Concave Dimples Research Articles

Rapid, microwave-assisted deposition of anisotropic silver nanostructures on various substrates.

A facile, rapid, and scalable in situ microwave-assisted solvothermal technique (MAST) has been developed to deposit anisotropic silver nanoparticles (AgNP) on various substrates in a solution medium. SEM-EDS and XRD were used to characterize the morphology and structure of the deposits. Deposition on non-patterned aluminium led to near-spherical AgNP agglomerates all across the surface. Deposition on the glass at optimum solution concentration led to mirror-like coatings comprising spherical ∼50 nm particles, whereas no coating occurred at lower concentrations. AgNPs decorated the hexagonal pattern formed on a nano-patterned aluminium (NPA) substrate. Among various precursor concentrations used for deposition on NPA, the 10 μM concentration resulted in conformal deposition, with nanoparticles decorating the hexagons in NPA. In contrast, AgNP density was lower in the concave dimples on NPA. Our work demonstrates a quick and easy approach for the AgNPs' deposition, with control over size, and morphology. It can be used for deposition on large substrates, potentially making it suitable for surface-enhanced spectroscopic applications.

Performance of textured dual mobility total hip prosthesis with a concave dimple during Muslim prayer movements

The single mobility bearing as a previous bearing design of total hip prosthesis has severe mobility constraints that can result in dislocation during Muslim (people who follow the Islam as religion) prayer movements, specifically shalat that requires intense movement. There are five intense movements (i.e., bowing, prostration, sitting, transition from standing to prostration, and final sitting) during Muslim prayer that may generate an impingement problem for patients with total hip prosthesis. In this work, textured dual mobility total hip prosthesis with two textured cases (i.e., textured femoral head and textured inner liner) are presented and their performances are numerically evaluated against untextured surface model during Muslim prayer movement. The concave dimple design is chosen for surface texturing, while for simulating femoral head materials, SS 316L and CoCrMo is choosen. To represent the real condition, three-dimensional computational fluid dynamics (CFD) coupled with two-way fluid–structure interaction (FSI) methods are employed to analyze elastohydrodynamic lubrication problem with non-Newtonian synovial fluid model. The main aim of the present study is to investigate the tribological performance on dual mobility total hip prosthesis with applied textured surface with concave dimple in femoral head and inner liner surface under Muslim prayer movements. It is found that applying surface texturing has a beneficial effect on the lubrication performance for some intense movements. The textured femoral head model performs better than textured inner liner model and untextured model (both femoral head and inner liner). The numerical results also indicate superior performance of CoCrMo femoral head compared to SS 316L femoral head. These findings can be used as a reference for biomedical engineers and orthopedic surgeons in designing and choosing suitable total hip prosthesis for Muslims makes they can carry out Muslim prayer movements like humans in general who have normal hip joints.

Reconfigurable THz metamaterial based on microelectromechanical cantilever switches with a dimpled tip.

We numerically and experimentally proposed a reconfigurable THz metamaterial (MM) by employing microelectromechanical cantilevers into a ladder-shaped MM (LS-MM). A fixed-free cantilever array with a dimpled tip behaved as Ohmic switches to reshape the LS-MM so as to actively regular the transmission response of THz waves. The cantilever tip was designed to be a concave dimple to improve the operational life without sacrificing the mechanical resonant frequency (fmr), and a fmr of 635 kHz was demonstrated. The device actively achieved a 115-GHz change in transmittance resonant frequency and a 1.82-rad difference in transmission phase shift, which can practically benefit advancing THz applications such as fast THz imaging and 6 G communications.

