scholarly journals Role of Curvature on Heat Flow Visualization and Irreversibilities during Natural Convection in Enclosures

2018 ◽  
Author(s):  
Damodara Priyanka ◽  
Tanmay Basak
Keyword(s):  
Natural Convection ◽  
Heat Flow ◽  
Flow Visualization

Natural convection in a corrugated slot

2017 ◽  
Vol 815 ◽  
pp. 537-569 ◽  
Author(s):  
Arman Abtahi ◽  
J. M. Floryan
Keyword(s):  
Natural Convection ◽  
Heat Flow ◽  
Convective Heat ◽  
Phase Difference ◽  
Conductive Heat ◽  
Heat Transfer Augmentation ◽  
Conductive Heat Flow ◽  
Secondary Motion ◽  
Prandtl Numbers

Analysis of natural convection in a horizontal slot formed by two corrugated isothermal plates has been carried out. The analysis is limited to subcritical Rayleigh numbers$Ra$where no secondary motion takes place in the absence of corrugations. The corrugations have a sinusoidal form characterized by the wavenumber, the upper and lower amplitudes and the phase difference. The most intense convection occurs for corrugation wavelengths comparable to the slot height; it increases proportionally to$Ra$and proportionally to the corrugation height. Placement of corrugations on both plates may either significantly increase or decrease the convection depending on the phase difference between the upper and lower corrugations, with the strongest convection found for corrugations being in phase, i.e. a ‘wavy’ slot, and the weakest for corrugations being out of phase, i.e. a ‘converging–diverging’ slot. It is shown that the shear forces would always contribute to the corrugation build-up if erosion was allowed, while the role of pressure forces depends on the location of the corrugations as well as on the corrugation height and wavenumber, and the Rayleigh number. Placing corrugations on both plates results in the formation of a moment which attempts to change the relative position of the plates. There are two limiting positions, i.e. the ‘wavy’ slot and the ‘converging–diverging’ slot, with the latter being unstable. The system would end up in the ‘wavy’ slot configuration if relative movement of the two plates was allowed. The presence of corrugations affects the conductive heat flow and creates a convective heat flow. The conductive heat flow increases with the corrugation height as well as with the corrugation wavenumber; it is largest for short-wavelength corrugations. The convective heat flow is relevant only for wavenumbers of$O(1)$, it increases proportionally to$Ra^{3}$and proportionally to the second power of the corrugation height. Convection is qualitatively similar for all Prandtl numbers$Pr$, with its intensity increasing for smaller$Pr$and with the heat transfer augmentation increasing for larger$Pr$.

Heatlines visualization of convective heat flow during differential heating of porous enclosures with concave/convex side walls

2018 ◽  
Vol 28 (7) ◽  
pp. 1506-1538 ◽  
Author(s):  
Pratibha Biswal ◽  
Tanmay Basak
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Porous Media ◽  
Natural Convection ◽  
Heat Flow ◽  
Flow Visualization ◽  
Convex Side ◽  
Content Type ◽  
Side Walls ◽  
Element Method

Purpose This paper is aimed to study natural convection in enclosures with curved (concave and convex) side walls for porous media via the heatline-based heat flow visualization approach. Design/methodology/approach The numerical scheme involving the Galerkin finite element method is used to solve the governing equations for several Prandtl numbers (Prm) and Darcy numbers (Dam) at Rayleigh number, Ram = 106, involving various wall curvatures. Finite element method is advantageous for curved domain, as the biquadratic basis functions can be used for adaptive automated mesh generation. Findings Smooth end-to-end heatlines are seen at the low Dam involving all the cases. At the high Dam, the intense heatline cells are seen for the Cases 1-2 (concave) and Cases 1-3 (convex). Overall, the Case 1 (concave) offers the largest average Nusselt number ( Nur¯) at the low Dam for all Prm. At the high Dam, Nur¯ for the Case 1 (concave) is the largest involving the low Prm, whereas Nur¯ is the largest for Case 1 (convex) involving the high Prm. Practical implications Thermal management for flow systems involving curved surfaces which are encountered in various practical applications may be complicated. The results of the current work may be useful for the material processing, thermal storage and solar heating applications Originality/value The heatline approach accompanied by energy flux vectors is used for the first time for the efficient heat flow visualization during natural convection involving porous media in the curved walled enclosures involving various wall curvatures.

THE ROLE OF NATURAL CONVECTION ON DROPLET EVAPORATION

2019 ◽  
Author(s):  
Abgail Paula Pinheiro ◽  
João Marcelo Vedovoto
Keyword(s):  
Natural Convection ◽  
Droplet Evaporation
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