Heat transfer and pressure drop characteristics of alternating clockwise and counter clockwise twisted tape inserts in the transitional flow regime

Abstract

The purpose of this study was to experimentally investigate the heat transfer and pressure drop characteristics in a smooth circular tube with alternating clockwise and counter clockwise twisted tape (CCCTT) inserts. The CCCTT inserts were fabricated from copper plate strips with a length, width and thickness of 450 mm, 18 mm and 1 mm respectively. The strips were twisted to obtain a twist ratio of 5 and 12 strips were joined longitudinally so that a clockwise direction twisted tape insert was connected to a counter clockwise direction twisted tape. The assembling was at connection angles of 0°, 30° and 60°, to form CCCTT inserts with an overall length of 5.27 m. The CCCTT inserts were placed in a smooth circular copper tube with an inner diameter of 19 mm. Water was used as the test fluid and experiments were conducted at constant heat fluxes of 1.35, 2, 3 and 4 kW/m 2 between Reynolds numbers of 300 and 11 404. This covered the laminar, transitional and turbulent flow regimes. Specific attention was given to the identification of the transitional flow regime with the CCCTT inserts and the influence of the connection angle and heat flux on the transitional flow regime. It was found that both the start and the end of the transitional flow regime were influenced by the connection angle and the heat flux. When different connection angles were compared it was found that an increase in connection angle enhanced the heat transfer in the transitional flow regime. An increase in heat flux significantly enhanced the heat transfer in the laminar flow regime and delayed transition. Heat transfer and pressure drop correlations were developed to predict the experimental data in the laminar, transitional and turbulent regimes as a function Reynolds number, modified Grashof number and connection angle.

Analysis on flow structure and improvement of heat transfer in 3D circular tube with varying axial groove turbulator configurations

“…Hence, all these changes can improve the heat performance in the grooved pipe compared to the normal one. These results agreed with References [2] and [6]. Figure 5 depicts the distributions in pressure inside both smooth and grooved pipes with different geometrical configurations.…”

“…To improve the convective heat transfer in the circular tubes, many types of turbulators have been applied. Turbulence is an important factor that has a direct effect on the thermal performance ratings, such as dimple, groove, 3,4 twisted tape, [5][6][7] wire coil, 8,9 and wing. 10 A numerical investigation of turbulent flows in the periodically grooved channels in 2D has been reported by Eiamsa-ard and Promvonge 11 with a range of Reynolds numbers 6000-18,000 and the (B/H) of 0.5-1.75, they found that the tube with groove increases the heat transfer up to 158% compared with the smooth tube, and the highest gain of 1.33 on thermal performance factor is obtained for the case of groove-width to the channel-height ratio by about 0.75.…”

Hydrodynamic and Thermal Performance Twisted Tape Insert Provided in Heat Exchanger Tubes: A Review

“…At constant pumping power, the maximum thermal performance factor obtained is 1.433, 1.396 and 1.24 respectively for perforated twisted tapes with alternate axis, perforated twisted tapes and regular twisted tapes. Abolarin et al (2019) experimentally investigate the heat transfer and pressure drop characteristics in a smooth circular tube with alternating clockwise and counter clockwise twisted tape inserts. An increase in heat flux significantly enhanced the heat transfer in the laminar flow regime and delayed transition.…”

Thermal Performance Enhancement Using Absorber Tube with Inner Helical Axial Fins in a Parabolic Trough Solar Collector

“…Bahiraei et al [14] have checked on a triple-tube that their outcomes show that, based on heat exchange efficiency, an increase in height and reduced pitch are suggested. Abolarin et al [15] have checked the impact of various geometries in twisted tapes, and the results pointed out that connection angle increases heat transfer. They found that when the wavelength is smaller, the temperatures near the walls increased.…”