Trapezoidal Grooves Research Articles

Numerical study on the nonwetting ability of trapezoid topography

Pattern texturing has been proved to effectively improve the water repellency on hydrophobic surfaces. To explore the effect of pattern profile on the dynamic wetting state, here, we conduct numerical study of a water droplet impinging on surfaces with a single trapezoid, rectangular, and V-shaped grooves, respectively. Simulations are performed using a volume-of-fluid method based interFoam solver shipped with OpenFOAM. We begin with a numerical validation by comparing with experiment. Subsequently, the wetting states of the droplet on these three substrates are examined, which demonstrate the capability of trapezoid topography to prevent being wetted. Theoretical model well explains that trapezoid structure can lead to a great increase in energy barrier brought by the penetration of liquid–air interface, which in turn improves its non-wetting ability even under impingement conditions. By masking the surface with mix-hydrophobicity, we also prove that wettability in grooves plays a significant role on the dynamic wetting state. A stable dry surface can be obtained by only masking the groove side-wall by superhydrophobic patterns.

Effect of Heat Input on the Microstructure and Mechanical Properties of Local Dry Underwater Welded Duplex Stainless Steel

Duplex stainless steel welded metals were underwater local dry prepared on S32101 lean duplex stainless steel trapezoidal groove plates with a self-made drain cover employing Supercore 2205P flux-cored filler wire. Different heat inputs were employed to investigate the effects on mechanical characteristics and the microstructure of welded metals. The results demonstrated that as the heat was applied, austenite concentrations in the weld metals increased. It was found that the austenite concentration and the fraction of Σ3-austenite twin-grain boundaries followed the same trends. With increasing heat input, the recrystallized ferrite and austenite grains initially decreased and subsequently increased, whereas the fraction of interphase boundaries between special ferrite and austenite exhibited the reverse trend. With a heat input of 1.4 kJ/mm, the toughness and plasticity of the weld metals were enhanced by an increase in austenite content, Σ3 recrystallized grains, and austenite twin-grain boundaries. The plasticity and tensile strength values of the welded metal changed more when the heat input was raised from 1.0 to 1.2 kJ/mm than when it was raised from 1.2 to 1.4 kJ/mm. Considering energy conservation, it is recommended to adopt 1.2 kJ/mm for welding heat input.

Effective electromechanical coupling coefficient () enhancement of a Lamb wave resonator with trapezoid grooves configuration

A first-order () Lamb wave resonator (LWR) with a trapezoid grooves configuration on the top surface of the aluminum nitride membrane between interdigital electrodes is proposed in this paper. Both the simulation and experiment results demonstrate that the can be enhanced with the depth of the trapezoid grooves increasing. Meanwhile, the spurious modes can be suppressed by the trapezoid grooves. A 75% improvement on the has been achieved in a 2.45 GHz mode LWR with trapezoid grooves with spurious modes free. The reaches up to 5.47% without quality factor degradation.

Sealing performance and mechanical response of mud pump piston

In order to explore the effect of piston cup structure on its sealing characteristics and mechanical properties, a numerical simulation model of the piston cup in the BW-160 mud pump was established. Effects of work load, friction coefficient and cup structure parameters on the sealing and mechanical properties of the piston were discussed under mud discharge condition. The results show that stress concentration on the root and lips of the cup is becoming more and more obvious with the working load increases. The average contact pressure increases with the friction coefficient increases, but an excessive friction coefficient accelerate the wear of the cup and the heat generation. Effect of the piston lip interference and thickness on the sealing performance of the cup is greater than that of the inner wall width. The piston with groove structure can effectively improve the sealing performance of the piston. The mechanical properties of triangular groove cup are better than that of semicircular and trapezoidal groove cup.

