OCR Text |
Show saturation vapor pressure curve for water just above, ablation which promotes surface irregularities is therefore possible for Q+ B = 400 meal cm" 2 min" 1 over 0CL= 50 meal cm" 2 min" 1 deg" 1. At Q+ B = 0 the boundary curve coincides with the saturation vapor pressure curve ( here plotted as the middle curve), which is also true for the boundary curve at ( Q+ B)/^ = - 2 deg within the possible accuracy of computation (± 0.02 torr). For p = 525 torr, - 100 ^ Q+ B ^ 400 meal cm" 2 min" 1 and ( XL = 50 meal cm" 2 min" 1 deg" 1, the relation - dM/ d 0CL < 0 can thus occur only when the plotted points of / tr^ and e^ lie in the two designated domains in Fig. 6. For a non-melting surface this can occur only in the narrow zone with low air temperature and high relative humidity beneath the saturation vapor pressure curve for water. For a melting surface it can occur only in the zone with relatively high air temperature to the left of the line which intersects the abscissa at ixr. = 13.5° C. 8. The Dependency of Ablation on the Heat Transfer Coefficient Figs. 7a through 7c show variations of ablation, - M, as a function of the heat transfer coefficient for several characteristic cases. These figures were calculated with p = 525 torr and Q+ B = 200 meal cm" 2 min" 1. The abscissa CC, , whose value is entered beneath each diagram, spans four orders of magnitude and thus covers values ranging from a plane surface to ridges with equivalent radii of curvature around 1 micron. Corresponding values for the latter are entered along the upper margin of Fig. 7a. The ordinate - M, whose values are given along the left of each diagram, includes negative quantities as well which indicate accumulation. Fig. 7a was calculated for e = 4.29 torr in order to overlap the two domains of Fig. 6 and to characterize the relations for high humidity ( ablation which 21 |