Machining operation and presence of water droplets cause increase the surface roughness of wet steam ejector walls and change its performance in the refrigeration cycle. The purpose of this work is to investigate the influences of the primary nozzle surface roughness on wet steam ejectors in the refrigeration cycle with steam water as a working flow. The Eulerian-Eulerian model is validated by a comparison of numerical results with experimental data. Moreover, different surface roughness has been successfully applied to the primary nozzle, and its effect on the entire flow is shown. Six properties of wet steam are selected, including pressure, temperature, Mach number, average droplet radius, droplet growth rate, and liquid mass fraction. The result shows increasing roughness resulted in a shift of the shock chain to the primary nozzle, damping shock strength, and rising temperature in the diffuser. In addition, increment of the primary nozzle surface roughness decreases ER and COP of the refrigeration cycle by 3.67% and 3.8%, respectively. The designers and operators should be considered the roughness effects in the design and operation of wet steam ejectors due to the vital impact of the roughness on the liquid mass fraction, average droplet radius, droplet growth rate, ER, and COP. © 2022, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.