Experimental characterization of convective heat transfer with MWCNT based nanofluids under laminar flow conditions

Abstract When condensation first forms on a surface, it starts as tiny droplets. As the surface continues to collect condensation, the droplets grow together and form a film. The film increases the thermal resistance of the system. It is possible to remove the fluid from the condensing surface before it develops into a film. Dropwise condensation has the capability of providing up to an order of magnitude higher heat transfer than film condensation. A hydrophobic surface is capable of sustaining dropwise condensation but creates a high energy barrier that restricts nucleation. A hydrophilic surface has a low energy barrier for nucleation but retains the water quickly transitioning to film condensation. A hydrophilic and hydrophobic patterned surface creates a surface with a low nucleation energy barrier and is capable of sustaining dropwise condensation. Surface patterns are evaluated under laminar flow conditions to maximize mass collection. The surfaces are evaluated using a thermal model, which includes an equivalent thermal resistance for diffusion. Laminar flow rates are evaluated using Reynolds numbers from 1,218 to 4 × 105. Hydrophilic nodules sizes are evaluated from 0.1 mm to 3.7 mm. Under natural convection flow, mass collection can be increased by 20% with respect to film heat transfer.

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HYDRAULIC AND THERMAL PERFORMANCES OF LAMINAR FLOW IN FRACTAL TREELIKE BRANCHING MICROCHANNEL NETWORK WITH WALL VELOCITY SLIP

Fractals ◽

10.1142/s0218348x2050022x ◽

2020 ◽

Vol 28 (02) ◽

pp. 2050022 ◽

Cited By ~ 11

Author(s):

DALEI JING ◽

JIAN SONG ◽

YI SUI

Keyword(s):

Heat Transfer ◽

Laminar Flow ◽

Convective Heat Transfer ◽

Hydraulic Resistance ◽

Convective Heat ◽

Slip Length ◽

Velocity Slip ◽

Diameter Ratio ◽

Slip Condition ◽

Wall Velocity

This work theoretically studies the effects of wall velocity slip on the hydraulic resistance and convective heat transfer of laminar flow in a microchannel network with symmetric fractal treelike branching layout. It is found that the slip can reduce the hydraulic resistance and enhance the Nusselt number of laminar flow in the network; furthermore, the slip can also affect the optimal structure of the fractal treelike microchannel network with minimum hydraulic resistance and maximum convective heat transfer. Under the size constraint of constant total channel surface area, the optimal diameter ratio of microchannels at two successive branching levels of the symmetric fractal treelike microchannel network with a minimized hydraulic resistance is only dependent on branching number [Formula: see text] in the manner of [Formula: see text] for no slip condition, but decreases with the increasing slip length, the increasing branching number and the increasing length ratio of microchannels at two successive branching levels for slip condition. The convective heat transfer of the treelike microchannel network is independent on the diameter ratio for no slip condition, but displays an increasing after decreasing trend with the increasing diameter ratio for slip condition. The symmetric treelike microchannel network with the worst convective heat transfer performance is the network with diameter ratio equaling one for slip condition.

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