This work describes an experimental investigation into the influence of geometric micro-groove texture patterns on the tribological performance of stainless steel.Five geometries were studied:one with untextured and f...This work describes an experimental investigation into the influence of geometric micro-groove texture patterns on the tribological performance of stainless steel.Five geometries were studied:one with untextured and four with micro-groove textured making parallel,triangular,square and hexagonal patterns.The micro-groove textures were produced using an MFT-20laser system as well as a two-step laser surface texturing(LST)process.Tribological performance was measured using a pin-on-disk tribometer.The investigation showed that the two-step LST process could fabricate high-precision micro-grooves.The experimental data indicated that the micro-groove textured surfaces achieved the lower frictional coefficients than the untextured surface and the geometric patterns had significantly affected the tribological properties of samples in both lubricated and unlubricated states.The results were analyzed from the lubricant supplying and fluid dynamic pressure effect under lubricated conditions as well as abrasive capture and remove under dry friction conditions.展开更多
Nano-long chains were grafted over the replicated micro-grooves of shark skin in a novel attempt to replicate bio-synthetic drag reduction structure with high precision through synthetic bio-replication. Pre-treated s...Nano-long chains were grafted over the replicated micro-grooves of shark skin in a novel attempt to replicate bio-synthetic drag reduction structure with high precision through synthetic bio-replication. Pre-treated shark skin was used as casting template to prepare a flexible female die of silicone rubber by soft die formation. A waterborne epoxy resin was then used to graft long-chains of drag reduction agent and prepare a synthetic drag reduction shark skin with nano-long chain drag reduction interface and lifelike micro-grooves. Replication precision analysis shows that this technology could replicate the complicated three-dimensional morphology of a biological drag reduction surface with high precision. Drag reduction experiments show that the material had an excellent synthetic drag reduction effect, with a maximal drag reduction rate of up to 24.6% over the velocities tested.展开更多
The high-speed oil-filled ball spinning and drawing process was put forward to manufacture the axially grooved heat pipe with highly efficient heat-transfer performance,and the forming mechanism of micro-grooves insid...The high-speed oil-filled ball spinning and drawing process was put forward to manufacture the axially grooved heat pipe with highly efficient heat-transfer performance,and the forming mechanism of micro-grooves inside the pipe was investigated.The key factors influencing the configurations of micro-grooves were analyzed.When the spinning depth varies between 0.4 mm and 0.5 mm,drawing speed varies from 200 mm/min to 450 mm/min,rotary speed is beyond 6 000 r/min and working temperature is less than 50 ℃,the grooved tubes are formed with high quality and efficiency.The ball spinning process uses full oil-filling method to set up the steady dynamic oil-film that reduces the drawing force and improves the surface quality of grooved copper tube.展开更多
A textured surface with a micro-groove structure exerts a distinct characteristic on drag reduction behavior. The fluid dynamic models of four textured surfaces are constructed in various profile geometries. Computati...A textured surface with a micro-groove structure exerts a distinct characteristic on drag reduction behavior. The fluid dynamic models of four textured surfaces are constructed in various profile geometries. Computational fluid dynamics is used to study the friction factors and drag reduction properties with various flow speeds on the textured surfaces. The friction coefficient varieties in the interface between the fluid and the textured surface are examined according to the simulation of the four geometries with V-shaped, saw tooth, rectangular, and semi-circular sections. The drag reduction efficiencies decrease with the increase in water velocity while it is less than a certain value. Moreover, the simulation results of the velocity, shear stress, energy, and turbulence effect on the V-shaped groove surface are presented in comparison with those of the smooth surface to illustrate the drag reduction mechanism. The results indicate that the peaks of the V-shaped grooves inhibit the lateral movement of the turbulent flow and generate the secondary vortex, which plays a key role in the impeding momentum exchange, thereby decreasing turbulent bursting intensity and reducing shear stress in the near-wall flow field. The kinetic energy and turbulence analysis shows that the vortex in the near-wall flow field on the textured surface is more stable compared to that on the smooth surface.展开更多
