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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。
In order to study the convective heat transfer characteristics under supercritical pressure, the experimental study on the rising heat transfer of the supercritical pressure freon R134a in a 25 mm ID vertical tube was performed. The pressures of 4.5 MPa and 4.7 MPa were obtained, and the mass flow rate G = 400 ~ 700 kg / (m2 · s) and heat flux q = 30 ~ 60 k W / m2, the laws and characteristics of heat transfer enhancement and heat transfer deterioration and their influencing factors were analyzed. The results show that near supercritical pressure area, supercritical pressure R134a shows obvious heat transfer phenomenon. Heat transfer deterioration occurs at low mass flow rates or high heat flux density, with a deteriorating boundary of q / G> 0.06 kJ / kg. Two heat transfer excursions were observed under specific operating conditions: the first occurred in the immediate vicinity of the inlet, and the second was in the area far away from the inlet, only at a range of fluid enthalpy values Memory exists. The sensitivity analysis of the experimental parameters shows that heat transfer enhancement increases with mass flow rate, heat flux density decreases, pressure decreases, and heat transfer deteriorates.