含有不凝气蒸汽管内直接接触凝结流动特征及热质传递机理

Oscillation of thermal parameter and deterioration of heat and mass transfer induced by direct contact condensation of steam with non-condensable gas is increasingly paid more and more attention. This project is to reveal mechanism of heat and mass transfer of direct contact condensation of steam with non-condensable gas in a tube as the objective orientation, to analyze the mechanism of heat and mass transfer on the condensation interface of gas and liquid, to establish a dual component-double resistance model for direct contact condensation of steam with non-condensable gas. Analysis of evolution law of gas-liquid interface and flow characteristics of two-phase flow are completed through visual experiment and transition criterion of condensation pattern is proposed. Based on the dual component-double resistance condensation model, condensation is numerically simulated for experiment case in order to reproduce experiment phenomena by numerical result, and then characteristics of temperature and pressure oscillations are characterized. Condensation pattern map and correlations of mass and heat transfer coefficient are developed for steam direct contact condensation with non-condensable gas. With Difference from pure steam direct contact condensation, this project focuses on mechanism reveal of component increase of non-condensable gas during the condensation as key scientific problem, which causes deterioration of heat and mass transfer. Establishment of internal connection of non-condensable gas and condensation phenomenon, characteristics of temperature and pressure oscillations, and rule of heat and mass transfer forms the research feature and innovation to explore the nature cause and to establish some theoretical foundation of thermal parameter oscillations and deterioration of heat and mass transfer during steam direct contact condensation due to non-condensable gas.

含有不凝气蒸汽直接接触凝结引起的热工参数振荡和热质传递恶化，日益受到广泛关注。本项目以含有不凝气蒸汽管内直接接触凝结热质传递机理揭示为目标导向，剖析气液凝结界面处热质传递机制，构建含有不凝气蒸汽直接接触凝结“双元双阻力”凝结模型；通过可视化实验，分析气液界面演变规律、两相流流动特征，提出凝结流型转捩判据；基于“双元双阻力”凝结模型，对实验工况下的凝结过程进行数值模拟，数值结果能够“复现”实验现象，进而对温度和压力振荡特征进行表征，发展适用于含有不凝气蒸汽凝结流型相图、传热传质系数关联式。较纯蒸汽接触凝结不同，本项目紧密围绕不凝气组分随着凝结过程持续增加，导致凝结界面热质传递恶化的机理揭示这一关键科学问题，在构建不凝气与凝结现象、温度和压力振荡特征、热质传递规律的内在关联方面，形成研究特色和创新，为探究含有不凝气蒸汽直接接触凝结诱发热工参数振荡及热质传递恶化致因本质奠定一定的理论基础。

蒸汽直接接触凝结因其具有接触面积大、驱动能耗低、传热传质效率高等优点被广泛应用在诸多工业生产领域。然而在实际工程应用中，蒸汽中往往掺混不凝气，不凝气对蒸汽直接接触凝结过程中的传热传质及温度压力振荡具有重要影响。本项目首先设计构建了含不凝气蒸汽管内直接接触凝结实验平台，开展了大量的实验研究。通过可视化实验研究，获得含不凝气蒸汽管内直接接触凝结过程中气液界面的空间分布和运动状态，对含不凝气蒸汽管内直接接触凝结现象获得表观认知，并对典型凝结流型进行了甄别，观察到了四种典型的凝结流型，即喘振凝结、振荡泡状流、段塞流和分层流。分析了不凝气含量、混合气体质量流率、过冷水雷诺数和过冷水温度对凝结流型产生和转捩的影响，构建了二维和三维的凝结流型图，直观表现凝结流型与各影响因素的关系。其次，基于实验测得的温度与压力数据，分析和总结了不凝气含量、混合气体质量流率、过冷水雷诺数与温度对含不凝气蒸汽管内直接接触凝结振荡特性和凝结流型的影响规律，阐述凝结压力振荡的诱发机制及不凝气对凝结压力振荡的削弱机制。最后，建立了适用于含不凝气蒸汽直接接触凝结“双元双阻力”凝结数学模型，数值预测了不凝气对管内蒸汽直接接触凝结多相流动与传热传质过程的影响，与实验结果相比，数值结果具有一定的可靠性。综合实验结果和数值结果，理论分析了气液界面运动形态和凝结温度与压力振荡之间的内在联系，揭示了含不凝气蒸汽管内直接接触凝结过程的流动与相变机理和凝结压力振荡的产生及不凝气对其振荡峰值的抑制机制，研究成果可为蒸汽直接接触凝结的工程应用和压力振荡抑制提供了技术手段和理论指导。