Normally , coefficient of convective heat transfer is gotten through experiments which is heating testing tube by electricity and computed through newton cooling law 通常,对流换热系数是在实验中以电加热试验管壁面后根据牛顿冷却定律计算得来的。
At the same time , we suggest a correction factor to the before coefficient of convective heat transfer formula at the second boundary condition 然后研究平均对流换热系数在电加热边界条件和传热边界条件下的区别,同时提出对以往在电加热条件下所得出的换热系数经验式的修正。
So if there is any difference of coefficient of convective heat transfer between this two boundary condition ? both numerical simulation and experiment were adopted to research ducted heat convection 探讨这两种边界条件下管内外的对流换热系数的差别及相应的对应关系对于换热设备的设计具有重要的意义。
Fist we resarch local wall temperature ouside and inside of tube , local fluid temperature inside and outside of tube , local heat flux inside and outside of tube , local coefficient of convective heat transfer inside and ouside of tube along the tube axial direction 首先研究在这两种情况下管内(外)壁温、管内(外)流温、管内(外)壁面局部热流密度、管内(外)局部对流换热系数沿管子轴向的变化。
The end show that coefficient of convective heat transfer at thermal boundary condition is higher than that at definite heat flux boundary condition . if according to dimensionless equation of heat convection , nu number of the latter almost is mutiplied 1 . 47 times of the formal , but the coefficient of convective heat transfer in tube between this two condition is almost equal 研究结果表明:在实验室中电加热方式得到的管外对流换热系数低于工程中传热条件下的管外对流换热系数,若按传热准则式关系,后者的努谢尔特数约为前者的1 . 4倍;而管内的对流换热系数在两种边界条件下的差别不大。
In this condition heat convection inside and outside of tube are coupled . coefficient of convective heat transfer inside and outside of tube gotten through such way compare with coefficient of convective heat transfer inside and outside of tube gotten through by electricity . for comparability between this two condition , the average heat flux on the tube must be equal for this two condition 这种情况下管内外对流换热是藕合的,得到的管内外对流换热系数分别与电加热管道壁面的边界条件下管内和管外流动的对流换热系数相对比,为了使他们具有可比性,我们规定在这两种边界条件下通过管子的平均热流密度相等。