Roughness induced forced convective laminar-transitional micropipe flow: energy and exergy analysis |
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Authors: | A Alper Ozalp |
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Institution: | (1) Department of Mechanical Engineering, University of Uludag, 16059 Gorukle, Bursa, Turkey |
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Abstract: | Variable fluid property continuity, Navier–Stokes and energy equations are solved for roughness induced forced convective
laminar-transitional flow in a micropipe. Influences of Reynolds number, heat flux and surface roughness, on the momentum-energy
transport mechanisms and second-law of thermodynamics, are investigated for the ranges of Re = 1–2,000, Q = 5–100 W/m2 and ε = 1–50 μm. Numerical investigations put forward that surface roughness accelerates transition with flatter velocity profiles
and increased intermittency values (γ); such that a high roughness of ε = 50 μm resulted in transitional character at Re
tra = 450 with γ = 0.136. Normalized friction coefficient (C
f*) values showed augmentation with Re, as the evaluated C
f* are 1.006, 1.028 and 1.088 for Re = 100, 500 and 1,500, respectively, at ε = 1 μm, the corresponding values rise to C
f* = 1.021, 1.116 and 1.350 at ε = 50 μm. Heat transfer rates are also recorded to rise with Re and ε; moreover the growing influence of ε on Nusselt number with Re is determined by the Nu
ε=50 μm/Nu
ε=1 μm ratios of 1.086, 1.168 and 1.259 at Re = 500, 1,000 and 1,500. Thermal volumetric entropy generation values decrease with Re and ε in heating; however the contrary is recorded for frictional volumetric entropy generation data, where the augmentations in are more considerable when compared with the decrease rates of |
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