Internal Flow Analysis of a Heat Transfer Enhanced Tube with a Segmented Twisted Tape Insert

Abstract

A heat exchanger is a device that transfers unneeded heat from one region to another, and transferred heat may be fully reused, thus improving energy efficiency. To augment this positive process, many studies and investigations on automation technologies have been performed. Inserts are widely used in pipe flow for heat transfer enhancement, since they can break the boundary layer and promote the heat exchange. Segmented twisted tape, which is applicable in 3D printing, is a novel insert and has potential in heat transfer enhancement. To clarify its advantages and disadvantages, this research presents a numerical investigation of vortex flow and heat enhancement in pipes containing one segmented twisted element. Flow state and heat transfer behaviour are obtained by simulation under constant wall temperature with different Reynolds numbers, ranging from 10,000 to 35,000. The effects of geometric parameters, including twist ratio (P/D = 2.0, 3.3 and 4.6) and length ratio (L/P = 0.3, 0.5 and 0.7), on the Nusselt number (Nu) and friction factor (f) are investigated. Streamline and temperature distribution are presented. Meanwhile, local and overall heat transfer performance is compared with those of a smooth tube, and the overall performance is evaluated by performance evaluation factor (η). The results indicate that the twist ratio (P/D) plays a dominant role in heat transfer enhancement while the length ratio (L/P) also has considerable influence. It is shown that a segmented tape insert can increase the overall heat transfer rate by 23.5% and the friction factor by 235%, while local improvement along the tube can be 2.8 times more than the plain tube.

Review on Heat Transfer Enhancement by Insert Devices

“…In the other recent investigation of Liu et al, [16] indicates that the geometric parameters like twist ratio and length ratio play an important role in heat transfer enhancement. The results showed that a segmented tape insert in pipe flow can increase the overall heat transfer rate by 23.5% and the friction factor by 235%, while local improvement along the tube can be 2.8 times more than the plain tube [16]. Figure 8 illustrates the relationships between heat transfer coefficient and twist ratio along the tube.…”

“…(3) The tube having T-W inserts with P/W of 1.18 produces the highest friction factor, which is 11.6 and 2.72 times greater than the plain tube. Segmented twisted tape Insert [16] Air (10000 ≤ Re ≤ 35000); Twist ratio = (2.0, 3.3 and 4.6); Length ratio = (0.3, 0.5 and 0.7)…”

“…As can be seen from the figure the twisted tape inserts have the highest heat transfer enhancement of 400% followed by that for air-foil shaped inserts having a value of 300% followed by that for nanofluids with baffles having a value of 255% followed by that for wire coil having a value of 9%. PTTT [11] X-shaped tape insert [13] Sparsely placed TT [14] Segmented TT [16] TT with helical tube [17] Wire coil Insert…”

Numerical Study of Heat Transfer Intensification in a Circular Tube Using a Thin, Radiation-Absorbing Insert. Part 2: Thermal Performance

“…(a) T b calculated as the average volumetric temperature of the whole channel. This method of calculation is most often used by most researchers, both for empty channels and those equipped with inserts or other turbulators, e.g., [22][23][24][25][26][27][28][29][30][31][32]. The heat flux is transferred to the fluid in contact with the channel wall, and its average temperature is a result of the heat transfer conditions and the medium's velocity on both sides of the insert.…”

Numerical and Experimental Analysis of the Thermal Performances of SiC/Water and Al2O3/Water Nanofluid Inside a Circular Tube with Constant-Increased-PR Twisted Tape

“…An approach for increasing the thermal performance of a thermal system is to adopt a passive method, such as alteration of the fluid flow inside a tube including having a corrugated channel/tube or using insert inside the channel/tube [1,2]. Therefore, several modifications have been made to the twisted tape by researchers to produce better fluid mixing with lower ∆P including serrated twisted tape (TPP) [3], multiple twisted tape [4], square and V-cut twisted tape [5], segmented twisted tape [6], and self-rotating twisted tape [7]. Even though all these methods are able to enhance η at a certain point, a decreasing trend is shown as Re increases.…”