OCR Text |
Show Curve No. 9 (^ = 0.97 ( a), 7.66 ( b) , 13.36 ( c) ° C) is plotted with the equivalent air temperature determined with r_ equal to that for saturated air at 0° C, which in this instance is 15.3° C. In this case and for still higher air temperatures, a non- melting surface can no longer occur. 9. The Most Favorable Conditions for Selective Ablation As shown in Figs. 7a through 7c, ablation can vary greatly at locations with different &.^ in spite of otherwise equal meteorological conditions ( Q+ B, o/ J , e I , u). If the vapor pressure e, of the air at temperature a/ T is higher than the saturation vapor pressure over ice at the same temperature, ice accretion in the form of rime formation can even take place on suitably sharp edges. Here the fact that the occurrence of ablation is not involved is disregarded. Such would not be the case for ablation which accentuates irregularities at a non- melting surface. As the discussion for Curve No. 3 pointed out, this would play practically no part, for the differentiation produced would be very small. Disregarding these cases, the ablation - M for a non- melting surface increases with increasing Oi. for practical purposes only at negative air temperatures and especially in this case at high relative humidities. This shown by the appropriate curves in Fig. 6. For a melting surface the ablation - M also increases with increasing if for « L 4,0 3,0 2,0 1,0 0,0 Torr p = 760 Torr ( 0 m) bL 1.2 3.2 5.3 7,3 9.3 ° C p = 525 Torr ( 3000 m) 9t 1.7 4.7 7,6 10.6 13.5 ° C p = 354 Torr ( 6000 m) 0L 2,5 6.9 11,3 15,7 20,1 ° C 25 |