Experimental study on the characteristics of heat transfer and flow resistance in turbulent pipe flows of viscoelastic-fluid-based Cu nanofluid

Experimental studies were performed to investigate the characteristics of convective heat transfer and flow resistance in turbulent pipe flows of viscoelastic fluid, water-based and viscoelastic-fluid-based nanofluids (VFBN) containing copper (Cu) nanoparticles. The viscoelastic fluid used both as testing fluid and for preparation of VFBN was aqueous solution of cetyltrimethylammonium chloride (CTAC)/sodium salicylate (NaSal). The thermophysical and rheological properties of VFBN were measured at first. Experimental results of heat transfer and flow resistance indicated that the VFBN flows showed better heat transfer properties than viscoelastic base fluid flows and lower flow resistances than water-based nanofluid flows. The convective heat transfer coefficients were increased with increase of temperature for all the tested flows, whereas temperature had no essential influence on pressure drop in the flows of Cu–water based nanofluid and VFBN. For viscoelastic fluid flows, the pressure drop was decreased with the increase of temperature. The present experimental results do have shown a synergetic effect of both viscoelasticity and nanoparticles that is expected for VFBN flow, i.e. either turbulent drag reduction (DR) and heat transfer enhancement (HTE) compared with water based nanofluid flow, or DR and heat transfer reduction (HTR) but with HTR rate being smaller than DR rate (for viscoelastic base fluid only, HTR rate is larger than DR rate). This synergetic effect is dependent on both the rheological and physical properties of viscoelastic base fluid (solution concentration) and flow conditions (flow velocity).