Experimental investigation on heat and moisture transfer of propylene glycol-mixed steam in porous media.

Propylene glycol (PG)-mixed steam enhanced extraction is a promising remediation technique for removing semi-volatile organic compounds (SVOCs) from the unsaturated zone. However, the mechanisms of heat and moisture transfer during PG-mixed steam injection remain unclear. In this study, a 2D experimental system was developed to enable non-invasive monitoring of the spatio-temporal distribution of temperature and degree of saturation during steam injection into porous media. Experiments were conducted to observe the migration of PG-mixed steam in horizontal and vertical planes across three varying particle sizes, while pure superheated steam injection experiments serving as a comparison. Temperature field results show that the addition of PG decreases the zone of influence during steam migration, while significantly enhancing the emergence of the superheated steam zone. The influence of particle size on the area variance of the saturated steam zone is greater than that of the superheated steam zone. The downward migration of the superheated steam front due to density different between PG vapor and air is impeded with decreasing permeability. Furthermore, saturation field results reveal that the condensed liquid within the superheated zone is a PG solution. The downward migration of condensates with high PG concentration might increase the potential risk of beneath groundwater pollution, highlighting the significance of understanding PG migration during PG-mixed steam injection.