Flow and heat transfer of a pseudo-plastic power-law fluid over a stretching permeable surface with the magnetic effect is investigated. In the boundary conditions,the nonlinear temperature jump and the velocity slip ...Flow and heat transfer of a pseudo-plastic power-law fluid over a stretching permeable surface with the magnetic effect is investigated. In the boundary conditions,the nonlinear temperature jump and the velocity slip are considered. Semi-similarity equations are obtained and solved by bvp4c with MATLAB. The problem can be considered as an extension of the previous work done by Mahmoud(Mahmoud, M. A. A. Slip velocity effect on a non-Newtonian power-law fluid over a moving permeable surface with heat generation. Mathematical and Computer Modelling, 54, 1228–1237(2011)). Efforts are made to discuss the effects of the power-law number, slip velocity, and temperature jump on the dimensionless velocity and temperature distribution.展开更多
The effects of the second-order velocity slip and temperature jump boundary conditions on the magnetohydrodynamic (MHD) flow and heat transfer in the presence of nanoparticle fractions are investigated. In the model...The effects of the second-order velocity slip and temperature jump boundary conditions on the magnetohydrodynamic (MHD) flow and heat transfer in the presence of nanoparticle fractions are investigated. In the modeling of the water-based nanofluids containing Cu and A1203, the effects of the Brownian motion, thermophoresis, and thermal radiation are considered. The governing boundary layer equations are transformed into a system of nonlinear differential equations, and the analytical approximations of the solutions axe derived by the homotopy analysis method (HAM). The reliability and efficiency of the HAM solutions are verified by the residual errors and the numerical results in the literature. Moreover, the effects of the physical factors on the flow and heat transfer are discussed graphically.展开更多
The study of the hydrogen evolution reaction(HER)aimed to reach a deeper understanding of the parameters that control the rate of this reaction is of great importance given the technical relevance of hydrogen producti...The study of the hydrogen evolution reaction(HER)aimed to reach a deeper understanding of the parameters that control the rate of this reaction is of great importance given the technical relevance of hydrogen production as an energy vector in the so-called hydrogen economy.In previous works,laser-induced temperature jump(LITJ)experiments on Pt(111)modified with Ni(OH)_(2)in alkaline media have revealed the importance of the interfacial electric field in the rate of the HER.It was hypothesised that small amounts of Ni(OH)_(2)cause a decrease of the electric field because of a negative shift of the pzfc toward the onset of the hydrogen evolution.In this work,to test the validity of this hypothesis,the study has been extended to Pt(111)surfaces modified with Fe(OH)_(2).The modified surfaces have been studied voltammetrically,and the voltammetric charges have been analysed.The voltammograms show a peak in the hydrogen evolution region that suggest the transformation in the adlayer from Fe(II)to Fe(0).In agreement with the coulometric analysis,the voltammetric features in the OH adsorption region would be related with the oxidation to the+3 valence state.The results obtained with LITJ method reflect the existence of a strong interaction of the Fe oxophilic species with the water molecules,shifting the potential of maximum entropy away from the onset of the HER.Hence,the most catalytic surface is the one with the lowest Fe coverage.展开更多
The fast phase-transitional process of ploy(N-isopropylacrylamide) (PNIPAM) in deuterated solution was studied by laser induced temperature jump technique combined with time-resolved mid-infrared absorbance differ...The fast phase-transitional process of ploy(N-isopropylacrylamide) (PNIPAM) in deuterated solution was studied by laser induced temperature jump technique combined with time-resolved mid-infrared absorbance difference spectroscopy on nanosecond level. The multi-peaks of amide I'band of PNIPAM among the energy range of 1565-1700 cm^-1 was experimentally resolved to three groups (i, ii, iii) for the first time, while the distinct threestage procedure in the phase transitional process of long-chain PNIPAM was observed firstly too. Furthermore, proper assignments were also made for the three group peaks in amide I'band and the three steps in the kinetics process of long-chain PNIPAM.展开更多
