A mathematical model was developed to predict the maximum heat transfer capacity of high temperature heat pipe with triangular grooved wick. The effects of the inclination angle and geometry structure were considered ...A mathematical model was developed to predict the maximum heat transfer capacity of high temperature heat pipe with triangular grooved wick. The effects of the inclination angle and geometry structure were considered in the proposed model.Maximum heat transfer capacity was also investigated experimentally. The model was validated by comparing with the experimental results. The maximum heat transfer capacity increases with the vapor core radius increasing. Compared with the inclination angle of0°, the maximum heat transfer capacity increases at the larger inclination angle, and the change with temperature is larger. The performance of heat pipe with triangular grooved wick is greatly influenced by gravity, so it is not recommended to be applied to the dish solar heat pipe receiver.展开更多
This investigation numerically examined the combined impacts of different turbulator shapes,Al_(2)O_(3)/water nanofluid,and inclined magnetic field on the thermal behavior of micro-scale inclined forward-facing step(M...This investigation numerically examined the combined impacts of different turbulator shapes,Al_(2)O_(3)/water nanofluid,and inclined magnetic field on the thermal behavior of micro-scale inclined forward-facing step(MSIFFS).The length and height for all turbulators were considered 0.0979 and 0.5 mm,respectively,and the Reynolds number varied from 5000 to 10000.In order to compare the skin friction coefficient(SFC) and the heat transfer rate(HTR)simultaneously,the thermal performance factor parameter(TPF) was selected.The results show that all considered cases equipped with turbulators were thermodynamically more advantageous over the simple MSIFFS.Besides,using Al_(2)O_(3)/water nanofluid with different nanoparticles volume fractions(NVF) in the presence of inclined magnetic field(IMF)increased HTR.With an increment of NVF from 1% to 4% and magnetic field density(MFD) from 0.002 to 0.008 T,HTR and subsequently TPF improved.The best result was observed for MSIFFS equipped with a trapezoidal-shaped turbulator with 4% Al_(2)O_(3) in the presence of IMF(B=0.008 T).The TPF increased with the augmentation of Re,and the maximum value of it was 5.2366 for MSIFFS equipped with a trapezoidal-shaped turbulator with 4% Al_(2)O_(3),B=0.008 T,and Re=10000.展开更多
Flame is prone to lose its stability in micro-combustors due to the large amount of heat loss from the external walls. On the other hand, heat recirculation through the upstream combustor walls can enhance flame stabi...Flame is prone to lose its stability in micro-combustors due to the large amount of heat loss from the external walls. On the other hand, heat recirculation through the upstream combustor walls can enhance flame stability. These two aspects depend on the structural heat transfer, which is associated with the thickness and thermal conductivity of the combustor walls. In the present study, the effects of wall thickness and material on flame stability were numerically investigated by selecting two thicknesses (δ=0.2 and 0.4 mm) and two materials (quartz and SiC). The results show that when δ=0.2 mm, flame inclination occurs at a certain inlet velocity in both combustors, but it happens later in SiC combustor. For δ=0.4 mm, flame inclination still occurs in quartz combustor from a larger inlet velocity compared to the case of δ=0.2 mm. However, flame inclination in SiC combustor with δ=0.4 mm does not happen and it has a much larger blowout limit. Analysis reveals that a thicker wall can enhance heat recirculation and reduce heat loss simultaneously. Moreover, SiC combustor has larger heat recirculation ratio and smaller heat loss ratio. In summary, the micro-combustor with thicker and more conductive walls can harvest large flame stability limit.展开更多
基金Project(51076062)supported by the National Natural Science Foundation of China
文摘A mathematical model was developed to predict the maximum heat transfer capacity of high temperature heat pipe with triangular grooved wick. The effects of the inclination angle and geometry structure were considered in the proposed model.Maximum heat transfer capacity was also investigated experimentally. The model was validated by comparing with the experimental results. The maximum heat transfer capacity increases with the vapor core radius increasing. Compared with the inclination angle of0°, the maximum heat transfer capacity increases at the larger inclination angle, and the change with temperature is larger. The performance of heat pipe with triangular grooved wick is greatly influenced by gravity, so it is not recommended to be applied to the dish solar heat pipe receiver.
文摘This investigation numerically examined the combined impacts of different turbulator shapes,Al_(2)O_(3)/water nanofluid,and inclined magnetic field on the thermal behavior of micro-scale inclined forward-facing step(MSIFFS).The length and height for all turbulators were considered 0.0979 and 0.5 mm,respectively,and the Reynolds number varied from 5000 to 10000.In order to compare the skin friction coefficient(SFC) and the heat transfer rate(HTR)simultaneously,the thermal performance factor parameter(TPF) was selected.The results show that all considered cases equipped with turbulators were thermodynamically more advantageous over the simple MSIFFS.Besides,using Al_(2)O_(3)/water nanofluid with different nanoparticles volume fractions(NVF) in the presence of inclined magnetic field(IMF)increased HTR.With an increment of NVF from 1% to 4% and magnetic field density(MFD) from 0.002 to 0.008 T,HTR and subsequently TPF improved.The best result was observed for MSIFFS equipped with a trapezoidal-shaped turbulator with 4% Al_(2)O_(3) in the presence of IMF(B=0.008 T).The TPF increased with the augmentation of Re,and the maximum value of it was 5.2366 for MSIFFS equipped with a trapezoidal-shaped turbulator with 4% Al_(2)O_(3),B=0.008 T,and Re=10000.
基金Project(51576084) supported by the National Natural Science Foundation of China
文摘Flame is prone to lose its stability in micro-combustors due to the large amount of heat loss from the external walls. On the other hand, heat recirculation through the upstream combustor walls can enhance flame stability. These two aspects depend on the structural heat transfer, which is associated with the thickness and thermal conductivity of the combustor walls. In the present study, the effects of wall thickness and material on flame stability were numerically investigated by selecting two thicknesses (δ=0.2 and 0.4 mm) and two materials (quartz and SiC). The results show that when δ=0.2 mm, flame inclination occurs at a certain inlet velocity in both combustors, but it happens later in SiC combustor. For δ=0.4 mm, flame inclination still occurs in quartz combustor from a larger inlet velocity compared to the case of δ=0.2 mm. However, flame inclination in SiC combustor with δ=0.4 mm does not happen and it has a much larger blowout limit. Analysis reveals that a thicker wall can enhance heat recirculation and reduce heat loss simultaneously. Moreover, SiC combustor has larger heat recirculation ratio and smaller heat loss ratio. In summary, the micro-combustor with thicker and more conductive walls can harvest large flame stability limit.
