The significant decrease in battery performance at low temperatures is one of the critical challenges that electric vehicles(EVs)face,thereby affecting the penetration rate in cold regions.Alternating current(AC)heati...The significant decrease in battery performance at low temperatures is one of the critical challenges that electric vehicles(EVs)face,thereby affecting the penetration rate in cold regions.Alternating current(AC)heating has attracted widespread attention due to its low energy consumption and uniform heating advantages.This paper introduces the recent advances in AC heating from the perspective of practical EV applications.First,the performance degradation of EVs in low-temperature environments is introduced briefly.The concept of AC heating and its research methods are provided.Then,the effects of various AC heating methods on battery heating performance are reviewed.Based on existing studies,the main factors that affect AC heating performance are analyzed.Moreover,various heating circuits based on EVs are categorized,and their cost,size,complexity,efficiency,reliability,and heating rate are elaborated and compared.The evolution of AC heaters is presented,and the heaters used in brand vehicles are sorted out.Finally,the perspectives and challenges of AC heating are discussed.This paper can guide the selection of heater implementation methods and the optimization of heating effects for future EV applications.展开更多
Using the perturbation method, we theoretically study the spin current and its heat effect in a multichannel quantum wire with Rashba spin-orbit coupling. The heat generated by the spin current is calculated. With the...Using the perturbation method, we theoretically study the spin current and its heat effect in a multichannel quantum wire with Rashba spin-orbit coupling. The heat generated by the spin current is calculated. With the increase of the width of the quantum wire, the spin current and the heat generated both exhibit period oscillations with equal amplitudes. When the quantum-channel number is doubled, the oscillation periods of the spin current and of the heat generated both decrease by a factor of 2. For the spin current js,xy, the amplitude increases with the decrease of the quantum channel; while the amplitude of the spin current js,yx remains the same. Therefore we conclude that the effect of the quantum-channel number on the spin current js,xy is greater than that on the spin current js,yx. The strength of the Rashba spin-orbit coupling is tunable by the gate voltage, and the gate voltage can be varied experimentally, which implies a new method of detecting the. spin current. In addition, we can control the amplitude and the oscillation period of the spin current by controlling the number of the quantum channels. All these characteristics of the spin current will be very important for detecting and controlling the spin current, and especially for designing new spintronic devices in the future.展开更多
We study the steady-state entanglement and heat current of two coupled qubits, in which two qubits are connected with two independent heat baths(IHBs) or two common heat baths(CHBs). We construct the master equation i...We study the steady-state entanglement and heat current of two coupled qubits, in which two qubits are connected with two independent heat baths(IHBs) or two common heat baths(CHBs). We construct the master equation in the eigenstate representation of two coupled qubits to describe the dynamics of the total system and derive the solutions in the steadystate with stronger coupling regime between two qubits than qubit–baths. We do not make the rotating wave approximation(RWA) for the qubit–qubit interaction, and so we are able to investigate the behaviors of the system in both the strong coupling regime and the weak coupling regime, respectively. In an equilibrium bath, we find that the entanglement decreases with the bath temperature and energy detuning increasing under the strong coupling regime. In the weak coupling regime,the entanglement increases with coupling strength increasing and decreases with the bath temperature and energy detuning increasing. In a nonequilibrium bath, the entanglement without RWA is useful for entanglement at lower temperatures.We also study the heat currents of the two coupled qubits and their variations with the energy detuning, coupling strength and low temperature. In the strong(weak) coupling regime, the heat current increases(decreases) with coupling strength increasing when the temperature of one bath is lower(higher) than the other, and the energy detuning leads to a positive(negative) effect when the temperature is low(high). In the weak coupling regime, the variation trend of heat current is opposite to that of coupling strength for the IHB case and the CHB case.展开更多
A mathematical model is presented to describe transient behavior of heat transfer and fluid flow in stationary pulsed current tungsten inert gas (PC-TIG) weld pool, which considers three kinds of driving, forces for w...A mathematical model is presented to describe transient behavior of heat transfer and fluid flow in stationary pulsed current tungsten inert gas (PC-TIG) weld pool, which considers three kinds of driving, forces for weld pool convection, i,e. buoyancyforce, electromagnetic force and surface tension force. furthermore. the effect of vaporization heat flux at the free surface of weld pool and the temperature coefficient of surface tenston which is a function of temperatuer and composition are considered in the model In order to accelerate the convergence of iteration the AST(additive source term)method which concerns with the thermal energv boundary conditions is extended successfully to deal with the momentum boundary conditions by which the transient momentum equation and energy equation are mutually coupled. At the same time. ADI (Alternating direction implicit) method and DBC (double blocks correction) technque are employed to solve the finite difference equations. The results of numerical simulation demonstrate the transient behavior of PC-TIG weld pool, as well as the periodic variation of fluid flow and heat transfer with the periodic variation of welding current in stationary PC-TIG weld pool. The theoretical predictions based on this model are, shown to be in good accordance with the experimental measurements.展开更多
