Entropy generation analyses have been applied, in recent years, to a variety of systems, including Wells turbines. This can be a very powerful method, as it can provide important insights into the irreversibilities of the system, as well as a methodology for identifying, and possibly minimizing, the main sources of loss. However, some of the simplifications used in recent studies raise more than a concern on the validity of the approach. This work proposes a method based on RANS equations to evaluate the entropy production in Wells turbines. An estimation of the second-law efficiency of different Wells turbine rotors is also presented, under conditions representative of the air flow inside an OWC device. The main sources of entropy generation are highlighted and compared for the different geometries.