Search Results (28)

How suspended grains traverse energy-dissipating micro-passages determines whether sediment-laden water can be used without rapid emitter deterioration. A novel cylindrical asteroid-shaped drip emitter was investigated through laboratory anti-clogging tests and two-way coupled computational fluid dynamics–discrete element method (CFD–DEM) simulations. The laboratory tests comprised 20 intermittent irrigation cycles at five pressures ranging from 60 to 140 kPa, with relative discharge used to characterize hydraulic performance. The simulations tracked particle motion, wall collisions, and mass transmission over a 0.20 s observation window to examine the effects of operating pressure, injected particle mass, and flow-path radius. Numerical cases isolated hydraulic forcing and, at 100 kPa, changes in solids dose and cavity radius. Measured discharge retention occupied a narrow 96.45–97.83% interval, whereas the fraction of particulate mass leaving the domain spanned 81.3–92.7%. Despite representing different responses, both indices followed pressure in a closely associated manner (Pearson r = 0.975, p = 0.0046). Stronger forcing extended the high-speed portion of individual trajectories and brought the final wall contacts forward in time, although contact totals did not follow a monotonic sequence. Changing the dose between 1.0 and 2.0 × 10⁻⁶ kg altered the selected upper-speed statistics by only +1.8% and −2.1% but reshaped the contact histories. Expanding the radius from 0.65 to 0.85 mm produced much larger reductions of 28.1% and 91.3%; the latter record then showed sustained near-stagnation with relatively few impacts. Thus, low collision frequency cannot independently demonstrate effective sediment passage. Combining effluent mass balance with trajectory and contact information provides a mechanistic basis for diagnosing retention in irrigation microchannels. Full article

Efficient thermal management is critical for maintaining the safety, durability, and performance of lithium-ion batteries used in electric vehicles (EVs). In this study, a comprehensive numerical investigation is conducted to evaluate the heat transfer characteristics of mono- and hybrid-nanofluids in a microchannel-cooled lithium-ion battery module. A three-dimensional computational model of a 5S7P battery module composed of cylindrical 21700 cells is developed. Battery heat generation during 3C high discharge rate operation is predicted using the Newman-Tiedemann-Gu-Kim (NTGK) electrochemical model, while coolant flow and heat transfer are simulated using the governing conservation equations for mass, momentum, and energy. The cooling system consists of six liquid-cooling plates with circular microchannels. The performance of water-glycol (50/50) coolant is compared with several mono nanofluids of Al₂O₃ and Cu, and hybrid nanofluids of Al₂O₃-Cu, Al₂O₃-MWCNT, Al₂O₃-Graphene, Cu-MWCNT, and Cu-Graphene across multiple coolant flow rates from 1–5 LPM. The results demonstrate that nanofluids significantly enhance convective heat transfer and reduce battery temperature compared with the conventional water-glycol coolant. Among the investigated coolants, the Al₂O₃-Cu hybrid nanofluid (0.45–0.45%) operating at 1 LPM achieves the best overall thermo-hydraulic performance with a performance evaluation criterion (PEC) of 1.065. Further analysis of nanoparticle composition ratios shows that a Cu-dominant hybrid mixture (Al₂O₃-Cu: 0.27–0.63%) slightly improves the PEC to 1.0657, indicating marginally superior cooling performance. The findings highlight the potential of hybrid nanofluids as advanced coolants for microchannel-based battery thermal management systems in EVs, particularly under moderate coolant flow conditions. Full article

Effective thermal management is critical for high-power lithium-ion batteries to mitigate excessive heat generation and ensure operational reliability. Failure to maintain a uniform temperature distribution can lead to accelerated capacity fading and severe safety risks, such as thermal runaway. In this study, a ferrofluid-based magnetohydrodynamic (MHD) microchannel cooling system was numerically investigated to elucidate the influence of magnetic intensity, magnet geometry, and electrical boundary conditions on flow behavior and heat transfer performance for battery cooling applications. A fully coupled multiphysics model incorporating electromagnetic, fluid flow, and heat transfer phenomena was developed and validated against experimental and numerical data from the literature. The results show that increasing the applied voltage enhances current density and Lorentz force almost linearly, leading to significant flow acceleration and improved convective heat transfer. Electrical insulation effectively suppresses current leakage into the channel walls, increasing the average current density by up to 222% and the Lorentz force by more than 300%. Compared with a cylindrical magnet, a rectangular magnet provides a more uniform magnetic field distribution and stronger near-wall Lorentz forcing, resulting in superior cooling performance. Under a 4C discharge condition, the insulated rectangular magnet reduces the maximum battery temperature by approximately 30% and increases the average Nusselt number by up to 103% relative to the non-insulated case. The findings reveal the critical roles of magnetic-field-controlled flow symmetry and near-wall forcing in MHD-driven microchannels, and provide practical design guidelines for battery cooling systems with no moving mechanical parts and active electromagnetic flow control. Full article

