Direct numerical simulation based on OpenFOAM is carried out for two-dimensional RayleighBénard( RB) convection in a square domain at high Rayleigh number of 107 and Pr = 0.71. Proper orthogonal decomposition( PO...Direct numerical simulation based on OpenFOAM is carried out for two-dimensional RayleighBénard( RB) convection in a square domain at high Rayleigh number of 107 and Pr = 0.71. Proper orthogonal decomposition( POD) is used to analyze the flow and temperature characteristics from POD energy spectrum and eigenmodes. The results show that the energy spectrum converges fast and the scale of vortex structures captured by eigenmodes becomes smaller as the eigenmode order increases. Meanwhile,a low-dimensional model( LDM) for RB convection is derived based on POD eigenmodes used as a basis of Galerkin project of Navier-Stokes-Boussinesq equations. LDM is built based on different number of eigenmodes and through the analysis of phase portraits,streamline and isothermal predicted by LDM,it is suggested that the error between LDM and DNS is still large.展开更多
Multi-dimensional heat transfers modeling is crucial for building simulations of insulated buildings,which are widely used and have multi-dimensional heat transfers characteristics.For this work,state-model-reduction ...Multi-dimensional heat transfers modeling is crucial for building simulations of insulated buildings,which are widely used and have multi-dimensional heat transfers characteristics.For this work,state-model-reduction techniques were used to develop a reduced low-order model of multi-dimensional heat transfers.With hot box experiment of hollow block wall,heat flow relative errors between experiment and low-order model predication were less than 8% and the largest errors were less than 3%.Also,frequency responses of five typical walls,each with different thermal masses or insulation modes,the low-order model and the complete model showed that the low-order model results agree very well in the lower excitation frequency band with deviations appearing only at high frequency.Furthermore,low-order model was used on intersection thermal bridge of a floor slab and exterior wall.Results show that errors between the two models are very small.This low-order model could be coupled with most existing simulation software for different thermal mass envelope analyses to make up for differences between the multi-dimensional and one-dimensional models,simultaneously simplifying simulation calculations.展开更多
The present study deals with natural convection flow in a vertical open-ended channel with wall constant heat flux. The experimental and numerical investigations are both conducted using water as the working fluid. Th...The present study deals with natural convection flow in a vertical open-ended channel with wall constant heat flux. The experimental and numerical investigations are both conducted using water as the working fluid. The numerical code is developed using finite differences scheme to solve the Navier-Stokes equations under the Boussinesq assumption. Concerning the experimental apparatus, it consists of two heated walls immersed in water. Temperature and velocity measurements are provided for different modified Rayleigh numbers based on the walls spacing b Rab = 1.67 x 10 6,3.6 x 10 6,8.97 x10 6,1.69 x 10 7,4.29 x 10 7. The numerical code is first validated with a numerical benchmark. Then, comparison between experimental and numerical results is performed. The code provides a satisfactory prediction of main quantities compared to the experimental results but only for the lowest Rayleigh numbers. For higher modified Rayleigh numbers, the flow becomes three-dimensional and turbulent. Therefore, 2D numerical simulations fail to predict flow and heat transfer for this range of modified Rayleigh number.展开更多
Water adsorption and capillarity are key phenomena involved during heat and moisture transfer in porous building materials.They account for interaction between solid matrix,liquid water and moist air.They are consider...Water adsorption and capillarity are key phenomena involved during heat and moisture transfer in porous building materials.They account for interaction between solid matrix,liquid water and moist air.They are considered through Water Vapor Adsorption Isotherm(WVAI)and Retention Curve(RC)functions which are constitutive laws characterizing water activity within a porous medium.The objective of this paper is to present a water vapor adsorption and retention models built from multimodal Pore Size Distribution Function(PSDF)and to see how its parameters modify moisture storage for hygroscopic and near saturation ranges.The microstructure of the porous medium is represented statistically by a bundle of tortuous parallel pores through its PSDF.Firstly,the influence of contact angle and temperature on storage properties were investigated.Secondly,a parametric study was performed to see the influence of the PSDF shape on storage properties.Three cases were studied considering the number of modalities,the weight of each modality and the dispersion around mean radius.Finally,as a validation,the proposed model for WVAI were compared to existing model from literature showing a good agreement.This study showed that the proposed models are capable to reproduce various shapes of storage functions.It also highlighted the link between microstructure and adsorption-retention phenomena.展开更多
