Detached eddy simulation(DES)model was used to better capture large vortex structure and unsteady flow feature near cone base.Good base heating results were achieved using proper grid and numerical method.The influenc...Detached eddy simulation(DES)model was used to better capture large vortex structure and unsteady flow feature near cone base.Good base heating results were achieved using proper grid and numerical method.The influence of inflow conditions(like Mach number,Reynolds number)and configuration(bluntness ratio of the cone)on base heating was discussed based on numerical computational results.Compared with base heat flux,base pressure can be predicted more accurately by numerical simulation and the time consuming was shorter.A hybrid method combining numerical simulation with experimental correlation was proposed to predict supersonic turbulent base heating.A review of base heating experiment and correlations for slender cone was presented,and a revised correlation was proposed based on the above simulation results.Compared with the experiment data,the maximum error was 24%,agood result for base heating prediction.This proves that the hybrid method using the revised correlation performs well in predicting supersonic turbulent base heating of slender sphere cone and can meet needs of engineering design.展开更多
The cooling rate of the center and edge of vacuum induction melting(VIM)or vacuum arc remelting(VAR)ingots exhibit substantial difference,leading to markedly distinct dendritic structures and precipitates.The current ...The cooling rate of the center and edge of vacuum induction melting(VIM)or vacuum arc remelting(VAR)ingots exhibit substantial difference,leading to markedly distinct dendritic structures and precipitates.The current lack of precise predictions for dendritic segregation and the distribution of precipitates in ingot makes it difficult to determine the annealing and homogenization heat treatment process.Thus,clarifying the impact of cooling rate on the solidification behavior of alloy is significantly important.The dendritic structure and precipitation characteristics of as-cast C-HRA-3 Ni–Cr–Co–Mo-based heat-resistant alloy were investigated using Thermo-Calc thermodynamic calculations,scanning electron microscopy observations,and electron probe microanalyzer.Based on high temperature observation system,the effects of cooling rate on the dendritic structure,dendritic segregation,and precipitation in this alloy were explored.The results showed that the precipitates in the as-cast C-HRA-3 alloy primarily consist of blocky Ti(C,N)phases,large-sized Ti(C,N)–M_(6)C–M_(23)C_(6) symbiotic phases and M_(6)C–M_(23)C_(6) carbides,and small-sized dispersed M_(6)C and M_(23)C_(6) carbides surronding these symbiotic phases.The primary constituent elements of these precipitates are Mo,Cr,C,and Ti,which predominantly concentrate in the interdendritic regions of the as-cast alloy.There is a clear power-law relationship between the secondary dendrite arm spacing and the cooling rate.The dendritic segregation ratio of Mo,Cr,and Ti exhibits a piecewise functional relationship with the cooling rate,under equiaxed dendritic solidification condition.These predictive models and theoretical analyses were validated using numerical simulations and experimental results from the 200 kg grade VIM electrode.展开更多
We investigate the thermal characteristics of standard organic light-emitting diodes （OLEDs） using a simple and clear 1D thermal model based on the basic heat transfer theory. The thermal model can accurately estima...We investigate the thermal characteristics of standard organic light-emitting diodes （OLEDs） using a simple and clear 1D thermal model based on the basic heat transfer theory. The thermal model can accurately estimate the device temperature, which is linearly with electrical input power. The simulation results show that there is almost no temperature gradient within the OLED device working under steady state conditions. Furthermore, thermal analysis simulation results show that the surface properties （convective heat transfer coetficient and surface emissivity） of the substrate or cathode can significantly affect the temperature distribution of the OLED.展开更多
Convective heating of the rocket base caused by high-temperature reverse flow has long been a focus of thermal protection research.With distinctive structural characteristics,the base thermal environment of a twin-noz...Convective heating of the rocket base caused by high-temperature reverse flow has long been a focus of thermal protection research.With distinctive structural characteristics,the base thermal environment of a twin-nozzle engine proves more susceptible to the recirculation region than its multi-nozzle counterparts.During the transonic stage,significant alterations in the flow field structure at the rocket base strongly influence the recirculation region.This study investigated the thermal environment of the rocket base with a twin-nozzle configuration in freestream at Mach numbers of 0.6 to 3.0.Results indicate that the freestream Mach number significantly affects the thermal environment at the rocket base during the transonic stage.The increase of Mach number from 0.6 to 1.0 causes the convective heating of the rocket base to increase by 7.7 times.This phenomenon arises due to the plume-induced shock wave caused by the impact of the supersonic free shear layer and plume shear layer while the flight speed exceeds the sound speed.The interaction between the shock wave and the shear layer amplifies turbulence in the recirculation region and at the inflection point,resulting in a stronger high-temperature reverse flow.In addition,the cause of low-altitude base heating was analyzed,and it was found that the mechanism is different from the high-temperature countercurrent effect caused by plume interaction.展开更多
