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

Abstract

Nitrogen used for pressurization of a fire extinguisher could be partially dissolved in the fire extinguishing agent, forming a binary mixture accompanied by a phase change while flowing inside the pipeline. Notwithstanding the widespread use of fire extinguishing system, an effective method has never been considered to predict two-phase flow performance of nitrogen + extinguishant in the pipeline. This paper presents investigation of the steady-state two-phase flow of extinguishant in the pipeline, including C3HF7 (HFC227ea), CF3I, and C2HF5 (HFC125). The average viscosity of mixture was calculated using six quoted methods (VM-1 to VM-6).Subsequently, inspired by one-dimensional adiabatic isenthalpic flow of refrigerant in a capillary tube, the corresponding prediction models (STFM-1 to STFM-6) for large mass flux nitrogen + extinguishant in a fire extinguishing pipeline were developed based on the VM-1 to VM-6. In comparison with previous experimental and theoretical data, the applicability and accuracy of the proposed mathematical models was examined from two different aspects, mass flow rate and pressure drop. The results indicated that both models, STFM-2 and STFM-3, predicted accurately for mass flow rate, and STFM-2 model predicted accurately for pressure drop. Finally, new correlations for mass flow rate and pressure drop have been established accurately based on summarizing the relevant predicted data, respectively. This work contributes to a good theoretical approach on the analysis of two-phase flow of nitrogen + extinguishant. Keywords: steady-state two-phase flow; adiabatic isenthalpic expansion; average viscosity; mass flow rate; pressure drop Nomenclature T' presumptive temperature r' parameter of the PRμ model defined in Eq. (5) p pressure, Pa μ dynamic viscosity, 10 -7 Pa•s