The main objective of this study is the technical optimization of a Shell-and-Tube Heat Exchanger(STHE).In order to do so,a simulation model is introduced that takes into account the related gas-phase circulation.Then...The main objective of this study is the technical optimization of a Shell-and-Tube Heat Exchanger(STHE).In order to do so,a simulation model is introduced that takes into account the related gas-phase circulation.Then,simulation verification experiments are designed in order to validate the model.The results show that the tem-peraturefield undergoes strong variations in time when an inlet wind speed of 6 m/s is considered,while the heat transfer error reaches a minimum of 5.1%.For an inlet velocity of 9 m/s,the heat transfer drops to the lowest point,while the heat transfer error reaches a maximum,i.e.,9.87%.The pressure drop increasesfirst and then decreases with an increase in the wind speed and reaches a maximum of 819 Pa under the 9 m/s wind speed con-dition.Moreover,the pressure drops,and the heat transfer coefficient increases with the Reynolds number.展开更多
Thermal characteristic of cavitation has great influence on the process of occurrence,development and collapse of bubble in hydraulic system. By choosing the stage of bubble growth as the research object,combining wit...Thermal characteristic of cavitation has great influence on the process of occurrence,development and collapse of bubble in hydraulic system. By choosing the stage of bubble growth as the research object,combining with the characteristic of the process of bubble occurrence and development in hydraulic system, and ignoring the impact of thermal radiation,the heat transfer situation of bubble growth was analyzed under appropriate assumptions of thermodynamic conditions in the bubble generation and development process. The mathematical expression of the temperature change of bubble was deduced using thermodynamic principle. Through combining the expression with classic Rayleigh-Plesset Equation,numerical calculation was carried out and the temperature variation over time( or bubble radius) was obtained. The influences of convective heat transfer coefficient of bubble and polytropic exponent on the thermodynamic process of bubble were analyzed. Finally,the thermal characteristic of bubble growth after cavitation occurrence was summarized.展开更多
The flow past a fixed single transmission conductor and the related heat transfer characteristics are investigated using computational fluid dynamics and a relevant turbulence model.After validating the method through...The flow past a fixed single transmission conductor and the related heat transfer characteristics are investigated using computational fluid dynamics and a relevant turbulence model.After validating the method through comparison with relevant results in the literature,this thermofluid-dynamic problem is addressed considering different working conditions.It is shown that the resistance coefficient depends on the Reynolds number.As expected,the Nusselt number is also affected by Reynolds number.In particular,the Nusselt number under constant heat flux is always greater than that under a constant wall temperature.展开更多
Mineral dissolution and mechanical deformation of granite are two main mechanisms that affect permeability evolution of rock fracture.In this study,two water flow-through experiments with large granite fractures were ...Mineral dissolution and mechanical deformation of granite are two main mechanisms that affect permeability evolution of rock fracture.In this study,two water flow-through experiments with large granite fractures were conducted at 200 0C with a constant flow rate for 24 h,under confining pressures of 5 and 10 MPa,respectively.Water pressure and temperature were measured,fracture aperture and permeability were calculated,and chemical element concentrations in effluent water were tested for mechanism analysis.The permeability fluctuates up and down between 2.62 × 10^(-12)and 3.16 ×10^(-12)m^(2)at confining pressure of 5 MPa;while it decreased monotonously by 24% from 1.92 × 10^(-12)to1.45 × 10^(-12)m^(2)at a confining pressure of 10 MPa.The heat transfer rates at both experiments stay stable at about 0.25 J/s.The mass concentration of Ca,Na,K,and Si in effluent water are between 5 to 23mg/L,indicating slight dissolution of Ca-plagioclase,Na-plagioclase,and K-feldspar,as well as possible precipitation of minor amount of kaolinite or quartz.The total amount of free-face dissolution and pressure dissolution are similar at 5 and 10 MPa.The geochemical reaction counts for only small part of the aperture change,while the mechanical deformation counts the major part of the aperture change.展开更多
Considering utilization of the original chromium-bronze material, two processing techniques including hydraulic expansion and high temperature vacuum welding were proposed for the optimization of heat-sink structure i...Considering utilization of the original chromium-bronze material, two processing techniques including hydraulic expansion and high temperature vacuum welding were proposed for the optimization of heat-sink structure in EAST. The heat transfer performance of heat-sink with or without cooling tube was calculated and different types of connection between tube and heat-sink were compared by conducting a special test. It is shown from numerical analysis that the diameter of heat-sink channel can be reduced from 12 mm to 10 mm. Compared with the original sample, the thermal contact resistance between tube and heat-sink for welding sample can reduce the heat transfer performance by 10%, while by 20% for the hydraulic expansion sample. However, the welding technique is more complicated and expensive than hydraulic expansion technique. Both the processing technique and the heat transfer performance of heat-sink prototype should be further considered for the optimization of heat-sink structure in EAST.展开更多
