CH3CH2OD/D2O binary condensation in a supersonic Laval nozzle: Presence of small clusters inferred from a macroscopic energy balance

Shinobu Tanimura, Barbara E. Wyslouzil, Gerald Wilemski
2010 Journal of Chemical Physics  
We determined the heat released in the condensing flow of a CH 3 CH 2 OD/ D 2 O/carrier gas mixture ͑EtOD/ D 2 O for brevity͒ through a supersonic Laval nozzle by integrating the equations for supersonic flow with condensation, using the static pressure, temperature, and mole fractions of EtOD and D 2 O monomers ͓S. Tanimura, B. E. Wyslouzil, M. S. Zahniser, et al., J. Chem. Phys. 127, 034305 ͑2007͔͒ as inputs. By considering the depletion of the monomer species, the deviation of the pressure
more » ... om the isentropic value, and the heat released, we estimated that ϳ10% of the EtOD molecules are present as pure clusters ͑dimer to tetramer͒ upstream of the onset point of condensation. In contrast, clustering was not detected when only pure EtOD was present under the same conditions ͑temperature and the partial pressure of EtOD͒ for which clustering was observed in the EtOD/ D 2 O flow. This suggests that the formation of EtOD clusters is facilitated by D 2 O in the EtOD/ D 2 O flow. A comparison of the heat released to the flow and the expected heat of dissociation of the EtOD/ D 2 O droplets suggests that small EtOD clusters persist downstream of the onset point. Both upstream and downstream of the onset point of condensation, the concentration of these clusters in the nozzle is higher than that expected at equilibrium. A possible mechanism for the overabundance of pure EtOD clusters is that they form in the mixed EtOD/ D 2 O particles ͑droplets or clusters͒ and evaporate from them.
doi:10.1063/1.3360304 pmid:20405990 fatcat:iflnxwzwwza4lbwsb5u3outxnq