Begell House Inc.
Multiphase Science and Technology
MST
0276-1459
18
3
2006
ON THE NUMERICAL SIMULATION OF ACCELERATION-DRIVEN MULTI-FLUID MIXING
199-230
10.1615/MultScienTechn.v18.i3.10
True-Nam
Dinh
Center for Risk Studies and Safety, University of California, Santa Barbara, 6740 Cortona Drive, Goleta, CA-93117, California, USA; and Royal Institute of Technology, Stockholm S-10044, Sweden USA
R. R.
Nourgaliev
Center for Risk Studies and Safety, University of California, Santa Barbara, 6740 Cortona Drive, Goleta, CA-93117, California, USA
Theo G.
Theofanous
Center for Risk Studies and Safety, University of California, Santa Barbara, 6740 Cortona Drive, Goleta, CA-93117, California, USA
This paper is concerned with computational prediction of acceleration-induced multi-fluid mixing phenomena. Premises and performance of existing approaches are reviewed and analyzed with focus on a late phase behavior. We introduce a new framework whose central idea is to use an interfacial area transport equation (IATE) and a subgrid scale model (SGS) of multi-fluid turbulence to provide a natural transition from DNS-based simulation toward an effective-field model (EFM) and deeply into well-mixed states with continuous refinement of length scale. We present new results and important insights derived from our work on four platform technologies: DNS, EFM, IATE and SGS. We discuss the approach to ensure that developments in different areas effectively emerge and function seamlessly in an overall computational platform for multi-fluid mixing.
RECENT PROGRESS IN COMPUTATIONAL STUDIES OF DISPERSE BUBBLY FLOWS
231-249
10.1615/MultScienTechn.v18.i3.20
Gretar
Tryggvason
Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD, 21218, USA
A.
Esmaeeli
Dept. of Mechanical Engineering, Worcester Polytechnic Institute, Worcester, MA, USA
J.
Lu
Dept. of Mechanical Engineering, Worcester Polytechnic Institute, Worcester, MA, USA
S.
Homma
Dept. of Applied Chemistry, Saitama University, Saitama 338-8570, Japan
S.
Biswas
Dept. of Mechanical Engineering, Worcester Polytechnic Institute, Worcester, MA, USA
Direct numerical simulations of bubbly flows are reviewed and recent progress is discussed. Simulations of homogenious bubble distribution in fully periodic domains at relatively low Reynolds numbers have already yielded considerable insight into the dynamics of such flows. The challenge now is to examine bubbles at higher Reynolds numbers, bubbles in channels and confined geometries, bubble interactions with turbulent flows, as well as more complex flows. We discuss current studies of these problems, as well as recent results on bubble formation in boiling.
HIGH HEAT FLUX BOILING AND BURNOUT AS MICROPHYSICAL PHENOMENA: MOUNTING EVIDENCE AND OPPORTUNITIES
251-276
10.1615/MultScienTechn.v18.i3.30
Theo G.
Theofanous
Center for Risk Studies and Safety, University of California, Santa Barbara, 6740 Cortona Drive, Goleta, CA-93117, California, USA
True-Nam
Dinh
Center for Risk Studies and Safety, University of California, Santa Barbara, 6740 Cortona Drive, Goleta, CA-93117, California, USA; and Royal Institute of Technology, Stockholm S-10044, Sweden USA
In our recent works [Theofanous et al., 2002a-b], we have demonstrated that burnout in pool boiling is not hydrodynamically limited, at least not in the sense that has been perceived in the past. In this paper, we discuss the opportunities created by the new understanding of mechanisms that govern the boiling crisis. This understanding is built upon a scales separation phenomenon, referring to a vapor blanket separating the liquid film on the heater surface from the chaotic, churning flow in the two-phase pool. In essence, the scales separation suggests that mechanisms of boiling crisis should be sought within the micro-hydrodynamics of the evaporating liquid microlayer rather than in the pool thermal-hydraulics. Detail analysis of surface temperature patterns obtained by infrared imaging at high heat fluxes points to a nearly static picture of boiling heat transfer, with intense cooling at locations which were nucleation sites activated at lower heat fluxes. Furthermore, we show that control of the surface and coolant chemistry offers the potential to enhance resistance to burnout and achieve critical heat fluxes (CHF) exceeding those defined by the so-called hydrodynamic limit. Our more recent experiments show an improved resilience of the heater to burnout when a high-solubility salt or nanoparticles are added to the coolant (water). We explain the observed phenomenon through the increase in disjoining pressure at the meniscus contact line that promotes liquid spreading towards the dry area. It is noteworthy that the scales separation phenomenon provides a basis to suggest that mechanisms of enhancement to burnout in pool boiling are also active, even to a larger extent, in spray cooling and flow boiling.
NUMERICAL SIMULATION OF THE DYNAMICS OF MULTIPLE BUBBLE MERGER DURING POOL BOILING UNDER REDUCED GRAVITY
277-304
10.1615/MultScienTechn.v18.i3.40
H. S.
Aparajith
Mechanical and Aerospace Eng. Dept., University of California, Los Angeles, USA
Dean Vijay K.
Dhir
Henry Samueli School of Engineering and Applied Science, Mechanical and Aerospace Engineering Department, University of California, Los Angeles, Los Angeles, California 90095, USA
Gihun
Son
Sogang University, Baekbeomro 35, Mapo, Seoul, 04107, Rep. of Korea
Numerical simulation of the growth and departure of multiple merging bubbles and associated heat transfer on a horizontal heated surface during pool boiling under low gravity conditions has been performed. A finite difference scheme is used to solve the equations governing mass, momentum and energy in the vapor liquid phases. The vapor-liquid interface is captured by level set method, which is modified to include the influence of phase change at the liquid-vapor interface. PF5060 is used as test liquid. The effects of reduced gravity condition and orientation of the cavities on the bubble diameter, interfacial structure, bubble merger time and departure time as well as local heat fluxes are studied.