Intensification of forced convection heat transfer using biological nanofluid in a double-pipe heat exchanger

• A novel biological Ag/WEG50 nanofluid is introduced.
• Convective heat transfer of nanofluid is evaluated in a heat exchanger.
• Heat transfer coefficient remarkably enhanced at vol.% = 1 of nanofluid.
• A small penalty is reported in case of using biological nanofluid.
• A new correlation for Nusselt number is proposed with A.A.D of 8.77%.

This work mainly focuses on forced convective heat transfer coefficient of a biologically produced nanofluid flowing in a circular tube inside a heat exchanger. Diameters of inner and outer tubes (ID and OD) were 6.35 and 12.7 mm respectively (in accordance with ANSI/ASME/API 5L). Experiments were conducted at laminar, transient and turbulent flow regimes. Nanofluids were prepared at volume fractions of 0.1%, 0.5% and 1% and well-dispersed in ethylene–glycol/water (50:50 by volume) as a base fluid. Particles were produced using plant extract method from green tea leaves and silver nitrate. Thermal conductivity of nanofluids were experimentally measured and compared to well-known predicting correlations. Due to fairly agreement of obtained results with existing equations, a new correlation is proposed with absolute average deviation of ±3.43. Influence of different operating parameters including: flow rate, concentration of nanofluid and inlet bulk temperature on heat transfer coefficient were experimentally investigated and briefly discussed. Influence of nanofluids on pressure drop and friction factor was experimentally investigated. Results demonstrated a remarkable enhancement of heat transfer coefficient up to 67% at vol.% = 1.

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