Development and performance investigation of coffee husk-derived carbon-based nanofluid for solar thermal applications

Abstract

Managing agricultural waste effectively is a serious concern, particularly in agrarian economies, where poor disposal practices cause environmental and public health problems. This paper discusses the synthesis of a carbon-based nanofluid from coffee husk char for solar thermal applications, utilising pyrolysis as an effective method for valorising agro-residue. The synthesis used the left-over solid residue during coffee husk pyrolysis after gaseous product extraction. The feasibility of the synthesized fluid for solar thermal application is studied by physical, chemical and optical characterisations. The synthesized fluid had a thermal conductivity of 0.87 W/mK and a pH of 10.26. The fluid was stable with a zeta potential value of −59.4 mV. The mean size of particles in the synthesized fluid was 6.24 nm. The optical characteristics of the synthesized fluid were studied from UV–Vis absorption spectroscopy. The solar-weighted absorption fraction of carbon-based nanofluid was 62.6 %, and that of deionised water was 12.3 %. When investigated with a solar simulator (at irradiance values of 700, 800, 900, 1000 and 1100 W/m2), the maximum improvement in photothermal conversion efficiency was 14.35 % at 1100 W/m2. At all irradiance levels, the sensible heat gain and the photothermal conversion efficiency were found to be greater than those of deionised water.