低温压驱动下直接接触沸腾换热气泡群演变过程的场均匀性精确表征及其强化传热机理

Compared with other heat transfer methods, direct contact heat transfer has the advantages of small corrosion, no scaling, high thermal efficiency and is especially suitable for running under low temperature difference driving. In its boiling heat transfer bubble swarm evolution process, the uniformity of concentration field, temperature field and temperature difference field are closely related to the effectiveness of heat exchanger. In order to solve the traditional problem of bubble superposition imaging and answer the adaptability question of field uniformity measurement method in different local area, which are existed in using visualization technology to characterize flow pattern, this project proposes to study the accurate characterization of field uniformity in a direct contact boiling heat transfer bubble swarm evolution process under small temperature difference driving by introducing discrepancy theory and uniformity principle of temperature difference field. Studies involve exploration of accurate characterization and evolution law of 2-dimension, 3-dimension flow patterns of organic working fluid and heat transfer fluid in a boiling heat transfer bubble swarm evolution process under the influence of lighting, establishing the characterization methods of field uniformity of concentration field, temperature field and temperature difference field in the bubble swarm evolution process, stating the impact law and regulatory mechanism of the nozzle shape, the arranging of nozzle, density of heat flow, the rate of flow and the height of heat transfer fluid on the heat transfer performance, investigating the intrinsic relationship among multiple fields and the multi-index influencing mechanism between field uniformity and heat transfer performance, obtaining field uniformity characterization in the direct contact heat transfer bubble swarm evaluation process and the coupling relationship model between that and heat transfer enhancement. From multi-dimension, by revealing the relationship between field uniformity and heat transfer, provide theoretical foundation for heat transfer and optimization design of efficient heat exchanger.

与其他传热方式相比，直接接触式换热腐蚀小、无结垢、换热效率高，且特别适应于低温压驱动下运行，其效能与气泡群演变过程浓度场、温度场和温差场的均匀性密切相关。本项目拟解决传统可视化技术表征流型中的气泡重叠成像及不同局域的场均匀性评价方法的适应性，引入偏差理论和温差场均匀性原则研究低温压驱动下直接接触沸腾换热气泡群演变过程的场均匀性精确表征及其强化传热机理。研究内容包括：通过探索光照影响下沸腾传热过程有机工质和导热油二维、三维流型精确表征及演变规律，构建气泡群演变过程的浓度场、温度场和温差场均匀性精确表征方法，阐明喷嘴结构与布置、热流密度、流量及导热油液位等参数对换热性能的影响规律及调控机制，探究多场均匀性之间内在关联及其与传热性能的多指标影响关系，获得气泡群演变过程的场均匀性特征及其强化传热机理。从多维度视角揭示场均匀性与传热的关系，为强化传热、高效换热器的优化设计提供理论依据。

我国余热资源丰富，探索高效余热资源利用设备和强化传热手段是解决能源危机的有效途径，与间壁式换热器相比，直接接触式换热器具有腐蚀小、无结垢、换热效率高等优点，研究直接接触沸腾换热气泡群演变过程的场均匀性精确表征及其强化传热机理对直接接触式换热器商业化应用具有指导意义。利用高速相机和ECT图像重构算法的流型图像；利用统计学前沿理论和方法，揭示光照均匀性对不同参数条件下气泡群演变和流型识别的影响机制，获得新的光照均匀性指标及其变化规律。提出基于图像信息熵理论的目标分割二值化阈值选择准则，针对现有二值化阈值选择方法导致气泡目标贝蒂数计算结果差异大、不统一的关键科学问题，提出基于熵理论和代数拓扑学的图像挖掘方法，将贝蒂数指标与熵理论指标应用于气泡群数字图像的分割，推导了描述多相流混合均匀性的数学模型和判断准则，通过ImageJ软件计算获得目标分割阈值介于67-101之间。提出了基于人工智能的直接接触换热器换热性能的预测方法；利用红外热像仪获得了不同时刻气液两相混合的连续温度场分布，基于时间和空间分别构建适应于连续温度场的温差场均匀性因子φ，分析了场协同数Fc与换热因子j之间的关联性，以及获得了连续温度场均匀性因子与场协同数之间的关系，结果发现两者之间的皮尔逊相关系数均在0.8以上。提出气泡平均宽度的一种新度量，用于评估直接接触沸腾传热过程中气泡群的动态演化。建立了贝蒂数斜率变化与平均容积换热系数的相关模型，并建立了表征η≥4传热效率的实验优化策略。改进了新指标，用于基于灰度图像分析的力矩的准确测量。与二值图像中的倾斜角方法相比，测试结果表明这两种方法具有显着的正相关性。与其他方法相比，通过矩演化拟合曲线获得的混合性能指标（t）与传热性能强相关（Pearson相关系数a = -0.94）。