Array Of Dimples Research Articles

Durability of deterministic textures produced by maskless electrochemical texturing (MECT) during Skin pass cold rolling

Skin pass is a fundamental finishing process to control the sheet roughness in cold metal rolling. The energetic and tribological efficiency of this process can be improved by surface texturing to control the roll surface topography and consequently the final sheet roughness. In this work, deterministic textures were produced on flat segments of skin pass rolls using the maskless electrochemical texturing (MECT) technique. The textures consisted of arrays of circular dimples. After texturing, the specimens were coated either with hard chrome or NiP electroless coatings, aiming to evaluate the ability of electroless NiP coating to protect textures as a potential replacement of the carcinogenic hard chrome coating. The evaluation of the texture durability was carried out via dry reciprocating sliding tests with samples extracted from cold rolling work rolls. The test configuration and conditions were chosen to intensify the wear process in order to evaluate the durability of the textures during skin pass cold rolling. Wear evaluation was also by analyzing changes in roughness parameters. The results indicated that the best tribological performance occurred for the textured surfaces coated with NiP. The average coefficient of friction of the textured surfaces coated with NiP was around 16 % lower than that of the uncoated textures and around 19 % lower than that of textures coated with hard chrome coated. Although the mass loss was negligible in the tests, the analysis of surface topography parameters showed that both hard chrome and electroless NiP coatings acted to decrease the wear of MECT textured surfaces.

Investigation of a sacrificial template material suitable for fabrication of anode support microtubes in microtubular solid oxide fuel cells

This study investigates the use of various sacrificial template materials in the form of a solid rod, including wood, carbon fiber, polyamide, resin and polylactic acid (PLA), for fabricating anode supports in microtubular solid oxide fuel cells (SOFCs) via tape casting and isostatic pressing. Anode support strips, produced via tape casting, are wound around these sacrificial rods. The rods are then burnout through co-sintering to yield microtubular anode supports. The results highlight PLA as a particularly promising material due to its balance of cost and performance. A novel rod design involving hollow PLA pipe is then explored to enhance the fabrication process. The anode support tape length or the wall thickness of anode support microtube is also considered. Microtubular cells are fabricated on the anode supports by dip coating other cell layers, and electrochemical and microstructural investigations are carried out. The final cell provides 0.365 W/cm2 maximum power density at 800 °C under 0.3 NL/min hydrogen flow and stationary air. Moreover, a patterned microtubular anode support is successfully fabricated using a 3D printed PLA tube featuring an array of dimples. The overall findings indicate that the proposed methodology not only simplifies the manufacturing process but also supports the feasibility of producing high-performance microtubular SOFCs with enhanced electrolyte-electrode interfaces through patterned anode designs.

Performance of surface structures in enhancing heat transfer rates of miniaturized pulsating heat pipe

Enhancement of the thermal performance by modifying the evaporator surface of a miniaturized pulsating heat pipe (PHP) is the primary target of the present work. Four PHPs having different evaporator surface types i.e., smooth, dimple cavity array, tunnel cavity, and rectangular cavity array were investigated numerically to compare the gas-liquid interfacial behavior and evaluate the role of bubble nucleation, slug-plug movement, and drop-film condensation on the thermal performance. Detailed modeling of evaporating and condensing interfaces shows that activation of nucleation sites at all defined discrete structures and undisturbed liquid flow path at the evaporator promote heat transfer rate. Through thermo fluidic analysis around different surface structures, evaporation dynamics is analyzed to understand the suitability of a structure type for enhancement of heat transfer. Associated slug-plug motion through the adiabatic zone and processes at the condenser have been also discussed to propose the characteristics of an ideal enhanced PHP. The capacity to transfer heat has been also characterized using thermal resistance for different structured PHPs which may be a guiding factor for the design of heat sinks for thermal applications.

