Exergy analysis of a shell-and-tube heat exchanger using graphene oxide nanofluids

Abstract

Nanofluids are the new-generation heat transfer fluids largely used in heat exchangers for thermal energy transport applications. In this paper, graphene oxide was prepared in-house and used for nanofluid development and characterization. The graphene oxide was prepared by oxidizing purified natural flake graphite via the modified Hummers method. The morphology and structure of fabricated graphene oxide were characterized using X-ray diffraction analysis (XRD) and a scanning electron microscope (SEM). The graphene oxide nanofluids were prepared at 0.01 and 0.1wt.% concentrations. The particle size and zeta potential of nanofluids were measured using the dynamic light scattering (DLS) technique. The rheological behaviors of nanofluids were investigated at 25 and 40°C at different shear rates (10–1001/s). Thermal conductivity of nanofluids was measured using the transient hot wire method at 25 and 40°C. Exergy analysis showed that increasing the graphene oxide concentration from 0.01wt.% to 0.1wt.% resulted in 8.7% and 18.9% thermal conductivity enhancement at 25 and 40°C, respectively. Furthermore, the thermal performance of graphene oxide nanoparticles in a shell-and-tube heat exchanger was studied experimentally. The effect of nanofluid concentration, flow rates, temperature inlet and flow regime on the system’s exergy loss was studied experimentally. The results showed that using graphene oxide nanofluids as the hot fluid resulted in less exergy loss in the shell-and-tube heat exchanger under both laminar and turbulent conditions. Comparing the exergy loss of graphene oxide nanofluids to distilled (DI) water showed that DI water caused 22% and 109% higher exergy loss than in laminar conditions.