The goal of this article is to study numerically the mixed convection in a differentially heated rid-driven cavity with non-uniform heating of the bottom wall. The velocity field is solved by a hybrid scheme with mult...The goal of this article is to study numerically the mixed convection in a differentially heated rid-driven cavity with non-uniform heating of the bottom wall. The velocity field is solved by a hybrid scheme with multiple relaxation time Lattice Boltzmann （MRT-LBM） model, while the temperature field is obtained by resolution of the energy balance equation using the finite difference method （FDM）. First, the model is checked and validated using data from the riterature. Validation of the present resuJts with those available in the literature shows a good agreement. A good efficiency in time simulation is confirmed. Thereafter, the model has been applied to mixed convection in a driven cavity with non-uniform heating wall at the fixed Grashof number Gr = 106. It is found that, the heat transfer is weakened as the Richardson number is augmented. For Gr = 106, we note the appearance of secondary vortices at different positions of the cavity corners.展开更多
Final properties and behavior of polymer parts are known to be directly linked to the thermomechanical history experienced during their processing. Their quality depends on their structure, which is the result of the ...Final properties and behavior of polymer parts are known to be directly linked to the thermomechanical history experienced during their processing. Their quality depends on their structure, which is the result of the interactions between the process and the polymers in terms of thermomechanical kinetics. To study the actual behavior of a polymer during its transformation, it is necessary to take into account all the thermal dependencies of their thermophysical properties. In this paper, a complete experimental thermal characterization of a semi-crystalline polymer is performed. Thermal conductivity is measured using the hot wire method. The PVT diagram is obtained by means of an isobaric piston type dilatometer. Heat capacity is characterized versus temperature by differential scanning calorimetry (DSC). A modification of the Schneider rate crystallization equations is proposed, allowing to identify in a simple way all the crystallization kinetics parameters, using only DSC measurements. Finally, a multiphysical coupled model is built in order to numerically simulate the cooling of a polypropylene plate, as in the cooling stage of the injection molding process. Calculated evolutions of temperature, crystallinity, pressure and specific volume across the plate thickness are presented and commented.展开更多
This paper is concerned with the determination of the thermal energy performances of individual houses built with ＂H＂ shape bricks in hot and dry tropical climate （different cities of Burkina Faso and the city of B...This paper is concerned with the determination of the thermal energy performances of individual houses built with ＂H＂ shape bricks in hot and dry tropical climate （different cities of Burkina Faso and the city of Bamako in Mali）. The bricks＇ matrices include three void spaces which are filled during construction with either clay-grass mixture or with entirely clay matter. After measuring the diffusivity of the clay matter and cement bricks samples utilizing the Flash method, we determine the ＂H＂ shape bricks＇ thermal equivalent conductivity using the HEAT software. The house, modeled utilizing the TRNSYS software, reveals that, besides their economical and environmental advantages, houses constructed with ＂H＂ shape bricks filled with clay, show approximately the same energy consumption patterns as void cement bricks houses. On the other hand, houses built utilizing ＂H＂ shape bricks filled with clay-grass mixture, which have low thermal conductivity, show a reduced air conditioning load. We also study the influence of the building orientation on the energy consumption.展开更多