Heat transfer enhancement mechanics of different micro-disturbing structures for transcritical hydrocarbon fuel using 3-D secondary flow intensity analysis

Heat transfer enhancement based upon micro-disturbing structures becomes increasingly important for thermal protection of air-breathing propulsion systems. To explore the influence mechanism of different structures on heat transfer in regenerative cooling channels of scramjet engines, flow structures and heat transfer of supercritical-pressure n-Decane in mini-channels with dimple and micro-rib arrays are numerically investigated. Results indicate effective heat transfer enhancement inside the channels depends more on efficient transverse turbulence disturbance rather than longitudinal or perpendicular turbulence disturbance. Severe thermal stratification generates strong shear layers in channels, where transverse secondary flows bring much intenser flow mixing than longitudinal secondary flows, especially in transcritical temperature region where the best heat transfer enhancement is obtained. With same characteristic dimensions, longitudinal micro-disturbing structures like dimples have lower flow resistance, but transverse micro-disturbing structures like micro-ribs achieve stronger heat transfer enhancement. Besides, the performance of micro-ribs is much more sensitive to the dimensional change. Therefore, micro-ribs have larger working excursion for enhancing performance factor than dimples. With optimal structure parameters: hr = e = 0.3 mm, pr = 3 mm, hd = 0.225 mm, dd = 1.5 mm, overall performance factor in micro-ribbed channel is 1.14 times of that in dimpled channel. Those conclusions provide effective support for optimization design for the regenerative cooling structures.

Uncommon Cold-Rolling Faults in an Fe–Mn–Si–Cr Shape-Memory Alloy

The paper analyzes the occurrence of evenly spaced cracks on the surface of lamellar specimens of Fe-28Mn-6Si-5Cr (mass %) shape-memory alloy (SMA), during cold rolling. The specimens were hot rolled and normalized and developed cold rolling cracks with an approximate spacing of about 1.3 mm and a depth that increased with the thickness-reduction degree. At normalized specimens, X-ray diffraction patterns revealed the presence of multiple crystallographic variants of brittle α′ body-bcc martensite, which could be the cause of cold-rolling cracking. Both normalized and cold-rolled specimens were analyzed using scanning electron microscopy SEM. SEM micrographs revealed the presence of several crystallographic variants of α′-body-centered cubic (bcc) and ε hexagonal close-packed (hcp) martensite plates within a γ-face-centered cubic (fcc) austenite matrix in a normalized state. High-resolution SEM, recorded after 25% thickness reduction by cold-rolling, emphasized the ductile character of the cracks by means of an array of multiple dimples. After additional 33% cold-rolling thickness reduction, the surface of crack walls became acicular, thus revealing the fragile character of failure. It has been argued that the specimens cracked in the neutral point but preserved their integrity owing to the ductile character of γ-fcc austenite matrix.

Development of micro-texture patterns of cemented carbide cutting tools to improve cutting performance

Micro texture on cutting tool inserts obtained via laser micro-machining has recently emerged as an environment friendly method to reduce adhesion on the tool’s rake face and to improve friction conditions during machining. However, these benefits are strictly correlated with a correct design and behavior of the texture to be replicated on the tool surface. This paper reports an experimental study of developing an array of dimples on both rake and flank of commercial, cemented carbide cutting inserts using a picosecond laser source. Experiments of orthogonal dry cutting on E235 steel tubes were performed using textured and untextured tools to evaluate the improvements obtained. The improvements achieved were assessed in terms of cutting force and their impact on cutting performances. A predictive finite element model was developed to optimize the design of the dimples, to be replicated onto the rake surface of the tool.