In order to obtain the suitable phase change material(PCM) with low phase change temperature and improve its heat transfer rate, experimental investigation was conducted. Firstly, different mass ratios of lauric aci...In order to obtain the suitable phase change material(PCM) with low phase change temperature and improve its heat transfer rate, experimental investigation was conducted. Firstly, different mass ratios of lauric acid(LA) and stearic acid(SA) eutectic mixtures were prepared and characterized by differential scanning calorimetry(DSC). Then, the performance of eutectic mixture during charging process under different fin widths in vertical condition, and performance during charging and discharging processes under different inlet temperature heat transfer fluid(HTF) in horizontal condition were investigated, respectively. The results revealed that the LA-SA eutectic mixture had the suitable phase change temperature and desired latent heat for low-temperature water floor heating system. Wide fins and high inlet temperature HTF significantly enhanced the transfer rate and decreased the melting time.展开更多
Development and use of nuclear energy is currently growing very rapidly, in order to achieve increasingly advanced technology, both in terms of design, economic factors and safety factors. Thermal-hydraulics aspects o...Development and use of nuclear energy is currently growing very rapidly, in order to achieve increasingly advanced technology, both in terms of design, economic factors and safety factors. Thermal-hydraulics aspects of nuclear reactors should be done with calculation and near-perfect condition. Including today began development of a nuclear reactor with low power below 300 MW, or commonly called the Small Modular Reactor (SMR). One is CAREM-25 developed by Argentina with a power of 25 MW, where in CAREM already using natural circulation system and the use of nanofluid as coolant fluid. In this research, analytic modeling of thermal-hydraulics nuclear reactor SMR CAREM-25, when the nanofluid Al<sub>2</sub>O<sub>3</sub>-Water used as cooling fluid in the cooling system of a nuclear reactor. Further to this analytic modeling will be done on CFD. Analytic modeling with CFD to determine the flow phenomena and distribution as well as the effect of nano-particles of Al<sub>2</sub>O<sub>3</sub>-Water based on the volume fraction (1% and 3%) of the coefficient of heat transfer by natural convection.展开更多
Phase change materials(PCMs)have remarkable energy storage capacity and promising applications in the field of thermal control of electronic products.The problem of thermal property improvement and heat transfer of PC...Phase change materials(PCMs)have remarkable energy storage capacity and promising applications in the field of thermal control of electronic products.The problem of thermal property improvement and heat transfer of PCMs in metal-foam heatsinks is an important task for thermal management of electronic components.Mixed paraffin samples were prepared by mixing appropriate proportions of paraffin(mass)at various temperatures.Differential scanning calorimetry analysis revealed that the maximum enthalpy of 206.3 J/g is obtained by mixing 20%of 17°C liquid paraffin and 80%of 29℃ solid paraffin.Heating and cooling cycling tests revealed that mixed paraffin exhibits excellent thermal stability and that the regulation method marginally affects thermal stability.Moreover,composites were prepared by embedding PCM into a copper foam by melt impregnation.The thermal conductivity of the composites increased to 4.35 W/(m K),corresponding to 20 times its original value.In addition,density functional theory and experimental results were in good agreement,indicating that the regulation method is practical and effective.展开更多
Compacts of a-Al2O3 and Mo powder were heated in radio-frequency (RF) induced low pressure N2, H2,Ar, and their mixture plasma. An optical pyrometer, a radiation pyrometer, and a system called Accufiber Model310 we...Compacts of a-Al2O3 and Mo powder were heated in radio-frequency (RF) induced low pressure N2, H2,Ar, and their mixture plasma. An optical pyrometer, a radiation pyrometer, and a system called Accufiber Model310 were used to measure the temperature of compacts heated in the plasma. The results indicate that there are different heat transfer mechanisms from plasma to specimens of different physical properties. The Ar plasma showed thehighest heating ability among N2, H2, and Ar plasma for Al2O3 specimens, whereas the H2 plasma could heat Mospecimens to a higher temperature than the Ar plasma did, even under the same generating conditions.展开更多
