Intensification of performance of pipe with nanoparticle flow along turbulator with obstacles

https://doi.org/10.1016/j.cep.2021.108426Get rights and content

Highlights

  • Turbulators were employed in a pipe with considering hybrid nanofluid.

  • Hybrid particles were dispersed into water to intensify thermal features.

  • Nu augments about 202.84% with augment of Re.

  • Adding twisted tape leads to maximum value of PEC when Re=5000.

  • Influence of adding barrier on xd enhances if inlet velocity increases.

Abstract

In this article, to save the energy, turbulators were employed in a pipe with considering hybrid nanofluid. Due to low concentration, empirical correlations have been utilized to calculate the features of new carrier fluid. For selecting the turbulent model, different models were tested to find the best accommodation with experimental data for turbulent flow in existence of twisted tape and results indicated the nice accuracy of K-ε Realizable. With augment of secondary flow due to external device, the radial velocity enhances and convection coefficient enhances as well as resistance of fluid. Two configurations of turbulators were compared and outcomes were reported in term of bar charts and contours. Nu augments about 202.84% with augment of Re when TT with barrier has been utilized. Insertion of barrier makes Nu to intensify about 28.43% when Re=20,000. Friction factor declines about 3.6% with rise of inlet velocity in existence of barriers. Exergy drop reduces with rise of inlet velocity about 79.93% and 83.03% in absence and presence of barriers. Influence of adding barrier on Xd enhances if inlet velocity increases. When Re=20,000, insert of barriers make exergy drop to decline about 33.38%. Adding twisted tape leads to maximum value of PEC when Re=5000.

Introduction

Passive methods are employed to increase heat transfer rate so that the new designed system obtains the minimum size considering the limitation of pressure fall. To obtain any of the mentioned targets, numerous heat transfer increment methods showing various benefits in views of friction and heat transfer efficiency [1]. The growth of convective rate can be obtained in many paths such as using nanomaterial as a testing fluid, turbulator to grow the local turbulence, extended surface installed to the internal side of the pipe to raise the area. The most favorable property of a turbulence promoter is known by its maximum Nu and the its lowest growth of pressure fall. Many kinds of nano-powders such as nanotubes, ceramics and metals have been analyzed to increase the heat conductivity of testing fluid [2]. Some techniques to increase heat transfer performance such as suspending nano-powders into typical fluid and employing instruments in the pipe were presented by Ahmad et al. [3]. An alternative method for choosing the highest appropriate turbulence promoter for increasing the heat transfer rate in tubular system was proposed by Picón-Núñez and Melo-González [4]. Their outcomes showed that the greatest thermal performance belong the V-cut TT, the straight tape including center wings and the square-cut twisted tape. The heat transfer efficiency of TiO2 nanomaterial in a pipe was scrutinized by Bhanvase et al. [5]. The researchers observed 105 percent increment in heat transfer rate at the Re=1500 for 0.5 vol% nanomaterial. Effect of TT on heat transfer rate of nanomaterial inside a circular channel has been scrutinized by Sundar and Sharma [6]. The authors observed that the Nu increase up to 33.5 percent by applying alumina oxide/H2O nanomaterial as the operant liquid in their analysis.

