Fertilizer plants are most complex plants in the world (Rashid et al., 2013, Process Safety Progress) and its good opportunity to learn science from operations involved in these plants. Fluid mechanics and heat transf...Fertilizer plants are most complex plants in the world (Rashid et al., 2013, Process Safety Progress) and its good opportunity to learn science from operations involved in these plants. Fluid mechanics and heat transfer operations combination involved in fertilizer complexes are explored in this article.展开更多
Studying the agricultural spatial distribution characteristics of Jianghan Plain from 2000 to 2018 and its spatial-temporal transformation with ecological space and urban space is of great significance for optimizing ...Studying the agricultural spatial distribution characteristics of Jianghan Plain from 2000 to 2018 and its spatial-temporal transformation with ecological space and urban space is of great significance for optimizing the spatial structure of the country, enhancing the supply capacity of agricultural products, and ensuring food security. The research results show that during the period from 2000 to 2018, the agricultural spatial concentration in the area along the “Xiaogan-Jingzhou” link was relatively high, and the areas with large declines were mainly distributed in the flat areas between the Yangtze River and Han River;the space is continuously reduced by the occupation of ecological space and urban space, and ecological space and urban space have been improved respectively;agricultural space has been transformed into ecological space, and the largest urban space has been transformed. Ecological space has been transformed into agricultural space and urban space. Less urban space has been transformed into agricultural space and ecological space.展开更多
In order to improve the control precision of strip coiling temperature for hot strip mill,the BP neural network was combined with mathematical model to calculate convective heat-transfer coefficient of laminar flow co...In order to improve the control precision of strip coiling temperature for hot strip mill,the BP neural network was combined with mathematical model to calculate convective heat-transfer coefficient of laminar flow cooling.The off-line calculated results indicate that the standard deviation of coiling temperature prediction is reduced by 22.84 % with the convective heat-transfer coefficient calculated by BP neural network.The prospects of this method for online application are bright.This method is more helpful to increasing the control precision of coiling temperature for hot strip steel.展开更多
Porous particle flow is universal in nature and industry.However,in previous numerical simulations,porous particles have usually been assumed to be solid.It is necessary to study the flow and heat-transfer characteris...Porous particle flow is universal in nature and industry.However,in previous numerical simulations,porous particles have usually been assumed to be solid.It is necessary to study the flow and heat-transfer characteristics around porous particles because they are greatly different from those of impermeable particles.In this study,two-dimensional steady flow and heat transfer around and through a porous particle with a constant temperature placed in a cold fluid were numerically investigated.The effects of the Reynolds number(Re)and Darcy number(Da)on the flow and heat-transfer characteristics were investigated in detail.The investigated ranges of the parameters were 10≤Re≤40 and 10^(−6)≤Da≤10^(−2).It is sophisticated to simulate porous particles with traditional simulation methods because of their complicated structure.Therefore,the lattice Boltzmann method was used to solve the generalized macroscopic governing equations because of its simplicity.The drag coefficient decreased with increasing Re or Da,but the decrease was not prominent in the range 10^(−6)≤Da≤10^(−4).The heat-transfer efficiency of the front surface was much stronger than that of the rear surface.The heat-transfer efficiency between the particle and the fluid increased with increasing Re or Da.However,for 10^(−6)≤Da≤10^(−4),the increase was not prominent and the heat-transfer enhancement ratio was slightly larger than one.Furthermore,the effect of Da became more prominent at larger Re.In addition,new correlations for the drag coefficient and surface-averaged Nusselt number were obtained based on the simulated results.展开更多
A theoretical analysis for MHD boundary layer flow on a moving surface with the power-law velocity is presented. An accurate expression of the skin friction coefficient is derived. The analytical approximate solution ...A theoretical analysis for MHD boundary layer flow on a moving surface with the power-law velocity is presented. An accurate expression of the skin friction coefficient is derived. The analytical approximate solution is obtained by means of Adomian decomposition methods. The reliability and efficiency of the approximate solutions are verified by numerical ones in the literature.展开更多
