本文将我们在前文中提出的修正van der Waals模型,推广到了液态聚合物中,从而建立了一个能在宽阔温度范围内准确计算聚合物热压力系数的关系式γ=RMv/(Mv)~2-AMv+0.2535A^2式中v和M分别为聚合物的比体积和链节的摩尔质量,A为聚合物的特...本文将我们在前文中提出的修正van der Waals模型,推广到了液态聚合物中,从而建立了一个能在宽阔温度范围内准确计算聚合物热压力系数的关系式γ=RMv/(Mv)~2-AMv+0.2535A^2式中v和M分别为聚合物的比体积和链节的摩尔质量,A为聚合物的特性常数.对于本文考察的五种聚合物,发现它们的链节大小均为聚合物的三个结构单元.展开更多
本文测定25～85℃温度范围内正戊醇、正己醇、正庚醇和正辛醇的热压力系数,发现这些醇类液体的内压几乎不随温度而变.本文还将修正的van der Waals模型推广到了醇类液体,与非缔合液体一样,它们的排斥体积亦与密度呈线性关系.但是,模型...本文测定25～85℃温度范围内正戊醇、正己醇、正庚醇和正辛醇的热压力系数,发现这些醇类液体的内压几乎不随温度而变.本文还将修正的van der Waals模型推广到了醇类液体,与非缔合液体一样,它们的排斥体积亦与密度呈线性关系.但是,模型参数之比B/A^2不再是个常数,而是随醇分子中碳原子数的增多而快速地减小,这个比值可作为自缔合能力的一种量度.展开更多
利用实验测得的液体的热压力系数,修正原始van der Waals模型中的排斥体积,得到了一个适用于高密度流体的推广的van der Waals压缩因子。将它与Redlich和Kwong提出的吸引项相结合,建立了一个流体状态方程。用某些有代表性的超临界流体的...利用实验测得的液体的热压力系数,修正原始van der Waals模型中的排斥体积,得到了一个适用于高密度流体的推广的van der Waals压缩因子。将它与Redlich和Kwong提出的吸引项相结合,建立了一个流体状态方程。用某些有代表性的超临界流体的pVT数据检验,结果表明,其对体积、压力和逸度系数的计算准确度可与CS-RK方程相媲美。展开更多
A mathematical model of principal elements of the aircraft hydraulic system is presented based on the heat transfer theory. The dynamic heat transfer process of the hydraulic oil and the pump shells within an aircraft...A mathematical model of principal elements of the aircraft hydraulic system is presented based on the heat transfer theory. The dynamic heat transfer process of the hydraulic oil and the pump shells within an aircraft hydraulic system are analyzed by the difference method. A kind of means for the prediction to variational trends of the aircraft hydraulic system temperature is provided during operation. The numerical prediction and simulation under the operational conditions are presented for ground trial running and the decelerated operation in flight. Computational results show that there is a good coincidence between the experimental data and the numerical predictions.展开更多
The paper presents an experimental investigation on enhanced heat transfer and pressure loss characteristics by using single, double, triple, and quadruple twisted-tape inserts in a round tube having a uniform heat-fl...The paper presents an experimental investigation on enhanced heat transfer and pressure loss characteristics by using single, double, triple, and quadruple twisted-tape inserts in a round tube having a uniform heat-fluxed wall. The investigation has been conducted in the heat exchanger tube inserted with various twisted-tape numbers for co- and counter-twist arrangements for the turbulent air flow, Reynolds number （Re） from 5300 to 24000. The typical single twisted-tape inserts at two twist ratios, y/w = 4 and 5, are used as the base case, while the other multiple twisted-tape inserts are aty/w = 4 only. The experimental results of heat transfer and pressure drop in terms of Nusselt number （Nu） and friction factor 00, respectively, reveal that Nu increases with the increment of Re and of twisted-tape number. The values of Nu for the inserted tube are in a range of 1.15-2.12 times that for the plain tube while f is 1.9-4.1 times. The thermal enhancement factor of the inserted tube under similar pumping power is evaluated and found to be above unity except for the single and the double co-twisted tapes. The quadruple counter-twisted tape insert provides the maximum thermal performance.展开更多
Boiling of water/triethyleneglycol(TEG)binary solution has a wide-ranging application in the gas processing engineering.Design,operation and optimization of the involved boilers require accurate prediction of boiling ...Boiling of water/triethyleneglycol(TEG)binary solution has a wide-ranging application in the gas processing engineering.Design,operation and optimization of the involved boilers require accurate prediction of boiling heat transfer coefficient between surface and solution.In this investigation,nucleate pool boiling heat transfer coefficient has been experimentally measured on a horizontal rod heater in water/TEG binary solutions in a wide range of concentrations and heat fluxes under ambient condition.The present experimental data are correlated using major existing correlations.In addition a correlation is presented for prediction of pool boiling heat transfer for the system in which the vapour pressure of one component is negligible.This model is based on the mass transfer rate equation for prediction of the concentration at the bubble vapor/liquid interface.Based on this prediction,the temperature of the interface and accordingly,the boiling heat transfer coefficient could be straightforwardly calculated from the known concentration at the interface.It is shown that this simple model has sufficient accuracy and is acceptable below the medium concentrations of TEG when the vapor equilibrium concentration of TEG is almost zero.The presented model excludes any tuning parameter and requires very few physical properties to apply.展开更多