Fracture mechanism and model of AA7075 multi-cavity component formed under complex stress states

During the multi-directional loading forming process of AA7075 aluminum alloy multi-cavity component, the stress states of material are complex and cracking defects are easy to occur, which seriously restricts the smooth process implementation and the improvement of forming quality. In this paper, based on the characteristic structure of AA7075 multi-cavity component, the material flow and stress states were studied. A trapezoidal groove shape specimen and test device were ingeniously designed. Then the fracture morphology, microstructure and mechanism of AA7075 alloy under different stress states are revealed. The results show that when the stress state changes from tensile-shear to pure shear and compression-shear, the fracture is easy to occur at the second phase particles, inclusions, the interface of elongated and equiaxed grains. The fracture modes are the mixture of surface shear fracture and core tensile fracture, but the proportion of shear plane is increasing. The grain morphology at the fracture surface is long grain with slightly increased axial diameter ratio, equiaxial grain with sufficient dynamic recrystallization, and slender shear band with large angle deflection, respectively. Further, a thermoforming fracture model under complex stress states in the process of multi-directional loading forming of multi-cavity components is established.

Armature Structure Optimization of Annular Multipole Solenoid Valves Based on Electromagnetic Force Distribution

To improve the dynamic response speed of high-speed solenoid valves in electric fuel injection systems of marine diesel engines, a numerical simulation model of the solenoid valve is described in this paper. The accuracy of the simulation model was verified on the test bed of the solenoid valve. The effect of the punch position and the size of the dynamic response of the solenoid valve were investigated by using the distribution law of the electromagnetic force in the armature. The results of the test showed that armature drilling in the inter-yoke zone can optimize the solenoid closing response time, but it has little impact on the solenoid opening response time. From this rule, two groove schemes were further designed. Through comparison and calculation, it can be concluded that the fan groove scheme is better than the trapezoidal groove scheme, and that the opening and closing response times of the solenoid valve should be targeted in order to multi-target optimize the fan groove geometric parameters and the armature thickness. The results show that after optimization, the weight of the motion part is reduced by 21.6%, the opening response time of the solenoid valve is reduced by 11.1%, and the closing response time is reduced by 30.0%. While reducing the oil film damping of the armature motion, the overall dynamic response characteristics of the solenoid valve are improved.

Overshoot temperature control on evaporator wall of loop heat pipe for space vehicle thermal control through bypass line under high thermal load

• The thermal performance of the heat pipe was able to be enhanced by the bypass line. • The thermal performance was significantly enhanced by the bypass line. • Bypass line is a passive means for start-up thermal performance control of loop heat pipe. This paper presents the experimental results of controlling an evaporator wall temperature overshoot problem under a high thermal load by applying a bypass line to the loop heat pipe (LHP). To solve the overshoot problem during the LHP start-up, any nucleation bubbles generated on the wick surface should be removed from the vapor channel as soon as possible. In special cases, a serious evaporator wall temperature overshoot problem at high thermal loads can cause start-up failure. The LHP must be operated stably within an appropriate temperature range during start-up because any sudden rise in the evaporator wall temperature may cause serious damage to the temperature control target. To control the evaporator wall temperature overshoot of the LHP with a flat evaporator and sintered metal wick, a bypass line was installed between the evaporator and the liquid reservoir. The bypass line was integrated into the LHP using a sintered metal wick and flat evaporator, of dimensions (width and length) 40 × 50 mm. The body of the LHP was made of stainless steel, and distilled water was used as the working fluid. The vapor generated in the evaporator was supplied to the vapor transport tube through inverted axial trapezoidal grooves. The inner diameters of the liquid and vapor transport tubes were 2 mm and 4 mm, respectively, and both tubes were 0.5 m long. The input thermal load ranged up to 270 W for a coolant temperature of 10°C. The LHP was aligned at a favorite tilt angle of 15°, where an evaporator wall temperature overshoot was observed. The experimental results demonstrated the ability of the bypass line to effectively control the evaporator wall temperature overshoot during start-up under high thermal loads.

Casting of Wire Using Twin Wheel Caster with Melt Holding Nozzle

A twin-wheel caster with a hole nozzle was developed to cast thin aluminum alloy wire. The lower large wheel had a trapezoid groove with a cross-sectional area of 22.5 mm2, and the upper small wheel was flat. Molten-metal flow onto the wheel was controlled by the gap between the wheel and the nozzle, and the ejection angle of the molten metal. When the gap was not appropriate, bulges formed on the free solidified surface of the molten metal on the wheel. The bulges were flattened by setting the gap to the correct size of 3 to 4 mm. The appropriate angle was found to be 60°. A thin wire of 6061 aluminum alloy could be cast continuously at a speed of 5 m/min. The cross-sectional area of the nozzle hole was 3 mm2. The cross-sectional area of the as-cast wire was 42.7 mm2.