Two narrowly-distributed poly(N-isopropylacrylamide)(PNIPAM) samples were prepared via atom transfer radical polymerization (ATRP) with a novel dansyl functionalized initiator. The other end of the PNIPAM was function...Two narrowly-distributed poly(N-isopropylacrylamide)(PNIPAM) samples were prepared via atom transfer radical polymerization (ATRP) with a novel dansyl functionalized initiator. The other end of the PNIPAM was functionalized by dabcyl group via click reaction. From the static fluorescence measurements, the fluorescence intensity of dansyl group and energy transfer efficiency between dansyl and dabcyl groups increased when the temperature increased from 36 °C to 45 °C, indicating that the microenvironment surrounding dansyl became hydrophobic and the distance between dansyl and dabcyl decreased. The kinetics of the conformational change of the dye-labeled PNIPAM was studied by a home-made laser-induced temperature jump device with fluorescent measurement. Our results revealed that the characteristic transition time was 3.8 and 5.8 ms for PNIPAM with degrees of polymerization of 85 and 142, respectively, indicating that the characteristic transition time was related to the chain length. Besides, characteristic transition time for the change of the energy transfer efficiency was 2.9 ms for PNIPAM with the degree of polymerization of 85, suggesting that the energy transfer efficiency change was faster than the fluorescence intensity change of dansyl group.展开更多
The velocity slip and temperature jump in micro-Couette flow are investigated with the lattice Boltzmann method(LBM).A new slip boundary condition with the non-equilibrium extrapolation scheme is used in a thermal lat...The velocity slip and temperature jump in micro-Couette flow are investigated with the lattice Boltzmann method(LBM).A new slip boundary condition with the non-equilibrium extrapolation scheme is used in a thermal lattice Boltzmann model(TLBM)where double distribution functions are used to simulate the velocity and the temperature fields in order to capture the velocity slip and the temperature jump of the wall boundary.The simulated velocity and temperature profiles are in good agreement with the analytic results,which shows the suitability of the present model and the new boundary treatment for describing thermal microflows with viscous heat dissipation.展开更多
The velocity slip and temperature jump for a two-dimensional rough plate under hypersonic conditions were analyzed using the Direct Simulation Monte Carlo(DSMC)method.Surface roughness was explicitly modeled by introd...The velocity slip and temperature jump for a two-dimensional rough plate under hypersonic conditions were analyzed using the Direct Simulation Monte Carlo(DSMC)method.Surface roughness was explicitly modeled by introducing various structures on the flat plate.The influences of relative roughness height,which involves the roughness height,roughness spacing,incoming velocity,and the degree of rarefaction,were analyzed and discussed.It is found that with the increase of the relative roughness height,the jump temperature increases,while the slip velocity decreases gradually.The effects of surface roughness on the slip coefficients can be attributed to the change of accommodation coefficients.A new slip model for rough surfaces was established in this paper,which accounts for the coupling effects of gas rarefaction and surface roughness,without the effort to model the surface roughness explicitly.The nitrogen flows in the microchannel,and flows over a blunt cone and an axisymmetric bi-conic body,were simulated under the modified and conventional slip boundary conditions,respectively.The numerical solutions were validated with experimental data.It can be safely concluded that compared with the traditional first-order slip boundary conditions,the modified slip model improves the accuracy of macroscopic properties,especially the heat transfer coefficient.展开更多
In this research paper,exact solution for fully developed magnetohydrodynamic(MHD)natural convection flow of viscous,incompressible,electrically conducting fluid in parallel walls in the presence of velocity slip and ...In this research paper,exact solution for fully developed magnetohydrodynamic(MHD)natural convection flow of viscous,incompressible,electrically conducting fluid in parallel walls in the presence of velocity slip and temperature jump at the micro-channel walls electrically conducting fluid in the presence of transverse magnetic field is taken into equations are coupled.The exact solutions in dimensionless form have been obtained under temperature field,induced current density and skin friction have been obtained.The effects of interaction,Hartmann number and the magnetic Prandtl number are demonstrated through number causes a pronounced reduction in volume flow rate.展开更多
The axisymmetric stagnation point flow over a stretching/shrinking surface with second-order slip and temperature jump is studied numerically.The governing partial differential equations are transformed into ordinary(...The axisymmetric stagnation point flow over a stretching/shrinking surface with second-order slip and temperature jump is studied numerically.The governing partial differential equations are transformed into ordinary(similarity)differential equations.These equations along with the corresponding boundary conditions are solved numerically using a boundary value problem solver bvp4c in Matlab software.It is observed that dual(first and second)solutions exist for the similarity equations.The effects of different parameters on the velocity and the temperature distributions as well as the skin friction coefficient and the Nusselt number are analyzed and discussed.展开更多
