Bubble Science behind Boiling Water


The boiling phenomenon is important as an elementary process in energy equipment that utilize vapor and also in the cooling control systems utilizing high heat-transfer rates of boiling. Technically, such critical applications (in the latter category) are favored by the capability of the boiling phenomenon to accommodate large heat fluxes with relatively small driving temperature difference. Nonetheless, the distribution of steam in a boiling mixture affects the heat transfer rate and may cause unfavorable conditions; for instance, in Light Water Reactor (LWR) nuclear power plants where the distribution of vapor in the LWR sub-channels can cause burn-out phenomenon at certain wall superheat known as Departure from Nucleate Boiling. Overall, due to its complex nature, better understanding and modeling of boiling process remains a major challenge in multiphase flow research. In the past, experimental approaches presented valuable insights with regard to understand the boiling phenomena at various scales. These techniques were however limited when it comes to special flow geometries and flow conditions in engineering applications. Recently, technological advances have yielded better simulation techniques that are efficient but demand data of high-quality and high resolution. In particular, Interface tracking simulation (ITS) has emerged as one of the most promising approaches to describe heat transfer of boiling phenomena and their underlying mechanisms.

Advancing the ITS modeling is desirable and could unlock various benefits for engineering systems relying on two-phase heat transfer. To this end, researchers from the Department of Nuclear Engineering at North Carolina State University: Dr. Mengnan Li and Professor Igor A. Bolotnov developed a new evaporation and condensation model designed for large scale boiling simulation. The researchers focused on developing the model for simulations with local mesh refinement, unstructured mesh and highly scalable algorithm for parallel computing. Their work is currently published in the International Journal of Heat and Mass Transfer.

In their approach, verification of the evaporation and condensation model was performed by comparing the bubble growth rate with analytical solutions. Both pool boiling and flow boiling simulations were performed using the ITS evaporation and condensation model. The researchers then validated the bubble nucleation frequency in pool boiling simulation, against experimentally-based correlations. The bubble evolution and growth rate were compared with experimental data to validate the model performance under flow boiling condition.

The authors reported good agreement was found between the model prediction and the experimental measurements. Additionally, the researchers noted that compared to the structured-grid based solvers, which are challenging to apply to complex engineering geometries, the presented boiling model implementation was capable of conducting high-resolution boiling simulations in engineering geometries and resolving the detailed hydrodynamics and thermal information for quantities of interest at/around the interface.

In summary, the study Dr. Mengnan Li and Professor Igor Bolotnov demonstrated the successful implementation, verification and validation of the modeling capability of the evaporation process using a massively parallel unstructured grid flow solver, PHASTA. The study further showed the potential of the ITS boiling model in studying bubble dynamics and heat transfer mechanism in large scale engineering applications. In a statement to Advances in Engineering, the authors said that the newly presented boiling model will serve as one of the most important building blocks for high resolution boiling simulations in realistic engineering geometries. They are excited to continue the work exploring the boiling phenomenon with numerical approaches and their latest results just came out in Nuclear Engineering and Design [2].

Bubble Science behind Boiling Water - Advances in Engineering Bubble Science behind Boiling Water - Advances in Engineering Bubble Science behind Boiling Water - Advances in Engineering

About the author

Dr. Mengnan Li received her Bachelor of Science degree in Nuclear Engineering and Technology in May 2014 from Sichuan University, Chengdu, China. She earned a master’s degree and a Ph. D degree in Nuclear Engineering at North Carolina State University in 2016 and 2019 respectively.

Her research focuses on multi-phase flow simulation and their applications in real-world complex engineering system. The complex interaction of liquids, gases and solids is of interest in many areas including nuclear reactor thermal hydraulics, carbon capture and sequestration, etc. These interactions are heavily influenced by properties and phenomena, such as the phase change, interfacial physics, capillary actions, and chemical reaction. High-fidelity multi-phase flow simulation can provide valuable insight, especially when the flow system is complex and hard to be directly measured by experimental instruments. however accurately simulating multi-phase flow has proven to be a challenging area for existing numerical methods.

From June 2015 to December 2018, Dr. Mengnan Li conducted research as a Graduate Research Assistant at NCSU. She developed an innovative boiling model that integrates the mechanistic study on local boiling phenomena with practical engineering problems of nuclear plant coolant channel, an effort aiming to enhance the efficiency of advanced nuclear design and safety of the nuclear power plant. Boiling phenomenon accommodates large heat fluxes with relatively small driving temperature difference. This makes boiling ideal for applications that demands substantial heat transfer rates like nuclear power plants. The distribution of steam in a boiling mixture affects the heat transfer rate and may cause unfavorable conditions such as reactor unplanned shutdowns and even accidents. Due to boiling’s complex nature, better understanding and modeling of boiling process remains a major challenge in nuclear engineering research. Dr. Mengnan Li developed this innovative boiling model to conduct high-resolution large-scale boiling simulations in complex engineering geometries and study the detailed information inside the nuclear plant coolant channel. This approach provides valuable detailed information that cannot be obtained by traditional experimental approaches and help fill the data gap between boiling experiments in the lab and boiling flow in nuclear plant coolant channel.

Since 2019, Dr. Mengnan Li has been working in the School of Earth Science at The Ohio State University (OSU), located at Columbus, as a Postdoctoral Researcher. She has been addressing the challenging problem of modifying the versatile compositional reservoir simulator to incorporate complex geochemical and mineralogical reactions typically observed during subsurface fluid-gas-rock interaction. With this capability, the reservoir simulation tool can quantify the degree of CO2 dissolution, dispersion, geochemical reactions, fingering, and other transport properties of the CO2 plume and further get a detailed picture of the CO2 plume area and information regarding control leakage and induced seismicity risk.

About the author

Dr. Bolotnov is an associate professor of nuclear engineering at NCSU, where he teaches nuclear system energy conversion and multiscale simulation of two-phase flow. Dr. Bolotnov is specialized in computational fluid dynamics applications in nuclear reactor engineering in general, and in multiphase turbulent flow in particular. His research includes multiscale approach for nuclear reactor simulations; development of new multiphase turbulence models for application in nuclear, chemical, and biochemical engineering; and direct numerical simulation of single and multiphase turbulent flows. Dr. Bolotnov had been a member of the Consortium for Advanced Simulation of Light Water Reactors (CASL) for 10 years, an energy innovation hub for nuclear reactor modeling and simulation funded by the U.S. Department of Energy (DOE).

His research has also been funded by DOE-NEUP program, National Science Foundation, U.S. Nuclear Regulatory Commission as well as some industry partners. Dr. Bolotnov brings to the project experience and capability with cutting-edge high-performance-computing enabled CFD simulation of complex single- and multi-phase flow, using PHASTA, OpenFOAM and NPHASE-CMFD codes. He plays an active role in American Nuclear Society (ANS), currently holding the position of the Program Chair in Thermal Hydraulics Division (THD) and member of Executive Committee of THD. Dr. Bolotnov hold a Ph.D. and M.S. in Engineering Physics from Rensselaer Polytechnic Institute in New York.


[1] Mengnan Li, Igor A. Bolotnov. 2020 “The evaporation and condensation model with interface tracking” , International Journal of Heat and Mass Transfer, volume 150 (2020) 119256.

Go To International Journal of Heat and Mass Transfer

[2] Li, Mengnan, Joachim Moortgat, and Igor A. Bolotnov. “Nucleate boiling simulation using interface tracking method.” Nuclear Engineering and Design 369 (2020): 110813.

Go To Nuclear Engineering and Design

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