Prediction of the release process of the nitrogen-extinguishant binary mixture considering surface tension

Abstract

Nitrogen used for pressurization in the extinguisher can be partially dissolved in the fire extinguishing agent. Consequently, the evolution of the dissolved nitrogen has a significant effect on the release behavior of the fire extinguishing agent in a rapid process. In this article, a new model was developed to predict the critical pressure of the nitrogen evolution and the release process of the fire extinguishing agent was described in detail. According to the Peng-Robinson (PR) equation of state and van der Waals mixing rule, the effect of the dissolved nitrogen on the surface tension of the fire extinguishant was analyzed by considering surface phase and fugacity coefficient. A method to calculate the surface tension of the liquid agent dissolved with nitrogen was proposed. The results showed that the proposed model can determine the accurate critical pressure of the evolution of the dissolved nitrogen and further evaluated whether nitrogen escapes. At different initial filling pressure, in addition, the release process of the nitrogen-extinguishant such as CF3I, FC218 (C3F8), HFC125 (C2HF5), and Halon1301 (CF3Br) was well predicted by the fluid release model when taking the surface tension and adiabatic index of the mixture into account. Compared with the previously obtained experimental data, the predictions obtained indicated that the present model can adequately describe the liquid and the gas mixture release stage in the release process of the nitrogenextinguishant.

Prediction of steady-state two-phase flow of nitrogen + extinguishant in the pipeline and a correlation for mass flow rate

“…In this study, the corresponding relationship among the fluid temperature, pressure and the ratio of each component in the flow process, can be derived by the phase equilibrium calculation [2] based on VTPR EOS [31] with classical one parameter van der Waals mixing rule [32]. The method on pure component properties used to calculate the parameters of VTPR EOS and the binary interaction parameters could be found from Ref.…”

“…In the 1990s, Halon 1301 was widely used as the fire extinguishing agent; however, green halon alternatives are being produced and used for protecting the environment in recent years [1], such as HFC227ea, CF3I, FC218 and HFC125. In order to release the extinguishant rapidly and put out the fire efficiently, fire extinguishing bottle is usually pre-filled with nitrogen, which provides the driving force during release [2]. As the extinguishing agent is released, the nitrogen in the bottle may escape and cause the extinguishant to change from a single phase to gas-liquid phase.…”

“…Therefore, as the two-phase nitrogen + extinguishant flows in the pipeline, the heat transferred to the two-phase flow through the pipe wall is principally ignored and thus regarded as adiabatic flow. Two typical filling pressures of 2.5 MPa and 4.2 MPa are always applied [2]. After the extinguisher valve is opened, the pressurised nitrogen and fire extinguishing agent vapor drive the liquid extinguishant to promptly fill the fire extinguishing pipeline, which leads to the "front end" (the part in contact with the outside) of the liquid extinguishant reaching the critical two-phase state [3,4].…”