Experimental and numerical study on thermal-hydraulic performance of wing-shaped-tubes-bundle equipped with winglet vortex generators

The present work evaluates, experimentally and numerically, by the aid of commercial code FLUENT 6.3.26, the effects of relative locations (∆X or ∆Y), heights (hw), and span-angle (θ) of winglet-vortex-generators (WVGs) on thermal-hydraulic performance enhancement for down-stream and/or up-stream wing-shaped-tubes bundle heat exchangers for air Re ranging from 1.85 × 103 to 9.7 × 103 while water Re = 5 × 102. hw is set as 5 mm, 7.5 mm and 10 mm. For tube down-stream, θ is set as 0° (Base-line-case) and from 5° to 45° clockwise common-flow up (CFUp) and counterclockwise common-flow down (CFDn) while for tube up-stream it is set as −5°, −10° and −15° CFUp. Results show that the increase of θ counterclockwise-(CFDn) or clockwise-(CFUp) leads to increase the values of Nu number. Using WVGs with (+5 ° ≤ θ ≤ +45°) results in increasing Nu number by about from 34 to 48% comparing with that of base-line-case. The lowest values of drag coefficient (f) for tube down-stream are obtained at +5° CFDn and −15° CFUp with respect to the base-line case. For tube up-stream, Nu number increases by increasing θ from 0° to −5° and the values of Nu number for θ varying from −5° to −15° have no significant changes. (f) increases with hw and has negligible effect on ha. Furthermore, optimization analyses of θ and longitudinal fin (LF) are utilized, in four cases, for finding the optimum combination and maximum efficiency. The highest values of heat transfer parameters such as effectiveness (ε), area goodness factor (G) and efficiency index (η) and the lowest values of fluid-flow parameters like (f) and hence the best efficiency, are achieved for −15° CFUp down-stream, (“case 3” of −15° CFUp down-stream and 6 mm LF height) and +5° CFDn down-stream. Correlations of Nu number, (f) and (ε) as a function of θ and Re for the studied cases are performed.

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