自然循环窄矩形通道内单相水对流传热特性

Convectional heat transfer characteristics of single-phase natural circulation flow in a narrow rectangular channel

为探究单面加热窄矩形通道内,单相自然循环对流传热特性,进行了实验压力为0.2 MPa和0.3 MPa,入口欠热度范围为35~60 K,加热功率范围为30~90 kW/m^2的单相对流传热实验。实验结果表明,对流换热系数与Gnielinski公式符合较好,92%的实验数据与公式的相对误差在20%以内。引入斯坦顿数(St),对数据分析发现:自然循环流动中,实验段入口欠热度及加热功率对换热能力有明显影响,换热能力随着入口欠热度的增加而减小,随着加热功率的增加而变大。在窄矩形通道内的向上自然循环流动中,通过提高入口欠热度而导致的浮升力增加会引起同向对流,从而使换热减弱;单面加热条件下,提高加热功率引起的横向热驱动力增加会使传热得到强化。

To investigate the heat transfer characteristic of single-phase natural circulation flow in a one-side heating narrow rectangular channel, experiments were performed at pressures of 0. 2 and 0. 3 MPa, at an inlet sub-cooling temperature from 35 K to 60 K, and heat flux from 30 kW/m2 to 90 kW/m2. Experimental results indicate that the heat transfer coefficient agrees with the predictions of the Gnielinski correlation, and 92% of the experimental results are within a ± 20% error range of the correlation predictions. The heat transfer performance was investigated by introducing the Stanton number. The heat transfer coefficient increased with an increase in heat flux and a decrease in inlet sub-cooling. For upward natural circulation flow in a narrow rectangular channel, the increase in buoyancy induced by increasing the inlet sub-cooling resulted in the relaminarization effect, leading to a passive effect on heat transfer. However, the increase in thermal driven force induced by increasing heat flux makes the boundary layer unstable, thereby enhancing heat transfer.