Using ploughing-extrusion method, a cross-connected finned micro-grooves structure was formed on the surface of copper strips with thickness of 0.4 mm. The structure was fabricated by making ‘V’-grooves in copper st...Using ploughing-extrusion method, a cross-connected finned micro-grooves structure was formed on the surface of copper strips with thickness of 0.4 mm. The structure was fabricated by making ‘V’-grooves in copper strips and perpendicular ‘V’-grooves on the opposite side that intersect the first set of grooves. Micro pores appear at the intersection of these cross-connected grooves, and micro fins appear on the groove fringes. So it can be defined as ‘pore-groove-fin’ structure. The preferable ‘pore-groove-fin’ structure can be obtained under the condition that the tool edge inclination angle (χγ) is 45°, both the major extrusion angle (γo) and the minor extrusion angle (γ 0′ ) are 30°, both the major formation angle (β) and the minor formation angle (β′) are 10°, the ploughing-extrusion depth (fd) is 0.32 mm and the groove pitch is 0.4 mm on surfaces A and B. The formed included angle of groove A is 70°, and the groove depth is 0.3 mm, while the included angle of opposite perpendicular groove B is 20° with the groove depth of 0.35 mm. The obtained fin height is 0.15 mm, the elliptical pore length is 0.2 mm and the width is 0.05 mm. Experiments show that fd has the greatest influence on the formation of micro pores. Bulges appear on the opposite surface B when the ploughing-extrusion depth on surface A (fdA) reaches a critical value. The ploughing-extrusion depth on surface B (fdB) has great influence on the re-growth of fin structure.展开更多
In view of the technical development bottleneck of 3D printing manufacturing compact heat exchanger for supercritical LNG,a new passive enhanced heat transfer technology is proposed by developing circumferential micro...In view of the technical development bottleneck of 3D printing manufacturing compact heat exchanger for supercritical LNG,a new passive enhanced heat transfer technology is proposed by developing circumferential micro-grooves on the top and bottom walls of rectangular small channels.Numerical simulation of heat transfer enhancement and flow resistance characteristics of LNG in the enhanced channels with micro-grooves is performed.The geometrical dimensions such as the groove depth,the groove width and the center distance between two adjacent micro-grooves were optimized,and then the heat transfer enhancement and flow of LNG within the range of 120 K-250 K which across the critical temperature after the use of the strengthening technology were discussed.Then,further effects of working fluid temperature,mass flow(Reynolds number),and inlet pressure on heat transfer coefficient(Nusselt number),friction factor,and comprehensive coefficient were investigated.In addition,by the analysis of local flow characteristics near the micro-grooves,the heat transfer mechanism is discussed.展开更多
基金Project(51305023) supported by the National Natural Science Foundation of ChinaProject(FRF-GF-17-B20) supported by the Fundamental Research Funds for the Central Universities of China
文摘This work describes an experimental investigation into the influence of geometric micro-groove texture patterns on the tribological performance of stainless steel.Five geometries were studied:one with untextured and four with micro-groove textured making parallel,triangular,square and hexagonal patterns.The micro-groove textures were produced using an MFT-20laser system as well as a two-step laser surface texturing(LST)process.Tribological performance was measured using a pin-on-disk tribometer.The investigation showed that the two-step LST process could fabricate high-precision micro-grooves.The experimental data indicated that the micro-groove textured surfaces achieved the lower frictional coefficients than the untextured surface and the geometric patterns had significantly affected the tribological properties of samples in both lubricated and unlubricated states.The results were analyzed from the lubricant supplying and fluid dynamic pressure effect under lubricated conditions as well as abrasive capture and remove under dry friction conditions.
基金supported by the National Natural Science Foundation of China (50775006)the National Defense Basic Science Research Special Foundation (D2120060002)the Key Project of National High-Tech R&D Program of China (2009AA043802)
文摘Nano-long chains were grafted over the replicated micro-grooves of shark skin in a novel attempt to replicate bio-synthetic drag reduction structure with high precision through synthetic bio-replication. Pre-treated shark skin was used as casting template to prepare a flexible female die of silicone rubber by soft die formation. A waterborne epoxy resin was then used to graft long-chains of drag reduction agent and prepare a synthetic drag reduction shark skin with nano-long chain drag reduction interface and lifelike micro-grooves. Replication precision analysis shows that this technology could replicate the complicated three-dimensional morphology of a biological drag reduction surface with high precision. Drag reduction experiments show that the material had an excellent synthetic drag reduction effect, with a maximal drag reduction rate of up to 24.6% over the velocities tested.
