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

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.

Direct absorption nanofluid-based solar collectors for low and medium temperatures. A review

“…To the authors knowledge, the scientific literature dedicated to hybrid [152,153] and plasmonic [154] nanofluids is very scarce, preventing any conclusion concerning their potential in concentrating NDASC to be established. The influence of the volume fraction and fluid depth has been evaluated and similar conclusions are achieved: there is an optimum volume fraction and fluid depth for which the collector efficiency reaches a maximum value (Figure 9) [89,[155][156][157][158]. To our knowledge, the impact of the particle size and shape on the efficiency of concentrating NDASC has not been studied.…”

“…Several methods are commonly used to characterize the absorption properties of the nanofluid depending on the particle type, shape and mean size. The Rayleigh scattering approximation is the most accurate and popular solution method [1,12,26,31,32,[83][84][85][86][87][88][89][90][91][92][93][94], other methods such as the Mie scattering theory [92,[95][96][97] or the Maxwell-Garnett theory being less used [91,98]. Among metal nanoparticles, gold (Au), silver (Ag), copper (Cu), and aluminum (Al) show the best optical properties for NDASC.…”

Thermal and hydrodynamic performance of an improved passive solar water heater equipped with asymmetric U-type evacuated tubes

“…The other is to further improve the thermal performance of evacuated tubes. Researchers have studied different aspects in this regard (Bellos et al, 2019;Kasaeian et al, 2020;Nkwetta et al, 2012;Shariatifard et al, 2022;Yang et al, 2015). Teles et al (2019) focused on the effect of a solar tracking system on the performance of the evacuated tube solar collector.…”

Thermal performance of parabolic-trough solar collector using double-population LBM with single-node/curved scheme and experimental evaluation on properties of SiO2-TiO2/EG nanofluid

“…The results showed that the cylinder with a 30 mm diameter is the best choice to improve thermal efficiency. Moreover, the thermal enhancement is found to be greater at higher temperature levels and can reach up to 1% for an inlet temperature of 650 K. Kasaeian et al (2019) evaluated the influence of MWCNT/ethylene glycol (EG) nanofluid for the application of a parabolic trough collector. They focused on the impact of direct absorption nanofluid in parabolic trough collector which is a new generation of solar collector.…”