Eiamsa-ard and Kiatkittipong [7] analyzed the efficiency of multiple TT, titanium oxide/H2O within a tube and observed that the maximum thermal efficiency was 1.59 where Darcy factor and Nu grew to 11.7 times and 3.52 times of those in the smooth instance with the basis fluid. The use of nanomaterial inside heat exchangers was summarized by Olabi et al. [8]. The researchers stated that the existence of the nanomaterial increases the heat transfer rate. CNT nanomaterial applying double distilled water and combined surfactant with the ratio of 1 was provided by Singh et al. [9]. The authors observed that the friction coefficient was grown with the growth in Re. Nu was 62 percent greater for CNT nanomaterial at Re=5000 in comparison to H2O. Gkountas et al. [10] analyzed PCHE applied as pre-cooler for Brayton cycle and using alumina oxide/H2O nanomaterial is presented. Based on their results, the maximum utilized nano-powder concentration of 5 percent leads to an increase of 75 percent for Nu and a decrease 8 percent in pressure fall. Liu et al. [11] defined a principle for convective flow and introduced factor for accessible work, and an equation of local exergy destruction has been defined. Empirically, Singh and Sarkar [12] analyzed the effect of applying V-cuts TT insert and PCM suspended hybrid or mono nanomaterial on the hydrothermal features of the double pipe. Results demonstrated that the Δp and the heat transfer rate grow with the growth in powder fraction. Murthy and Hegde [13] analyzed the impact of the mixed passive methods on heat transfer increment, heat efficiency and Darcy factor of a double-tube which was fitted with various turbulators and applying alumina nanomaterial. Their outcomes demonstrated that grown Nu by 29 percent and 22 percent, grown heat efficiency by 1.33 and 1.25. Numerically and empirically, Plant and Saghir [14] analyzed the effect of an Al2O3 nanomaterial on the fluid stream-based mechanism included of permeable foam to test their effect on the heat efficiency of the mechanism. Based on their achievements, the utilization of great fraction (1 percent vol) nanomaterial paired with the utilization of 2 disparate channel designs, both including permeable media led to a mean heat increment 15 percent and a highest increment of 24.5 percent in comparison to that of 2 percent fraction of alumina. Suresh et al. [15] scrutinized the thermal efficiency of helical tape in laminar stream of alumina oxide/H2O and copper oxide/H2O nanomaterials within a circular duct with fixed thermal flux boundary conditions. The authors observed that the heat efficiency of helical screw tape inserts applying copper oxide/H2O nanomaterial is greater than applying alumina oxide/H2O. Eiamsa-ard et al. [16] analyzed the convective flow within dimpled tubes mounted with TT applying titanium oxide/H2O nanomaterial as the test liquids. Their outcomes proved that the dimpled tube including TT obtained greater Nu compared to sole dimpled tube. Empirically, Hekmatipour and Jalali [17] analyzed the impact of applying CO2/thermal oil on pressure fall and convective heat transfer in an upward stream inside a tilted micro fin tube. Their findings showed that the fluid resistance grows with the increase of Re, tilted angle and nano-powder concentration.

According to aforementioned literature review, few papers have been published about combinations of twisted tape and barrier in existence of hybrid nanofluid. To reduce the exergy loss and augmentation of performance, turbulator can be utilized and changing carrier fluid to hybrid nanofluid has promising output. In current article, FVM has been applied for modeling the hybrid nanofluid exergy loss and convective heat transfer with turbulent regime. Homogeneous model for concerning the effect of hybrid nanofluid was used because of its low concentration. In next step, the geometry has been introduced and governing equations were mentioned. Forced convection in absence of buoyancy has been considered. In validation step, the best turbulent model has been introduced and then grid independency analysis has been presented. Two shapes of turbulators were utilized: sole twisted tape (TT) and TT with barrier. Friction factor, exergy loss, performance and Nusselt number have been calculated. Also, the variations of contours for isotherms, pressure and velocity have been presented.

Section snippets

Geometry and formulation

Utilizing turbulators is promising way for intensification of mixing of fluid. Fig. 1 shows tube equipped with twisted tape (TT) and barrier. Length of tube is 1.5 m and the middle section is test section where turbulators install there. The diameter of pipe is 2 inch. Pitch ratio of TT is 0.125 m. Thickness and width of barrier are 1.5 mm and 9.25 mm. Carrier fluid is hybrid nanofluid (mixture of Fe3O4+CuO and water). The properties of nano-powder and base fluid and formulations for nanofluid

Results and discussion

In current modeling, combination of obstacle and twisted tape has been compared with sole twisted tape in view of thermal performance and exergy loss. This system can be utilized as an absorber of solar system. The range of Re (5000–20,000) indicates turbulent flow and for simulation of such flow, K-ɛ has been utilized. Hybrid nanofluid has been selected as working fluid and inlet temperature is 298.15 K. To involve the feature of hybrid nanoparticles, empirical formulas were utilized as single

Conclusion

In this article, efficiency of heat exchanger with insertion of twisted tape with obstacle has been presented. Two main factors were utilized to augment the thermal performance: dispersion of hybrid nanoparticles and insertion of swirl flow device. To apply the effect of nano-powders, homogeneous model was implemented. Two different shapes of turbulator have been employed and in second one, obstacle was combined with twisted tape. This change in shape of device has promising effect of Nu while

Declaration of Competing Interest

All authors declare that there is no conflict of interest in our paper.

References (24)

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