为了探究由光伏光热(PV/T)驱动的双热质耦合加湿除湿海水淡化系统的水电综合性能,基于能量与质量守恒原理构建了PV/T组件与加湿除湿系统的数学模型,揭示了液气比对系统相关热力学参数的影响规律,对比分析了不同顶温条件下系统的热力学性...为了探究由光伏光热(PV/T)驱动的双热质耦合加湿除湿海水淡化系统的水电综合性能,基于能量与质量守恒原理构建了PV/T组件与加湿除湿系统的数学模型,揭示了液气比对系统相关热力学参数的影响规律,对比分析了不同顶温条件下系统的热力学性能,并在某典型天气状况下探究了逐时辐照度对系统性能的综合影响。研究结果表明:热容比为1对应的液气比大小是系统的最佳性能点,此时系统造水比(GOR)与产水量均达到最大值,产电量取得最小值;当顶温为60℃时,系统产电量与产水量的极值分别为481.13 k W·m^(-2)和43.10 kg·h^(-1);系统产水性能随顶温的升高而增强。当顶温从55?C升高到60和65℃时,系统最大产水量分别增加了34.5%和68.06%,三种顶温条件下的最大GOR分别为1.31、1.56和1.71。展开更多
Cavity-based flameholder is expected to be applied for ramjets or afterburners,which could work efficiently in the high-altitude space with low pressure.The detailed fluid structure helps to understand the flame stabi...Cavity-based flameholder is expected to be applied for ramjets or afterburners,which could work efficiently in the high-altitude space with low pressure.The detailed fluid structure helps to understand the flame stability principle of the flameholder.The fluid structure in the center section and side section of the cavity-based flameholder is experimentally measured at the inlet pressure of 0.04–0.10 MPa,Mach number of 0.1,and temperature of 300 K.Results indicate that the inlet pressure has a significant effect on the fluid-structure in the cavity.The bluff body affects the generation of the vortex in the cavity.As the inlet pressure decreases from 0.10 MPa to 0.04 MPa,the classical dual-vortex maintains excellent stability in the side section of the cavity.Whereas the single-vortex in the center section gradually becomes incomplete with the inlet pressure varying from 0.10 MPa to 0.06 MPa,and it disappears at 0.04 MPa.The reason is that with the reduction of inlet pressure,the density decreases as well,and the proportion of the mass flow rate attracted to the low-pressure area downstream of the bluff body increases,which leads to the vortex being gradually pulled and destroyed.展开更多
A series of experiments have been performed to demonstrate the significant drag reduction of the laminar flow in the ultrahydrophobic channels with dual-scale micro-nano structured surfaces.However,in previous experim...A series of experiments have been performed to demonstrate the significant drag reduction of the laminar flow in the ultrahydrophobic channels with dual-scale micro-nano structured surfaces.However,in previous experiments,the ultrahydrophobic surfaces were fabricated with micro-structures or nano-structures and the channels were on the microscale.For the drag reduction in macro-scale channels few reports are available.Here a new method was developed to fabricate ultrahydrophobic surfaces with micro-nano hierarchical structures made from carbon nanotubes.The drag reductions up to 36.3% were observed in the macro-channels with ultrahydrophobic surfaces.The micro-PIV was used to measure the flow velocity in channels.Compared with the traditional no-slip theory at walls,a significant slip velocity was observed on the ultrahydrophobic surfaces.展开更多
The dynamic wetting characteristics of water droplets on silicon wafers with microscale regular pillars structures and fresh lotus leaves are investigated experimentally.We measured the static contact angle,contact an...The dynamic wetting characteristics of water droplets on silicon wafers with microscale regular pillars structures and fresh lotus leaves are investigated experimentally.We measured the static contact angle,contact angle hysteresis,and roll-off angle of water droplets on both of these superhydrophobic surfaces with a high speed contact angle meter.The dynamic contact angles and internal velocity distribution of water droplets on superhydrophobic surfaces were studied with a high-speed camera system and a particle image velocimetry (PIV) system,respectively.We found that the acceleration of water droplets when they slide off lotus leaves is greater than that of water droplets sliding off the silicon wafers with microscale pillar structures although the static contact angles of water droplets on lotus leaves are slightly smaller than those on the silicon wafers.The reason is that water droplets sliding off lotus leaves have smaller contact angle hysteresis and larger slip velocities.These results indicate that the dynamic contact angle hysteresis and sliding acceleration of liquid droplets are more suitable for reflecting the hydrophobicity of material surfaces compared with static contact angles.Our experiments also show that lotus leaves with multiscale micro/nanostructures have stronger hydrophobicity and self-cleaning properties compared with the micro-structured superhydrophobic surfaces.展开更多
