This thesis presents a detailed analysis of vapor bubble dynamics and the interfacial process of liquid-vapor phase change. A spherically symmetric model for a single vapor bubble is employed to present a numerical and theoretical analysis of the intermediate bubble collapse, where, in contrast to the thermally induced or inertia dominated collapse, both the effects of liquid-vapor interfacial heat transfer and the advection of the surrounding liquid play an important role. The contrast in thermal, intermediate, and inertial behavior of collapse is represented in the form of a regime map defined by two non-dimensional quantities, Bsat and Îl, which can be directly evaluated from the initial system conditions of collapse. The same model is also used to simulate a spherically symmetric bubble growth configuration to assess the physical validity of a constant interface temperature assumption made by Highly-Resolved Simulation (HRS) studies aimed at solving flows undergoing phase change. Results show that HRS predictions are inaccurate during the initial period of bubble growth, which coincides with the inertial growth stage. A closed-form expression for a threshold time is derived, beyond which the commonly employed HRS assumptions hold. Forgoing the limitation of spherical symmetry, the second theme of this thesis is on the development of a general two-phase flow solver that can handle the phase change process. Under a finite volume framework using a geometric Volume of Fluid (gVoF) approach, two key challenges with phase change flows have been addressed in this work, namely, (i) added deformation of the interface, and (ii) capture of velocity and pressure gradient discontinuity at the interface, both caused due to phase change. To track the interface in the gVoF scheme, an effective flux is defined that captures the effect of phase change on interface motion. This method improves upon the source term approach used in other studies. For the solution of velocity and pressure, a ghost fluid approach has been implemented, which is the first of its kind in a VoF-based phase change solver.

Due to the complex nature of the subprocesses involved in nucleate boiling, it has not been possible to develop comprehensive models or correlations despite decades of accumulated data and analysis. Complications such as the presence of dissolved gas in the liquid further confound attempts at modeling nucleate boiling. Moreover, existing empirical correlations may not be suitable for new applications, especially with regards to varying gravity level. More recently, numerical simulations of the boiling process have proven to be capable of reliably predicting bubble dynamics and associated heat transfer by showing excellent agreement with experimental data. However, most simulations decouple the solid substrate by assuming constant wall temperature. In the present study complete numerical simulations of the boiling process are performed--including conjugate transient conduction in the solid substrate and the effects of dissolved gas in the liquid at different levels of gravity. Finite difference schemes are used to discretize the governing equations in the liquid, vapor, and solid phases. The interface between liquid and vapor phases is tracked by a level set method. An iterative procedure is used at the interface between the solid and fluid phases. Near the three-phase contact line, temperatures in the solid are observed to fluctuate significantly over short periods. The results show good agreement with the data available in the literature. The results also show that waiting and growth periods can be related directly to wall superheat. The functional relationship between waiting period and wall superheat is found to agree well with empirical correlations reported in the literature. For the case of a single bubble in subcooled nucleate boiling, the presence of dissolved gas in the liquid is found to cause noncondensables to accumulate at the top of the bubble where most condensation occurs. This results in reduced local saturation temperature and condensation rates. The numerical predictions show reasonable agreement with the results from experiments performed at microgravity. For nucleate boiling at microgravity the simulations predict a drastic change in vapor removal pattern when compared to Earth normal gravity. The predictions match well with experimental results. However, simulated heat transfer rates were significantly under-predicted.

Since the second edition of Liquid-Vapor Phase-Change Phenomena was written, research has substantially enhanced the understanding of the effects of nanostructured surfaces, effects of microchannel and nanochannel geometries, and effects of extreme wetting on liquid-vapor phase-change processes. To cover advances in these areas, the new third edition includes significant new coverage of microchannels and nanostructures, and numerous other updates. More worked examples and numerous new problems have been added, and a complete solution manual and electronic figures for classroom projection will be available for qualified adopting professors.

This work deals with modeling and numerical simulation of fluid flow and heat transfer associated with phase change process inside both isotropic and anisotropic porous media, based on the Two-Phase Mixture Model (TPMM) along with the assumption of Local Thermal Equilibrium (LTE) and Non-Equilibrium (LTNE) conditions. In particular, it demonstrates the necessity and usefulness of a newly proposed smoothing algorithm for handling the sharp discontinuities in the effective diffusion coefficient in order to avoid the occurrence of non-physical “jump” in the predicted temperature distribution during the numerical simulation of the complete phase change process inside porous media. For the purpose of demonstration, one- and two-dimensional phase change problems operated in the Darcy flow regime have been considered.The Finite Volume Method (FVM) has been used on both staggered and non-staggered grid layouts in order to solve the governing conservation equations. In this work, after critically analyzing the drawbacks of the existing enthalpy formulation based on TPMM, a modified formulation has been also developed that can easily accommodate substantial density variations in the single phase regions. The results obtained from the modified enthalpy formulation have been compared with that predicted by the existing modified volumetric enthalpy formulation and excellent agreements have been observed for all tested cases. A thorough parametric study, using both LTE and LTNE models, indicates that the adoption of the proposed smoothing algorithm successfully eliminates “jump” in the predicted temperature distribution and does not alter the overall energy and momentum balance. All tested cases, covering applicable ranges of parametric variations, could be physically interpreted. The methodology is, therefore, recommended for future simulations of complete phase change process inside porous media. The results also show that the modified enthalpy formulation requires significantly less computation time thanmodified volumetric enthalpy formulation.

Provides a comprehensive coverage of the basic phenomena. It contains twenty-five chapters which cover different aspects of boiling and condensation. First the specific topic or phenomenon is described, followed by a brief survey of previous work, a phenomenological model based on current understanding, and finally a set of recommended design equa

Convective Heat and Mass Transfer, Second Edition, is ideal for the graduate level study of convection heat and mass transfer, with coverage of well-established theory and practice as well as trending topics, such as nanoscale heat transfer and CFD. It is appropriate for both Mechanical and Chemical Engineering courses/modules.