The parallel-plate flow chamber (PPFC), of which the height is far smaller than its own length and width, is one of the main apparatus for the in vitro study of the mechanical behaviors of cultured cells at the bottom...The parallel-plate flow chamber (PPFC), of which the height is far smaller than its own length and width, is one of the main apparatus for the in vitro study of the mechanical behaviors of cultured cells at the bottom of PPFC undergoing shear stress. The PPFC of which the upper and lower plates are rectangular is usually used by research workers, and the flow field in this kind of PPFC (except for the regions near the entrance and exit) is uniform([1]), so only the effect the shear stress with one value has on cultured cells can be observed during each experiment. A kind of PPFC of which the upper and lower plates are not rectangular is proposed in this paper. The distributions of the velocities inside and the shear stresses at the bottom of the chamber are given by analyzing the flow field of the steady flow in the PPFC. The results show that the mechanical behaviors of cultured cells undergoing the shear stresses with various values may be simultaneously observed by the use of this kind of irrectangular PPFC. The theoretical and experimental results obtained by Ultrasonic Doppler Technique show good agreement.展开更多
Introduction Blood flow provides a mechanical condition for blood cells and vessels,especially for endothelial cells.It is important to understand the mechanical characteristics of
Many in vitro studies focus on effects of wall shear stress (WSS) and wall shear stress gradient (WSSG) on endothelial cells, which are linked to the initiation and progression of atherosclerosis in the arterial syste...Many in vitro studies focus on effects of wall shear stress (WSS) and wall shear stress gradient (WSSG) on endothelial cells, which are linked to the initiation and progression of atherosclerosis in the arterial system. Limitation in available flow chambers with a constant WSSG in the testing region makes it difficult to quantify cellular responses to WSSG. The current study proposes and characterizes a type of converging parallel plate flow chamber (PPFC) featuring a constant gradient of WSS. A simple formula was derived for the curvature of side walls, which relates WSSG to flow rate (Q), height of the PPFC (h), length of the convergent section (L), its widths at the entrance (w0) and exit (w1). CFD simulation of flow in the chamber is carried out. Constant WSSG is observed in most regions of the top and bottom plates except those in close proximity of side walls. A change in Q or h induces equally proportional changes in WSS and WSSG whereas an alteration in the ratio between w0 and w1 results in a more significant change in WSSG than that in WSS. The current design makes possible an easy quantification of WSSG on endothelial cells in the flow chamber.展开更多
The Parallel-Plate Flow Chamber （PPFC）, of which the height is far smaller than its own length and width, is one of the main apparatus for the in-vitro study of the mechanical behavior of cultured vascular Endotheli...The Parallel-Plate Flow Chamber （PPFC）, of which the height is far smaller than its own length and width, is one of the main apparatus for the in-vitro study of the mechanical behavior of cultured vascular Endothelical Cells （ECs） exposed to fluid shear stress. The steady flow in different kinds of PPFC has been extensively investigated, whereas, the pulsatile flow in the PPFC has received little attention. In consideration of the characteristics of geometrical size and pulsatile flow in the PPFC, the 3-D pulsatile flow was decomposed into a 2-D pulsatile flow in the vertical plane, and an incompressible plane potential flow in the horizontal plane. A simple method was then proposed to analyze the pulsatile flow in the PPFC with spatial shear stress gradient. On the basis of the method, the pulsatile fluid shear stresses in several reported PPFCs with spatial shear stress gradients were calculated. The results were theoretically meaningful for applying the PPFCs in-vitro, to simulate the pulsatile fluid shear stress environment, to which cultured ECs were exposed.展开更多
A flow chamber whose length and width are far larger than its own height was widely used to study cell's mechanical behavior in vitro , especially the cell's adhesion property. The paper analyzed the flow fiel...A flow chamber whose length and width are far larger than its own height was widely used to study cell's mechanical behavior in vitro , especially the cell's adhesion property. The paper analyzed the flow field of the flow chamber in detail, and gave the analytical expressions of the velocity, pressure and shear stress when the fluid flowed in and out the chamber through a small crevice. Then, full and clear discussion of flow field was made. Also the velocity field was measured by an Ultrasonic Doppler Velocity-metre. It was found that the experimental values coincided with the theoretical values. These results were important to study the cell's mechanical behavior in vitro .展开更多
The velocity profile around cells in a flow chamber coated with the immobilized protein and the endothelial cells is studied using the micro particle image velocimetry（PIV）. The main purpose is to study the effect o...The velocity profile around cells in a flow chamber coated with the immobilized protein and the endothelial cells is studied using the micro particle image velocimetry（PIV）. The main purpose is to study the effect of the endothelial cells on the local hydrodynamic environment and the local shear rates above a single polymorphonuclear neutrophil（PMN） and a melanoma cell when they adhere to different immobilized protein substrates. Micro-PIV images are taken in the top-view and the side-view under 10 X and 40 X objective lens and the ensemble correlation method is used to analyze the data. The results show that the endothelial monolayer has changed the patterns of the flow velocity profile of the side-view flow on the chamber bottom, and also increased the wall shear rates. The melanoma cells adhered on the immobilized fibrin disturb the local flow more than those adhered on the immobilized fibrinogen, but one sees no significant difference between the local shear rates above the PMNs adhered on the immobilized fibrinogen and those above the PMNs adhered on the immobilized fibrin.展开更多
