A mathematical model for heap bioleaching is developed to analyze heat transfer,oxygen flow,target ion distribution and oxidation leaching rate in the heap.The model equations are solved with Comsol Multiphysics softw...A mathematical model for heap bioleaching is developed to analyze heat transfer,oxygen flow,target ion distribution and oxidation leaching rate in the heap.The model equations are solved with Comsol Multiphysics software.Numerical simulation results show the following facts:Concentration of oxygen is relatively high along the boundary of the slope,and low in the center part where leaching rate is slow.Temperature is relatively low along the slope and reaches the highest along the bottom region near the slope,with difference being more than 6 C.Concentration of target mental ions is the highest in the bottom region near the slope.Oxidation leaching rate is relatively large in the bottom and slope part with a fast reaction rate,and small in the other part with low oxygen concentration.展开更多
This work presents the results of a set of steady-state numerical simulations about heat transfer in hollow blocks in the presence of coupled natural convection,conduction and radiation.Blocks with two air cells deep ...This work presents the results of a set of steady-state numerical simulations about heat transfer in hollow blocks in the presence of coupled natural convection,conduction and radiation.Blocks with two air cells deep in the vertical direction and three identical cavities in the horizontal direction are considered(typically used for building ceilings).Moreover,their outside horizontal surface is subjected to an incident solar flux and outdoor environment temperature while the inside surface is exposed to typical indoor environment conditions.The flows are considered laminar and two-dimensional over the whole range of parameters examined.The conservation equations are solved by means of a finite difference method based on the control volumes approach,relying on the SIMPLE algorithm for what concerns the coupling of pressure and velocity.The effects of the number of cells in the horizontal direction and the thermal conductivity on the heat transfer through the alveolar structure have been investigated.The results show that the number of holes has a significant impact on the value of the overall heat flux through the considered structure.展开更多
In this paper,we first establish a new fractional magnetohydrodynamic(MHD)coupled flow and heat transfer model for a generalized second-grade fluid.This coupled model consists of a fractional momentum equation and a h...In this paper,we first establish a new fractional magnetohydrodynamic(MHD)coupled flow and heat transfer model for a generalized second-grade fluid.This coupled model consists of a fractional momentum equation and a heat conduction equation with a generalized form of Fourier law.The second-order fractional backward difference formula is applied to the temporal discretization and the Legendre spectral method is used for the spatial discretization.The fully discrete scheme is proved to be stable and convergent with an accuracy of O(τ^(2)+N-r),whereτis the time step-size and N is the polynomial degree.To reduce the memory requirements and computational cost,a fast method is developed,which is based on a globally uniform approximation of the trapezoidal rule for integrals on the real line.The strict convergence of the numerical scheme with this fast method is proved.We present the results of several numerical experiments to verify the effectiveness of the proposed method.Finally,we simulate the unsteady fractional MHD flow and heat transfer of the generalized second-grade fluid through a porous medium.The effects of the relevant parameters on the velocity and temperature are presented and analyzed in detail.展开更多
The moisture performance of building envelopes largely depends on the building materials,construction tech-niques,and exposure loads from the indoor and outdoor regions.A ventilated air interlayer placed in a wall can...The moisture performance of building envelopes largely depends on the building materials,construction tech-niques,and exposure loads from the indoor and outdoor regions.A ventilated air interlayer placed in a wall can help dehumidify the wall and indoor air.This paper presents an experimental study of the heat,air,and moisture variations within the envelope wall of a chamber featuring different air interlayer settings under real outdoor air conditions during the summer of 2020 in Shanghai,China.Self-developed humidity-controlling building mate-rials were applied to the inner building envelope.Temperature,humidity,wind velocity,and heat-flow sensors were placed at different positions in the middle of the wall.These parameters were measured and recorded in real-time under three working conditions:humidification,dehumidification,and ventilation.The experimental results show that under the ventilation working conditions,moisture content of 0.52 kg can be removed after a 2-h air layer ventilation,which can benefit the design strategy for the humidification and ventilation of dehu-midification walls.展开更多
