Numerical Investigation of Flow Boiling Phenomena

摘要

The effects of surface roughness and surface geometry on vertical flow boiling heat transfer are explored by conducting a literature review of current studies to determine experimental heat transfer correlations under different surface and fluid conditions, focusing on convective and nucleate boiling regimes, i.e. before the system achieves critical heat flux and dry-out; as well as conducting a model simulation of a 2-D Volume of Fluid (VoF), 2 factorial Design of Experiment (DoE), for nucleate pool boiling, with varying surface friction factor and macroscopic surface geometry. A detailed examination and explanation of the self-assembly and correlations utilized by the software (FLUENT) as well as their source, shall be investigated. Bubble nucleation is a highly studied aspect of the boiling process, and nucleation mechanisms play a key role both in stagnant pool boiling scenarios, and in the bubbly regime of flow boiling in tubes and channels. This paper includes a literature review of several experiments that investigate how liquid-solid surface interactions and factors such as surface roughness and wettability affect bubble nucleation in stagnant pool boiling, as well as some of the empirical correlations that have been developed to predict local heat transfer coefficients for different pool boiling conditions. We initially desired to design a CFD simulation that would be comparable to the stagnant pool boiling experiments found in the literature, however, due to time constraints and lack of required experimental data, we designed simulations for steady state vertical upflow boiling in narrow, axially symmetric tubes with constant wall heat flux. The simulations were created in FLUENT software using the RPI boiling model, and four different variations were computed: two with surface material specified as aluminum, and two with a steel surface, and two tubes with a constant diameter, and two with a sinusoidally varying diameter along their length. The computatio