Effects of staggered dimple array under different flow conditions for enhancing cooling performance of solar systems

Enhancing cooling performance of internal channel with dimple array is promising technology for various solar energy systems. In this study, we investigate the use of dimple arrays within these coolant channels as a means of achieving higher cooling performance while minimizing pressure loss. Experiments were conducted to evaluate the effects of dimple arrays under various flow conditions (laminar, transition, and turbulent). Flow measurements revealed that the dimple array promotes secondary flows and turbulent intensity, particularly under transitional flow conditions. Among the tested flow conditions, the highest thermal performance ratio of 1.8 was achieved at ReH = 2000 and 3000 (transition flow cases), resulting in a 47% increase in heat transfer compared to the laminar flow case (ReH = 1000). These results suggest that dimple arrays with transitional flow conditions could be an effective means of improving the cooling performance of solar energy systems and ultimately contribute to reducing carbon dioxide emissions and preventing climate change. Further research is needed to optimize the dimple array design for specific flow conditions cooling applications for solar energy systems.

Experimental and numerical study on an enhanced swirl cooling with convergent tube wall and local dimple arrangements

This paper experimentally and numerically investigates an enhanced swirl cooling structure, featuring multiple connected convergent swirl tubes and dimpled wall. The dimpled swirl tube adopts a novel local dimpled wall scheme, only arranging dimple arrays under the tangential jets, which takes advantage of the heat transfer potential of the individual dimple. A counterpart multistage convergent swirl tube without dimples is also studied as a comparison baseline to clarify the action of local dimple arrays on swirling flow. The spatially resolved heat transfer data are measured by applying transient thermochromic liquid crystal (TLC) technique. Four channel Reynolds numbers (Re = 20,000 to 50,000) are tested based on the maximum tube parameters. The results show that the enhanced dimpled swirl tube performs a synergistic reinforcement of the high-speed swirling flow over the dimple arrays, which produces many local high Nusselt number patterns. Under the individual injection slot, the upstream dimples have a better enhanced heat transfer performance. For the studied working conditions, the globally averaged Nusselt number of the dimpled swirl tube can be increased by 6.0%–11.5% in comparison with the baseline convergent swirl tube. Besides, the dimpled wall also suppresses the swirl intensity, which leads to the weakening of wall-fluid shear stress action and the disappearance of downstream vortex breakdown, and consequently reduces the pressure loss by 2.0%–10.2%. Based on the well-validated CFD results, the dimpled wall under incoming jets redistributes the contribution of the near-wall turbulence and the forced convection due to the near-wall flow motion to the heat transfer enhancement in the swirl tube, which achieve an ideal cooling performance of high heat transfer in combination with low pressure loss. This provides a new inspiration for the design and optimization of swirl cooling device.

Numerical Study of the Ratio of Depth-to-Print Diameter on the Performance and Flow Characteristics for a Dimpled, Highly Loaded Compressor Cascade

The influence of the ratio of dimple depth-to-print diameter (λ) on the highly loaded compressor cascade NACA0065-K48 is investigated based on the Reynolds-averaged Navier–Stokes (RANS) method. Simulations are conducted with a validated shear-stress transportation (SST) turbulence model coupled with the Gamma-Theta (γ−Reθ) transition model at the inlet Mach number of 0.7. At 5~25% of the axial chord on the suction surface, four rows of dimples are arranged in parallel, and the dimples’ spacing is 4 mm. Moreover, there are five kinds of λ, ranging from 0.125 to 0.875, which determine the pressed arc of a spherical dimple. Three flow regimes (diffuser–confuser flow, tornado-like vortex and horseshoe vortex) with the same topological structure are observed in these dimples, which affect the flow and performance of the cascade by changing the energy distribution. The distribution of turbulent kinetic energy (TKE) reflects the disturbance of the tornado-like vortex in the inferior arc dimples (λ=0.375) intensely, whereas the disturbance of the horseshoe vortex in superior arc dimples (λ=0.625, 0.875) is relatively weak. Numerical results indicate that the loss of the corner separation can be reduced with a dimples array, which is mainly related to the vertical climbing of the lateral flow that delays the starting point of the corner separation and weakens the mixing process. However, the loss in the wake of the dimpled cascades increases, which is caused by the thickened boundary layer induced by the high turbulent vortices. The dimpled cascade with λ=0.625 can achieve the most significant loss reduction (13.47%), while ensuring the pressurization capacity.