Heat generated by electric current in a quantum dot device contacting a phonon bath is studied using the non- equilibrium Green function technique. Spin-polarized current is generated owing to the Zeeman splitting of ...Heat generated by electric current in a quantum dot device contacting a phonon bath is studied using the non- equilibrium Green function technique. Spin-polarized current is generated owing to the Zeeman splitting of the dot level. The current's strength and the spin polarization are further manipulated by changing the frequency of an applied photon field and the ferromagnetism on the leads. We find that the associated heat by this spin- polarized current emerges even if the bias voltage is smaller than the phonon energy quanta and obvious negative differential of the heat generation develops when the photon frequency exceeds that of the phonon. It is also found that both the strength and the resonant peaks' position of the heat generation can be tuned by changing the value and the arrangement configurations of the magnetic moments of the two leads, and then provides an effective method to generate large spin-polarized current with weak heat. Such a result may be useful in designing low energy consumption spintronic devices.展开更多
Four sources of surface heat flux (SHF) and the satellite remote sensing sea surface temperature (SST) data are combined to investigate the heat budget closure of the Huanghai Sea (HS) in winter.It is found that...Four sources of surface heat flux (SHF) and the satellite remote sensing sea surface temperature (SST) data are combined to investigate the heat budget closure of the Huanghai Sea (HS) in winter.It is found that heat loss occurs all over the HS during winter and the area averaged heat content change decreases with a rate of-106 W/m 2.Comparing with the area averaged SHF of-150 W/m 2 from the four SHF data sets,it can be concluded that the SHF plays a dominant role in the HS heat budget during winter.In contrast,the heat advection transported by the Huanghai Warm Current (Yellow Sea Warm Current,HWC) accounted for up to 29% of the HS heat content change.Close correlation,especially in February,between the storm events and the SST increase demonstrates that the HWC behaves strongly as a wind-driven compensation current.展开更多
The aim of the paper is to investigate the effect of heat and mass transfer on the unsteady magnetohydrodynamic free convective flow with Hall current, heat source, and viscous dissipation. The problem is governed by ...The aim of the paper is to investigate the effect of heat and mass transfer on the unsteady magnetohydrodynamic free convective flow with Hall current, heat source, and viscous dissipation. The problem is governed by the system of coupled non-linear partial differential equations whose exact solution is difficult to obtain. Therefore, the problem is solved by using the Galerkin finite element method. The effects of the various parameters like Hall current, Eckert number, heat source parameter, Prandtl number, and Schmidt number on the velocity components, the temperature, and the concentration are also examined through graphs.展开更多
Pulse current heating (PCH) was used to join Ti-6Al-4V alloy at two cases of with die and without die. Hot-pressing (HP) method was used to provide a comparison between the two methods. Microstructures near the contac...Pulse current heating (PCH) was used to join Ti-6Al-4V alloy at two cases of with die and without die. Hot-pressing (HP) method was used to provide a comparison between the two methods. Microstructures near the contacting surfaces were observed in optical microscope. Temperature distribution was analyzed. After joining, the tensile properties of the samples were evaluated. Experimental results show that grains and phases grow transversely on contacting surfaces, which makes two parts into a whole with a certain of tensile strength. PCH joining is a different temperature joining method. The highest temperature is located at the interface. The comparison of tensile strengths of samples joined by the two methods indicates that joining temperature and holding time needed by PCH are lower and less than those needed for HP.展开更多
