浮力对混合对流流动及换热特性的影响

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 / Red2 )来表示,其中,基于管道直径的雷诺数Red变化范围为900~18000, 浮力参数Ω变化范围为0.004899~0.5047. 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.

Buoyancy Effects On Mixed Convection Flow And Heat Transfer

A combination of a hot/cold wire technique was used for thesimultaneous measurements of instantaneous velocity and temperature in avertical pipe. The detailed study of the effects of buoyancy on flowcharacteristics and heat transfer of opposing mixed convection had beencarried out experimentally. The performance of cold wire for temperaturecompensating the velocity reading of a hot-wire probe due to varying fluidtemperature was assessed. Heat transfer results for opposing mixedconvection have been presented in non-dimensional equations using thebuoyancy parameterΩ(Ω= Grd / Red2), inwhich Red ranges from 900 to 18,000 andΩfrom 0.004899 to0.5047. It is found that theheat transfer is enhanced due to buoyancy effect. With the increasing ofGrd (Grashof number), the temperature fluctuation, streamwise Reynoldsnormal stress and streamwise heat flux are increased, especially in the nearwall region. The combination of hot/cold wire enables the study ofnon-isothermal flow characteristics, thus it is helpful to look inside ofbuoyancy effects on heat transfer in the mixed convection flows.