Dual-Colored Janus Microspheres with Photonic and Plasmonic Faces.

Photonic and plasmonic colors, stemming from nanostructures of dielectric materials and metals, are promising for pigment-free coloration. In particular, nanostructures with structural colors have been employed in stimuli-responsive Janus microparticles to provide active color pixels. Here, the authors report a simple strategy to produce electro-responsive Janus microspheres composed of photonic and plasmonic faces for active color change. The photonic microspheres are first prepared by self-assembly of silica particles in emulsion droplets of photocurable resin. The silica particles form 3D crystalline arrays in the interior and 2D hexagonal arrays on the interface. The emulsion droplets are photocured and the silica particles are selectively removed to make porous photonic microspheres with hexagonal arrays of dimples on the surface. Directional deposition of gold or aluminum on the photonic microsphere develops plasmonic color on the top hemisphere while maintaining photonic color on the bottom hemisphere. Moreover, the metal deposited on one side renders the Janus microspheres electro-responsive. Therefore, the photonic and plasmonic colors are switchable by the orientation control of the Janus microspheres with an external electric field. The photonic and plasmonic colors are independently adjustable by employing two different sizes of silica particles in core-shell emulsion drops.

Two-phase heat transfer correlations in three-dimensional hierarchical tube

Development of novel enhanced surface tubes is an important way to advance two-phase flow heat transfer. To make correlations of two-phase flow heat transfer in enhanced tubes with acceptable prediction has been a challenge for many years. The paper presents a method: two-phase heat transfer correlations in enhanced tubes are directly developed through existing two-phase heat transfer smooth-tube models by introducing several modifying factors and dimensionless numbers. An enhanced heat transfer tube containing staggered arrays of three-dimensional dimples and secondary petal-shaped protrusions (EHT) is one of the most complicated internal surface-tube configurations on the market. Visualizations of flow patterns and measurements of heat transfer coefficients of two-phase flow using refrigerant R410A in smooth and EHT tube are conducted. Detailed visualization experiments during two-phase flows show good agreements between flow regimes and flow-pattern maps in smooth and EHT tube. The equation of continuity is adopted to provide understanding of the mechanism of the agreements. Both theoretical analysis and experimental studies support the method. As a result of using it, new two-phase heat transfer correlations are developed in enhanced tubes as the EHT tube is an example. Flow boiling correlation can predict data points within +10% to -20% and flow condensation correlation can predict data points within ±10% in the EHT tube.

Experimental study of turbulent flow heat transfer and pressure loss over surfaces with dense micro-depth dimples under viscous sublayer

Presented are experimentally-measured heat transfer and pressure loss characteristics for dimpled surfaces, placed along one surface of a channel, with different ratios of dimple depth to channel height δ/H, and for Reynolds numbers ranging from 10,000 to 70,000. With the same relative dimple spacing to dimple print diameter, and the same ratio of dimple depth to dimple print diameter of δ/d = 0.20, experimental results for arrays of spherical indentation dimples with micro depths of δ = 0.6 and 1.0 mm (δ/H = 0.03 and 0.05) are compared with thermal characteristics for arrays of larger dimples with δ = 4.0 mm and δ/H = 0.20. Local surface heat transfer distributions are measured using transient liquid crystal thermography. Additional steady-state experiments are also employed to provide overall heat transfer enhancement and friction factor augmentation values. Results indicate that Nusselt number ratios and friction factor ratios of a turbulent flow in the channel are dependent upon the ratio of dimple micro depth to channel height, which are different findings from previous studies with larger-depth dimples in the cooling channels. As such, the present data for micro-depth dimples with ratios of dimple depth to channel height δ/H of 0.03 and 0.05 are firstly provided. The importance of a critical Reynolds number is demonstrated by the results, which is determined when the ratio of viscous sublayer layer thickness to the dimple depth is equal to unity, and has been ignored in the previous dimpled channel heat transfer design. Nusselt number enhancements for the micro dimples are generally lower at lower Reynolds numbers, but increase as the Reynolds number becomes larger and approaches the critical Reynolds number. Nusselt number enhancements are then approximately invariant with Reynolds number, when Reynolds number then exceeds the critical value.

