Computational Fluid Dynamic (CFD) Modeling and Experimental Study of the Formation and Buoyancy-Driven Detachment of Bubbles in Variable Gravity Environments
Abstract
The United States and other nations plan to return humans to the surface of the Moon in this decade. On the horizon, the United States plans to send humans to the surface of Mars. Multiphase fluid systems, including boiling heat exchangers, chemical processes, cryogenic fuel management, life-support systems, In-Situ Resource Utilization (ISRU), and microfluidics, will be critical components of human missions to the Lunar and Martian surfaces. Both the Moon and Mars have reduced, or partial gravity environments (1/6 g and 3/8 g, respectively). While much is known about fluids in microgravity, the effects of partial gravity on fluid behavior are not well understood. In microgravity, surface tension dominates fluid behavior, whereas on Earth, buoyancy dominates. Modeling the transition from buoyancy-dominated fluid flows to surface tension dominated fluid flows is critical to understanding partial gravity heat and mass transfer.
Of specific importance, is understanding two-phase fluid systems in contact with a solid surface. This research investigates the adiabatic and isothermal formation, growth, and buoyancy-driven detachment of a gas bubble from an orifice submerged in a liquid. Specifically, the effect of gravitational acceleration and orifice plate material surface energy on a bubble's volume at detachment was measured. The research is presented in three phases. First, a theoretical force balance analysis was conducted, in order to isolate the forces acting on a bubble forming at an orifice. Secondly, a volume of fluid (VOF) Computational Fluid Dynamic (CFD) model was developed to model bubble growth and detachment as a function of gravitational acceleration and orifice plate surface energy. Thirdly, the results of the CFD model were validated in 1 g by experiment.
The research presents three important results: (1) The volume of a gas bubble at the point of detachment from a submerged orifice, under gravitational accelerations ranging from microgravity to Earth's gravity (1g), is directly proportional to g^-1.5, where g is the acceleration due to gravity. (2) Bubble volume at detachment from an orifice is highly dependent upon the apparent surface energy of the orifice plate. This has significant implications for heat and mass transfer in reduced gravity. (3) A new dimensionless quantity, Bu, was derived, which describes submerged orifice bubble behavior across gravity levels and orifice plate materials. Additionally, a critical value of Bu, denoted Bu*, was derived. For a given material and fluid combination, Bu* predicts the point at which the bubble will detach from the orifice. Bu* is constant across all gravity levels and is entirely dependent upon the orifice plate's apparent surface energy and fluid surface tension. The results of this research demonstrate that the design of multiphase fluid systems for the Moon and Mars must involve the judicious selection of materials which are in contact with the fluids.
Subject
Partial GravityReduced Gravity
Microgravity
Fluids
Fluid
CFD
Computational Fluid Dynamic
Model
Computational Fluid Dynamics
Bubbles
Orifice
Multiphase Fluids
Two-phase Fluids
Shadowgraphy
High-Speed Imagery
Detachment
Bubble Formation
Dimensionless Quantity
Dimensionless Number
Bubble Scaling Number
Nondimensional Number
Nondimensional Quantity
Burke
Hypogravity
Fluid Flow
Lunar
Moon
Mars
Space
Fluid Systems
Gravity
Cryogenic Fuel Management
Life Support Systems
Boiling
Pool Boiling
In-Situ Resource Utilization
ISRU
Microfluidics
Bubble Control
Surface Energy
Buoyancy
Surface Tension
Heat Transfer
Mass Transfer
Heat and Mass Transfer
Fluid Systems
Volume of Fluid
OpenFOAM
VOF
Model Validation
Gravitational Acceleration
Experimental Validation
Material Selection
Mesh Generation
Mesh Optimization
Heat Exchanger
Computational
Force Balance
Force Balance Analysis
Image Processing
Gas Injection
Orifice Plate
Gravity Variation
Bubble Shape
Bubble
Bubble Volume
Bubble Spreading
Bond Number
Weber Number
Eötvös Number
Bubble Detachment
Citation
Burke, Paul Andrew (2021). Computational Fluid Dynamic (CFD) Modeling and Experimental Study of the Formation and Buoyancy-Driven Detachment of Bubbles in Variable Gravity Environments. Doctoral dissertation, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /195768.
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