In this paper,some effort is provided to optimize the geometry of a concrete hollow brick(used in the construction of building roofs)in order to increase the related thermal resistance,thereby reducing energy consumpt...In this paper,some effort is provided to optimize the geometry of a concrete hollow brick(used in the construction of building roofs)in order to increase the related thermal resistance,thereby reducing energy consumption.The analysis is conducted for three different configurations of the hollow concrete bricks.Coupling of conduction,natural convection and thermal radiation phenomena is considered.Moreover,the flows are assumed to be laminar and two-dimensional for the whole range of parameters examined.The conservation equations are solved by a finite difference method based on the control volumes approach and the SIMPLE algorithm for velocity-pressure coupling.The results show that the aspect ratio affects neither the nature of the fluid flow nor the number of convective cells.However,the extension of the circulation cells increases with this parameter.Moreover,the cavities with a large aspect ratio lead to significant reductions in the heat transfer through the hollow block,these reductions reaching approximately 14%.展开更多
In this paper,the composite inner cooling structures of the rotating blade in the first stage heavy gas turbine were modeled and simulated by coupling heat transfer (CHT).The flow characteristics and heat transfer per...In this paper,the composite inner cooling structures of the rotating blade in the first stage heavy gas turbine were modeled and simulated by coupling heat transfer (CHT).The flow characteristics and heat transfer performances were comparatively analyzed under two operations of the stationary and the rotational states.The results show that the turbulence intensity,the flow resistance and the heat transfer level of the rotating coolant are significantly increased compared with the stationary state,which is considered to be obtained by the combined effects of the Coriolis force,the centrifugal force and their derived buoyancy forces.It is pointed out that the rotation leads to the non-uniform flow of film holes at the leading edge of the pressure surface along blade height.In addition,it increases the slope of the limiting streamline,which has a decisive influence on the heat transfer of both the pressure and suction surfaces.The paper provides guidance for the design of a rotating composite cooling structure based on the relations between the stationary and rotational conditions.展开更多
This study examines the benefits of incorporating passive techniques into multilayer hollow clay brick walls to improve their dynamic thermal performance.The finite element approach was used to solve the incompressibl...This study examines the benefits of incorporating passive techniques into multilayer hollow clay brick walls to improve their dynamic thermal performance.The finite element approach was used to solve the incompressible Navier-Stokes and energy equations to analyze the dynamic thermal response of walls exposed to real thermal excitations of the Marrakesh climate.The results show that increasing the emissivity from 0.1 to 0.9 significantly increases the total heat load over 24 h.Furthermore,filling 100% of the cavities with insulation materials delayed the temperature peak by about 2.3 h and lowered the decrement factor by roughly 43%,with a value smaller than 0.07.In addition,it is demonstrated that the total thermal load is reduced by approximately 28% for improved wall configurations(100% insulation filling cavities)compared to traditional wall configurations(100% air filling cavities),which aids in improving building energy efficiency.展开更多
Many ongoing tunnel projects provide a favorable opportunity for the investigation and application of tunnel lining ground heat exchangers(GHEs).Tunnel lining GHEs can be connected to a heat pump to extract geothermal...Many ongoing tunnel projects provide a favorable opportunity for the investigation and application of tunnel lining ground heat exchangers(GHEs).Tunnel lining GHEs can be connected to a heat pump to extract geothermal energy for heating and cooling buildings.Numerous studies have focused on the thermal performance of tunnel lining GHEs;however,the studies on the interaction between heat pumps and tunnel lining GHEs are relatively rare.In this study,a coupled heat transfer model of heat pumps and tunnel lining GHEs was proposed and then calibrated based on in situ test results.The model was used to evaluate the energy efficiency of a heat pump with tunnel lining GHEs under different conditions.The results show that the energy efficiency ratio(EER)increases exponentially with