Heat pipes are most frequently used for thermal management solutions.Selection of right type of heat pipe for a specific scenario is utmost necessary for best outcomes.The purpose of this research is comparison of the...Heat pipes are most frequently used for thermal management solutions.Selection of right type of heat pipe for a specific scenario is utmost necessary for best outcomes.The purpose of this research is comparison of thermal performance characteristics of sintered copper wicked and grooved heat pipes,which are mostly used types of heat pipes.Distilled water filled heat pipes were tested through experimentation in gravity assisted position.Experimental outcomes have been compiled in terms of capillary pressure,operating temperature,thermal resistance and heat transfer coefficient.Capillary pressure is high in sintered heat pipes compared to grooved heat pipes irrespective of groove dimensions.Grooved heat pipes have lower operating temperature compared to sintered heat pipes at the same heat load.At 8 W,compared to sintered heat pipes,grooved heat pipes have 8.24% lower condenser surface temperature,4.41% lower evaporator surface temperature and 7.79% lower saturation temperature.Thermal resistance of sintered heat pipe is much lower than grooved heat pipe.The maximum relative difference of 63.8% was observed at 8 W.Heat transfer coefficient of sintered heat pipe was observed double compared to grooved heat pipe at 8 W heat load.Thermal resistance and hence heat transfer coefficient of sintered heat pipe change almost in a linear manner with respect to heat load but unexpectedly turning point is observed in thermal resistance and heat transfer coefficient of grooved heat pipe.Grooved heat pipes attain equilibrium much earlier compared to sintered ones.Varying heat loads from 4 to 20 W causes variation in equilibrium establishment time from 7 to 4 min for grooved and from 10 to 7 min for sintered heat pipes.展开更多
The effect of operating pressure on the radial heat transfer coefficients, in a non-adiabatic fixed packed bed was studied at atmospheric and higher pressures, The study was concerned with investigating the effect of ...The effect of operating pressure on the radial heat transfer coefficients, in a non-adiabatic fixed packed bed was studied at atmospheric and higher pressures, The study was concerned with investigating the effect of the pressure on the radial thermal conductivity （K^r） and wall heat transfer coefficient （h~） for both pellets and monolith catalysts. The study included beds that were packed with pellets and monoliths, separately. The radial temperature distribution was measured at different beds heights and feed flow rates for both types of packing. Steady-state temperatures were measured using nine chromel-alumel thermocouples arranged on a stainless steel-cross. After temperatures were collected, the radial thermal conductivity and wall heat transfer coefficient were calculated using a two-dimensional pseudo-homogeneous model. The results showed that, the radial temperature profile at the entrance of the heating section was nearly even, and a constant temperature along the radius （0F/0r=0） taken as a boundary condition to solve the partial differential equation controlling the heat transfer. Temperature profiles obtained at elevated pressures were smoother at the center of the reactor and increased sharply near the wall, than profiles at atmospheric pressure. It could also be observed, that the radial temperature profiles in the center of the reactor using a monolith catalyst at elevated pressure were more even and smoother than those of pellets. Temperature profiles in fixed beds were found to be very sensitive to Ker and hw. In pressures between atmospheric and 10 bars, there was no change in the effective heat transport parameters （i.e. they are independent of pressure in this range）. Both parameters were strongly affected by the pressure changes, above 10 bars. For the same Reynolds number （Ker） increased by 27% and 53% at 11 and 20 bars, respectively, in pellets catalyst. And they increased by factors of 2.3 and 4, when the pressure increased to the same pressures, in monolith catalyst. On the other hand, the effect of pressure on （hw） was completely the opposite, h,~ for pellets and monolith catalysts were found to be decreasing with increasing the pressure. Moreover, both coefficients increased with the Reynolds number at all applied pressures. This increase was higher for pellets than it for monoliths.展开更多
