Abstract:

Experimental study on the heat transfer characteristics of ultra high parameter CO₂ in a vertically upward pipe was carried out. The experiment of CO₂ heat transfer was performed in a 10.0mm inner diameter tube, covering ranges of p=8.21—20.6MPa, q _w=95—300kW/m² and G=1000—1232.5kg/(m²·s). The effects of inlet temperature, pressure and heat flux on heat transfer were analyzed. Results showed that, under certain conditions of heat flux, pressure and mass flux, the inlet temperature has obvious effect on heat transfer. When the T _in<T _pc, wall temperature exists a local peak value ahead of the pseudo-critical point. Temperature increases largely and then decreases as the bulk enthalpy increases, which indicates heat transfer deterioration occurs. However, the wall temperature increases monotonously when the T _in>T _pc, no obvious peak wall temperature was observed. This means heat transfer deterioration was found to occur only in the region of T _in<T _pc. In the region of T _in>T _pc, pressure and heat flux have little effect on heat transfer, it follows single-phase forced convection heat transfer. The results showed that the heat transfer coefficient and wall temperature calculated by the classical D-B single-phase turbulent convection formula have achieved satisfactory prediction accuracy.

Key words: supercritical CO₂, ultra high parameter, convection, heat transfer, experiment

摘要：

在均匀加热条件下，开展了超高参数二氧化碳在垂直上升管中的传热特性实验研究。实验段内径为10.0mm，实验参数范围：压力p=8.21～20.6MPa，热流密度q _w=95～300kW/m²，质量流速G= 1000～1232.5kg/(m²·s)。分析了入口温度、压力和热流密度对传热的影响规律。实验结果表明，在热流密度、压力和质量流速一定的条件下，入口温度对传热有明显影响，当T _in<T _pc时，在拟临界温度前壁温出现峰值，达到峰值点随后又逐渐下降，即传热出现了恶化现象。但是当T _in>T _pc时在同样的工况下，壁温沿着主流焓值单调上升，无明显的壁温峰值出现，这意味着传热恶化只发生在T _in<T _pc时。在T _in>T _pc的超临界工况下，压力和热流密度对传热的影响较小，工质遵循单相强制对流换热。将实验数据与选取的典型传热关联式作比较，结果显示，经典的D-B单相湍流对流公式计算的换热系数和壁温已达到了满意的预测精度。

关键词: 超临界二氧化碳, 超高参数, 对流, 传热, 实验