This paper presents an improved understanding of coupled hydro-thermo-mechanical(HTM) hydraulic fracturing of quasi-brittle rock using the bonded particle model(BPM) within the discrete element method(DEM). BPM has be...This paper presents an improved understanding of coupled hydro-thermo-mechanical(HTM) hydraulic fracturing of quasi-brittle rock using the bonded particle model(BPM) within the discrete element method(DEM). BPM has been recently extended by the authors to account for coupled convective econductive heat flow and transport, and to enable full hydro-thermal fluidesolid coupled modeling.The application of the work is on enhanced geothermal systems(EGSs), and hydraulic fracturing of hot dry rock(HDR) is studied in terms of the impact of temperature difference between rock and a flowing fracturing fluid. Micro-mechanical investigation of temperature and fracturing fluid effects on hydraulic fracturing damage in rocks is presented. It was found that fracture is shorter with pronounced secondary microcracking along the main fracture for the case when the convectiveeconductive thermal heat exchange is considered. First, the convection heat exchange during low-viscosity fluid infiltration in permeable rock around the wellbore causes significant rock cooling, where a finger-like fluid infiltration was observed. Second, fluid infiltration inhibits pressure rise during pumping and delays fracture initiation and propagation. Additionally, thermal damage occurs in the whole area around the wellbore due to rock cooling and cold fluid infiltration. The size of a damaged area around the wellbore increases with decreasing fluid dynamic viscosity. Fluid and rock compressibility ratio was found to have significant effect on the fracture propagation velocity.展开更多
The scientific article examines the physical and mechanical properties of raw cotton stored in buntings in cotton palaces. Because during the storage of raw cotton in bunts, some of its properties deteriorate, some im...The scientific article examines the physical and mechanical properties of raw cotton stored in buntings in cotton palaces. Because during the storage of raw cotton in bunts, some of its properties deteriorate, some improvements. Therefore, the mathematical modeling of storage conditions of raw cotton in bunts and the physical and mechanical conditions that occur in it is of great importance. In the developed mathematical model, the main factor influencing the physical and mechanical properties of raw cotton is the change in temperature. Due to the temperature, kinetic and biological processes accumulated in the raw cotton in Bunt, it can spread over a large surface, first in a small-local state, over time with a nonlinear law. As a result, small changes in temperature lead to a qualitative change in physical properties. In determining the law of temperature distribution in the raw cotton in Bunt, Laplace’s differential equation of heat transfer was used. The differential equation of heat transfer in Laplace’s law was replaced by a system of ordinary differential equations by approximation. Conditions are solved in MAPLE-17 program by numerical method. As a result, graphs of temperature changes over time in raw cotton were obtained. In addition, the table shows the changes in density, pressure and mass of cotton, the height of the bun. As the density of the cotton raw material increases from the top layer of the bunt to the bottom layer, an increase in the temperature in it has been observed. This leads to overheating of the bottom layer of cotton and is the main reason for the deterioration of the quality of raw materials.展开更多
文摘The main objective of this study is the technical optimization of a Shell-and-Tube Heat Exchanger(STHE).In order to do so,a simulation model is introduced that takes into account the related gas-phase circulation.Then,simulation verification experiments are designed in order to validate the model.The results show that the tem-peraturefield undergoes strong variations in time when an inlet wind speed of 6 m/s is considered,while the heat transfer error reaches a minimum of 5.1%.For an inlet velocity of 9 m/s,the heat transfer drops to the lowest point,while the heat transfer error reaches a maximum,i.e.,9.87%.The pressure drop increasesfirst and then decreases with an increase in the wind speed and reaches a maximum of 819 Pa under the 9 m/s wind speed con-dition.Moreover,the pressure drops,and the heat transfer coefficient increases with the Reynolds number.
基金National Natural Science Foundation of China(No.51275123)
文摘Thermal characteristic of cavitation has great influence on the process of occurrence,development and collapse of bubble in hydraulic system. By choosing the stage of bubble growth as the research object,combining with the characteristic of the process of bubble occurrence and development in hydraulic system, and ignoring the impact of thermal radiation,the heat transfer situation of bubble growth was analyzed under appropriate assumptions of thermodynamic conditions in the bubble generation and development process. The mathematical expression of the temperature change of bubble was deduced using thermodynamic principle. Through combining the expression with classic Rayleigh-Plesset Equation,numerical calculation was carried out and the temperature variation over time( or bubble radius) was obtained. The influences of convective heat transfer coefficient of bubble and polytropic exponent on the thermodynamic process of bubble were analyzed. Finally,the thermal characteristic of bubble growth after cavitation occurrence was summarized.