As an experimental technique, it’s desired that the temperature in specimen is uniform in high temperature split Hopkinson pressure bar (SHPB) experiments. However, the temperature in specimen decreases and the tempe...As an experimental technique, it’s desired that the temperature in specimen is uniform in high temperature split Hopkinson pressure bar (SHPB) experiments. However, the temperature in specimen decreases and the temperature of bars increases when specimen starts to contact with bars, which induces the nonuniform temperature distribution in specimen, and may result in inac-curacy of experimental results. In this paper, the temperature distributions of specimen and bars in high temperature SHPB experiments were investigated while the specimen was heated alone. Firstly, the temperature history of specimen was measured at different initial temperatures by ex-periments, then simulation was carried out. Simulation results were consistent with experimental results by adjusting the thermal contact coefficient between specimen and bars. By this way, the thermal contact coefficient and simulation results were validated, and the proper cold contact times of specimen and bars in high temperature SHPB experiments were discussed. Finally, the results were compared with those in references.展开更多
The increasing use of gas turbines in combined cycle power plants together with the high amount of kinetic energy in modem gas turbine exhaust flows focuses attention on the design of gas turbine diffusers as the conn...The increasing use of gas turbines in combined cycle power plants together with the high amount of kinetic energy in modem gas turbine exhaust flows focuses attention on the design of gas turbine diffusers as the connecting part between the Brayton/Joule and the Rankine parts of the combined cycle. A scale model of a typical gas turbine exhaust diffuser is investigated experimentally. The test rig consists of a radial type, variable swirl generator which provides the exhaust flow corresponding to different gas turbine operating conditions. Static pressure measurements are carried out along the outer diffuser walls and along the hub of the annular part and along the centerline of the conical diffuser. Velocity distributions at several axial positions in the annular and conical diffuser have been measured using a Laser Doppler Velocimeter （LDV）. Pressure recovery coefficients and velocity profiles are depicted as a function of diffuser length for several combinations of swirl strength, tip flow and strut geometries. The diffuser without struts achieved a higher pressure recovery than the diffuser with struts at all swirl angle settings. The diffuser with cylindrical struts achieved a higher pressure recovery than the diffuser with profiled struts at all swirl angle seO.ings. Inlet flows with swirl angles over 18° affected the pressure recovery negatively for all strut configurations.展开更多
We study the thermal transport of few-layer graphene nanoribbons in the presence of the transversal pressure by using molecular dynamics simulations. It is reported that the pressure can improve the thermal conductivi...We study the thermal transport of few-layer graphene nanoribbons in the presence of the transversal pressure by using molecular dynamics simulations. It is reported that the pressure can improve the thermal conductivity of few-layer graphene nanoribbons. This improvement can reach 37.5% in the low temperature region. The pressure dependence of thermal conductivity is also investigated for different length, width and thickness of few-layer graphene. Our results provide an alternative option to tuning thermal conductivity of few-layer graphene nanoribbons, b-arthermore, it maybe indicate a so-called pressure-thermM effect in nanomaterials.展开更多
文摘本文将我们在前文中提出的修正van der Waals模型,推广到了液态聚合物中,从而建立了一个能在宽阔温度范围内准确计算聚合物热压力系数的关系式γ=RMv/(Mv)~2-AMv+0.2535A^2式中v和M分别为聚合物的比体积和链节的摩尔质量,A为聚合物的特性常数.对于本文考察的五种聚合物,发现它们的链节大小均为聚合物的三个结构单元.
文摘本文测定25～85℃温度范围内正戊醇、正己醇、正庚醇和正辛醇的热压力系数,发现这些醇类液体的内压几乎不随温度而变.本文还将修正的van der Waals模型推广到了醇类液体,与非缔合液体一样,它们的排斥体积亦与密度呈线性关系.但是,模型参数之比B/A^2不再是个常数,而是随醇分子中碳原子数的增多而快速地减小,这个比值可作为自缔合能力的一种量度.
