本工作的目的是评估自然循环锅炉蒸发器管在不同运行压力和热通量下的性能。当前工作的一个重要关注点是评估自然循环锅炉现有蒸发器降液管系统的干涸/临界热通量极限和临界循环比 (CR)。从安全运行的角度来看,对这些参数的分析至关重要。为了进行研究,开发了三种两相流模型,即均匀流模型(HFM)、分离流模型(SFM)和漂移通量模型(DFM)。评估了模型对各种热工水力参数、流态变化和循环比的敏感性。对一系列实验、数值、以及与两相流热虹吸管相关的工厂设计数据。结果表明,HFM 预测的低(< 40 bar)和中(40-80 bar)压力下的安全循环比相对较高,并且与其他两个模型有很大不同。然而,超过 80 bar 压力(高工作压力)时,不同模型预测的 CR 相当低,并且彼此更加一致。不同容量锅炉的实际性能研究表明,不同模型对不同容量锅炉的临界热流密度预测的最大差异在15%以内。这些数据将帮助与锅炉运行相关的工程师和锅炉设计部门的相关人员。结果表明,HFM 预测的低(< 40 bar)和中(40-80 bar)压力下的安全循环比相对较高,并且与其他两个模型有很大不同。然而,超过 80 bar 压力(高工作压力)时,不同模型预测的 CR 相当低,并且彼此更加一致。不同容量锅炉的实际性能研究表明,不同模型对不同容量锅炉的临界热流密度预测的最大差异在15%以内。这些数据将帮助与锅炉运行相关的工程师和锅炉设计部门的相关人员。结果表明,HFM 预测的低(< 40 bar)和中(40-80 bar)压力下的安全循环比相对较高,并且与其他两个模型有很大不同。然而,超过 80 bar 压力(高工作压力)时,不同模型预测的 CR 相当低,并且彼此更加一致。不同容量锅炉的实际性能研究表明,不同模型对不同容量锅炉的临界热流密度预测的最大差异在15%以内。这些数据将帮助与锅炉运行相关的工程师和锅炉设计部门的相关人员。超过 80 bar 压力(高工作压力)时,不同模型预测的 CR 会显着降低,并且彼此更加一致。不同容量锅炉的实际性能研究表明,不同模型对不同容量锅炉的临界热流密度预测的最大差异在15%以内。这些数据将帮助与锅炉运行相关的工程师和锅炉设计部门的相关人员。超过 80 bar 压力(高工作压力)时,不同模型预测的 CR 会显着降低,并且彼此更加一致。不同容量锅炉的实际性能研究表明,不同模型对不同容量锅炉的临界热流密度预测的最大差异在15%以内。这些数据将帮助与锅炉运行相关的工程师和锅炉设计部门的相关人员。
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Performance assessment of the evaporator tubes of a natural circulation boiler by different two-phase flow models
The objective of the present work is to evaluate the performance of the evaporator tubes of a natural circulation boiler under different operating pressure and heat flux. A significant concern of the present work is assessing the dry-out/critical heat flux limit and the critical circulation ratio (CR) of an existing evaporator downcomer system of a natural circulation boiler. The analysis of these parameters is crucial from a safe operation perspective. To carry out the study, three two-phase flow models, namely homogeneous flow model (HFM), separated flow model (SFM), and drift-flux model (DFM), are developed. The sensitivity of the models on various thermo-hydraulic parameters, change of flow regime, and circulation ratio is assessed. A rigorous validation exercise is carried out for a host of experimental, numerical, and plant design data pertaining to two-phase flow thermosyphon. The results indicate that the safe circulation ratio at low (< 40 bar) and intermediate (40–80 bar) pressure predicted by HFM is relatively high and differs substantially from the two other models. However, beyond 80 bar pressure (high operating pressure), the CR predicted by different models is considerably less and in closer agreement with each other. The practical boiler performance studies with different capacities indicate that the maximum difference of critical heat flux predicted by different models for boilers of different capacities lies within a 15% margin. These data will help the engineers associated with boiler operation and the associated persons with the boiler design sector.