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Optical-thermal properties of an MWCNT/EG nanofluid intended as the working fluid in a direct absorption solar collector
Jeonggyun Ham, Yunchan Shin and Honghyun Cho
In this study, the light-thermal properties of a direct absorption solar collector (DASC) were improved using a multi-walled carbon nanotube (MWCNT) nanofluid based on ethylene glycol (EG), which is a typical solar collector working fluid. The results confirmed that the thermal conductivity increased as the concentration of the MWCNT nanofluid increased from 0.001 to 0.01 wt%, the transmittance uniformly improved over the spectral range of 300–1300 nm, and excellent optical absorption performance characteristics were observed, particularly in the 300–700 nm spectral range. When the concentration of the MWCNT nanofluid exceeded 0.005 wt% and the penetration distance was longer than 1 cm, the solar weight absorption rate converged to one, which indicates the solar energy was almost completely absorbed. The thermal conductivity of the MWCNT/EG nanofluid increased nonlinearly as the concentration and operating nanofluid increased from 0 to 0.01 wt%, the thermal conductivity improved by 3.6% compared to that of the basic fluid.
Keywords: Nanofluid, Transmittance, Extinction coefficient, Thermal conductivity, Multi-walled carbon nanotube (MWCNT), Ethylene glycol(EG)