Numerical simulation of turbulent flow and particle deposition in heat transfer channels with concave dimples

The efficiency of heat transfer will be significantly reduced if airborne particles deposit in the heat transfer channel. Better understandings on particle deposition characteristics in heat exchanger channel are crucial for the energy efficiency improvement. In this study, the particle deposition in a three-dimensional dimpled rough channel was simulated using the Reynolds stress model (RSM) and discrete particle model (DPM). For the turbulent diffusion of particles, the random walk model (DRW) was employed, and for the particle–wall contact, user-defined functions(UDF) are developed in this study to achieve motions such as bouncing and deposition of particles. Grid independence testing and numerical verification were followed by an analysis and study of the flow structures, secondary flow, temperature distribution, and particle deposition distribution in the dimpled rough channel. On the turbulent structure and particle deposition characteristics, the impacts of several significant parameters, including particle size, airflow velocity, the ratio of dimple depth to inner diameter (h/d), and the ratio of inner diameter of dimple to distance between dimples (d/s), were examined. The findings demonstrate that the primary mechanisms influencing the deposition characteristics of particles in dimpled channels are gravity deposition, thermophoresis force distribution, turbulence structure, secondary flow, and particle inertia, and the effects of these mechanisms change significantly with particle size. For small particles (dp ≤ 10 μm), the presence of dimples will encourage deposition; however, for large particles (dp > 10 μm), the presence of dimples will only have a little impact on the distribution of where the particles are deposited.

Microfluidic synthesis of graphene oxide/MnO2-incorporated self-propelling micromotors for organic dye removal

Microfluidically synthesized anisotropically-shaped micromotors with concave dimple, embedded with MnO2 and graphene oxide, exploit their autonomous motion to successfully capture and remove organic dye molecules from an aqueous environment.

Numerical Simulation of Heat Transfer Performance of a Dimpled Tubular Heat Exchanger

The processing of dimple on the outer wall of tube will produce corresponding protrusion dimple on the inner wall. The turbulent flow and heat transfer performance of a tubular heat exchanger containing a dimpled inner tube is studied numerically. The results show that the main reason for the enhancement of heat transfer ability of the dimple is the flow vortex in the concave dimple and the shock to the wall induced by the protrusion dimple. Compared with the smooth wall of the tube, the maximum enhancement of heat transfer was 1.94 times in concave dimple and 2.74 times in protrusion dimple. By comparing the heat transfer performance, flow resistance, and comprehensive heat transfer factor of the tube and shell of different sizes of exchange heat pipe, it is determined that the combination of inner and outer wall dimple size of 10–15 mm is a structure with better comprehensive heat transfer performance.

Experimental investigation of exergetic efficiency of 3 side concave dimple roughened absorbers

The present work deals with evaluation of exergetic efficiency (ηII) of 3 side concave dimple roughened solar air heater duct system and the results were compared with 1 side roughened system experimentally and theoretically. Exergy analysis uses quality of useful energy i.e., what fraction of solar radiation is actually being converted into useful heat gain of air leaving beside possible losses. Experiments were performed under actual outdoor condition in open sun and relevant input data were recorded for exergy evaluation. Each day’s data was recorded under different sets of parameters viz., Reynolds number (Re) 2500–13500, relative roughness pitch (p/e) 8–15, relative roughness height (e/Dh) 0.018–0.045 and dimple’s depth to diameter ratio (e/d) 1–2. Variation in exergetic efficiency with Reynolds number and rise in temperature parameter (To-Ti)/I at varying p/e, e/Dh and e/d reveals that as Reynolds number changes, both 1 and 3 side roughness shows maximum exergetic efficiency at same Re but 1 side roughened duct shows maximum exergetic efficiency at (To-Ti/I) of 0.0172, 0.0125 and 0.017 for different p/e, e/Dh and e/d respectively. For 3 side roughened duct, maximum exergetic efficiency was seen at (To-Ti/I) of 0.023, 0.0212 and 0.022 for different p/e, e/Dh and e/d respectively.

Thermal and thermohydraulic performance analysis of three sides artificially roughened solar collectors

Thermal and thermohydraulic performance characteristics for 3-sides concave dimple roughened collector has been investigated and presented here. The geometrical parameter of roughness element covers relative dimple pitch, height and depth 8–15, 0.018–0.045 and 1–2 respectively along with flow Reynolds number 2500–13,500. Thermal performance of artificially roughened SAH doesn’t include a frictional loss that is generated while the air is propelled through the roughened ducts. Three sides roughened ducts have high thermal efficiency compared to 1-side roughened duct but that hike should not come at the cost of tremendous rise in frictional losses. The present investigation is aimed at determining the optimum roughness parameters at which maximum possible efficiency is obtained at minimum frictional losses. The optimum roughness parameter yielding the maximum thermal efficiency is ‘p/e’ = 12, ‘e/Dh’ = 0.036 & ‘e/d’ = 1.5 for both ducts. 3-sides concave dimple roughened SAH were having 44–67% more thermal efficiency than 1-side roughened duct under similar flow condition. Maximum effective (thermohydraulic) efficiency at varying ‘e/Dh’ obtained was 0.78 and 0.49 and that at varying ‘p/e’ obtained was 0.74 and 0.47 in the case of 3-sides and 1-side roughened ducts respectively.