The heat transfer enhancement of diamond-shaped ribs mounted in the periodic merging chambers of microchannel (MC) heat sinks is investigated using a numerical method for Reynolds number in the region of 300–700. Compared to triangular, rectangular, and cylindrical ribs, diamond-shaped ribs achieve 3.59%, 13.24%, and 6.34% higher enhancement effects, respectively, under the same mass flow rate. Further analysis of geometric parameters (length, width, and height) and rib positioning reveals that a rib height of h/H_ch = 0.8 provides optimal heat dissipation performance. For Re < 500, the optimal configuration is a rib length of l/L_merg = 0.55 and a width of b/W_ch = 0.8, while for 500 < Re < 700, it shifts to l/L_merg = 0.36 and b/W_ch = 1.6. For s/L_merg, the smaller it is, the shorter the main flow separation time, thereby improving heat transfer efficiency. Full article

This study analyzes the impact of slip-dependent zeta potential on the heat transfer characteristics of nanofluids in cylindrical microchannels with consideration of thermal radiation effects. An analytical model is developed, accounting for the coupling between surface potential and interfacial slip. The linearized Poisson–Boltzmann equation, along with the momentum and energy conservation equations, is solved analytically to obtain the electrical potential field, velocity field, temperature distribution, and Nusselt number for both slip-dependent (SD) and slip-independent (SI) zeta potentials. Subsequently, the effects of key parameters, including electric double-layer (EDL) thickness, slip length, nanoparticle volume fraction, thermal radiation parameters, and Brinkman number, on the velocity field, temperature field, and Nusselt number are discussed. The results show that the velocity is consistently higher for the SD zeta potential compared to the SI zeta potential. Meanwhile, the temperature for the SD case is higher than that for the SI case at lower Brinkman numbers, particularly for a thinner EDL. However, an inverse trend is observed at higher Brinkman numbers. Similar trends are observed for the Nusselt number under both SD and SI zeta potential conditions at different Brinkman numbers. Furthermore, for a thinner EDL, the differences in flow velocity, temperature, and Nusselt number between the SD and SI conditions are more pronounced. Full article

This study proposes a platinum catalytic plate burner with a clover-shaped microchannel design to reduce the maximum temperature difference (ΔT_max) and improve long-term hydrogen production (HP) performance in an autothermal methanol steam reforming (ATMSR) microreactor. The burner integrates with a plate reformer within a cylindrical adiabatic container. By optimizing catalyst arrangement and incorporating a parallel clover-type microchannel design, thermal gradients inside the burner are minimized, enabling better operation conditions for the plate reformer. Three Pt catalyst gradients (50/50, 40/60, and 30/70) reduce ΔT_max from 48.2 °C and 38.3 °C to 25.8 °C. Additionally, the startup time to 250 °C is reduced from 35, 25, and 14 min, respectively. The integration of the plate burner and reformer with the 30/70 catalyst type shows a higher methanol conversion rate (98%), better hydrogen yield, and lower CO selectivity compared to the 50/50 type. Long-term testing for 30 h shows a low catalyst degradation rate, making it suitable for sustained operation. Full article

The use of a cylindrical lens in femtosecond laser surface structuring is receiving attention to improve the processing efficiency. Here, we investigate the structures produced on a copper target, in air, by exploiting both spherical and cylindrical lenses for beam focusing, aiming at elucidating similarities and differences of the two approaches. The morphological features of the surface structures generated by ≈180 fs laser pulses at 1030 nm over areas of 8 × 8 mm² were analyzed. For the spherical lens, micron-sized parallel channels are formed on the target surface, which is covered by subwavelength ripples and nanoparticles. Instead, the cylindrical lens leads to a surface decorated with ripples and nanoparticles with a negligible presence of micro-channels. Moreover, the morphological features achieved by focusing ≈180 fs laser pulses at 515 nm with the cylindrical lens and varying the scanning parameters were also studied. The experimental results evidence a direct effect of the hatch distance used in the scanning process on the target surface that contains dark and bright bands corresponding to regions where the rippled surface contains a richer decoration or a negligible redeposition of nanoparticles. Our findings can be of interest in large area surface structuring for the selection of the more appropriate focusing configuration according to the final application of the structured surface. Full article

