The flow of incompressible couple stress fluid in a circular tube with stenosis and dilatations has been investigated. The stenosis was assumed to be axially symmetric and mild. The flow equations have been linearized...The flow of incompressible couple stress fluid in a circular tube with stenosis and dilatations has been investigated. The stenosis was assumed to be axially symmetric and mild. The flow equations have been linearized and the expressions for the resistance to the flow, velocity, pressure drop, wall shear stress have been derived. The effects of various parameters on these flow variables have been investigated. It is found that the resistance to the flow and pressure drop increase with height of the stenosis and decrease with post stenotic dilatation. Pressure drop decreases with couple stress fluid parameter for both stenosis and post stenotic dilatation. Further, the wall shear stress increases with height of the stenosis and couple stress parameter but decreases with post stenotic dilatation and couple stress fluid parameter.展开更多
A novel direct measurement strategy of bottom velocities and shear stresses based on the use of ferrofluids is presented. Such a strategy overcomes some of the limits of state-of-the-art instruments. A preliminary exp...A novel direct measurement strategy of bottom velocities and shear stresses based on the use of ferrofluids is presented. Such a strategy overcomes some of the limits of state-of-the-art instruments. A preliminary experimental campaign has been carried out in the presence of currents in steady flow conditions in order to test the effects of ferrofluid quantity and of the controlling permanent magnetic force. An alternating current （AC） circuit and a direct current （DC） conditioning circuit have been tested. For velocities larger than 0.05 m/s, the near-bottom velocity-output voltage calibration curve has a monotone parabolic shape. The sensitivity of the instrument is increased by a factor of 30 when the DC circuit is used.展开更多
A mathematical model for pulsatile flow of blood in a catheterized artery in presence of an axisymmetric stenosis with a velocity slip at the constricted wall is proposed. The expressions for the flow characteristics,...A mathematical model for pulsatile flow of blood in a catheterized artery in presence of an axisymmetric stenosis with a velocity slip at the constricted wall is proposed. The expressions for the flow characteristics, velocity profiles, the flow resistance, the wall shear stress, the effective viscosity are obtained in the present analysis. The effects of slip velocity on the blood flow characteristics are shown graphically and discussed briefly.展开更多
Soft and hard micromachining techniques used to develop microfluidic devices can yield microchannels of many different cross-sectional profiles. For semi-circular microchannels, these techniques often produce only par...Soft and hard micromachining techniques used to develop microfluidic devices can yield microchannels of many different cross-sectional profiles. For semi-circular microchannels, these techniques often produce only partialsemicircular (PSC) cross-sections. This study investigated fully developed laminar flow in PSC microchannels as a function of a circularity index, κ, defined as the ratio of the radiuses along the curved and flat surfaces of the PSC profile. A correction factor, K, to the Hagen-Poiseuille relation was determined and was well-fitted by the power-law relationship K=5.299/κ2.56. Actual correction factors were compared to estimates based on several hydraulic models for flow in microchannels of arbitrary cross-section, as well as the half-ellipsoid cross-section. The level of wall shear stress, when normalized by the pressure drop per unit length, increased approximately linearly with increase in the circularity index, κ.展开更多
为表征粗粒级膏体充填材料的抗离析性能，基于固液两相流体力学及非牛顿流体力学，对粗颗粒的静动态受力进行分析，构建膏体充填料浆静动态抗离析力学模型。综合考虑浆体屈服应力、粗颗粒粒级分配和固液密度，提出抗离析性能表征模型，...为表征粗粒级膏体充填材料的抗离析性能，基于固液两相流体力学及非牛顿流体力学，对粗颗粒的静动态受力进行分析，构建膏体充填料浆静动态抗离析力学模型。综合考虑浆体屈服应力、粗颗粒粒级分配和固液密度，提出抗离析性能表征模型，即离析判定值M。为检测该模型，以料浆浓度、粗颗粒最大粒径、尾碎比为三因素，进行9组正交实验，并对实验结果进行拟合分析。研究结果表明：离析判定值 M 的预测结果与实际结果一致，其中，M的最大值Mmax和M的平均值Mavg的拟合复相关参数均达到0.9以上，模型具有可靠性。合理选取粗颗粒粒径计算标准，即可实现对粗粒级膏体料浆抗离析性能的准确预测。建议离析判定值Mavg为1.0-2.5，离析判定值Mmax为1.0-1.2。展开更多
文摘The flow of incompressible couple stress fluid in a circular tube with stenosis and dilatations has been investigated. The stenosis was assumed to be axially symmetric and mild. The flow equations have been linearized and the expressions for the resistance to the flow, velocity, pressure drop, wall shear stress have been derived. The effects of various parameters on these flow variables have been investigated. It is found that the resistance to the flow and pressure drop increase with height of the stenosis and decrease with post stenotic dilatation. Pressure drop decreases with couple stress fluid parameter for both stenosis and post stenotic dilatation. Further, the wall shear stress increases with height of the stenosis and couple stress parameter but decreases with post stenotic dilatation and couple stress fluid parameter.
