Growth Of Vapor Film Research Articles

Heat transfer performance and influences of spray cooling under quenching

In this study, a closed-loop spray cooling system using R134a as the working fluid was established. The heat transfer characteristics and influencing mechanism of transient spray cooling were studied. The transient spray cooling curve under quenching was built accurately. The results show that the vapor film suppressed time, tsup, is the main period that the spray cooling must pass through. The flow rate and the sub-cooling of R134a have little effect on the cooling rate but the critical heat flux, which are mainly affected by chamber pressure. The transient Jacob number decreases with the increases of chamber pressure. As Jacob number decreases, the growth of vapor film is inhibited, then the tsup reduces in consequence. The surface temperature drop point and critical heat flux increases with the rise of chamber pressure. The maximum critical heat flux is 70.08 W/cm2 in this experiment.

Direct numerical simulation of incompressible multiphase flow with vaporization using moving particle semi-implicit method

In this paper, the moving particle semi-implicit (MPS) method is developed towards the simulation of multiphase incompressible flows with mass transfer due to vaporization. Traditional MPS method assumes particle volume to be constant and encounters difficulty in modeling vapor-liquid phase change due to abrupt volume change in vaporization process. In the proposed model, particle volume is assumed variable and volume change due to vaporization is considered. Particle splitting technique is developed to avoid large volume difference among particles. Source term accounting for mass transfer rate in vaporization process is developed in the pressure Poisson equation (PPE). Combined with enhanced MPS schemes developed in our previous studies, the numerical method is tested on single rising bubble, one-dimensional Stefan problem, vapor film growth around a sphere without gravity and then used in simulations of two-dimensional film boiling on both horizontal surface and cylindrical surface.

Modeling the growth of a vapor film formed in contact between a hot metal sphere and water in pressure vessels

The contact between a hot object such as the particles of a molten metal and a cool and relatively volatile fluid such as water likely takes place in metal casting, paper manufacturing industries, and nuclear reactors. The highly intensive and quick heat transfer caused by the contact may increase the pressure in the vapor film formed on a hot particle within a short period leading to the vapor explosion followed by a strong pressure wave in a vessel containing a volatile matter. The present study aims to provide a mathematical model for contacting between a small hot copper metal sphere and water and explain the effect of pressure change in water vessel on the vapor film radius, pressure inside vapor film, as well as the saturation temperature at the interface. In addition, it examines the results of vapor film growth and the internal pressure of the film for such a phenomenon in nuclear power plants with fuel rod coolant pressures ranged between 60 and 150 bar. The results of the extremely high pressures of the vessels indicated an increase in the pressure pulse inside the vapor film within a short period which raised the likelihood of vapor explosion.

The stability of vapor film immersed in superfluid helium on the surface of the hot ball

In this article, the evolution of vapor film on the surfaces of hot objects immersed in a cryogenic superfluid helium liquid is considered. It is assumed that at the beginning of the process, a thin film of steam exists on the surface of the object that has a spherical shape. If the heat flux is greater than the critical heat flux, the growth of vapor film will continue, otherwise it will collapse. Survey and analysis of the previously mentioned problem has been done using numerical method and the main onjectives are as follows: (a) study the evolution of the vapor film immersed in superfluid helium on the surface of the hot ball and (b) the stability of vapor film immersed in superfluid helium on the surface of the hot ball.

Thermo-physical investigation of the explosive rapid boiling during the contact of a single water drop with liquid methane

Safe transportation of natural gas, mostly in liquid form such as liquefied natural gas to international market is very important. In the case of exterior material contact to liquefied natural gas, intensive boiling and exploding should be anticipated. This paper investigates the thermo-physical contact between a single drop of water (0 ℃ as a fluid with higher temperature) with liquid methane, which is similar to liquefied natural gas, at a very low temperature (−162 ℃). Heat transfer between water drop and liquefied methane results in rapid pressure increase in a vapor film. It causes the generation and rapid growth of methane vapor film which is a result of abrupt evaporation and causes liquid methane explosion. In this situation, the intense vapor explosion phenomena endanger the safety of system. A mathematical model for these phenomena has been developed by assuming saturation condition on interface surface. Then, the effects of the variation of different thermo-physical parameters on the vapor film growth have been investigated. The results show that in some cases, the vapor pressure pulse created in the film can reach more than three times the initial pressure, which can endanger the safety of system.

A Sphericosymmetric VOF Approach for Investigating Immiscible Two-Phase Systems with One Liquid Phase

A numerical model based on the volume-of-fluid (VOF) method in sphericosymmetric geometry containing two immiscible phases is developed. The model is successfully validated using a wide class of available results. These include the inward and outward solidification problems and growth of vapor film in a saturated and metastable liquid. The model is also used to simulate the very rapid collapse phenomenon of vapor film around a hot metal in subcooled water. In each case, the results indicate that the numerical simulation successfully captures the essential physics, even at small length and time scales. It is established that the proposed numerical scheme correctly predicts the advection within the VOF framework in situations with pronounced curvature.