Two-Parameter Equations of State for ARPCS Applications

This work summarizes the limitations of the Ideal Gas Law and the use of simple but accurate two-parameter equations of state for air, oxygen, and nitrogen in the operations of ECLS/EVA hardware. The equation-of-state parameters can be determined for pure gases and for mixtures by mixture combination rules. The parameters of two equations of state in Redlich-Kwong equation of state and Peng-Robinson equation of state have been calculated here. Technical evaluations for spacecraft applications and relevant ranges in temperatures and pressures have been performed. The equations are applicable for several ECLS subsystems: Temperature and Humidity Control, THC; Atmospheric Revitalization System, ARS; and Atmospheric Control System, ACS. The goal is to focus on equations of state for ECLS/EVA applications, especially in depress/repress/compression of air and gases. The purpose of this paper is to enlighten and empower our scientists and engineers with an accurate but simple tool in lieu of actual data of air and gas properties.