Limitations of Matching Condensing Film Profile on a Micro Fin with the Groove: Critical Effect of Disjoining Pressure

Condensation on a fin top terminating with a groove involves several simultaneous phenomena including vapor-liquid boundaries whose shapes are unknown a priori, fluid flow due to capillary and disjoining pressure gradients, and condensation over thin films. This problem occurs in grooved heat pipes,...

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Bibliographic Details
Published in:Nanoscale and microscale thermophysical engineering 2019-10, Vol.23 (4), p.289-303
Main Authors: Alipour, Mobin, Dursunkaya, Zafer
Format: Article
Language:English
Subjects:
Boundary conditions
Capillary flow
Capillary pressure
Computational fluid dynamics
Condensation
Conservation laws
disjoining pressure
Fluid flow
Grooves
Heat pipes
Matching
micro region
micro-grooved heat pipe
Pressure effects
Pressure gradients
Temperature gradients
Thermal resistance
Thin films
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Summary:Condensation on a fin top terminating with a groove involves several simultaneous phenomena including vapor-liquid boundaries whose shapes are unknown a priori, fluid flow due to capillary and disjoining pressure gradients, and condensation over thin films. This problem occurs in grooved heat pipes, where the condensation is predominantly present on fin tops due to the thinner liquid film - having a lower thermal resistance compared to inside the groove where the fluid is substantially thicker. Majority of the studies in the literature assume an approximate profile for the liquid film surface and apply an integral balance for conservation laws, accounting for the effect of the capillary pressure only. In addition, this approximate profile is matched with the liquid profile inside the groove, which serves as a boundary condition. Although intuitive, validity of the matching is not straightforward, and its limitations have never been discussed in the literature, despite the presence of experimental findings to the contrary. In the current study, the effect of disjoining pressure and matching conditions with the groove is investigated using a comprehensive model. The results suggest that for small temperature differences and small slopes, the effect of disjoining pressure is non-negligible, and beyond limiting values of edge angles, the effect of disjoining pressure precludes solutions where the fin top film matches the groove in a smooth transition.
ISSN:1556-7265
1556-7273
DOI:10.1080/15567265.2019.1633712