Thermo-Hydraulic Performance Enhancement of Finned Elliptical Tube Heat Exchangers by Utilizing Innovative Dimple Turbulators

As a new type of fin structure in finned tube heat exchangers, dimple turbulators exhibit excellent potential for thermo-hydraulic performance enhancement. A three-dimensional numerical simulation study was conducted to investigate the influences of five kinds of innovative concave dimple turbulators (CDTs), namely – elliptical dimple, conical frustum dimple, trapezoidal prism dimple, leeward triangular dimple and upward triangular dimple (UwTD) on the thermo-hydraulic performance enhancement in a plate fin-and-elliptical tube (PFET) heat exchanger, where CDTs are textured on the fin surface transversely between the elliptical tubes. The computational results are analyzed by considering the performance evaluation criterion for the PFET heat exchangers with different types of CDT shapes. The present investigation demonstrates that the heat transfer enhancement is intimately pertained to ejection with longitudinal counter-rotating flow, strengthened secondary flow and vortex structures at the downstream rim of CDT. A parametric study on the CDTs indicated that the UwTD vortex turbulators give better thermo-hydraulic performance under the present conditions. The numerical simulation results illustrated different secondary flow structures and heat transfer characteristics of the CDTs with various shapes, which disclosed the influential mechanisms of differently shaped dimple turbulators on the heat transfer augmentation in PFET heat exchangers.

Non-uniform spontaneous surface curvature gives limited shape control in simulated single-polymer micelles

Polymeric micelles are used in a variety of applications, with the micelle’s shape often playing an important role. Consequently, it is desirable to identify a simple set of control parameters having an easily understood effect on micelle shape. In a previous study, we showed that a model two-dimensional linear multiblock copolymer may be designed to exhibit a dimpled shape. Extending this study, this paper characterizes in greater detail how such a dimpled micelle’s shape can be controlled by adjusting the copolymer block lengths. Using basic physical principles governing amphiphilic polymer, we identify a few aspects of the multiblock composition that are expected to have a well-behaved effect on micelle shape. Starting from a reference micelle composition, itself already exhibiting a nonstandard shape having a moderately sized concave dimple, we alter these aspects of the multiblock composition and observe the response of two features of the micelle shape: the size of the dimple and the magnitude of shape fluctuations. We find the response of the shape is smooth and regular for small excursions from a base composition, but larger excursions gave rise to nonmonotonic effects on the shape, suggesting that sophisticated techniques may be required to aid in micelle design.

Nusselt number and friction factor correlations of three sides concave dimple roughened solar air heater

Performance analysis of roughened solar air heater becomes hectic due to absence of statistical correlation for heat transfer and friction factor. For understanding flow behavior, researchers have developed statistical correlations for different roughness geometries. This paper presents the outcome of experimental investigations upon 1 & 3-sides concave dimple roughened ducts. The results are presented as variation in Nusselt number & friction factor with Reynolds number. The geometrical & flow parameters has been varied as relative dimple pitch (p/e), relative dimple height (e/Dh), relative dimple depth (e/d) & Reynolds number in the range of 8–15, 0.018–0.045, 1–2 & 2000–13500 respectively. Statistical correlations for Nusselt number and friction factor in terms of roughness and flow parameters were derived based on data collected from experiment. Optimized value of flow & roughness parameter yielding maximum performance is determined. The maximum enhancement in Nusselt number for varying relative dimple pitch, relative dimple height & relative dimple depth was respectively of the order of 2.6–3.55, 1.91 to 3.42, 3.09 to 3.94 times and that of friction factor was of the order of 1.62–2.79, 1.52 to 2.34 and 2.21 to 2.56 times over those of 1-side roughened ones.

