Evaluation of heat-exchange performance of carbon-based nanofluids for air-cooled exchangers with different cross-section shapes

In this study, a vortex trap method was employed to produce carbon-based nanofluids (CBNFs) as working fluids for air-cooled heat exchangers (ACHEs) with rectangular and circular tubes. Poly(sodium 4-styrenesulfonate) was added to the produced CBNFs as a dispersant to enhance their stability, and the CBNF concentration was adjusted to 0.01 wt% (S1) and 0.05 wt% (S2). The viscosity, density, and specific heat of CBNFs were measured and analyzed. Finally, CBNFs were tested in the rectangular- and circular-tube ACHEs to evaluate their heat-exchange capacity, the electricity consumption of pumps, and the system efficiency factor under various temperatures (40 and 55 °C) and flow rates. The results revealed that for S2, a maximum enhancement ratio of 8.17% was achieved for the heat-exchange capacity at a flow rate of 2.0 L/min (LPM) and temperature of 40 °C in the rectangular-tube ACHE, whereas for S1, that of 4.88% was achieved at a flow rate of 2.5 LPM and temperature of 40 °C in the circular-tube ACHE. Moreover, for S1 achieved a maximum enhancement ratio of 8.24% for the system efficiency factor at a flow rate of 2.0 LPM and a temperature of 40 °C in the rectangular-tube ACHE and of 6.37% at a flow rate of 2.5 LPM and temperature of 55 °C in the circular-tube ACHE. Considering the overall trend of system efficiency based on the experimental parameters of the rectangular- and circular-tube ACHEs, S1 was deemed more suitable than S2 to serve as the working fluid.