A kinetic model of droplet heating and evaporation: Effects of inelastic collisions and a non-unity evaporation coefficient

Handle URI:
http://hdl.handle.net/10754/562561
Title:
A kinetic model of droplet heating and evaporation: Effects of inelastic collisions and a non-unity evaporation coefficient
Authors:
Sazhin, Sergei S.; Xie, Jianfei; Shishkova, Irina N.; Elwardani, Ahmed Elsaid ( 0000-0002-2536-2089 ) ; Heikal, Morgan Raymond
Abstract:
The previously developed kinetic model for droplet heating and evaporation into a high pressure air is generalised to take into account the combined effects of inelastic collisions between molecules in the kinetic region, a non-unity evaporation coefficient and temperature gradient inside droplets. It is pointed out that for the parameters typical for Diesel engine-like conditions, the heat flux in the kinetic region is a linear function of the vapour temperature at the outer boundary of this region, but practically does not depend on vapour density at this boundary for all models, including and not including the effects of inelastic collisions, and including and not including the effects of a non-unity evaporation coefficient. For any given temperature at the outer boundary of the kinetic region the values of the heat flux are shown to decrease with increasing numbers of internal degrees of freedom of the molecules. The rate of this decrease is strong for small numbers of these degrees of freedom but negligible when the number of these degrees exceeds 20. This allows us to restrict the analysis to the first 20 arbitrarily chosen degrees of freedom of n-dodecane molecules when considering the effects of inelastic collisions. The mass flux at this boundary decreases almost linearly with increasing vapour density at the same location for all above-mentioned models. For any given vapour density at the outer boundary of the kinetic region the values of the mass flux are smaller for the model, taking into account the contribution of internal degrees of freedom, than for the model ignoring these degrees of freedom. It is shown that the effects of inelastic collisions lead to stronger increase in the predicted droplet evaporation time in Diesel engine-like conditions relative to the hydrodynamic model, compared with the similar increase predicted by the kinetic model considering only elastic collisions. The effects of a non-unity evaporation coefficient are shown to be noticeable for gas temperatures of 1500 K. The application of the rigorous kinetic model, taking into account the effects of inelastic collisions and a non-unity evaporation coefficient, and the model taking into account the temperature gradient inside droplets, is recommended when accurate predictions of the values of droplet surface temperature and evaporation time in Diesel engine-like conditions are essential. © 2012 Elsevier Ltd. All rights reserved.
KAUST Department:
Mechanical Engineering Program
Publisher:
Elsevier
Journal:
International Journal of Heat and Mass Transfer
Issue Date:
Jan-2013
DOI:
10.1016/j.ijheatmasstransfer.2012.09.046
Type:
Article
ISSN:
00179310
Appears in Collections:
Articles; Mechanical Engineering Program

Full metadata record

DC FieldValue Language
dc.contributor.authorSazhin, Sergei S.en
dc.contributor.authorXie, Jianfeien
dc.contributor.authorShishkova, Irina N.en
dc.contributor.authorElwardani, Ahmed Elsaiden
dc.contributor.authorHeikal, Morgan Raymonden
dc.date.accessioned2015-08-03T10:42:48Zen
dc.date.available2015-08-03T10:42:48Zen
dc.date.issued2013-01en
dc.identifier.issn00179310en
dc.identifier.doi10.1016/j.ijheatmasstransfer.2012.09.046en
dc.identifier.urihttp://hdl.handle.net/10754/562561en
dc.description.abstractThe previously developed kinetic model for droplet heating and evaporation into a high pressure air is generalised to take into account the combined effects of inelastic collisions between molecules in the kinetic region, a non-unity evaporation coefficient and temperature gradient inside droplets. It is pointed out that for the parameters typical for Diesel engine-like conditions, the heat flux in the kinetic region is a linear function of the vapour temperature at the outer boundary of this region, but practically does not depend on vapour density at this boundary for all models, including and not including the effects of inelastic collisions, and including and not including the effects of a non-unity evaporation coefficient. For any given temperature at the outer boundary of the kinetic region the values of the heat flux are shown to decrease with increasing numbers of internal degrees of freedom of the molecules. The rate of this decrease is strong for small numbers of these degrees of freedom but negligible when the number of these degrees exceeds 20. This allows us to restrict the analysis to the first 20 arbitrarily chosen degrees of freedom of n-dodecane molecules when considering the effects of inelastic collisions. The mass flux at this boundary decreases almost linearly with increasing vapour density at the same location for all above-mentioned models. For any given vapour density at the outer boundary of the kinetic region the values of the mass flux are smaller for the model, taking into account the contribution of internal degrees of freedom, than for the model ignoring these degrees of freedom. It is shown that the effects of inelastic collisions lead to stronger increase in the predicted droplet evaporation time in Diesel engine-like conditions relative to the hydrodynamic model, compared with the similar increase predicted by the kinetic model considering only elastic collisions. The effects of a non-unity evaporation coefficient are shown to be noticeable for gas temperatures of 1500 K. The application of the rigorous kinetic model, taking into account the effects of inelastic collisions and a non-unity evaporation coefficient, and the model taking into account the temperature gradient inside droplets, is recommended when accurate predictions of the values of droplet surface temperature and evaporation time in Diesel engine-like conditions are essential. © 2012 Elsevier Ltd. All rights reserved.en
dc.publisherElsevieren
dc.subjectDropletsen
dc.subjectEvaporationen
dc.subjectEvaporation coefficienten
dc.subjectHeatingen
dc.subjectInelastic collisionsen
dc.subjectKinetic modellingen
dc.subjectN-dodecaneen
dc.titleA kinetic model of droplet heating and evaporation: Effects of inelastic collisions and a non-unity evaporation coefficienten
dc.typeArticleen
dc.contributor.departmentMechanical Engineering Programen
dc.identifier.journalInternational Journal of Heat and Mass Transferen
dc.contributor.institutionSir Harry Ricardo Laboratories, Centre for Automotive Engineering, University of Brighton, Brighton, BN2 4GJ, United Kingdomen
dc.contributor.institutionLow Temperature Department, Moscow Power Engineering Institute, Krasnokazarmennaya 14, Moscow 111250, Russian Federationen
dc.contributor.institutionDepartment of Mechanical Engineering, Universiti of Teknologies, PETRONAS, Bandar Sri Iskandar, 31750 Tronoh, Perak Darul Ridzuan, Malaysiaen
kaust.authorElwardani, Ahmed Elsaiden
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