Elastic particle deformation in rectangular channel flow as a measure of particle stiffness.

In this study, we experimentally observed and characterized soft elastic particle deformation in confined flow in a microchannel with a rectangular cross-section. Hydrogel microparticles of pNIPAM were produced using two different concentrations of crosslinker. This resulted in particles with two different shear moduli of 13.3 ± 5.5 Pa and 32.5 ± 15.7 Pa and compressive moduli of 66 ± 10 Pa and 79 ± 15 Pa, respectively, as measured by capillary micromechanics. Under flow, the particle shapes transitioned from circular to egg, triangular, arrowhead, and ultimately parachute shaped with increasing shear rate. The shape changes were reversible, and deformed particles relaxed back to circular/spherical in the absence of flow. The thresholds for each shape transition were quantified using a non-dimensional radius of curvature at the tip, particle deformation, circularity, and the depth of the concave dimple at the trailing edge. Several of the observed shapes were distinct from those previously reported in the literature for vesicles and capsules; the elastic particles had a narrower leading tip and a lower circularity. Due to variations in the shear moduli between particles within a batch of particles, each flow rate corresponded to a small but finite range of capillary number (Ca) and resulted in a series of shapes. By arranging the images on a plot of Ca versus circularity, a direct correlation was developed between shape and Ca and thus between particle deformation and shear modulus. As the shape was very sensitive to differences in shear modulus, particle deformation in confined flow may allow for better differentiation of microparticle shear modulus than other methods.

Heat transfer enhancement on a microchannel heat sink with impinging jets and dimples

The introduction of dimples to heat transfer surface can effectively improve the heat transfer performance of a microchannel heat sink with impinging jets (MIJ). MIJs with different dimple structures, including convex, concave, and mixed dimples, are compared with MIJs without dimples by numerical simulation and the application of the field synergy principle. Results indicate that (1) MIJs with convex dimples exhibited the best cooling performance, followed those without dimples, with mixed dimples, and with concave dimples; (2) the application of convex dimples could decrease flow resistance in MIJs; and (3) among all tested cases, MIJs with convex dimples exhibited the best overall performance, followed by MIJs without dimples, with mixed dimples, and with concave dimples.

Thermal-hydraulic performance of a multiple jet cooling module with a concave dimple array in a helium-cooled divertor

A numerical study was performed to evaluate the thermal-hydraulic performance of a finger type cooling module, where multiple jets impinge on the surface with concave dimples, in the divertor of a nuclear fusion reactor. Conjugate heat transfer was analyzed in both the solid and fluid domains using three-dimensional Reynolds-averaged Navier-Stokes equations with the shear stress transport turbulence model. The computational domain consisted of a single fluid domain and three solid domains: tile, thimble, and cartridge. The numerical results for the temperature variation on the tile were validated in comparison with the experimental data. A parametric study was performed with two design variables, the ratios of dimple diameter and dimple height to the nozzle diameter, and two dimple arrays (inline and staggered arrays). The parametric study showed that the heat transfer rate was increased by up to 2.62% by introducing concave dimples, and that the heat transfer and pressure drop performances increased with increasing diameter and height of the dimples for a specified dimple array.

Rhomboid Concave and Convex Dimples Applied for Cooling in Gas Turbines

Rhomboid Concave and Convex Dimples Applied for Cooling in Gas Turbines

Kinetic modeling and design of colloidal lock and key assembly

We investigate the kinetics of colloidal lock and key particle assembly by modeling transitions between free, non-specifically and specifically (dumbbells) bound pairs to enable the rapid formation of specific pairs. We expand on a model introduced in a previous publication (Colón-Meléndez et al., 2015) to account for the shape complementarity between the lock and the key particle. Specifically we develop a theory to predict free energy differences between specific and non-specific states based on the interaction potential between arbitrary surfaces and apply this to the interaction of a spherical key particle with the concave dimple surface. Our results show that a lock particle dimple slightly wider than the key particle radius results in optimal binding, but also show escape rates much smaller than those observed in experimental measurements described in the paper cited above. We assess the possible sources of error in experiments and in analysis, including spatial and temporal resolution of the confocal microscopy method used to measure kinetic coefficients, the polydispersity of the lock dimple size, and the sedimentation of the particles in a quasi-two-dimensional layer. We find that the largest sources of variation are in the limited temporal resolution of the experiments, which we account for in our theory, and in the quasi-two-dimensional nature of the experiment that leads to misidentification of non-specific pairs as specific ones. Accounting for these sources of variation results in very good quantitative agreement with experimental data.

