Air-Water Jet (Mist-Jet) for Ship Propulsion 



DISCUSSION 



R. Pallabazzer 



Istituto di Fisica Tecnica e Macchine, Politecnico 



Milan, Italy 



I have a few remarks to make about this paper. The first question is about 

 the values for the drag coefficient C^ and the heat transfer h^ for the droplet 

 motion. I would like to know whether, as it appears, the Stokes flow hypothesis 

 was assumed. If this was the case, I would like to point out that the real motion 

 of the particle is probably not in the Stokes range, because of the high local tur- 

 bulant speed, which especially affects the heat transfer. It is obvious, in fact, 

 that the very low value of the components of the relative speed in the axial di- 

 rection (Vg - Vp) is not an index for the heat transfer, when a Brownian motion 

 is present. 



A second remark relates to the analysis of the mixing phase. The inlet 

 conditions in the nozzle have been assumed as reference or as a datum; in the 

 propulsor, actually, they are not known, because we know the flow conditions 

 just at the inlet of the propulsor. It seems to me that the mixing phase, which 

 occurs in the chamber, is highly unpredictable but it strongly affects the flow 

 parameters at the nozzle inlet. Therefore, I think that the exactness of the 

 particle -flow analysis developed here instead of an homogeneous two -phase 

 flow analysis can be useless when the initial flow conditions are not well known. 



Finally, I would like to observe that it is the hypothesis of a constant slip 

 ratio which determines the shape of the nozzle. This fact was clearly observed 

 by Kliegel in some papers he presented, I think, about ten or fifteen years ago, 

 on gas -solid particle flow. In his works, the only one of which I can now re- 

 member was entitled "Two-Phase Gas-Particle Flow," Kliegel developed a par- 

 ticle flow analysis which is quite the same as that developed by Dr. Quandt, but 

 for application to rocket exhaust gases. 



REPLY TO DISCUSSION 



E. R. Quandt 



Both discussers have raised some interesting questions concerning the fun- 

 damental nature of the homogeneity and internal transport characteristics of 

 two-phase flows. Taking first Dr. Kostilainen's question, I would like to recom- 

 mend Ref. (7) of my paper as one approach to determining whether or not grav- 

 ity effects are important. In low-velocity flow, such as encountered in natural 

 circulation, gravity does prove controlling. However, in the applications I have 

 considered, i.e., thrust devices for high-speed ships, the axial acceleration 



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