The traditional generalized Ohm’s law in MHD (Magnetohydrodynamics) does not explicitly present the relation of electric currents and electric fields in fully ionized plasma, and leads to some unexpected concepts, su...The traditional generalized Ohm’s law in MHD (Magnetohydrodynamics) does not explicitly present the relation of electric currents and electric fields in fully ionized plasma, and leads to some unexpected concepts, such as ``the magnetic frozen-in plasma'', magnetic reconnection etc. In the single fluid model, the action between electric current and magnetic field is not considered. In the two-fluid model, the derivation is based on the two dynamic equations of ions and electrons. The electric current in traditional generalized Ohm's law depends on the velocities of the plasma, which should be decided by the two dynamic equations. However, the plasma velocity, eventually not free, is inappropriately considered as free parameter in the traditional generalized Ohm's law. In the present paper, we solve the balance equation that can give exact solution of the velocities of electrons and ions, and then derive the electric current in fully ionized plasma. In the case ignoring boundary condition, there is no electric current in the plane perpendicular to the magnetic field when external forces are ignored. The electric field in the plane perpendicular to magnetic field do not contribute to the electric currents, so do the induced electric field from the motion of the plasma across magnetic field. The lack of induced electric current will keep magnetic field in space unaffected. The velocity of the bulk velocity of the plasma perpendicular to magnetic field is not free, it is decided by electromagnetic field and the external forces. We conclude that the bulk velocity of the fully ionized plasma is not coupled with the magnetic field. The motion of the plasma do not change the magnetic field in space, but the plasma will be confined by magnetic field. Due to the confinement of magnetic field, the plasma kinetic energy will be transformed into plasma thermal energy by the Lamor motion and collisions between the same species of particles inside plasma. Because the electric field perpendicular to magnetic field do not contribute electric current, the variation of magnetic field will transfer energy directly into the plasma thermal energy by induced electric field. The heating of plasma could be from the kinetic energy and the variation of magnetic field.展开更多
The present numerically study investigates the influence of the Hall current and constant heat flux on the Magneto hydrodynamic (MHD) natural convection boundary layer viscous incompressible fluid flow in the manifest...The present numerically study investigates the influence of the Hall current and constant heat flux on the Magneto hydrodynamic (MHD) natural convection boundary layer viscous incompressible fluid flow in the manifestation of transverse magnetic field near an inclined vertical permeable flat plate. It is assumed that the induced magnetic field is negligible compared with the imposed magnetic field. The governing boundary layer equations have been transferred into non-similar model by implementing similarity approaches. The physical dimensionless parameter has been set up into the model as Prandtl number, Eckert number, Magnetic parameter, Schmidt number, local Grashof number and local modified Grashof number. The numerical method of Nactsheim-Swigert shooting iteration technique together with Runge-Kutta six order iteration scheme has been used to solve the system of governing non-similar equations. The physical effects of the various parameters on dimensionless primary velocity profile, secondary velocity profile, and temperature and concentration profile are discussed graphically. Moreover, the local skin friction coefficient, the local Nusselt number and Sherwood number are shown in tabular form for various values of the parameters.展开更多
In this paper, an investigation of the effects of some physical parameters and Hall current on magneto hydrodynamics (MHD) fluid flow with heat flux over a porous medium was carefully examined, taking into considerati...In this paper, an investigation of the effects of some physical parameters and Hall current on magneto hydrodynamics (MHD) fluid flow with heat flux over a porous medium was carefully examined, taking into consideration Hall effects where the temperature and concentration are assumed to be oscillating with time. Furthermore, perturbation method is used in solving the governing equations. The profiles of velocity, temperature and concentration are presented graphically, going into the problem the primary and secondary velocity are presented and compute for some physical parameters such as mass Grashof number (<em>Gc</em>), Schmidt number <em>Sc</em>, Prandtl number (<em>Pr</em>) viscoelastic parameter (<em>K</em><sub>1</sub>) and hall current parameter (<em>m</em>). Results indicated that primary velocity increases with increase in values of <em>Gc</em> on one hand and on the other hand it decreases with increase in the values of <em>Pr</em>, <em>K</em><sub>1</sub> and <em>m</em>. Secondary velocity demonstrated opposite trend.展开更多
Unsteady MHD natural convective heat and mass transfer flow through a semi-infinite vertical porous plate in a rotating system have been investigated with the combined Soret and Dufour effects in the presence of Hall ...Unsteady MHD natural convective heat and mass transfer flow through a semi-infinite vertical porous plate in a rotating system have been investigated with the combined Soret and Dufour effects in the presence of Hall current and constant heat flux. It is considered that the porous plate is subjected to constant heat flux. The obtained non-dimensional, non-similar coupled non-linear and partial differential equations have been solved by explicit finite difference technique. Numerical solutions for velocities, temperature and concentration distributions are obtained for various parameters by the above mentioned technique. The local and average shear stresses, Nusselt number as well as Sherwood number are also investigated. The stability conditions and convergence criteria of the explicit finite difference scheme are established for finding the restriction of the values of various parameters to get more accuracy. The obtained results are illustrated with the help of graphs to observe the effects of various legitimate parameters.展开更多