Pitot probes enable a simple and convenient way of measuring mean velocity in air flow. The contrastive numerical simulation between free supersonic airflow and pitot tube at different positions in supersonic air flow...Pitot probes enable a simple and convenient way of measuring mean velocity in air flow. The contrastive numerical simulation between free supersonic airflow and pitot tube at different positions in supersonic air flow was performed using Navier-Stokes equations, the ENN scheme with time-dependent boundary conditions （TDBC） and the Spalart-Allmaras turbulence model. The physical experimental results including pitot pressure and shadowgraph are also presented. Numerical results coincide with the experimental data. The flow characteristics of the pitot probe on the supersonic flow structure show that the measure- ment gives actually the total pressure behind the detached shock wave by using the pitot probe to measure the total pressure. The measurement result of the distribution of the total pressure can still represent the real free jet flow. The similar features of the intersection and reflection of shock waves can be identified. The difference between the measurement results and the actual ones is smaller than 10%. When the pitot probe is used to measure the region of L=0-4D, the measurement is smaller than the real one due to the increase of the shock wave strength. The difference becomes larger where the waves intersect. If the pitot probe is put at L=SD-10D, where the flow changes from supersonic to subsonic, the addition of the pitot probe turns the original supersonic flow region subsonic and causes bigger measurement errors.展开更多
With the development of the micro-electro-mechanical system (MEMS),the flow characteristics in micro-channels have drawn increasing attention.In this paper,numerical simulations are conducted to investigate the flow c...With the development of the micro-electro-mechanical system (MEMS),the flow characteristics in micro-channels have drawn increasing attention.In this paper,numerical simulations are conducted to investigate the flow characteristics of compressible flow through micro-channels and micronozzles.An improved surface roughness viscosity model is used to simulate the effect of surface roughness on micro-channels flow characteristics.Using this model,better agreements between the computational results and the experimental data are found.The result indicates that the surface roughness is one of the important factors affecting the flow characteristics of gas through micro-channels.The numerical investigation on the expansion channel shows that by using the laminar model that considers surface roughness,the computational results and experimental data are consistent when Re<450,whereas deviation increases when Re>450.Based on the synthetic model with considerations of turbulence viscosity and surface roughness,the numerical results and the experimental data are identical.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
文摘为了探究由光伏光热(PV/T)驱动的双热质耦合加湿除湿海水淡化系统的水电综合性能,基于能量与质量守恒原理构建了PV/T组件与加湿除湿系统的数学模型,揭示了液气比对系统相关热力学参数的影响规律,对比分析了不同顶温条件下系统的热力学性能,并在某典型天气状况下探究了逐时辐照度对系统性能的综合影响。研究结果表明:热容比为1对应的液气比大小是系统的最佳性能点,此时系统造水比(GOR)与产水量均达到最大值,产电量取得最小值;当顶温为60℃时,系统产电量与产水量的极值分别为481.13 k W·m^(-2)和43.10 kg·h^(-1);系统产水性能随顶温的升高而增强。当顶温从55?C升高到60和65℃时,系统最大产水量分别增加了34.5%和68.06%,三种顶温条件下的最大GOR分别为1.31、1.56和1.71。
基金supported by the National Science and Technology Major Project(No.2017-III-0008-0034)。
文摘Cavity-based flameholder is expected to be applied for ramjets or afterburners,which could work efficiently in the high-altitude space with low pressure.The detailed fluid structure helps to understand the flame stability principle of the flameholder.The fluid structure in the center section and side section of the cavity-based flameholder is experimentally measured at the inlet pressure of 0.04–0.10 MPa,Mach number of 0.1,and temperature of 300 K.Results indicate that the inlet pressure has a significant effect on the fluid-structure in the cavity.The bluff body affects the generation of the vortex in the cavity.As the inlet pressure decreases from 0.10 MPa to 0.04 MPa,the classical dual-vortex maintains excellent stability in the side section of the cavity.Whereas the single-vortex in the center section gradually becomes incomplete with the inlet pressure varying from 0.10 MPa to 0.06 MPa,and it disappears at 0.04 MPa.The reason is that with the reduction of inlet pressure,the density decreases as well,and the proportion of the mass flow rate attracted to the low-pressure area downstream of the bluff body increases,which leads to the vortex being gradually pulled and destroyed.