The Navier-Stokes equations for slip flow between two very closely spaced parallel plates are transformed to an ordinary differential equation based on the pressure gradient along the flow direction using a new simila...The Navier-Stokes equations for slip flow between two very closely spaced parallel plates are transformed to an ordinary differential equation based on the pressure gradient along the flow direction using a new similarity transformation. A powerful easy-to-use homotopy analysis method was used to obtain an analytical solution. The convergence theorem for the homotopy analysis method is presented. The solutions show that the second-order homotopy analysis method solution is accurate enough for the current problem.展开更多
Momentum and energy laminar boundary layers of an incompressible fluid with thermal radiation about a moving plate in a quiescent ambient fluid are investigated numerically. Also, it has been underlined that the analy...Momentum and energy laminar boundary layers of an incompressible fluid with thermal radiation about a moving plate in a quiescent ambient fluid are investigated numerically. Also, it has been underlined that the analysis of the roles of both velocity and temperature gradient at infinity is of key relevance for our results.展开更多
Heat-transfer coefficients(HTC)on surfaces exposed to convection environments are often measured by transient techniques such as thermochromic liquid crystal(TLC)or infrared thermography.In these techniques,the surfac...Heat-transfer coefficients(HTC)on surfaces exposed to convection environments are often measured by transient techniques such as thermochromic liquid crystal(TLC)or infrared thermography.In these techniques,the surface temperature is measured as a function of time,and that measurement is used with the exact solution for unsteady,zero-dimensional(0-D)or one-dimensional(1-D)heat conduction into a solid to calculate the local HTC.When using the 0-D or 1-D exact solutions,the transient techniques assume the HTC and the free-stream or bulk temperature characterizing the convection environment to be constants in addition to assuming the conduction into the solid to be 0-D or 1-D.In this study,computational fluid dynamics(CFD)conjugate analyses were performed to examine the errors that might be invoked by these assumptions for a problem,where the free-stream/bulk temperature and the heat-transfer coefficient vary appreciably along the surface and where conduction into the solid may not be 0-D or 1-D.The problem selected to assess these errors is flow and heat transfer in a channel lined with a staggered array of pin fins.This conjugate study uses three-dimensional(3-D)unsteady Reynolds-averaged Navier-Stokes(RANS)closed by the shear-stress transport(SST)turbulence model for the gas phase(wall functions not used)and the Fourier law for the solid phase.The errors in the transient techniques are assessed by comparing the HTC predicted by the time-accurate conjugate CFD with those predicted by the 0-D and 1-D exact solutions,where the surface temperatures needed by the exact solutions are taken from the time-accurate conjugate CFD solution.Results obtained show that the use of the 1-D exact solution for the semi-infinite wall to give reasonably accurate“transient”HTC(less than 5%〇relative error).Transient techniques that use the 0-D exact solution for the pin fins were found to produce large errors(up to 160%relative error)because the HTC varies appreciably about each pin fin.This study also showed that HTC measured by transient techniques could differ considerably from the HTC obtained under steady-state conditions with isothermal walls.展开更多
Curzon and Ahlborn considered firstly the irreversibility of heat-transfer in the Carnot cycle, and derived the efficiency of a Carnot cycle at maximum power
The gas quenching is a modern, effective processing technology. On the basis of nonlinear surface heat-transfer coefficient obtained by Cheng during the gas quenching, the coupled problem between temperature and phase...The gas quenching is a modern, effective processing technology. On the basis of nonlinear surface heat-transfer coefficient obtained by Cheng during the gas quenching, the coupled problem between temperature and phase transformation during gas quenching in high pressure was simulated by means of finite element method. In the numerical calculation, the thermal physical properties were treated as the functions of temperature and the volume fraction of phase constituents. In order to avoid effectual "oscillation" of the numerical solutions under smaller time step, the Norsette rational approximate method was used.展开更多
