竖直直管和螺旋管内超临界CO2换热特性对比研究

采用SST k-ω湍流模型对比研究了在q=20.5~40 kW.m^-2,G=205.92~262.51 kg·m^-2·s^-1,p=8~10 MPa边界条件下超临界CO2在加热竖直直管和螺旋管内的换热差异。结果表明,在相同工况下,由于离心力引起的二次流的作用使得螺旋管相比于直管对换热有一定的强化作用,并能有效地抑制换热恶化的发生。但在拟临界点区域螺旋管的换热系数反而低于直管,主要原因是在拟临界点附近物性对换热起主导作用,离心力对管外侧的强化作用有限,而由于离心力和浮升力的弱化作用使内侧会出现显著的局部换热恶化(湍动能被抑制),从而使得截面上平均换热系数低于直管。

Comparative Study on Heat Transfer Characteristics of Supercritical CO2 Heated in Vertical Straight Tube and Helically Coiled Tube

The SST k-ω turbulence model was used to compare the heat transfer difference of supercritical CO2 heated in vertical straight tube(ST) and helically coiled tube(HCT) with q=20.5~40 kW·m^-2,G=205.92~262.51 kg·m^-2·s^-1,p=8~10 MPa.The results showed that under the same boundary conditions,the effect of the secondary flow caused by the centrifugal force strengthen the heat transfer on the HCT compared to the ST,and can effectively suppress the heat transfer deterioration.However,near the pseudo-critical temperature,the heat transfer coefficient(HTC) in the HCT is lower than ST due to the centrifugal force.The main reason is that near the pseudo-critical region the thermal physical properties domain the heat transfer and the enhancement effects of the centrifugal force is limited.But due to the weakening role of centrifugal force and buoyancy force,the transfer deterioration occurred on the inner side of the cross section(the turbulent energy suppressed) in the HCT.Hence,the average HTC is lower than that of ST.