文摘The flow past a fixed single transmission conductor and the related heat transfer characteristics are investigated using computational fluid dynamics and a relevant turbulence model.After validating the method through comparison with relevant results in the literature,this thermofluid-dynamic problem is addressed considering different working conditions.It is shown that the resistance coefficient depends on the Reynolds number.As expected,the Nusselt number is also affected by Reynolds number.In particular,the Nusselt number under constant heat flux is always greater than that under a constant wall temperature.
基金funded by the National Natural Science Foundation of China (Nos. 42072304 and 41702387)The Science and Technology Innovation Program of Hunan Province (2021RC3009)the Natural Science Foundation of Hunan Province (No. 2021JJ40726)。
文摘Mineral dissolution and mechanical deformation of granite are two main mechanisms that affect permeability evolution of rock fracture.In this study,two water flow-through experiments with large granite fractures were conducted at 200 0C with a constant flow rate for 24 h,under confining pressures of 5 and 10 MPa,respectively.Water pressure and temperature were measured,fracture aperture and permeability were calculated,and chemical element concentrations in effluent water were tested for mechanism analysis.The permeability fluctuates up and down between 2.62 × 10^(-12)and 3.16 ×10^(-12)m^(2)at confining pressure of 5 MPa;while it decreased monotonously by 24% from 1.92 × 10^(-12)to1.45 × 10^(-12)m^(2)at a confining pressure of 10 MPa.The heat transfer rates at both experiments stay stable at about 0.25 J/s.The mass concentration of Ca,Na,K,and Si in effluent water are between 5 to 23mg/L,indicating slight dissolution of Ca-plagioclase,Na-plagioclase,and K-feldspar,as well as possible precipitation of minor amount of kaolinite or quartz.The total amount of free-face dissolution and pressure dissolution are similar at 5 and 10 MPa.The geochemical reaction counts for only small part of the aperture change,while the mechanical deformation counts the major part of the aperture change.
文摘Considering utilization of the original chromium-bronze material, two processing techniques including hydraulic expansion and high temperature vacuum welding were proposed for the optimization of heat-sink structure in EAST. The heat transfer performance of heat-sink with or without cooling tube was calculated and different types of connection between tube and heat-sink were compared by conducting a special test. It is shown from numerical analysis that the diameter of heat-sink channel can be reduced from 12 mm to 10 mm. Compared with the original sample, the thermal contact resistance between tube and heat-sink for welding sample can reduce the heat transfer performance by 10%, while by 20% for the hydraulic expansion sample. However, the welding technique is more complicated and expensive than hydraulic expansion technique. Both the processing technique and the heat transfer performance of heat-sink prototype should be further considered for the optimization of heat-sink structure in EAST.
基金Funded by the Key Project of National Natural Science Foundation of China(No.51432007)the National Key Research and Development Program of China(No.2016 YFC0700201)+1 种基金the Science,Technology Support Program of Hubei Province(Nos.2014BAA134 and 2015BAA107)the Postdoctoral Fund of China(2017M612629)
文摘In order to obtain the suitable phase change material(PCM) with low phase change temperature and improve its heat transfer rate, experimental investigation was conducted. Firstly, different mass ratios of lauric acid(LA) and stearic acid(SA) eutectic mixtures were prepared and characterized by differential scanning calorimetry(DSC). Then, the performance of eutectic mixture during charging process under different fin widths in vertical condition, and performance during charging and discharging processes under different inlet temperature heat transfer fluid(HTF) in horizontal condition were investigated, respectively. The results revealed that the LA-SA eutectic mixture had the suitable phase change temperature and desired latent heat for low-temperature water floor heating system. Wide fins and high inlet temperature HTF significantly enhanced the transfer rate and decreased the melting time.
文摘Development and use of nuclear energy is currently growing very rapidly, in order to achieve increasingly advanced technology, both in terms of design, economic factors and safety factors. Thermal-hydraulics aspects of nuclear reactors should be done with calculation and near-perfect condition. Including today began development of a nuclear reactor with low power below 300 MW, or commonly called the Small Modular Reactor (SMR). One is CAREM-25 developed by Argentina with a power of 25 MW, where in CAREM already using natural circulation system and the use of nanofluid as coolant fluid. In this research, analytic modeling of thermal-hydraulics nuclear reactor SMR CAREM-25, when the nanofluid Al<sub>2</sub>O<sub>3</sub>-Water used as cooling fluid in the cooling system of a nuclear reactor. Further to this analytic modeling will be done on CFD. Analytic modeling with CFD to determine the flow phenomena and distribution as well as the effect of nano-particles of Al<sub>2</sub>O<sub>3</sub>-Water based on the volume fraction (1% and 3%) of the coefficient of heat transfer by natural convection.
