A hybrid identification model based on multilayer artificial neural networks(ANNs) and particle swarm optimization(PSO) algorithm is developed to improve the simultaneous identification efficiency of thermal conductiv...A hybrid identification model based on multilayer artificial neural networks(ANNs) and particle swarm optimization(PSO) algorithm is developed to improve the simultaneous identification efficiency of thermal conductivity and effective absorption coefficient of semitransparent materials.For the direct model,the spherical harmonic method and the finite volume method are used to solve the coupled conduction-radiation heat transfer problem in an absorbing,emitting,and non-scattering 2D axisymmetric gray medium in the background of laser flash method.For the identification part,firstly,the temperature field and the incident radiation field in different positions are chosen as observables.Then,a traditional identification model based on PSO algorithm is established.Finally,multilayer ANNs are built to fit and replace the direct model in the traditional identification model to speed up the identification process.The results show that compared with the traditional identification model,the time cost of the hybrid identification model is reduced by about 1 000 times.Besides,the hybrid identification model remains a high level of accuracy even with measurement errors.展开更多
A detailed numerical modeling is performed to investigate heat transfer in high-porous, high-temperature non-gray semitransparent silica insulation materials. Radiation between fibers, conduction within fibers and con...A detailed numerical modeling is performed to investigate heat transfer in high-porous, high-temperature non-gray semitransparent silica insulation materials. Radiation between fibers, conduction within fibers and convection from the fibers to the surrounding fluid are considered. Macroscopic (porous media) modeling is used to determine the velocity, pressure and temperatures fields for fibrous insulation with a random packing geometry under natural convection. Based on a non-gray application of the solution to the radiative transfer equation, the value of the refractive index(n,m)is used to generate macroscopic average radiative properties such as extinction coefficient, scattering albedo and phase function. Key features of the macroscopic model include two-dimensional effects,non-gray radiative exchange, and the relaxation of the local thermodynamic non-equilibrium. The effectiveness of this numerical model is validated by the previous experimental data.展开更多
The objective of the present work is to model the magnetohydrodynamic(MHD) three dimensional flow of viscoelastic fluid passing a stretching surface. Heat transfer analysis is carried out in the presence of variable t...The objective of the present work is to model the magnetohydrodynamic(MHD) three dimensional flow of viscoelastic fluid passing a stretching surface. Heat transfer analysis is carried out in the presence of variable thermal conductivity and thermal radiation. Arising nonlinear analysis for velocity and temperature is computed. Discussion to importantly involved parameters through plots is presented. Comparison between present and previous limiting solutions is shown. Numerical values of local Nusselt number are computed and analyzed. It can be observed that the effects of viscoelastic parameter and Hartman number on the temperature profile are similar in a qualitative way. The variations in temperature are more pronounced for viscoelastic parameter K in comparison to the Hartman number M. The parameters N and ε give rise to the temperature. It is interesting to note that values of local Nusselt number are smaller for the larger values of ε.展开更多
It is promising to simultaneously develop multiple products through the combined utilization of seawater by solar chimney technology. A small scale experimental system was set up. The collector temperature, the seawat...It is promising to simultaneously develop multiple products through the combined utilization of seawater by solar chimney technology. A small scale experimental system was set up. The collector temperature, the seawater temperature, and the temperature and humidity of the airflow under the collector were measured. Thermal network analysis of the system was carried out. The results show that the airflow is nearly saturated at the entrance of the chimney, and the mean dry-bulb and wet-bulb temperatures of the airflow have increased by 8.4 ℃ and 9.6 ℃, respectively. The radiation heat transfer between the collector and the sky is the biggest heat loss in the system, which is up to 29.1% on average of the solar energy. However, the water evaporation heat is about 23.6% on average of the solar energy. To reduce the heat loss and enhance the water evaporation, it is necessary to reduce the emissivity and thermal conductivity of the collector and increase the evaporation areas.展开更多
Normal skylights bring light into the spaces located below them. By the use of IR （infrared radiation） transmissive polymer films and IR-emitting and absorbing gases, an advanced version of the skylight may supply p...Normal skylights bring light into the spaces located below them. By the use of IR （infrared radiation） transmissive polymer films and IR-emitting and absorbing gases, an advanced version of the skylight may supply passive cooling and thermal insulation to the room located below it. This novel radiative skylight can, in its cooling mode, lead heat from the room below, to the cool skies located above the skylight. When cooling is no longer needed or attainable, the skylight will in its cooling mode provide the room with an optimal amount of thermal resistance. This article is a progress reporting on the modeling of the skylight. The main work is done to combine the different heat transfer methods into one single model by the use of the commercial program Comsol 4.1. The results show that a cooling effect of 100 W/ma is achievable when the skylight is compared with a similar skylight containing only air.展开更多
基金supported by the Fundamental Research Funds for the Central Universities (No.3122020072)the Multi-investment Project of Tianjin Applied Basic Research(No.23JCQNJC00250)。
文摘A hybrid identification model based on multilayer artificial neural networks(ANNs) and particle swarm optimization(PSO) algorithm is developed to improve the simultaneous identification efficiency of thermal conductivity and effective absorption coefficient of semitransparent materials.For the direct model,the spherical harmonic method and the finite volume method are used to solve the coupled conduction-radiation heat transfer problem in an absorbing,emitting,and non-scattering 2D axisymmetric gray medium in the background of laser flash method.For the identification part,firstly,the temperature field and the incident radiation field in different positions are chosen as observables.Then,a traditional identification model based on PSO algorithm is established.Finally,multilayer ANNs are built to fit and replace the direct model in the traditional identification model to speed up the identification process.The results show that compared with the traditional identification model,the time cost of the hybrid identification model is reduced by about 1 000 times.Besides,the hybrid identification model remains a high level of accuracy even with measurement errors.
