Utilization of heat for different purposes like electricity generation or moving the locomotives is usually mediated by specialized devices called heat exchangers. These devices can be easily designed and are compact and economical with some disadvantages like leakage, fouling, etc. Heat exchangers are used to exchanging the heat between hot and cold fluid for proper utilization of heat in various engineering applications. Several studies have been done to improve the performance of heat exchangers. Utilizing porous (metal foams) filled heat exchangers proves to be a very effective passive technique for improving the thermal performance of the heat exchanger [1]. Also, nanofluids with their enhanced effective thermal conductivity are used as working fluid to increase the heat transfer rate [2]. A recent study focused on the simultaneous application of porous media and nanofluids in the heat exchanger [3]. This work focuses on the functioning of Double Pipe Heat Exchangers (DPHE) and the ways to improve its effectiveness by using different arrangements of porous fins and nanofluid as working fluid. While porous media increases the retention time of fluid in heat exchanger thus increasing heat transfer rate, nanofluids are reported to enhance the heat transfer rate stemming from the increased surface area-volume ratio. However, these come at cost of increased pumping power for the fluids.In this work, five different designs of DPHE are investigated numerically:1. DPHE with no porous fins (HE-1).2. DPHE with porous fins attached on the inner side of the middle wall only (HE-2).3. DPHE with porous fins attached on the outer side of the middle wall only (HE-3).4. DPHE with porous fins attached on both sides of the middle wall with inline arrangement (HE-4).5. DPHE with porous pins attached on both sides of the middle wall with staggered arrangement (HE-5).We used Al2O3-H2O nanofluid as a working fluid. Porous media and non-porous media are simulated using Darcy-Brinkman-Forchheimer equation and Navier Stokes equation respectively. The simulations are performed in COMSOL MULTIPHYSICS considering different Reynolds and Darcy Number combinations. The thermal performance of the heat exchanger is evaluated using ɛ-NTU method. The performance evaluation criterion (PEC) is used to consider the effect of pressure drop along with heat transfer performance and to find an optimal design.The novelty of the present work is the utilization of porous fins with different sets of arrangements and nanofluid as working fluid. While most of the previous studies used fully filled annulus with porous media, we used DPHE partly filled with porous fins arranged with different sets. The partly filled space with porous fins and nanofluid as working fluid together enhances the heat exchange rate with a minimum increase in pressure drop. Also, we present an optimization study to find the balance between the heat exchange rate and pumping power and find the optimal design among the above-mentioned DPHE.&nbsp;&nbsp;

Optimizing Effectiveness of Double Pipe Heat Exchanger Using Nanofluid and Different Porous Fins Arrangement

Paper Proceedings: https://asmedigitalcollection.asme.org/POWER/POWER2021/volume/85109

ASME 2021 Power Conference (POWER2021)

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