基金Projects(50705031, 50436010) supported by the National Natural Science Foundation of ChinaProject(KF0707) supported by the Open Foundation of the Key Laboratory of Enhanced Heat Transfer and Energy Conservation, Ministry of Education, ChinaProject (8151064101000058) supported by the Natural Science Foundation of Guangdong Province, China
文摘The high-speed oil-filled ball spinning and drawing process was put forward to manufacture the axially grooved heat pipe with highly efficient heat-transfer performance,and the forming mechanism of micro-grooves inside the pipe was investigated.The key factors influencing the configurations of micro-grooves were analyzed.When the spinning depth varies between 0.4 mm and 0.5 mm,drawing speed varies from 200 mm/min to 450 mm/min,rotary speed is beyond 6 000 r/min and working temperature is less than 50 ℃,the grooved tubes are formed with high quality and efficiency.The ball spinning process uses full oil-filling method to set up the steady dynamic oil-film that reduces the drawing force and improves the surface quality of grooved copper tube.
基金This research work was jointly supported by the National Natural Science Foundation of China，the State Key Program of National Natural Science Foundation of China
文摘A textured surface with a micro-groove structure exerts a distinct characteristic on drag reduction behavior. The fluid dynamic models of four textured surfaces are constructed in various profile geometries. Computational fluid dynamics is used to study the friction factors and drag reduction properties with various flow speeds on the textured surfaces. The friction coefficient varieties in the interface between the fluid and the textured surface are examined according to the simulation of the four geometries with V-shaped, saw tooth, rectangular, and semi-circular sections. The drag reduction efficiencies decrease with the increase in water velocity while it is less than a certain value. Moreover, the simulation results of the velocity, shear stress, energy, and turbulence effect on the V-shaped groove surface are presented in comparison with those of the smooth surface to illustrate the drag reduction mechanism. The results indicate that the peaks of the V-shaped grooves inhibit the lateral movement of the turbulent flow and generate the secondary vortex, which plays a key role in the impeding momentum exchange, thereby decreasing turbulent bursting intensity and reducing shear stress in the near-wall flow field. The kinetic energy and turbulence analysis shows that the vortex in the near-wall flow field on the textured surface is more stable compared to that on the smooth surface.
基金National Natural Science Foundation of China (No.52205453)Natural Science Foundation of Shanghai,China (No.22ZR1402700)Opening Foundation of Shanghai Collaborative Innovation Center of High Performance Fibers and Composites (Province-Minitry Joint),China (No.X12812101/019)。
基金Projects(50436010, 50605023, 50675070) supported by the National Natural Science Foundation of ChinaProject(04105942) supported by the Natural Science Foundation of Guangdong Province, China
文摘Using ploughing-extrusion method, a cross-connected finned micro-grooves structure was formed on the surface of copper strips with thickness of 0.4 mm. The structure was fabricated by making ‘V’-grooves in copper strips and perpendicular ‘V’-grooves on the opposite side that intersect the first set of grooves. Micro pores appear at the intersection of these cross-connected grooves, and micro fins appear on the groove fringes. So it can be defined as ‘pore-groove-fin’ structure. The preferable ‘pore-groove-fin’ structure can be obtained under the condition that the tool edge inclination angle (χγ) is 45°, both the major extrusion angle (γo) and the minor extrusion angle (γ 0′ ) are 30°, both the major formation angle (β) and the minor formation angle (β′) are 10°, the ploughing-extrusion depth (fd) is 0.32 mm and the groove pitch is 0.4 mm on surfaces A and B. The formed included angle of groove A is 70°, and the groove depth is 0.3 mm, while the included angle of opposite perpendicular groove B is 20° with the groove depth of 0.35 mm. The obtained fin height is 0.15 mm, the elliptical pore length is 0.2 mm and the width is 0.05 mm. Experiments show that fd has the greatest influence on the formation of micro pores. Bulges appear on the opposite surface B when the ploughing-extrusion depth on surface A (fdA) reaches a critical value. The ploughing-extrusion depth on surface B (fdB) has great influence on the re-growth of fin structure.
基金supported by the National Natural Science Foundation of China(No.51876121)。
文摘In view of the technical development bottleneck of 3D printing manufacturing compact heat exchanger for supercritical LNG,a new passive enhanced heat transfer technology is proposed by developing circumferential micro-grooves on the top and bottom walls of rectangular small channels.Numerical simulation of heat transfer enhancement and flow resistance characteristics of LNG in the enhanced channels with micro-grooves is performed.The geometrical dimensions such as the groove depth,the groove width and the center distance between two adjacent micro-grooves were optimized,and then the heat transfer enhancement and flow of LNG within the range of 120 K-250 K which across the critical temperature after the use of the strengthening technology were discussed.Then,further effects of working fluid temperature,mass flow(Reynolds number),and inlet pressure on heat transfer coefficient(Nusselt number),friction factor,and comprehensive coefficient were investigated.In addition,by the analysis of local flow characteristics near the micro-grooves,the heat transfer mechanism is discussed.
