This work is to predict the shape and collapse of the molten layer surrounding the keyhole filled with vapor and droplets during drilling or high power density beam welding process. Investigating collapse of the liquid layer is essentially required for an understanding of pore formation in keyhole welding. The collapse of the keyhole is similar to transition between the slug and annular two-phase flows encountered in fluid flow field. In this study, quasi-steady, averaged one-dimensional models widely used in two-phase flow areas thus are provided. The core region filled with vapor and entrained droplets is treated as a homogeneous fluid. In the absence of friction and gravitational forces and energy absorption, the shape and transport variables in the keyhole subject to a supersonic flow at the base are found to be divided into four regions for different liquid entrainments. The effects of vapor compressibility, surface tension, and distinct transport properties between vapor and liquid layer on transport variables and keyhole shape are presented.