In this paper, the impact of an extended surface on the passage of a microchannel using cylindrical ribs with variable sector angles on heat transfer rate is presented using computer simulation. Extended surfaces in the form of cylindrical ribs of varying sector angles in the passage of microchannel in a staggered manner have been designed. The sidewalls of a new kind of microchannel incorporating five distinct ribs with sector angles ranging from 45° to 80° have been analyzed. Ansys Fluent workbench software has been exploited to simulate this novel design of a microchannel heat sink. A three-dimensional heat transfer and fluid flow model of the microchannel heat sink (MCHS) was developed, and the fluid and solid regions were discretized in very fine meshes. All CFD simulations were performed for Reynolds numbers between 100 and 900. Nusselt numbers are varied in the following ranges: 6.93 to 13.87, 6.93 to 14.38, 6.93 to 17.80, 7.15 to 27.86, and 7.20 to 37.38 at sector angles of 45°, 50°, 60°, 70°, and 80°, respectively. It is concluded that the Nusselt number is strongly influenced by the Reynolds number. At an angle of 80°, the maximum friction factor and pumping power requirements were observed. Additionally, a 45° angle has been proven to be the minimal friction factor and pumping power requirement. It is revealed that the THPP has all values larger higher than 1. At angles of 80° and 45°, the maximum and minimum values of THPP have been discovered, respectively. In addition, thermo-hydraulic performance parameters have been evaluated, which are greater than one for all sector angles. Full article

In this study, we fabricated a poly(dimethylsiloxane) (PDMS) surface coated with polydopamine (PDA) to enhance cell adhesion. PDA is well known for improving surface adhesion on various surfaces due to the abundant reactions enabled by the phenyl, amine, and catechol groups contained within it. To confirm the successful surface coating with PDA, the water contact angle and X-ray photoelectron spectroscopy were analyzed. Human umbilical vein endothelial cells (HUVECs) and human-bone-marrow-derived mesenchymal stem cells (MSCs) were cultured on the PDA-coated PDMS surface to evaluate potential improvements in cell adhesion and proliferation. HUVECs were also cultured inside a cylindrical PDMS microchannel, which was constructed to mimic a human blood vessel, and their growth and performance were compared to those of cells grown inside a rectangular microchannel. This study provides a helpful perspective for building a platform that mimics in vivo environments in a more realistic manner. Full article

In this work, the network simulation method is presented as a tool for the numerical resolution of the electroosmotic and pressure-driven flow problem in microchannels with rectangular and cylindrical geometries. Based on the Brinkman equation for steady flow and constant porosity, the network model is designed using spatial discretization. An equivalent electrical circuit is obtained by establishing an analogy between the physical variable fluid velocity and electric potential. The network model is solved quickly and easily employing an electrical circuit resolution code, providing solutions for the velocity profile in the channel cross-section and the total circulating flow. After simulating two practical cases, the suitability of the grid is discussed, relating the relative errors made in the variables of interest with the number of cells used. Finally, two other applications, one for rectangular geometries and the other for cylindrical channels, show the effects the main parameters controlling the flow in these types of channels have on velocities and total flow: the zeta potential of the soil pores, applied potential and pressure gradients, and the boundary condition modified by the zeta potential in the walls of the channel. Full article

Electroosmotic force has been used extensively to manipulate fluid flow in a microfluidic system with various channel shapes, especially an elliptic cylinder. However, developing a computational domain and simulating fluid flow for a system involving an elliptic channel consumes a large amount of time. Moreover, the mathematical expression for the fluid velocity of electroosmotic flow in an elliptic channel may be given in the form of the Mathieu functions that have difficulty in achieving the numerical result. In addition, there is clear scientific evidence that confirms the slippage of fluid at the solid-fluid interface in a microscale system. In this study, we present the mathematical model of combined pressure-driven and electroosmotic flow through elliptic microchannels under the slip-fluid condition. From the practical point of view in fluidics, the effect of the eccentricity of the channel cross-section is investigated on the volumetric flow rate to overcome the difficulty. The results show that the substitution of the equivalent circular channel for an elliptic channel provides a valid flow rate under the situation that the areas of both channel cross-sections are equal and the eccentricity of the elliptic cross-section is less than 0.5. Additionally, the flow rate obtained from the substitution is more accurate when the slip length increases or the pressure-gradient-to-external-electric-field ratio decreases. Full article

