Experimental Study On Heat Transfer Characteristics Of Non-Uniform Heating Tube Bundle Channel Under Natural Circulation

In the vertical natural circulation steam generator,the coolant continuously transfers heat to the secondary side as it flows inside the U-shaped tube,resulting in a continuous decrease in temperature and a change in heat flux along the flow direction.Therefore,the tube of the steam generator is usually divided into the cold side and the hot side.There are significant differences in boiling heat transfer and flow characteristics between the cold side and hot side.And rolling motion will make the flow and heat transfer process between the tube bundles more complex.This article adopts experimental methods to study the flow and heat transfer characteristics of tube bundle channels under natural circulation conditions,and analyzes the coupling effects of non-uniform heating and rolling motion on its heat transfer characteristics.In the vertical state,uniform and non-uniform heating experiments were conducted on the tube bundle,and thermal balance verification was conducted on the experimental section.Compared with uniform heating,under non-uniform heating conditions,the boiling state on both sides of the tube bundle is affected by the heat flux ratio.The fluid boiling between the high-power side tube bundles is more intense,which suppresses the boiling of the low-power side fluid.When the heat flux of one tube bundle increases,the heat transfer coefficient of the other tube bundle also increases.Under inclined conditions,uniform and non-uniform heating experiments were conducted on tube bundles at different inclinations.Inclines has a significant impact on the boiling condition between the two side tube bundles.In inclined conditions,the boiling condition of the upper side tube bundle becomes more severe,and as the inclination angle increases,it will further enhance the boiling heat transfer of the upper side tube bundle.Compared with uniform heating,there is a significant difference in the boiling heat transfer process in inclined tube bundle channels under non-uniform heating conditions.When the high-power tube bundle side is located on the upper side of the experimental section,boiling between the upper side tube bundles becomes more intense.When the high-power side is located on the lower side of the experimental section,both the upper and lower side tube bundles may be in a state of more intense boiling.Under rolling conditions,uniform and non-uniform heating experiments were conducted on the tube bundle under different rolling parameters.Under rolling conditions,the transient natural circulation flow rate exhibits periodic changes,with a period consistent with the rolling period.However,the average natural circulation flow rate is less affected by the rolling period and amplitude,and its magnitude is mainly determined by the heating power of the tube bundle.The transient heat transfer coefficient of the tube bundle undergoes a sinusoidal periodic change with the rolling motion,and the change period is consistent with the rolling period.Under uniform heating conditions,the time averaged heat transfer coefficient of the tube bundle is little affected by changes in rolling parameters.Under non-uniform heating conditions,as the rolling period decreases and the rolling amplitude increases,the time averaged heat transfer coefficient of the tube bundle slightly increases.Compared with uniform heating,under nonuniform heating conditions,the time-averaged heat transfer coefficient of the oscillating tube bundle is somewhat enhanced.