基金funded by the EC project HYDRALAB IV (Contract No. 261520)by the PRIN 2010-2011 project HYDROCARby the PON 2007-2013 project SEAPORT funded by MIUR (Italy)
文摘A novel direct measurement strategy of bottom velocities and shear stresses based on the use of ferrofluids is presented. Such a strategy overcomes some of the limits of state-of-the-art instruments. A preliminary experimental campaign has been carried out in the presence of currents in steady flow conditions in order to test the effects of ferrofluid quantity and of the controlling permanent magnetic force. An alternating current （AC） circuit and a direct current （DC） conditioning circuit have been tested. For velocities larger than 0.05 m/s, the near-bottom velocity-output voltage calibration curve has a monotone parabolic shape. The sensitivity of the instrument is increased by a factor of 30 when the DC circuit is used.
文摘A mathematical model for pulsatile flow of blood in a catheterized artery in presence of an axisymmetric stenosis with a velocity slip at the constricted wall is proposed. The expressions for the flow characteristics, velocity profiles, the flow resistance, the wall shear stress, the effective viscosity are obtained in the present analysis. The effects of slip velocity on the blood flow characteristics are shown graphically and discussed briefly.
文摘Soft and hard micromachining techniques used to develop microfluidic devices can yield microchannels of many different cross-sectional profiles. For semi-circular microchannels, these techniques often produce only partialsemicircular (PSC) cross-sections. This study investigated fully developed laminar flow in PSC microchannels as a function of a circularity index, κ, defined as the ratio of the radiuses along the curved and flat surfaces of the PSC profile. A correction factor, K, to the Hagen-Poiseuille relation was determined and was well-fitted by the power-law relationship K=5.299/κ2.56. Actual correction factors were compared to estimates based on several hydraulic models for flow in microchannels of arbitrary cross-section, as well as the half-ellipsoid cross-section. The level of wall shear stress, when normalized by the pressure drop per unit length, increased approximately linearly with increase in the circularity index, κ.
文摘为表征粗粒级膏体充填材料的抗离析性能，基于固液两相流体力学及非牛顿流体力学，对粗颗粒的静动态受力进行分析，构建膏体充填料浆静动态抗离析力学模型。综合考虑浆体屈服应力、粗颗粒粒级分配和固液密度，提出抗离析性能表征模型，即离析判定值M。为检测该模型，以料浆浓度、粗颗粒最大粒径、尾碎比为三因素，进行9组正交实验，并对实验结果进行拟合分析。研究结果表明：离析判定值 M 的预测结果与实际结果一致，其中，M的最大值Mmax和M的平均值Mavg的拟合复相关参数均达到0.9以上，模型具有可靠性。合理选取粗颗粒粒径计算标准，即可实现对粗粒级膏体料浆抗离析性能的准确预测。建议离析判定值Mavg为1.0-2.5，离析判定值Mmax为1.0-1.2。
