Using CFD To Assess The Impact of Helical Ba e On The First- Law And Second-Law Performance of Water-CuO Nano uid Inside A Hairpin Heat Exchanger


 This study is devoted to the numerical assessment of the influence of helical baffle on the hydrothermal aspects and irreversibility behavior of the turbulent forced convection flow of water-CuO nanofluid (NF) inside a hairpin heat exchanger. The variations of the first-law and second-law performance metrics are investigated in terms of Reynolds number (Re), volume concentration of NF (φ) and baffle pitch (B). The results showed that the NF Nusselt number grows the rise of both the Re and φ whereas it declines by boosting with the rise of baffle pitch. In addition, the outcomes depicted that the rise of both the T and φ results in the rise of pressure drop, while it declines with the increase of baffle pitch. Moreover, it was found that the best first-law performance of the NF belongs to the case B=33.3 mm, φ=2% and Renf=10000. Furthermore, it was shown that irreversibilities due to fluid friction and heat transfer augment with the rise of Re while the rise of baffle pitch results in the decrease of frictional irreversibilities. Finally, the outcomes revealed that with the rise of baffle pitch, the heat transfer irreversibilities first intensifies and then diminishes.


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It is well known that the turbulent flow has a higher heat exchange and pumping power than the 33 laminar flow, the former being desirable and the latter undesirable. So, the idea came into the 34 researchers' minds to put equipment in the path of laminar flow and create local turbulence. The 35 idea was very successful and has been widely used in the industry today. This equipment is 36 called turbulator, and so far, various types of turbulators have been introduced and their 37 performance has been studied experimentally and numerically [1][2][3][4][5][6][7][8][9][10]. 38 Although the use of turbulators has led to an improvement in the performance of heat transfer 39 systems, this has not prevented researchers from looking for ways to further improve the 40 performance of these systems. One of these amazing techniques, which originated from the low 41 thermal conductivity of heat transfer fluids, is nanofluid (NF). Choi [11] first made these modern 42 fluids and called them NFs. After the introduction of NFs and their amazing thermal properties, 43 much research has been done on their performance in diverse applications [12][13][14][15]. 44 The literature inspection shows that the performance of thermal systems with NF coolants 45 equipped with turbulators has been investigated by various researchers. Bellos et al. [16] 46 analyzed the efficacy of oil-CuO NF in a parabolic trough collector equipped with turbulators. 47 They found that using the combination of NF and turbulator causes a 1.54% thermal efficiency 48 improvement. Nakhchi and Esfahani [17] inspected the efficacy of aqueous Cu NF inside a 49 heated tube equipped with perforated conical rings in a turbulent regime. It was reported that 50 using compound NF and turbulator results in a considerable heat transfer intensification. 51 Akyurek et l. [18] experimentally evaluated the forced convection flow of water-Al2O3 NF inside 52 a horizontal tube equipped with wire coil turbulator. They utilized two turbulators with different 53 pitches and found that the performance metrics of tube filled with NF without any turbulator is superior to that of the cases with turbulator. irreversibility production of a NF in a heat exchanger. It was reported that the maximum 77 irreversibility belongs to the platelet shape nanomaterials.

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The aim of this numerical work is to evaluate the features of turbulent flow of a NF through a 79 hairpin heat exchanger equipped with helical baffles in the annulus side from both the fist and 80 second-law perspectives. The impacts of baffle pitch, and on the NF efficacy are assessed.

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This investigation is the first work on the consequences of using helical baffle on the 82 irreversibility production inside an annulus of a hairpin heat exchanger filled with NF. internal diameter. Additionally, the wall thickness for both the inner and outer tubes is 1 mm.

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Moreover, the baffle pitch varies from 25 mm to 100 mm.

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The purpose of using this device is to cool the NF passing through the annulus with the help of 133 The characteristic of a NF includes its thermo-physical properties that establish the relationship 134 between the base fluid and the nanoparticles. These basic relationships are defined as follows 135 [28-33]: The heat transfer rates for hot and cold fluids are calculated as follows: where: where; 152 ′′ is the total heat flux that the fluid receives over the entire computational domain and is 153 calculated as [28, 29]: The pressure drop (∆ ) is defined as follows: Thermal performance can be computed as:

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In the current numerical investigation, the simulations are conducted using the ANSYS Fluent 162 18.1 software. The governing equations are discretized using the second-order upwind technique.

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Besides, the SIMPLE scheme is utilized to perform the pressure-velocity coupling. The 164 convergence metric is set to 10 -6 .

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Four different types of grids are used to make the outputs of the problem independent of the 166 mesh. Tetrahedral mesh is used. The walls have a boundary layer mesh with a factor of 5%. The

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Nusselt number is used to perform the mesh study. Finally, it was found that the most 168 appropriate mesh is the one with 650538 element number.

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To ensure the accuracy and validity of the results of present work, the experimental findings of 170 reported in Fig. 2 As can be seen in Fig. 3, at low velocities, a good consistency is observed, and as the flow 178 velocity elevates, the discrepancy of the results is elevated and reaches to 7%.