A variety of turbulence models were used to perform numerical simulations of heat transfer for hydrocarbon fuel flowing upward and downward through uniformly heated vertical pipes at supercritical pressure. Inlet temp...A variety of turbulence models were used to perform numerical simulations of heat transfer for hydrocarbon fuel flowing upward and downward through uniformly heated vertical pipes at supercritical pressure. Inlet temperatures varied from 373 K to 663 K, with heat flux rang- ing from 300 kW/m2 to 550 kW/m2. Comparative analyses between predicted and experimental results were used to evaluate the ability of turbulence models to respond to variable thermophysical properties of hydrocarbon fuel at supercritical pressure. It was found that the prediction performance of turbulence models is mainly determined by the damping function, which enables them to respond differently to local flow conditions. Although prediction accuracy for experimental results varied from condition to condition, the shear stress transport （SST） and launder and sharma models performed better than all other models used in the study. For very small buoyancy-influenced runs, the thermal-induced acceleration due to variations in density lead to the impairment of heat transfer occurring in the vicinity of pseudo-critical points, and heat transfer was enhanced at higher temperatures through the combined action of four thermophysical properties： density, viscosity, thermal conductivity and specific heat. For very large buoyancy- influenced runs, the thermal-induced acceleration effect was over predicted by the LS and AB models.展开更多
At high rotation numbers,the rotational effects on heat transfer and flow could be diverse among the channels with different blockage ratios.However,most studies are conducted under low rotation number(less than 0.25)...At high rotation numbers,the rotational effects on heat transfer and flow could be diverse among the channels with different blockage ratios.However,most studies are conducted under low rotation number(less than 0.25)and selected blockage ratio.This paper experimentally investigates the effect of rib blockage ratio(ranges from 0 to 0.3)on pressure loss and heat transfer in a rotating square channel under high rotation number(up to 0.81).The ribs staggered on leading and trailing walls were oriented 90°to the mainstream flow.The Reynolds number and the wall-to-fluid temperature ratio varied from 20000 to 40000 and 0.08 to 0.2,respectively.The results showed that a larger blockage ratio resulted in a better heat transfer but a higher pressure drop.The optimum blockage ratio was 0.1 for the best thermal performance.The rotational effects were weakened in the passage with a higher blockage ratio,where the critical rotation number could not be observed.Moreover,the heat transfer enhancement induced by rotation was more significant when the temperature ratio increased.Finally,the correlations were developed for the pressure drop and the convective heat transfer on the leading and trailing edges.展开更多
基金funding support from National Natural Science Foundation of China (No.51406005)Defense Industrial Technology Development Program of China (No.B2120132006)
文摘A variety of turbulence models were used to perform numerical simulations of heat transfer for hydrocarbon fuel flowing upward and downward through uniformly heated vertical pipes at supercritical pressure. Inlet temperatures varied from 373 K to 663 K, with heat flux rang- ing from 300 kW/m2 to 550 kW/m2. Comparative analyses between predicted and experimental results were used to evaluate the ability of turbulence models to respond to variable thermophysical properties of hydrocarbon fuel at supercritical pressure. It was found that the prediction performance of turbulence models is mainly determined by the damping function, which enables them to respond differently to local flow conditions. Although prediction accuracy for experimental results varied from condition to condition, the shear stress transport （SST） and launder and sharma models performed better than all other models used in the study. For very small buoyancy-influenced runs, the thermal-induced acceleration due to variations in density lead to the impairment of heat transfer occurring in the vicinity of pseudo-critical points, and heat transfer was enhanced at higher temperatures through the combined action of four thermophysical properties： density, viscosity, thermal conductivity and specific heat. For very large buoyancy- influenced runs, the thermal-induced acceleration effect was over predicted by the LS and AB models.
文摘At high rotation numbers,the rotational effects on heat transfer and flow could be diverse among the channels with different blockage ratios.However,most studies are conducted under low rotation number(less than 0.25)and selected blockage ratio.This paper experimentally investigates the effect of rib blockage ratio(ranges from 0 to 0.3)on pressure loss and heat transfer in a rotating square channel under high rotation number(up to 0.81).The ribs staggered on leading and trailing walls were oriented 90°to the mainstream flow.The Reynolds number and the wall-to-fluid temperature ratio varied from 20000 to 40000 and 0.08 to 0.2,respectively.The results showed that a larger blockage ratio resulted in a better heat transfer but a higher pressure drop.The optimum blockage ratio was 0.1 for the best thermal performance.The rotational effects were weakened in the passage with a higher blockage ratio,where the critical rotation number could not be observed.Moreover,the heat transfer enhancement induced by rotation was more significant when the temperature ratio increased.Finally,the correlations were developed for the pressure drop and the convective heat transfer on the leading and trailing edges.
