Flow resistance characteristics of two-phase CO2 with a large pressure gradient: Theoretical and experimental research

Abstract

Two-phase CO2 transport in pipelines with large pressure gradients is very common in industrial processes, such as jettisoning of CO2 carriers and carbon dioxide fire extinguishing system action under emergency conditions. Under the condition of a large pressure drop, a lower temperature will cause a series of safety issues including pipeline blockage and ductile fracture. In this paper, the CO2 transport characteristics of different nozzle sizes were experimentally studied, including pressure, temperature and mass flow rate, and a modified homogeneous equilibrium model (HEM) was built to simulate the pressure drop behaviour considering the flashing delay phenomenon, and assuming that the delayed liquid/ vapour transition was related to the pressure drop. Experimental results show that the flow can be divided into the mutation stage, transition stage, and stable stage, and the superheating of liquid CO2 due to flashing delay was observed in the stable stage. The modified model has good accuracy for predicting pipe pressure drop, especially the delayed liquid/ vapour transition under large pressure gradients, and this model was also used to analyse the effect of equivalent roughness, mass flow, ambient temperature and elevation on the pressure drop.