The ongoing energy transition,essential for mitigating global warming,stands to benefit significantly from advances in building energy consumption prediction.With the rise of big data,data-driven models have become in...The ongoing energy transition,essential for mitigating global warming,stands to benefit significantly from advances in building energy consumption prediction.With the rise of big data,data-driven models have become increasingly effective in forecasting,with machine learning emerging as the most efficient method for constructing these predictive models.While previous reviews have typically listed various machine learning models for energy consumption prediction,they have often lacked a theoretical perspective explaining why certain models are suitable for different aspects of this domain.In contrast,this review introduces machine learning techniques based on their application phases,covering preprocessing techniques such as feature selection,extraction,and clustering,as well as state-of-the-art predictive models.We provide a comparative theoretical analysis of various models,examining their strengths,weaknesses,and suitability for different forecasting tasks.Additionally,we discuss spatial-temporal considerations in energy consumption forecasting,including the role of Graph Neural Networks and multitask learning.Furthermore,we address a significant challenge in the field,the difficulty of accurately predicting high-fluctuation electricity consumption,and propose potential solutions to tackle this issue.展开更多
Biomass,which is derived from abundant renewable resources,is a promising alternative to fossil-fuel-based carbon materials for building a green and sustainable society.Biomass-based carbon materials(BCMs)with tailore...Biomass,which is derived from abundant renewable resources,is a promising alternative to fossil-fuel-based carbon materials for building a green and sustainable society.Biomass-based carbon materials(BCMs)with tailored hierarchical pore structures,large specific surface areas,and various surface functional groups have been extensively studied as energy and catalysis-related materials.This review provides insights from the perspectives of intrinsic physicochemical properties and structure-property relationships for discussing several fundamental yet significant issues in BCMs and their consequences.First,the synthesis,properties,and influencing factors of BCMs are discussed.Then,the causes and effects of the poor mechanical properties of biochar are explored.The factors affecting the properties of BCMs are presented,and the approaches for tuning these properties of biochar are summarized.Further,the applications of BCMs in energy storage and conversion are highlighted,including hydrogen storage and production,fuel cells,supercapacitors,hybrid electrodes,catalytic reforming,oxygen and CO_(2) reduction,and acetylene hydrochlorination.Finally,the future trends and prospects for biochar are proposed.This review aims to serve as a useful,up-to-date reference for future studies on BCMs for energy and catalytic applications.展开更多
This paper presents the simulation models of the plate-fin, air-to-water (or water vapour) heat exchangers used as air-heating or air-cooling and dehumidifying coils in the HVAC (Heating, Ventilation and Air-Condition...This paper presents the simulation models of the plate-fin, air-to-water (or water vapour) heat exchangers used as air-heating or air-cooling and dehumidifying coils in the HVAC (Heating, Ventilation and Air-Conditioning) systems. The thermal models are used to calculate the heat exchange between distributing air and coil pipes and outlet temperatures of air and heat or chilled fluid. The aerodynamic models are used to account for the pressure drop of the air crossing the coil tubes. They can also be used to optimize the structures of such coils. The models are based on principal laws of heat and mass conservation and fluid mechanics. They are transparent and easy to use. In our work, a coil is considered as an assembly of numbers of basic elements in which all the state variables are unique. Therefore we can conveniently simulate the coils with different structures and different geometric parameters. Two modular programs TRNSYS (Transient System Simulation) and ESACAP are utilized as supporting softwares which make the programming and simulation greatly simplified. The coil elements and a real coil were simulated. The results were compared with the data offered by the manufacturer (company SOFICA) and also with those obtained using critical methods such as NTU method, etc. and good agreement is attained.展开更多
