טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentSher Ilai
SubjectHeating and Boiling of Water and of Water with Surfactants
DepartmentDepartment of Mechanical Engineering
Supervisor Professor Emeritus Gad Hetsroni (Deceased)


Abstract

Heating and boiling of water are amongst the most basic processes. A model of nucleate pool boiling with surfactant enhancers is developed. The model combines a classical mechanistic approach of heat transfer, along with a molecular approach of diffusion-controlled dynamic surface tensions. A main feature of the model is a suggested explanation of the non-monotonous (“S-shaped”) boiling curves. A simple model of surface tension is developed. The model is based on the general van der Waals fluid theory, and features a new equation of state, unique for a liquid-vapor interfacial region. It is applied in conjunction with the gradient theory, to predict surface tension. The predicted surface tension values are in good agreement with experimental data, for a variety of fluids. The phenomenon of drag reduction in walled turbulent flows of polymer solutions is theoretically modeled. A new mechanistic model of a polymer molecule in a turbulent flow field is suggested, according to which, an additional route of dissipation exists. A novel approach is then illustrated, where this mechanistic model is accounted for as a turbulent scale alteration, which enables the Reynolds classical dimensional analysis of a turbulent boundary layer to apply. Correct-form velocity profiles are obtained, and Virk’s asymptote and slope are predicted. Drag - flow rate curves are also calculated. The onset of drag reduction phenomenon is also explained by this model. A model of heater scaling is suggested, as a coupled mass and heat diffusion process at the heater interface, under the idealization of equilibrium dissolution conditions. Scaling rate is concluded to depend on the Lewis number, temperature, and heat flux. Optimal heating strategy (functional) to minimize heater scaling is computed.