PHDThesis Proposed Defense Session (Mr. Ali Doostali)

Title: Modeling of film boiling of liquid layer formed in the impact of dense spray on the surface at high mass flux

Presenter: Ali Doostali

Supervisor: Dr. Mohsen Davazdah Emami

Advisor: Dr. Ramin Kouhikamali

Reviewer

                     Dr. Ahmad Reza Pishevar ,Mohammad Reza Tavakoli

Abstract

The cooling spray is an effective and fast heat transfer method that utilizes liquid droplets impacting hot surfaces to significantly enhance cooling efficiency in various industries, including steel, nuclear reactors, X-ray medical devices, computer systems, and data centers. In many industries, such as the steel industry, due to the high temperature, two-phase film and transitional boiling regimes prevail, and high mass flux are required to transfer heat at this temperature. However, the formation of a steam film between the hot surface and the liquid layer greatly reduces the heat transfer rate. In the regimes of film boiling in dilute spray cooling, which occurs at lower mass flux, heat transfer is highly dependent on drop impact parameters, and the modeling of these types of sprays with single drop impact can be justified. In dense sprays that occur at high mass flux, the interactions and interference of droplets during collisions reduce these dependencies, and the film boiling modeling of these types of sprays is not suitable due to the formation of a vapor film and flooding conditions with a single droplet. Wall film models are used in nucleation boiling and single-phase heat transfer regimes, and existing numerical methods are not suitable for simulating film boiling regimes in high mass flux. Therefore, appropriate numerical modeling is required for film boiling regimes with high-mass flux droplets in contact with the surface. In the upcoming research, the numerical modeling of the heat transfer of the film boiling regime, the collision of droplets as a discrete phase in the continuous phase of air to the liquid layer formed in high mass flux in the Eulerian field will be done by the volume of fluid technique. The transfer of mass, momentum, and energy of the droplets to the liquid layer will represented through the source terms. Due to symmetry, this modeling will be conducted in two dimensions under steady-state conditions, assuming incompressible flow and the effects of high mass flux and droplet temperature on the heat transfer rate and hydrodynamic parameters of the liquid layer will be discussed, and finally, a mathematical correlation for the heat transfer coefficient will be estimated according to the effective parameters. To validate the numerical solution, the results of an experimental study were conducted in the mass flux range of (3-30) , will be utilized

Keywords: Spray cooling, Film boiling, Numerical modeling, High mass flux, liquid film