Experimental data and calculated results for the onset of nucleate boiling （ONB） in natural circula- tion systems show that for the same operating conditions, the equilibrium vapor quality for ONB in natural circula...Experimental data and calculated results for the onset of nucleate boiling （ONB） in natural circula- tion systems show that for the same operating conditions, the equilibrium vapor quality for ONB in natural circulation is lower than for forced convections. The differences can be explained using second stir theory. The weak vortices and small stir energy in natural circulation systems result in nucleate boiling occurring earlier than in forced convection systems. In natural circulation systems high mass flow rates are accompa- nied by large kinetic energies and large stir energies, which enables changes in the directions of flow eddies and energy transport. The equilibrium vapor qualities at ONB are then higher at higher mass flow rates. The influence of other flow parameters on ONB can be evaluated by the relationships between these flow pa- rameters and the mass flow rate. The same values can lead to different results due to different eddy direc- tions. This indicates that the quantitative comparability in mathematics cannot be considered as only scien- tific standard. The second stir theory offers a new visual angle for researches on natural circulation.展开更多
Based on the experiment of onset of nucleate boiling(ONB)in natural circulation and the nonequilibrium thermodynamics dissipative theory,the mechanism of ONB in narrow rectangle channels of natural circulation is prop...Based on the experiment of onset of nucleate boiling(ONB)in natural circulation and the nonequilibrium thermodynamics dissipative theory,the mechanism of ONB in narrow rectangle channels of natural circulation is proposed.It points out that the onset of nucleate boiling is influenced by the degree of superheat and the special conditions of narrow channels.Under the conditions of both density difference in natural circulation and narrow rectangle channels,the prediction model of ONB in natural circulation of narrow channels based on fluctuating is established.The experimental results show that the present model can be used to predict the heat flux of ONB in narrow rectangle channels.Features of ONB in natural circulation narrow rectangle channels are as follows:heating power is the incentive of the happen of ONB;the higher the heating power is,the higher the degree of superheat is,and the earlier the ONB will appear.With the pressurizing,the appearance of ONB will be delayed.The higher the degree of supercooling is,the later the ONB appears.The ONB will happen easier when there are noncondensable gases and roughness in the channels.展开更多
在系统压力P=412~850 k Pa,过冷度?Tsub=4.7~15.0℃,热通量q"=0.11~10.90 k W·m^(-2),质量流量G=147.5~443.7 kg·m^(-2)·s-1的条件下,对立式和卧式螺旋管内R134a过冷流动沸腾起始点特性进行了实验研究。研究结果表...在系统压力P=412~850 k Pa,过冷度?Tsub=4.7~15.0℃,热通量q"=0.11~10.90 k W·m^(-2),质量流量G=147.5~443.7 kg·m^(-2)·s-1的条件下,对立式和卧式螺旋管内R134a过冷流动沸腾起始点特性进行了实验研究。研究结果表明:当实验系统参数相同时,立式和卧式螺旋管内过冷沸腾起始点的热通量基本相同,但是立式螺旋管内过冷沸腾起始点壁面过热度小于卧式螺旋管;过冷沸腾起始点的热通量、壁面过热度随着过冷度和质量流量的增大而增大,但随着压力、螺旋直径的增大而减小。通过无量纲分析对实验数据进行非线性拟合,发展了适用于螺旋管过冷沸腾起始点的关联式。展开更多
为更好地开展自主化压水堆(pressurized water reactor,PWR)子通道分析软件传热模型的评价工作,对国家核安全局目前在审的几款国产自主化压水堆子通道分析软件的传热模型开展分析研究。首先,确认传热模型对于自主化压水堆子通道分析软...为更好地开展自主化压水堆(pressurized water reactor,PWR)子通道分析软件传热模型的评价工作,对国家核安全局目前在审的几款国产自主化压水堆子通道分析软件的传热模型开展分析研究。首先,确认传热模型对于自主化压水堆子通道分析软件的实际意义,即软件传热模型计算的相关参数主要体现在液相能量守恒方程的封闭过程中。然后通过对核态沸腾起始点(onset of nucleate boiling,ONB)模型的实验确认以及敏感性分析。最终得到ONB模型的计算偏差对通道内轴向压力、燃料包壳外壁面温度等参数的计算结果影响很小。虽然ONB模型的计算偏差会对通道内空泡份额以及偏离泡核沸腾比(departure from nucleate boiling ratio,DNBR)产生一定影响,但仅局限于ONB起始点附近位置,对后续高空泡份额、更小DNBR的通道轴向位置的参数计算影响很小。展开更多