文摘利用实验测得的液体的热压力系数,修正原始van der Waals模型中的排斥体积,得到了一个适用于高密度流体的推广的van der Waals压缩因子。将它与Redlich和Kwong提出的吸引项相结合,建立了一个流体状态方程。用某些有代表性的超临界流体的pVT数据检验,结果表明,其对体积、压力和逸度系数的计算准确度可与CS-RK方程相媲美。
文摘A mathematical model of principal elements of the aircraft hydraulic system is presented based on the heat transfer theory. The dynamic heat transfer process of the hydraulic oil and the pump shells within an aircraft hydraulic system are analyzed by the difference method. A kind of means for the prediction to variational trends of the aircraft hydraulic system temperature is provided during operation. The numerical prediction and simulation under the operational conditions are presented for ground trial running and the decelerated operation in flight. Computational results show that there is a good coincidence between the experimental data and the numerical predictions.
基金the Thailand Research Fund(TRF)(Grant No.Ph D/0143/2552)
文摘The paper presents an experimental investigation on enhanced heat transfer and pressure loss characteristics by using single, double, triple, and quadruple twisted-tape inserts in a round tube having a uniform heat-fluxed wall. The investigation has been conducted in the heat exchanger tube inserted with various twisted-tape numbers for co- and counter-twist arrangements for the turbulent air flow, Reynolds number （Re） from 5300 to 24000. The typical single twisted-tape inserts at two twist ratios, y/w = 4 and 5, are used as the base case, while the other multiple twisted-tape inserts are aty/w = 4 only. The experimental results of heat transfer and pressure drop in terms of Nusselt number （Nu） and friction factor 00, respectively, reveal that Nu increases with the increment of Re and of twisted-tape number. The values of Nu for the inserted tube are in a range of 1.15-2.12 times that for the plain tube while f is 1.9-4.1 times. The thermal enhancement factor of the inserted tube under similar pumping power is evaluated and found to be above unity except for the single and the double co-twisted tapes. The quadruple counter-twisted tape insert provides the maximum thermal performance.
文摘Boiling of water/triethyleneglycol(TEG)binary solution has a wide-ranging application in the gas processing engineering.Design,operation and optimization of the involved boilers require accurate prediction of boiling heat transfer coefficient between surface and solution.In this investigation,nucleate pool boiling heat transfer coefficient has been experimentally measured on a horizontal rod heater in water/TEG binary solutions in a wide range of concentrations and heat fluxes under ambient condition.The present experimental data are correlated using major existing correlations.In addition a correlation is presented for prediction of pool boiling heat transfer for the system in which the vapour pressure of one component is negligible.This model is based on the mass transfer rate equation for prediction of the concentration at the bubble vapor/liquid interface.Based on this prediction,the temperature of the interface and accordingly,the boiling heat transfer coefficient could be straightforwardly calculated from the known concentration at the interface.It is shown that this simple model has sufficient accuracy and is acceptable below the medium concentrations of TEG when the vapor equilibrium concentration of TEG is almost zero.The presented model excludes any tuning parameter and requires very few physical properties to apply.
文摘Heat pipes are most frequently used for thermal management solutions.Selection of right type of heat pipe for a specific scenario is utmost necessary for best outcomes.The purpose of this research is comparison of thermal performance characteristics of sintered copper wicked and grooved heat pipes,which are mostly used types of heat pipes.Distilled water filled heat pipes were tested through experimentation in gravity assisted position.Experimental outcomes have been compiled in terms of capillary pressure,operating temperature,thermal resistance and heat transfer coefficient.Capillary pressure is high in sintered heat pipes compared to grooved heat pipes irrespective of groove dimensions.Grooved heat pipes have lower operating temperature compared to sintered heat pipes at the same heat load.At 8 W,compared to sintered heat pipes,grooved heat pipes have 8.24% lower condenser surface temperature,4.41% lower evaporator surface temperature and 7.79% lower saturation temperature.Thermal resistance of sintered heat pipe is much lower than grooved heat pipe.The maximum relative difference of 63.8% was observed at 8 W.Heat transfer coefficient of sintered heat pipe was observed double compared to grooved heat pipe at 8 W heat load.Thermal resistance and hence heat transfer coefficient of sintered heat pipe change almost in a linear manner with respect to heat load but unexpectedly turning point is observed in thermal resistance and heat transfer coefficient of grooved heat pipe.Grooved heat pipes attain equilibrium much earlier compared to sintered ones.Varying heat loads from 4 to 20 W causes variation in equilibrium establishment time from 7 to 4 min for grooved and from 10 to 7 min for sintered heat pipes.