The presented work addresses the topic of energy savings in existing public buildings, when no significant retrofits on buitding envelope or plants can be done and savings can be achieved by designing intelligent ICT-...The presented work addresses the topic of energy savings in existing public buildings, when no significant retrofits on buitding envelope or plants can be done and savings can be achieved by designing intelligent ICT-based service to monitor and contro[ environmental conditions, energy loads and plants operation. At the end of 2010 the European Commission, within the Seventh Framework Program, has founded a project entitled ＂Smart Energy Efficient Middleware for Public Spaces＂ （SEEMPubS）. To achieve this goal the project will implement, in a set of demonstrator buildings, an interoperab[e web-based software and hardware solution for real-time monitoring and control of lighting, heating, ventilation and air conditioning servfces, through both wired and wireless sensor networks. In this paper the first phase of the project, concerning the selection of the environments to be used as demonstrator and the definition of the control and monitoring strategies to reduce energy consumptions for lighting and air conditioning, are presented.展开更多
Based on segmentation-recombination principle, a specific optical device is designed to homogenize a highpower CO2 laser beam which is used as a heating source. A model is developed to simulate the intensity distribut...Based on segmentation-recombination principle, a specific optical device is designed to homogenize a highpower CO2 laser beam which is used as a heating source. A model is developed to simulate the intensity distribution of converted laser beam. The results show that the theoretical simulation is consistent with experimental record. The uniformity of converted beam spot is discussed. After modifying the optical parameters of current device, a new optical system is given, through which the uniformity of shaped beam spot is improved remarkably.展开更多
基金Sponsored by the National Natural Science Foundation of China(Grant o.51576051)
文摘Direct numerical simulation based on OpenFOAM is carried out for two-dimensional RayleighBénard( RB) convection in a square domain at high Rayleigh number of 107 and Pr = 0.71. Proper orthogonal decomposition( POD) is used to analyze the flow and temperature characteristics from POD energy spectrum and eigenmodes. The results show that the energy spectrum converges fast and the scale of vortex structures captured by eigenmodes becomes smaller as the eigenmode order increases. Meanwhile,a low-dimensional model( LDM) for RB convection is derived based on POD eigenmodes used as a basis of Galerkin project of Navier-Stokes-Boussinesq equations. LDM is built based on different number of eigenmodes and through the analysis of phase portraits,streamline and isothermal predicted by LDM,it is suggested that the error between LDM and DNS is still large.
基金Project(51178023)supported by the National Natural Science Foundation of China
文摘Multi-dimensional heat transfers modeling is crucial for building simulations of insulated buildings,which are widely used and have multi-dimensional heat transfers characteristics.For this work,state-model-reduction techniques were used to develop a reduced low-order model of multi-dimensional heat transfers.With hot box experiment of hollow block wall,heat flow relative errors between experiment and low-order model predication were less than 8% and the largest errors were less than 3%.Also,frequency responses of five typical walls,each with different thermal masses or insulation modes,the low-order model and the complete model showed that the low-order model results agree very well in the lower excitation frequency band with deviations appearing only at high frequency.Furthermore,low-order model was used on intersection thermal bridge of a floor slab and exterior wall.Results show that errors between the two models are very small.This low-order model could be coupled with most existing simulation software for different thermal mass envelope analyses to make up for differences between the multi-dimensional and one-dimensional models,simultaneously simplifying simulation calculations.
文摘The present study deals with natural convection flow in a vertical open-ended channel with wall constant heat flux. The experimental and numerical investigations are both conducted using water as the working fluid. The numerical code is developed using finite differences scheme to solve the Navier-Stokes equations under the Boussinesq assumption. Concerning the experimental apparatus, it consists of two heated walls immersed in water. Temperature and velocity measurements are provided for different modified Rayleigh numbers based on the walls spacing b Rab = 1.67 x 10 6,3.6 x 10 6,8.97 x10 6,1.69 x 10 7,4.29 x 10 7. The numerical code is first validated with a numerical benchmark. Then, comparison between experimental and numerical results is performed. The code provides a satisfactory prediction of main quantities compared to the experimental results but only for the lowest Rayleigh numbers. For higher modified Rayleigh numbers, the flow becomes three-dimensional and turbulent. Therefore, 2D numerical simulations fail to predict flow and heat transfer for this range of modified Rayleigh number.
