in comparison to the reference design.

A cratered film-cooling hole was investigated to determine the effect of shape parameters on film-cooling performance, and shape of the hole was optimized to improve film-cooling effectiveness. Numerical analyses were performed using three-dimensional Reynolds-averaged Navier-Stokes (RANS) equations. The numerical results were validated by comparison with experimental data for film-cooling effectiveness for cratered film cooling. The ratio of the major axis length of the crater to the diameter of the hole, the ratio of the minor axis length of the crater to the diameter of the hole, and the ratio of the depth of the crater to the diameter of the hole were chosen as the design variables. From the results of a parametric study, the effects of these three design variables on film-cooling effectiveness were evaluated. The spatially-averaged film-cooling effectiveness was defined as the objective function. The values of the objective function were numerically evaluated through a RANS analysis at the design points determined by Latin hypercube sampling to construct surrogate models, i.e., RSA, RBNN, and Kriging models. Sequential quadratic programming was applied to search for the optimal point from the constructed surrogate models. The result showed that the Kriging model gave best optimization result and the film-cooling effectiveness for a cratered hole was improved by about 20% through the optimization in comparison with the reference geometry.

Micromixers are important components of microfluidic systems [...]

Vortex flow increases the interface area of fluid streams by stretching along with providing continuous stirring action to the fluids in micromixers. In this study, experimental and numerical analyses on a design of micromixer that creates vortex flow were carried out, and the mixing performance was compared with a simple micro T-mixer. In the vortex micro T-mixer, the height of the inlet channels is half of the height of the main mixing channel. The inlet channel connects to the main mixing channel (micromixer) at the one end at an offset position in a fashion that creates vortex flow. In the simple micro T-mixer, the height of the inlet channels is equal to the height of the channel after connection (main mixing channel). Mixing of fluids and flow field have been analyzed for Reynolds numbers in a range from 1–80. The study has been further extended to planar serpentine microchannels, which were combined with a simple and a vortex T-junction, to evaluate and verify their mixing performances. The mixing performance of the vortex T-mixer is higher than the simple T-mixer and significantly increases with the Reynolds number. The design is promising for efficiently increasing mixing simply at the T-junction and can be applied to all micromixers.

In order to maximize the mixing performance of a micromixer with an integrated three-dimensional serpentine and split-and-recombination configuration, multi-objective optimizations were performed at two different Reynolds numbers, 1 and 120, based on numerical simulation. Numerical analyses of fluid flow and mixing in the micromixer were performed using three-dimensional Navier-Stokes equations and convection-diffusion equation. Three dimensionless design variables that were related to the geometry of the micromixer were selected as design variables for optimization. Mixing index at the exit and pressure drop through the micromixer were employed as two objective functions. A parametric study was carried out to explore the effects of the design variables on the objective functions. Latin hypercube sampling method as a design-of-experiment technique has been used to select design points in the design space. Surrogate modeling of the objective functions was performed by using radial basis neural network. Concave Pareto-optimal curves comprising of Pareto-optimal solutions that represents the trade-off between the objective functions were obtained using a multi-objective genetic algorithm at Re = 1 and 120. Through the optimizations, maximum enhancements of 18.8% and 6.0% in mixing index were achieved at Re = 1 and 120, respectively.

Shape optimization of heat transfer augmentation device employed in turbine blade internal cooling passage has been performed numerically using single as well as multi-objective optimization procedures. Polynomial response surface approximation method and multi-objective genetic algorithm are used for single and multi-objective optimizations, respectively. Problem to enhance heat transfer rate considering staggered dimples on single surface of cooling passage has been formulated, and Reynolds-averaged Navier-Stokes equations are solved to analyze the flow field and the heat transfer. Three design variables defining channel and dimple dimensions, and two objective functions related to Nusselt number and friction drag are employed. Latin hypercube sampling is used to generate sampling points in design space, and the evaluated objectives are used to generate a set of optimal designs. Optimal shapes show higher heat transfer rates in the case of lower channel height, higher dimple depth and higher dimple spacing, but these geometries also produce higher pressure drops.

Performance characteristics of an axial flow fan having distorted inlet flow have been investigated using numerical analysis. Two kinds of hub-cap, rounded and right-angled front shape, are tested to investigate the effect of inlet flow distortion on the fan performance. In case of right-angled front shape, axisymmetric distorted inflow is induced by flow separation at the sharp edge of hub-cap, and the characteristics of the inflow depend on the distance between hub-cap and blade leading edge. Three-dimensional Reynolds-averaged Navier-Stokes equations are introduced to analyze the flow characteristics inside the blade passage. Numerical solutions are validated in comparison with experimental data measured by a five-hole probe downstream of the fan rotor. It is found from the numerical results that non-uniform axial inlet velocity profile near the hub results in the change of inlet flow angle. Large recirculation flow upstream the fan rotor for the right-angled hub-cap induces separated flow on the blade surfaces near the hub region, and thus deteriorates the performance of fan rotor. The effect of the distance between hub-cap and blade leading edge on the efficiency is also discussed.

A T-shaped micromixer featuring electroosmotic flow with heterogeneous charged surface patches on the channel walls was analyzed, and an improved design was proposed to enhance mixing performance. Numerical analysis was performed using steady Navier-Stokes equations with an additional electrokinetic body force. The numerical results for species concentration were validated with available experimental data. A parametric analysis of the micromixer was performed by varying channel height, channel width, patch width, and externally applied voltage. The effects of these parameters on the flow structure and mixing performance were analyzed in detail. A quantitative measurement based upon the mass variance was employed to quantify the mixing performance. Numerical results of the parametric study were used to propose an improved micromixer design with spacing between adjacent charged patches. The proposed design provided a more favorable flow structure to allow for enhanced mixing performance.

Performance analysis of double-layer microchannel heat sinks was performed under non-uniform heating conditions having randomly distributed hotspots. Two parallel-channel (parallel-flow and counter-flow) and one cross-channel (transverse-flow) designs of double-layer heat sink were evaluated with three sets of heating schemes. Each set of heating scheme consisted of eleven randomly distributed hotspots generated by Latin hypercube sampling. The heat flux, area, and location of the hotspots were selected as the design parameters. Conjugate heat transfer analysis of the heat sinks was performed by solving three-dimensional Navier–Stokes and energy equations. Water with temperature-dependent properties was selected as the coolant. The thermal resistance, pressure drop, maximum temperature rise, and temperature variation among hotspots were evaluated for all the heat sinks. The transverse-flow microchannel heat sink exhibited the lowest thermal resistance, temperature rise and temperature variation among the hotspots throughout the specified range of flow rate. The lowest pressure drop was exhibited by the counter-flow heat sink.