A numerical attempt is made to explore the time variation of two-phase nitrogen flow regimes in a microchannel in the presence of a heat interaction between the ambient and the cryogen across the tube wall due to the existence of a huge temperature gradient. The FVM-based VOF model coupled with Lee’s phase change model is employed to get the numerical results. To study the generated flow regimes and the associated flow characteristics, three different mass flow rates are considered, and for each, three different heat fluxes across the wall are chosen. The bubbly flow regime is observed just at the start of the boiling, and gradually it is converted to slug flow with a short transitional period of confined bubble flow. The transition from bubbly flow to slug flow is delayed at higher mass flow rates.