Experimental study on the thermal conductivity of ethylene glycol-based nanofluid containing Gr-CNT hybrid material

Abstract

In this paper, we present the results of the preparation and thermal conductivity of ethylene glycol-based nanofluid containing graphene‑carbon nanotube (Gr-CNT) hybrid material. First, Gr and CNT were surfaces modified with different functional groups including hydroxyl (-OH) and carboxyl (-COOH), then mixed to attain Gr-CNT (1:1, v/v) hybrid material. The hybrid material was then dispersed in ethylene glycol (EG) to obtain hybrid nanofluid by ultrasonication technique. Thermal conductivity of nanofluids was measured using guarded hot plate (GHP) technique. The nanofluid containing 0.07 vol% Gr-CNT hybrid material showed the enhancement in thermal conductivity of 18 and 50% at 30 and 50 °C, respectively. The enhancement was attributed to the combination of high thermal conductivity of CNT and Gr and high surface area of Gr-CNT hybrid structure. By analyzing the experimental results using EMT and Murshed model, the thermal boundary resistance (TBR), thermal boundary conductance (TBC) and interface layer thermal conductivity (Ki) between Gr-CNT hybrid material and EG were estimated to be 0.8 × 10−8 m2 kW−1, 125 MW m−2 K−1 and 20.5 Wm−1·K−1, respectively.