The downstream water-air heat and moisture transfer system in a moving coordinate was studied. The relationship between the diameter of the misted droplets and the spray pressure was determined. Based on the theory of...The downstream water-air heat and moisture transfer system in a moving coordinate was studied. The relationship between the diameter of the misted droplets and the spray pressure was determined. Based on the theory of the relative velocity,the two-phase flow mode of the spray chamber and the efficiency equation for heat and moisture exchange were established. Corrections were carried out for the efficiency equation with spray pressure of 157 kPa. The results show that the pressure plays an important part in determining the efficiency of heat and moisture exchange. When the spray pressure is less than 157 kPa,better coincidence is noticed between the theoretical analysis and the test results with the error less than 6%. Greater error will be resulted in the case when the spray pressure is beyond 157 kPa. After the correction treatment,the coincidence between the theoretical and the experimental results is greatly improved.展开更多
To improve the performance of the Stairmand cyclone, the effects of an expansion chamber on the flow field, the pressure drop and the separation efficiency were investigated numerically and experimentally. The experim...To improve the performance of the Stairmand cyclone, the effects of an expansion chamber on the flow field, the pressure drop and the separation efficiency were investigated numerically and experimentally. The experimental results showed that compared with the Stairmand cyclone, the cyclone with an upper expansion chamber worked better at low inlet velocity(less than 14 m/s in this study), while the cyclone with a lower expansion chamber achieved higher efficiency at a relatively high inlet velocity(14-20 m/s). The presence of an expansion chamber can generally result in a slight decrease in the cyclone pressure drop. The simulated results, which were used to further analyze the reason behind the experimental phenomena, suggested that the expansion chamber had insignificant effects on the tangential velocity profiles in the cylindrical part of cyclones. While in the cone part, the expansion chamber and the dipleg, the tangential velocity slightly decreased. Nevertheless, the expansion chamber decreased the possibility of the vortex end to sweep the wall and then reduce the particle re-entrainment. Therefore, installing the expansion chamber at a proper position could improve the separation performance of Stairmand cyclones. Both the experimental and simulated results represent a potential improvement of the Stairmand cyclone performance.展开更多
New designs and adaptation methods are experimented to ensure compliance to ever increasing emissions and efficiency requirements of modern diesel engines. Piston head structure which influences the mixing rate and ti...New designs and adaptation methods are experimented to ensure compliance to ever increasing emissions and efficiency requirements of modern diesel engines. Piston head structure which influences the mixing rate and timing of the fuel within in the combustion chamber is known to enable increase in combustion efficiency and thus lower emission rates. In this paper, computation analysis of flow within a diesel engine cylinder with a twin swirl combustion chamber design throughout a full cycle is presented. The results obtained indicate that the effect of the twin swirl combustion chamber on the cold flow conditions is noteworthy and further analysis together with experiments may reveal information that may prove to be useful in further new designs.展开更多
The adhesion of endothelial progenitor cells（EPCs） on endothelial cells（ECs） is one of the critical physiological processes for the regenesis of vascular vessels and the prevention of serious cardiovascular diseas...The adhesion of endothelial progenitor cells（EPCs） on endothelial cells（ECs） is one of the critical physiological processes for the regenesis of vascular vessels and the prevention of serious cardiovascular diseases.Here,the rolling and adhesion behavior of EPCs on ECs was studied numerically.A two-dimensional numerical model was developed based on the immersed boundary method for simulating the rolling and adhesion of cells in a channel flow.The binding force arising from the catch bond of a receptor and ligand pair was modeled with stochastic Monte Carlo method and Hookean spring model.The effect of tumor necrosis factor alpha（TNF-α） on the expression of the number of adhesion molecules in ECs was analyzed experimentally.A flow chamber system with CCD camera was set up to observe the top view of the rolling of EPCs on the substrate cultivated with ECs.Numerical results prove that the adhesion of EPC on ECs is closely related to membrane stiff-ness of the cell and shear rate of the flow.It also suggests that the adhesion force between EPC and EC by P-selectin glycoprotein ligand-1 only is not strong enough to bond the cell onto vessel walls unless contributions of other catch bond are considered.Experimental results demonstrate that TNF-α enhanced the expressions of VCAM,ICAM,P-selectin and E-selectin in ECs,which supports the numerical results that the rolling velocity of EPC on TNF-α treated EC substrate decreases obviously compared with its velocity on the untreated one.It is found that because the adhesion is affected by both the rolling velocity and the deformability of the cell,an optimal stiffness of EPC may exist at a given shear rate of flow for achieving maximum adhesion rates.展开更多
文摘The parallel-plate flow chamber (PPFC), of which the height is far smaller than its own length and width, is one of the main apparatus for the in vitro study of the mechanical behaviors of cultured cells at the bottom of PPFC undergoing shear stress. The PPFC of which the upper and lower plates are rectangular is usually used by research workers, and the flow field in this kind of PPFC (except for the regions near the entrance and exit) is uniform([1]), so only the effect the shear stress with one value has on cultured cells can be observed during each experiment. A kind of PPFC of which the upper and lower plates are not rectangular is proposed in this paper. The distributions of the velocities inside and the shear stresses at the bottom of the chamber are given by analyzing the flow field of the steady flow in the PPFC. The results show that the mechanical behaviors of cultured cells undergoing the shear stresses with various values may be simultaneously observed by the use of this kind of irrectangular PPFC. The theoretical and experimental results obtained by Ultrasonic Doppler Technique show good agreement.
