F • CONVECTIVE HEAT TRANSFER IN GASES 



nozzle. The lower curve indicates an even greater reduction when the 

 coolant was injected midway between the entrance and throat of the 

 nozzle where the heat transfer was increasing rapidly. Observations of 

 the nozzle after the tests showed that film cooling persisted throughout 

 the nozzle throat. For the particular motor used, maximum cooling was 

 attained when the coolant flow rate was 5 per cent of the propellant con- 

 sumption rate. From the results of his experiments, Boden concluded that 

 film cooling reduces the heat transfer in rocket motors up to 70 per cent, 

 and that proper control of the operating mixture ratio and the propellant 



Z) 

 H 



>; 



o 



JZ 



c 



LU 



u 2 4 6 8 10 12 14 16 18 20 22 24 



Temperature, °R X 10"^ 



Fig. F,22a. Enthalpy of air as a function of 

 temperature and pressure. 



composition would gain an additional 10 to 15 per cent reduction. Al- 

 though the above results were obtained using water as the film coolant, 

 other data indicated that fuel was equally effective. 



A similar set of experiments was conducted by Greenfield [68] to deter- 

 mine the coefficients of heat transfer in a rocket motor designed to pro- 

 duce a 1000-lb thrust with a liquid oxygen-ethyl alcohol propellant. The 

 experimental procedure for measuring the heat transfer rate utilized the 

 transient temperature rise of the five uncooled segments which comprised 

 the walls of the motor nozzle. Two series of tests were carried out: one 

 series using the liquid oxygen-ethyl alcohol propellant which developed 

 an estimated 3000°F, the other using high pressure air at 1400°F. No film 



< 418 ) 



