Abstract: The invention concerns a process for extraction of a liquefiable substance from a gaseous carrier fluid. According to that process on one hand, we force the fluid to flow across a convergent-divergent nozzle such as that in that nozzle, the fluid is submitted to a fast expansion and, on the other hand, we define the cross sections (A(x)/Ao) along the axis (x) of the nozzle such as that the pressure diagram and the velocity diagram exhibit in the neighbourhood of the throat one landing section at least. Within those conditions, the liquefiable substance condenses and forms a cloud of drops of larger diameter and reduced concentration.