A two-step approach was employed to create a composite coating consisting of TiO_(2)nanoparticles and extremely elastic polydimethylsiloxane(PDMS).The TiO_(2)-PDMS composite coating demonstrates exceptional superhydro...A two-step approach was employed to create a composite coating consisting of TiO_(2)nanoparticles and extremely elastic polydimethylsiloxane(PDMS).The TiO_(2)-PDMS composite coating demonstrates exceptional superhydrophobicity and antifouling efficacy,as evidenced by the static contact angle,contact angle hysteresis,and antifouling tests.The electron microscopic analysis reveals that the composite coating consists of TiO_(2)particles and agglomerates,which forms a dual-level roughness structure at the nanometer and micron scales.This unique structure promotes the Cassie-Baxter state of the coating when in contact with the liquid,resulting in an increased static contact angle and a reduced contact angle hysteresis.The PDMS primer facilitates the attachment of TiO_(2)particles,resulting in a composite coating with excellent scratch-resistant characteristics.Additionally,the PDMS primer possesses the capacity to retain low surface energy modifiers.Simultaneously,the PDMS primer serves as a reservoir for a low surface energy modifier,enhancing the self-repairing properties of the TiO_(2)-PDMS composite coating.This composite coating exhibits effective self-cleaning capabilities against many forms of contaminants,including liquids,solids,and slurries.展开更多
The wind tunnel simulations of wind loading on a solid structure of revolution with one smooth and five rough surfaces were conducted using wind tunnel tests. Timemean and fluctuating pressure distributions on the sur...The wind tunnel simulations of wind loading on a solid structure of revolution with one smooth and five rough surfaces were conducted using wind tunnel tests. Timemean and fluctuating pressure distributions on the surface were obtained, and the relationships between the roughness Reynolds number and pressure distributions were analyzed and discussed. The results show that increasing the surface roughness can significantly affect the pressure distribution, and the roughness Reynolds numbers play an important role in the change of flow patterns. The three flow patterns of subcritical, critical and supercritical flows can be classified based on the changing patterns of both the mean and the fluctuating pressure distributions. The present study suggests that the wind tunnel results obtained in the supercritical pattern reflect more closely those of full-scale solid structure of revolution at the designed wind speed.展开更多
There are many examples that fluid flows on rough wall, such as channel flow in nature, pipe flow, etc. In order to know the flow structure of real fluids, it is important to study the effects of wall roughness on coh...There are many examples that fluid flows on rough wall, such as channel flow in nature, pipe flow, etc. In order to know the flow structure of real fluids, it is important to study the effects of wall roughness on coherent structure in turbulent shear flows. The experiments were carried out in a square glass channel, which is 600cm long, with the cross section of 30×25cm^2. The flow velocity was varied from 2 to 40 cm/s. Uniform sands whose diameters were 0.0012cm, 0.2gcm, 0.385cm, 0.594cm and 0.896cm respectively were glued to the floor of the channel. The rough Reynolds number Re_Δ= U_*Δ/ν=0.04～73, where U_*is the shear velocity, Δ is the diame- ter of uniform sand, v is the kinematic viscosity coefficient. Hydrogen bubble technique for flow visualization and HWL-II hot-film anemometer for velocity mea- surement were used in the experiments.展开更多
Static and dynamic wetting behaviors of sessile droplet on smooth,microstructured and micro/nanostructured surface under condensation condition are systematically studied.In contrast to the conventional droplet wettin...Static and dynamic wetting behaviors of sessile droplet on smooth,microstructured and micro/nanostructured surface under condensation condition are systematically studied.In contrast to the conventional droplet wetting on such natural materials by dropping,we demonstrate here that when dropwise condensation occurs,the sessile droplet will transit from the Cassie-Baxter wetting state to the Wenzel wetting state or partial Cassie-Baxter wetting state on the microstructured surface or the micro/nanostructured surface,which leads to a strong adhesion between the droplet and the substrate.In contrast,the apparent contact angle and the sliding angle on the smooth surface changes a little before and after the condensation because of small roughness.Theoretical analysis shows that the roughness factor controls the adhesion force of the droplet during condensation,and a theoretical model is constructed which will be helpful for us to understand the relationship between the adhesion force and the geometry of the surface.展开更多