An unusual form of localized corrsion in copper tubes was detected early in service and in leakage tests after manufacturing.The morphology of this corrosion is similar to that of an ant's nest when viewed in cros...An unusual form of localized corrsion in copper tubes was detected early in service and in leakage tests after manufacturing.The morphology of this corrosion is similar to that of an ant's nest when viewed in cross section. The corrosion mechanisms, cases ofant's nest corrosion, and preventive measures are presented.展开更多
Temperature drop is commonly observed in subsea vertical X-mas trees during shutdown.The presence of a huge temperature difference between internal crude oil and external seawater can cause severe equipment degradatio...Temperature drop is commonly observed in subsea vertical X-mas trees during shutdown.The presence of a huge temperature difference between internal crude oil and external seawater can cause severe equipment degradation of the oil flow channel(e.g.,hydrate precipitation),which can block the oil flow channel and interrupt the production process.The most vulnerable parts of a subsea vertical X-mas tree tend to be components with high convective heat transfer rates,such as production modules and short joints.We proposed an innovative approach for the insulation design of underwater equipment under a shutdown condition.First,we obtained a heat transfer analysis of the tree under working conditions through computational fluid dynamics to ascertain the initial temperature condition for an unsteadystate analysis.Second,we investigated the unsteady heat transfer characteristics of the tree with an insulation layer in the shutdown state and derived the relationships between insulation duration and thickness by data analysis.We used data analysis to identify the relationship between insulation duration and thickness.Finally,we derived the empirical formula of insulation thickness for underwater equipment given the effect of environmental factors on the heat preservation effect.We performed the experiment with an oil pipeline,and the results showed that the internal oil of the equipment did not hydrate within 8 h under the shutdown condition with insulation layers.展开更多
An algorithm using the discrete element method(DEM)for simulating the particulate behaviour of flow and heat transfer is developed and described,the reasonable hypothesis and the ingenious design of which have been pr...An algorithm using the discrete element method(DEM)for simulating the particulate behaviour of flow and heat transfer is developed and described,the reasonable hypothesis and the ingenious design of which have been presented in detail.The organizational structure of the developed algorithm contains an efficient method for determining particle collisions,the status analysis for each particle and the particulate-kinematics analysis during the time step.The reasonability and correctness of the developed DEM algorithm are validated by laboratory experiments:the discharge process of glass beads from a silo;and heating of metal alloy particles in a calciner.Afterwards,a group of validated mechanics parameter values for coal and sand have been tested and verified in the article,preparing for the simulation of the pyrolysis process in a downer or screw reactor in subsequent research projects.展开更多
文摘Fertilizer plants are most complex plants in the world (Rashid et al., 2013, Process Safety Progress) and its good opportunity to learn science from operations involved in these plants. Fluid mechanics and heat transfer operations combination involved in fertilizer complexes are explored in this article.
文摘Studying the agricultural spatial distribution characteristics of Jianghan Plain from 2000 to 2018 and its spatial-temporal transformation with ecological space and urban space is of great significance for optimizing the spatial structure of the country, enhancing the supply capacity of agricultural products, and ensuring food security. The research results show that during the period from 2000 to 2018, the agricultural spatial concentration in the area along the “Xiaogan-Jingzhou” link was relatively high, and the areas with large declines were mainly distributed in the flat areas between the Yangtze River and Han River;the space is continuously reduced by the occupation of ecological space and urban space, and ecological space and urban space have been improved respectively;agricultural space has been transformed into ecological space, and the largest urban space has been transformed. Ecological space has been transformed into agricultural space and urban space. Less urban space has been transformed into agricultural space and ecological space.