Effects of Hall current on heat transfer and magnetohydrodynamic (MHD) boundary layer flow induced by a continuous surface in a parallel free stream of a second-order viscoelastic fluid are studied for uniform suction...Effects of Hall current on heat transfer and magnetohydrodynamic (MHD) boundary layer flow induced by a continuous surface in a parallel free stream of a second-order viscoelastic fluid are studied for uniform suction/injection by taking viscous dissipation into account. Complex nonsimilar solutions to the stream function and temperature are developed by means of an elegant technique, known as homotopy analysis method (HAM). Convergence of the solutions is ensured with the help of -curves. Graphical and tabular results for the effects of Hall current reveal that it has a significant influence on: complex velocity, complex temperature, magnitude of the shear stress at the surface, magnitude of the rate of heat transfer at the surface and on boundary layer thickness.展开更多
The HTS current leads of superconducting magnets for large scale fusion devices and high energy particle colliders can reduce the power consumption for cooling by 2/3 compared with conventional leads. The resistive se...The HTS current leads of superconducting magnets for large scale fusion devices and high energy particle colliders can reduce the power consumption for cooling by 2/3 compared with conventional leads. The resistive sections of high-rated current leads are usually made of a heat exchanger cooled by gas flow. The supply of the cooling mass flow incurs more than 90% of the cooling cost for the HTS leads. The mass flow rate requirement depends not only on the length and material of the resistive heat exchanger, but also on the heat transfer coefficient and HEX surface, the joint resistance at the cold end of a sheet-stack HEX with a larger specific presented in the paper. The test results of efficiency can be achieved. and its cooling approach. The design and operation surface and a much smaller hydraulic diameter are an HTS lead optimized for 8 kA show that a 98.4%展开更多
The effect of the Hall current on the magnetohydrodynamic (MHD) natural convection flow from a vertical permeable flat plate with a uniform heat flux is analyzed in the presence of a transverse magnetic field.It is ...The effect of the Hall current on the magnetohydrodynamic (MHD) natural convection flow from a vertical permeable flat plate with a uniform heat flux is analyzed in the presence of a transverse magnetic field.It is assumed that the induced magnetic field is negligible compared with the imposed magnetic field.The boundary layer equations are reduced to a suitable form by employing the free variable formulation (FVF) and the stream function formulation (SFF).The parabolic equations obtained from FVF are numerically integrated with the help of a straightforward finite difference method.Moreover,the nonsimilar system of equations obtained from SFF is solved by using a local nonsimilarity method,for the whole range of the local transpiration parameter ζ.Consideration is also given to the regions where the local transpiration parameter ζ is small or large enough.However,in these particular regions,solutions are acquired with the aid of a regular perturbation method.The effects of the magnetic field M and the Hall parameter m on the local skin friction coefficient and the local Nusselt number coefficient are graphically shown for smaller values of the Prandtl number P r (= 0.005,0.01,0.05).Furthermore,the velocity and temperature profiles are also drawn from various values of the local transpiration parameter ζ.展开更多
Combined cooling and power(CCP)system driven by low-grade heat is promising for improving energy efficiency.This work proposes a CCP system that integrates a regenerative organic Rankine cycle(RORC)and an absorption c...Combined cooling and power(CCP)system driven by low-grade heat is promising for improving energy efficiency.This work proposes a CCP system that integrates a regenerative organic Rankine cycle(RORC)and an absorption chiller on both driving and cooling fluid sides.The system is modeled by using the heat current method to fully consider nonlinear heat transfer and heat-work conversion constraints and resolve its behavior accurately.The off-design system simulation is performed next,showing that the fluid inlet temperatures and flow rates of cooling water as well as RORC working fluid strongly affect system performance.The off-design operation even becomes infeasible when parameters deviate from nominal values largely due to limited heat transfer capability of components,highlighting the importance of considering heat transfer constraints via heat current method.Design optimization aiming to minimize the total thermal conductance is also conducted.RORC efficiency increases by 7.9%and decreases by 12.4%after optimization,with the hot fluid inlet temperature increase from 373.15 to 403.15 K and mass flow rate ranges from 10 to 30 kg/s,emphasizing the necessity of balancing system cost and performance.展开更多
基金supported in part by the National Key Research and Development Program of China under Grant 2021YFB1600200in part by the Shaanxi Province Postdoctoral Research Project under grant 2023BSHEDZZ223+3 种基金in part by the Fundamental Research Funds for the Central Universities,CHD,under grant 300102383101in part by the Shaanxi Province Qinchuangyuan High-Level Innovation and Entrepreneurship Talent Project under grant QCYRCXM-2023-112the Key Research and Development Program of Shaanxi Province under grant 2024GX-YBXM-442in part by the National Natural Science Foundation of China under grand 62373224.
