Understanding buoyant-particle- induced heat and mass transfer through integrated experiments and simulations

Iowa State University, Ames IA

Investigators

Abstract

Recent experimental studies show that the addition of small amounts of gas bubbles in a liquid drastically improves heat transfer, making it up to twenty times more intense than in the same system without bubbles. This significant improvement in heat transfer is attributed to the fluctuations in the liquid velocity caused by the bubble motion, leading to a phenomenon called bubble-induced pseudoturbulence. While there is substantial experimental evidence of this phenomenon, and physical models for pseudoturbulence have been developed for homogeneous flows without walls, there is a knowledge gap concerning pseudoturbulence in gas-liquid flows involving walls, as those encountered in many practical applications like chemical reactors, fermenters and heat exchangers. The main aim of this project is to gain an improved understanding of the physics of pseudoturbulence in gas-liquid flows in the presence of solid walls with a combination of detailed numerical simulations and experiments, and to formulate models usable by engineers to more accurately predict heat transfer in gas-liquid systems. The project will also contribute to the development of specialized workforce by training two graduate students, one in Aerospace Engineering and one in Mechanical Engineering, who will be fully supported for the three years of the project. Workshops to educate students about the importance of diversity and team science will be organized and offered to the engineering students at ISU. A canonical natural convection problem of a gas-liquid flow between two walls, subject to a temperature gradient will be taken as reference to investigate pseudoturbulence in wall-bounded gas-liquid flows. Particle-resolved direct numerical simulations (PR-DNS) of such a canonical problem will be performed using the immersed boundary method, previously developed by one of the investigators. Results from the PR-DNS simulations will be used to formulate algebraic closures for the pseudoturbulent velocity fluctuations and heat flux that appear in the phase-averaged Euler-Euler equations to enable the application of the PR-DNS results when simulating devices of practical interest. Experiments will be performed in a bubble column subject to a temperature gradient in the wall-normal direction in the presence of buoyant particles or bubbles. The collected experimental data will then be leveraged to validate the PR-DNS predictions, and the closures for the Euler-Euler model. The insights gained from the project will be disseminated to the scientific and engineering community through publication in the scientific literature and participation in relevant conferences. The implementation of the model closures formulated during the project into a computational fluid dynamic code will be published in an openly accessible code repository with test cases and documentation to facilitate their use by the engineering community. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.