中文摘要：

针对窄通道内过冷沸腾起始点（ONB）发生特点较难把握的问题,基于热流体理论所描述的热阻力和热绕流机制,对不同循环方式下窄环形通道内ONB的发生机理进行研究.研究表明：热阻力的增加可能延缓ONB的发生;热绕流的增加可能提早ONB的发生.热阻力和热绕流是相互依存而生的,通道结构、具体流动特性的综合影响决定了其作用是提早还是延缓ONB的发生.通过适当的窄环形通道自然循环和强迫循环流动模型,分析了入口过冷度和压力等参数对ONB点发生的影响.研究发现：随着质量流量和压力的分别提高,自然循环和强迫循环窄环形通道的ONB点发生都会推迟;随着入口温度的提高,自然循环和强迫循环ONB点均提前;而当质量流量、入口温度和压力分别改变时,自然循环ONB的发生都要早于强迫循环.

英文摘要：

The research investigation of the difficulties of grasping the developing characteristics of onset of nucleate boiling（ONB） in narrow channels,and ONB developing mechanism in narrow annular channels under different cycling modes was conducted based on the thermal drag and thermal roundabout flow mechanism.The research study results indicated that,the increase of thermal drag might delay the occurrence of ONB,while the increase of thermal roundabout flow may advance the occurrence of ONB,and the thermal drag and thermal roundabout flow exist interdependently.The influences on occurrence of ONB are determined by the combination effects of channel structures and flow characteristics.Based on the appropriate natural and forced circulation models applied in narrow annular channels,the influences of flow mass,inlet sub-cooling and pressure on the occurrence of ONB have been analyzed thoroughly.Results showed that the ONB occurrences of both natural and forced circulations in narrow annular channels were delayed as mass flow or pressure was increased.As the temperature of inlet fluid increased,the occurrences of ONB in natural and forced circulations were both advanced.The occurrences of ONB in natural circulations preceded those in forced circulations as mass flow,inlet temperature,and pressure changed.