An Investigation Of The Coefficient Of Convective Heat Transfer At Different Boundary Condition

The coefficient of convective heat transfer is important to design a heat exchanger. Normally, coefficient of convective heat transfer is gotten through experiments which is heating testing tube by electricity and computed through Newton cooling law. The wall of this testing tube is in definite heat flux (e.g. the second boundary condition). But actually much of condition of tube wall is in thermal boundary condition(e.g.the third boundary condition). 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. For thermal boundary condition, the gas wash across a tube and the water flow in the tube at the same time. 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. 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. At the same time , we suggest a correction factor to the before coefficient of convective heat transfer formula at the second boundary condition.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...