[Paper Review] Implementation and validation of two-phase boiling flow models in OpenFOAM

Kai Fu, Henryk Anglart|arXiv (Cornell University)|Sep 6, 2017

Lattice Boltzmann Simulation Studies3 citations

TL;DR

This paper presents the implementation and validation of a two-phase boiling flow model in OpenFOAM using a two-fluid approach with Reynolds-averaged turbulence modeling. The model predicts subcooled and saturated nucleate boiling with closure laws for interfacial heat transfer, phase change, and interfacial area concentration, achieving good agreement with experimental data for void fraction and temperature profiles, though bubble size prediction remains underperforming due to limitations in coalescence modeling.

ABSTRACT

Prediction of two-phase boiling flows using the computational fluid dynamics (CFD) approach is very challenging since several sub-models for interfacial mass, momentum and energy transfer in such flows are still not well established and require further development and validation. Once validating a particular model, it is important that all key parameter involved in the model are carefully verified. Such verification is typically performed by separate effect tests, where one parameter at a time is compared to a measured or otherwise known value. Needless to say that for complex models, which are typical for CFD applications to two-phase flow, the number of independent parameters that need to be verified can be quite high. This particular feature makes the validation process of complex CFD models in open source codes very attractive, since full access to the implementation details is possible. This paper is concerned with implementation and validation of two-phase boiling bubbly flow models using the OpenFOAM, open source environment. The model employs the two-fluid formulation of the conservation equations with the Reynolds-averaged treatment of the turbulent terms. The model consists of six conservation equations for the liquid and the vapor phase, allowing for the thermodynamic non-equilibrium and compressibility of both phases. In addition, the model includes two transport equations for the turbulence kinetic energy and energy dissipation and one transport equation for the interfacial area concentration. New models for wall heat partitioning as well as for the phase change terms in nucleate boiling have been implemented. Sensitivity studies as well as validation of the model against measured data available in the open literature have been performed and it has been shown that a reasonable agreement between predictions and experiments has been achieved.

Motivation & Objective

• To develop and implement a comprehensive two-phase boiling flow model in the open-source CFD code OpenFOAM for accurate simulation of subcooled and saturated nucleate boiling.
• To address the lack of validated closure laws for interfacial mass, momentum, and energy transfer in two-phase boiling flows.
• To enable full verification and validation of complex CFD models through open-source access to implementation details.
• To improve prediction accuracy of void fraction, temperature distribution, and phase change mechanisms in vertical upward flow in heated pipes.
• To identify limitations in current interfacial area transport models, particularly in predicting bubble size distribution.

Proposed method

• Adopted a two-fluid formulation with six conservation equations for liquid and vapor phases, including thermodynamic non-equilibrium and compressibility.
• Incorporated transport equations for turbulence kinetic energy, dissipation rate, and interfacial area concentration (IAC) to close the system.
• Implemented new models for wall heat partitioning and phase change terms in nucleate boiling, including quenching, sensible heating, and vapor generation.
• Used the Boussinesq hypothesis for turbulent stress modeling and applied the standard k-ε turbulence model with wall functions.
• Employed upwind discretization for interfacial velocity and included source/sink terms for bubble coalescence, breakup, and nucleation.
• Validated the model against Bartolomej and DEBORA experimental data using sensitivity studies and parametric tuning of coefficients such as the turbulent dispersion force.

Experimental results

Research questions

• RQ1 Can a two-fluid two-phase boiling model with comprehensive closure laws be successfully implemented in OpenFOAM for subcooled flow boiling simulations?
• RQ2 How accurately can the model predict void fraction and liquid temperature profiles compared to experimental data in vertical upward flow?
• RQ3 What is the impact of key model parameters—particularly the turbulent dispersion force coefficient—on prediction accuracy?
• RQ4 Why is the predicted bubble size significantly underestimated in the test section, and what does this imply about current interfacial area transport models?
• RQ5 To what extent can the model reproduce experimental radial temperature distributions and phase change mechanisms?

Key findings

• The model achieved reasonable agreement with experimental data for void fraction and liquid temperature profiles in both Bartolomej and DEBORA test cases.
• Sensitivity analysis showed that the turbulent dispersion force coefficient in the range of 1.0 to 2.5 significantly improves overall prediction accuracy.
• The radial temperature distribution was predicted with very good agreement to measured data, indicating reliable thermal field resolution.
• Bubble size prediction was found to be unsatisfactory, with significant underestimation in the observation region, likely due to underestimation of bubble coalescence rates.
• The model's implementation in OpenFOAM enables full transparency and verification, supporting further development of closure laws for boiling flows.
• The results highlight the need for improved interfacial area transport models, particularly for coalescence and breakup processes in subcooled boiling.