This study is devoted to investigate the effect of induced magnetic field on fully developed magnetohydrodynamic(MHD)natural convection flow of electrically conducting fluid in a vertical annular micro-channel formed ...This study is devoted to investigate the effect of induced magnetic field on fully developed magnetohydrodynamic(MHD)natural convection flow of electrically conducting fluid in a vertical annular micro-channel formed by two concentric cylinders in the presence of imposed radial magnetic field.The velocity slip and temperature jump at the annular micro-channel surfaces are taken into account.The influence of induced magnetic field arising due to the motion of an electrically conducting fluid is taken into consideration.The governing equations of the motion are a set of simultaneous ordinary differential equations and their exact solutions in dimensionless form have been obtained under relevant boundary conditions.The expressions for velocity field,the induced magnetic field,temperature field,induced current density and skin friction have been obtained.A parametric study of the physical parameters is conducted and a representative set of numerical results for the velocity field,the induced magnetic field,temperature,induced current density,volume flow rate and skin friction are illustrated graphically to show interesting features of the radius ratio,rarefaction,fluid wall interaction,Hartmann number and the magnetic Prandtl number.During the course of investigation,it is found that for fixed value of Hartmann number,the skin friction profiles in the presence of induced magnetic field are higher compared to the case when the induced magnetic field is neglected.展开更多
Theoretical investigation on the interaction between conducting and nonconducting walls on hydromagnetic natural convection flow of viscous incompressible and electrically conducting fluid through a vertical micro-cha...Theoretical investigation on the interaction between conducting and nonconducting walls on hydromagnetic natural convection flow of viscous incompressible and electrically conducting fluid through a vertical micro-channel taking into account the effects of induced magnetic field in presence of Hall current is presented.Governing coupled equations responsible for the flow are obtained when either the micro-channel walls are electrically conducting or are electrically non-conducting.Using the method of undetermined coefficients,exact solution are obtained and presented in dimensionless form subject to relevant boundary conditions.Expressions for fluid velocity,induced magnetic field,skin friction,volume flow rate and induced current density in both primary and secondary flow directions are also obtained.Effects of some governing parameters like Hall current parameter,rarefaction parameter and Hartmann number on the different flow situations are given using the aid of line graphs and Tables.The main conclusion of the present analysis is that,in the existence of rarefaction parameter,primary fluid velocity could be enhanced with the increase in Hall parameter when the micro-channel walls are either insulated or when the left micro-channel wall is electrically conducting.Results obtained in this work are relevant in many magnetically controlled devices and could also be used as a benchmark in checking the accuracies of result obtained in some empirical experiments.展开更多
基金Project supported by the National Natural Science Foundation of China(No.11302024)the Fundamental Research Funds for the Central Universities(No.FRF-TP-12-108A)the Foundation of the China Scholarship Council in 2014(No.154201406465041)
文摘Flow and heat transfer of a pseudo-plastic power-law fluid over a stretching permeable surface with the magnetic effect is investigated. In the boundary conditions,the nonlinear temperature jump and the velocity slip are considered. Semi-similarity equations are obtained and solved by bvp4c with MATLAB. The problem can be considered as an extension of the previous work done by Mahmoud(Mahmoud, M. A. A. Slip velocity effect on a non-Newtonian power-law fluid over a moving permeable surface with heat generation. Mathematical and Computer Modelling, 54, 1228–1237(2011)). Efforts are made to discuss the effects of the power-law number, slip velocity, and temperature jump on the dimensionless velocity and temperature distribution.
基金Project supported by the National Natural Science Foundation of China(Nos.51276014 and51476191)the Fundamental Research Funds for the Central Universities(No.FRF-BR-12-004)
文摘The effects of the second-order velocity slip and temperature jump boundary conditions on the magnetohydrodynamic (MHD) flow and heat transfer in the presence of nanoparticle fractions are investigated. In the modeling of the water-based nanofluids containing Cu and A1203, the effects of the Brownian motion, thermophoresis, and thermal radiation are considered. The governing boundary layer equations are transformed into a system of nonlinear differential equations, and the analytical approximations of the solutions axe derived by the homotopy analysis method (HAM). The reliability and efficiency of the HAM solutions are verified by the residual errors and the numerical results in the literature. Moreover, the effects of the physical factors on the flow and heat transfer are discussed graphically.
