Convective Heat Transfer and Pumping Power Analysis of MWCNT + Fe3O4/Water Hybrid Nanofluid in a Helical Coiled Heat Exchanger with Orthogonal Rib Turbulators

Misagh Irandoost Shahrestani,Ehsan Houshfar,Mehdi Ashjaee,Payam Allahvirdizadeh

doi:10.3389/fenrg.2021.630805

Misagh Irandoost Shahrestani, Ehsan Houshfar + Show 2 more

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https://doi.org/10.3389/fenrg.2021.630805

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Abstract

Utilizing nanofluids in heat exchangers can lead to improved thermal performance. Nanofluids with suspended carbon nanotubes are specifically desirable in thermal systems because of their unique capabilities. In this study, convective heat transfer and required pumping power are studied simultaneously for a helical coiled heat exchanger with laminar water flow while incorporating 0.1 and 0.3 percent volume fraction of the hybrid nanofluid MWCNT + Fe3O4/water. Two different geometries of bare and ribbed tubes are used for the heat exchanger part. The ribs are chosen to be orthogonal, i.e., 90° with respect to the inclined ones. Three different Reynolds numbers are selected for investigation, all in laminar flow regime based on the non-dimensional M number defined in coiled tubes. Computational fluid dynamics is used to study thermal and fluid behavior of the problem. The convective heat transfer coefficient can serve as a criterion to measure the effectiveness of utilizing nanofluids in heat exchangers by taking the pressure drop and pumping power of the system into consideration. Finally, the artificial neural network curve fitting tool of MATLAB is used to make a good fit in the data range of the problem. It is shown that for most cases of the study, the pumping power ratio is less than 1 that can be considered appropriate from energy consumption viewpoint.

Highlights

The present trend of gradual decrease in the size of electronic devices and equipment demands improvements in heat transfer and cooling methods Ramezanizadeh et al (2018)
This paper aims at addressing this gap and it can be considered as a criterion for effectiveness evaluation of hybrid nanofluids for helical heat exchangers with or without rib turbulators
Helical coiled heat exchangers with bare and 90-degree inclined ribbed tubes at different Reynold numbers of 2,000, 2,500, and 3,000 and MWCNT + Fe3O4/water hybrid nanofluid with volume fractions of 0, 0.1, and 0.3% were investigated in this study

Summary

Introduction

The present trend of gradual decrease in the size of electronic devices and equipment demands improvements in heat transfer and cooling methods Ramezanizadeh et al (2018). The techniques used for improving heat transfer rate in thermal systems are mainly categorized as passive and active ones. An external medium such as a fan or a pump is used for heat transfer enhancement which leads to an increment in the overall cost of the system. Nanofluids are Helical Heat Exchanger’s Thermo-Fluid Analysis synthesized by dispersing solid particles of nanometer dimension in a base fluid, which can be pure or mixture of some fluids Sheremet et al (2016). Nanofluids improve thermal conductivity of the working fluid owing to the presence of highly conductive solid particles (Komeilibirjandi et al, 2019; Maleki et al, 2020a)

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