Amorphous carbon based nanofluids for direct radiative absorption in solar thermal concentrators – Experimental and computational study

Anurag Pramanik,Harjit Singh,Ram Chandra,Virendra Kumar Vijay,S Suresh

doi:10.1016/j.renene.2021.11.047

Abstract

Directly solar radiation absorbing nanofluids have the potential to absorb a wide spectrum of solar radiation and displace selectively coated metallic receivers in solar thermal collectors. Parameters including nanoparticle concentration, synthesis and storage conditions, can influence their long-term usage. In this study, 60 min was found to be optimal sonication duration to synthesise a uniform suspension of nanofluid containing amorphous-carbon nanoparticles and ethylene glycol as base fluid. Nanoparticle concentration can be used to tune extinction coefficient of nanofluid in the range of 75–400 m−1 for wavelength range of 320–1000 nm. Long-term stability and high temperature studies showed a time and temperature dependent increase in transmittance of nanofluid which is restored by 5 min of stirring. Computational modelling highlighted the role of incident intensity, nanoparticle concentration as well as inlet flow rate on receiver exit temperature. A ray-optics model employing weather data for Delhi (India) can predict the optical efficiency of an Asymmetric Compound Parabolic Concentrator solar collector. This combined approach can enable to predict the flow rate required to achieve a desired supply temperature at target locations. This rational framework combining experimental and computational approaches can be used to identify design parameters relevant for application of nanofluids in thermal collectors.

Highlights

The use of solar energy for electricity generation, desalination and thermal applications has significantly increased owing to advances in receiver designs to enhance optical efficiency as well as reduce heat losses and improved sun-tracking mechanisms [1]
It is important to note that these sonication studies were conducted for ethylene glycol as base fluid using a bath sonicator with a double-frequency ultrasonication power of 28 kHz and the optimal duration is likely to vary for different base fluids or sonication frequencies
A framework which allows to design, size, and optimize the important parameters related to implementation of solar thermal collectors using nanofluids was developed

Summary

Introduction

The use of solar energy for electricity generation, desalination and thermal applications has significantly increased owing to advances in receiver designs to enhance optical efficiency as well as reduce heat losses and improved sun-tracking mechanisms [1]. Nanofluids, a suspension of nanoparticles in heat transfer fluids, can significantly enhance (by up to 7 orders of magnitude) the solar energy absorption capability of working fluids and the use of nanofluids holds a huge potential in solar thermal applications [2,5,7,8]. Nanofluid stability is one of the major challenges for their applications in solar energy systems [16,17] For their use with Concentrating Solar Thermal (CST) panels, nanofluids can reach very high temperatures which can influence the stability of the suspension. Protocols for efficient synthesis as well as maintaining longterm and high temperature stability of nanofluids are important for widespread application of nanofluids for solar thermal applications

Methods

Results

Conclusion