基金funded by Ministerio de Ciencia e Innovación (Spain) (PID2019-105653GB-I00)Generalitat Valenciana (Spain) (PROMETEO/2020/063)。
文摘The study of the hydrogen evolution reaction(HER)aimed to reach a deeper understanding of the parameters that control the rate of this reaction is of great importance given the technical relevance of hydrogen production as an energy vector in the so-called hydrogen economy.In previous works,laser-induced temperature jump(LITJ)experiments on Pt(111)modified with Ni(OH)_(2)in alkaline media have revealed the importance of the interfacial electric field in the rate of the HER.It was hypothesised that small amounts of Ni(OH)_(2)cause a decrease of the electric field because of a negative shift of the pzfc toward the onset of the hydrogen evolution.In this work,to test the validity of this hypothesis,the study has been extended to Pt(111)surfaces modified with Fe(OH)_(2).The modified surfaces have been studied voltammetrically,and the voltammetric charges have been analysed.The voltammograms show a peak in the hydrogen evolution region that suggest the transformation in the adlayer from Fe(II)to Fe(0).In agreement with the coulometric analysis,the voltammetric features in the OH adsorption region would be related with the oxidation to the+3 valence state.The results obtained with LITJ method reflect the existence of a strong interaction of the Fe oxophilic species with the water molecules,shifting the potential of maximum entropy away from the onset of the HER.Hence,the most catalytic surface is the one with the lowest Fe coverage.
基金This work was supported by the National Natural Science Foundation of China (No.20673107), the National Key Basic Research Special Foundation of China (No.2007CB815203), and the Knowledge Innovation Foundation of the Chinese Academy of Science (No.KJCX2-SW-H08).
文摘The fast phase-transitional process of ploy(N-isopropylacrylamide) (PNIPAM) in deuterated solution was studied by laser induced temperature jump technique combined with time-resolved mid-infrared absorbance difference spectroscopy on nanosecond level. The multi-peaks of amide I'band of PNIPAM among the energy range of 1565-1700 cm^-1 was experimentally resolved to three groups (i, ii, iii) for the first time, while the distinct threestage procedure in the phase transitional process of long-chain PNIPAM was observed firstly too. Furthermore, proper assignments were also made for the three group peaks in amide I'band and the three steps in the kinetics process of long-chain PNIPAM.
基金supported by the National Natural Science Foundation of China(No.21674107 and No.21274140)the Fundamental Research Funds for the Central Universities(No.WK2340000066)
文摘Two narrowly-distributed poly(N-isopropylacrylamide)(PNIPAM) samples were prepared via atom transfer radical polymerization (ATRP) with a novel dansyl functionalized initiator. The other end of the PNIPAM was functionalized by dabcyl group via click reaction. From the static fluorescence measurements, the fluorescence intensity of dansyl group and energy transfer efficiency between dansyl and dabcyl groups increased when the temperature increased from 36 °C to 45 °C, indicating that the microenvironment surrounding dansyl became hydrophobic and the distance between dansyl and dabcyl decreased. The kinetics of the conformational change of the dye-labeled PNIPAM was studied by a home-made laser-induced temperature jump device with fluorescent measurement. Our results revealed that the characteristic transition time was 3.8 and 5.8 ms for PNIPAM with degrees of polymerization of 85 and 142, respectively, indicating that the characteristic transition time was related to the chain length. Besides, characteristic transition time for the change of the energy transfer efficiency was 2.9 ms for PNIPAM with the degree of polymerization of 85, suggesting that the energy transfer efficiency change was faster than the fluorescence intensity change of dansyl group.
基金study was financially supported by the National Basic Research Program of China(2006CB705804)the National Natural Science Foundation of China(70271069).
文摘The velocity slip and temperature jump in micro-Couette flow are investigated with the lattice Boltzmann method(LBM).A new slip boundary condition with the non-equilibrium extrapolation scheme is used in a thermal lattice Boltzmann model(TLBM)where double distribution functions are used to simulate the velocity and the temperature fields in order to capture the velocity slip and the temperature jump of the wall boundary.The simulated velocity and temperature profiles are in good agreement with the analytic results,which shows the suitability of the present model and the new boundary treatment for describing thermal microflows with viscous heat dissipation.
基金supported by the National Natural Science Foundation of China(Nos.12002306,U20B2007).