文摘The significant decrease in battery performance at low temperatures is one of the critical challenges that electric vehicles(EVs)face,thereby affecting the penetration rate in cold regions.Alternating current(AC)heating has attracted widespread attention due to its low energy consumption and uniform heating advantages.This paper introduces the recent advances in AC heating from the perspective of practical EV applications.First,the performance degradation of EVs in low-temperature environments is introduced briefly.The concept of AC heating and its research methods are provided.Then,the effects of various AC heating methods on battery heating performance are reviewed.Based on existing studies,the main factors that affect AC heating performance are analyzed.Moreover,various heating circuits based on EVs are categorized,and their cost,size,complexity,efficiency,reliability,and heating rate are elaborated and compared.The evolution of AC heaters is presented,and the heaters used in brand vehicles are sorted out.Finally,the perspectives and challenges of AC heating are discussed.This paper can guide the selection of heater implementation methods and the optimization of heating effects for future EV applications.
文摘Using the perturbation method, we theoretically study the spin current and its heat effect in a multichannel quantum wire with Rashba spin-orbit coupling. The heat generated by the spin current is calculated. With the increase of the width of the quantum wire, the spin current and the heat generated both exhibit period oscillations with equal amplitudes. When the quantum-channel number is doubled, the oscillation periods of the spin current and of the heat generated both decrease by a factor of 2. For the spin current js,xy, the amplitude increases with the decrease of the quantum channel; while the amplitude of the spin current js,yx remains the same. Therefore we conclude that the effect of the quantum-channel number on the spin current js,xy is greater than that on the spin current js,yx. The strength of the Rashba spin-orbit coupling is tunable by the gate voltage, and the gate voltage can be varied experimentally, which implies a new method of detecting the. spin current. In addition, we can control the amplitude and the oscillation period of the spin current by controlling the number of the quantum channels. All these characteristics of the spin current will be very important for detecting and controlling the spin current, and especially for designing new spintronic devices in the future.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61675115 and 11704221)
文摘We study the steady-state entanglement and heat current of two coupled qubits, in which two qubits are connected with two independent heat baths(IHBs) or two common heat baths(CHBs). We construct the master equation in the eigenstate representation of two coupled qubits to describe the dynamics of the total system and derive the solutions in the steadystate with stronger coupling regime between two qubits than qubit–baths. We do not make the rotating wave approximation(RWA) for the qubit–qubit interaction, and so we are able to investigate the behaviors of the system in both the strong coupling regime and the weak coupling regime, respectively. In an equilibrium bath, we find that the entanglement decreases with the bath temperature and energy detuning increasing under the strong coupling regime. In the weak coupling regime,the entanglement increases with coupling strength increasing and decreases with the bath temperature and energy detuning increasing. In a nonequilibrium bath, the entanglement without RWA is useful for entanglement at lower temperatures.We also study the heat currents of the two coupled qubits and their variations with the energy detuning, coupling strength and low temperature. In the strong(weak) coupling regime, the heat current increases(decreases) with coupling strength increasing when the temperature of one bath is lower(higher) than the other, and the energy detuning leads to a positive(negative) effect when the temperature is low(high). In the weak coupling regime, the variation trend of heat current is opposite to that of coupling strength for the IHB case and the CHB case.
