【作者】 幸奠川；

【导师】 阎昌琪；

【作者基本信息】 哈尔滨工程大学 ， 核能科学与工程， 2013， 博士

【摘要】 小通道换热技术是实现船舶动力系统换热设备小型化的有效方法之一。不同于陆基核反应堆，船舶核反应堆始终处于运动条件下，其中船身摇摆过程对冷却剂热工水力特性的影响最为复杂。摇摆使冷却剂受惯性力作用，同时引起重力沿流动方向分量改变，从而影响动力装置的运行特性。本文对摇摆条件下矩形小通道内流动阻力特性进行了实验研究和理论分析。实验在常温常压下进行，以空气和去离子水为工质。5个实验段当量直径的范围为2.73~5.99mm，高宽比为0.033~0.075。分液相雷诺数和分气相雷诺数的范围分别为200~21000和221~8310，摇摆周期和摇摆振幅的范围分别为8s~20s和10°~30°。采用调节离心泵转速的方式获得不同驱动压头，以比较摇摆运动对单相强迫循环的不同影响。单相可视化实验及流量波动理论模型表明，开放回路和闭合回路流量波动特性主要影响因素分别为总重位压降和附加压降。单相流量波动幅值随有效驱动压头增加而减小，随波动压降幅值增加而增大，当有效驱动压头大于波动压降幅值的10~11倍时，流动趋于稳定。单相流阻力特性实验表明，摇摆对单相流摩擦阻力的影响随驱动压头增加而减弱，驱动压头较高时，摇摆的影响可忽略。驱动压头较低时流量周期性波动，摩擦压降波动幅值随摇摆振幅增加而增大，随平均流速增加而减小，随摇摆周期的变化因回路不同而存在差异。建立了单相层流二维动量守恒方程，其预测的摩阻系数与实验值有较好的一致性。摇摆运动对单相流摩擦阻力的影响机理为：驱动压头较低时，摇摆引起入口流量周期性波动，从而导致壁面切应力周期性变化，进而引起宏观摩擦阻力周期性波动；驱动压头较高时，摇摆仅引起沿流动方向的附加压降，不影响壁面切应力及宏观摩擦阻力。得到了高驱动压头下单相层流摩阻系数和转捩雷诺数理论关系式；并基于能量梯度法研究摇摆运动引起的流量波动对流态转捩的影响。对于两相流动，摇摆对摩擦阻力的影响随液流速增加而减弱。液流速较低时，相对摩擦压降梯度波动幅值随气流速增加而降低，随摇摆参数的改变没有明显变化；液流速较高时，摩擦压降梯度不波动。摇摆运动对两相流时间平均摩擦阻力没有明显影响。Chisholm C、Lee&Lee及Mishima&Hibiki关系式能很好地预测摇摆条件下平均摩擦阻力，但不能用于周期性瞬变摩擦压降的计算。基于分相流模型提出了能预测周期性瞬变摩擦压降的关系式。摇摆运动通过改变气液界面摩擦特性来影响两相流宏观摩擦阻力。稳态倾斜条件下相界面分布不变，摩擦阻力不波动。摇摆条件下瞬变力引起气泡加速度沿流动方向周期性改变，同时引起气泡周期性横向运动，从而导致宏观摩擦阻力周期性波动，后者为主要影响因素。摇摆周期较大时，重力横向分量为主要影响因素；摇摆周期较小时，科氏惯性力的影响不可忽略。更多还原

【Abstract】 Small channel heat transfer technology is one of the effective methods which miniaturizethe heat transfer equipment of ship power systems. Different from the land-based nuclearreactor, the barge-mounted nuclear reactor always works under motion conditions, amongwhich the influence of rolling process of a ship on the thermal-hydraulic behavior is the mostcomplex. The rolling motion induces inertia force acting on the coolant and changes thegravity along flow direction, both of which may influence the operational characteristic ofpower plants.This dissertation investigates flow resistance in mini rectangular duct under rollingcondition experimentally and theoretically. The experiments were conducted under ambienttemperature and pressure, and water and air were used as the test fluids. The5test sectionshad the diameters of2.73~5.99mm, with aspect ratios ranging from0.033to0.075. Theliquid Reynolds number and gas Reynolds number ranges were200~21000and221~8310,respectively, and the rolling period and rolling amplitude were8s~20s and10°~30°,respectively. Different pressure head were acquired by regulating the rotation speed of thecentrifugal pump, in order to compare different influences of rolling motion on single-phaseforced circulation.The flow visualization experiment combining with single-phase flow fluctuation modelindicate that the flow fluctuation of the open loop and closed loop are mainly produced by thegravitational and additional pressure drop, respectively. The flow fluctuation amplitudedecreases as the effective pressure head increases, while increases as the oscillatory pressuredrop increases. Finally, the flow tends to be steady, if the effective pressure head is larger than10~11times of the oscillatory pressure drop. The flow resistance experiments indicate thateffects of rolling motion on single-phase flow resistance wears off as the pressure headincreases, which could be neglected if the pressure head was high enough. For relative lowpressure head, larger rolling amplitude and smaller averaged velocity give rise to largeramplitude of frictional pressure drop, whereas, rolling period have different effects on thefluctuation amplitude because of the inequable flow loops.The momentum conservation equation for single-phase laminar flow was set up, by which the predicted frictional coefficient agrees well with the experiments. The mechanism ofrolling motion on frictional resistance is discussed theoritically. For low pressure head, rollinginduced periodically pulsing flow leads to the periodical variation of the wall shear stress,which results in the fluctuation of frictional resistance. While the pressure head is high,rolling motion just induces the additional pressure drop, nearly having no influnce on the wallshear stress and frictional resistance. Theoretical correlations for frictional coefficient oflaminar flow and transition Reynolds number were obtained for the condition of high pressurehead, and effects of rolling induced flow fluctuation on flow regime transition wereinvestigated by energy gradient method.For two-phase flow, the effect of rolling motion on frictional resistance weakens as theliquid velocity increases. When the liquid velocity is low, the amplitude of relative frictionalpressure gradient decreases as the gas velocity increases, whereas it is nearly independent ofthe rolling parameters. While for relative high liquid velocity, the frictional pressure gradientis nearly invariable. Rolling motion nearly has no influence on time-averaged frictionalresistance. The Chisholm C、Lee&Lee and Mishima&Hibiki correlations work well fortime-averaged frictional resistance, even under rolling condition, but not for the transientfrictional resistance which varies periodically. A correlation for periodical frictional pressuredrop was also achieved by modifying the separate flow model.The rolling motion influences frictional resistance by changing interfacial friction of thetwo phases. The interface distribution is nearly invariable, and the frictional resistance doesnot fluctuate under inclined condition. Different from steady state, the transient force inducesperiodical acceleration of bubbles along flow direction, and leads periodical lateral bubblemotion in transverse direction under rolling condition, which results in periodically frictionalpressure drop. For larger rolling periods, the fluctuation is mainly due to the transversecomponent of the gravity, while for a smaller rolling period, the effect of Coriolis forcecouldn’t be neglected.更多还原