基金Supported by the National Natural Science Foundation of China(No. 50976033)the National Key Laboratory of Bubble Physicsand Natural Circulation Funds
文摘Experimental data and calculated results for the onset of nucleate boiling （ONB） in natural circula- tion systems show that for the same operating conditions, the equilibrium vapor quality for ONB in natural circulation is lower than for forced convections. The differences can be explained using second stir theory. The weak vortices and small stir energy in natural circulation systems result in nucleate boiling occurring earlier than in forced convection systems. In natural circulation systems high mass flow rates are accompa- nied by large kinetic energies and large stir energies, which enables changes in the directions of flow eddies and energy transport. The equilibrium vapor qualities at ONB are then higher at higher mass flow rates. The influence of other flow parameters on ONB can be evaluated by the relationships between these flow pa- rameters and the mass flow rate. The same values can lead to different results due to different eddy direc- tions. This indicates that the quantitative comparability in mathematics cannot be considered as only scien- tific standard. The second stir theory offers a new visual angle for researches on natural circulation.
基金Supported by National Natural Science Foundation of China(No.50976033)National Key Laboratory of Bubble Physics and Natural Circulation(No.9140C7 101030905)North China Electric Power University’s 211 Project
文摘Based on the experiment of onset of nucleate boiling(ONB)in natural circulation and the nonequilibrium thermodynamics dissipative theory,the mechanism of ONB in narrow rectangle channels of natural circulation is proposed.It points out that the onset of nucleate boiling is influenced by the degree of superheat and the special conditions of narrow channels.Under the conditions of both density difference in natural circulation and narrow rectangle channels,the prediction model of ONB in natural circulation of narrow channels based on fluctuating is established.The experimental results show that the present model can be used to predict the heat flux of ONB in narrow rectangle channels.Features of ONB in natural circulation narrow rectangle channels are as follows:heating power is the incentive of the happen of ONB;the higher the heating power is,the higher the degree of superheat is,and the earlier the ONB will appear.With the pressurizing,the appearance of ONB will be delayed.The higher the degree of supercooling is,the later the ONB appears.The ONB will happen easier when there are noncondensable gases and roughness in the channels.
文摘在系统压力P=412~850 k Pa,过冷度?Tsub=4.7~15.0℃,热通量q"=0.11~10.90 k W·m^(-2),质量流量G=147.5~443.7 kg·m^(-2)·s-1的条件下,对立式和卧式螺旋管内R134a过冷流动沸腾起始点特性进行了实验研究。研究结果表明:当实验系统参数相同时,立式和卧式螺旋管内过冷沸腾起始点的热通量基本相同,但是立式螺旋管内过冷沸腾起始点壁面过热度小于卧式螺旋管;过冷沸腾起始点的热通量、壁面过热度随着过冷度和质量流量的增大而增大,但随着压力、螺旋直径的增大而减小。通过无量纲分析对实验数据进行非线性拟合,发展了适用于螺旋管过冷沸腾起始点的关联式。
文摘为更好地开展自主化压水堆(pressurized water reactor,PWR)子通道分析软件传热模型的评价工作,对国家核安全局目前在审的几款国产自主化压水堆子通道分析软件的传热模型开展分析研究。首先,确认传热模型对于自主化压水堆子通道分析软件的实际意义,即软件传热模型计算的相关参数主要体现在液相能量守恒方程的封闭过程中。然后通过对核态沸腾起始点(onset of nucleate boiling,ONB)模型的实验确认以及敏感性分析。最终得到ONB模型的计算偏差对通道内轴向压力、燃料包壳外壁面温度等参数的计算结果影响很小。虽然ONB模型的计算偏差会对通道内空泡份额以及偏离泡核沸腾比(departure from nucleate boiling ratio,DNBR)产生一定影响,但仅局限于ONB起始点附近位置,对后续高空泡份额、更小DNBR的通道轴向位置的参数计算影响很小。