文摘A mathematical model is presented to describe transient behavior of heat transfer and fluid flow in stationary pulsed current tungsten inert gas (PC-TIG) weld pool, which considers three kinds of driving, forces for weld pool convection, i,e. buoyancyforce, electromagnetic force and surface tension force. furthermore. the effect of vaporization heat flux at the free surface of weld pool and the temperature coefficient of surface tenston which is a function of temperatuer and composition are considered in the model In order to accelerate the convergence of iteration the AST(additive source term)method which concerns with the thermal energv boundary conditions is extended successfully to deal with the momentum boundary conditions by which the transient momentum equation and energy equation are mutually coupled. At the same time. ADI (Alternating direction implicit) method and DBC (double blocks correction) technque are employed to solve the finite difference equations. The results of numerical simulation demonstrate the transient behavior of PC-TIG weld pool, as well as the periodic variation of fluid flow and heat transfer with the periodic variation of welding current in stationary PC-TIG weld pool. The theoretical predictions based on this model are, shown to be in good accordance with the experimental measurements.
基金Supported by the National Natural Science Foundation of China under Grant No 61274101
文摘Heat generated by electric current in a quantum dot device contacting a phonon bath is studied using the non- equilibrium Green function technique. Spin-polarized current is generated owing to the Zeeman splitting of the dot level. The current's strength and the spin polarization are further manipulated by changing the frequency of an applied photon field and the ferromagnetism on the leads. We find that the associated heat by this spin- polarized current emerges even if the bias voltage is smaller than the phonon energy quanta and obvious negative differential of the heat generation develops when the photon frequency exceeds that of the phonon. It is also found that both the strength and the resonant peaks' position of the heat generation can be tuned by changing the value and the arrangement configurations of the magnetic moments of the two leads, and then provides an effective method to generate large spin-polarized current with weak heat. Such a result may be useful in designing low energy consumption spintronic devices.
基金The National Natural Science Foundation Project "Sedimentary dynamic mechanism of the Huanghai Warm Current" of China under contract No.40906025the National Natural Science Foundation of China " The process and mechanism of the increasing of surface temperature in the past 30 years in the adjacent seas of China" under contract No.40930844+4 种基金the National Natural Science Foundation of China under contract No.41006002the State Basic Research Program of China under contract No.2010CB428704the Formation and development of the muddy deposition in the central southern Huanghai Sea,and its relation with climate and environmental change of Ocean University of China under contract No.41030856the Scientific Research Fund of the Second Institute of Oceanography,State Oceanic Administration of China under contract No.JT1007the Public Science and Technology Research Funds Projects of Ocean under contract Nos 200905001 and 201005019
文摘Four sources of surface heat flux (SHF) and the satellite remote sensing sea surface temperature (SST) data are combined to investigate the heat budget closure of the Huanghai Sea (HS) in winter.It is found that heat loss occurs all over the HS during winter and the area averaged heat content change decreases with a rate of-106 W/m 2.Comparing with the area averaged SHF of-150 W/m 2 from the four SHF data sets,it can be concluded that the SHF plays a dominant role in the HS heat budget during winter.In contrast,the heat advection transported by the Huanghai Warm Current (Yellow Sea Warm Current,HWC) accounted for up to 29% of the HS heat content change.Close correlation,especially in February,between the storm events and the SST increase demonstrates that the HWC behaves strongly as a wind-driven compensation current.
基金supported by the University Grants Commission,New Delhi,India
文摘The aim of the paper is to investigate the effect of heat and mass transfer on the unsteady magnetohydrodynamic free convective flow with Hall current, heat source, and viscous dissipation. The problem is governed by the system of coupled non-linear partial differential equations whose exact solution is difficult to obtain. Therefore, the problem is solved by using the Galerkin finite element method. The effects of the various parameters like Hall current, Eckert number, heat source parameter, Prandtl number, and Schmidt number on the velocity components, the temperature, and the concentration are also examined through graphs.
