ABSTRACT

It is hypothesized that the heat transfer in microgravity bubbly flow boiling can be computed through a single-flow simulation that accounts for the acceleration of the liquid as bubbles form since the slip velocity in microgravity is negligible. Measurements within the bubbly flow regime were obtained in a 6 mm ID sapphire tube in microgravity using HFE-7000 at four mass fluxes, six heat fluxes, and two subcoolings at atmospheric pressure. Flow visualization was performed and time and space resolved temperature and heat transfer distributions at the wall–fluid interface were measured using a Temperature Sensitive Paint (TSP) applied to the inside of the tube. The local liquid velocity was determined from the movement of small bubbles in the flow. The local, time-averaged heat transfer data were compared to numerical simulations of single-phase flow in a tube whose diameter was varied to match the experimentally obtained local liquid velocity. When the flow within the tube was laminar (low heat flux and mass flux cases), the measured heat transfer agreed well with the numerical results. For cases where the flow became transitional/turbulent and significant bubble coalescence was present, the measured heat transfer was higher, but was bounded by numerical solutions assuming laminar and turbulent flow.

摘要

假设微重力气泡流沸腾中的传热可以通过单流模拟计算，该模拟考虑了气泡形成时液体的加速度，因为微重力中的滑移速度可以忽略不计。在微重力环境下，使用 HFE-7000 在四个质量通量、六个热通量和两个大气压过冷条件下，在 6 毫米内径蓝宝石管中获得气泡流态内的测量值。进行了流动可视化，并使用涂在管子内部的温度敏感涂料 (TSP) 测量壁-流体界面处的时间和空间分辨温度和传热分布。局部液体速度由流动中小气泡的运动确定。本地的，将时间平均传热数据与管中单相流的数值模拟进行比较，该管的直径是变化的，以匹配实验获得的局部液体速度。当管内流动为层流时（低热通量和质量通量情况），测得的传热与数值结果吻合良好。对于流动变为过渡/湍流且存在显着气泡合并的情况，测得的传热更高，但受限于假设层流和湍流的数值解。