【摘要】 用热线和冷线相结合的技术测量垂直圆管内逆混合对流流体的平均速度、温度以及它们的脉动.较详细地研究了浮力对逆混合对流的流动特性和传热特性的影响.评估了实验中采用的冷线测量温度补偿速度探头温度敏感的影响.逆混合对流的传热结果用无量纲参数Ω(Ω=Grd/Re2d)来表示,其中,基于管道直径的雷诺数Rea变化范围为900-18000,浮力参数Ω变化范围为0.004 899-0.504 7.研究结果表明,浮力对逆混合对流的换热有强化作用.随着葛拉晓夫数Grd的增加,温度脉动,流向雷诺正应力和流向温度通量增大,并且在靠近壁面的流体区域尤其明显.热线与冷线相结合的技术适合于研究非绝热的流动测量,可以用于研究浮力对流动和换热特性的影响.更多还原

【Abstract】 A combination of a hot/cold wire technique was used for the simultaneous measurements of instantaneous velocity and temperature in a vertical pipe. The detailed study of the effects of buoyancy on flow characteristics and heat transfer of opposing mixed convection had been carried out experimentally. The performance of cold wire for temperature compensating the velocity reading of a hot-wire probe due to varying fluid temperature was assessed. Heat transfer results for opposing mixed convection have been presented in non-dimensional equations using the buoyancy parameter Ω (Ω = Grd/Re2d), in which Red ranges from 900 to 18000 and f2 from 0.004899 to 0.5047. It is found that the heat transfer is enhanced due to buoyancy effect. With the increasing of Grd (Grashof number), the temperature fluctuation, streamwise Reynolds normal stress and streamwise heat flux are increased, especially in the near wall region. The combination of hot/cold wire enables the study of non-isothermal flow characteristics, thus it is helpful to look inside of buoyancy effects on heat transfer in the mixed convection flows.更多还原