基金supported by grant from National Natural Science Foundation of China No10772127,30570450Program for New Century Excellent Talents in University NCET-06-0789Sichaun Youth Science and Technology Foundation 06ZQ026-009
文摘Introduction Blood flow provides a mechanical condition for blood cells and vessels,especially for endothelial cells.It is important to understand the mechanical characteristics of
文摘Many in vitro studies focus on effects of wall shear stress (WSS) and wall shear stress gradient (WSSG) on endothelial cells, which are linked to the initiation and progression of atherosclerosis in the arterial system. Limitation in available flow chambers with a constant WSSG in the testing region makes it difficult to quantify cellular responses to WSSG. The current study proposes and characterizes a type of converging parallel plate flow chamber (PPFC) featuring a constant gradient of WSS. A simple formula was derived for the curvature of side walls, which relates WSSG to flow rate (Q), height of the PPFC (h), length of the convergent section (L), its widths at the entrance (w0) and exit (w1). CFD simulation of flow in the chamber is carried out. Constant WSSG is observed in most regions of the top and bottom plates except those in close proximity of side walls. A change in Q or h induces equally proportional changes in WSS and WSSG whereas an alteration in the ratio between w0 and w1 results in a more significant change in WSSG than that in WSS. The current design makes possible an easy quantification of WSSG on endothelial cells in the flow chamber.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 10472027, 30670511).
文摘The Parallel-Plate Flow Chamber （PPFC）, of which the height is far smaller than its own length and width, is one of the main apparatus for the in-vitro study of the mechanical behavior of cultured vascular Endothelical Cells （ECs） exposed to fluid shear stress. The steady flow in different kinds of PPFC has been extensively investigated, whereas, the pulsatile flow in the PPFC has received little attention. In consideration of the characteristics of geometrical size and pulsatile flow in the PPFC, the 3-D pulsatile flow was decomposed into a 2-D pulsatile flow in the vertical plane, and an incompressible plane potential flow in the horizontal plane. A simple method was then proposed to analyze the pulsatile flow in the PPFC with spatial shear stress gradient. On the basis of the method, the pulsatile fluid shear stresses in several reported PPFCs with spatial shear stress gradients were calculated. The results were theoretically meaningful for applying the PPFCs in-vitro, to simulate the pulsatile fluid shear stress environment, to which cultured ECs were exposed.
文摘A flow chamber whose length and width are far larger than its own height was widely used to study cell's mechanical behavior in vitro , especially the cell's adhesion property. The paper analyzed the flow field of the flow chamber in detail, and gave the analytical expressions of the velocity, pressure and shear stress when the fluid flowed in and out the chamber through a small crevice. Then, full and clear discussion of flow field was made. Also the velocity field was measured by an Ultrasonic Doppler Velocity-metre. It was found that the experimental values coincided with the theoretical values. These results were important to study the cell's mechanical behavior in vitro .
基金Project supported by the National Institute of Health(NIH,USA,Grant No.CA-125707)the National Science Foundation(NSF,USA,Grant No.CBET-0729091)+1 种基金the National Natural Science Foundation of China(Grant Nos.11302129,11432006 and 31170887)the Fellowship from Chinese Scholarship Council
文摘The velocity profile around cells in a flow chamber coated with the immobilized protein and the endothelial cells is studied using the micro particle image velocimetry（PIV）. The main purpose is to study the effect of the endothelial cells on the local hydrodynamic environment and the local shear rates above a single polymorphonuclear neutrophil（PMN） and a melanoma cell when they adhere to different immobilized protein substrates. Micro-PIV images are taken in the top-view and the side-view under 10 X and 40 X objective lens and the ensemble correlation method is used to analyze the data. The results show that the endothelial monolayer has changed the patterns of the flow velocity profile of the side-view flow on the chamber bottom, and also increased the wall shear rates. The melanoma cells adhered on the immobilized fibrin disturb the local flow more than those adhered on the immobilized fibrinogen, but one sees no significant difference between the local shear rates above the PMNs adhered on the immobilized fibrinogen and those above the PMNs adhered on the immobilized fibrin.