Particle selection through topographic templates in nematic colloids.

Liquid crystal colloids have been proposed as suitable candidates for responsive photonic crystals. Large scale growth of such colloidal systems is, however, a challenge and recently template-assisted assembly has been proposed to guide the growth of colloidal crystals, with controlled symmetries, in nematic liquid crystals. Known for their long-range anisotropic interactions, these colloidal systems are stabilized typically at the center of the cells due to strong particle-wall repulsion from the confining substrates. This behaviour is dramatically changed in the presence of topographic patterning. Here we propose the use of topographic modulation of surfaces to select and localize particles in nematic colloids. By considering convex and concave deformations of one of the confining surfaces we show that the colloid-flat surface repulsion may be enhanced or switched into an attraction. In particular, we find that when the colloidal particles have the same anchoring conditions as the patterned surfaces, they are strongly attracted to concave dimples, while if they exhibit different anchoring conditions they are pinned at the top of convex protrusions. Although dominated by elastic interactions the first mechanism is reminiscent of the depletion induced attraction or of the key-lock mechanism, while the second is specific to liquid crystal colloids. These long-ranged, highly tunable, surface-colloid interactions contribute to the development of template-assisted assembly of large colloidal crystals, with well defined symmetries, as required for applications.

Micro Dimple Milling for Structured Surface

A micro dimple machining is presented to control the surface functions with the micro-scale structures on the solid surfaces. The micro dimples are machined in milling with the inclined ball end mill. When an inclined two flutes end mill removes the material in a depth of cut less than the tool radius, the air cutting time during neither edges contact with the workpiece appears in a rotation of cutter. When the tool is fed at a high feed rate so that the removal areas of an edge and another edge do not overlap each other, the concave dimples are machined. A mechanistic model is presented to control the shape and the size of the dimples to be machined. The micro dimples were machined to verify the mechanistic model in milling. The micro asperities were also formed in molding using the dimpled surface. As applications of the functional surfaces, wettability and friction coefficient were measured on the surfaces with the dimples and the asperities. The surface functions change with the alignments of the dimples and the asperities.

The study of the efficiency enhancement of bionic coupling centrifugal pumps

The objective of this paper is to investigate a new method to increase the efficiency of the centrifugal pump under the guidance of the bionic coupling theory. A centrifugal pump with a bionic coupling impeller called a bionic coupling centrifugal pump (BCCP) was developed. Either riblets or concave dimples were engraved on the flank or blade back of the impellers and then coated with polyurethane. This design was inspired by the specific skin structure of living creatures and the theory of biological coupling. The BCCP efficiency was investigated using the method of pseudo-level orthogonal testing. The results show that the efficiency of BCCPs obviously improved and the efficiency curve became more compressed than that of a conventional centrifugal pump over the effective working range. This indicates that the BCCPs would still function within a higher efficiency range even when they deviate from the highest efficiency point. The efficiency enhancement of the BCCP could be attributed to the effect of the delayed release of energy because of the elastic deformation of polyurethane. Polyurethane coupled with non-smooth surface structures stabilized the turbulent flow. This coupling consequently reduced the turbulence and stabilized the water in the boundary layer of the impeller blade.

An Error Model in Micro Dimple Milling

A micro dimple machining is studied to control the surface functions with the micro-scale structures on the solid surfaces. The micro dimples are machined in milling with the inclined ball end mill. When the feed rate of the tool is high enough that the removal area of an edge does not overlap with that of the previous edge, periodical concave dimples are machined. A mechanistic model is presented to control the shape and the size of the dimples to be machined. Then, a machining error model is presented to control the deviation of the dimple shapes. Some machining examples are shown to verify the dimple model and the error model.