Investigation of the Thermal Performance of a Nanofluid-filled Grooved Cylindrical Heat Pipe for Electronics Cooling

Thermal management of electric and electronic components is a critical issue and needs to consider enhanced cooling systems such as heat pipes. This study deals with the theoretical modeling of a nanofluid-filled copper cylindrical heat pipe for electronics cooling applications. The heat pipe includes helicoidal and trapezoidal capillary grooves. The model can predict the capillary limit as well as the heat transfer in the different sections of the heat pipe. The thermal resistances of the evaporation and condensation sections are calculated based on correlations for heat transfer, which are determined from experiments. Two working nanofluids are considered: water/CuO and water/Al2O3. The thermal performances are predicted for different concentrations and heat sink temperatures, and the heat pipe is positioned horizontally. For both nanofluids, the results indicate that augmenting the concentration of the nanoparticles leads to a capillary limit increase reaching up to 14 % and 25 % for water/Al2O3 and water/CuO, respectively, and an overall thermal resistance decrease reaching up to 51 % and 68 % for water/Al2O3 and water/CuO. Moreover, decreases up to 24 %, and up to 18 % in the evaporator wall temperatures are obtained for water/CuO and water/Al2O3 nanofluids, respectively. The nanofluid water/CuO gives the best thermal performance whatever the nanoparticle concentration and heat sink temperature.

EDM milling based on a 6-DOF serial robot

Aiming at the problems of insufficient flexibility and limited size of the workpiece in traditional EDM milling, an EDM milling based on a 6-DOF serial robot is proposed in this study. To realize the rapid adjustment of the machining gap, a tool electrode servo motion device was invented and installed at the end of a 6-DOF serial robot, and a servo control strategy of the tool electrode vertical trajectory fallback was proposed. Then, to achieve the controllable thickness of every layer in EDM milling based on a 6-DOF serial robot, the servo control strategy of limited motion of the tool electrode on the basis of vertical servo control and a fix-length compensation method to compensate the tool electrode wear was proposed. Finally, to verify the correctness and effectiveness of the servo control strategy and wear compensation of the tool electrode, the trapezoidal groove structures on the plane workpiece and cylindrical workpiece were machined by EDM milling based on a 6-DOF serial robot, respectively. Also, to verify the machining ability of complex trajectories on the space surface of the workpiece of EDM milling based on a 6-DOF serial robot, three complex trajectories, such as EDM, Chinese character “China,” and “Chinese knot,” was designed and machined on the hemispherical workpiece with the radius of 38 mm. The feasibility and effectiveness of EDM milling technology based on a 6-DOF serial robot were verified, which has great market application potential.

Influence of trapezoidal groove geometry on the microstructure and mechanical properties of stainless steel 316L parts repaired by laser metal deposition

As a mainstream metal additive manufacturing technique, laser metal deposition (LMD) opens up new possibilities for the repair of damaged metal parts. The repair process is composed of different steps, such as three-dimensional scanning, defect detection, pre-repair machining, material addition, post-repair finishing machining, and material testing. In this work, the steps of pre-repair machining and material addition of stainless steel (SS) 316L powder on SS316L substrate using LMD were studied. Three types of grooves with different opening angles (105°, 120°, and 135°) were machined. Both the substrate and the repaired parts were characterized to investigate the influence of the opening angles on the relative density, microstructure, and mechanical properties. As compared to the substrate, the repaired parts feature heterogeneous microstructure, a peak in microhardness in the heat-affected zone, similar ultimate tensile strength but low elongation at break for tensile tests, and reduced absorbed energy for Charpy impact tests. The decrease of the opening angle decreases the relative density and tensile properties but increases the energy absorption of the repaired parts.

