Title

Delta winglets for enhancing solar energy: Turbulent strain rate-heat convection relationship

Document Type

Article

Publication Date

1-1-2021

Publication Title

Journal of Green Building

Volume

16

Issue

2

First Page

97

Keywords

Delta-winglet pair, Heat transfer enhancement, Turbulent strain rate

Last Page

114

Abstract

Delta winglets are an effective means for enhancing heat exchange and thus the performance of renewable energy technologies, including solar energy. A pair of 0.1 mm thick, 15 mm high (h) and 30 mm long aluminum winglets separated with transversal spacing, s, of 2h, h and 0 were scrutinized in a closed-loop wind tunnel at a Reynolds number based on h of 6300. The turbulent flow was characterized using a 3D hotwire probe, and the heat convection augmentation was quantified in terms of the normalized Nusselt number (Nu/Nu0), indicating the heat transfer improvement compared to the reference case without the winglets. The interaction of the organized counter-rotational vortices intensifies and they become indiscernible at s = 0. The peak strain rate at 10h downstream increased from 390 s–1, to 478 s–1, to 514 s–1, when the spacing decreased from 2h to h to 0, respectively. The zero-spaced winglet pair provided the largest Nu/Nu0, of around 1.21, at X/h = 10 and Y/h = 0, approximately 21% higher than that of 2h-spaced winglet pair, due to the strongest strain rate and the absence of upwash flow. On the other hand, the 2h-spaced winglet pair provided the largest span-averaged Nu/Nu0, which is of practical significance.

DOI

10.3992/jgb.16.2.97

ISSN

15526100

E-ISSN

19434618

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