An analytical study of steady laminar, filmwise condensation of a saturated vapor in forced flow in a vertical tube has been conducted for the case when the vapor velocity profile at the tube inlet is fully developed and the tube wall temperature is maintained constant. Equations and boundary conditions governing the condensation process have been examined in detail in order to determine relevant parameters of the problem. For a wide range of conditions of practical interest it is found that the condensation process is governed by five parameters. These are the ratio of vapor Froude to Reynolds number, Buoyancy number, vapor to liquid viscosity ratio, liquid Prandtl number and Subcooling number. A numerical solution of the resulting set of equations shows considerable differences in hydrodynamics and heat transfer with variations in these parameters. Comparison of the results with Nusselt's analytic solution of constant interphase shear is also made and it is found that at high pressures, high Prandtl numbers and high ratios of Froude to Reynolds numbers, his analytic solution underpredicts the condensation length and film thickness and overpredicts the interphase mass and heat transfer. Significant disparities at low Prandtl numbers are found between analytic and numerical solutions for heat-transfer results as well as the hydrodynamic results. These disparities are a consequence of neglecting inertia terms in the liquid and vapor equations of motion in the analytic model and their inclusion in the model presented in this work.
ASJC Scopus subject areas
- Condensed Matter Physics
- Mechanical Engineering
- Fluid Flow and Transfer Processes