Experimental studies on shape and size effects on particle breakage of railway ballast

Particle breakage, which contributes to ballast bed deforms and degradation, highly affect the performance of the railway track. Experimental studies on particle breakage of ballast are difficult, not only due to the large size and high strength of the material, but also because of complex shape and size effects. In this study, these effects on the particle breakage of ballast are investigated, by a self-designed trapezoidal groove device for single particles and an impact loading device for uniform aggregate. The results show as follows. (1) Single ballast particle is broken as a brittle shear failure, with penetrating cracks and small particles. The more uniform the contact positions are, the less likely shear failure happens. (2) Under the impact energy of 26.8 kJ, the mass loss of flaky particles and elongated particles can exceed 40 %, mainly by fracture breakage; yet that of cube particles is less than 4 %, mainly by wear-out failure. (3) The particle breakage index Bg could be a reasonable index describing the breakage evolution. (4) There is a critical particle size where the ballast takes the highest energy per volume to break. (5) There are three stages in the volumetric change: void filling, skeleton failure, and final stabilization.

Effect of Inclination Angles on Thermal Performance of a Heat Pipe with Axially Trapezoidal Grooves

Effect of Inclination Angles on Thermal Performance of a Heat Pipe with Axially Trapezoidal Grooves

The effect of laser energy density on microstructural evolution and mechanical properties of laser clad 316L stainless steel for repair

Laser energy density can affect the powder forming state in laser metal deposition (LMD), ultimately altering the evolution pattern and mechanical properties of formed structures. This work uses high-speed LMD technology to repair the 316L austenitic stainless steel plate with a trapezoidal groove. By analyzing the microstructural evolution and mechanical properties of repaired specimens under different laser energy densities, we revealed the effects of density on LMD shaping. Results indicated that the microstructure in the repair zone developed alternately in forms of columnar, branch, and isometric crystals in the opposite direction of heat flow. Increased laser energy density could enlarge crystal grains in formed structures. Meanwhile, γ-Fe tended to transform into δ phase that was distributed among crystal grains in γ-Fe. When the density reached its peak, the number of the δ phase plummeted. The average microhardness of specimens first increased and then decreased in the repair zone, with its distribution fluctuating repeatedly, and the values in this zone were 1.5–1.7 times that of the substrate. The mechanical properties of repaired specimens were superior to those of the rolled steel substrate at room temperature, and these specimens' ultimate tensile strength (UTS) and elongation at this temperature were positively correlated with the laser energy density. There were dimples and typical cleavage patterns around the fracture of tensile specimens, indicating that the fracture mechanism at room temperature was of quasi-cleavage type. As the density rose, the UTS first increased and then reduced in a tensile test conducted at 500 °C, during which the strain kept growing. Simultaneously, numerous dimples with congregate micropores but without typical cleavage patterns were observed in the fracture, which revealed that all specimens exhibited ductile fracture at high temperatures.

Continuous repair of groove damages using solid-state friction rolling additive manufacturing method

A solid-state and continuous groove repair technology was proposed for aluminium alloy based on friction rolling additive manufacturing (FRAM). The feasibility of FRAM was explored by repairing three types of prefabricated groove damages in aluminium alloy plates. A well-repaired joint for trapezoidal groove was obtained when the press-in depth of the tool head was 2 mm. The press-in depth was the key factor to complete filling of the groove damage. Effective grain refinement of the repair centre and the significant refinement area are observed, which leads to the hardness of these two areas reaching 99% and 102% of the substrate, respectively. The material migration behaviour of the filling material during the process was clarified.

Investigation of the hydrothermal enhancement of grooved pin fins heat sinks

In this paper, a numerical investigation was conducted to analyse heat transfer and fluid flow on a new design of heat exchangers with grooved pin-fin heat sinks (G-PFHS), which included the optimisation of shape, size, and groove number (Ng ). The simulation results indicate that all-novel geometries have the highest heat dissipation rates compared to conventional geometry (Cylindrical pin fins heat sink, CPFHS). However, the configuration with semi-circular grooves exhibits the most design compared to other configurations (pin-fins heat sinks with a rectangle, triangular, trapezoidal grooves and CPFHS). Also, after optimisation of the size and number of grooves, the Nusselt number and thermal resistance are improved by 21.01% and 16.70%, respectively, with an increase in the pressure drop by 15.42% compared with the CPFHS at the highest Reynolds number. Therefore, this case provides the best hydrothermal performance factor (HTPF) of 1.18 at Re = 8740.