Approximately 36,000 units of red blood cells (RBCs) are used every day in the U.S. and there is a great challenge for hospitals to maintain a reliable supply, given the 42-day expiration period from the blood donation date. For many years, research has been conducted to develop ex vivo storage solutions that limit RBC lysis and maintain a high survival rate of the transfused cells. However, little attention is directed towards potential fractionation methods to remove unwanted cell debris or aged blood cells from stored RBC units prior to transfusion, which could not only expand the ex vivo shelf life of RBC units but also avoid adverse events in transfused patients. Such fractionation methods could also limit the number of transfusions required for treating certain pathologies, such as sickle cell disease (SCD). In this work, magnetic fractionation is studied as a potential technology to fractionate functional and healthy RBCs from aged or sickle cells. It has been reported that during ex vivo RBC storage, RBCs lose hemoglobin (Hb) and lipid content via formation of Hb-containing exosomes. Given the magnetic character of deoxygenated- or met-Hb, in this work, we propose the use of a quadrupole magnetic sorter (QMS) to fractionate RBCs based on their Hb content from both healthy stored blood and SCD blood. In our QMS, a cylindrical microchannel placed inside the center of the quadrupolar magnets is subjected to high magnetic fields and constant field gradients (286 T/m), which causes the deflection of the paramagnetic, Hb-enriched, and functional RBCs from their original path and their collection into a different outlet. Our results demonstrated that although we could obtain a significant difference in the magnetic mobility of the sorted fractions (corresponding to a difference in more than 1 pg of Hb per cell), there exists a tradeoff between throughput and purity. Therefore, this technology when optimized could be used to expand the ex vivo shelf life of RBC units and avoid adverse events in transfused individuals or SCD patients requiring blood exchange therapy. Full article

This study discusses entropy generation analysis for a peristaltic flow in a rotating medium with generalized complaint walls. The goal of the current analysis is to understand the fluid flow phenomena particular to micro devices. Nano materials with a size less than 100 nm have applications in micro heat exchangers to cool electronic circuits, blood analyzers, biological cell separations, etc. For this study, we considered the effects of radiation, viscous dissipation and heat flux on the flow of nanomaterial inside a cylindrical micro-channel. To investigate the slip effects on the flow, the second order slip condition for axial velocity, the first order slip condition for secondary velocity and the thermal slip conditions were used. The flow was governed by partial differential equations (PDE’s), which were turned into a system of coupled ordinary differential equations (ODE’s) that were highly non-linear and numerically solved using the NDSolve command in Mathematica. The impacts of different involved parameters on the flow field were investigated with the aid of graphical illustrations. Entropy generation and the Bejan number were given special attention, and it was found that they decreased as the Hartman number, rotation, and radiation parameters increased. Full article

Active pumps are often used in microfluidic devices for programmable fluid flowrate in a microchannel. Active pumps have some drawbacks due to their large size and requirement of external power. To overcome them, a new class of passive pumps based on capillary action in cellulose material, known as paper-based microfluidic pumps, has recently been explored. In this study, fluid flow in 3D paper-based pumps was investigated using flowrate measurements in microchannels. In order to develop 3D cylindrical pumps, Whatman filter paper grade 1 was shredded, mixed with water, molded and dried. The patterned serpentine channel was created using a CO₂ Laser Cutting/Engraving machine. The 3D paper-based pump was integrated with microfluidic channel. The effect of paper pumps of different porosities on the fluid flowrate through a serpentine microchannel was investigated. It was found that flowrate of the fluid flowing through the channel increases with an increase in the pump’s porosity. Moreover, these pumps have the ability to transport larger volumes of liquid with improved flowrate, programmability and control, in addition to being inexpensive and simple to design and fabricate. These 3D pumps will help researchers move closer to developing an effective miniaturized diagnostic platform for point-of-care (POC) diagnostic applications. Full article

In a methanol-reforming system, because the mixture of methanol and water must be evaporated before reaching the reforming reaction zone, having an appropriate evaporator design is a fundamental requirement for completing the reforming reaction. This study investigates the effect of the evaporator design for the stable reforming of methanol–water mixtures. Four types of evaporator are compared at the same heat duty of the methanol-reforming system. The four evaporators are planar heat exchangers containing a microchannel structure, cylindrical shell-and-tube evaporators, zirconia balls for internal evaporation, and combinations of cylindrical shell-tubes and zirconia balls. The results show that the evaporator configuration is critical in performing stable reform reactions, especially for the flow-field mode of the evaporator. Additionally, the combination of both internal and external evaporation methods generates the highest performance for the methanol-reforming system, with the methanol conversion reaching almost 98%. Full article