文摘Water adsorption and capillarity are key phenomena involved during heat and moisture transfer in porous building materials.They account for interaction between solid matrix,liquid water and moist air.They are considered through Water Vapor Adsorption Isotherm(WVAI)and Retention Curve(RC)functions which are constitutive laws characterizing water activity within a porous medium.The objective of this paper is to present a water vapor adsorption and retention models built from multimodal Pore Size Distribution Function(PSDF)and to see how its parameters modify moisture storage for hygroscopic and near saturation ranges.The microstructure of the porous medium is represented statistically by a bundle of tortuous parallel pores through its PSDF.Firstly,the influence of contact angle and temperature on storage properties were investigated.Secondly,a parametric study was performed to see the influence of the PSDF shape on storage properties.Three cases were studied considering the number of modalities,the weight of each modality and the dispersion around mean radius.Finally,as a validation,the proposed model for WVAI were compared to existing model from literature showing a good agreement.This study showed that the proposed models are capable to reproduce various shapes of storage functions.It also highlighted the link between microstructure and adsorption-retention phenomena.
文摘The goal of this article is to study numerically the mixed convection in a differentially heated rid-driven cavity with non-uniform heating of the bottom wall. The velocity field is solved by a hybrid scheme with multiple relaxation time Lattice Boltzmann （MRT-LBM） model, while the temperature field is obtained by resolution of the energy balance equation using the finite difference method （FDM）. First, the model is checked and validated using data from the riterature. Validation of the present resuJts with those available in the literature shows a good agreement. A good efficiency in time simulation is confirmed. Thereafter, the model has been applied to mixed convection in a driven cavity with non-uniform heating wall at the fixed Grashof number Gr = 106. It is found that, the heat transfer is weakened as the Richardson number is augmented. For Gr = 106, we note the appearance of secondary vortices at different positions of the cavity corners.
文摘Final properties and behavior of polymer parts are known to be directly linked to the thermomechanical history experienced during their processing. Their quality depends on their structure, which is the result of the interactions between the process and the polymers in terms of thermomechanical kinetics. To study the actual behavior of a polymer during its transformation, it is necessary to take into account all the thermal dependencies of their thermophysical properties. In this paper, a complete experimental thermal characterization of a semi-crystalline polymer is performed. Thermal conductivity is measured using the hot wire method. The PVT diagram is obtained by means of an isobaric piston type dilatometer. Heat capacity is characterized versus temperature by differential scanning calorimetry (DSC). A modification of the Schneider rate crystallization equations is proposed, allowing to identify in a simple way all the crystallization kinetics parameters, using only DSC measurements. Finally, a multiphysical coupled model is built in order to numerically simulate the cooling of a polypropylene plate, as in the cooling stage of the injection molding process. Calculated evolutions of temperature, crystallinity, pressure and specific volume across the plate thickness are presented and commented.
文摘This paper is concerned with the determination of the thermal energy performances of individual houses built with ＂H＂ shape bricks in hot and dry tropical climate （different cities of Burkina Faso and the city of Bamako in Mali）. The bricks＇ matrices include three void spaces which are filled during construction with either clay-grass mixture or with entirely clay matter. After measuring the diffusivity of the clay matter and cement bricks samples utilizing the Flash method, we determine the ＂H＂ shape bricks＇ thermal equivalent conductivity using the HEAT software. The house, modeled utilizing the TRNSYS software, reveals that, besides their economical and environmental advantages, houses constructed with ＂H＂ shape bricks filled with clay, show approximately the same energy consumption patterns as void cement bricks houses. On the other hand, houses built utilizing ＂H＂ shape bricks filled with clay-grass mixture, which have low thermal conductivity, show a reduced air conditioning load. We also study the influence of the building orientation on the energy consumption.
文摘The ongoing energy transition,essential for mitigating global warming,stands to benefit significantly from advances in building energy consumption prediction.With the rise of big data,data-driven models have become increasingly effective in forecasting,with machine learning emerging as the most efficient method for constructing these predictive models.While previous reviews have typically listed various machine learning models for energy consumption prediction,they have often lacked a theoretical perspective explaining why certain models are suitable for different aspects of this domain.In contrast,this review introduces machine learning techniques based on their application phases,covering preprocessing techniques such as feature selection,extraction,and clustering,as well as state-of-the-art predictive models.We provide a comparative theoretical analysis of various models,examining their strengths,weaknesses,and suitability for different forecasting tasks.Additionally,we discuss spatial-temporal considerations in energy consumption forecasting,including the role of Graph Neural Networks and multitask learning.Furthermore,we address a significant challenge in the field,the difficulty of accurately predicting high-fluctuation electricity consumption,and propose potential solutions to tackle this issue.
