4 l at stp mean molecular weight of air 288 129 gl

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Unformatted text preview: 8.8; 1.29 g/l Molecular weight of CO2: 44; 1.96 g/l Molecular weight of water: 18; 0.8 g/l In g e n e r a l, a p u r e C O 2 p lu m e w ill b e to o d e n s e to e v e r b e c o m e c o n v e c tiv e . C o n v e c tiv e s ta b ility b e c o m e s m o r e d iffic u lt a s C O 2 / H 2 O r a tio in c r e a s e s . L a r g e c la s ts w ill te n d to fa ll o u t e a r ly , d ilu tin g th e ash. 9 Air entrainment A c h ie v in g c o n v e c tiv e c o n d itio n s r e q u ir e s th a t a ir be entrained to dilute the ash. At the vent, even a cloud produced by magma with 10% H2O will be 5 times more dense than the atmosphere. In the gas thrust region, a volume of column can entrain up to 4 times its volume in air. Entrainment is enhanced by turbulence (indeed, requires turbulence). Turbulence is promoted by high velocity Therefore, higher velocities lead to greater entrainment. Entrainment occurs only at the sides Therefore, the wide columns (wide vents) entrain proportionally less air than narrow columns (narrow vents) Effect of Vent Radius E n tr a in m e n t o c c u r s a t th e in te r fa c e b e tw e e n c o lu m n a n d s u r r o u n d in g a ir This is proportional to the circumference of the column (and ultimately the vent), so it increases linearly with radius M a s s flu x ( s p e c ific a lly o f p a r tic le s ) is p r o p o r tio n a l to th e a r e a o f th e v e n t Mass flux increases with square of vent radius (for a fixed velocity) T h e r e fo r e , a t la r g e r , in c r e a s in g r w o r k s a g a in s t c o n v e c tiv e s ta b ility 10 Heat E n tr a in e d a ir m u s t b e h e a te d a n d e x p a n d e d to o v e r c o m e d e n s ity o f a s h . B e c a u s e th e h e a t c a p a c ity o f g a s is lo w , h e a t c o m...
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This document was uploaded on 03/04/2014 for the course EAS 458 at Cornell University (Engineering School).

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