F,21 • HEAT TRANSFER IN ROCKET MOTORS 



measuring the change in bulk temperature of the jacket coolant. The 

 film coolant used in these experiments was water. 



Fig. F,21a shows a typical distribution of heat transfer through the 

 walls of the motor using fresh oxidizing acid in the propellant and no 

 film cooling. It is at once observed that the rate of heat transfer is highest 

 just upstream of the nozzle throat, probably because in that vicinity the 

 boundary layer is the thinnest owing to the favorable pressure gradient. 

 It is also seen that the heat transfer in the combustion chamber is rela- 

 tively low. In this region where the gases are very hot, radiation from the 

 gas contributes a good share (up to 30 per cent) of the heat transmitted to 

 the walls, the remainder being caused by convection. In the nozzle where 

 ambient temperatures are lower, radiation is considered unimportant. 



0.5 



0.1 0.2 0.3 0.4 



Film coolant, lb/sec 



Fig. F,21b. Effect of rate of film-coolant flow upon heat transfer at nozzle throat. 



It was found that fresh acid always produced low heat transfer. Also, 

 the presence of iron, chromium, and nickel dissolved from the shipping 

 containers could increase the heat transfer as much as 50 per cent. A 

 factor which decreased the heat transfer rate was, of course, a decrease in 

 temperature as indicated by a decrease in oxidizer-fuel mixture ratio. No 

 significant loss in motor performance was observed with change in mix- 

 ture ratio. The design of the propellant injector as well as the nozzle 

 shape were other more or less important factors. 



How film cooling affects the rate of heat transfer at the throat section 

 of the nozzle is shown in Fig. F,21b. Fresh acid was used in the experi- 

 ments represented in this figure. The upper curve shows the decrease in 

 heat transfer through the wall when film coolant is injected tangentially 

 to the circumference of the combustion chamber at the entrance to the 



(417 > 