文摘A detailed numerical modeling is performed to investigate heat transfer in high-porous, high-temperature non-gray semitransparent silica insulation materials. Radiation between fibers, conduction within fibers and convection from the fibers to the surrounding fluid are considered. Macroscopic (porous media) modeling is used to determine the velocity, pressure and temperatures fields for fibrous insulation with a random packing geometry under natural convection. Based on a non-gray application of the solution to the radiative transfer equation, the value of the refractive index(n,m)is used to generate macroscopic average radiative properties such as extinction coefficient, scattering albedo and phase function. Key features of the macroscopic model include two-dimensional effects,non-gray radiative exchange, and the relaxation of the local thermodynamic non-equilibrium. The effectiveness of this numerical model is validated by the previous experimental data.
基金supported by the Deanship of Scientific Research (DSR) of King Abdulaziz University, Jeddah, Saudi Arabia
文摘The objective of the present work is to model the magnetohydrodynamic(MHD) three dimensional flow of viscoelastic fluid passing a stretching surface. Heat transfer analysis is carried out in the presence of variable thermal conductivity and thermal radiation. Arising nonlinear analysis for velocity and temperature is computed. Discussion to importantly involved parameters through plots is presented. Comparison between present and previous limiting solutions is shown. Numerical values of local Nusselt number are computed and analyzed. It can be observed that the effects of viscoelastic parameter and Hartman number on the temperature profile are similar in a qualitative way. The variations in temperature are more pronounced for viscoelastic parameter K in comparison to the Hartman number M. The parameters N and ε give rise to the temperature. It is interesting to note that values of local Nusselt number are smaller for the larger values of ε.
基金Supported by Tianjin Technological Development Program Project of China (No05YFGZSF02800 and No06YFSZSF04600)the Key Research Program of the National Eleventh Five-Year Plan of China (No 2006BAA04B03-03)
文摘It is promising to simultaneously develop multiple products through the combined utilization of seawater by solar chimney technology. A small scale experimental system was set up. The collector temperature, the seawater temperature, and the temperature and humidity of the airflow under the collector were measured. Thermal network analysis of the system was carried out. The results show that the airflow is nearly saturated at the entrance of the chimney, and the mean dry-bulb and wet-bulb temperatures of the airflow have increased by 8.4 ℃ and 9.6 ℃, respectively. The radiation heat transfer between the collector and the sky is the biggest heat loss in the system, which is up to 29.1% on average of the solar energy. However, the water evaporation heat is about 23.6% on average of the solar energy. To reduce the heat loss and enhance the water evaporation, it is necessary to reduce the emissivity and thermal conductivity of the collector and increase the evaporation areas.
文摘Normal skylights bring light into the spaces located below them. By the use of IR （infrared radiation） transmissive polymer films and IR-emitting and absorbing gases, an advanced version of the skylight may supply passive cooling and thermal insulation to the room located below it. This novel radiative skylight can, in its cooling mode, lead heat from the room below, to the cool skies located above the skylight. When cooling is no longer needed or attainable, the skylight will in its cooling mode provide the room with an optimal amount of thermal resistance. This article is a progress reporting on the modeling of the skylight. The main work is done to combine the different heat transfer methods into one single model by the use of the commercial program Comsol 4.1. The results show that a cooling effect of 100 W/ma is achievable when the skylight is compared with a similar skylight containing only air.
