This research delves into different velocity-slip and temperature jump models applicable near the inner wall of micronozzles during numerical simulations using N–S equations. It also investigates how wall surface roughness influences flow parameters. The study compares the Maxwell first-order slip and Langmuir–Maxwell slip models to determine their accuracy in predicting flow behavior. Moreover, it examines the impact of wall surface roughness on flow characteristics, including pressure, temperature, Mach number, and mass flow rate. The study reveals intriguing micronozzle sub-choking phenomena, leading to unexpected flow restrictions. Understanding these phenomena is crucial for the efficient and dependable design of micronozzles. The research findings contribute to advancing microfluidic and aerospace technologies, optimizing micronozzle performance across various applications.