在低质量流率条件下,对垂直上升内螺纹管在亚临界和近临界压力区的传热特性进行了实验研究。实验参数范围为压力p=12~22.5 MPa,质量流率G=170~420 kg/(m2·s),内壁热负荷q=150~366 k W/m2。实验结果表明:在亚临界压力区,垂直上升内螺纹管发生了第二类传热恶化,即干涸(dryout)。内壁热负荷和压力的增大,均会导致干涸点的提前以及干涸后内壁温度的峰值增大。质量流率对干涸点的影响呈现非单调性,存在一界限质量流率。当质量流率小于界限质量流率时,干涸点随质量流率的增加而提前;当质量流率大于界限质量流率时,干涸点随质量流率的增加而推迟。在近临界压力区的亚临界压力部分,内壁热负荷较高时容易发生第一类传热恶化,即膜态沸腾(DNB)。内壁热负荷的增大和质量流率的减小,均会导致传热恶化的提前以及膜态沸腾后的温度飞升值增加。在近临界压力区的超临界压力部分,内螺纹管传热良好,在拟临界区域出现一定程度的传热强化,其传热特性和亚临界压力区的传热特性相似。 Under low mass flow rate conditions, the heat transfer characteristics of vertically-rising female-thread tubes in subcritical and near-critical pressure zones were experimentally studied. The experimental parameters ranged from p = 12-22.5 MPa, mass flow rate G = 170-420 kg / (m2 · s) and thermal wall load q = 150-366 k W / m2. The experimental results show that in the subcritical pressure zone, the second type of heat transfer deterioration, ie, dryout, occurs in the vertically rising female pipe. Internal wall heat load and pressure increases, will lead to dry-up point in advance and the dry wall temperature after the peak increased. The effect of mass flow rate on dry spots is not monotonic, and there is a limit mass flow rate. When the mass flow rate is less than the limit mass flow rate, the dry point advances with the increase of the mass flow rate. When the mass flow rate is greater than the limit mass flow rate, the dry point is delayed with the increase of the mass flow rate. In the near-critical pressure zone of the subcritical pressure part of the inner wall when the heat load is prone to the first type of heat transfer deterioration, that film boiling (DNB). The increase of heat load on the inner wall and the decrease of mass flow rate will lead to the advance of heat transfer deterioration and the increase of the temperature rise value after membrane boiling. In the supercritical pressure region near the critical pressure zone, the heat transfer of the internally threaded tube is good, and a certain degree of heat transfer enhancement occurs in the pseudo-critical zone. The heat transfer characteristics are similar to those of the subcritical pressure zone.