基金Project(50272047) supported by the National Natural Science Foundation of China
文摘Pulse current heating (PCH) was used to join Ti-6Al-4V alloy at two cases of with die and without die. Hot-pressing (HP) method was used to provide a comparison between the two methods. Microstructures near the contacting surfaces were observed in optical microscope. Temperature distribution was analyzed. After joining, the tensile properties of the samples were evaluated. Experimental results show that grains and phases grow transversely on contacting surfaces, which makes two parts into a whole with a certain of tensile strength. PCH joining is a different temperature joining method. The highest temperature is located at the interface. The comparison of tensile strengths of samples joined by the two methods indicates that joining temperature and holding time needed by PCH are lower and less than those needed for HP.
文摘The traditional generalized Ohm’s law in MHD (Magnetohydrodynamics) does not explicitly present the relation of electric currents and electric fields in fully ionized plasma, and leads to some unexpected concepts, such as ``the magnetic frozen-in plasma'', magnetic reconnection etc. In the single fluid model, the action between electric current and magnetic field is not considered. In the two-fluid model, the derivation is based on the two dynamic equations of ions and electrons. The electric current in traditional generalized Ohm's law depends on the velocities of the plasma, which should be decided by the two dynamic equations. However, the plasma velocity, eventually not free, is inappropriately considered as free parameter in the traditional generalized Ohm's law. In the present paper, we solve the balance equation that can give exact solution of the velocities of electrons and ions, and then derive the electric current in fully ionized plasma. In the case ignoring boundary condition, there is no electric current in the plane perpendicular to the magnetic field when external forces are ignored. The electric field in the plane perpendicular to magnetic field do not contribute to the electric currents, so do the induced electric field from the motion of the plasma across magnetic field. The lack of induced electric current will keep magnetic field in space unaffected. The velocity of the bulk velocity of the plasma perpendicular to magnetic field is not free, it is decided by electromagnetic field and the external forces. We conclude that the bulk velocity of the fully ionized plasma is not coupled with the magnetic field. The motion of the plasma do not change the magnetic field in space, but the plasma will be confined by magnetic field. Due to the confinement of magnetic field, the plasma kinetic energy will be transformed into plasma thermal energy by the Lamor motion and collisions between the same species of particles inside plasma. Because the electric field perpendicular to magnetic field do not contribute electric current, the variation of magnetic field will transfer energy directly into the plasma thermal energy by induced electric field. The heating of plasma could be from the kinetic energy and the variation of magnetic field.
文摘The present numerically study investigates the influence of the Hall current and constant heat flux on the Magneto hydrodynamic (MHD) natural convection boundary layer viscous incompressible fluid flow in the manifestation of transverse magnetic field near an inclined vertical permeable flat plate. It is assumed that the induced magnetic field is negligible compared with the imposed magnetic field. The governing boundary layer equations have been transferred into non-similar model by implementing similarity approaches. The physical dimensionless parameter has been set up into the model as Prandtl number, Eckert number, Magnetic parameter, Schmidt number, local Grashof number and local modified Grashof number. The numerical method of Nactsheim-Swigert shooting iteration technique together with Runge-Kutta six order iteration scheme has been used to solve the system of governing non-similar equations. The physical effects of the various parameters on dimensionless primary velocity profile, secondary velocity profile, and temperature and concentration profile are discussed graphically. Moreover, the local skin friction coefficient, the local Nusselt number and Sherwood number are shown in tabular form for various values of the parameters.
文摘In this paper, an investigation of the effects of some physical parameters and Hall current on magneto hydrodynamics (MHD) fluid flow with heat flux over a porous medium was carefully examined, taking into consideration Hall effects where the temperature and concentration are assumed to be oscillating with time. Furthermore, perturbation method is used in solving the governing equations. The profiles of velocity, temperature and concentration are presented graphically, going into the problem the primary and secondary velocity are presented and compute for some physical parameters such as mass Grashof number (<em>Gc</em>), Schmidt number <em>Sc</em>, Prandtl number (<em>Pr</em>) viscoelastic parameter (<em>K</em><sub>1</sub>) and hall current parameter (<em>m</em>). Results indicated that primary velocity increases with increase in values of <em>Gc</em> on one hand and on the other hand it decreases with increase in the values of <em>Pr</em>, <em>K</em><sub>1</sub> and <em>m</em>. Secondary velocity demonstrated opposite trend.
