Laminar Film Flow Phenomena--Theory and Application to the Two-Phase Closed Thermosyphon

摘要

In Part I the hydrodynamic and thermal characteristics of thin, laminar wavy-film flow are considered. A theoretical model is developed to predict the hydrodynamic features of asymptotic wavy-flow states. The mathematical closure question arising in asymptotic-state analyses is satisfactorily resolved here for the first time. The model accurately predicts published experimental data for mean film thickness, trough-to-crest dimension, wave celerity, and wavelength. The Nusselt theory for laminar film condensation is shown to significantly under-predict existing experimental data due to the presence of waves on the condensate film surface. Consequently, a heat transfer model is developed incorporating the wavy-film hydrodynamic model results. The subsequent predictions agree well with experimental data and, in addition, indicate the appropriate data trend with flow length. In Part II other thin film phenomena are described, including continuous-film breakdown, rivulet flow, and sputtering. All of these phenomena are present in the operation of a heat transfer device known as the two-phase closed thermosyphon (wickless heat pipe). This device was experimentally investigated. Parameters of investigation include the tube material, working fluid, fill quantity, heat flux, condenser/adiabatic/evaporator section lengths, condenser temperature, and tube inclination.