Heat transfer enhancement for microchannel heat sink by strengthening fluids mixing with backward right-angled trapezoidal grooves in channel sidewalls

To strengthen the fluids mixing in channels for enhancing heat transfer, a new design of microchannel heat sink with periodic gradual-expansion and sudden-constriction cross-sections was proposed by arranging backward right-angled trapezoidal grooves in channel sidewalls. The flow and heat transfer characteristics in the new design was numerically investigated and compared with those in two comparative microchannels, which have the same channel volume and the same or almost the same convective heat transfer area as the new design. The pressure and viscous resistances of channel walls were innovatively analyzed for explaining why grooves can maintain a lower pressure drop for microchannels. The results indicate that the new microchannel shows a significant improvement of heat transfer enhancement and overall performance although its pressure resistance and viscous resistance are much higher than those of other ones. The pressure drop and Nusselt number of the new microchannel are 1.02–1.45 and 1.31–2.14 times higher than those of the smooth straight microchannel, respectively. After an optimum process of the forward angle (θ) of grooves, the relative Nusselt number of the new microchannel can be achieved up to 2.23 at θ = 15°and Re = 737 while the overall heat transfer factor can be achieved up to 1.89 at θ = 18°and Re = 442.

Optimum profiles of trapezoidal grooves in polarizer mirrors for high-power ECRH systems, and the ohmic loss calculation

Two grooved mirrors are normally uses in electron cyclotron resonance heating (ECRH) systems to induce an appropriate polarization in the microwave for efficient plasma coupling in fusion reactors. In the high-power systems, sharp edges of the grooves may lead to an electrical arc discharge and disable further operation, and in the high-frequency systems where the skin depth is smaller than the surface roughness, the high-power transmission may be limited by the resultant ohmic loss. In this work, parametric profiles of rounded trapezoidal- and rectangular-shaped grooves have been designed based on the free space wavelength to find the best profiles that are suitable for the polarizers in the high-power transmission lines at any frequency. Extensive work has been carried out on the optimum ellipticity of the polarization by employing vector theory integrated with numerical simulations. Then the trapezoidal profiles with desired results have been used to model the grooved mirrors for both polarizers and calculated the ohmic loss on the mirrors for a 5-s pulse of 580 kW Gaussian beam at 110 GHz. Effect of the surface roughness has been also involved in the analysis.

Effects of geometric parameters on fluid-flow and heat transfer in micro-channel heat sink with trapezoidal grooves in sidewalls

Trapezoidal grooves were arranged in channel sidewalls of the proposed micro-channel heat sinks to enhance heat transfer for cooling microelectronic systems. The 3-D numerical simulations were carried out to investigate the characteristics of fluid-flow and heat transfer in the proposed micro-channels. Field structures of thermal fluid-flow, Nusselt number, and friction factor, f, were employed to study the effects of the relative groove depth, ?, and relative grooves spacing length, ?, of trapezoidal grooves on the thermal and hydraulic performance of the proposed micro-channels. The results showed that the proposed micro-channel presented better flow and thermal performance than the smooth straight one for Re <597.74 with f/f0 < 1 and for Re >149.44 with Nu/Nu0 > 1, respectively. The thermal enhancement factor, ?, was achieved up to 1.197 with ? = 0.4 and ? = 1 for Re = 714.18. Furthermore, the relative groove depth had much more significant influence on the overall performance than the relative groove spacing length.

Experimental analysis on the evaporator startup behaviors in a trapezoidally grooved heat pipe

The startup behaviors of evaporation heat transfer in a trapezoidal groove are experimentally studied by using an axial heat pipe with trapezoidal grooves. The effects of heat load and inclined angles on the evaporation startup behaviors are analyzed and discussed. The startup regime diagram is provided to quantitatively describe the behaviors of evaporation heat transfer based on the Weber number and Bond number. The results indicate that, only the gradual startup is observed for the evaporation heat transfer in trapezoidal grooves, however the gradual startup and overshoot startup is experienced in sequence in the tilt condition as the heat load increases. The appearance of evaporation startup regime transition from the gradual startup to overshoot startup is induced by the evaporation regime transition from the fin-film evaporation to the corner-film evaporation inside the evaporator section. The gradual startup occurs for a small Weber number and the overshoot startup occurs for a large Weber number. Increase in Bond number introduces a larger transition Weber number for the startup regime variation of evaporation heat transfer in a trapezoidal groove. Interestingly, the occurrence of the temperature overshoot of few Celsius degrees can be observed to verify whether the grooved heat pipe is in a horizontal position.