基金Project(06YFJMCI5500) supported by the Natural Science Foundation of Tianjin City of China
文摘The downstream water-air heat and moisture transfer system in a moving coordinate was studied. The relationship between the diameter of the misted droplets and the spray pressure was determined. Based on the theory of the relative velocity,the two-phase flow mode of the spray chamber and the efficiency equation for heat and moisture exchange were established. Corrections were carried out for the efficiency equation with spray pressure of 157 kPa. The results show that the pressure plays an important part in determining the efficiency of heat and moisture exchange. When the spray pressure is less than 157 kPa,better coincidence is noticed between the theoretical analysis and the test results with the error less than 6%. Greater error will be resulted in the case when the spray pressure is beyond 157 kPa. After the correction treatment,the coincidence between the theoretical and the experimental results is greatly improved.
基金the financial assistance from the National Natural Science Foundation (Grant No.21276274)the National Key Project of Basic Research of the Ministry for Science and Technology of China (Grant No. 2014CB744304)
文摘To improve the performance of the Stairmand cyclone, the effects of an expansion chamber on the flow field, the pressure drop and the separation efficiency were investigated numerically and experimentally. The experimental results showed that compared with the Stairmand cyclone, the cyclone with an upper expansion chamber worked better at low inlet velocity(less than 14 m/s in this study), while the cyclone with a lower expansion chamber achieved higher efficiency at a relatively high inlet velocity(14-20 m/s). The presence of an expansion chamber can generally result in a slight decrease in the cyclone pressure drop. The simulated results, which were used to further analyze the reason behind the experimental phenomena, suggested that the expansion chamber had insignificant effects on the tangential velocity profiles in the cylindrical part of cyclones. While in the cone part, the expansion chamber and the dipleg, the tangential velocity slightly decreased. Nevertheless, the expansion chamber decreased the possibility of the vortex end to sweep the wall and then reduce the particle re-entrainment. Therefore, installing the expansion chamber at a proper position could improve the separation performance of Stairmand cyclones. Both the experimental and simulated results represent a potential improvement of the Stairmand cyclone performance.
文摘New designs and adaptation methods are experimented to ensure compliance to ever increasing emissions and efficiency requirements of modern diesel engines. Piston head structure which influences the mixing rate and timing of the fuel within in the combustion chamber is known to enable increase in combustion efficiency and thus lower emission rates. In this paper, computation analysis of flow within a diesel engine cylinder with a twin swirl combustion chamber design throughout a full cycle is presented. The results obtained indicate that the effect of the twin swirl combustion chamber on the cold flow conditions is noteworthy and further analysis together with experiments may reveal information that may prove to be useful in further new designs.
基金supported by the National Natural Science Foundation of China (10732070, 11072155)Shanghai Pujiang Program (09PJ1405800)
文摘The adhesion of endothelial progenitor cells（EPCs） on endothelial cells（ECs） is one of the critical physiological processes for the regenesis of vascular vessels and the prevention of serious cardiovascular diseases.Here,the rolling and adhesion behavior of EPCs on ECs was studied numerically.A two-dimensional numerical model was developed based on the immersed boundary method for simulating the rolling and adhesion of cells in a channel flow.The binding force arising from the catch bond of a receptor and ligand pair was modeled with stochastic Monte Carlo method and Hookean spring model.The effect of tumor necrosis factor alpha（TNF-α） on the expression of the number of adhesion molecules in ECs was analyzed experimentally.A flow chamber system with CCD camera was set up to observe the top view of the rolling of EPCs on the substrate cultivated with ECs.Numerical results prove that the adhesion of EPC on ECs is closely related to membrane stiff-ness of the cell and shear rate of the flow.It also suggests that the adhesion force between EPC and EC by P-selectin glycoprotein ligand-1 only is not strong enough to bond the cell onto vessel walls unless contributions of other catch bond are considered.Experimental results demonstrate that TNF-α enhanced the expressions of VCAM,ICAM,P-selectin and E-selectin in ECs,which supports the numerical results that the rolling velocity of EPC on TNF-α treated EC substrate decreases obviously compared with its velocity on the untreated one.It is found that because the adhesion is affected by both the rolling velocity and the deformability of the cell,an optimal stiffness of EPC may exist at a given shear rate of flow for achieving maximum adhesion rates.
