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Evaluation of MWCNT/ethylene glycol nanofluid flow in a parabolic trough collector with glass-glass absorber tube

Ab Kasaeian (University of Tehran, Tehran, Iran)
Reza Daneshazarian (Department of Mechanical and Industrial Engineering, Ryerson University, Toronto, Canada)
Fathollah Pourfayaz (Faculty of New Science and Technologies, University of Tehran, Tehran, Iran)
Sahar Babaei (Faculty of New Science and Technologies, University of Tehran, Tehran, Iran)
Mojgan Sheikhpour (Department of Mycobacteriology and Pulmonary Research, Pasteur Institute of Iran, Tehran, Iran)
Shima Nakhjavani (College of Engineering, University of Yazd, Yazd, Iran)

International Journal of Numerical Methods for Heat & Fluid Flow

ISSN: 0961-5539

Article publication date: 6 August 2019

Issue publication date: 15 January 2020

Abstract

Purpose

Because of its increased absorptance in fluid and reduced heat loss, direct absorption nanofluid (DANF) is receiving intense interest as an efficient way to harvest solar energy. This work aims to investigate, for the first time, the application of DANF in parabolic trough collectors (PTC), a promising collector for solar thermal systems.

Design/methodology/approach

A representative flow and heat transfer study of different fluids in a straight tube is conducted, and the basic energy equation and radiative transfer equations are numerically solved to obtain the fluid temperature distribution and energy conversion efficiency. Ethylene glycol (EG) and different concentrations of (i.e., 0.1-0.6 per cent) multi-wall carbon nanotubes (MWCNT) in EG are used as sample fluids. Four cases are studied for a traditional PTC (i.e., using metal tube) and a direct absorption PTC (i.e., using transparent tube) including a bare tube, a tube with an air-filled glass envelope and a tube with vacuumed glass envelop. The numerical results are verified by an experimental study using a copper-glass absorber tube, which reveals the good potential of DANFs.

Findings

Compared with a conventional PTC, using DANF shows an increase of 8.6 per cent and 6.5 K, respectively, in thermal efficiency and outlet temperature difference at a volume fraction (0.5 per cent) of nanoparticles. The results also show that the improvement in solar efficiency increases with increasing particle concentrations, and the vacuum insulated case has the highest efficiency.

Originality/value

In all previous studies, an important section was missing as the effect of photons on the direct solar absorption trough collector, which is considered in this study. This paper proposes a new concept of using direct solar absorption nanofluids for concentrated solar collectors and analyzes the performance of both absorptance and transmittance efficiency considerations. To reveal the potential of the new concept, an analytical model based on energy balance is developed, and two case studies are performed.

Keywords

Citation

Kasaeian, A., Daneshazarian, R., Pourfayaz, F., Babaei, S., Sheikhpour, M. and Nakhjavani, S. (2020), "Evaluation of MWCNT/ethylene glycol nanofluid flow in a parabolic trough collector with glass-glass absorber tube", International Journal of Numerical Methods for Heat & Fluid Flow, Vol. 30 No. 1, pp. 176-205. https://doi.org/10.1108/HFF-11-2018-0693

Publisher

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Emerald Publishing Limited

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