Heat Transfer Intensification in a Heat Exchanger by Means of Twisted Tapes in Rib and Sawtooth Forms

Abstract

This experimental study aimed to intensify the aerothermal performance index (API) in a round tube heat exchanger employing twisted tapes in rib and sawtooth forms (TTRSs) as swirl/vortex flow generators. The TTRSs have a constant twist ratio of 3.0, a constant rib pitch ratio (p/e) of 1.0, and six different sawtooth angles (α = 20°, 30°, 40°, 50°, 60°, and 70°). Experiments were carried out in an open flow using air as the working fluid for Reynolds numbers between 6000 and 20,000 in the current study, which was conducted in a heated tube under conditions of uniform wall heat flux. A typical twisted tape (TT) was also tested for comparison. The experimental results suggest that TTRSs yield Nusselt numbers ranging from 1.42 to 2.10 times of those of a plain tube. TTRSs with larger sawtooth angles (α) offer superior heat transfer. The TTRSs with α = 20°, 30°, 40°, 50°, 60°, and 70° respectively, enhance average Nusselt numbers by 158%, 162%, 166%, 172%, 180%, and 187% with average friction factors of 3.51, 3.55, 3.60, 3.67, 3.75 and 3.82 times higher than a plain tube. Additionally, TTRSs with sawtooth angles (α) of 20°, 30°, 40°, 50°, 60°, and 70° offer APIs in the ranges of 0.99 to 1.19, 1.01 to 1.21, 1.03 to 1.26, 1.05 to 1.31, 1.07 to 1.42, and 1.09 to 1.48, respectively, which are higher than those of the typical twisted tape (TT) by around 5%, 7%, 11%, 16%, 25%, and 31%, respectively. This demonstrates that twisted tapes in rib and sawtooth form (TTRSs), with appropriate geometries, give a promising trade-off between enhanced heat transfer and an increased friction loss penalty.

Thermal hydraulic performance of a tubular heat exchanger with in‐line perforated baffle with shutter type saw tooth turbulator

“…They have made advancements by using coiled structures, 38 twisted strips, 39 and coneshaped rings with perforations. 40 Different patterns of perforation 41,42 with deflectors, including triangles, 36 rectangles, 32 circles, and trapezoids, 30,31 saw tooth ribs 27 and guide vanes, 24 have been studied to determine the most effective way to increase heat transfer per unit pressure drop. However, there is still limited knowledge about saw tooth profile deflectors and their implication as multiple flow deflectors on baffle plates as turbulence promotors in HX.…”

“…In a recent study conducted by Poonpakdee et al, 27 the aerothermal performance index (API) of tubular heat exchangers was experimentally improved using twisted tapes with rib and sawtooth designs, generating swirl/vortex flow. The twisted tapes had a consistent twist ratio of 3.0 and a fixed rib pitch ratio ( p / e ) of 1.0.…”

Enhanced Heat Transfer of a Heat Exchanger Tube Installed with V-Shaped Delta-Wing Baffle Turbulators

“…Heat transfer enhancement techniques have been widely applied for energy savings in different systems such as refrigeration, automobiles, the process sector, and solar air heaters. Several investigations [1][2][3][4][5][6][7][8] have been carried out to minimize heat exchangers' energy consumption and operating expenses. In the field of heat transfer engineering, turbulators, also known as vortex/reverse flow devices, are extensively utilized.…”