An experimental and numerical study of laminar wavy film condensation of fluorocarbon vapor
Abstract
A combined experimental and numerical study of laminar wavy film condensation of fluorocarbon vapor was performed. Because fluorocarbons exhibit unique thermophysical properties, it was unknown whether their condensation characteristics could be accurately calculated using existing correlations. Experimental studies were conducted on three vertical condenser surfaces, resulting in film Reynolds numbers ranging from 17 to 238. Correspondingly, conditions in the condensate film varied from smooth laminar flow to wavy laminar flow. The experimentally measured film condensation heat transfer rates with 3M FC-72 fluorocarbon were found to be in good agreement with condensation data for other fluids and standard film condensation correlations in both the laminar and wavy laminar regimes. Wave evolution on the condensate film was experimentally captured using high-speed video photography. Wave velocities and wavelengths were experimentally measured on a condensate film. The author is unaware of any prior experimental measurements of these quantities. Wave velocities in the condensing film appear to be slightly smaller than isothermal falling film wave velocities due to condensation at the vapor-liquid interface. A numerical model was developed to simulate wavy condensate films in which the time-dependent evolution of the liquid-vapor interface was determined as part of the solution of the governing equations. A nonorthogonal coordinate transformation was used to accurately track the position of the wavy liquid film surface. The governing equations and boundary conditions were transformed and then discretized using the control volume formulation. Small amplitude disturbances were sustained through the use of a single-frequency forcing perturbation. The numerical model captures the evolution of the wavy interface of the condensate film as it transitions from a smooth surface to one with small amplitude, sinusoidal type waves and finally to one with large amplitude, non-sinusoidal type waves. The local heat transfer coefficients associated with the wavy condensate film were found to be approximately 40 to 50 percent greater than predicted by the Nusselt smooth film model. Time-averaged thinning and increased fluid convection due to increased time-averaged velocities in the large amplitude, non-sinusoidal wave regime in the condensate film were both found to be significant and approximately equal contributing mechanisms to the heat transfer enhancement.
Degree
Ph.D.
Advisors
Ramadhyani, Purdue University.
Subject Area
Mechanical engineering
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