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



velocity divided by shaft power into the air compressor for the given total thrust. 

 Figures 11-13 show typical computed levels of propulsion efficiency versus 

 pressure ratio, ship speed, and water-to-air mass flow ratio, respectively. It 

 can be seen that for the range of loss coefficients assumed herein the propulsive 

 efficiency tends to peak slightly below a value of 0.50. Furthermore, it is ap- 

 parent that air system pressure ratios less than 1.5 atm are desirable and would 

 require water-to-air mass flow ratios from 5 to 20 depending upon ship speed. 

 It may be recalled that the large difference in density between air and water re- 

 sults in a very disperse mixture even at the higher mass flow ratios. Figure 13 

 shows that overall efficiency is quite sensitive to average phase slip, so that a 

 considerable effort is required to assure a satisfactory slip ratio a in practical 

 cases. In summary, it appears that propulsion efficiencies up to 50% may be 

 achieved for Mist- Jet systems at pressure ratios from 1.2 to 1.5 and water 

 mass augmentation ratios near 10. It should be noted that at these high mass 

 augmentation ratios virtually all the system thrust is developed by rearward 

 acceleration of the liquid phase. Hence, the air phase is acting much as a pump 

 or propeller would. Of course, one conceptual difference between the air sys- 

 tem and a water pump is that the air system will deliver about half thrust in the 

 absence of any water, thus making the propulsion system inherently amphibious. 



2.0 

 PRESSURE RATIO, V 



Fig. 11 - Propulsion efficiency versus pressure ratio 



1073 



