Study on Two-Phase Hydrodynamic Structure of Bubble Layers under Forced Convective Subcooled Flow Boiling

最初的研究计划已经扩展到不仅涵盖气泡层的多流体流体动力结构，而且还包括强制对流过冷流沸腾和临界热流密度的更广泛的实验和分析。这包括(1)在DNB点之前的气泡行为，(2)各种通道中的相分布和湍流机制，(3)二维时膜流动行为，(4)湍流剪切流场中液滴的湍流分散，(5)DNB和膜干的预测。实验观测揭示了控制气泡横向迁移的几种不同机制，导致相和湍流的不均匀分布。通过数值模拟成功地预测了这些总体趋势。我们还建立了一个基于多流体模型的临界热流密度（DNB和干干热流密度）数值预测的解析模型。为了使这些模型更准确地反映随时间变化的膜厚和液滴行为对湍流气体流动的影响，我们开发了一种新的具有高空间和时间分辨率的超声回波技术和基于双向耦合方法的液滴沉积和湍流扩散的数值模拟模型。后一种方法已被证明是客观评估现有相关性有效性的好工具。

The initial research plan has been extended to cover, not only multi-fluid hydrodynamic structure of bubble layers, but also wider aspects of forced convection subcooled flow boiling and critical heat flux both experimentally and analytically. This includes (1) bubble behaviors under conditions up to the DNB point, (2) phase distribution and turbulence mechanisms in various channels, (3) 2-dimensional time-dependent film flow behavior, (4) turbulent dispersion of liquid droplets in turbulent shear flow field, awl (5) prediction of the DNB and film dryout.Experimental observations have revealed several different mechanisms dominating bubble lateral migrations, resulting in non-uniform distributions of phases and turbulence. These general trends were successfully predicted by numerical simulations. We also developed an analytical model to numerically predict critical heat fluxes (DNB and dryout heat flux) based on multi-fluid models. In order for these models to incorporate more accurately the effects of time-dependent spatially varying film thickness and liquid droplets behavior in turbulent gas flow, we have developed a new ultrasonic echo technique with high spatial and time resolutions and a numerical simulation model to calculate deposition and turbulent diffusion of liquid droplets based on two-way coupling method. The latter method has been shown to be a good tool to objectively evaluate the validity of existing correlations.