Pallabazzer 



As previously outlined, such an optimization can result only from a 

 theoretical-experimental analysis restricted to the propulsive ejector. On 

 the other hand, no extensive works appear to have been developed on this sub- 

 ject, and no exact indications are available about the validity of the hypotheses 

 that can be done. 



Besides, one must have in mind that the most delicate and uncertain phase 

 of the two-phase flow is the first mixing phase, which takes place soon after 

 the gas injection; it is generally a very turbulent phenomenon on a macro- 

 scopic scale, where the bubbles' path is random and analytically unforseeable. 

 In this phase, only statistical, experimental data are available, reducing the 

 overall merit of more exact analysis of the successive quasi-homogeneous 

 nozzle flow. 



Generally speaking, a wide bibliography on two-phase flow was published 

 recently by Gouse [lOj. 



More pertinent works on propulsive-type ejectors are listed in Refs. 

 [7,9,11,12], while the theoretical bases of the most logical hypotheses are 

 available in Refs. [7,9,13,14]. The only actual projects of two-phase propulsor 

 appear to be those reported in Refs. [8,15,16,17]. In Ref . [18], a preliminary 

 analysis of two-phase powerplant with a turbine as gas generator was devel- 

 oped, while in Ref. [19] a liquid- metal-water reactor was studied as a gas 

 generator for two-phase underwater propulsion. 



From another point of view, a propulsor based on cryptosteady energy ex- 

 change [1,2] can be ideally considered as a combination of a pump with an ejec- 

 tor, because of the mixing energy exchange phase which follows the pressure 

 exchange phase. This means that, as compared with a shrouded propeller, the 

 propulsor offers the ideal advantages of no cavitation, no mechanical connec- 

 tion or mixing contribution, while as compared with an ejector it offers the 

 advantage of a highly efficient pressure energy exchange preceding the mixing 

 phase. From a power-plant point of view, it will be immaterial how any per- 

 formances can be actually obtained by a propulsor, when the propulsor be- 

 havior is idealized and when there are experimental confirmations of these 

 performances. 



On the basis of the previous considerations, several power plant- propulsor 

 configurations have been analyzed by a simplified model of ejector behavior. 

 Such an analysis allows a comparison either among configurations which have 

 been studied under the same hypotheses or among configurations which require 

 different kinds of hypotheses, when experimental data can confirm their validity 

 under the same order of approximation. Some of these hypotheses can be 

 considered as rather questionable because insufficiently confirmed by experi- 

 mental data available at present. However, they represent a compromise be- 

 tween the exigencies of trustworthiness and simplification. While in fact a 

 particle analysis of the two-phase exchange can be, and really was, already 

 developed under a lower manifold of hypotheses [9,12] for studies regarding 

 the propulsor alone, this kind of analysis would be absolutely impossible when 

 evaluating the powerplant performances, because of the exceedingly high num- 

 ber of variables one should have to consider for an exhaustive investigation. 



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