基金Item Sponsored by National Natural Science Foundation of China(50104004)
文摘In order to improve the control precision of strip coiling temperature for hot strip mill,the BP neural network was combined with mathematical model to calculate convective heat-transfer coefficient of laminar flow cooling.The off-line calculated results indicate that the standard deviation of coiling temperature prediction is reduced by 22.84 % with the convective heat-transfer coefficient calculated by BP neural network.The prospects of this method for online application are bright.This method is more helpful to increasing the control precision of coiling temperature for hot strip steel.
基金supported by the National Natural Science Foundation of China(grant No.51922086).
文摘Porous particle flow is universal in nature and industry.However,in previous numerical simulations,porous particles have usually been assumed to be solid.It is necessary to study the flow and heat-transfer characteristics around porous particles because they are greatly different from those of impermeable particles.In this study,two-dimensional steady flow and heat transfer around and through a porous particle with a constant temperature placed in a cold fluid were numerically investigated.The effects of the Reynolds number(Re)and Darcy number(Da)on the flow and heat-transfer characteristics were investigated in detail.The investigated ranges of the parameters were 10≤Re≤40 and 10^(−6)≤Da≤10^(−2).It is sophisticated to simulate porous particles with traditional simulation methods because of their complicated structure.Therefore,the lattice Boltzmann method was used to solve the generalized macroscopic governing equations because of its simplicity.The drag coefficient decreased with increasing Re or Da,but the decrease was not prominent in the range 10^(−6)≤Da≤10^(−4).The heat-transfer efficiency of the front surface was much stronger than that of the rear surface.The heat-transfer efficiency between the particle and the fluid increased with increasing Re or Da.However,for 10^(−6)≤Da≤10^(−4),the increase was not prominent and the heat-transfer enhancement ratio was slightly larger than one.Furthermore,the effect of Da became more prominent at larger Re.In addition,new correlations for the drag coefficient and surface-averaged Nusselt number were obtained based on the simulated results.
基金Supported by the National Natural Science Foundation of China under Grant No 50476083.
文摘A theoretical analysis for MHD boundary layer flow on a moving surface with the power-law velocity is presented. An accurate expression of the skin friction coefficient is derived. The analytical approximate solution is obtained by means of Adomian decomposition methods. The reliability and efficiency of the approximate solutions are verified by numerical ones in the literature.
基金Supported by the National Natural Science Foundation of China under Grant Nos 50776006.
文摘The Navier-Stokes equations for slip flow between two very closely spaced parallel plates are transformed to an ordinary differential equation based on the pressure gradient along the flow direction using a new similarity transformation. A powerful easy-to-use homotopy analysis method was used to obtain an analytical solution. The convergence theorem for the homotopy analysis method is presented. The solutions show that the second-order homotopy analysis method solution is accurate enough for the current problem.
文摘Momentum and energy laminar boundary layers of an incompressible fluid with thermal radiation about a moving plate in a quiescent ambient fluid are investigated numerically. Also, it has been underlined that the analysis of the roles of both velocity and temperature gradient at infinity is of key relevance for our results.
基金This research was supported by the National Energy Technology Laboratory of the US Department of Energy with Robin Ames and Richard Dennis as the technical monitors.The authors are grateful for this support.