Various designs have been introduced to build heat pumps using the electrocaloric effect (ECE). Each of all the curent designs usesat least one moving part, which significantly reduces the reliability of the pump and ...Various designs have been introduced to build heat pumps using the electrocaloric effect (ECE). Each of all the curent designs usesat least one moving part, which significantly reduces the reliability of the pump and adds complexities. In this work, a new all-soliddesign is introduced, in which two layers of an electrocaloric material (ECM) are permanently sandwiched in the source and sink,which would significantly increase the device's reliability since nothing moves and all are permanently bound together. Moreimportantly, the electric fields applied on two ECM layers are independently controlled. A special sequence for the electric fields on .two ECM layers is introduced. Numerical calculation was used to simlulate the device's performance by using the newly introducedanalytical solutions for the heat conduction in the system. It is concluded that a continuous heat transformation from the source tosink at the same temperature can be achieved when the contacting cofficient, K_(ε)=√(k^(c)p^(c)c^(c)_(p))/(k^(o)p^(o)c^(o)_(p)), is very small, where k,ρ, and Cp are thermal conductivity, density, and heat capacity, respectively, while the superscript c and 0 represent the ECM andsource/sink, respectively.展开更多
基金National Natural Science Foundation of China(11302016)
文摘Detached eddy simulation(DES)model was used to better capture large vortex structure and unsteady flow feature near cone base.Good base heating results were achieved using proper grid and numerical method.The influence of inflow conditions(like Mach number,Reynolds number)and configuration(bluntness ratio of the cone)on base heating was discussed based on numerical computational results.Compared with base heat flux,base pressure can be predicted more accurately by numerical simulation and the time consuming was shorter.A hybrid method combining numerical simulation with experimental correlation was proposed to predict supersonic turbulent base heating.A review of base heating experiment and correlations for slender cone was presented,and a revised correlation was proposed based on the above simulation results.Compared with the experiment data,the maximum error was 24%,agood result for base heating prediction.This proves that the hybrid method using the revised correlation performs well in predicting supersonic turbulent base heating of slender sphere cone and can meet needs of engineering design.
基金funded by the National Key R&D Program Funded Projects(No.2021YFB3704102).
文摘The cooling rate of the center and edge of vacuum induction melting(VIM)or vacuum arc remelting(VAR)ingots exhibit substantial difference,leading to markedly distinct dendritic structures and precipitates.The current lack of precise predictions for dendritic segregation and the distribution of precipitates in ingot makes it difficult to determine the annealing and homogenization heat treatment process.Thus,clarifying the impact of cooling rate on the solidification behavior of alloy is significantly important.The dendritic structure and precipitation characteristics of as-cast C-HRA-3 Ni–Cr–Co–Mo-based heat-resistant alloy were investigated using Thermo-Calc thermodynamic calculations,scanning electron microscopy observations,and electron probe microanalyzer.Based on high temperature observation system,the effects of cooling rate on the dendritic structure,dendritic segregation,and precipitation in this alloy were explored.The results showed that the precipitates in the as-cast C-HRA-3 alloy primarily consist of blocky Ti(C,N)phases,large-sized Ti(C,N)–M_(6)C–M_(23)C_(6) symbiotic phases and M_(6)C–M_(23)C_(6) carbides,and small-sized dispersed M_(6)C and M_(23)C_(6) carbides surronding these symbiotic phases.The primary constituent elements of these precipitates are Mo,Cr,C,and Ti,which predominantly concentrate in the interdendritic regions of the as-cast alloy.There is a clear power-law relationship between the secondary dendrite arm spacing and the cooling rate.The dendritic segregation ratio of Mo,Cr,and Ti exhibits a piecewise functional relationship with the cooling rate,under equiaxed dendritic solidification condition.These predictive models and theoretical analyses were validated using numerical simulations and experimental results from the 200 kg grade VIM electrode.
