OCR Text |
Show restriction that for ablation which accentuates surface irregularities the value of CCL is understood to equal or exceed 50 meal cm" 2 min" 1 deg" 1, the additional boundary ( QfB)/ CTL = 8 deg. is determined, which is plotted in Fig. 6 to the. left of the first boundary. For a non- melting surface the boundary between ablation which accentuates irregularities and which reduces them follows from Equation ( 10) dM dxL PppPeCpp L< aZffrr ddxxLL J for in this case the surface temperature / T> depends on CC. . If the term dv/ ad. in ( 22) is eliminated with the aid of the following expression obtained by differentiating the heat balance Equation ( 11) in respect to CC. d* d 0.623 rg dE\ t 0,623rE \ / a 0,623 rE „\ XL j II - I - TTT = ( f r t i - eL - ( fr- l Ej, ( 23) dxL \ pcp afr/ \ pcp I \ pcp I one then obtains the boundary relation dE eL = E + - (& L-&), ( 24) still dependent on ny- , which, together with the heat balance Equation ( 11) containing /\ r, the relation /\ r z* 0° C, and plausible assumptions about the limiting value of ( C+ B)/ Ci:, , enables the boundary to be defined. The value - 100 meal cm" 2 min" 1 can be regarded as the lower limit of Q+ B, just as 400 meal cm" 2 min" 1 was for the upper limit. Together with ( XL= 50 meal cm" 2 min- 1 deg" 1, this leads to - 2 deg ^ ( Q+ B)/ fl, - 8 deg. The upper boundary value ( Q+ B)/ Cf, = 8 deg yields the lower of the three curves plotted in Fig. 6. For values of /\ r and e. whose plotted points lie between this curve and the 20 |