基金supported by the National Natural Science Foundation of China (Grant No. 10872106)
文摘A series of experiments have been performed to demonstrate the significant drag reduction of the laminar flow in the ultrahydrophobic channels with dual-scale micro-nano structured surfaces.However,in previous experiments,the ultrahydrophobic surfaces were fabricated with micro-structures or nano-structures and the channels were on the microscale.For the drag reduction in macro-scale channels few reports are available.Here a new method was developed to fabricate ultrahydrophobic surfaces with micro-nano hierarchical structures made from carbon nanotubes.The drag reductions up to 36.3% were observed in the macro-channels with ultrahydrophobic surfaces.The micro-PIV was used to measure the flow velocity in channels.Compared with the traditional no-slip theory at walls,a significant slip velocity was observed on the ultrahydrophobic surfaces.
基金supported by the National Natural Science Foundation of China(Grant Nos. 11072126 and 10872106)
文摘The dynamic wetting characteristics of water droplets on silicon wafers with microscale regular pillars structures and fresh lotus leaves are investigated experimentally.We measured the static contact angle,contact angle hysteresis,and roll-off angle of water droplets on both of these superhydrophobic surfaces with a high speed contact angle meter.The dynamic contact angles and internal velocity distribution of water droplets on superhydrophobic surfaces were studied with a high-speed camera system and a particle image velocimetry (PIV) system,respectively.We found that the acceleration of water droplets when they slide off lotus leaves is greater than that of water droplets sliding off the silicon wafers with microscale pillar structures although the static contact angles of water droplets on lotus leaves are slightly smaller than those on the silicon wafers.The reason is that water droplets sliding off lotus leaves have smaller contact angle hysteresis and larger slip velocities.These results indicate that the dynamic contact angle hysteresis and sliding acceleration of liquid droplets are more suitable for reflecting the hydrophobicity of material surfaces compared with static contact angles.Our experiments also show that lotus leaves with multiscale micro/nanostructures have stronger hydrophobicity and self-cleaning properties compared with the micro-structured superhydrophobic surfaces.
基金supported by the National Natural Science Foundation of China (Grant No. 30970822)
文摘Pitot probes enable a simple and convenient way of measuring mean velocity in air flow. The contrastive numerical simulation between free supersonic airflow and pitot tube at different positions in supersonic air flow was performed using Navier-Stokes equations, the ENN scheme with time-dependent boundary conditions （TDBC） and the Spalart-Allmaras turbulence model. The physical experimental results including pitot pressure and shadowgraph are also presented. Numerical results coincide with the experimental data. The flow characteristics of the pitot probe on the supersonic flow structure show that the measure- ment gives actually the total pressure behind the detached shock wave by using the pitot probe to measure the total pressure. The measurement result of the distribution of the total pressure can still represent the real free jet flow. The similar features of the intersection and reflection of shock waves can be identified. The difference between the measurement results and the actual ones is smaller than 10%. When the pitot probe is used to measure the region of L=0-4D, the measurement is smaller than the real one due to the increase of the shock wave strength. The difference becomes larger where the waves intersect. If the pitot probe is put at L=SD-10D, where the flow changes from supersonic to subsonic, the addition of the pitot probe turns the original supersonic flow region subsonic and causes bigger measurement errors.
基金supported by the National Natural Science Foundation of China(Grant No. 10872106)
文摘With the development of the micro-electro-mechanical system (MEMS),the flow characteristics in micro-channels have drawn increasing attention.In this paper,numerical simulations are conducted to investigate the flow characteristics of compressible flow through micro-channels and micronozzles.An improved surface roughness viscosity model is used to simulate the effect of surface roughness on micro-channels flow characteristics.Using this model,better agreements between the computational results and the experimental data are found.The result indicates that the surface roughness is one of the important factors affecting the flow characteristics of gas through micro-channels.The numerical investigation on the expansion channel shows that by using the laminar model that considers surface roughness,the computational results and experimental data are consistent when Re<450,whereas deviation increases when Re>450.Based on the synthetic model with considerations of turbulence viscosity and surface roughness,the numerical results and the experimental data are identical.
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.