文摘The effect of operating pressure on the radial heat transfer coefficients, in a non-adiabatic fixed packed bed was studied at atmospheric and higher pressures, The study was concerned with investigating the effect of the pressure on the radial thermal conductivity （K^r） and wall heat transfer coefficient （h~） for both pellets and monolith catalysts. The study included beds that were packed with pellets and monoliths, separately. The radial temperature distribution was measured at different beds heights and feed flow rates for both types of packing. Steady-state temperatures were measured using nine chromel-alumel thermocouples arranged on a stainless steel-cross. After temperatures were collected, the radial thermal conductivity and wall heat transfer coefficient were calculated using a two-dimensional pseudo-homogeneous model. The results showed that, the radial temperature profile at the entrance of the heating section was nearly even, and a constant temperature along the radius （0F/0r=0） taken as a boundary condition to solve the partial differential equation controlling the heat transfer. Temperature profiles obtained at elevated pressures were smoother at the center of the reactor and increased sharply near the wall, than profiles at atmospheric pressure. It could also be observed, that the radial temperature profiles in the center of the reactor using a monolith catalyst at elevated pressure were more even and smoother than those of pellets. Temperature profiles in fixed beds were found to be very sensitive to Ker and hw. In pressures between atmospheric and 10 bars, there was no change in the effective heat transport parameters （i.e. they are independent of pressure in this range）. Both parameters were strongly affected by the pressure changes, above 10 bars. For the same Reynolds number （Ker） increased by 27% and 53% at 11 and 20 bars, respectively, in pellets catalyst. And they increased by factors of 2.3 and 4, when the pressure increased to the same pressures, in monolith catalyst. On the other hand, the effect of pressure on （hw） was completely the opposite, h,~ for pellets and monolith catalysts were found to be decreasing with increasing the pressure. Moreover, both coefficients increased with the Reynolds number at all applied pressures. This increase was higher for pellets than it for monoliths.
文摘As an experimental technique, it’s desired that the temperature in specimen is uniform in high temperature split Hopkinson pressure bar (SHPB) experiments. However, the temperature in specimen decreases and the temperature of bars increases when specimen starts to contact with bars, which induces the nonuniform temperature distribution in specimen, and may result in inac-curacy of experimental results. In this paper, the temperature distributions of specimen and bars in high temperature SHPB experiments were investigated while the specimen was heated alone. Firstly, the temperature history of specimen was measured at different initial temperatures by ex-periments, then simulation was carried out. Simulation results were consistent with experimental results by adjusting the thermal contact coefficient between specimen and bars. By this way, the thermal contact coefficient and simulation results were validated, and the proper cold contact times of specimen and bars in high temperature SHPB experiments were discussed. Finally, the results were compared with those in references.
文摘The increasing use of gas turbines in combined cycle power plants together with the high amount of kinetic energy in modem gas turbine exhaust flows focuses attention on the design of gas turbine diffusers as the connecting part between the Brayton/Joule and the Rankine parts of the combined cycle. A scale model of a typical gas turbine exhaust diffuser is investigated experimentally. The test rig consists of a radial type, variable swirl generator which provides the exhaust flow corresponding to different gas turbine operating conditions. Static pressure measurements are carried out along the outer diffuser walls and along the hub of the annular part and along the centerline of the conical diffuser. Velocity distributions at several axial positions in the annular and conical diffuser have been measured using a Laser Doppler Velocimeter （LDV）. Pressure recovery coefficients and velocity profiles are depicted as a function of diffuser length for several combinations of swirl strength, tip flow and strut geometries. The diffuser without struts achieved a higher pressure recovery than the diffuser with struts at all swirl angle settings. The diffuser with cylindrical struts achieved a higher pressure recovery than the diffuser with profiled struts at all swirl angle seO.ings. Inlet flows with swirl angles over 18° affected the pressure recovery negatively for all strut configurations.
基金Supported in part by the National Natural Science Foundation of China under Grant Nos.11004082 and 11175067the Natural Science Foundation of Guangdong Province under Grant Nos.10451063201005249 and S201101000332the Fundamental Research Funds for the Central Universities,JNU under Grant Nos.21611437 and 50421288
文摘We study the thermal transport of few-layer graphene nanoribbons in the presence of the transversal pressure by using molecular dynamics simulations. It is reported that the pressure can improve the thermal conductivity of few-layer graphene nanoribbons. This improvement can reach 37.5% in the low temperature region. The pressure dependence of thermal conductivity is also investigated for different length, width and thickness of few-layer graphene. Our results provide an alternative option to tuning thermal conductivity of few-layer graphene nanoribbons, b-arthermore, it maybe indicate a so-called pressure-thermM effect in nanomaterials.
