Flow Loop Experiments Using Polyalphaolefin Nanofluids

Experiments were performed using a flow-loop apparatus to explore the performance of nanofluids in cooling applications. The experiments were performed using exfoliated graphite nanoparticle fibers suspended in polyalphaolefin at mass concentrations of 0.6 and 0.3 %. The experimental setup consisted of a test section containing a plain offset fin cooler apparatus (gap or nongap fin), which was connected to a flow loop consisting of a gear pump, a shell and tube heat exchanger (that was cooled or heated by a constant temperature bath chiller/heater), and a reservoir. Experiments were conducted using nanofluid and polyalphaolefin for two different fin strip layouts. Heat transfer data were obtained by parametrically varying the operating conditions (heat flux and flow rates). The heat transfer data for nanofluids were compared with the heat transfer data for neat polyalphaolefin fluid under similar conditions. The change in surface morphology of the fins was investigated using scanning electron micrography. The nanofluid properties were measured using rheometry for the viscosity, differential scanning calorimetry for the specific heat, and laser flash apparatus for the thermal diffusivity. It was observed that the viscosity was ∼10 times higher for nanofluids compared with polyalphaolefin and increased with temperature (in contrast, the viscosity of polyalphaolefin decreased with temperature). The specific heat of nanofluids was found to be 50% higher for nanofluids compared with polyalphaolefin and increased with temperature. The thermal diffusivity was found to be 4 times higher for nanofluids compared with polyalphaolefin and increased with temperature. It was found that, in general, the convective heat transfer was enhanced by ∼10% using nanofluids compared with using polyalphaolefin. Scanning electron micrography measurements show that the nanofluids deposit nanoparticles on the surface, which act as enhanced heat transfer surfaces (nanofins).