E,9 • NUCLEATE BOILING 



allows boiling at less superheat, the bubble velocity and agitation is less, 

 and lower heat transfer results. The values for carbon tetrachloride are 

 still lower because of its low thermal diffusivity which influences the heat 

 transfer directly and also leads to lower bubble velocity (see above). As 

 already stated, the effect of increasing gas content is similar to that of 

 decreasing the surface tension. In addition, gas diffusion influences bubble 

 motion to some extent and gas bubbles can rather easily become stable 

 and adhere to the heating surface [64]- For both of these reasons the 



3 

 I- 



D 

 0) 



£ 

 'x 



D 



10.0 



5.0 

 4.0 



2.0 

 1.0 



Experimental 



Calculated from 

 Sieder-Tate equation 



turnout point - 

 500 Ib/iniabs 

 • 1 5 ft/sec~ 



Burnout point 

 50lb/in2abs 

 ,15 ft/sec 



Burnout point 



.500 Ib/in^ ab.s 

 |48_ft7sec 



\ Burnout point 

 50 Ib/in^abs 

 ' 4 8 ft/sec 



100 200 



T T °P 



' W ' iiq/ r 



400 



Fig. E,9i. Heat transfer to red fuming nitric acid. Forced convection-nucleate boil- 

 ing. Burnout points are indicated. Liquid temperature 80°F. Heat transfer surface 

 SS347. NO2 content of acid 6^ per cent, water content | to 2 per cent [82]. 



burnout points of the two hquids, when containing gas, are below the 

 values which are obtained when they are degassed. Fig. E,9h also con- 

 tains some burnout points for aerated water which were not caused by 

 the adherence of bubbles, a random process which generally cannot be 

 controlled. For design purposes the lower curve would have to be taken. 

 Further experimental results on boiling heat transfer are given in Fig. 

 E,9i, which contains information on nitric acid [82]. Burnout points for 

 Freon have already been given in Fig. E,8f and for "jet fuel" in Fig. 

 E,8g. For information on the heat transfer to a number of hydrocarbons 

 under bulk boiling conditions, the reader is referred to [70]. 



(331 > 