the absorber pipe length and thermal conductivity of the surrounding rock.The EER is governed by the convection heat transfer coefficient,which varies exponentially;meanwhile,the EER decreases approximately linearly with the annual average air temperature in the tunnel.Different types of heat pumps affect the EER significantly,and the EER of a Type-3 heat pump is higher than that of a Type-1 heat pump by 27.1%.Based on the aforementioned results,an empirical formula for the EER and absorber pipe length was established.Moreover,a preliminary design method for the absorber pipe length based on this empirical formula was developed.The method was employed to determine the appropriate absorber pipe length for the tunnel lining GHEs in the Shapu tunnel in Shenzhen,China.Finally,groups of absorber pipe layouts with a pipe spacing of 0.5 m,area of 135 m2,and length of 293.5 m were preliminarily determined.展开更多
In the high-humidity, hot-summer-cold-winter(HSCW) zone of China, the moisture buffering effect in the envelope is found to be significant in optimum insulation thickness. However, few studies have considered the effe...In the high-humidity, hot-summer-cold-winter(HSCW) zone of China, the moisture buffering effect in the envelope is found to be significant in optimum insulation thickness. However, few studies have considered the effects of indoor moisture buffering on the optimum insulation thickness and energy consumption. In this study, we considered the energy load of an exterior wall under moisture transfer from the outdoor to the indoor environment. An optimum insulation thickness was obtained by integrating the P1-P2model. A residential building was selected for the case study to verify the proposed method. Finally, a comparison was made with two other widely used methods, namely the transient heat transfer model(TH) and the coupled heat and moisture transfer model(CHM). The results indicated that the indoor moisture buffering effect on the optimum insulation thickness is 2.54 times greater than the moisture buffering effect in the envelope, and the two moisture buffering effects make opposing contributions to the optimum insulation thickness. Therefore, when TH or CHM was used without considering the indoor moisture buffering effect, the optimum insulation thickness of the southern wall under one air change per hour(1 ACH) and 100% normal heat source may be overestimated by 2.13% to 3. 59%, and the annual energy load on a single wall may be underestimated by 10.10% to 11.44%. The decrease of airtightness and the increase of indoor heat sources may result in a slight reduction of optimum insulation thickness. This study will enable professionals to consider the effects of moisture buffering on the design of insulation thickness.展开更多
基金Project supported by the National Natural Science Foundation of China (Nos. 50934002 and 50774011)the Postdoctoral Science Foundation of China (No. 20090450014)the DoctoralNatural Science Foundation of China (No. 20070008038)
文摘A mathematical model for heap bioleaching is developed to analyze heat transfer,oxygen flow,target ion distribution and oxidation leaching rate in the heap.The model equations are solved with Comsol Multiphysics software.Numerical simulation results show the following facts:Concentration of oxygen is relatively high along the boundary of the slope,and low in the center part where leaching rate is slow.Temperature is relatively low along the slope and reaches the highest along the bottom region near the slope,with difference being more than 6 C.Concentration of target mental ions is the highest in the bottom region near the slope.Oxidation leaching rate is relatively large in the bottom and slope part with a fast reaction rate,and small in the other part with low oxygen concentration.
文摘This work presents the results of a set of steady-state numerical simulations about heat transfer in hollow blocks in the presence of coupled natural convection,conduction and radiation.Blocks with two air cells deep in the vertical direction and three identical cavities in the horizontal direction are considered(typically used for building ceilings).Moreover,their outside horizontal surface is subjected to an incident solar flux and outdoor environment temperature while the inside surface is exposed to typical indoor environment conditions.The flows are considered laminar and two-dimensional over the whole range of parameters examined.The conservation equations are solved by means of a finite difference method based on the control volumes approach,relying on the SIMPLE algorithm for what concerns the coupling of pressure and velocity.The effects of the number of cells in the horizontal direction and the thermal conductivity on the heat transfer through the alveolar structure have been investigated.The results show that the number of holes has a significant impact on the value of the overall heat flux through the considered structure.