基金Funded by the National Science and Technology Major Project(No.J2019-VII-0015-0155)the National Natural Science Foundation of China(No.51705533)。
文摘A two-step approach was employed to create a composite coating consisting of TiO_(2)nanoparticles and extremely elastic polydimethylsiloxane(PDMS).The TiO_(2)-PDMS composite coating demonstrates exceptional superhydrophobicity and antifouling efficacy,as evidenced by the static contact angle,contact angle hysteresis,and antifouling tests.The electron microscopic analysis reveals that the composite coating consists of TiO_(2)particles and agglomerates,which forms a dual-level roughness structure at the nanometer and micron scales.This unique structure promotes the Cassie-Baxter state of the coating when in contact with the liquid,resulting in an increased static contact angle and a reduced contact angle hysteresis.The PDMS primer facilitates the attachment of TiO_(2)particles,resulting in a composite coating with excellent scratch-resistant characteristics.Additionally,the PDMS primer possesses the capacity to retain low surface energy modifiers.Simultaneously,the PDMS primer serves as a reservoir for a low surface energy modifier,enhancing the self-repairing properties of the TiO_(2)-PDMS composite coating.This composite coating exhibits effective self-cleaning capabilities against many forms of contaminants,including liquids,solids,and slurries.
文摘The wind tunnel simulations of wind loading on a solid structure of revolution with one smooth and five rough surfaces were conducted using wind tunnel tests. Timemean and fluctuating pressure distributions on the surface were obtained, and the relationships between the roughness Reynolds number and pressure distributions were analyzed and discussed. The results show that increasing the surface roughness can significantly affect the pressure distribution, and the roughness Reynolds numbers play an important role in the change of flow patterns. The three flow patterns of subcritical, critical and supercritical flows can be classified based on the changing patterns of both the mean and the fluctuating pressure distributions. The present study suggests that the wind tunnel results obtained in the supercritical pattern reflect more closely those of full-scale solid structure of revolution at the designed wind speed.
文摘There are many examples that fluid flows on rough wall, such as channel flow in nature, pipe flow, etc. In order to know the flow structure of real fluids, it is important to study the effects of wall roughness on coherent structure in turbulent shear flows. The experiments were carried out in a square glass channel, which is 600cm long, with the cross section of 30×25cm^2. The flow velocity was varied from 2 to 40 cm/s. Uniform sands whose diameters were 0.0012cm, 0.2gcm, 0.385cm, 0.594cm and 0.896cm respectively were glued to the floor of the channel. The rough Reynolds number Re_Δ= U_*Δ/ν=0.04～73, where U_*is the shear velocity, Δ is the diame- ter of uniform sand, v is the kinematic viscosity coefficient. Hydrogen bubble technique for flow visualization and HWL-II hot-film anemometer for velocity mea- surement were used in the experiments.
基金supported by the National Natural Science Foundation of China(Grant Nos.11072126,11272176,91326108 and 51206042)the Foundation of Stake Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources(Grant No.LAPS14018)
文摘Static and dynamic wetting behaviors of sessile droplet on smooth,microstructured and micro/nanostructured surface under condensation condition are systematically studied.In contrast to the conventional droplet wetting on such natural materials by dropping,we demonstrate here that when dropwise condensation occurs,the sessile droplet will transit from the Cassie-Baxter wetting state to the Wenzel wetting state or partial Cassie-Baxter wetting state on the microstructured surface or the micro/nanostructured surface,which leads to a strong adhesion between the droplet and the substrate.In contrast,the apparent contact angle and the sliding angle on the smooth surface changes a little before and after the condensation because of small roughness.Theoretical analysis shows that the roughness factor controls the adhesion force of the droplet during condensation,and a theoretical model is constructed which will be helpful for us to understand the relationship between the adhesion force and the geometry of the surface.
