Effect of pressure variations on film boiling characteristics of liquid nitrogen

Liquid nitrogen is a widely used cryogenic fluid in various industrial and scientific applications. Film boiling is inevitable when a hot surface is exposed to a cryogenic fluid like liquid nitrogen. This mode of boiling can affect the heat transfer rate and cooling efficiency of the process. The present study investigated the effect of operating pressure on film boiling characteristics of liquid nitrogen using continuum-based numerical simulations. Simulations were performed at atmospheric, intermediate, and near-critical pressures using a coupled level-set and volume of fluid method of interface tracking. Bubble dynamics and heat flux variations were examined at different degrees of wall superheat. The results show that the pressure condition significantly affects the bubble dynamics and boiling of liquid nitrogen. At higher pressure, the specific heat of the vapor phase increases, resulting in a higher heat transfer rate. It was also noted that at high levels of superheat, the bubbles detach from the heating surface faster, resulting in a higher transfer of heat. The effect of pressure on the number of bubble formation sites was also investigated. The simulations also reveal that the local thermodynamic conditions, such as pressure, temperature, and vapor concentration, significantly influence the bubble size.