基金supported by the Project of the National Key R&D Program(Grant No.2021YFA1000202)National Natural Science Foundation of China(Grant Nos.12120101001,12001326 and 12171283)+2 种基金Natural Science Foundation of Shandong Province(Grant Nos.ZR2021ZD03,ZR2020QA032 and ZR2019ZD42)China Postdoctoral Science Foundation(Grant Nos.BX20190191 and 2020M672038)the Startup Fund from Shandong University(Grant No.11140082063130)。
文摘In this paper,we first establish a new fractional magnetohydrodynamic(MHD)coupled flow and heat transfer model for a generalized second-grade fluid.This coupled model consists of a fractional momentum equation and a heat conduction equation with a generalized form of Fourier law.The second-order fractional backward difference formula is applied to the temporal discretization and the Legendre spectral method is used for the spatial discretization.The fully discrete scheme is proved to be stable and convergent with an accuracy of O(τ^(2)+N-r),whereτis the time step-size and N is the polynomial degree.To reduce the memory requirements and computational cost,a fast method is developed,which is based on a globally uniform approximation of the trapezoidal rule for integrals on the real line.The strict convergence of the numerical scheme with this fast method is proved.We present the results of several numerical experiments to verify the effectiveness of the proposed method.Finally,we simulate the unsteady fractional MHD flow and heat transfer of the generalized second-grade fluid through a porous medium.The effects of the relevant parameters on the velocity and temperature are presented and analyzed in detail.
基金financially supported by the National Natural Science Foundation of China(No.51778358)the Shanghai Municipality Natural Science Foundation(No.21ZR1434400)Sponsored by Key Laboratory of New Technology for Construction of Cities in Mountain Area,Ministry of Education,Chongqing University,Chongqing 400045,China(LNTCCMA-20210103).
文摘The moisture performance of building envelopes largely depends on the building materials,construction tech-niques,and exposure loads from the indoor and outdoor regions.A ventilated air interlayer placed in a wall can help dehumidify the wall and indoor air.This paper presents an experimental study of the heat,air,and moisture variations within the envelope wall of a chamber featuring different air interlayer settings under real outdoor air conditions during the summer of 2020 in Shanghai,China.Self-developed humidity-controlling building mate-rials were applied to the inner building envelope.Temperature,humidity,wind velocity,and heat-flow sensors were placed at different positions in the middle of the wall.These parameters were measured and recorded in real-time under three working conditions:humidification,dehumidification,and ventilation.The experimental results show that under the ventilation working conditions,moisture content of 0.52 kg can be removed after a 2-h air layer ventilation,which can benefit the design strategy for the humidification and ventilation of dehu-midification walls.
文摘In this paper,some effort is provided to optimize the geometry of a concrete hollow brick(used in the construction of building roofs)in order to increase the related thermal resistance,thereby reducing energy consumption.The analysis is conducted for three different configurations of the hollow concrete bricks.Coupling of conduction,natural convection and thermal radiation phenomena is considered.Moreover,the flows are assumed to be laminar and two-dimensional for the whole range of parameters examined.The conservation equations are solved by a finite difference method based on the control volumes approach and the SIMPLE algorithm for velocity-pressure coupling.The results show that the aspect ratio affects neither the nature of the fluid flow nor the number of convective cells.However,the extension of the circulation cells increases with this parameter.Moreover,the cavities with a large aspect ratio lead to significant reductions in the heat transfer through the hollow block,these reductions reaching approximately 14%.
基金This research work was funded by the Foundation for Innovative Research Groups of National Nature Science Foundation of China(Grant No.51121004).
文摘In this paper,the composite inner cooling structures of the rotating blade in the first stage heavy gas turbine were modeled and simulated by coupling heat transfer (CHT).The flow characteristics and heat transfer performances were comparatively analyzed under two operations of the stationary and the rotational states.The results show that the turbulence intensity,the flow resistance and the heat transfer level of the rotating coolant are significantly increased compared with the stationary state,which is considered to be obtained by the combined effects of the Coriolis force,the centrifugal force and their derived buoyancy forces.It is pointed out that the rotation leads to the non-uniform flow of film holes at the leading edge of the pressure surface along blade height.In addition,it increases the slope of the limiting streamline,which has a decisive influence on the heat transfer of both the pressure and suction surfaces.The paper provides guidance for the design of a rotating composite cooling structure based on the relations between the stationary and rotational conditions.