Designing Multicolor Graphics of Plasmonic Metasurfaces through Gradual Protrusion of Particles at Free Interface

AbstractMetal nanostructures show plasmonic colors in the absence of pigments, which are promising for various optical applications. Colloidal lithography is one of the cost‐effective methods for a wide‐area production of plasmonic metasurfaces. However, it remains an important challenge to regioselectively control plasmonic property in a facile and reliable manner. Here, a novel strategy is reported to produce multicolor plasmonic graphics using the gradual protrusion of colloids at a water‐resin interface. Particles anchored at free interfaces slowly migrate toward the equilibrium position. Therefore, the degree of protrusion into the opposite phase is determined by the duration of aging. With this phenomenon, dimple arrays with controlled depths is produced by capturing the particles at the water‐resin interface through photopolymerization and removing the particles. Directional deposition of aluminum on the dimple arrays renders plasmonically colored surfaces, where the resonant wavelengths, or colors, vary with dimple depth. As the resin is regioselectively photocurable by ultraviolet irradiation through photomasks, plasmonic graphics can be produced. In addition, multi‐steps of regioselective photocuring with controlled durations of incubation produce multicolor graphics. The graphics show consistent plasmonic colors for specular reflection while displaying iridescent diffraction colors from hexagonal arrays of dimples for off‐specular conditions, enhancing the visibility of graphics.

Investigation on the roll-to-plate imprinting of metallic surface micro dimples

Large-area functional metallic surface microstructures have been increasingly utilized in various industrial fields. As an efficient and economical method in fabricating large-area functional metallic surface microstructures, the roll-to-plate (R2P) imprinting process with the flat die was proposed to experimentally fabricate functional micro dimple arrays on the surface of the metallic substrate. The effects of the rolling direction, die cavity aspect ratio, die feature density and grain sizes on the forming results were investigated using pure copper specimens with different grain sizes. The transfer ratio of surface structures decreases with the increase of the die feature density and die cavity aspect ratio, respectively. The flowing differences of material in the rolling direction and transverse directions lead to the inconformity of section profile of formed dimples in the two directions. The depth of dimples in the rolling direction is prominently greater than that in the transverse direction. The depth difference of dimples in the two directions increases with the increase of rolling depth and reduces with the increase of die cavity width. The surface morphology of formed specimens obviously depends on the material flowing direction, grain sizes and rolling depth. The surface roughness, surface roughness scatter and flatness of the formed specimens increase with the grain size. The symmetry of cross sectional micro hardness distribution on both sides of the formed dimple in the rolling direction is poorer than that on both sides of the formed dimple in the transverse direction. The asymmetry of cross sectional micro hardness distribution on both sides of the formed dimple in the rolling direction becomes more prominent with the increase of grain sizes.

Rotational heat transfer in a rectangular cooling channel with compound turbulators of pin-fins and dimples

