Direct Computational Simulations for Internal Condensing Flows and Results on Attainability/Stability of Steady Solutions, Their Intrinsic Waviness, and Their Noise Sensitivity

Abstract

The paper presents a new two-dimensional computational approach and results for laminar/laminar internal condensing flows. Accurate numerical solutions of the full governing equations are presented for steady and unsteady film condensation flows on a sidewall inside a vertical channel. It is found that exit conditions and noise sensitivity are important. Even for stable steady solutions obtained for nearly incompressible vapor phase flows associated with unconstrained exit conditions, the noise sensitivity to the condensing surface’s minuscule transverse vibrations is high. The structure of waves, the underlying characteristics, and the “growth/damping rates” for the disturbances are discussed. A resonance condition for high “growth rates” is proposed and its efficacy in significantly enhancing wave motion and heat transfer rates is computationally demonstrated. For the unconstrained exit cases, the results make possible a separately reported study of the effects of shear, gravity, and surface tension on noise sensitive stable solutions.

Effects of exit-condition, gravity, and surface-tension on stability and noise-sensitivity issues for steady condensing flows inside tubes and channels

“…The numerical scheme used here exploits the rigorous analytical and numerical knowledge that exists (see [19]) for solving a reduced hyperbolic form of the interface tracking equation-this ensures convergence and accuracy of both the amplitude and the phase of the predicted interfacial waves. Due to an algorithm improvement, the convergence, grid independence, and satisfaction of all interface/boundary conditions for the results reported here are better than what were reported in [1,2].…”

“…The in-tube geometry (see Fig. 1a) is considered here while some new and improved results for the horizontal and zero gravity channel flow cases-formulated elsewhere [1,2]-are also presented. The results are important for a qualitative understanding of experiments (see, e.g., [3]) dealing with the behavior of a condenser-section (typically of hydraulic diameters in millimeter or sub-millimeter range).…”

“…The simulation tool used here is more completely described in [1,2]. The interface tracking equation used here and in [1,2] is the same one that is used for locating the interface in the interface capturing approaches for flow with phase-change (level-set method of Son and Dhir [12], etc.)…”

“…The interface tracking equation used here and in [1,2] is the same one that is used for locating the interface in the interface capturing approaches for flow with phase-change (level-set method of Son and Dhir [12], etc.) or without phase-change (level-set method of Sussman et al [13], VOF method of Hirt and Nichols [14], etc.…”

Analysis of laminar film condensation over vertical permeable hollow short fins

“…They concluded that the elliptical section tube has a clear improvement of the vapor condensation over horizontal cylinder. Recently, the stability of the condensing flows has been discussed numerically and experimentally in several works [23][24][25][26][27]. The effect of the free-stream vapor-striking angle on the condensation over a vertical plate was analyzed by Khaled et al [28].…”