方形再生冷却通道内超临界正癸烷湍流传热数值研究

Numerical Study on Turbulent Heat Transfer of Supercritical

关键词:  再生冷却  超临界压力  正癸烷  湍流传热  传热恶化  数值研究

Key words:  Regenerative cooling  Supercritical pressure  n-Decane  Turbulent heat transfer  Heat transfer deterioration  Numerical study

摘要:

为了深入理解再生冷却过程中碳氢燃料的超临界湍流传热特性，以正癸烷为研究对象，对其在非对称受热(上壁面外侧加热)方形通道内的流动传热进行了数值研究。在数值方法可靠性得到充分验证的基础上，详细探讨了进口温度和压力等运行参数对通道上壁面和侧壁面内侧平均壁温和平均努塞尔数分布的影响。计算结果表明:在运行压力接近临界压力且主流温度处于拟临界温度附近的综合条件下，流体热物性剧烈变化导致的类膜态沸腾效应，引起了上壁面内侧显著的传热恶化现象。同时，不平衡压差诱发的通道截面速度场异常分布，进一步影响了上壁面内侧近壁区域流体的换热性能。另外，类膜态沸腾效应致使上壁面热流更多地传递到侧壁面，导致侧壁面平均努塞尔数大幅增大，相比于正常换热的最大增幅约为50%。

Abstract:

In order to deeply understand the supercritical turbulent heat transfer characteristics of hydrocarbon fuel in the regenerative cooling process，numerical study on flow and heat transfer of n-decane in a square channel with asymmetric heating imposed on the top exterior channel surface was conducted. After the reliability of the numerical methods was fully validated，effects of two operating parameters，including the inlet temperature and pressure，on the distribution of averaged wall temperature and averaged Nusselt number of the top and side internal channel surfaces，have been discussed in detail. Results indicate that under the compositive conditions of the operational pressure being close to the critical pressure and the bulk fluid temperature being in the vicinity of the pseudo-critical temperature，a pseudo-film boiling effect occurs due to the drastic fluid thermophysical properties variations，and thus leads to a significant heat transfer deterioration phenomenon at the top internal wall. Simultaneously，abnormal distribution of the velocity field appears in the channel cross-sections owing to the imbalance pressure difference，further affects the heat transfer performance of near-wall fluid at the top internal wall. Moreover，the pseudo-film boiling effect forces more heat flux from the top to the side wall surface，so the averaged Nusselt number at the side wall greatly increases，and the largest increase amplitude compared to the normal heat transfer is about 50%.