This paper reports on an experimental investigation on natural circulation and air-injection enhanced circulation performed adopting different fluids. This work is aimed at providing information on the basic mechanisms proposed in the design of future reactors relying on such circulation mechanisms for core cooling. Though the final objective of the research is the study of heavy metal cooling, the work is here limited to nonmetallic fluids. The working fluid adopted in past analyses was water. Further experimental campaigns were recently performed using the Novec™ HFE-7100 fluid, providing additional information on basic phenomena and the related scaling laws. The new fluid has a greater density and a greater thermal expansion coefficient with respect to water. Air was adopted for gas injection. Both natural circulation and gas-injection enhanced circulation are addressed in this work, drawing quantitative conclusions about the observed parametric trends. A systematic comparison is performed with the results obtained in previous experimental activities using water.