文摘Heat-transfer coefficients(HTC)on surfaces exposed to convection environments are often measured by transient techniques such as thermochromic liquid crystal(TLC)or infrared thermography.In these techniques,the surface temperature is measured as a function of time,and that measurement is used with the exact solution for unsteady,zero-dimensional(0-D)or one-dimensional(1-D)heat conduction into a solid to calculate the local HTC.When using the 0-D or 1-D exact solutions,the transient techniques assume the HTC and the free-stream or bulk temperature characterizing the convection environment to be constants in addition to assuming the conduction into the solid to be 0-D or 1-D.In this study,computational fluid dynamics(CFD)conjugate analyses were performed to examine the errors that might be invoked by these assumptions for a problem,where the free-stream/bulk temperature and the heat-transfer coefficient vary appreciably along the surface and where conduction into the solid may not be 0-D or 1-D.The problem selected to assess these errors is flow and heat transfer in a channel lined with a staggered array of pin fins.This conjugate study uses three-dimensional(3-D)unsteady Reynolds-averaged Navier-Stokes(RANS)closed by the shear-stress transport(SST)turbulence model for the gas phase(wall functions not used)and the Fourier law for the solid phase.The errors in the transient techniques are assessed by comparing the HTC predicted by the time-accurate conjugate CFD with those predicted by the 0-D and 1-D exact solutions,where the surface temperatures needed by the exact solutions are taken from the time-accurate conjugate CFD solution.Results obtained show that the use of the 1-D exact solution for the semi-infinite wall to give reasonably accurate“transient”HTC(less than 5%〇relative error).Transient techniques that use the 0-D exact solution for the pin fins were found to produce large errors(up to 160%relative error)because the HTC varies appreciably about each pin fin.This study also showed that HTC measured by transient techniques could differ considerably from the HTC obtained under steady-state conditions with isothermal walls.
文摘Curzon and Ahlborn considered firstly the irreversibility of heat-transfer in the Carnot cycle, and derived the efficiency of a Carnot cycle at maximum power
基金Project supported by the National Natural Science Foundation of China (No.10162002) the Key Project of Ministry of Education of China (No.204138)
文摘The gas quenching is a modern, effective processing technology. On the basis of nonlinear surface heat-transfer coefficient obtained by Cheng during the gas quenching, the coupled problem between temperature and phase transformation during gas quenching in high pressure was simulated by means of finite element method. In the numerical calculation, the thermal physical properties were treated as the functions of temperature and the volume fraction of phase constituents. In order to avoid effectual "oscillation" of the numerical solutions under smaller time step, the Norsette rational approximate method was used.
文摘An unusual form of localized corrsion in copper tubes was detected early in service and in leakage tests after manufacturing.The morphology of this corrosion is similar to that of an ant's nest when viewed in cross section. The corrosion mechanisms, cases ofant's nest corrosion, and preventive measures are presented.
基金financed by the Scientific Research Project of Ocean Engineering Equipment,Ministry of Industry and Information Technology of China。
文摘Temperature drop is commonly observed in subsea vertical X-mas trees during shutdown.The presence of a huge temperature difference between internal crude oil and external seawater can cause severe equipment degradation of the oil flow channel(e.g.,hydrate precipitation),which can block the oil flow channel and interrupt the production process.The most vulnerable parts of a subsea vertical X-mas tree tend to be components with high convective heat transfer rates,such as production modules and short joints.We proposed an innovative approach for the insulation design of underwater equipment under a shutdown condition.First,we obtained a heat transfer analysis of the tree under working conditions through computational fluid dynamics to ascertain the initial temperature condition for an unsteadystate analysis.Second,we investigated the unsteady heat transfer characteristics of the tree with an insulation layer in the shutdown state and derived the relationships between insulation duration and thickness by data analysis.We used data analysis to identify the relationship between insulation duration and thickness.Finally,we derived the empirical formula of insulation thickness for underwater equipment given the effect of environmental factors on the heat preservation effect.We performed the experiment with an oil pipeline,and the results showed that the internal oil of the equipment did not hydrate within 8 h under the shutdown condition with insulation layers.
文摘An algorithm using the discrete element method(DEM)for simulating the particulate behaviour of flow and heat transfer is developed and described,the reasonable hypothesis and the ingenious design of which have been presented in detail.The organizational structure of the developed algorithm contains an efficient method for determining particle collisions,the status analysis for each particle and the particulate-kinematics analysis during the time step.The reasonability and correctness of the developed DEM algorithm are validated by laboratory experiments:the discharge process of glass beads from a silo;and heating of metal alloy particles in a calciner.Afterwards,a group of validated mechanics parameter values for coal and sand have been tested and verified in the article,preparing for the simulation of the pyrolysis process in a downer or screw reactor in subsequent research projects.