This work reports the effects of magnetic field on an electrically conducting fluid with low electrical conductivity flowing in a smooth expanded channel. The governing nonlinear magnetohydrodynamic(MHD) equations in ...This work reports the effects of magnetic field on an electrically conducting fluid with low electrical conductivity flowing in a smooth expanded channel. The governing nonlinear magnetohydrodynamic(MHD) equations in inductionfree situations are derived in the framework of MHD approximations and solved numerically using the finite-difference technique. The critical values of Reynolds number(based on upstream mean velocity and channel height) for symmetry breaking bifurcation for a sudden expansion channel(1:4) is about 36, whereas the value in the case of the smooth expansion geometry used in this work is obtained as 298, approximately(non-magnetic case). The flow of an electrically conducting fluid in the presence of an externally applied constant magnetic field perpendicular to the plane of the flow is reduced significantly depending on the magnetic parameter(M). It is found that the critical value of Reynolds number for smooth expansion(1:4) is about 475 for the magnetic parameter M = 2. The separating regions developed behind the smooth symmetric expansion are decreased in length for increasing values of the magnetic parameter. The bifurcation diagram is shown for a symmetric smoothly expanding channel. It is noted that the critical values of Reynolds number increase with increasing magnetic field strength.展开更多
Compared with conventional channels, experiments of microchannel often exhibit some controversial findings and sometimes even opposite trends, most notably the effects of the Reynolds number and the scaled channel hei...Compared with conventional channels, experiments of microchannel often exhibit some controversial findings and sometimes even opposite trends, most notably the effects of the Reynolds number and the scaled channel height on the Poiseuille number. The experimental method has still been constrained by two key facts, firstly the current ability to machine microstructures and secondly the limitation of measurement of parameters related to the Poiseuille number. As a consequence, numerical method was adopted in this study in order to analyze a flow in two-dimensional rectangular microchannels using water as working fluid. Results are obtained by the solution of the steady laminar incompressible Navier-Stokes equations using control volume finite element method(CVFEM) without pressure correction. The computation was made for channel height ranging from 50 ?m to 4.58 ?m and Reynolds number varying from 0.4 to 1 600. The effect of Reynolds number and channel heights on flow characteristics was investigated. The results showed that the Poiseuille numbers agree fairly well with the experimental measurements proving that there is no scale effect at small channel height. This scaling effect has been confirmed by two additional simulations being carried out at channel heights of 2.5 ?m and 0.5 ?m, respectively and the range of Reynolds number was extended from 0.01 up to 1 600. This study confirm that the conventional analysis approach can be employed with confidence for predicting flow behavior in microchannels when coupled with carefully matched entrance and boundary conditions in the dimensional range considered here.展开更多
A series of numerical analyses have been performed to investigate the flow structures in a narrow confined channel with 12 staggered circular impingement holes and one bigger exit hole. The flow enters the channel thr...A series of numerical analyses have been performed to investigate the flow structures in a narrow confined channel with 12 staggered circular impingement holes and one bigger exit hole. The flow enters the channel through the impingement holes and exits through the far end outlet. The flow fields corresponding to two jet Reynolds numbers(25000 and 65000) and three channel configurations with different ratios of the channel height to the impingement hole diameter(Zr= 1,3, 5) are analyzed by solving the Reynolds averaged Navier–Stokes equations with the realizable k–e turbulence model. Detailed flow field information including the secondary flow, the interaction between the jets and the cross flow, and flow distribution along the channel has been obtained.Comparisons between the numerical and experimental results of the flow fields at the four planes along the channel are performed to validate the numerical method. The calculated impingement pattern, high velocity flow distribution, low velocity separation region and vortices are in good agreement with the experimental data, implying the validity and effectiveness of the employed numerical approach for analyzing relevant flow field.展开更多
基金support by the UGC(SAP),DSA-I in the Mathematics Department,Burdwan University,India
文摘This work reports the effects of magnetic field on an electrically conducting fluid with low electrical conductivity flowing in a smooth expanded channel. The governing nonlinear magnetohydrodynamic(MHD) equations in inductionfree situations are derived in the framework of MHD approximations and solved numerically using the finite-difference technique. The critical values of Reynolds number(based on upstream mean velocity and channel height) for symmetry breaking bifurcation for a sudden expansion channel(1:4) is about 36, whereas the value in the case of the smooth expansion geometry used in this work is obtained as 298, approximately(non-magnetic case). The flow of an electrically conducting fluid in the presence of an externally applied constant magnetic field perpendicular to the plane of the flow is reduced significantly depending on the magnetic parameter(M). It is found that the critical value of Reynolds number for smooth expansion(1:4) is about 475 for the magnetic parameter M = 2. The separating regions developed behind the smooth symmetric expansion are decreased in length for increasing values of the magnetic parameter. The bifurcation diagram is shown for a symmetric smoothly expanding channel. It is noted that the critical values of Reynolds number increase with increasing magnetic field strength.
基金support from MESC laboratory (Laboratoire de Mécanique Energétique et systèmes de conversion)U.S.T.H.B University (Code Number of Research Project J0300220130012)
文摘Compared with conventional channels, experiments of microchannel often exhibit some controversial findings and sometimes even opposite trends, most notably the effects of the Reynolds number and the scaled channel height on the Poiseuille number. The experimental method has still been constrained by two key facts, firstly the current ability to machine microstructures and secondly the limitation of measurement of parameters related to the Poiseuille number. As a consequence, numerical method was adopted in this study in order to analyze a flow in two-dimensional rectangular microchannels using water as working fluid. Results are obtained by the solution of the steady laminar incompressible Navier-Stokes equations using control volume finite element method(CVFEM) without pressure correction. The computation was made for channel height ranging from 50 ?m to 4.58 ?m and Reynolds number varying from 0.4 to 1 600. The effect of Reynolds number and channel heights on flow characteristics was investigated. The results showed that the Poiseuille numbers agree fairly well with the experimental measurements proving that there is no scale effect at small channel height. This scaling effect has been confirmed by two additional simulations being carried out at channel heights of 2.5 ?m and 0.5 ?m, respectively and the range of Reynolds number was extended from 0.01 up to 1 600. This study confirm that the conventional analysis approach can be employed with confidence for predicting flow behavior in microchannels when coupled with carefully matched entrance and boundary conditions in the dimensional range considered here.
基金supported by the National Natural Science Foundation of China(No.51206180)the Natural Science Basic Research Plan in Shaanxi Province of China(No.2014JQ7276)
文摘A series of numerical analyses have been performed to investigate the flow structures in a narrow confined channel with 12 staggered circular impingement holes and one bigger exit hole. The flow enters the channel through the impingement holes and exits through the far end outlet. The flow fields corresponding to two jet Reynolds numbers(25000 and 65000) and three channel configurations with different ratios of the channel height to the impingement hole diameter(Zr= 1,3, 5) are analyzed by solving the Reynolds averaged Navier–Stokes equations with the realizable k–e turbulence model. Detailed flow field information including the secondary flow, the interaction between the jets and the cross flow, and flow distribution along the channel has been obtained.Comparisons between the numerical and experimental results of the flow fields at the four planes along the channel are performed to validate the numerical method. The calculated impingement pattern, high velocity flow distribution, low velocity separation region and vortices are in good agreement with the experimental data, implying the validity and effectiveness of the employed numerical approach for analyzing relevant flow field.
