Abstract: The International Space Station(ISS) employs catalytic wet oxidation carried out in a Volatile Reactor Assembly (VRA) for water recycling.Previous earth gravity experiments show that the VRA is very effective at removing polar,low molecular weight organics.To compare the reactor performance under micro-gravity and Earth gravity conditions,a tracer study was performed on a space shuttle in 1999 by using 0.2% potassium carbonate as the chemical tracer.In this paper, the experimental data were analyzed and it is indicated that the reactor can be considered as a plug flow one under both micro-gravity and earth gravity experimental conditions.It has also been proved that dispersion is not important in the VRA reactor under the experimental conditions.Tracer retardation was observed in the experiments and it is most likely caused by catalyst adsorption.It is concluded that the following reasons may also have influence on the retardation of mean residence time: (1) the liquid can be held by appurtenances, which will retard the mean residence time; (2) the pores can hold the tracer, which can also retard the mean residence time.

Key words: Tracer study, Micro-gravity, Dispersion model, Tank in series model, Catalytic wet oxidation