文摘This study examines the benefits of incorporating passive techniques into multilayer hollow clay brick walls to improve their dynamic thermal performance.The finite element approach was used to solve the incompressible Navier-Stokes and energy equations to analyze the dynamic thermal response of walls exposed to real thermal excitations of the Marrakesh climate.The results show that increasing the emissivity from 0.1 to 0.9 significantly increases the total heat load over 24 h.Furthermore,filling 100% of the cavities with insulation materials delayed the temperature peak by about 2.3 h and lowered the decrement factor by roughly 43%,with a value smaller than 0.07.In addition,it is demonstrated that the total thermal load is reduced by approximately 28% for improved wall configurations(100% insulation filling cavities)compared to traditional wall configurations(100% air filling cavities),which aids in improving building energy efficiency.
基金funded by the National Natural Science Foundation of China(Grant numbers:51778138,and 51978162).
文摘Many ongoing tunnel projects provide a favorable opportunity for the investigation and application of tunnel lining ground heat exchangers(GHEs).Tunnel lining GHEs can be connected to a heat pump to extract geothermal energy for heating and cooling buildings.Numerous studies have focused on the thermal performance of tunnel lining GHEs;however,the studies on the interaction between heat pumps and tunnel lining GHEs are relatively rare.In this study,a coupled heat transfer model of heat pumps and tunnel lining GHEs was proposed and then calibrated based on in situ test results.The model was used to evaluate the energy efficiency of a heat pump with tunnel lining GHEs under different conditions.The results show that the energy efficiency ratio(EER)increases exponentially with the absorber pipe length and thermal conductivity of the surrounding rock.The EER is governed by the convection heat transfer coefficient,which varies exponentially;meanwhile,the EER decreases approximately linearly with the annual average air temperature in the tunnel.Different types of heat pumps affect the EER significantly,and the EER of a Type-3 heat pump is higher than that of a Type-1 heat pump by 27.1%.Based on the aforementioned results,an empirical formula for the EER and absorber pipe length was established.Moreover,a preliminary design method for the absorber pipe length based on this empirical formula was developed.The method was employed to determine the appropriate absorber pipe length for the tunnel lining GHEs in the Shapu tunnel in Shenzhen,China.Finally,groups of absorber pipe layouts with a pipe spacing of 0.5 m,area of 135 m2,and length of 293.5 m were preliminarily determined.
基金supported by the National Natural Science Foundation of China (Nos. 51978623 and 52076189)。
文摘In the high-humidity, hot-summer-cold-winter(HSCW) zone of China, the moisture buffering effect in the envelope is found to be significant in optimum insulation thickness. However, few studies have considered the effects of indoor moisture buffering on the optimum insulation thickness and energy consumption. In this study, we considered the energy load of an exterior wall under moisture transfer from the outdoor to the indoor environment. An optimum insulation thickness was obtained by integrating the P1-P2model. A residential building was selected for the case study to verify the proposed method. Finally, a comparison was made with two other widely used methods, namely the transient heat transfer model(TH) and the coupled heat and moisture transfer model(CHM). The results indicated that the indoor moisture buffering effect on the optimum insulation thickness is 2.54 times greater than the moisture buffering effect in the envelope, and the two moisture buffering effects make opposing contributions to the optimum insulation thickness. Therefore, when TH or CHM was used without considering the indoor moisture buffering effect, the optimum insulation thickness of the southern wall under one air change per hour(1 ACH) and 100% normal heat source may be overestimated by 2.13% to 3. 59%, and the annual energy load on a single wall may be underestimated by 10.10% to 11.44%. The decrease of airtightness and the increase of indoor heat sources may result in a slight reduction of optimum insulation thickness. This study will enable professionals to consider the effects of moisture buffering on the design of insulation thickness.
