Abstract
The hydrothermal performance of multiple semi-twisted tape inserts inside a heat exchanger pipe is numerically examined in three-dimensions. This study aims to find the optimum case for having the highest heat transfer enhancement with the lowest friction factor using nanofluid (Al2O3/water). A performance evaluation criterion (PEC) is defined to characterize the performance based on both friction factor and heat transfer. It was found that increasing the number of semi-twisted tapes increases the number of swirl flow streams and leads to an enhancement in the local Nusselt number as well as the friction factor. The average Nusselt number increases from 15.13 to 28.42 and the average friction factor enhances from 0.022 to 0.052 by increasing the number of the semi-twisted tapes from 0 to 4 for the Reynolds number of 1000 for the base fluid. By using four semi-twisted tapes, the average Nusselt number increases from 12.5 to 28.5, while the friction factor reduces from 0.155 to 0.052 when the Reynolds number increases from 250 to 1000 for the base fluid. For the Reynolds number of 1000, the increase in nanofluid concentration from 0 to 3% improves the average Nusselt number and friction factor by 6.41% and 2.29%, respectively. The highest PEC is equal to 1.66 and belongs to the Reynolds number of 750 using four semi-twisted tape inserts with 3% nanoparticles. This work offers instructions to model an advanced design of twisted tape integrated with tubes using multiple semi-twisted tapes, which helps to provide a higher amount of energy demand for solar applications.
Highlights
The results showed that the friction factor and Nusselt number were enhanced by factors of 10 and 3, respectively
This study provides guidelines to design an improved configuration of twisted tape inserted tubes using multiple semi-twisted tapes
The numerical simulations are conducted to evaluate the thermo-hydraulic performance of laminar swirl flow through the circular tube equipped with multiple semitwisted tapes
Summary
The increasing energy demand will require improving the energy efficiency of heat transfer applications [1,2]. Due to high energy demand, renewable energies, especially solar energy, have been widely employed in recent decades [3,4]. Collectors are one of the solar energy technologies that have been widely employed to convert solar energy into useful thermal energy [5,6,7]. The solar radiation is reelected to the absorber tube and provides an almost uniform heat flux around the tube’s wall [8,9,10]
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