The future problem of oil loss is a major obstacle to the airline’s companies and this research aims at solving this problem. Solar or nuclear power plants use liquefied air; the liquefied air is used instead of hydrocarbon fuel by heating and then passing through the De Laval nozzle. This is the main reason for this investigation. This paper focuses on the nozzle design and the effect of inlet pressure change (for air) on the Mach number of the nozzle outlet. Two models were designed. The total pressure (gauge) of air at the entrance is equal to 9 & 11 bar. The change in the Mach number at the exit of the De Laval nozzle is observed in both models due to the change in the total pressure. The models were practically designed and applied. The results obtained from the practical models were compared with the theories of gas dynamics and ANSYS Fluent program. Total and static air pressure is measured at the outlet of the nozzle. Experimentally, good results for air discharge in the nozzle were obtained and a good agreement was established between numerical and experimental results.