The convective heat transfer characteristics in a rotating trailing edge channel roughened with compound turbulators of pin-fin and dimple arrays were experimentally investigated via copper plate technique. The effects of Reynolds number (Re), rotation number (Ro) and buoyancy number (Buo) on the local and averaged heat transfer for the leading and trailing walls of current pin fin-dimpled channel were studied at conditions of 12,000 ≤ Re ≤ 20,000, 0 ≤ Ro ≤ 0.89 and 0 ≤ Buo ≤ 1.32. Both the static-to-rotating Nusselt number ratio (Nu/Nus) and the normalized Nusselt number ratio (Nu/Nu0) were compared with that in a similar pin-fin channel. To examine the coupling and individual Coriolis force and centrifugal buoyancy effects in current compound channel, experiments were designed and performed with three density ratios (d.r. = 0.05, 0.08, 0.10) for each given Re and Ro. In the static cases, it was found that heat transfer at most of the measured locations was promoted by adding dimples onto the pin-fin wall, including the high radius region where the worst heat transfer level was observed in the traditional pin-fin channel. The overall averaged heat transfer was respectively enhanced by 15.8% and 21.0% at Re = 12,000 and 20,000. In the rotating compound channel, the heat transfer augmentation in the high radius region reduced with rotation, and the reduction expanded towards the low radius with ascending Ro. A turning point at each location were observed after which heat transfer stopped decreasing and started to recover with rotation. Those turning points were diverse at various locations, but they appeared to be approximately 1.0 once the local rotation number were adopted. Moreover, the heat transfer data indicated that the centrifugal buoyancy abated or promoted heat transfer at lower or higher Ro, respectively. Further study revealed that the local parameters were more instructive than the inlet ones to analyze the coupling and isolated Coriolis force and centrifugal buoyancy effects in current compound channel.

Ideally Ordered Anodic Porous Alumina on Si Substrate Prepared by Anodization of Sputtered Al–Mg Thin Film

Anodic porous alumina with an ideally ordered hole arrangement was formed on a Si substrate by nanoimprinting and subsequent anodization. In this process, the arrayed shallow dimples formed by nanoimprinting using a mold act as initiation sites of hole development during the anodization. To realize the precise transfer of the mold patterns to the Al surface during nanoimprinting, we used sputtered Al alloy film as a starting material. This is because the Al alloy with appropriate impurities as a sputtering target can suppress the crystal grain growth during sputtering and allow the formation of Al alloy films with smooth surfaces on the substrate. Dimple arrays with 100 nm intervals could be formed on the flat surface of the Al–Mg film on the Si substrate. Ideally ordered anodic porous alumina with an interpore distance of 100 nm was successfully obtained by subsequent anodization. A Co/alumina composite was also obtained by the electrodeposition of Co into the alumina holes. The obtained samples are expected to be applied to various functional devices requiring an ideally ordered structure on a substrate.

Fabrication of micro-structured surface with controllable randomness by using FTS-based diamond turning

Random micro-structured surfaces (RSS) have great application potentials as various functional surface elements, such as optical diffusers, with homogeneous surface properties. Conventional fabrication methods for RSS, such as chemical etching, can no longer meet modern requirements of high precision and controllability. In this study, a novel method was proposed for fabricating micro dimple arrays with controllable randomness in dimple size and depth by using fast tool servo (FTS)-based single-point diamond turning. Firstly, for tool path generation, a computer program was developed to periodically arrange small patches of quadratic surfaces over a large surface area. Then the position, height, and size of each quadratic surface were adjusted by applying random values, whose dynamic range was preset, to control the spatial difference among the dimples. Finally, the designed RSS was machined by continuous and segment cutting methods, respectively, to evaluate their effects on dimple edge formation. Results showed that the segmented cutting method improved the edge accuracy, thus was effective for RSS machining. The machined surface matched precisely with the designed surface with a form error of 10 nm level. The machining method proposed in this study enables high-precision patterning of mold inserts for molding/imprinting RSS on polymer materials.

