中文摘要：

为研究超临界压力下的对流传热特性,对超临界压力氟利昂R134a在内径25 mm垂直圆管中的受热上升流动传热进行了实验研究,获得压力4.5 MPa和4.7 MPa、质量流速G=400~700 kg/（m2·s）、热流密度q=30~60 k W/m2的实验数据,对换热强化和传热恶化的规律和特性以及其影响因素进行了分析。结果发现,在拟临界区附近,超临界压力R134a出现明显的强化换热现象。在低质量流速或高热流密度下发生传热恶化,其恶化边界为q/G〉0.06 k J/kg。在特定的工况下观察到两次传热恶化：第一次发生在临近入口区域,在不同流体入口温度下均观测到恶化;第二次发生在远离入口区域,仅在一定流体焓值范围内存在。实验参数敏感性分析表明,传热强化随质量流速的增加、热流密度的减小、压力的降低而增加,而传热恶化则相反。

英文摘要：

In order to investigate the convective heat transfer at supercritical pressures, experimental research was conducted on heated Freon R134a flowing upward through an I.D 25mm vertical circular tube under supercritical pressure condition. The experimental data covers a wide range of conditions. The pressure is at 4.5MPa and 4.7MPa. The mass flow flux varies from 400 to 700 kg/（me-s） and the heat flux ranges from 30 to 60kW/m2. Both enhanced and deteriorated heat transfer were analyzed and the parametric sensitivity was also carried out. The heat transfer performance was evidently enhanced near the pseudo-critical point. The deteriorated heat transfer appeared at lower mass flow velocity or at higher heat flux under a certain ratio of q/G=0.06kJ/kg. At a mass flux of 500 kg/（m2.s） two types of deteriorated heat transfer were observed in the experiment： the first type appeared at the near entrance region of the tube and existed within different range of fluid inlet temperature; The second type appeared at any section inside the tube than entrance but only within a certain enthalpy range. Heat transfer can be enhanced by increasing mass flow velocity, decreasing heat flux or decreasing pressure, while the variance of the heat transfer deterioration is opposite.