Modeling Solubility of Nitrogen in Clean Fire Extinguishing Agent by Peng-Robinson Equation of State and a Correlation of Henry’s Law Constants
Nitrogen is usually used to increase the total pressure of the fluid in aircraft fire suppression bottle. The amount of nitrogen required in the bottle is a significant factor to assure complete and effective discharge into the protected area and it depends on the solubility of the nitrogen in the fire extinguishing agent. In this article, the Peng-Robinson equation of state (PR EOS) including both the classical van der Waals mixing rule and the Wong-Sandler mixing rule is utilized to correlate the Gas-Liquid Equilibrium (GLE) data from available open published literature and to analyze the solubility of nitrogen in halon alternatives such as HFC227ea (C3HF7), CF3I, FC218 (C3F8), and HFC125 (C2HF5) with Halon1301 (CF3Br) as a reference. A new method is proposed to compute the adjustable interaction parameters in the van der Waals mixing rule and in the Wong-Sandler mixing rule based on the measurements of nitrogen required to pressurize the fire suppression bottle to a specified equilibrium pressure at room temperature. Results show that the PR EOS reproduces the GLE data very well with both van der Waals mixing rule and the Wong-Sandler mixing rule and it is then utilized to predict the temperature dependence of the Henry’s law constants of nitrogen dissolved in the fire extinguishing agents. The PR EOS with van der Waals mixing rule is much more appropriate for determining the Henry’s constants than that with the Wong-Sandler mixing rule and the results calculated by the current model are used to establish a new correlation for the Henry’s law constants. This correlation will be very helpful for fire extinguishing bottle designers to acquire the pressure-temperature relationships for the mixture of nitrogen and agents.