基金supported by the National Natural Science Foundation of China(Grant No.51976126)the Natural Science Foundation of Shanghai(Grant Nos.22ZR1442700,22WZ2503100,and 20ZR1438600)Shanghai Municipal Science and Technology Committee of Shanghai Outstanding Academic Leaders Plan(Grant No.21XD1402400)。
文摘Phase change materials(PCMs)have remarkable energy storage capacity and promising applications in the field of thermal control of electronic products.The problem of thermal property improvement and heat transfer of PCMs in metal-foam heatsinks is an important task for thermal management of electronic components.Mixed paraffin samples were prepared by mixing appropriate proportions of paraffin(mass)at various temperatures.Differential scanning calorimetry analysis revealed that the maximum enthalpy of 206.3 J/g is obtained by mixing 20%of 17°C liquid paraffin and 80%of 29℃ solid paraffin.Heating and cooling cycling tests revealed that mixed paraffin exhibits excellent thermal stability and that the regulation method marginally affects thermal stability.Moreover,composites were prepared by embedding PCM into a copper foam by melt impregnation.The thermal conductivity of the composites increased to 4.35 W/(m K),corresponding to 20 times its original value.In addition,density functional theory and experimental results were in good agreement,indicating that the regulation method is practical and effective.
文摘Compacts of a-Al2O3 and Mo powder were heated in radio-frequency (RF) induced low pressure N2, H2,Ar, and their mixture plasma. An optical pyrometer, a radiation pyrometer, and a system called Accufiber Model310 were used to measure the temperature of compacts heated in the plasma. The results indicate that there are different heat transfer mechanisms from plasma to specimens of different physical properties. The Ar plasma showed thehighest heating ability among N2, H2, and Ar plasma for Al2O3 specimens, whereas the H2 plasma could heat Mospecimens to a higher temperature than the Ar plasma did, even under the same generating conditions.
基金Financial support provided by the U.S. Department of Energy under DOE Grant No. DE-FE0002760
文摘This paper presents an improved understanding of coupled hydro-thermo-mechanical(HTM) hydraulic fracturing of quasi-brittle rock using the bonded particle model(BPM) within the discrete element method(DEM). BPM has been recently extended by the authors to account for coupled convective econductive heat flow and transport, and to enable full hydro-thermal fluidesolid coupled modeling.The application of the work is on enhanced geothermal systems(EGSs), and hydraulic fracturing of hot dry rock(HDR) is studied in terms of the impact of temperature difference between rock and a flowing fracturing fluid. Micro-mechanical investigation of temperature and fracturing fluid effects on hydraulic fracturing damage in rocks is presented. It was found that fracture is shorter with pronounced secondary microcracking along the main fracture for the case when the convectiveeconductive thermal heat exchange is considered. First, the convection heat exchange during low-viscosity fluid infiltration in permeable rock around the wellbore causes significant rock cooling, where a finger-like fluid infiltration was observed. Second, fluid infiltration inhibits pressure rise during pumping and delays fracture initiation and propagation. Additionally, thermal damage occurs in the whole area around the wellbore due to rock cooling and cold fluid infiltration. The size of a damaged area around the wellbore increases with decreasing fluid dynamic viscosity. Fluid and rock compressibility ratio was found to have significant effect on the fracture propagation velocity.
文摘The scientific article examines the physical and mechanical properties of raw cotton stored in buntings in cotton palaces. Because during the storage of raw cotton in bunts, some of its properties deteriorate, some improvements. Therefore, the mathematical modeling of storage conditions of raw cotton in bunts and the physical and mechanical conditions that occur in it is of great importance. In the developed mathematical model, the main factor influencing the physical and mechanical properties of raw cotton is the change in temperature. Due to the temperature, kinetic and biological processes accumulated in the raw cotton in Bunt, it can spread over a large surface, first in a small-local state, over time with a nonlinear law. As a result, small changes in temperature lead to a qualitative change in physical properties. In determining the law of temperature distribution in the raw cotton in Bunt, Laplace’s differential equation of heat transfer was used. The differential equation of heat transfer in Laplace’s law was replaced by a system of ordinary differential equations by approximation. Conditions are solved in MAPLE-17 program by numerical method. As a result, graphs of temperature changes over time in raw cotton were obtained. In addition, the table shows the changes in density, pressure and mass of cotton, the height of the bun. As the density of the cotton raw material increases from the top layer of the bunt to the bottom layer, an increase in the temperature in it has been observed. This leads to overheating of the bottom layer of cotton and is the main reason for the deterioration of the quality of raw materials.