Characterization of discharge during depressurization of foaming systems using conductivity wire-mesh sensors

To characterize depressurization events the discharge over time needs to be determined as well as its composition. In depressurization research so far the use of gamma densitometers is well established [1]. An alternative technology is wire-mesh tomography. In the experiments carried out their usability to characterize the discharge while venting is investigated for the first time.
Application of wire-mesh tomography allows investigation of multiphase flows with high spatial and temporal resolution. The cross-sectional phase distribution in a vessel or pipe can be characterized based on local measurements of electrical conductivity of the fluid by means of crossing electrodes. This sensing technology was introduced about ten years ago as a conductivity measuring modality [2]. Since then it has been employed to the study of numerous single phase and two-phase flow phenomena, such as gas/water and steam/water two-phase flows in components in nuclear power plants, cavitation and pressure shock phenomena in fluid pipelines, water transport processes in soil and flow structures in bubble columns. The general design of a wire-mesh sensor can be seen in Figure 1. Additional information, such as flow rates, can be gained by combining signals of two wire-mesh sensors. By analysing the cross-sectional phase distributions of two distant sensors in a pipe with cross-correlation techniques one obtains velocity and consequently flow rate information.
First experiments using a setup equipped with wire-mesh sensors show that discharge over time and its composition can be measured. Analysis of experiments depressurizing a reactor filled 66.7% with water at a pressure of 5barg shows that in the horizontal pipe slug flow can be observed. Waves of the slug flow can be identified. A distinction between single-phase and two-phase discharge can be made using the sensors. Most importantly it can be seen, Figure 2, that comparing these experiments with experiments without sensors shows no differences in pressure decrease over time in the reactor and mass discharge.
Experiments depressurizing comparable foaming systems with the same experimental conditions show differing results. Foaming was achieved by adding Falterol, isobutanol and SDS. Results of the wire-mesh sensors are comparable to the results of non-foaming systems. Slug flow can be observed that can be characterized concerning mass discharge rates and composition. As shown in Figure 3 major differences crop up when looking at pressure decrease over time and mass discharge. The sensors either hinder the flow or foam the liquid which results in slower pressure decrease rates in the reactor. Thus longer periods of two-phase discharge can be observed. This increases the overall mass discharge from 23% to 39%.