基金Supported by the National Natural Science Foundation of China under Grant No 11304247the Shaanxi Provincial Research Plan for Young Scientific and Technological New Stars(No 2015KJXX-40)the Youth Foundation of Xi’an University of Post&Telecommunication under Grant Nos 1011215 and 1010473
文摘We investigate the thermal characteristics of standard organic light-emitting diodes （OLEDs） using a simple and clear 1D thermal model based on the basic heat transfer theory. The thermal model can accurately estimate the device temperature, which is linearly with electrical input power. The simulation results show that there is almost no temperature gradient within the OLED device working under steady state conditions. Furthermore, thermal analysis simulation results show that the surface properties （convective heat transfer coetficient and surface emissivity） of the substrate or cathode can significantly affect the temperature distribution of the OLED.
基金supported by the Outstanding Research Project of Shen Yuan Honors CollegeAcademic Excellence Foundation of BUAA for PhD StudentsNational Key Laboratory of aerospace liquid propulsion
文摘Convective heating of the rocket base caused by high-temperature reverse flow has long been a focus of thermal protection research.With distinctive structural characteristics,the base thermal environment of a twin-nozzle engine proves more susceptible to the recirculation region than its multi-nozzle counterparts.During the transonic stage,significant alterations in the flow field structure at the rocket base strongly influence the recirculation region.This study investigated the thermal environment of the rocket base with a twin-nozzle configuration in freestream at Mach numbers of 0.6 to 3.0.Results indicate that the freestream Mach number significantly affects the thermal environment at the rocket base during the transonic stage.The increase of Mach number from 0.6 to 1.0 causes the convective heating of the rocket base to increase by 7.7 times.This phenomenon arises due to the plume-induced shock wave caused by the impact of the supersonic free shear layer and plume shear layer while the flight speed exceeds the sound speed.The interaction between the shock wave and the shear layer amplifies turbulence in the recirculation region and at the inflection point,resulting in a stronger high-temperature reverse flow.In addition,the cause of low-altitude base heating was analyzed,and it was found that the mechanism is different from the high-temperature countercurrent effect caused by plume interaction.
文摘Various designs have been introduced to build heat pumps using the electrocaloric effect (ECE). Each of all the curent designs usesat least one moving part, which significantly reduces the reliability of the pump and adds complexities. In this work, a new all-soliddesign is introduced, in which two layers of an electrocaloric material (ECM) are permanently sandwiched in the source and sink,which would significantly increase the device's reliability since nothing moves and all are permanently bound together. Moreimportantly, the electric fields applied on two ECM layers are independently controlled. A special sequence for the electric fields on .two ECM layers is introduced. Numerical calculation was used to simlulate the device's performance by using the newly introducedanalytical solutions for the heat conduction in the system. It is concluded that a continuous heat transformation from the source tosink at the same temperature can be achieved when the contacting cofficient, K_(ε)=√(k^(c)p^(c)c^(c)_(p))/(k^(o)p^(o)c^(o)_(p)), is very small, where k,ρ, and Cp are thermal conductivity, density, and heat capacity, respectively, while the superscript c and 0 represent the ECM andsource/sink, respectively.
