Abstract
The impact of double-sided delta-winglet tape (DWTs) inserts on convective heat transfer and friction behaviors in a tube was experimentally investigated. Three DWTs with ratios of winglet-height (b) to inner tube diameter (di) called blockage ratio (Rb) of 0.28, 0.35 and 0.42 were tested and their performance was compared to that of a longitudinal strip and plain tube under similar test flow conditions. Experiments were conducted over a wide range of flow rates, 3.35 × 10−5–8.33 × 10−5 m3/s, which correspond to 5500 ≤ Reynolds number (Re) ≤ 14,500 in the 14.3 mm i.d. tube. The results revealed that using DWTs dramatically increased the Nusselt number (Nu) by as much as 364.3% and the friction factor (f) by 15.5 times compared with those of a plain tube. Thermal performance (η) increased with a corresponding increase in Rb. The highest thermal performance (η) obtained was 1.4. Showing a notable improvement on the thermal performance of the system, DWTs are proposed as a favorable insert device.
Highlights
Vortex generators (VGs) have received extensive attention by researchers [1,2,3,4,5] as devices for obtaining high thermal performance by enhancing the heat-transfer coefficients of a tube heat exchanger.VGs are regarded as potential heat-transfer augmentation devices because they create vortices that lead to high heat-transfer rates [5]
The results showed that a tube with delta winglets had better thermal performance than a plain tube, and that the arrangements of two sides cut with four delta winglets outperformed all other arrangements
The present study examines the effect of double-sided delta-winglet tape (DWT) VGs having varying values of
Summary
Vortex generators (VGs) have received extensive attention by researchers [1,2,3,4,5] as devices for obtaining high thermal performance by enhancing the heat-transfer coefficients of a tube heat exchanger. VGs are regarded as potential heat-transfer augmentation devices because they create vortices that lead to high heat-transfer rates [5]. VGs that form longitudinal vortices are extremely attractive because they experience only a small pressure drop penalty. These longitudinal vortices can be generated by using wing or winglet type VGs, which create flow separation at the leading edge of the wing [7]. An experimental and numerical study on a rectangular channel fitted with a delta-winglet vortex generator was conducted by Wu and Tao [8]
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