Abstract
In subcooled boiling flows beyond a certain heat flux, heat transfer is hampered due to a phenomenon known as Departure from Nucleate Boiling (DNB). Conducting DNB experiments at one-to-one nuclear reactor operating conditions is highly challenging and expensive. Another alternative approach is to use Look-up table data. However, its applicability is limited due to its dependence on rod bundle correction factors. In the present investigation, a state-of-the-art Eulerian-Eulerian two-fluid model coupled with an extended heat flux partitioning model is used to predict DNB in tubes and rod bundles with square and hexagonal lattices (relevant to Pressurized Water Reactors). In this approach, bubble departure characteristics are modeled using semi-mechanistic models based on force balance analysis. The predicted DNB values are compared with experimental and Look-up table data and found out to be within 1.8% to 20%.
Highlights
Flow boiling is widely used in many industries as a heat transfer mechanism due to its excellent heat transfer characteristics
The ratio between Departure from Nucleate Boiling (DNB) and the actual operating local heat flux is called the departure from nucleate boiling ratio (DNBR), which may change axially and radially in the reactor
DNB has been modeled using the EEHFP model with semimechanistic models for determining bubble departure characteristics
Summary
Flow boiling is widely used in many industries as a heat transfer mechanism due to its excellent heat transfer characteristics. It is important to note that conducting experiments at high pressure and high temperature (HPHT) conditions, especially for PWR rod bundles, is technically challenging and highly expensive Another approach for DNB evaluation is to use Look-up tables [5,6], which are developed based on large sets of experimental data. Li et al [16] predicted DNB in vertical tubes using an extending wall boiling model based on the near-wall cell’s void fraction They used Look-up table [5] data for validation and found the maximum deviation to be 20% for uniform heat flux profiles. When the outlet quality was more than or equal to −0.10, the predictions were within 6% compared with experimental data [21] In all these previous numerical works based on the EEHFP model for DNB prediction, as discussed above, empirical models were used to determine bubble departure characteristics. The hexagonal lattice DNB predictions have been compared with Look-up tables with appropriate corrections
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