The thesis defense by Mr. Masoud Sahami a Ph.D. candidate in mechanical engineering, entitled "Modeling the condensation of multi-component gases in high-speed flows", will be held on 2024-July-02 at 14:00 (Tehran time) at the School of Mechanical Engineering of Iranian University of Science and Technology (IUST). The members of the Space Propulsion Research Laboratory (SPRL) invite all interested parties in this field and the other relevant areas to participate in this defense.
 

The homogeneous condensation phenomenon occurs in high-speed expanding flows in many industrial equipment, such as the last stages of steam turbines, supersonic separators, and thrusters. As a result of temperature and pressure drop in the nozzles of these equipment, the conditions for the condensation and the formation of liquid droplets in high-speed flows are provided. Due to the complexity of droplet formation and growth kinetics, modeling this phenomenon in multi-component high-speed flows is a complex and practical issue. Many previous studies have been limited to ideal gas assumption and equilibrium condensation, which do not match the thermodynamic conditions governing this phenomenon. Therefore, it is necessary to study the effect of this phenomenon on the target parameters to improve the nozzle performance in the different applications, while removing the above assumptions. Determining the location of condensation in the flow and studying the droplet growth physics based on the geometrical and thermodynamic conditions of the nozzle inlet is of particular importance. During the occurrence of non-equilibrium condensation shock, due to the release of latent heat resulting from the phase change, the temperature and pressure increase, affecting the flow thermodynamics and the performance of the nozzles. In this thesis, the effects of non-equilibrium condensation in expanding flows on the performance of converging-diverging nozzles are studied, focusing on improving the propulsion and separation performance of nozzles. For this purpose, the 1D coupled equations of gas dynamics, models of nucleation, and growth of droplets in single-component expanding flows are introduced first. Then, by generalizing the governing equations to binary component gas flow, the condensation phenomenon in a flow composed of hydrogen peroxide propellant decomposition products is modeled based on the numerical method. To increase the model accuracy, especially for high inlet pressure cases, real gas equations of state are used to determine the properties of gas mixtures. The results show that passing through the saturation line of the condensable component and forming droplets during the expansion of the flow in the divergent section of the nozzle improves the propulsion parameters, such as the thrust coefficient, by about 6% compared to the dry state. Due to the small growth of droplets during the free molecular regime, non-equilibrium condensation continues to the thruster nozzle exit. Increasing the length of the nozzle leads to larger nano-droplets, the formation of a higher liquid mass fraction up to 4%, and the transfer of the Wilson point to the upstream parts of the nozzle. Next, generalizing the droplet growth model to a new multi-diameter and multi-component flow, the condensation phenomenon in the combustion products of expanding flue gas has been studied. In this problem, it has been shown that enriching the flow by hydrogen can overcome the limitation of the liquefaction efficiency of separators by increasing the thermal capacity of the carrier gas to absorb latent heat during droplet growth and increase the exit droplet size and liquefaction efficiency. In a particular case, this increase has been estimated to be about 1.3 and 1.5, respectively.
 

Keywords
Multi-component flow, Condensation shock, Nucleation, Droplet growth, Thrust coefficient, CO2 supersonic sparators