Dynamic contour error compensation in micro/nano machining of hardened steel by applying elliptical vibration sculpturing method

In this study, a novel dynamic contour error compensation technique has been proposed for the elliptical vibration cutting process achieved through the ultra-precision amplitude control. The influence of the contour error, triggered due to the inertial vibrations of the friction-less feed drive system, on the machining accuracy deterioration has been experimentally investigated. In order to reduce the contour error, a compensation method utilizing a real-time amplitude control in the elliptical vibration cutting process has been applied. In the proposed method, the dynamic motion error along the depth of cut direction is detected by utilizing the precise linear encoders installed on the feed drive system. The motion error in real-time is subsequently converted into cancelling amplitude command for the vibration control system of the ultrasonic vibrator, thus, guaranteeing that the envelope of the vibration amplitudes auto-tracks the dynamic reference position of the motion axis in the depth of cut direction. Due to this, a constant nominal depth of cut can be obtained even though the inertial vibrations disturb the feed drive control during machining. A series of experimental investigations have been conducted in order to analyze the machining performance by employing the proposed method. The maximum machining error is observed to significantly decrease from 0.6 to 0.04 μm by applying the proposed compensation method. Finally, the micro dimple array with a structural height from about 200 to 600 nm could be accurately fabricated with a maximum machining error of 36.8 nm, which verified the feasibility of the proposed amplitude control compensation method.

Reducing engine oil and fuel consumptions by multidimensional laser surface texturing on cylinder surface

• Proposed the multidimensional laser surface texturing (MLST) process, based on the engine motion characteristic. • Established hardware and software systems and optimized the parameters of MLST process. • The ablating position of each laser pulse is manipulated, and various depths of micro dimples are fabricated by controlling the repeat times of overlapped laser pulses. • Developed the post-process for MLST process, based on the finishing honing process to remove the recast bulges (RCB) induced by laser ablation. • Tested four schemes of cylinder liners (one prototype, three MLST) on a single cylinder diesel engine at rated power and speed. • One of MLST scheme reduced engine oil and fuel consumptions simultaneously. The optimization of cylinder surface topography draws immense amounts of researches, since it has far-reaching effects on engines’ overall performances. In order to promote the lubricity of ring/bore interface, the present study developed the multidimensional laser surface texturing (MLST) process, which fabricates controllable arrays of micro dimples on cylinder surface. The MLST process was achieved by a series of innovations, including its hardware and software systems, and optimization of process parameters and efficiency. A post-process was developed based on the finishing honing process to remove the recast bulges (RCB) induced by laser ablation. Additionally, the cylinder liners with different surface texturing schemes were bench tested on a single cylinder diesel engine. The experimental results indicated that near TDC (top dead center) region and piston skirt contacting region (SKIRT) were two high-impact regions for the technical efficiency of the MLST process. Benefiting from the reasonable optimization of oil distribution and enhanced hydrodynamic lubrication, the MLST process was able to reduce engine oil and fuel consumptions simultaneously. This paper provides a comprehensive introduction of equipment, pre- and post-process, and capacities of the newly developed surface modification technology.

Study the influence of concavity shapes on augmentation of heat‐transfer performance, pressure field, and fluid pattern in three‐dimensional pipe

AbstractIn this current study, the heat‐transfer augmentation mechanism and pressure drop with flow field structures over different dimple arrays in turbulent flow of three‐dimensional circular tube are investigated based on computational fluid dynamics numerical methods using the standard k − e turbulent model. The water is the working fluid over the range of Reynolds numbers from 1500 to 24,000, with three different tubes dimpling arrangements are analyzed. The numerical simulation results are validated through available experimental data, and they show good agreement results between them. The numerical analysis results showed that the flow fields are symmetric within the middle cross‐sectional direction in the pipe with and without dimples. Also, the flow near or close to the dimples is chaotic and including small vortexes and eddies. The results found that the temperature difference in the dimple tube with 2 mm diameter at low flow range 0.56 L/min was higher than that of smooth pipe, dimple tube 0.75 and 1.5 mm by 26.8%, 10.57%, and 3.68%, respectively. It can be concluded that using dimples in heat‐exchanger tubes can provide rates of heat transfer that is higher than that without dimpled tubes at the same operating conditions. Hence, this is an important enhancement in process industries for the energy conversion applications.