Heat transfer characteristics during transcritical depressurization transient process in circulating fluidized bed

doi:10.11949/0438-1157.20250433

Abstract

Abstract:

During the transcritical depressurization process of a circulating fluidized bed (CFB), abrupt changes in fluid thermophysical properties within heating surfaces can lead to heat transfer deterioration, causing a sharp rise in wall temperature. It is imperative to conduct transient safety analysis under transcritical conditions to ensure system operational safety. To address this, a mathematical model was established to simulate the transcritical depressurization process of supercritical water in CFB heating surfaces, and a numerical program was developed using Fortran. The program employs one-dimensional transient governing equations to describe fluid flow, while transient heat conduction equations are utilized to simulate heat transfer in the tube wall. At the transcritical moment, critical temperature and critical enthalpy are adopted as criteria for local heat transfer mode transitions. A wetting front migration model is integrated to simulate the sequential temperature recovery in dried-out wall regions. Comparison with experimental results demonstrates that the program can accurately simulate the flow and heat transfer characteristics of the transcritical processes. The program effectively predicts varying degrees of heat transfer deterioration, providing a reliable means for safety analysis of heating surfaces during depressurization.

Key words: circulating fluidized bed, supercritical water, transcritical, numerical analysis, heat transfer deterioration, wetting front

摘要：

循环流化床在跨临界降压过程中，受热面内流体因物性突变容易出现传热恶化，导致壁温急剧上升，亟需开展跨临界瞬态安全分析以保障系统安全运行。为此，建立了循环流化床受热面内超临界水跨临界降压过程的数学模型，并开发了基于Fortran语言的数值计算程序。程序采用一维瞬态控制方程描述流体流动，管壁传热则通过瞬态导热方程进行模拟。在跨临界时刻，使用临界温度、临界焓值作为局部管段传热模式判据，结合润湿前沿移动模型来模拟管段干涸区域壁温依次回落的过程。通过与实验结果的对比验证表明，该程序能够较为准确地模拟跨临界过程中的流动传热特性。程序可有效预测出不同程度的传热恶化情况，为受热面降压过程的安全性分析提供了有效工具。

关键词: 循环流化床, 超临界水, 跨临界, 数值分析, 传热恶化, 润湿前沿

CLC Number:

TK 124

Zerui GUO, Huimiao GAO, Boyao ZHANG, Tingting YU, Tianru ZHU, Dong YANG. Heat transfer characteristics during transcritical depressurization transient process in circulating fluidized bed[J]. CIESC Journal, 2025, 76(11): 5890-5900.

郭泽瑞, 高慧淼, 张博垚, 于婷婷, 朱天如, 杨冬. 循环流化床跨临界降压瞬态过程中的传热特性[J]. 化工学报, 2025, 76(11): 5890-5900.

Figures/Tables 11

Fig.1 The heat transfer state at the local pipe section during the transcritical moment

Fig.2 Physical model of the wetting front movement process

Fig.3 Determination method of heat transfer mode during transcritical process

Fig.4 Program flowchart

Fig.5 Experimental boundary conditions of Ref.[18]

Fig.6 Comparison of calculated and experimental results for inner wall temperature at various cross-sections

Fig.7 Calculation results of inner wall temperature

Fig.8 Variation of tube wall temperature under different heat flux

Fig.9 Variation of tube wall temperature under different mass flow rates

Fig.10 Fluid parameter variation curve at 200 mm during transcritical depressurization

Fig.11 Fluid parameter variation curve at 1900 mm during transcritical depressurization

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