基金financially supported by Key Research and Development Projects of Sichuan Province(2023YFG0222)“Tianfu Emei”Science and Technology Innovation Leader Program in Sichuan Province,University of Electronic Science and Technology of China Talent Start-up Funds(A1098531023601208)National Natural Science Foundation of China(21472235,21464015).
文摘Biomass,which is derived from abundant renewable resources,is a promising alternative to fossil-fuel-based carbon materials for building a green and sustainable society.Biomass-based carbon materials(BCMs)with tailored hierarchical pore structures,large specific surface areas,and various surface functional groups have been extensively studied as energy and catalysis-related materials.This review provides insights from the perspectives of intrinsic physicochemical properties and structure-property relationships for discussing several fundamental yet significant issues in BCMs and their consequences.First,the synthesis,properties,and influencing factors of BCMs are discussed.Then,the causes and effects of the poor mechanical properties of biochar are explored.The factors affecting the properties of BCMs are presented,and the approaches for tuning these properties of biochar are summarized.Further,the applications of BCMs in energy storage and conversion are highlighted,including hydrogen storage and production,fuel cells,supercapacitors,hybrid electrodes,catalytic reforming,oxygen and CO_(2) reduction,and acetylene hydrochlorination.Finally,the future trends and prospects for biochar are proposed.This review aims to serve as a useful,up-to-date reference for future studies on BCMs for energy and catalytic applications.
文摘This paper presents the simulation models of the plate-fin, air-to-water (or water vapour) heat exchangers used as air-heating or air-cooling and dehumidifying coils in the HVAC (Heating, Ventilation and Air-Conditioning) systems. The thermal models are used to calculate the heat exchange between distributing air and coil pipes and outlet temperatures of air and heat or chilled fluid. The aerodynamic models are used to account for the pressure drop of the air crossing the coil tubes. They can also be used to optimize the structures of such coils. The models are based on principal laws of heat and mass conservation and fluid mechanics. They are transparent and easy to use. In our work, a coil is considered as an assembly of numbers of basic elements in which all the state variables are unique. Therefore we can conveniently simulate the coils with different structures and different geometric parameters. Two modular programs TRNSYS (Transient System Simulation) and ESACAP are utilized as supporting softwares which make the programming and simulation greatly simplified. The coil elements and a real coil were simulated. The results were compared with the data offered by the manufacturer (company SOFICA) and also with those obtained using critical methods such as NTU method, etc. and good agreement is attained.
文摘The presented work addresses the topic of energy savings in existing public buildings, when no significant retrofits on buitding envelope or plants can be done and savings can be achieved by designing intelligent ICT-based service to monitor and contro[ environmental conditions, energy loads and plants operation. At the end of 2010 the European Commission, within the Seventh Framework Program, has founded a project entitled ＂Smart Energy Efficient Middleware for Public Spaces＂ （SEEMPubS）. To achieve this goal the project will implement, in a set of demonstrator buildings, an interoperab[e web-based software and hardware solution for real-time monitoring and control of lighting, heating, ventilation and air conditioning servfces, through both wired and wireless sensor networks. In this paper the first phase of the project, concerning the selection of the environments to be used as demonstrator and the definition of the control and monitoring strategies to reduce energy consumptions for lighting and air conditioning, are presented.
基金This work was supported by the National Natural Science Foundation of China (No. 60178004)ChinaScholarship Council (No. 22171004).
文摘Based on segmentation-recombination principle, a specific optical device is designed to homogenize a highpower CO2 laser beam which is used as a heating source. A model is developed to simulate the intensity distribution of converted laser beam. The results show that the theoretical simulation is consistent with experimental record. The uniformity of converted beam spot is discussed. After modifying the optical parameters of current device, a new optical system is given, through which the uniformity of shaped beam spot is improved remarkably.
