Abstract

Prediction of dryout location is essential to identify reliable heat flux margins for the safe operation of different thermal systems. The present study proposes a simple model to predict the dryout type critical heat flux location in a circular tube and an annulus. Based on the flow topology, the annular flow boiling regime is demarcated into two zones viz., vapour flow in the core region and liquid film flow in the annular gap between the vapour core and the wall surface. An expression is derived for the dryout location which is purely a function of operating conditions and fluid properties. The dryout location and quality predictions of the present model are found to be in very good agreement and within 10% error margin against the experimental data for tube and annulus geometries. The present study is extended to investigate the effect of eccentricity on the dryout location and the inner wall temperature. It is observed that the eccentricity results in early occurrence of dryout in the narrow gap region of an eccentric annulus. Furthermore, the predictions from the present model are compared with the look-up table data, sub-channel analysis and computational fluid dynamics simulation predictions.

摘要

预测干燥位置对于确定可靠的热通量裕度至关重要，以确保不同热系统的安全运行。本研究提出了一个简单的模型来预测圆管和环空中的变干型临界热通量位置。基于流动拓扑，将环形流动沸腾区划为两个区域，即例如，在芯区域中的蒸气流动和液膜在蒸气芯和壁表面之间的环形间隙中流动。得出干燥位置的表达式，其纯粹是操作条件和流体特性的函数。发现本模型的变干位置和质量预测非常吻合，并且相对于管和环几何形状的实验数据而言，误差范围在10％以内。本研究扩展到研究偏心率对干透位置和内壁温度的影响。观察到，偏心导致在偏心环的狭窄间隙区域中较早发生变干。此外，将来自本模型的预测与查找表数据，子通道分析和计算流体动力学模拟预测进行比较。