文摘Unsteady MHD natural convective heat and mass transfer flow through a semi-infinite vertical porous plate in a rotating system have been investigated with the combined Soret and Dufour effects in the presence of Hall current and constant heat flux. It is considered that the porous plate is subjected to constant heat flux. The obtained non-dimensional, non-similar coupled non-linear and partial differential equations have been solved by explicit finite difference technique. Numerical solutions for velocities, temperature and concentration distributions are obtained for various parameters by the above mentioned technique. The local and average shear stresses, Nusselt number as well as Sherwood number are also investigated. The stability conditions and convergence criteria of the explicit finite difference scheme are established for finding the restriction of the values of various parameters to get more accuracy. The obtained results are illustrated with the help of graphs to observe the effects of various legitimate parameters.
文摘Effects of Hall current on heat transfer and magnetohydrodynamic (MHD) boundary layer flow induced by a continuous surface in a parallel free stream of a second-order viscoelastic fluid are studied for uniform suction/injection by taking viscous dissipation into account. Complex nonsimilar solutions to the stream function and temperature are developed by means of an elegant technique, known as homotopy analysis method (HAM). Convergence of the solutions is ensured with the help of -curves. Graphical and tabular results for the effects of Hall current reveal that it has a significant influence on: complex velocity, complex temperature, magnitude of the shear stress at the surface, magnitude of the rate of heat transfer at the surface and on boundary layer thickness.
文摘The HTS current leads of superconducting magnets for large scale fusion devices and high energy particle colliders can reduce the power consumption for cooling by 2/3 compared with conventional leads. The resistive sections of high-rated current leads are usually made of a heat exchanger cooled by gas flow. The supply of the cooling mass flow incurs more than 90% of the cooling cost for the HTS leads. The mass flow rate requirement depends not only on the length and material of the resistive heat exchanger, but also on the heat transfer coefficient and HEX surface, the joint resistance at the cold end of a sheet-stack HEX with a larger specific presented in the paper. The test results of efficiency can be achieved. and its cooling approach. The design and operation surface and a much smaller hydraulic diameter are an HTS lead optimized for 8 kA show that a 98.4%
文摘The effect of the Hall current on the magnetohydrodynamic (MHD) natural convection flow from a vertical permeable flat plate with a uniform heat flux is analyzed in the presence of a transverse magnetic field.It is assumed that the induced magnetic field is negligible compared with the imposed magnetic field.The boundary layer equations are reduced to a suitable form by employing the free variable formulation (FVF) and the stream function formulation (SFF).The parabolic equations obtained from FVF are numerically integrated with the help of a straightforward finite difference method.Moreover,the nonsimilar system of equations obtained from SFF is solved by using a local nonsimilarity method,for the whole range of the local transpiration parameter ζ.Consideration is also given to the regions where the local transpiration parameter ζ is small or large enough.However,in these particular regions,solutions are acquired with the aid of a regular perturbation method.The effects of the magnetic field M and the Hall parameter m on the local skin friction coefficient and the local Nusselt number coefficient are graphically shown for smaller values of the Prandtl number P r (= 0.005,0.01,0.05).Furthermore,the velocity and temperature profiles are also drawn from various values of the local transpiration parameter ζ.
基金supported by National Natural Science Foundation of China(Grant No.52125604)。
文摘Combined cooling and power(CCP)system driven by low-grade heat is promising for improving energy efficiency.This work proposes a CCP system that integrates a regenerative organic Rankine cycle(RORC)and an absorption chiller on both driving and cooling fluid sides.The system is modeled by using the heat current method to fully consider nonlinear heat transfer and heat-work conversion constraints and resolve its behavior accurately.The off-design system simulation is performed next,showing that the fluid inlet temperatures and flow rates of cooling water as well as RORC working fluid strongly affect system performance.The off-design operation even becomes infeasible when parameters deviate from nominal values largely due to limited heat transfer capability of components,highlighting the importance of considering heat transfer constraints via heat current method.Design optimization aiming to minimize the total thermal conductance is also conducted.RORC efficiency increases by 7.9%and decreases by 12.4%after optimization,with the hot fluid inlet temperature increase from 373.15 to 403.15 K and mass flow rate ranges from 10 to 30 kg/s,emphasizing the necessity of balancing system cost and performance.