文摘The velocity slip and temperature jump for a two-dimensional rough plate under hypersonic conditions were analyzed using the Direct Simulation Monte Carlo(DSMC)method.Surface roughness was explicitly modeled by introducing various structures on the flat plate.The influences of relative roughness height,which involves the roughness height,roughness spacing,incoming velocity,and the degree of rarefaction,were analyzed and discussed.It is found that with the increase of the relative roughness height,the jump temperature increases,while the slip velocity decreases gradually.The effects of surface roughness on the slip coefficients can be attributed to the change of accommodation coefficients.A new slip model for rough surfaces was established in this paper,which accounts for the coupling effects of gas rarefaction and surface roughness,without the effort to model the surface roughness explicitly.The nitrogen flows in the microchannel,and flows over a blunt cone and an axisymmetric bi-conic body,were simulated under the modified and conventional slip boundary conditions,respectively.The numerical solutions were validated with experimental data.It can be safely concluded that compared with the traditional first-order slip boundary conditions,the modified slip model improves the accuracy of macroscopic properties,especially the heat transfer coefficient.
文摘In this research paper,exact solution for fully developed magnetohydrodynamic(MHD)natural convection flow of viscous,incompressible,electrically conducting fluid in parallel walls in the presence of velocity slip and temperature jump at the micro-channel walls electrically conducting fluid in the presence of transverse magnetic field is taken into equations are coupled.The exact solutions in dimensionless form have been obtained under temperature field,induced current density and skin friction have been obtained.The effects of interaction,Hartmann number and the magnetic Prandtl number are demonstrated through number causes a pronounced reduction in volume flow rate.
基金The authors wish to thank the reviewers for their very good comments and suggestions.The financial supports received from Ministry of Higher Education Malaysia,Malaysia(Project Code:FRGS/1/2015/SG04/UKM/01/1)Universiti Kebangsaan Malaysia,Malaysia(Project Code:DIP-2015-010)are gratefully acknowledged.
文摘The axisymmetric stagnation point flow over a stretching/shrinking surface with second-order slip and temperature jump is studied numerically.The governing partial differential equations are transformed into ordinary(similarity)differential equations.These equations along with the corresponding boundary conditions are solved numerically using a boundary value problem solver bvp4c in Matlab software.It is observed that dual(first and second)solutions exist for the similarity equations.The effects of different parameters on the velocity and the temperature distributions as well as the skin friction coefficient and the Nusselt number are analyzed and discussed.
文摘This study is devoted to investigate the effect of induced magnetic field on fully developed magnetohydrodynamic(MHD)natural convection flow of electrically conducting fluid in a vertical annular micro-channel formed by two concentric cylinders in the presence of imposed radial magnetic field.The velocity slip and temperature jump at the annular micro-channel surfaces are taken into account.The influence of induced magnetic field arising due to the motion of an electrically conducting fluid is taken into consideration.The governing equations of the motion are a set of simultaneous ordinary differential equations and their exact solutions in dimensionless form have been obtained under relevant boundary conditions.The expressions for velocity field,the induced magnetic field,temperature field,induced current density and skin friction have been obtained.A parametric study of the physical parameters is conducted and a representative set of numerical results for the velocity field,the induced magnetic field,temperature,induced current density,volume flow rate and skin friction are illustrated graphically to show interesting features of the radius ratio,rarefaction,fluid wall interaction,Hartmann number and the magnetic Prandtl number.During the course of investigation,it is found that for fixed value of Hartmann number,the skin friction profiles in the presence of induced magnetic field are higher compared to the case when the induced magnetic field is neglected.
文摘Theoretical investigation on the interaction between conducting and nonconducting walls on hydromagnetic natural convection flow of viscous incompressible and electrically conducting fluid through a vertical micro-channel taking into account the effects of induced magnetic field in presence of Hall current is presented.Governing coupled equations responsible for the flow are obtained when either the micro-channel walls are electrically conducting or are electrically non-conducting.Using the method of undetermined coefficients,exact solution are obtained and presented in dimensionless form subject to relevant boundary conditions.Expressions for fluid velocity,induced magnetic field,skin friction,volume flow rate and induced current density in both primary and secondary flow directions are also obtained.Effects of some governing parameters like Hall current parameter,rarefaction parameter and Hartmann number on the different flow situations are given using the aid of line graphs and Tables.The main conclusion of the present analysis is that,in the existence of rarefaction parameter,primary fluid velocity could be enhanced with the increase in Hall parameter when the micro-channel walls are either insulated or when the left micro-channel wall is electrically conducting.Results obtained in this work are relevant in many magnetically controlled devices and could also be used as a benchmark in checking the accuracies of result obtained in some empirical experiments.