In this work computational fluid dynamics (CFD) technique has been used to analyze the detailed flow structures of refrigerant R-134a in an adiabatic capillary tube using volume of fluid based finite volume method. Also, an attempt has been made to understand the flashing phenomenon within the adiabatic capillary tube. A source term has been incorporated in the governing equations to model the mass transfer rate from liquid phase to vapor phase during the flashing process. The developed numerical model has been validated with the available experimental data. The unsteady variations of flow properties such as velocity, void fraction distributions, and flow turbulence across the cross section and at different axial length of the tube have been presented. It has been observed that flashing initiates from the wall of the tube. With the inception of vapor, the flow properties change drastically with very short transient period. As far as flow turbulence is concerned, the role of flashing parameter seems to be stronger than internal tube wall roughness.